Separation membrane, separation membrane layered body, separation module or separation tower, hydrogen recovery system, and hydrogen separation and recovery method

Abstract

A separation membrane for hydrogen and a gas L (excepting hydrogen), wherein the activation energy Ep(S) (kJ / mol) for a hydrogen permeance P(S) (mol / (m2∙s∙Pa)) through the separation membrane, as derived within a temperature Tam (°C) range satisfying the following expression (1-I), and the activation energy Ep(L) (kJ / mol) for a gas L permeance P(L) (mol / (m2∙s∙Pa)) through the separation membrane, as derived within the same temperature range, satisfy the following expression (1-II).　(1-I): 5(°C)≤Tam(°C)≤200(°C)　(1-II): |Ep(L)|<|Ep(S)|　The present invention can provide a separation membrane, a separation membrane layered body, a separation module or separation tower, a hydrogen recovery system, and a hydrogen separation and recovery method that are for separating and recovering hydrogen and in which hydrogen can be separated and recovered in a safe and highly efficient manner, even with a relatively low-pressure supply, from a mixed gas comprising molecules that are relatively close in kinetic diameter, one example being the separation and recovery of hydrogen from a hydrogen-oxygen mixed gas.

Description

Separation membrane, separation membrane stack, separation module or separation tower, hydrogen recovery system, and method for separating and recovering hydrogen

[0001] The present invention relates to a separation membrane that separates and recovers a desired component from a mixed gas containing a plurality of gas components, a separation membrane stack including the separation membrane, a separation module or separation tower equipped with the separation membrane, a hydrogen recovery system using the separation membrane, and a method for separating and recovering hydrogen.

[0002] Hydrogen is expected to be actively utilized as a next-generation energy source, and various hydrogen production methods have been proposed. In particular, with regard to the production of so-called green hydrogen, methods such as electrolysis of water using renewable energy such as sunlight and photocatalytic total water decomposition to simultaneously generate hydrogen and oxygen, from which hydrogen can be separated and recovered, have been proposed. In the case of electrolysis, oxygen and hydrogen are obtained from the positive and negative electrodes, but in reality, hydrogen and oxygen are mixed to a certain extent, so it is necessary to separate and recover hydrogen from this mixture. Furthermore, in the case of photocatalytic total water decomposition, it is necessary to separate and recover hydrogen from a stoichiometric gas mixture, i.e., hydrogen:oxygen = 2:1.

[0003] A method for separating or concentrating gases has been proposed in which a mixed gas containing a plurality of gas components is brought into contact with a separation membrane, and the highly permeable component of the mixed gas is allowed to permeate, thereby separating the highly permeable component from the mixed gas, or the less permeable component is allowed to permeate from the mixed gas (see, for example, Patent Document 1). Also, a porous support-zeolite membrane composite has been proposed as the separation membrane (see, for example, Patent Documents 2 and 3).

[0004] However, a 2:1 hydrogen:oxygen mixture, also known as hydrogen detonation gas, can cause a detonation phenomenon in which a flame accompanied by a shock wave propagates at a speed exceeding the speed of sound once ignited, making it necessary to take sufficient safety precautions when handling it. For example, the explosive and detonation ranges of hydrogen-oxygen mixed gases at atmospheric pressure have been described, with hydrogen-oxygen mixed gases with a hydrogen concentration of 3.9% to 95.8% by volume falling within the explosive range, and hydrogen concentrations in the range of 15.5% to 92.6% by volume being considered to be in the detonation range in particular (see Non-Patent Document 1). From these perspectives, the generated hydrogen-oxygen mixed gas must be safely and efficiently separated into hydrogen (or a hydrogen-rich gas with a composition greater than the appropriate level) and oxygen (or an oxygen-rich gas with a composition greater than the appropriate level).

[0005] However, because the handling of this mixed gas is inherently difficult and the kinetic molecular diameters of hydrogen and oxygen are very close, techniques for separating and recovering hydrogen from hydrogen-oxygen mixed gases have not necessarily been fully studied. For example, Non-Patent Document 2 describes the kinetic molecular diameters, such as hydrogen 0.289 nm, oxygen 0.346 nm, carbon dioxide 0.330 nm, argon 0.34 nm, nitrogen 0.364 nm, and methane 0.38 nm. It cannot be said that separation and recovery techniques for such mixed gases with similar kinetic molecular diameters have necessarily been fully studied.

[0006] Furthermore, when separating a desired component from a mixed gas, the efficiency of the separation process is usually improved by pressurizing the supply side. However, it is known that pressurizing a hydrogen-oxygen mixed gas makes it more difficult to handle and increases the damage caused by ignition. For this reason, a high-performance separation membrane is desired that can configure a safe and highly efficient hydrogen-oxygen separation process at low supply pressures of tens of kPa (G) or less, or at normal pressure. In addition, when separating a mixed gas containing other components, such as a hydrogen-methane mixed gas or a hydrogen-carbon dioxide mixed gas, further improvements in safety and efficiency are desired for technologies for separating and recovering desired molecules under low supply pressure conditions.

[0007] A specific example is a separation process for hydrogen-oxygen mixed gas in an artificial photosynthesis plant where hydrogen-oxygen mixed gas flows. In the artificial photosynthesis plant, a photocatalyst is used to decompose water into hydrogen and oxygen, which is then separated into hydrogen-rich gas and oxygen-rich gas using a gas separation membrane or the like, followed by a process to improve the purity of the hydrogen using various methods. Furthermore, in a subsequent stage, the hydrogen and carbon dioxide gas can be used to produce lower olefins.

[0008] Here, particularly in the upstream side, i.e., in the separation process of the hydrogen-oxygen mixed gas, a stoichiometric hydrogen-oxygen mixed gas flows through various locations, so it is preferable that the separation membrane not only provides safe and highly efficient separation, but also has a flame-extinguishing function in case of ignition and subsequent detonation. Generally, the separation membrane used in the hydrogen-oxygen separation process can be selected, depending on its material, from inorganic membranes made mainly of inorganic materials, organic membranes made mainly of organic materials, mixed matrix membranes having a combination of these, etc.

[0009] Furthermore, when separating and recovering hydrogen from a gas mixture containing hydrogen and oxygen, it is often the case that the hydrogen permeance of any membrane increases when it is heated. However, the flame-extinguishing properties of heated hydrogen-oxygen gas mixtures are not entirely clear, in part because the experiments themselves are dangerous.

[0010] JP 2015-44162 A JP 2015-44163 A JP 2020-131184 A

[0011] Akizo Yagyu, Explosion Limits of Gases and Vapors, Japan Society of Safety Engineering, April 1977. Masato Kanesashi, Network Structure Control and Permeation Property Evaluation of Silica-Based Gas Separation Membranes, Membrane 41(4), 183-188, 2016

[0012] Under the circumstances described above, an object of the present invention is to provide a separation membrane, a separation membrane stack, a separation module or separation tower, a hydrogen recovery system, and a method for separating and recovering hydrogen that can safely and efficiently separate and recover hydrogen from a mixed gas consisting of molecules with relatively close dynamic molecular diameters, even when supplied at a relatively low pressure, including the separation and recovery of hydrogen from a hydrogen-oxygen mixed gas. Another object of the present invention is to provide a method for separating and recovering hydrogen with high separation performance and high permeability from a mixed gas containing at least hydrogen and oxygen, a separation module or separation tower, and a hydrogen recovery system that separate and recover hydrogen with high separation performance and high permeability.

[0013] The present inventors conducted extensive research to solve the above-mentioned problems and discovered a separation membrane whose temperature dependence of permeability for multiple types of molecules constituting a mixed gas is unique compared to that of conventional separation membranes. Furthermore, they discovered that a separation module or separation tower equipped with this separation membrane, as well as a recovery system using this separation membrane, are highly adaptable for separating and recovering hydrogen from mixed gases, particularly mixed gases containing hydrogen, and thus arrived at the present invention. Furthermore, a separation module or separation tower using the separation membrane of the present invention, as well as a recovery system using this separation membrane, can exhibit excellent separation capabilities even at relatively low supply pressures. Furthermore, they discovered that a separation and recovery method that actively utilizes the unique temperature characteristics of the separation membrane or the like to simultaneously improve the permeability of a desired component and the separation characteristics of the desired component and other components has excellent properties that can achieve both safety and efficiency in the separation of mixed gases, such as the ability to separate and recover hydrogen even under low supply pressure conditions, thereby arriving at the present invention. That is, the present invention provides the following [1] to

[27] , which are a first aspect of the present invention. Furthermore, as a result of extensive research to solve the above problems, the present inventors have discovered that when hydrogen-oxygen mixed gas flows in an artificial photosynthesis plant or an electrolysis plant and the mixed gas is separated, for example, by membrane separation, the permeability of the membrane separation and the flame-extinguishing performance for the hydrogen-oxygen mixed gas required for safety can be compatible within a certain temperature range, and have arrived at the present invention. That is, the present invention provides the following

[28] to

[56] , which are a second aspect of the present invention.

[0014] [1] The hydrogen permeance P (S) (mol / (m)) of the separation membrane, calculated within the temperature range Tam (°C) that satisfies the following formula (1-I): ２ The activation energy Ep(S) (kJ / mol) of the gas L (at least one selected from the group consisting of carbon dioxide, argon, oxygen, nitrogen, and methane) through the separation membrane, which is derived within the same temperature range, is ２and the activation energy Ep(L) (kJ / mol) of the pressure (MPa) at the surface of the separator 100°C satisfies the following formula (1-II): 5 (°C)≦Tam(°C)≦200 (°C) (1-I) |Ep(L)|<|Ep(S)| (1-II) [2] The separation membrane according to the above [1], which satisfies the following formula (1-III): P(L)<P(S) (1-III) [3] The separation membrane according to the above [1] or [2], which satisfies the following formula (1-IV): 0<Ep(L)<Ep(S) (1-IV) [4] The separation membrane according to any one of the above [1] to [3], which is an inorganic membrane. [5] The separation membrane according to any one of the above [1] to [4], which has a surface-modified zeolite membrane. [6] A separation membrane stack comprising a separation membrane on a support, wherein the separation membrane is the separation membrane according to any one of the above [1] to [5], the support is tubular, and the inner diameter φi (mm) of the support satisfies the following formula (1-VI): 6 (mm)≦φi (mm)≦16 (mm) (1-VI) [7] A separation module or separation tower equipped with a separation membrane, wherein the separation membrane is the separation membrane according to any one of the above [1] to [5], and the temperature Tos (°C) of the separation module or separation tower satisfies the following formula (1-VII): 45 (°C)≦Tos (°C)≦200 (°C) (1-VII) [8] The separation module or separation tower according to the above [7], wherein the distance between the inner wall of the separation module or separation tower and the separation membrane closest to the inner wall is 0.1 cm or more and 50 cm or less. [9] A separation module or separation tower equipped with the separation membrane laminate according to [6] above, wherein the temperature Tos (°C) of the separation module or separation tower satisfies the following formula (1-VII): 45 (°C) ≦ Tos (°C) ≦ 200 (°C) (1-VII)

[10] The separation module or separation tower according to any one of [7] to [9] above, further comprising at least one of a dehumidifying mechanism, a heating mechanism, and a flame propagation suppression mechanism.

[11] A hydrogen recovery system equipped with a separation membrane, wherein the separation membrane is the separation membrane according to any one of [1] to [5] above, and wherein at least one temperature Tgm (°C) of the mixed gas M to be separated and recovered in the hydrogen recovery system or the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) (1-IX)

[12] A hydrogen recovery system equipped with the separation membrane laminate according to [6] above, and wherein at least one temperature Tgm (°C) of the mixed gas M to be separated and recovered in the hydrogen recovery system or the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) (1-IX)

[13] The hydrogen recovery system according to

[11] or

[12] , wherein the separation membrane is mounted in a separation module or a separation tower, and the distance between the inner wall of the separation membrane module or separation tower and the separation membrane closest to the inner wall is 0.1 cm or more and 50 cm or less.

[14] The hydrogen recovery system according to any of

[11] to

[13] above, which has a pressurization mechanism for the mixed gas M supplied to the separation membrane.

[15] The hydrogen recovery system according to any of

[11] to

[14] above, which further has at least one of a dehumidification mechanism, a heating mechanism, and a flame propagation suppression mechanism.

[16] The hydrogen recovery system according to any of

[11] to

[15] above, which has a pressure reduction mechanism on the permeation side of the separation membrane.

[17] A method for separating and recovering hydrogen from a mixed gas M of hydrogen and a gas L1 having a larger kinetic molecular diameter than hydrogen using a separation membrane, wherein the separation membrane is the separation membrane according to any one of the above [1] to [5], and at least one temperature Tgm (°C) of the mixed gas M or the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) (1-IX)

[18] A pressure F of the mixed gas M supplied to the separation membrane. Ｍ The method for separating and recovering hydrogen according to the above

[17] , wherein (MPa(G)) satisfies the following formula (1-XI): 0.0 (MPa(G))≦F Ｍ(MPa(G))≦0.2(MPa(G)) (1-XI)

[19] The method for separating and recovering hydrogen according to the above

[17] or

[18] , wherein the pressure on the permeation side of the separation membrane is reduced.

[20] The method for separating and recovering hydrogen according to the above

[19] , wherein the pressure on the permeation side of the separation membrane is −0.101 MPa(G) or more and −0.065 MPa(G) or less.

[21] The relative humidity RH in the mixed gas M Ｍ The method for separating and recovering hydrogen according to any one of the above

[17] to

[20] , wherein 0.0(%)≦RH Ｍ (%)≦5(%) (1-XIII)

[22] The method for separating and recovering hydrogen according to any one of the above

[18] to

[21] , wherein heating is performed so that at least one temperature Tgm (°C) of the mixed gas M or the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) (1-IX)

[23] The method for separating and recovering hydrogen according to any one of the above

[17] to

[22] , wherein the mixed gas M passes through a flame propagation suppression mechanism and then a separation membrane.

[24] The method for separating and recovering hydrogen according to any one of the above

[17] to

[23] , comprising a separation membrane module or a separation tower equipped with the separation membrane, and supplying the mixed gas M so that the maximum Reynolds number on the feed side of the separation membrane module or separation tower is 5 to 2000 and / or the maximum Reynolds number on the permeation side is 5 to 2000.

[25] The method for separating and recovering hydrogen according to any one of

[17] to

[24] above, wherein the gas L is oxygen, and the hydrogen-oxygen mixed gas is supplied so that the hydrogen concentration of the hydrogen-oxygen mixed gas on the permeate side after the separation and recovery step is more than 95.8 vol%.

[26] The method for separating and recovering hydrogen according to

[25] above, wherein the hydrogen-oxygen mixed gas is supplied so that the hydrogen concentration of the hydrogen-oxygen mixed gas on the permeate side after the separation and recovery step is 96.0 vol% or more and the hydrogen concentration of the hydrogen-oxygen mixed gas on the non-permeate side after the separation and recovery step is 15.5 vol% or less.

[27] The hydrogen permeance P(S) (mol / (m)) through the separation membrane, calculated within a temperature range Tam (°C) that satisfies the following formula (1-I), ２The activation energy Ep(S) (kJ / mol) of the separation membrane (except hydrogen) and the permeance P(L) (mol / (m ２ a separation membrane in which the activation energy Ep(L) (kJ / mol) of |Ep(L)| < |Ep(S)| satisfies the following formula (1-II): 5 (°C) ≦ Tam (°C) ≦ 200 (°C) (1-I) |Ep(L)| < |Ep(S)| (1-II)

[28] A method for separating and recovering hydrogen from a mixed gas M containing at least hydrogen and oxygen, wherein the temperature Tgm (°C) in the separation and recovery step satisfies the following formula (2-I): 45 (°C) ≦ Tgm (°C) ≦ 200 (°C) (2-I)

[29] The separation and recovery method according to

[28] above, wherein the composition ratio of hydrogen to oxygen in the mixed gas M supplied to the separation and recovery step is 2:1 or more, with an excess of hydrogen.

[30] The separation and recovery method according to

[28] or

[29] above, wherein the mixed gas M supplied to the separation and recovery step is within the explosive range.

[31] The separation and recovery method according to any one of

[28] to

[30] above, wherein a separation membrane is used in the separation and recovery step.

[32] The separation and recovery method according to

[31] above, wherein the separation membrane is an inorganic membrane.

[33] The separation and recovery method according to

[32] above, wherein the separation membrane has a surface-modified zeolite membrane.

[34] The separation and recovery method according to any one of

[31] to

[33] above, wherein the separation membrane is a polyimide membrane or a polyamide membrane.

[35] The pressure F of the mixed gas M supplied to the separation membrane Ｍ The separation and recovery method according to any one of the above

[31] to

[34] , wherein (MPa(G)) satisfies the following formula (2-III): 0.0 (MPa(G))≦F Ｍ (MPa(G))≦0.2(MPa(G)) (2-III)

[36] The separation and recovery method according to any one of the above

[31] to

[35] , wherein the pressure on the permeation side of the separation membrane is reduced.

[37] The separation and recovery method according to the above

[36] , wherein the pressure on the permeation side of the separation membrane is lower than −0.9 MPa(G).

[38] The relative humidity RH of the mixed gas M Ｍ The separation and recovery method according to any one of the above

[31] to

[37] , wherein 0.0(%)≦RH (%) satisfies the following formula (2-V): Ｍ(%)≦5.0(%) (2-V)

[39] The separation and recovery method according to any one of the above

[31] to

[38] , wherein at least one of the mixed gas M and the separation membrane is heated so that the temperature Tgm satisfies the above formula (2-I).

[40] The separation and recovery method according to any one of the above

[31] to

[39] , wherein the mixed gas M passes through a flame propagation suppression mechanism and then passes through a separation membrane.

[41] The separation and recovery method according to any one of the above

[31] to

[40] , wherein the mixed gas M is supplied so that the supply-side maximum Reynolds number and / or the permeation-side maximum Reynolds number is 5 or more and 2000 or less.

[42] The separation and recovery method according to any one of the above

[31] to

[41] , wherein the mixed gas M is supplied so that the hydrogen concentration of the mixed gas after permeation in the separation and recovery step is more than 95.8% by volume.

[43] The separation and recovery method according to

[42] above, wherein the mixed gas M is supplied so that the hydrogen concentration of the mixed gas on the permeate side after the separation and recovery step is 96.0 vol% or more and the hydrogen concentration of the mixed gas on the non-permeate side is 15.5 vol% or less.

[44] A separation module or separation tower for separating and recovering hydrogen from a mixed gas M containing at least hydrogen and oxygen, the separation module or separation tower having a temperature adjustment mechanism.

[45] The separation module or separation tower according to

[44] above, wherein the temperature adjustment mechanism includes a tubular flow path through which a heat transfer medium flows and / or an insulating section.

[46] The separation module or separation tower according to

[44] or

[45] above, wherein the temperature Tos (°C) of either the separation module or separation tower satisfies the following formula (2-VII): 51 (°C)≦Tos (°C)≦220 (°C) (2-VII)

[47] The separation module or separation tower according to any of

[44] to

[46] above, wherein the separation module or separation tower is equipped with a separation membrane.

[48] ​​The separation module or separation tower according to

[47] above, wherein the separation membrane is an inorganic membrane.

[49] The separation module or separation tower according to

[47] or

[48] above, wherein the separation membrane has a surface-modified zeolite membrane.

[50] The separation module or separation tower according to any of

[47] to

[49] above, wherein the distance between the inner wall of the separation module or separation tower and the separation membrane closest to the inner wall is 0.1 cm or more and 50 cm or less.

[51] The separation module or separation column according to any one of the above

[47] to

[50] , wherein the separation membrane has a tubular support, and the inner diameter φi (mm) of the support satisfies the following formula (2-IX): 6≦φi≦16 (2-IX)

[52] A hydrogen recovery system for separating and recovering hydrogen from a mixed gas M containing at least hydrogen and oxygen, the hydrogen recovery system comprising the separation module or separation column according to any one of the above

[44] to

[51] .

[53] The hydrogen recovery system according to the above

[52] , comprising a pressurizing mechanism for the mixed gas M supplied to the separation module or separation column.

[54] The hydrogen recovery system according to the above

[52] or

[53] , comprising a dehumidifying section for the mixed gas M and / or a heating section for the mixed gas M.

[55] The hydrogen recovery system according to any one of the above

[52] to

[54] , comprising a flame propagation suppression section.

[56] The hydrogen recovery system according to any one of

[52] to

[55] above, further comprising a pressure reducing mechanism downstream of the separation module or separation column.

[0015] According to the present invention, it is possible to provide a separation membrane for separating and recovering hydrogen, a separation membrane stack, a separation module or separation tower, a hydrogen recovery system, and a method for separating and recovering hydrogen, which are capable of separating and recovering hydrogen from a hydrogen-oxygen mixed gas, as well as from a mixed gas composed of molecules with relatively close dynamic molecular diameters, even when supplied at a relatively low pressure. Furthermore, it is possible to provide a method for separating and recovering hydrogen with high separation performance and high permeability from a mixed gas containing at least hydrogen and oxygen, a separation module or separation tower for separating and recovering hydrogen, and a hydrogen recovery system.

[0016] 1 is a schematic diagram of a composite separation membrane of the present invention. 2 is a schematic diagram of a gas flow type apparatus used to form a second separation section. 3 is a schematic diagram of the inside of a reaction tube of a gas flow type apparatus used to form a second separation section. 4 is a schematic diagram of a measurement apparatus (or separation apparatus) used to separate a mixed gas. 5 is an Arrhenius plot of the activation energy of each of hydrogen permeance and oxygen permeance (Example 1-1). 6 is a schematic diagram of a separation module having a heating mechanism. 7 is an Arrhenius plot of the activation energy of each of hydrogen permeance and oxygen permeance (Example 1-6). 8 is an Arrhenius plot of the activation energy of each of hydrogen permeance and oxygen permeance (Example 1-7). 9 is an Arrhenius plot of the activation energy of each of hydrogen permeance and nitrogen permeance (Example 1-8). 10 is an Arrhenius plot of the activation energy of each of hydrogen permeance and nitrogen permeance (Comparative Example 1-1). 11 is an Arrhenius plot of the activation energy of each of hydrogen permeance and oxygen permeance (Example 1-11). 1 is a schematic diagram of an experimental apparatus for determining the critical extinction pressure. 2 is a graph showing the relationship between the temperature of a hydrogen-oxygen mixed gas and the critical extinction pressure based on 20° C.

[0017] The following describes in more detail the embodiments of the present invention. However, the description of the constituent elements described below is an example of an embodiment of the present invention, and the present invention is not limited to these contents, and can be implemented in various modifications within the scope of its gist.

[0018] A first aspect of the present invention relates to a separation membrane, a separation membrane stack, a separation module or separation tower, a hydrogen recovery system, and a method for separating and recovering hydrogen. [Separation Membrane] The separation membrane of the present invention has a hydrogen permeance P(S) (mol / (m)) through the separation membrane, which is calculated within a temperature range Tam (°C) that satisfies the following formula (1-I): ２ The activation energy Ep(S) (kJ / mol) of the gas L (excluding hydrogen) for the separation membrane is calculated within the same temperature range. ２The activation energy Ep(L) (kJ / mol) of the hydrogen permeation constant (H2O 2 .s.Pa) satisfies the following formula (1-II): 5 (°C)≦Tam (°C)≦200 (°C) (1-I) |Ep(L)|<|Ep(S)| (1-II) When a mixed gas M described later is used, it is sufficient that at least one of the gases L constituting the mixed gas M satisfies the above formula (1-II), but preferably the gas other than hydrogen that accounts for the largest volume percentage in the mixed gas M satisfies the above formula (1-II), more preferably 80 volume % or more of the gases other than hydrogen in the mixed gas M satisfies the above formula (1-II), even more preferably 95 volume % or more of the gases other than hydrogen in the mixed gas M satisfies the above formula (1-II), and most preferably all of the gases L constituting the mixed gas M satisfies the above formula (1-II). In this specification, permeance (also referred to as "permeability") is the amount of a substance that permeates a separation membrane, expressed as a function of the membrane area (m ２ ), time (seconds), divided by the partial pressure difference (Pa) between the supply side and the permeation side of the permeating substance, and the unit is [mol / (m ２ .s.Pa)].

[0019] <Gas to be Separated> The gas to be separated in the present invention is a mixed gas containing hydrogen. There are no particular limitations on the gas to be separated, as long as hydrogen can be suitably separated and recovered using the separation membrane, separation membrane laminate, separation module or separation tower, hydrogen recovery system, and separation and recovery method of the present invention. In the present invention, when hydrogen is separated and recovered from a mixed gas M containing at least hydrogen having a relatively small kinetic molecular diameter and a gas L having a relatively large kinetic molecular diameter, any gas having a kinetic molecular diameter relatively larger than that of hydrogen can be selected as the gas L. Specific examples of the gas L include carbon dioxide, argon, oxygen, nitrogen, methane, etc., and it is preferable to include a gas selected from at least one of these. Furthermore, the gas L is more preferably composed of a gas selected from carbon dioxide, argon, oxygen, nitrogen, and methane, even more preferably composed of a gas selected from oxygen and nitrogen, and most preferably oxygen. Furthermore, the mixed gas may be a wet gas, but is more preferably a dry gas.

[0020] The separation membrane of the present invention is, for example, surface-modified in order to separate gases having a kinetic molecular diameter equal to or smaller than the pore size with high selectivity, and is based on the discovery that a unique tendency may be exhibited in the temperature dependence of the permeability (permeance) of each gas.

[0021] For comparison, the following two examples are given as general examples. The first general example is a zeolite membrane having a widely known CHA-type framework structure. The pore size of this zeolite membrane is 0.38 nm, but the activation energy of the permeance of hydrogen gas with a kinetic molecular diameter of 0.289 nm has a negative value, and increasing the temperature reduces the permeability. On the other hand, for example, the activation energy of the permeance of nitrogen gas with a relatively large kinetic molecular diameter of 0.364 nm also has a negative value, but this value is smaller (the absolute value is larger), and increasing the temperature reduces the permeability more significantly. In other words, there is a relationship in which the temperature dependence of molecules with large kinetic molecular diameters is high (the absolute value of the activation energy is large). Furthermore, from the perspective of process performance, in a hydrogen-nitrogen mixed gas, if the temperature is increased to achieve high selectivity for separating and recovering hydrogen gas, the permeability of hydrogen gas is sacrificed, and a sufficient recovery rate cannot be expected. Alternatively, if gas separation is performed at a lower temperature in order to achieve high permeability for separating and recovering hydrogen gas, selectivity is sacrificed, and the hydrogen purity of the permeated gas does not increase.

[0022] As a second general example, for example, a silica membrane produced by the widely known CVD method is exemplified. The pore size depends on the manufacturing method, and due to its amorphous structure, there is usually a distribution of pore sizes. However, the pore size of silica is small enough to fully exhibit its molecular sieve function, and its pore size is subnanometer. Here, the activation energy of the permeance of hydrogen gas with a kinetic molecular diameter of 0.289 nm has a positive value, and increasing the temperature improves the permeability. On the other hand, for example, the activation energy of the permeance of nitrogen gas with a relatively large kinetic molecular diameter of 0.364 nm also has a positive value, but its value is larger (the absolute value is also larger), and increasing the temperature improves the permeability more significantly. In other words, even in this case, the relationship that the temperature dependence of molecules with a large kinetic molecular diameter is large (the absolute value of the activation energy is large) holds true. Furthermore, from the viewpoint of process performance, if gas separation is performed at a lower temperature to achieve high selectivity for separating and recovering hydrogen gas from a hydrogen-nitrogen mixed gas, the hydrogen gas permeability will be sacrificed, and a sufficient recovery rate will not be expected. Alternatively, if gas separation is performed at a higher temperature to achieve high permeability for separating and recovering hydrogen gas, the selectivity will be sacrificed, and the hydrogen purity of the permeated gas will not increase.

[0023] As seen in these two general cases, for gases having a kinetic molecular diameter comparable to or smaller than the pore diameter of the separation membrane, the absolute value of the activation energy of the permeance of the gas consisting of molecules with a large kinetic molecular diameter is greater than the absolute value of the activation energy of the permeance of hydrogen. As a result, from the perspective of process performance, adjusting the separation / recovery temperature to achieve high selectivity for separating and recovering hydrogen usually sacrifices hydrogen permeability, resulting in a situation where a sufficient recovery rate cannot be expected. Alternatively, adjusting the separation / recovery temperature to achieve high permeability for separating and recovering hydrogen sacrifices selectivity, resulting in a lack of improvement in the purity of the hydrogen gas on the permeate side. In other words, when separating and recovering hydrogen from a mixed gas M containing hydrogen with a relatively small kinetic molecular diameter and a gas L with a relatively large kinetic molecular diameter, it has been difficult to improve the overall performance of the hydrogen separation / recovery process using the separation membrane, even if the separation / recovery temperature is adjusted, due to the relationship between the activation energy of the permeance of hydrogen and gas L and the kinetic molecular diameter of conventional separation membranes, particularly inorganic membranes.

[0024] However, by using the separation membrane of the present invention obtained by the process described in detail below, it is possible to separate gases with a dynamic molecular diameter equal to or smaller than the pore size with high selectivity. This is because the temperature dependence of the permeance of each gas exhibits a tendency not generally observed. When this separation membrane is used in a gas separation and recovery process, it is possible to improve the performance of the entire hydrogen separation and recovery process, i.e., to achieve both high selectivity and high permeability, which is a result that could not be achieved with conventional knowledge.

[0025] Specifically, as described above, the separation membrane of the present invention has a hydrogen permeance P(S) (mol / (m ２ The activation energy Ep(S) (kJ / mol) of the gas L (excluding hydrogen) for the separation membrane is calculated within the same temperature range. ２The activation energy Ep(L) (kJ / mol) of the hydrogen permeance (kJ / mol) of the hydrogen permeance (kJ / mol) is |Ep(L)| < |Ep(S)|. In other words, the absolute value of the activation energy of the hydrogen permeance, which has a small kinetic molecular diameter, is greater than the absolute value of the activation energy of the permeance of the gas L, which has a relatively large kinetic molecular diameter. This means that the "separation membrane has characteristics opposite to those of a general separation membrane." Note that a large absolute value of the activation energy means that the gas permeance, i.e., the permeation characteristics of the target gas, changes significantly whether the temperature is increased or decreased. Here, two typical cases will be described as examples.

[0026] In the first case, diffusion is considered to be the dominant factor in determining the gas permeance (gas permeability) of each gas to be separated. Normally, increasing the temperature improves the gas permeance of both molecules with small and large kinetic molecular diameters. However, molecules with large kinetic molecular diameters tend to be relatively temperature-dependent, while molecules with small kinetic molecular diameters, such as hydrogen, tend to be relatively temperature-dependent. Therefore, when the temperature is increased to allow molecules with small kinetic molecular diameters to pass through the membrane and be recovered, the gas permeability improves, but the gas separation performance decreases. When the gas permeance improves as the temperature is increased, the activation energy of the gas permeance has a positive value. Therefore, 0<Ep(S)<Ep(L).

[0027] In the second case, adsorption is considered to be the dominant factor in determining the gas permeance (gas permeability) of each gas to be separated. Normally, lowering the temperature improves the gas permeance of both molecules with small and large kinetic molecular diameters. However, molecules with large kinetic molecular diameters tend to be relatively temperature-dependent, while molecules with small kinetic molecular diameters, such as hydrogen, tend to be relatively temperature-dependent. Therefore, when lowering the temperature and passing the molecules through the membrane to recover molecules with small kinetic molecular diameters, the gas permeability improves, but the gas separation performance decreases. Note that when lowering the temperature improves the gas permeance, the activation energy of the gas permeance has a negative value, so Ep(L)<Ep(S)<0.

[0028] The relationship between the first and second cases can be expressed as |Ep(S)|<|Ep(L)|. Furthermore, depending on the combination of gases to be separated, one may be "dominated by adsorption" and the other may be "dominated by diffusion." Even in this case, |Ep(S)|<|Ep(L)| is generally true. In contrast, the present invention uses a separation membrane with the opposite characteristics to typical separation membranes, i.e., a large absolute value of activation energy indicating the temperature dependence of the permeance of gases having a relatively small kinetic molecular diameter, such as hydrogen, and a small absolute value of activation energy indicating the temperature dependence of the permeance of gases having a relatively large kinetic molecular diameter. By changing the temperature, the permeation performance of gases having a relatively small kinetic molecular diameter, such as hydrogen, can be improved while also increasing separation performance. It is possible to achieve both improved permeation performance and improved separation performance by increasing the temperature, or to achieve both improved permeation performance and improved separation performance by decreasing the temperature. In either case, the relationship can be expressed as |Ep(L)|<|Ep(S)|.

[0029] Furthermore, it is preferable that the separation membrane of the present invention always has a larger permeance for hydrogen gas with a small kinetic molecular diameter than for gas L with a relatively large kinetic molecular diameter. The separation membrane of the present invention has such properties, allowing it to efficiently and safely separate hydrogen from a mixed gas M. That is, it preferably satisfies the following formula (1-III): P(L)<P(S) (1-III) Furthermore, it is preferable that the separation membrane of the present invention satisfies the following formula (1-IV) for hydrogen with a relatively small kinetic molecular diameter and gas L with a relatively large kinetic molecular diameter: 0<Ep(L)<Ep(S) (1-IV) Such properties are highly preferable because they can be used in "heat separation," which heats the mixed gas to be separated, the separation membrane, the separation module or separation tower, the hydrogen recovery system, etc., to an appropriate temperature, thereby improving the permeance P(S) of hydrogen gas while simultaneously improving the selectivity α(S / L) of hydrogen gas relative to gas L, α(S / L)=P(S) / P(L).

[0030] <Activation Energy> The activation energy can be derived as follows. In the range of 5 ° C to 200 ° C (Tam (° C) in the above formula (1-I)), a temperature range for deriving the activation energy of permeance is appropriately set, and the permeance of each constituent gas in the mixed gas M to be separated is measured at multiple temperatures within that range, and this can be derived by least-squares approximation using the Arrhenius equation. It is reasonable that the temperature range for deriving the activation energy includes the temperature range in which the separation membrane of the present invention is actually used. In particular, since the separation membrane of the present invention can be suitably used for separating and recovering hydrogen gas from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1, safety is improved by setting the temperature to 200 ° C or less, and high hydrogen permeance can be obtained by setting the temperature to 5 ° C or more. Therefore, the lower limit of the temperature range for deriving the activation energy is 5 ° C or more, preferably 10 ° C or more, while the upper limit of the temperature range for deriving the activation energy is 200 ° C or less, preferably 150 ° C or less. That is, it is preferably in the range shown by the following formula (1-V): 10 (°C)≦Tam (°C)≦150 (°C) (1-V). Furthermore, the lower limit is more preferably 15°C or higher, even more preferably 20°C or higher, and particularly preferably 25°C or higher. Furthermore, the upper limit is more preferably 140°C or lower, even more preferably 130°C or lower, and particularly preferably 120°C or lower.

[0031] The gas supply form when deriving activation energy may be a single gas or a mixed gas for separation and recovery. The former is preferred from the viewpoint of eliminating the influence of interactions between different molecules when passing through the pores in the separation membrane. The latter is preferred from the viewpoint of constructing a separation and recovery process using a separation membrane, as it can derive activation energy that includes interactions between different molecules that occur in the actual separation and recovery process. In either gas supply form, it is preferable to derive the activation energy of the permeance of each gas by supplying it in the form of a dry gas. This is because in actual separation and recovery processes, a dehumidification process is required to avoid the influence of water vapor adsorption on the separation membrane.

[0032] Further, with regard to the supply pressure of the gas when deriving activation energy, since the separation membrane of the present invention can be suitably used for separating and recovering hydrogen gas from a hydrogen-oxygen mixed gas (hydrogen detonation gas) of hydrogen: oxygen = 2: 1, taking into consideration the possibility of suppressing flame propagation in the event of ignition, it is preferable to separate at as low a pressure as possible, and the upper limit of the supply pressure (gauge pressure, hereinafter referred to as (G)) is preferably 0.20 MPa (G) or less, more preferably 0.10 MPa (G) or less, even more preferably 0.05 MPa (G) or less, and particularly preferably 0.02 MPa (G) or less. On the other hand, the lower limit of the gas supply pressure when deriving activation energy is necessary to pressurize in consideration of the piping pressure loss, so it is preferable to be normal pressure, i.e., 0.0 MPa (G) or more, more preferably 0.005 MPa (G) or more, more preferably 0.010 MPa (G) or more, and particularly preferably 0.015 MPa (G) or more.

[0033] The pressure on the permeation side when deriving activation energy is preferably reduced. This is because the separation membrane of the present invention can be suitably used for separating and recovering hydrogen gas from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1. As described above, it is preferable for safety that the supply pressure be as low as possible, and in order to ensure the pressure difference between the supply side and the permeation side for separation, it is preferable to reduce the pressure on the permeation side.

[0034] In the separation membrane of the present invention, it is preferable to set the temperature range in which the activation energy is derived, the supply form of the gas to be separated, the supply pressure of the supplied mixed gas M, and the permeation side pressure so that the permeance of hydrogen gas having a small kinetic molecular diameter is always greater than the permeance of gas L having a relatively large kinetic molecular diameter.

[0035] The separation membrane of the present invention is preferably an inorganic membrane, more preferably a zeolite membrane, and particularly preferably a surface-modified zeolite membrane. These membranes are non-flammable and therefore highly safe, and also have high separation performance. Details will be described later.

[0036] [Separation Membrane Stack] The separation membrane stack of the present invention comprises a separation membrane on a support. The separation membrane used here is not particularly limited as long as it is the separation membrane of the present invention described above, i.e., has the above-described physical properties. Here, the support is preferably tubular, and the inner diameter φi (mm) satisfies the following formula (1-VI): 6 (mm)≦φi (mm)≦16 (mm) (1-VI). A specific structure, as shown in FIG. 1 , is preferably a separation membrane stack 100 having a support 101, a first separation section 103 arranged in contact with the support, and a second separation section 104 having an amorphous structure arranged in contact with the first separation section but not in contact with the support. The inner diameter may be the average diameter equivalent to a circle, but if there is no variation of 1 mm or more, the value (diameter) at the end may be used without calculating the average. The separation membrane stack of the present invention can be used in a separation module or a separation tower, as described below. Separation membrane stacks are described in detail below.

[0037] (Support) The support is not particularly limited as long as it can form the first separation section at its upper end, but it is preferably chemically stable for forming the first separation section. Furthermore, it preferably has sufficient mechanical strength for the separation process. From this perspective, examples include ceramics, ceramic sintered bodies, metals, metal sintered bodies, and various insulators, and inorganic porous materials are preferred. In particular, when the first separation section is a zeolite having various structures, the support is preferably an inorganic porous material. The support may also be composed of multiple inorganic porous materials with different pore sizes. When the first separation section is a zeolite, for example, a ceramic sintered body such as silica, α-alumina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride, or silicon carbide is preferred. Among these, inorganic porous supports containing at least one of alumina, silica, and mullite are preferred. Using these inorganic porous supports facilitates partial zeolite formation, strengthening the bond between the support and the zeolite and facilitating the formation of a dense membrane with high separation performance.

[0038] The shape of the inorganic porous support is not particularly limited as long as it can effectively separate the target mixed gas M, and specific examples include flat, tubular, and cylindrical shapes. In the present invention, it is preferable to form a zeolite membrane on such an inorganic porous support, i.e., on the upper end of the support. The upper end of the inorganic porous support is defined as the surface that forms the first separation section, and refers to the surface portion of the inorganic porous support where the zeolite is crystallized. As long as it is a surface, it may be any surface of each shape, or multiple surfaces. For example, in the case of a cylindrical support, it may be either the outer surface or the inner surface, or in some cases, both the outer and inner surfaces. In this case, either surface is considered to be the upper end.

[0039] The average pore diameter of the upper end of the inorganic porous support is not particularly limited, but a controlled pore diameter is preferred. The average pore diameter of the upper end of the inorganic porous support is usually 0.02 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, and usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less. When the average pore diameter is 0.02 μm or more, a sufficient permeation amount is obtained, and when it is 20 μm or less, the strength of the support itself is sufficient. In addition, the proportion of pores at the upper end of the inorganic porous support is appropriate, and a sufficiently dense zeolite membrane is formed. The average pore diameter from the lower end to the upper end of the support can be changed depending on the purpose. In particular, it is preferable to make the average pore diameter smaller at the upper end of the support where the first separation section is to be formed than in other parts of the support to obtain a dense zeolite membrane. The average pore diameter can be determined by mercury porosimetry, gas adsorption method, etc.

[0040] The average thickness (wall thickness) of the inorganic porous support is usually 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, and usually 7 mm or less, preferably 5 mm or less, more preferably 3 mm or less. The inorganic porous support is used for the purpose of imparting mechanical strength to the liberation structure consisting of the support and the zeolite membrane (hereinafter sometimes simply referred to as the "liberation structure"). When the average thickness of the inorganic porous support is 0.1 mm or more, the liberation structure has sufficient strength and is resistant to impact, vibration, etc. Furthermore, when the average thickness of the inorganic porous support is 7 mm or less, diffusion of the permeated substance is good, and sufficient permeability is obtained.

[0041] The porosity of the inorganic porous support is usually 20% by volume or more, preferably 25% by volume or more, more preferably 30% by volume or more, and usually 70% by volume or less, preferably 60% by volume or less, more preferably 50% by volume or less. The porosity of the inorganic porous support affects the permeation flow rate during gas separation, and if it is 20% by volume or more, sufficient diffusion of the permeant is likely to be obtained. On the other hand, if it is 70% by volume or less, sufficient strength of the inorganic porous support is likely to be obtained. Note that porosity can be easily determined by mercury intrusion porosimetry, Archimedes' method, cross-sectional scanning electron microscope (SEM) observation, etc. Porosity can also be calculated from volume and mass using true specific gravity. In addition, the upper end of the inorganic porous support may be polished with a file or the like as necessary. For example, if there are burrs on the surface, polishing with a file or the like can smooth the surface. Conversely, roughening a smooth surface can also improve the efficiency of subsequent processes such as crystal loading and crystal growth.

[0042] (First Separation Section) The constituent material of the first separation section is not particularly limited, and for example, an inorganic porous thin layer made of ceramics, a silica membrane, or the like can be used. However, it is preferable to use a zeolite polycrystalline thin film for the first separation section. That is, it is preferable to form the first separation section by forming a zeolite polycrystalline thin film on the inorganic porous support by crystal growth. The components constituting the first separation section may include, in addition to zeolite, inorganic binders such as silica and alumina, and organic compounds such as polymers, as necessary, but it is preferable that the first separation section be composed essentially of zeolite alone.

[0043] The thickness of the first separation section made of zeolite is not particularly limited, but is usually 0.1 μm or more, preferably 0.6 μm or more, more preferably 1.0 μm or more, and usually 100 μm or less, preferably 60 μm or less, more preferably 20 μm or less. A membrane thickness of 100 μm or less provides a sufficient permeation amount, while a membrane thickness of 0.1 μm or more provides good selectivity for the permeating gas and sufficient membrane strength. The particle size of the zeolite is not particularly limited, but is usually preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 100 nm or more, with the upper limit being equal to the membrane thickness. A zeolite particle size of 30 nm or more prevents the grain boundaries from becoming large, and sufficient permeation selectivity is obtained. Therefore, it is particularly preferred that the particle size of the zeolite is the same as the membrane thickness. When the particle size of the zeolite is the same as the membrane thickness, the zeolite grain boundaries are smallest. Zeolite membranes obtained by hydrothermal synthesis, as described below, are particularly preferred because the particle size of the zeolite and the membrane thickness tend to be the same. This average particle size can be determined from observation using an electron microscope or the like, or from diffraction when irradiated with a laser or the like. Specifically, for example, since the grain boundaries of zeolite crystals can be easily seen by observation using an electron microscope, the image can be processed to remove extremely large and small particles, and the average particle size equivalent to a circle can be determined.

[0044] The shape of the zeolite liberation structure (corresponding to 101 and 103 in FIG. 1 ), in which a zeolite membrane is formed on a support, is not particularly limited, and any shape can be adopted, such as a tubular (cylindrical), hollow fiber, monolith, or honeycomb shape. Among these, a tubular (cylindrical) shape is preferred in terms of ease of separation and recovery. The size of the zeolite liberation structure is also not particularly limited. For example, in the case of a tubular (cylindrical) structure, a length of 2 cm to 200 cm, an inner diameter of 0.05 cm to 2 cm, and a thickness of 0.5 mm to 4 mm are practical and preferred. As mentioned above, the membrane length is usually 2 cm to 200 cm. However, extremely short membranes can be difficult to handle and can result in disadvantages such as extremely low processable volumes during actual gas separation. Even extremely long membranes can be disadvantageous, such as requiring extremely large equipment during production. Therefore, the lower limit of the membrane length is preferably 5 cm or more, more preferably 8 cm or more, even more preferably 17.5 cm or more, and most preferably 35 cm or more. The upper limit of the membrane length is preferably 170 cm or less, more preferably 150 cm or less, even more preferably 130 cm or less, and most preferably 110 cm or less. In particular, separation membranes with a membrane length of about 38 cm to 102 cm during production are most preferable from various viewpoints, such as the size of the production equipment, production costs, and handling. One of the separation functions of the zeolite liberation structure is separation as a molecular sieve, and it can effectively separate gas molecules having a size greater than the effective pore size of the zeolite used from gas molecules having a size smaller than that. There is no upper limit to the molecules used for separation, but the molecular size is usually about 100 Å or less.

[0045] The type of main zeolite constituting the zeolite liberation structure is not particularly limited. All zeolite structure types defined by the International Zeolite Society are included. Zeolite having a pore structure of 12 or less oxygen rings is more preferred, and zeolite having a pore structure of 8 or less oxygen rings is even more preferred, and zeolite having a pore structure of 6 oxygen rings is also acceptable. The smaller the oxygen ring, the greater the effect of pore narrowing by the modification reaction, and the more likely the molecular sieve effect is to occur. In the present invention, zeolite having a 6-membered oxygen ring or 8-membered oxygen ring structure is particularly preferred.

[0046] The value of n in the zeolite having an n-membered oxygen ring here indicates the zeolite with the largest number of oxygen atoms among the pores formed by oxygen and T elements (elements other than oxygen that form the framework) that form the zeolite framework. For example, when pores with 12-membered oxygen rings and 8-membered oxygen rings exist, as in MOR-type zeolite, it is considered to be a 12-membered oxygen ring zeolite.

[0047] Examples of zeolites having a pore structure with an 8-membered oxygen ring or less include AEI, AFG, AFX, ANA, BRE, CAS, CDO, CHA, DDR, DOH, EAB, EPI, ERI, ESV, FAR, FRA, GIS, GIU, GOO, ITE, KFI, LEV, LIO, LOS, LTN, MAR, MEP, MER, MEL, MON, MSO, MTF, MTN, MWF, NON, PAU, PHI, RHO, RTE, RTH, RUT, SGT, SOD, TOL, TSC, UFI, VNI, and YUG.

[0048] Examples of zeolites having a 6- to 8-membered oxygen ring structure include AEI, AFG, AFX, ANA, CHA, EAB, ERI, ESV, FAR, FRA, GIS, ITE, KFI, LEV, LIO, LOS, LTN, MAR, MWF, PAU, RHO, RTH, SOD, TOL, UFI, etc. In this specification, the structure of zeolite is indicated by the code specifying the structure of zeolite established by the International Zeolite Association (IZA), as described above.

[0049] The oxygen n-membered ring structure determines the size of the pores in zeolites. In zeolites with smaller oxygen n-membered rings, the H ２ Since the pore size is smaller than the kinetic diameter of the O molecule, the permeability is low and it may not be practical. Also, if the oxygen is larger than the 8-membered ring structure, the pore size becomes large, which may reduce the separation performance for small gas components, limiting its application.

[0050] The framework density (T / 1000Å) of zeolite is not particularly limited, but is usually 17 or less, preferably 16 or less, more preferably 15.5 or less, and particularly preferably 15 or less, and is usually 10 or more, preferably 11 or more, and more preferably 12 or more. The framework density refers to the number of elements other than oxygen (T elements) that constitute the framework per 1000Å of the zeolite, and this value is determined by the structure of the zeolite. The relationship between framework density and zeolite structure is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2001 ELSEVIER.

[0051] In the present invention, preferred zeolite structures are AEI, AFG, AFX, CHA, EAB, ERI, ESV, FAR, FRA, GIS, ITE, KFI, LEV, LIO, LOS, LTN, MAR, MWF, PAU, RHO, RTH, SOD, TOL, and UFI, more preferred structures are AEI, CHA, ERI, KFI, LEV, PAU, RHO, RTH, and UFI, even more preferred structures are CHA and LEV, and the most preferred structure is CHA.

[0052] In the present invention, CHA-type zeolite refers to a CHA structure, a code for specifying the structure of zeolites established by the International Zeolite Association (IZA). This is a zeolite with a crystalline structure equivalent to that of naturally occurring chabazite. CHA-type zeolite has a structure characterized by three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 3.8 x 3.8 Å, and this structure is characterized by X-ray diffraction data.

[0053] The framework density (T / 1000 Å) of CHA zeolite is 14.5. In the present invention, when the zeolite liberation structure contains CHA zeolite, the intensity of the peak near 2θ = 17.9° in the X-ray diffraction pattern is preferably at least 0.5 times the intensity of the peak near 2θ = 20.8°.

[0054] Here, the peak intensity refers to the measured value minus the background value. The peak intensity ratio (hereinafter sometimes referred to as "peak intensity ratio A"), expressed as (peak intensity around 2θ = 17.9°) / (peak intensity around 2θ = 20.8°), is usually 0.5 or more, preferably 1 or more, more preferably 1.2 or more, and particularly preferably 1.5 or more. There is no particular upper limit, but it is usually 1,000 or less.

[0055] Furthermore, when the zeolite liberation structure contains CHA-type zeolite, it is preferable that the peak intensity around 2θ = 9.6° in the X-ray diffraction pattern is at least twice as large as the peak intensity around 2θ = 20.8°. In terms of the peak intensity ratio (hereinafter sometimes referred to as "peak intensity ratio B") expressed as (peak intensity around 2θ = 9.6°) / (peak intensity around 2θ = 20.8°), it is usually 2 or more, preferably 2.5 or more, more preferably 3 or more, more preferably 4 or more, even more preferably 6 or more, particularly preferably 8 or more, and most preferably 10 or more. There is no particular upper limit, but it is usually 1000 or less.

[0056] The X-ray diffraction pattern referred to here is obtained by irradiating the surface on which the zeolite is primarily attached with X-rays using a CuKα radiation source, with the scanning axis set to θ / 2θ. The shape of the sample to be measured is not particularly limited as long as it allows X-ray irradiation to the surface on which the zeolite of the liberation structure is primarily attached, and the produced liberation structure as is, or one cut to an appropriate size within the constraints of the apparatus, is preferred, as it effectively represents the characteristics of the liberation structure.

[0057] Here, when the upper end of the zeolite liberation structure is a curved surface, the X-ray diffraction pattern may be measured by fixing the irradiation width using an automatic variable slit. The X-ray diffraction pattern when an automatic variable slit is used refers to a pattern obtained by performing variable to fixed slit correction. Here, the peak near 2θ = 17.9° refers to the largest peak not attributable to the substrate that exists in the range of 17.9° ± 0.6°.

[0058] The peak around 2θ = 20.8° refers to the largest peak present in the range of 20.8° ± 0.6° among peaks not attributable to the substrate. The peak around 2θ = 9.6° refers to the largest peak present in the range of 9.6° ± 0.6° among peaks not attributable to the substrate. According to COLLECTION OF SIMULATED XRD POWDER PATTERNS FOR ZEOLITE Third Revised Edition 1996 ELSEVIER, the peak around 2θ = 9.6° in the X-ray diffraction pattern has a space group in the rhombohedral setting.

[0059]

[0060] When the compound is designated as No. 166, the peak is derived from the plane with index (1,0,0) in the CHA structure. In addition, the peak at around 2θ = 17.9° in the X-ray diffraction pattern is derived from the space group in the rhombohedral setting.

[0061]

[0062] When the compound is designated as No. 166, the peak originates from the plane with index (1,1,1) in the CHA structure. The peak at around 2θ = 20.8° in the X-ray diffraction pattern is in the rhombohedral setting and the space group is

[0063] This peak is derived from the plane with indices (2,0,-1) in the CHA structure when the zeolite is isolated from a CHA-type aluminosilicate (No. 166). According to Halil Kalipcilar et al., "Synthesis and Separation Performance of SSZ-13 Zeolite Membranes on Tubular Supports," Chem. Mater. 2002, 14, 3458-3464, the typical ratio (peak intensity ratio B) of the peak intensity derived from the (1,0,0) plane to the peak intensity derived from the (2,0,-1) plane in the zeolite liberation structure of a CHA-type aluminosilicate is less than 2.

[0064] Therefore, a peak intensity ratio B of 2 or greater is considered to mean that the zeolite crystals have grown in an oriented manner such that the (1,0,0) plane is nearly parallel to the upper end of the liberation structure when the CHA structure is in a rhombohedral setting. The growth of zeolite crystals in an oriented manner in the zeolite liberation structure is advantageous in that it allows for the production of a dense membrane with high separation performance.

[0065] In a zeolite liberation structure of a CHA-type aluminosilicate, the typical ratio (peak intensity ratio A) of the intensity of the peak derived from the (1,1,1) plane to the intensity of the peak derived from the (2,0,-1) plane is less than 0.5. Therefore, a peak intensity ratio A of 0.5 or more is considered to mean that, for example, when the CHA structure is in a rhombohedral setting, the zeolite crystals grow in an oriented state such that the (1,1,1) plane is nearly parallel to the upper end of the liberation structure. Oriented growth of zeolite crystals in a zeolite liberation structure is advantageous in that it allows for the production of a dense membrane with high separation performance.

[0066] Thus, the fact that either the peak intensity ratio A or B is within the above-mentioned specific range indicates that the zeolite crystals have grown in an oriented state, and a dense membrane with high separation performance has been formed. The larger the peak intensity ratio A or B, the stronger the degree of orientation, and generally, the stronger the degree of orientation, the denser the membrane that has been formed. Generally, the stronger the orientation, the higher the separation performance tends to be, but the optimal degree of orientation for high separation performance varies depending on the mixture to be separated (gas to be separated). Therefore, it is desirable to select and use a zeolite free separation structure with an optimal degree of orientation depending on the mixture to be separated.

[0067] <Method for Producing Liberation Structure> The method for producing the liberation structure is not particularly limited as long as it is a method that can form a first separation portion on the support. The method for producing the liberation structure is described in detail below. In the present invention, the method for producing the zeolite liberation structure is not particularly limited, but a method of forming zeolite on an inorganic porous support by hydrothermal synthesis is preferred. Specifically, for example, the zeolite liberation structure can be prepared by placing a reaction mixture for hydrothermal synthesis (hereinafter, this may be referred to as an "aqueous reaction mixture"), whose composition has been adjusted and made uniform, in a heat-resistant and pressure-resistant container such as an autoclave, inside which an inorganic porous support is loosely fixed, sealing the reaction mixture, and heating for a certain period of time.

[0068] The aqueous reaction mixture contains a Si source, an Al source, an alkali source, and water, and may further contain an organic template as needed. Examples of the Si source used in the aqueous reaction mixture include amorphous silica, colloidal silica, silica gel, sodium silicate, amorphous aluminosilicate gel, tetraethoxysilane (TEOS), and trimethylethoxysilane.

[0069] Examples of Al element sources that can be used include sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum oxide, and amorphous aluminosilicate gel. In addition to the Al element source, other element sources, such as Ga, Fe, B, Ti, Zr, Sn, and Zn, may also be included. In crystallizing the zeolite, an organic template (structure-directing agent) can be used as needed, and zeolite synthesized using an organic template is preferred. By synthesizing using an organic template, the ratio of silicon atoms to aluminum atoms in the crystallized zeolite increases, improving acid resistance and steam resistance.

[0070] The organic template may be of any type as long as it can form the desired zeolite liberation structure. One type of template may be used, or two or more types may be used in combination. When the zeolite is a CHA type, amines or quaternary ammonium salts are typically used as the organic template. For example, the organic templates described in U.S. Pat. No. 4,544,538 and U.S. Patent Publication No. 2008 / 0075656 are preferred.

[0071] Specific examples include cations derived from alicyclic amines such as cations derived from 1-adamantanamine, cations derived from 3-quinacridinal, and cations derived from 3-exo-aminonorbornene. Among these, cations derived from 1-adamantanamine are more preferred. When a cation derived from 1-adamantanamine is used as an organic template, CHA-type zeolite capable of forming a dense membrane is crystallized. By forming a dense membrane, CHA-type zeolite with high separation performance can be obtained.

[0072] Of the cations derived from 1-adamantanamine, N,N,N-trialkyl-1-adamantanammonium cations are more preferred. The three alkyl groups in the N,N,N-trialkyl-1-adamantanammonium cation are usually each independently an alkyl group, preferably a lower alkyl group, more preferably a methyl group. The most preferred compound among them is the N,N,N-trimethyl-1-adamantanammonium cation.

[0073] Such cations are accompanied by anions that are not detrimental to the formation of CHA-type zeolites. Representative of such anions are Cl, － ,Br － , I － Examples of suitable organic templates include halogen ions such as those mentioned above, hydroxide ions, sulfate ions, and carboxylate ions such as acetate ions. Of these, hydroxide ions are particularly preferred. Another organic template that can be used is the N,N,N-trialkylbenzylammonium cation. In this case, the alkyl groups are each independently selected, preferably lower alkyl groups, and more preferably methyl groups. Among these, the most preferred compound is the N,N,N-trimethylbenzylammonium cation. The anions associated with this cation are the same as those mentioned above.

[0074] The alkali source used in the aqueous reaction mixture may be a hydroxide ion of the counter anion of the organic template, an alkali metal hydroxide such as NaOH or KOH, or Ca(OH). ２ Alkaline earth metal hydroxides such as those mentioned above can be used. The type of alkali is not particularly limited, and typically, Na, K, Li, Rb, Cs, Ca, Mg, Sr, Ba, etc. are used. Among these, Li, Na, and K are preferred, and K is more preferred. Two or more types of alkali may be used in combination, and specifically, it is preferred to use Na and K, or Li and K in combination.

[0075] The ratio of the Si and Al element sources in the aqueous reaction mixture is typically determined by the molar ratio of the oxides of each element, i.e., SiO ２ / Al ２ O ３Expressed as a molar ratio. ２ / Al ２ O ３ The molar ratio is not particularly limited, but is usually 5 or more, preferably 8 or more, more preferably 10 or more, and even more preferably 15 or more. In addition, the molar ratio is usually 10,000 or less, preferably 1,000 or less, more preferably 300 or less, and even more preferably 100 or less.

[0076] SiO ２ / Al ２ O ３ When the molar ratio is within this range, a dense zeolite liberation structure is formed, resulting in a membrane with high separation performance. Furthermore, since the formed zeolite contains a moderate amount of Al atoms, separation ability is improved for gas components that are adsorbable to Al. Furthermore, when Al is within this range, a zeolite liberation structure with high acid resistance and water vapor resistance is obtained. The ratio of the silica source to the organic template in the aqueous reaction mixture is SiO ２ The molar ratio of the organic template to the SiO ２ (molar ratio)) is usually 0.005 or more, preferably 0.01 or more, more preferably 0.02 or more, and usually 1 or less, preferably 0.4 or less, more preferably 0.2 or less.

[0077] Organic template / SiO ２ When the molar ratio of the Si element source to the alkali source is within the above range, a dense zeolite liberation structure can be formed, and the formed zeolite has high resistance to acid and steam. （２／ｎ） O / SiO ２ (Here, M represents an alkali metal or alkaline earth metal, and n represents its valence, 1 (alkali metal) or 2 (alkaline earth metal).) The molar ratio is usually 0.02 or more, preferably 0.04 or more, more preferably 0.05 or more, and usually 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less.

[0078] When forming a CHA-type zeolite liberation structure, it is preferable to include K among the alkali metals in order to produce a denser and more crystalline film. In this case, the molar ratio of K to all alkali metals and / or alkaline earth metals including K is usually 0.01 or more and 1 or less, preferably 0.1 or more and 1 or less, and more preferably 0.3 or more and 1 or less. As described above, K is added to the aqueous reaction mixture in a rhombohedral setting to form a space group of 0.01 or more and 1 or less.

[0079]

[0080] When the compound (No. 166) is used, there is a tendency to increase the ratio (peak intensity ratio B) of the peak intensity around 2θ=9.6°, which is a peak derived from the plane with index (1,0,0), to the peak intensity around 2θ=20.8°, which is a peak derived from the plane (2,0,-1), or the ratio (peak intensity ratio A) of the peak intensity around 2θ=17.9°, which is a peak derived from the plane (1,1,1), to the peak intensity around 2θ=20.8°, which is a peak derived from the plane (2,0,-1).

[0081] The ratio of the Si element source to water is SiO ２ The molar ratio of water to ２ O / SiO ２ The molar ratio (molar ratio) is usually 10 or more, preferably 30 or more, more preferably 40 or more, and particularly preferably 50 or more, and usually 1000 or less, preferably 500 or less, more preferably 200 or less, and particularly preferably 150 or less. When the molar ratios of the substances in the aqueous reaction mixture are within these ranges, a dense zeolite liberation structure can be produced. The amount of water is particularly important in producing a dense zeolite liberation structure, and conditions in which the amount of water relative to silica is higher than the general conditions used in powder synthesis methods tend to produce denser membranes.

[0082] Generally, the amount of water used to synthesize powdered CHA-type zeolite is H ２ O / SiO ２ (molar ratio) is about 15 to 50. ２ O / SiO ２By using conditions where the (molar ratio) is high (50 to 1000), i.e., where there is a lot of water, it is possible to obtain a zeolite free separation structure with high separation performance, in which CHA-type zeolite is crystallized into a dense membrane on the inorganic porous support. Furthermore, while it is not necessary to have seed crystals present in the reaction system during hydrothermal synthesis, adding seed crystals can promote the crystallization of zeolite on the inorganic porous support. The method for adding seed crystals is not particularly limited, and methods such as adding seed crystals to an aqueous reaction mixture, as in the synthesis of powdered zeolite, or attaching seed crystals to the inorganic porous support can be used.

[0083] When producing a zeolite liberation structure, it is preferable to attach seed crystals to the inorganic porous support. By attaching seed crystals to the inorganic porous support in advance, it becomes easier to produce a dense zeolite liberation structure with good separation performance. The seed crystals used can be of any type as long as they promote crystallization, but for efficient crystallization, they preferably have the same crystal type as the zeolite liberation structure to be formed. When forming a CHA-type zeolite liberation structure, it is preferable to use CHA-type zeolite seed crystals.

[0084] The particle size of the seed crystals is usually 0.5 nm or more, preferably 1 nm or more, more preferably 2 nm or more, and usually 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less. The method for attaching the seed crystals to the inorganic porous support is not particularly limited, and examples thereof include a dipping method in which the seed crystals are dispersed in a solvent such as water and the support is immersed in the dispersion to attach the seed crystals, and a method in which the seed crystals are mixed with a solvent such as water to form a slurry, which is then applied to the inorganic porous support. The dipping method is desirable for controlling the amount of attached seed crystals and producing zeolite liberation structures with good reproducibility.

[0085] The solvent in which the seed crystals are dispersed is not particularly limited, but water is particularly preferred. The amount of the seed crystals to be dispersed is not particularly limited, and is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and particularly preferably 3% by mass or less, based on the total mass of the dispersion.

[0086] When the amount of dispersed seed crystals is equal to or greater than the above lower limit, the amount of seed crystals attached to the inorganic porous support is sufficient, so that zeolite is generated over the entire support during hydrothermal synthesis, and there are no areas where zeolite is not generated, resulting in a defect-free membrane. Since the amount of seed crystals attached to the inorganic porous support by the dipping method becomes almost constant when the amount of seed crystals in the dispersion is equal to or greater than a certain level, when the amount of seed crystals in the dispersion is equal to or less than the above upper limit, there is no waste of seed crystals, which is advantageous in terms of cost.

[0087] It is desirable to attach seed crystals to the inorganic porous support by dipping or by applying a slurry, and then dry the support, after which the zeolite liberation structure is formed. The amount of seed crystals to be attached to the inorganic porous support in advance is not particularly limited, and the amount of seed crystals to be attached to the inorganic porous support in advance is preferably 1 / m of the support. ２ The mass per unit area is usually 0.01 g or more, preferably 0.05 g or more, more preferably 0.1 g or more, and usually 100 g or less, preferably 50 g or less, more preferably 10 g or less, and even more preferably 8 g or less.

[0088] When the amount of seed crystals is equal to or greater than the lower limit, crystals are easily generated, the film grows sufficiently, and the film growth tends to be uniform. When the amount of seed crystals is equal to or less than the upper limit, the seed crystals do not increase the surface irregularities, and seed crystals that fall from the support do not easily promote the growth of spontaneous nuclei, so film growth on the support is not inhibited. Therefore, a dense zeolite liberation structure is easily generated.

[0089] When forming a zeolite liberation structure on an inorganic porous support by hydrothermal synthesis, there are no particular limitations on the method for immobilizing the inorganic porous support, and any form, such as vertical or horizontal placement, may be used. In this case, the zeolite liberation structure may be formed by a static method, or the zeolite liberation structure may be formed by stirring the aqueous reaction mixture. The temperature during the formation of the zeolite liberation structure is not particularly limited, but is usually 100°C or higher, preferably 120°C or higher, and more preferably 150°C or higher, and usually 200°C or lower, preferably 190°C or lower, and more preferably 180°C or lower. If the reaction temperature is above the lower limit, the zeolite is likely to crystallize. If the reaction temperature is below the upper limit, the reaction temperature is too high, and a zeolite type different from the desired zeolite is not produced.

[0090] The heating time is not particularly limited, but is usually 1 hour or more, preferably 5 hours or more, and more preferably 10 hours or more, and usually 10 days or less, preferably 5 days or less, more preferably 3 days or less, and even more preferably 2 days or less. If the reaction time is equal to or greater than the lower limit, the zeolite is sufficiently crystallized. On the other hand, if the reaction time is equal to or less than the upper limit, a zeolite of a different type from the desired zeolite is not produced.

[0091] The pressure during the formation of the zeolite liberation structure is not particularly limited, and the autogenous pressure generated when an aqueous reaction mixture placed in a sealed container is heated to this temperature range is sufficient. Furthermore, an inert gas such as nitrogen may be added as necessary. The zeolite liberation structure obtained by hydrothermal synthesis is washed with water and then heat-treated. Here, heat treatment refers to drying the zeolite liberation structure by applying heat, or, if a template is used, calcining and removing the template.

[0092] When the purpose of the heat treatment is drying, the temperature is usually 50° C. or higher, preferably 80° C. or higher, and more preferably 100° C. or higher, and usually 200° C. or lower, and preferably 150° C. or lower. When the purpose is to remove the template by firing, the temperature is usually 350° C. or higher, preferably 400° C. or higher, more preferably 430° C. or higher, and even more preferably 480° C. or higher, and usually 900° C. or lower, preferably 850° C. or lower, more preferably 800° C. or lower, and even more preferably 750° C. or lower.

[0093] When the purpose is to calcinate and remove the organic template, if the heat treatment temperature is equal to or higher than the lower limit, the organic template can be sufficiently calcined and removed, and no organic template remains, resulting in sufficient pores in the zeolite, ensuring a sufficient permeation flux during separation and concentration. On the other hand, if the heat treatment temperature is equal to or lower than the upper limit, the difference in thermal expansion coefficient between the support and the zeolite does not become large, preventing cracks from occurring in the zeolite liberation structure. Therefore, sufficient density of the zeolite liberation structure can be ensured, resulting in sufficient separation performance.

[0094] The heating time is not particularly limited as long as the zeolite liberation structure is sufficiently dried or the organic template is removed by calcination, and is preferably 0.5 hours or more, more preferably 1 hour or more. The upper limit is not particularly limited, and is usually within 200 hours, preferably within 150 hours, more preferably within 100 hours. When the purpose is to remove the template by calcination, the heating treatment may be carried out in an air atmosphere, but it is also possible to carry out the heating treatment in an N ２ The heating may be carried out in an atmosphere containing an inert gas such as the above or oxygen.

[0095] When hydrothermal synthesis is performed in the presence of an organic template, it is appropriate to wash the resulting zeolite liberation structure with water and then remove the organic template by, for example, heat treatment or extraction, preferably heat treatment, i.e., calcination. The heating rate during heat treatment for calcination removal of the organic template is desirably as slow as possible to minimize the difference in thermal expansion coefficients between the support and the zeolite, which could cause cracks in the zeolite liberation structure. The heating rate is typically 5°C / min or less, preferably 2°C / min or less, more preferably 1°C / min or less, and particularly preferably 0.5°C / min or less. Taking workability into consideration, the heating rate is typically 0.1°C / min or more.

[0096] The rate of temperature drop after calcination must also be controlled to avoid cracking in the zeolite liberation structure. As with the rate of temperature rise, the slower the rate, the more desirable. The rate of temperature drop is usually 5°C / min or less, preferably 2°C / min or less, more preferably 1°C / min or less, and particularly preferably 0.5°C / min or less. In consideration of workability, the rate is usually 0.1°C / min or more. The zeolite liberation structure may be ion-exchanged as needed. When synthesis is performed using an organic template, ion exchange is usually performed after removing the organic template. Ions to be exchanged include protons, Na, and the like. ＋ , K. ＋ , Li ＋ Alkali metal ions such as Ca ２＋ , Mg ２＋ , Sr ２＋ , Ba ２＋ and ions of transition metals such as Fe, Cu, and Zn. Among these, protons, Na ＋ , K. ＋ , Li ＋ Alkali metal ions such as are preferred.

[0097] Ion exchange is the process of converting the zeolite liberation structure after calcination (e.g., when an organic template is used) into NH ４ NO ３ , NaNO ３The zeolite may be treated with an aqueous solution containing an ammonium salt or ions to be exchanged, or in some cases with an acid such as hydrochloric acid, usually at a temperature of room temperature to 100°C, followed by washing with water. If necessary, the zeolite may be calcined at 200°C to 500°C. The air permeability [L / (m ２ ・h)] is usually 1400 L / (m ２ ·h) or less, preferably 1000 L / (m ２ ·h) or less, more preferably 700 L / (m ２ ·h) or less, more preferably 600 L / (m ２ ·h) or less, more preferably 500 L / (m ２ ·h) or less, particularly preferably 300 L / (m ２ h) or less, most preferably 200 L / (m ２ The lower limit of the permeation amount is not particularly limited, but is usually 0.01 L / (m ２ h) or more, preferably 0.1 L / (m ２ h) or more, more preferably 1 L / (m ２ ・h) or more.

[0098] (Second Separation Section) The material of the second separation section formed at the upper end of the first separation section is not particularly limited, but it must be a material that exhibits higher gas separation performance than the first separation section. For example, to exhibit high separation performance, a material with a smaller pore size or a higher density than the first separation section (layer) is preferable. Specifically, the main constituent elements are preferably Si and O, and silica is particularly preferable. In a preferred configuration of the separation membrane of the present invention, as described above, by forming a layer with smaller pores, preferably an amorphous layer, at the upper end of the liberation structure (e.g., zeolite liberation structure), separation performance that cannot be achieved by the function of the zeolite pore size can be easily achieved. Furthermore, in the separation membrane of the present invention, the density of the amorphous layer of the composite separation membrane is preferably higher than that of the underlying zeolite. If the ratio of the density of the amorphous layer to the density of the underlying zeolite is defined as relative density, a high relative density can increase the separation performance of the amorphous layer compared to zeolite, thereby achieving favorable separation performance. Specifically, a relative density of greater than 1 is preferable.

[0099] On the other hand, by setting the relative density of the amorphous layer to a certain level or less, the porosity of the amorphous layer becomes appropriate, the pores are not excessively narrowed, the permeation resistance becomes appropriate, and the expected permeance of the permeating component can be obtained. ３ ) and a CHA-type zeolite free separation structure are assumed, the relative density is 1.46. On the other hand, considering the low permeability reported for amorphous silica separation membranes, a relative density of 1.46 is considered to be the upper limit. Therefore, the relative density is 1.46 or less, preferably 1.30 or less, and more preferably 1.15 or less. The second separation section preferably contains Si atoms, and it is particularly preferable that the Si atoms are atoms supplied in the gas phase. In the gas phase, Si can be advantageously supplied to the upper end of the first separation section with higher reactivity, making it easier to fully achieve the desired separation performance. There are no particular limitations on the method of supplying in the gas phase, and for example, a liquid Si compound such as a silicate oligomer can be supplied using a bubbler or the like.

[0100] The thickness of the second separation section is the thickness from the end (lower end) of the second separation section that contacts the first separation section to the opposite end (upper end), and is preferably 5 nm or more and 200 nm or less. In order to exhibit practical permeability, it is preferable that the second separation section be formed to an appropriate thickness. According to the inventors' studies, the second separation section is preferably membrane-like, and the lower limit of its membrane thickness is 5 nm or more, preferably 7 nm or more, more preferably 10 nm or more, and particularly preferably 12 nm or more. By setting the thickness at such a level, the second separation section is less susceptible to minor defects and unevenness on the surface of the first separation section. On the other hand, the second separation section is preferably thinner than a certain thickness so as not to exhibit excessive gas permeation resistance, and the upper limit of its membrane thickness is 200 nm or less, preferably 100 nm or less, more preferably 50 nm or less, and most preferably 25 nm or less. Furthermore, when the first separation section is made of porous ceramics or zeolite, it is preferable that the second separation section has an adjustable thickness, and it is also preferable that the second separation section has a different type of structure with high density. For example, an amorphous structure is preferable. Alternatively, a different type of material with a high density, such as silica, is preferable. Therefore, amorphous silica having the above-mentioned film thickness is a more preferable embodiment. As described above, the second separation part is most preferably an amorphous silica film with a film thickness of 5 nm or more and 200 nm or less.

[0101] As described above, the separation membrane laminate (composite separation membrane) of the present invention preferably has a first separation section and a second separation section, and the relative density of the second separation section to the first separation section is preferably 1.05 or more and 1.30 or less. When the relative density is 1.05 or more, high separation performance is obtained. On the other hand, when the relative density is 1.30 or less, the pores are not narrowed and permeation resistance is maintained. From the above viewpoints, it is more preferable that the relative density of the second separation section to the first separation section is 1.11 or more and 1.15 or less.

[0102] In the separation membrane laminate (composite separation membrane) of the present invention, the absolute density of the second separation portion is 1.58 g / cm ３ Above, 1.96g / cm ３The absolute density of the second separation portion is preferably 1.58 g / cm or less. ３ On the other hand, when the absolute density of the second separation section is 1.96 g / cm or more, it is advantageous in terms of the denseness and density conditions required to exhibit separation performance. ３ When the absolute density of the second separation section is 1.67 g / cm or less, the permeation resistance of the permeating gas is low, and the pores are narrowed, allowing the separation performance to be exhibited. ３ Above, 1.72g / cm ３ More preferably, it is:

[0103] <Method for manufacturing separation membrane laminate> A liberation structure is produced by the method described above, and a second separation section is formed on the liberation structure by exposing the side of the first separation section opposite the side in contact with the support (top end) to a gas containing a molecular compound having at least Si atoms. Below, we will explain how to form an amorphous second separation section on the top end of a zeolite liberation structure in which the first separation section is zeolite. A Si compound containing Si atoms is made into a gaseous state and, depending on the conditions, is supplied to the top end of the zeolite liberation structure together with water vapor to undergo a reaction treatment (exposure treatment). This forms a thin layer of the Si compound on the top end of the zeolite liberation structure, resulting in a separation layer with pores smaller than the pore size inherent to zeolite, which is thought to improve separation performance.

[0104] As the molecular compound having Si atoms (Si compound) used in this upper end treatment, for example, alkylalkoxysilanes such as methyltriethoxysilane, 3-aminopropyltriethoxysilane, and 1,1,3,3-tetramethoxy-1,3-dimethylpropanedisiloxane, organosilicon compounds having siloxane such as hexamethyldisiloxane, organosilicon compounds having silazane such as hexamethyldisilazane, silicates such as tetramethoxysilane and tetraethoxysilane, silicate oligomers such as methylsilicate oligomer and ethylsilicate oligomer, colloidal silica, sodium silicate, silica sol, etc. can be used as the liquid raw material before vaporization of the gaseous raw material.

[0105] Among these, silicate or silicate oligomer is preferred in terms of reactivity, with tetraethoxysilane and methylsilicate oligomer being particularly preferred. Methylsilicate oligomer is more preferred, with polymethoxysiloxane being most preferred. These Si compounds may be used alone or in combination of two or more.

[0106] The Si compound can be converted into a gaseous state by vaporization from a Si compound liquid by heating, or by bubbling an inert gas for transportation, such as nitrogen, helium, argon, xenon, or krypton, into a container and generating a gas. The treatment method is not particularly limited as long as it allows a source gas to be supplied to the upper end of the zeolite liberation structure and reacted. For example, there are the following two methods. One method involves placing the zeolite liberation structure, the Si compound liquid, and water in a sealed reactor, and heating the three components to generate a gas generated by vaporization of the Si compound in the sealed reactor, and then reacting the gas generated by vaporization of the water at high temperature on the upper end of the zeolite liberation structure (hereinafter, this method may be referred to as the "sealed reactor method"). The other is a method in which a gas is passed through a bubbler (gas generator) containing a Si compound, and the generated Si compound gas is carried along with a carrier gas and supplied to a flow-type reaction tube in which a zeolite liberation structure is installed, and the reaction is carried out above the upper end of the zeolite liberation structure (hereinafter, this method may be referred to as a "flow-type reactor method").

[0107] First, we will explain the process using a sealed reaction vessel. The sealed reaction vessel method involves coexisting a zeolite liberation structure, a gas generated from a Si compound, and steam generated from water in a sealed reaction vessel under desired temperature conditions, and allowing the reaction to occur on the top end of the zeolite liberation structure. The sealed reaction vessel is not particularly limited, and any vessel capable of accommodating the shape and dimensions of the zeolite liberation structure can be used. For example, a stainless steel autoclave with a Teflon inner tube can be used. By placing a stainless steel autoclave with a Teflon inner tube in a thermostatic chamber set at a desired temperature, the saturated vapor pressure of the steam and gas generated from the Si source at that temperature is achieved, generating saturated steam of the gas generated from the Si source and the steam within the vessel. The steam and Si source sources can be placed in any shape as long as they fit within the sealed reaction vessel. The water and liquid Si source may be placed in small containers or impregnated into porous materials.

[0108] The treatment temperature is usually 20°C or higher, preferably 60°C or higher, more preferably 80°C or higher, and usually 200°C or lower, preferably 150°C or lower, more preferably 130°C or lower. When the temperature is above the lower limit, the dehydration condensation reaction and hydrolysis reaction between the Si compound, the upper end of the zeolite first separation section, and the Si compound proceed sufficiently, resulting in sufficient modification by the Si compound and sufficient improvement in the hydrophilicity of the upper end of the zeolite first separation section. On the other hand, when the temperature is below the upper limit, the reaction at the upper end of the zeolite first separation section does not proceed too far, resulting in low permeation resistance and a membrane sample with high permeation performance. In the production method of the present invention, it is preferable that all steps are carried out at 200°C or lower.

[0109] The treatment time is usually 1 hour or more, preferably 2 hours or more, more preferably 3 hours or more, and usually 24 hours or less, preferably 8 hours or less, more preferably 5 hours or less. When the treatment time is equal to or greater than the lower limit, the reaction at the upper end of the zeolite first separation section proceeds sufficiently, and a sufficient effect is obtained. On the other hand, when the treatment time is equal to or less than the upper limit, the reaction at the upper end of the zeolite first separation section does not proceed too much, and the permeation resistance is reduced, resulting in a membrane sample with high permeation performance.

[0110] Next, a flow-through reactor process for treating the upper end of the zeolite liberation structure will be described. In this case, gas generated from the Si compound and steam generated from water are generated separately and supplied to a reaction tube containing a zeolite liberation structure, causing a reaction at the upper end of the zeolite liberation structure. This process allows the gas generated from the Si compound and steam generated from water to be supplied to the reaction tube at any time, either separately or simultaneously. Therefore, the process can be carried out in multiple stages. Specifically, the process may include a stage in which the gas generated from the Si compound and steam generated from water are simultaneously supplied to and circulated through the reaction tube, or a stage in which the gas generated from the Si compound or steam generated from water is separately supplied to and circulated through the reaction tube. The overall process can be configured by arbitrarily combining these elementary stages.

[0111] For example, treatment of the upper end of the zeolite liberation structure in the reaction tube is carried out in three consecutive stages by controlling the supply gas. Specifically, in the first stage, only water vapor generated from water is supplied to the reaction tube using a carrier gas. In this stage, the water component is adsorbed to the upper end of the zeolite liberation structure in the reaction tube. In the second stage, both gas generated from the Si compound and water vapor generated from water are supplied to the reaction tube using a carrier gas. In this stage, the Si compound and water vapor react at the upper end of the first zeolite separation section. In the third stage, only water vapor generated from water is supplied to the reaction tube using a carrier gas. In this stage, the reaction of detaching organic groups from the Si compound proceeds.

[0112] The shape of the reaction tube for the upper end modification treatment is not particularly limited, and may be any container that can accommodate any shape and size of zeolite liberation structures, such as tubular, hollow fiber, monolith, honeycomb, etc.

[0113] The treatment time is usually 1 hour or more, preferably 2 hours or more, more preferably 3 hours or more, and usually 24 hours or less, preferably 12 hours or less, more preferably 8 hours or less. When the treatment time is equal to or greater than the lower limit, the reaction at the upper end of the zeolite first separation section proceeds sufficiently, and a sufficient effect is obtained. On the other hand, when the treatment time is equal to or less than the upper limit, the reaction at the upper end of the zeolite first separation section does not proceed too much, the permeation resistance is low, and a membrane sample with high permeation performance is obtained.

[0114] A preferred composite separation membrane of the present invention is obtained by forming an amorphous silica layer as the second separation section through the above reaction. While amorphous silica separation membranes have been reported in the past, there have been no reports of their widespread industrial use. This is due to the unstable performance of amorphous silica separation membranes, particularly their poor stability to moisture. The instability of these amorphous silica separation membranes is presumably due to the fact that the material is produced under high-temperature conditions of 300°C or higher, and the formed amorphous silica is metastable, structurally unstable, and reactive to moisture. After membrane formation, the amorphous silica reacts with moisture, altering its properties and changing its permeability. In other words, the instability of these amorphous silica separation membranes is thought to be due to the high-temperature conditions used in membrane formation. To obtain a second separation section composed of stable amorphous silica, a stable composite separation membrane can be produced by avoiding the formation of amorphous silica at temperatures above 300°C and forming the amorphous silica layer at lower temperatures, such as 200°C or lower. This allows for the production of a stable composite separation membrane with water resistance.

[0115] The treatment temperature is usually 20°C or higher, preferably 60°C or higher, more preferably 80°C or higher, and usually 200°C or lower, preferably 150°C or lower, more preferably 130°C or lower. A temperature of 100°C or lower is most preferred. When the temperature is above the lower limit, the dehydration condensation reaction and hydrolysis reaction between the Si compound, the upper end of the zeolite first separation section, and the Si compound proceed sufficiently, resulting in sufficient modification treatment with the Si compound and sufficient improvement in the hydrophilicity of the upper end of the zeolite first separation section. On the other hand, when the temperature is below the upper limit, the reaction at the upper end of the zeolite first separation section does not proceed too far, resulting in low permeation resistance and a membrane sample with high permeation performance.

[0116] In the flow reactor system (flow-type zeolite liberation structure upper end treatment), the flow rate of the gas bubbling or entraining and transporting the Si compound and water gas (hereinafter referred to as the "supply flow rate") is not particularly limited, but in order to supply the amount of Si compound or water necessary for the reaction, the flow rate is usually 0.1 ml / min or more, preferably 1 ml / min or more, more preferably 10 ml / min or more, and even more preferably 25 ml / min or more, and the supply flow rate is usually 5000 ml / min or less, preferably 1000 ml / min or less, and more preferably 500 ml / min or less.

[0117] The treatment of the upper end of the zeolite liberation structure can be carried out, for example, using an apparatus (flow-type reactor system; raw material supply gas flow-type zeolite liberation structure upper end reaction treatment apparatus) schematically shown in Fig. 2 as follows. That is, in Fig. 2, a container (bubbler) 1 for generating gas from a Si compound, a container (bubbler) 2 for generating steam from water, a tubular reaction tube 3, and a valve 8 are installed in a thermostatic chamber 11 through a piping system. A temperature control device is attached to the thermostatic chamber 11 so as to enable temperature control of the container (bubbler), reaction tube, and gas. The piping system is equipped with a gas flow controller 4, a steam recovery device 5 for the exhaust gas, a back pressure valve 6, and a gas flow meter 7 outside the thermostatic chamber 11. Fig. 3 shows a schematic diagram of a tubular reaction tube 21 (hereinafter sometimes simply referred to as "reaction tube") incorporated as part of a flow-type reactor system (raw material supply gas flow-type zeolite liberation structure upper end reaction treatment apparatus). In the example shown in FIG. 3 , the inner diameter of the tubular reaction tube 21 is 15 mm. A tubular zeolite liberation structure 22 with an outer diameter of 12 mm is installed in the reaction tube for treatment. The zeolite liberation structure 22 is fixed inside the reaction tube by a zeolite membrane fixing jig 23 (hereinafter, sometimes simply referred to as a "jig"). The jig 23 has holes or notches to prevent gas flow. The zeolite membrane fixing jig 23 maintains a constant distance between the upper end of the zeolite liberation structure 22 and the inner wall of the reaction tube 21, ensuring stable flow of the reaction feed gas. After the zeolite liberation structure 22 is installed, the reaction tube is sealed with a flange 24. The feed gas enters the reaction tube through a feed gas inlet pipe 25, passes through the upper end of the tubular zeolite liberation structure 22, and is discharged through an exhaust gas pipe 26. By changing the gas supply flow rate, the linear velocity and flow state of the gas at the upper end of the zeolite liberation structure 22 can be controlled.

[0118] The procedure and convenience of supplying the raw material gas in a flow-type reactor system (a raw material supply gas flow-type zeolite liberation structure upper end treatment device) are described using Figure 2. The porous monolayer-zeolite membrane composite (zeolite liberation structure) to be treated is placed in the tubular reaction tube 3, and the piping's built-in valve 8 is closed. Furthermore, a container (bubbler) 1 containing a Si compound raw material liquid and water, respectively, for generating Si compound gas, and a container (bubbler) 2 for generating water vapor from water are installed in the piping, and the valve 8 is closed. The temperature of the thermostatic chamber 11 is set to the desired setting value to uniformize the temperature inside the thermostatic chamber. Then, by controlling the necessary valves and operating the gas flow controller, a gas containing the Si compound gas and a gas containing water vapor are supplied to the tubular reaction tube 3. The type of gas supplied (gas containing the Si compound raw material, gas containing water vapor), flow rate, and duration can be adjusted as desired. After the treatment process, the gas supplied to the tubular reaction tube 3 passes through the steam collector 5, the back pressure valve 6 and the flow meter 7, and is then discharged to the outside of the apparatus. The pressure inside the tubular reaction tube 3 can be adjusted by controlling the back pressure valve 6.

[0119] It is not entirely clear why such a treatment results in the aforementioned tendency in the activation energy of gas permeance. However, it is possible that gas adsorption due to the polarity inherent in the CHA-type zeolite membrane is blocked to some extent by the siloxane network or silica-modified portion formed on its surface, and conversely, gas diffusion becomes dominant in the modified portion. In other words, it is possible that the aforementioned tendency in the activation energy of gas permeance is manifested by a complex phenomenon other than a simple molecular sieve. Considering this, it is possible that similar characteristics may be manifested in separation membranes having composite structures such as composite separation membranes having silica-modified portions formed on various zeolite membranes other than CHA-type, composite separation membranes having carbon networks formed on zeolite membranes, composite separation membranes having carbon networks formed on silica membranes prepared by various CVD / sol-gel methods, and composite separation membranes having silica-modified portions formed on carbon membranes. In other words, it is thought that such a tendency in the activation energy of gas permeance may occur when the first and second separation sections have different gas separation characteristics, such as gas adsorption characteristics, gas diffusion characteristics, and gas desorption characteristics, or when there is an interaction such as the second separation section shielding the characteristics of the first separation section.

[0120] This separation membrane can be suitably used to separate and recover hydrogen from mixed gases, but is particularly suitable for recovering hydrogen from mixed gases containing both hydrogen and oxygen. It is most suitable for recovering hydrogen from a hydrogen-oxygen mixed gas (hydrogen detonation gas) in which the supplied mixed gas has a stoichiometric composition of hydrogen:oxygen = 2:1. Once ignited, a mixed gas containing hydrogen and oxygen may undergo deflagration or detonation. Separation membranes intended for application to separation and recovery processes in such situations are required to be non-flammable, have high separation performance, and be able to safely and efficiently separate and recover hydrogen, the target gas. For this reason, inorganic membranes made of inorganic materials are preferred. Furthermore, among inorganic membranes, membranes containing zeolite and silica membranes are more preferable from the perspective of safety than carbon membranes. Furthermore, considering high recovery, zeolite membranes, which tend to have high permeance, are even more preferable. As mentioned above, surface-modified zeolite membranes are most preferable. In this case, the zeolite membrane is most preferably a zeolite membrane having a CHA-type framework structure in terms of membrane performance.

[0121] Furthermore, zeolite membranes, silica membranes, and carbon membranes may all be formed on tubular supports, and the lower limit of the inner diameter φi (mm) of the support is preferably 6 mm or more. On the other hand, the upper limit of the inner diameter of the support is preferably 16 mm or less. That is, the inner diameter φi (mm) of the support preferably satisfies the following formula (1-VI): 6 (mm)≦φi (mm)≦16 (mm) (1-VI). The lower limit is more preferably 7 mm or more, and even more preferably 8 mm or more. The upper limit of the inner diameter is more preferably 14 mm or less, even more preferably 12 mm or less, and particularly preferably 10 mm or less. This is the result of taking into consideration the mechanical strength of the tubular support. The feed gas may be supplied to the outside of the tubular support on which the separation active layer is formed, and hydrogen may be separated and recovered from the inside thereof. Alternatively, the feed gas may be supplied to the inside of the tubular support, and hydrogen may be separated and recovered from the outside of the tubular support on which the separation active layer is formed. However, in the separation of hydrogen-oxygen mixed gases and other mixed gases containing flammable gases, which are preferably applied in the present invention, the resistance of the separation membrane from the viewpoint of mechanical strength in the event of ignition is also important. In particular, according to the inventors' studies, when the support is made of ceramics such as alumina, the resistance to the pressure increase when an explosion / detonation occurs on the outside tends to be higher than the resistance to the pressure increase when an explosion / detonation occurs on the inside. It was also found that the inner diameter should be within the aforementioned range. Note that a tubular shape is preferable from the viewpoint of mechanical strength compared to a flat membrane configuration. In this case, the inner diameter may be the average diameter equivalent to a circle, and if it does not change significantly along the tube, the value (diameter) at the end may be used. More preferably, this diameter range is maintained throughout the entire tube.

[0122] [Separation module or separation tower] The separation membrane of the present invention can be adapted to separation and recovery processes by mounting it on an outer cylinder and modularizing it to form a separation module or an even larger separation tower. Here, the temperature Tos of the separation module or separation tower is 45 ° C. or higher and 200 ° C. or lower. The temperature range Tam for deriving activation energy is 5 ° C. or higher and 200 ° C. or lower, but for the following reason, the separation module or separation tower is 45 ° C. or higher and 200 ° C. or lower. That is, the temperature Tos (° C.) of the separation module or separation tower satisfies the following formula (1-VII). 45 (° C.) ≦ Tos (° C.) ≦ 200 (° C.) ... (1-VII) The reason why the temperature of the separation module or separation tower is 45 ° C. or higher and 200 ° C. or lower is that the separation membrane of the present invention can be suitably used for separating and recovering hydrogen gas from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen = 2:1 ratio. Therefore, it is preferable from the standpoint of safety to set the temperature to 200 ° C. or lower. Furthermore, the inventors' investigations have shown that a temperature of 45°C or higher is appropriate for the separation module or separation tower, particularly for increasing the permeance of hydrogen gas within an appropriate range. Therefore, the lower limit of the temperature range of the separation module or separation tower is 45°C or higher, and preferably 51°C or higher. On the other hand, the upper limit of the temperature range of the separation module or separation tower is 200°C or lower, and preferably 150°C or lower. That is, it is preferable to satisfy the following formula (1-VIII): 51 (°C)≦Tos (°C)≦150 (°C) (1-VIII). Furthermore, the lower limit is more preferably 60°C or higher, even more preferably 70°C or higher, and particularly preferably 80°C or higher. The upper limit is more preferably 140°C or lower, even more preferably 130°C or lower, and particularly preferably 120°C or lower.

[0123] The separation module or separation column of the present invention is equipped with the separation membrane of the present invention, and the temperature of the separation module or separation column is within the temperature range in which the activation energy of the separation membrane is derived. Therefore, under any condition selected from the temperature range of the separation module or separation column, the supply form of the gas to be separated, the supply pressure of the gas, and the permeation side pressure, it is preferable that the permeance of hydrogen gas having a small kinetic molecular diameter is always larger than the permeance of gas L having a relatively large kinetic molecular diameter. That is, it is preferable that the following formula (1-III) is satisfied: P(L)<P(S) (1-III) Furthermore, it is preferable that the separation module or separation column of the present invention satisfies the following formula (1-IV) for hydrogen having a relatively small kinetic molecular diameter and gas L having a relatively large kinetic molecular diameter. 0<Ep(L)<Ep(S) (1-IV) By "heat separation," in which the mixed gas to be separated is heated to an appropriate temperature using a separation module or separation tower, it is possible to improve the permeance P(S) of hydrogen gas while simultaneously improving the selectivity α(S / L) = P(S) / P(L) of hydrogen gas relative to gas L, which is preferable.

[0124] The separation membrane constituting the separation module or separation column of the present invention is preferably an inorganic membrane, more preferably a zeolite membrane, and particularly preferably a surface-modified zeolite membrane. These membranes are non-flammable and therefore highly safe, and also have high separation performance. Details will be described later.

[0125] Furthermore, when the separation module or separation column of the present invention is used to separate and recover hydrogen from a mixed gas M containing hydrogen with a relatively small kinetic molecular diameter and a gas L with a relatively large kinetic molecular diameter, any gas with a kinetic molecular diameter relatively larger than that of hydrogen can be selected as the gas L. Specific examples of the gas L include carbon dioxide, argon, oxygen, nitrogen, methane, etc., and it is preferable to include a gas selected from at least one of these. Furthermore, the gas L is more preferably composed of a gas selected from carbon dioxide, argon, oxygen, nitrogen, and methane, even more preferably composed of a gas selected from oxygen and nitrogen, and most preferably oxygen. The mixed gas may be a wet gas, but is more preferably a dry gas.

[0126] The separation module or separation column of the present invention can use a separation membrane stack having a separation membrane on a support, and it is preferable that the inner diameter φi (mm) of the support satisfies the following formula (1-VI): 6 (mm)≦φi (mm)≦16 (mm) (1-VI).

[0127] When separating a mixed gas using a separation module or separation tower incorporating the separation membrane of the present invention, it is preferable that the gas flow within the separation module or separation tower be laminar. In particular, in the separation of a hydrogen-oxygen mixed gas, to which the present invention is particularly suitable, it is desirable to accurately determine the hydrogen-to-oxygen composition ratio in the gas flow direction for the feed gas, permeate gas, and non-permeate gas. This is to determine whether the flowing hydrogen-oxygen mixed gas is in the explosive or detonation range relative to the gas flow direction. Generally, the viscosity of gas increases with increasing temperature, so that, other conditions being equal, a higher temperature makes it easier to achieve a laminar gas flow. From this perspective, performing heated separation within an appropriate temperature range using the separation membrane, separation module, or separation tower of the present invention not only improves both the permeability and separation performance of the separation membrane, but also has the synergistic effect of maintaining a laminar gas flow within the separation module or separation tower, making it highly preferable.

[0128] Furthermore, from this viewpoint, the lower limit of the distance between the inner wall of the separation membrane module or separation tower and the surface of the separation membrane closest to the inner wall is preferably 0.1 cm or more, taking into consideration the assembly tolerances required during actual module production, etc. Also, it is more preferably 0.2 cm or more, even more preferably 0.5 cm or more, and particularly preferably 1 cm or more. On the other hand, if the distance between the inner wall of the separation membrane module or separation tower and the surface of the separation membrane closest to the inner wall is excessively wide, it may not be possible to maintain a laminar flow as a gas flow, and the upper limit of this distance is preferably 50 cm or less, more preferably 25 cm or less, even more preferably 10 cm or less, and particularly preferably 2 cm or less.

[0129] Any material can be selected for the outer cylinder constituting the separation module or separation tower. However, from the viewpoint of use in the hydrogen-oxygen mixed gas separation and recovery process to which the present invention is suitably applied, metal is preferred, and from the viewpoint of cost, resin is preferred. In the former case, it is particularly preferable to construct the outer cylinder from stainless steel. The outer cylinder may be configured to contain only the separation membrane. For example, in a location where strong sunlight irradiation is expected, such as an artificial photosynthesis plant, the outer cylinder can be heated to a temperature of 45°C or higher simply by being installed outdoors without a special heating mechanism. In such cases, the surface color of the outer cylinder is preferably other than white, more preferably a color with a brightness of 7 or less, even more preferably a color with a brightness of 5 or less, and most preferably a color with a brightness of 3 or less. In the most preferred case, the surface color is black. The outer cylinder preferably has other additional functions, such as a built-in dehumidifying mechanism, a heating mechanism, and a flame propagation suppression function. That is, it is preferable that the device further has at least one of a dehumidifying mechanism, a heating mechanism, and a flame propagation suppression function.

[0130] <Dehumidifying mechanism> The dehumidifying mechanism is preferably located inside the outer casing of the separation membrane module or separation tower on the gas supply side thereof. The dehumidifying mechanism can be configured by arranging granular materials such as silica gel, zeolite, etc. on the gas supply side of the separation module or separation tower. Also, for example, it is possible to make a portion of the gas supply side of a zeolite membrane on a tubular alumina support function as the dehumidifying mechanism. Note that when granular materials such as silica gel, zeolite, etc. are arranged on the gas supply side of the separation module or separation tower, by appropriately controlling the particle size, it is possible for them to simultaneously perform part or all of the flame propagation suppression function.

[0131] <Heating mechanism> The heating mechanism may be, for example, a flow path for circulating a heat medium that is installed so as to be in contact with the outer wall surface of the outer cylinder of the separation module or separation tower, a mechanism for efficiently applying hot air to the outer wall surface of the outer cylinder, or a heating element that is directly wrapped around the outer wall surface of the outer cylinder. In the case of a flow path for circulating a heat medium, for example, when water is used as the heat medium, a mechanism for heating / cooling water may be provided in a location separate from the separation module or separation tower to adjust the temperature. Furthermore, in the case of a heating element that is directly wrapped around the outer wall surface, it is preferable for safety reasons that the heating element itself be covered with a metal sheath or the like. By heating the separation module or separation tower using such a heating mechanism, the separation membrane of the present invention can simultaneously achieve higher separation performance and higher permeability.

[0132] It is more preferable that the dehumidifying mechanism and the heating mechanism have the function of reducing the relative humidity of the mixed gas immediately before it is supplied to the separation membrane. This is because the relative humidity can be reduced in two stages by first removing some of the water vapor from the mixed gas supplied by the dehumidifying mechanism and then raising the temperature by the heating mechanism.

[0133] <Flame Propagation Suppression Mechanism> The flame propagation suppression mechanism is particularly suitable for use when separating and recovering hydrogen from a hydrogen-oxygen mixed gas or the like using a separation module or separation tower equipped with the separation membrane of the present invention. The flame propagation suppression mechanism can be installed in the outer casing of the separation module or separation tower at any location selected from the gas supply side, gas permeation side, and gas non-permeation side. The gas supply side, in particular, is where the mixed gas before separation flows, and therefore has the highest risk of ignition. Therefore, it is preferable to install a flame propagation suppression mechanism on the gas supply side. Furthermore, the non-permeation side will receive a hydrogen-oxygen mixed gas with a reduced hydrogen concentration or an increased oxygen concentration. However, since this does not necessarily mean that the non-permeation side is outside the detonation or explosion range, it is preferable to install a flame propagation suppression mechanism on the non-permeation side. Furthermore, the permeation side will receive a hydrogen-oxygen mixed gas with an increased hydrogen concentration or a decreased oxygen concentration. Generally, the flow of gases other than the target gas to be recovered to the permeation side cannot be completely avoided, and therefore the permeation side will also typically contain a hydrogen-oxygen mixed gas. Therefore, it is preferable to install a flame propagation suppression mechanism on the permeation side. The flame propagation suppression mechanism can be constructed from a narrow passage (a passage narrower than other parts), a sintered metal body, a mesh structure, etc. The former may be filled with explosion-resistant granules. The sintered metal body, etc. is preferably constructed from stainless steel.

[0134] [Hydrogen Recovery System] The hydrogen recovery system of the present invention is a hydrogen recovery system equipped with a separation membrane, and the hydrogen permeance P(S) (mol / (m ２ s Pa)) and the permeance P (L) (mol / (m ２ The activation energy Ep(L) (kJ / mol) of the gas mixture M to be separated and recovered in the recovery system satisfies the following formula (1-II), and at least one of the temperatures Tgm (°C) of the gas mixture M to be separated and recovered in the recovery system or the temperature of the separation membrane satisfies the following formula (1-IX): |Ep(L)|<|Ep(S)| (1-II) 45 (°C)≦Tgm(°C)≦200 (°C) (1-IX)

[0135] In the hydrogen recovery system of the present invention, it is preferable that formulas (1-III), (1-IV), and (1-X) are satisfied, as described above for the separation module or separation column, i.e., P(L)<P(S) (1-III), 0<Ep(L)<Ep(S) (1-IV), and 51 (°C)≦Tgm(°C)≦150 (°C) (1-X).

[0136] The separation membrane in the hydrogen recovery system of the present invention is preferably an inorganic membrane, more preferably a zeolite membrane, and particularly preferably a surface-modified zeolite membrane. These membranes are non-flammable and therefore highly safe, and also have high separation performance.

[0137] In the hydrogen recovery system of the present invention, there are no particular restrictions on the type of mixed gas containing hydrogen. Here, the mixed gas preferably contains a gas selected from at least one of carbon dioxide, argon, oxygen, nitrogen, and methane, and more preferably is composed of a gas selected from carbon dioxide, argon, oxygen, nitrogen, and methane in addition to the hydrogen to be recovered. Furthermore, the mixed gas is even more preferably composed of a gas selected from oxygen and nitrogen in addition to the hydrogen to be recovered. Furthermore, the mixed gas is most preferably composed of oxygen in addition to the hydrogen to be recovered. While the mixed gas may be a wet gas, it is more preferable that it is a dry gas.

[0138] In the hydrogen recovery system of the present invention, the temperature Tgm of at least one of the mixed gas, the separation module, or the separation tower is preferably 45°C or higher and 200°C or lower. The temperature range Tam for deriving activation energy is 5°C or higher and 200°C or lower, but for the following reasons, the temperature of at least one of the mixed gas, the separation module, or the separation tower is preferably 45°C or higher and 200°C or lower, and all temperatures are preferably 45°C or higher and 200°C or lower. In other words, it is preferable to satisfy the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) (1-IX)

[0139] In particular, since the separation membrane of the present invention can be suitably used for separating and recovering hydrogen gas from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1, a temperature of 200°C or less is appropriate from a safety perspective. Furthermore, in the studies of the present inventors, a temperature of 45°C or higher for the separation module or separation tower was found to be appropriate for increasing the permeance of hydrogen gas within an appropriate range. However, in addition to this, it was effective to preheat the temperature of the mixed gas to be separated in the same manner as the separation module or separation tower. Therefore, the lower limit of the temperature range of at least one of the mixed gas, separation module, or separation tower is 45°C or higher, preferably 51°C or higher, more preferably 60°C or higher, even more preferably 70°C or higher, and most preferably 80°C or higher. Furthermore, the upper limit of the temperature range of at least one of the mixed gas, separation module, or separation tower is 200°C or lower, preferably 150°C or lower, more preferably 140°C or lower, even more preferably 130°C or lower, and most preferably 120°C or lower. Studies by the inventors have shown that for separation of a hydrogen-oxygen mixed gas having a stoichiometric composition of hydrogen:oxygen = 2:1, a temperature range of 85°C to 115°C is preferable, and that preheating the mixed gas to be separated and also heating the outer casing of the separation module to perform heated separation is the most preferable and effective method. In particular, when water is used as the heat medium for the heating mechanism, preheating the mixed gas to be separated to 85°C to 95°C and also heating the outer casing of the separation module to perform heated separation is the most preferable and effective method.

[0140] 4, the hydrogen recovery system of the present invention is equipped with the separation membrane of the present invention, and the temperatures of the gas to be separated, the separation module, or the separation tower are within the temperature range for which the activation energy of the separation membrane is derived. Therefore, under any one condition selected from the temperature range of the gas to be separated, the temperature range of the separation module or the separation tower, the supply form of the gas to be separated, the supply pressure of the gas, and the permeation side pressure, it is preferable that the permeance of hydrogen gas having a small kinetic molecular diameter is always greater than the permeance of gas L having a relatively large kinetic molecular diameter.

[0141] The hydrogen recovery system of the present invention preferably includes a mechanism for adjusting the pressure of the mixed gas supplied to the separation membrane, separation membrane module, or separation tower according to the purpose. <Pressure Mechanism> First, when the separation and recovery process is performed to ensure a sufficient pressure difference across the separation membrane and to emphasize the efficiency of the separation process, it is preferable to include a pressurizing mechanism. That is, it is preferable to include a pressurizing mechanism for the mixed gas M supplied to the separation module or separation tower. In particular, as a pressurizing mechanism, a boost pump is preferably installed upstream of the separation membrane, separation membrane module, or separation tower (pressurizing mechanism A). It is also preferable to install a pressure relief valve on the non-permeate side of the separation membrane, separation membrane module, or separation tower (pressurizing mechanism B). For example, when water is totally decomposed using a photocatalyst to generate a hydrogen-oxygen mixed gas and hydrogen is separated and recovered from the mixed gas using the hydrogen recovery system of the present invention, using a boost pump to pressurize the mixed gas can increase the supply pressure of the gas to be separated without increasing the pressure on the photocatalyst panel side, thereby improving the separation and recovery efficiency of the process. This is preferable. On the other hand, from the viewpoint of reducing energy consumption, it is preferable to install a pressure relief valve on the non-permeate side to increase the supply pressure of the gas to be separated rather than using a booster pump. Secondly, from the viewpoint of safety, pressurizing the hydrogen-oxygen mixed gas should be avoided as much as possible, and it is preferable to supply it at a slight pressure or at normal pressure, and it is preferable to have a slight pressure relief pump or pressure relief valve to the extent that such a supply is possible.

[0142] <Pressure Reduction Mechanism> The hydrogen recovery system of the present invention preferably includes a pressure reduction mechanism for reducing the pressure on the side of the separation membrane, separation membrane module, or separation column through which the permeate gas flows. As described above, this is because ensuring a sufficient differential pressure across the separation membrane in the separation and recovery process can improve the process performance. Therefore, it is preferable to provide a vacuum pump, for example, on the permeation side to reduce the pressure. The vacuum pump preferably has a sufficient pumping speed to ensure a large differential pressure, preferably with a capacity of 100 L / min or more, more preferably 200 L / min or more, even more preferably 300 L / min or more, and most preferably 400 L / min or more. It is not necessary to ensure the above capacity with a single vacuum pump; multiple pumps may be installed to ensure the above capacity. The vacuum pump is preferably one that can be inrush with air, is highly airtight, has an oil-free flow path, and is explosion-resistant, etc. In particular, when separating and recovering hydrogen gas from a hydrogen-oxygen mixed gas, a diaphragm pump or a scroll pump is preferred, and a scroll pump is more preferred. Furthermore, in the recovery system, the temperature Tgm of at least one of the mixed gas, separation module, or separation column is preferably 45°C or higher and 200°C or lower, but in particular when Tgm is a relatively low temperature, it may be possible to use an ejector as a pressure reduction mechanism. In particular, when a water ejector using water is used, Tgm is preferably 45°C or higher and 90°C or lower, more preferably 45°C or higher and 80°C or lower, even more preferably 45°C or higher and 70°C or lower, and most preferably 45°C or higher and 60°C or lower. This is because an increase in the vapor pressure of water reduces the exhaust performance, and in order to suppress this, when an ejector is used as a pressure reduction mechanism, it is most preferably used at 45°C or higher and 60°C or lower.

[0143] It is preferable for the recovery system of the present invention to have other additional functions. For example, it is preferable to have a separate dehumidifying mechanism within the recovery system, such as the dehumidifying mechanism A in FIG. 4. It is also preferable to have the temperature adjustment mechanism A in FIG. 4 function as a heating mechanism, and to have a separate function for adjusting the temperature of the mixed gas itself within the recovery system. Furthermore, to ensure heated separation at the desired temperature, it is also preferable to have a function for heating the separation module or separation tower, such as the temperature adjustment mechanism B in FIG. 4. It is also preferable to have a separate flame extinguishing function in case of an emergency, such as the flame spread suppression mechanism A in FIG. 4. On the other hand, it is also preferable to integrate these additional functions as part of the separation module or separation tower, such as the dehumidifying mechanism B and flame spread suppression mechanism B in FIG. 4.

[0144] <Dehumidifying mechanism> The dehumidifying mechanism is preferably arranged as a standalone mechanism on the upstream side of the recovery system, corresponding to the mixed gas supply side, like a dehumidifying tower. Specific examples include a mode having a mixed gas dehumidifying section. On the other hand, as mentioned above, it is also preferable that the dehumidifying mechanism be arranged inside the outer casing of the separation membrane module or separation tower, on the gas supply side thereof. Furthermore, it is more preferable that both the former and the latter be arranged inside the recovery system, from the viewpoint of completely performing dehumidification.

[0145] The dehumidifying tower as the dehumidifying mechanism can be constructed by disposing granular materials such as silica gel or zeolite inside the tower. It is also possible to dispose a zeolite membrane on a tubular support inside the dehumidifying tower. When granular materials such as silica gel or zeolite are disposed inside the dehumidifying tower, it is possible to simultaneously perform part or all of the flame propagation suppression function by appropriately controlling the particle size.

[0146] <Heating Mechanism> The heating mechanism may be any heating unit for the mixed gas M. For example, it may be a flow path for circulating a heat medium that is installed in contact with the outer wall surface of the outer cylinder of the separation module or separation tower, a mechanism for efficiently applying hot air to the outer wall surface of the outer cylinder, or a heating element directly wrapped around the outer wall surface of the outer cylinder. The heating mechanism as a recovery system preferably includes a hot bath for heating the heat medium in addition to a flow path for circulating the heat medium. The heating mechanism as a recovery system preferably includes a heating element and an air blowing mechanism such as a blower in addition to a mechanism for efficiently applying hot air to the outer wall surface of the outer cylinder of the separation module or separation tower. The heating mechanism as a recovery system preferably includes a power source, a voltage converter, etc. that supplies power to the heating element that is directly wrapped around the outer wall surface of the outer cylinder of the separation module or separation tower. In the flow path for circulating the heat medium, for example, when water is used as the heat medium, a water heating / cooling mechanism may be provided in a location separate from the separation module or separation tower to adjust the temperature. Furthermore, in the case of a heating element that is directly wrapped around the outer wall surface, it is preferable for safety reasons that the heating element itself be covered with a metal sheath, etc. In the recovery system, by using such a heating mechanism to heat the separation module or separation column, the separation membrane of the present invention can simultaneously achieve higher separation performance and higher permeability.

[0147] It is more preferable that the dehumidifying mechanism and the heating mechanism have the function of reducing the relative humidity of the mixed gas immediately before it is supplied to the separation membrane, because this makes it possible to reduce the relative humidity in two stages, for example, by removing some of the water vapor from the mixed gas supplied by the dehumidifying tower and then raising the temperature by the heating mechanism.

[0148] <Flame Propagation Suppression Mechanism> The flame propagation suppression mechanism is particularly suitable for use when separating and recovering hydrogen from a hydrogen-oxygen mixed gas or the like using a separation module or separation tower equipped with the separation membrane of the present invention. In a recovery system, the flame propagation suppression mechanism is preferably installed as a mechanism independent of the separation module or separation tower at any location selected from the gas supply side, gas permeation side, and gas non-permeation side. Furthermore, as described above, the flame propagation suppression mechanism may be installed within the outer casing of the separation module or separation tower at any location selected from the gas supply side, gas permeation side, and gas non-permeation side. In particular, the gas supply side is where the mixed gas before separation flows, and therefore has the highest risk of ignition. Therefore, it is preferable to provide a flame propagation suppression mechanism on the gas supply side. That is, in the hydrogen separation and recovery method of the present invention, it is preferable to have a flame propagation suppression mechanism, and for the mixed gas M to pass through the separation membrane after passing through the flame propagation suppression mechanism. Furthermore, the non-permeation side receives a hydrogen-oxygen mixed gas with a reduced hydrogen concentration or an increased oxygen concentration. However, since this does not necessarily mean that the detonation or explosion range is exceeded, it is preferable to provide a flame propagation suppression mechanism on the non-permeate side. Furthermore, the permeate side will be a hydrogen-oxygen mixed gas with an increased hydrogen concentration or a decreased oxygen concentration. Since it is generally impossible to completely prevent gases other than the target gas from flowing to the permeate side, the permeate side will also usually be a hydrogen-oxygen mixed gas. Therefore, it is preferable to provide a flame propagation suppression mechanism on the permeate side.

[0149] The flame propagation suppression mechanism can be constructed from a narrowed flow path (a flow path narrower than other parts), a sintered metal body, a mesh structure, etc., and the former may be filled with explosion-resistant granules. Furthermore, the sintered metal body, etc., is preferably constructed from stainless steel. Furthermore, the mesh structure is preferably constructed by laminating metal mesh, etc. Furthermore, when constructed independently from the separation module used as the recovery system, a dry safety device, a flashback arrester, or a so-called flame arrester may also be applicable.

[0150] [Method for Separating and Recovering Hydrogen] The method for separating and recovering hydrogen using a separation membrane of the present invention is a method for separating and recovering hydrogen from a mixed gas M of hydrogen and a gas L1 having a larger kinetic molecular diameter than hydrogen. The hydrogen permeance P(S) (mol / (m ２ s Pa)) and the permeance P (L) (mol / (m ２ The activation energy Ep(L) (kJ / mol) of the hydrogen permeance P(S) (mol / (m s Pa)) satisfies the following formula (1-II), and at least one temperature Tgm (°C) of the temperature of the mixed gas M or the temperature of the separation membrane satisfies the following formula (IX): |Ep(L)|<|Ep(S)| (1-II) 45 (°C)≦Tgm(°C)≦200 (°C) (1-IX) Here, the hydrogen permeance P(S) (mol / (m ２ s Pa)) and the permeance P(L) of gas L (mol / (m ２ The activation energy Ep(L) (kJ / mol) of the reaction (s·Pa) is calculated at temperatures between 5°C and 200°C.

[0151] Furthermore, in the method for separating and recovering hydrogen using a separation membrane of the present invention, hydrogen is preferably separated and recovered using a separation membrane that satisfies the following formula (1-III) for hydrogen with a relatively small kinetic molecular diameter and gas L with a relatively large kinetic molecular diameter: P(L)<P(S) (1-III) When separating and recovering hydrogen gas from a mixed gas containing hydrogen gas, having such characteristics is highly preferable because it is possible to improve the permeance P(S) of hydrogen gas while simultaneously improving the selectivity α(S / L) of hydrogen gas relative to gas L, α(S / L)=P(S) / P(L), by "heat separation," in which the mixed gas to be separated, the separation membrane, the separation membrane module, the hydrogen recovery system, etc., are heated to an appropriate temperature.

[0152] The temperature during separation and recovery of the mixed gas M, particularly at least one of the temperature of the mixed gas or the temperature Tgm of the separation membrane, is 45 ° C. or higher and 200 ° C. or lower. Since the separation membrane of the present invention can be suitably used for separating and recovering hydrogen gas from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen = 2:1 ratio, it is appropriate from a safety standpoint to set the temperature to 200 ° C. or lower. In addition, in the studies of the present inventors, in particular, in order to increase the permeance of hydrogen gas within an appropriate range, the temperature of the mixed gas or the temperature Tgm of the separation membrane was appropriate to be 45 ° C. or higher. Therefore, the lower limit of the temperature range of the mixed gas temperature or the temperature Tgm of the separation membrane is 45 ° C. or higher, preferably 51 ° C. or higher, more preferably 60 ° C. or higher, even more preferably 70 ° C. or higher, and most preferably 80 ° C. or higher. Moreover, from a safety standpoint, the upper limit is 200 ° C. or lower, preferably 150 ° C. or lower, more preferably 140 ° C. or lower, even more preferably 130 ° C. or lower, and most preferably 120 ° C. or lower. The most preferable temperature range for separation and recovery is between 80°C and 120°C, taking into consideration the energy required for heating when achieving this and the heat resistance of various constituent members.

[0153] In the hydrogen separation and recovery method using the separation membrane of the present invention, the temperature of the separation module or separation column is within the temperature range in which the activation energy of the separation membrane is derived. Therefore, by setting the mixed gas to be separated, the separation membrane, the separation membrane module, the hydrogen recovery system, etc. to appropriate temperatures, under any one condition selected from the temperature range, the supply form of the gas to be separated, the supply pressure of the gas, and the permeation side pressure, the permeance of hydrogen gas with a small kinetic molecular diameter is always larger than the permeance of gas L with a relatively large kinetic molecular diameter. As described above, as well as improving the permeance P(S) of hydrogen gas, the selectivity α(S / L) for gas L can also be improved, which is very preferable.

[0154] In the method for separating and recovering hydrogen using the separation membrane of the present invention, it is preferable to adjust the pressure of the mixed gas supplied to the separation membrane, separation membrane module or separation column depending on the purpose.

[0155] (Pressure F of mixed gas M ＭFirst, in the separation and recovery process, when it is important to secure a sufficient pressure difference across the separation membrane and to prioritize the efficiency of the separation process, the pressure F of the mixed gas supplied to the separation membrane, separation membrane module, or separation tower can be increased by using the above-mentioned booster pump or exhaust valve. Ｍ is preferably 0.0 MPa(G) or more and 0.2 MPa(G) or less. In other words, it is preferable to satisfy the following formula (1-XI): 0.0 (MPa(G))≦F Ｍ (MPa(G))≦0.2(MPa(G)) (1-XI) In this case, the upper limit of the supply pressure (gauge pressure, hereinafter referred to as (G)) is preferably set to a pressure range in which the flame can be extinguished by the flame propagation suppression mechanism in the unlikely event of ignition. On the other hand, the lower limit of the supply pressure is preferably set to a pressure in which the mixed gas can be supplied to the separation membrane, separation membrane module, or separation tower even if there is pressure loss in piping or other mechanisms. From this perspective, when emphasis is placed on efficiency as a separation and recovery method, the upper limit of the pressure of the mixed gas supplied to the separation membrane, separation membrane module, or separation tower is preferably 0.18 MPa(G) or less, more preferably 0.16 MPa(G) or less, even more preferably 0.14 MPa(G) or less, and most preferably 0.12 MPa(G) or less. From this viewpoint, when emphasis is placed on the efficiency of the separation process, the lower limit of the pressure of the mixed gas supplied to the separation membrane, separation membrane module, or separation column is preferably 0.01 MPa (G) or more, more preferably 0.02 MPa (G) or more, even more preferably 0.03 MPa (G) or more, and most preferably 0.04 MPa (G) or more.

[0156] Secondly, from the viewpoint of safety, pressurizing the hydrogen-oxygen mixed gas should be avoided as much as possible, and it is preferable to supply it at a slight pressure or at about normal pressure, and it is preferable to use a slight pressure pump or a pressure relief valve to the extent that such supply is possible. Therefore, in the hydrogen separation and recovery method using the separation membrane of the present invention, when safety is important, it is preferable that the pressure of the mixed gas supplied to the separation membrane, separation membrane module, or separation tower be 0.0 MPa (G) or more and 0.02 MPa (G) or less. In other words, it is preferable that the following formula (1-XII) is satisfied: 0.0 (MPa (G))≦F Ｍ(MPa (G)) ≦ 0.02 (MPa (G)) ... (1-XII) In this case, the upper limit of the supply pressure is determined taking into consideration the pressure dependency, in particular the detonation power of hydrogen detonation gas, which has a stoichiometric composition among hydrogen-oxygen mixed gases, which increases rapidly with increasing pressure. On the other hand, the lower limit of the supply pressure is set to a pressure at which the mixed gas can be supplied to the separation membrane, separation membrane module, or separation tower even if there is pressure loss in piping or other mechanisms. From this perspective, when emphasizing safety and efficiency as a separation and recovery method, the upper pressure limit of the mixed gas supplied to the separation membrane, separation membrane module, or separation tower is preferably 0.019 MPa (G) or less, more preferably 0.018 MPa (G) or less, even more preferably 0.017 MPa (G) or less, and most preferably 0.016 MPa (G) or less. From this viewpoint, when safety is prioritized over efficiency in a separation and recovery method, the lower limit of the pressure of the mixed gas supplied to the separation membrane, separation membrane module, or separation column is preferably 0.001 MPa (G) or more, more preferably 0.002 MPa (G) or more, even more preferably 0.003 MPa (G) or more, and most preferably 0.004 MPa (G) or more.

[0157] In particular, in the hydrogen separation and recovery method using the separation membrane of the present invention, it is preferable to reduce the pressure on the side of the separation membrane, separation membrane module, or separation tower through which the permeate gas flows. As mentioned above, in the separation and recovery process, sufficient pressure differential across the separation membrane can improve the process performance, but excessive pressurization results in a sudden increase in the detonation power of the hydrogen-oxygen mixed gas and should be avoided as much as possible. In this case, the feed gas is kept at normal pressure or slightly pressurized, taking into account pressure loss in piping, etc., and the pressure differential across the separation membrane is ensured by reducing the pressure on the permeation side. This method is most preferable from the perspective of achieving both separation efficiency and safety. In the hydrogen separation and recovery method using the separation membrane of the present invention, the upper limit of the pressure on the permeation side is preferably −0.065 MPa (G) or less, more preferably −0.075 MPa (G) or less, even more preferably −0.085 MPa (G) or less, preferably lower than −0.9 MPa (G), and most preferably −0.095 MPa (G) or less. The lower limit of the pressure on the permeation side is about −0.101 MPa (G).

[0158] (Relative humidity (RH) of mixed gas M Ｍ In the hydrogen separation and recovery method using the separation membrane of the present invention, the relative humidity (RH) of the mixed gas supplied to the separation membrane, separation membrane module, or separation tower is Ｍ ) is preferably adjusted appropriately. The upper limit of the range is preferably 5% or less, more preferably 2.5% or less, even more preferably 1% or less, and most preferably 0.2% or less. The lower limit of the range is 0.0% or more, but excessive dehumidification is not necessarily required, and 0.05% or more is preferable, 0.08% or more is more preferable, 0.10% or more is even more preferable, and 0.15% or more is most preferable. That is, it is preferable to satisfy the following formula (1-XIII), and it is particularly preferable to satisfy the following formula (1-XIV). 0.0(%)≦RH Ｍ (%)≦5(%)...(1-XIII) 0.0(%)≦RH Ｍ (%)≦0.2(%)...(1-XIV)

[0159] In the hydrogen separation and recovery method using the separation membrane of the present invention, it is preferable to adjust the flow rate of the mixed gas supplied to the separation module or separation tower so that it is appropriate for the membrane area of ​​the separation membrane. As described above, in the present invention, "heated separation" in which the mixed gas to be separated, the separation membrane, the separation membrane module, the hydrogen recovery system, etc. are heated to an appropriate temperature can improve the hydrogen gas permeance P(S) while simultaneously improving the selectivity α(S / L) = P(S) / P(L) of hydrogen gas relative to the gas L, which is highly preferable, and membrane performance basically improves with increasing temperature. Therefore, in the hydrogen separation and recovery method of the present invention, it is preferable to heat the temperature Tgm (°C) of at least one of the mixed gas M or the separation membrane so that it satisfies the above formula (IX).

[0160] As mentioned above, by appropriately adjusting the supply pressure of the mixed gas, the pressure on the permeation side, etc., it is possible to separate and recover hydrogen gas appropriately according to the purpose. Furthermore, by adjusting the flow rate of the supply gas, it is possible to separate and recover hydrogen gas safely and efficiently relative to the membrane area, which is very preferable. For example, in the hydrogen separation and recovery method using the separation membrane of the present invention, it is preferable to separate and recover hydrogen by adjusting the supply flow rate so that the hydrogen concentration on the permeation side is outside the explosive range. Furthermore, for example, when separating and recovering hydrogen from a hydrogen-oxygen mixed gas, particularly a hydrogen detonation gas having a stoichiometric composition (hydrogen:oxygen = 2:1), which can be suitably used in the separation and recovery method of the present invention, the supply gas is a gas within the explosive range and detonation range.

[0161] On the other hand, for safe and highly efficient separation, a vacuum pump with moving parts is preferably placed on the permeate side, resulting in a reduced pressure on the permeate side. However, it is preferable to adjust the flow rate so that the mixed gas composition on the permeate side is outside the explosive range, especially when the mixed gas composition is sucked into the vacuum pump with moving parts and returns to normal pressure downstream (after the pump), so as to prevent ignition due to static electricity or the like. In this case, the lower limit of the hydrogen concentration range in the hydrogen-oxygen mixed gas on the permeate side must be above the upper limit of the explosive range, and therefore is preferably greater than 95.8 vol%, more preferably 96.0 vol% or more, even more preferably 96.2% or more, and most preferably 96.4 vol% or more. Furthermore, although the upper limit of the hydrogen concentration range in the hydrogen-oxygen mixed gas on the permeate side is ideally 100 vol% hydrogen, in reality, the upper limit is preferably 99.8 vol% or less, more preferably 99.6 vol% or less, even more preferably 99.4 vol% or less, and most preferably 99.2 vol% or less. By setting the range in this way, it is possible to realize a separation and recovery method that does not require excessive separation costs.

[0162] Furthermore, in the hydrogen separation and recovery method using the separation membrane of the present invention, it is preferable to separate and recover hydrogen by adjusting the supply flow rate so that the hydrogen concentration on the gas side flowing through the non-permeate side of the separation membrane, separation membrane module, or separation tower is outside the detonation range. There is no need to install a mechanism with moving parts, such as a vacuum pump, in the recovery system on the non-permeate side, and a hydrogen-oxygen mixed gas flowing at atmospheric to slightly pressurized pressure is used. Therefore, while it is ideal to keep the hydrogen concentration outside the detonation range for safe and highly efficient separation, keeping the hydrogen concentration outside the detonation range can ensure appropriate safety. This is because, in the event of ignition, if the hydrogen concentration is outside the detonation range, a margin of flame extinguishing capacity can be secured by a flame propagation suppression mechanism, etc. From this perspective, the upper limit of the hydrogen concentration on the non-permeate side must be below the lower limit of the detonation range. Therefore, in the hydrogen separation and recovery method using the separation membrane of the present invention, the upper limit of the hydrogen concentration on the gas side flowing through the non-permeation side of the separation membrane, separation membrane module, or separation tower, through which the mixed gas that has not permeated the separation membrane flows, is preferably 15.5 vol% or less, more preferably 12.5 vol% or less, even more preferably 9.5 vol% or less, and most preferably 6.5 vol% or less. Furthermore, 3.9 vol% or less is ideal, which satisfies the condition of being below the lower limit of the explosion range of the hydrogen-oxygen mixed gas. On the other hand, excessive reduction of the hydrogen concentration on the non-permeation side can cause problems such as the need to secure an excessively large membrane area, so the lower limit of the concentration is preferably 2 vol% or more, more preferably 3 vol% or more, even more preferably 4 vol% or more, and most preferably 5 vol% or more.

[0163] In the separation and recovery method of the present invention, it is preferable that the gas flow be laminar in all regions of the feed side, permeate side, and non-permeate side of a separation membrane module or separation tower equipped with a separation membrane. In particular, when the gas to be separated is a hydrogen-oxygen mixed gas, it is preferable from the viewpoint of safety to easily grasp the hydrogen concentration / oxygen concentration, etc., in the mixed gas at each location. Here, when the gas flow is laminar, it is easier to grasp the concentration than when the gas flow is turbulent. For example, by measuring the hydrogen concentration at the permeate side outlet, it is possible to accurately calculate the concentration at each location further upstream. From this perspective, on the feed side and non-permeate side of the present invention, it is assumed that the feed flow rate at the feed side inlet of the separation membrane module or separation tower flows directly to the non-permeate side outlet (a situation in which no flow is at all flowed to the permeate side), and the Reynolds number in this case is defined as the "maximum Reynolds number on the feed side" and used as an indicator of whether laminar flow can be maintained. In addition, the flow rate actually decreases by the amount of gas flowing from the feed side to the permeate side, and the linear velocity of the flow from the feed side inlet to the non-permeate side outlet decreases, resulting in a direction in which laminar flow can be maintained. Therefore, the maximum feed side Reynolds number is an index that gives the largest Reynolds number, and if this index is below 2000, it is also an index that can be reliably determined that the flow of the mixed gas is laminar.

[0164] According to the study by the present inventors, the upper limit of the maximum supply-side Reynolds number is preferably 1500 or less, more preferably 1000 or less, even more preferably 500 or less, and most preferably 250 or less. On the other hand, if the maximum supply-side Reynolds number is extremely small, excessive pressure loss may occur. Therefore, the lower limit of the maximum supply-side Reynolds number is preferably 5 or more, more preferably 10 or more, even more preferably 20 or more, and most preferably 30 or more. Therefore, in the separation and recovery method of the present invention, it is preferable to supply the mixed gas M to a separation membrane module or separation tower equipped with a separation membrane so that the mixed gas M falls within the above range.

[0165] On the other hand, on the permeate side of the present invention, assuming a situation in which the permeate flow rate at the permeate side outlet of the separation membrane module or separation column begins to flow directly from the separation starting point of the separation membrane (a situation in which the permeate side outlet flow rate continues to flow constantly from the separation starting point of the separation membrane to the separation end point), the Reynolds number in this case was defined as the "maximum permeate side Reynolds number" and used as an indicator of whether laminar flow can be maintained on the support side. Additionally, in reality, the flow on the permeate side gradually increases in flow direction as it flows in from the feed side, and the linear velocity of the flow at the permeate side outlet increases, making it difficult to maintain laminar flow. Therefore, the maximum permeate side Reynolds number is an indicator that gives the largest Reynolds number, and if this indicator is 2000 or less, it is also an indicator that the flow on the permeate side can be reliably determined to be laminar. Based on the inventor's investigations, the upper limit of the maximum permeate side Reynolds number is preferably 1500 or less, more preferably 1000 or less, even more preferably 500 or less, and most preferably 250 or less. On the other hand, if the maximum Reynolds number on the supply side is extremely small, excessive pressure loss may occur. Therefore, the lower limit of the maximum Reynolds number on the supply side is preferably 5 or more, more preferably 10 or more, even more preferably 20 or more, and most preferably 30 or more. Therefore, in the separation and recovery method of the present invention, it is preferable to supply the mixed gas M to a separation membrane module or separation tower equipped with a separation membrane so that the Reynolds number falls within the above range.

[0166] A second aspect of the present invention relates to a separation and recovery method, a separation module or column, and a hydrogen recovery system.

[0167] [Separation and Recovery Method] The present invention is a method for separating and recovering hydrogen from a mixed gas M containing at least hydrogen and oxygen (hereinafter, sometimes simply referred to as "mixed gas M"), and is characterized in that the temperature Tgm in the separation and recovery step satisfies the following formula (2-I): 45 (°C)≦Tgm(°C)≦200 (°C) (2-I) Here, Tgm is the temperature in the separation and recovery step, and specifically, is the mixed gas temperature or the temperature of the separation membrane inside at least one of a separation module or a separation tower, which will be described in detail later. It is preferable that Tgm further satisfies the following formula (2-II): 70 (°C)≦Tgm(°C)≦200 (°C) (2-II)

[0168] If the Tgm is less than 45°C, for example, in the case of separation and recovery using a separation membrane, the hydrogen permeability is poor, making it difficult to achieve the effects of the present invention. On the other hand, the higher the Tgm, the higher the permeance of hydrogen that permeates the separation membrane, which is preferable. It is more preferably 60°C or higher, even more preferably 70°C or higher, particularly preferably 80°C or higher, and most preferably 90°C or higher. On the other hand, the upper limit of Tgm, in the case of separation and recovery using a separation membrane, depends on the resistance, such as heat resistance, of the separation membrane. Specifically, Tgm may be 200°C or lower, which ensures the heat resistance of the separation membrane and also guarantees flame-extinguishing performance. From the above viewpoints, the upper limit of Tgm is preferably 200°C or lower. For example, when an inorganic membrane is used as the separation membrane, the resistance of the membrane is sufficiently ensured, and resistance, such as heat resistance, can also be ensured for the structure of the connecting parts of components such as the separation membrane. Furthermore, the upper limit is more preferably 150°C or lower. If the upper limit is 150°C or less, when an inorganic membrane is used as the separation membrane, long-term membrane denaturation of the separation membrane can be suppressed by removing water during membrane regeneration. Furthermore, the upper limit is preferably 120°C or less. If Tgm is 120°C or less, flame quenching performance can be ensured. From the above viewpoints, it is particularly preferable that Tgm is 95°C or less. Furthermore, when an organic membrane is used as the separation membrane, for example, it is preferable that the upper limit of Tgm is 100°C or less in order to prevent thermal degradation of the organic membrane.

[0169] <Gas to be Separated> The gas to be separated in the present invention (second aspect) is a mixed gas M containing hydrogen and oxygen, and is particularly suitable for a mixed gas in which the composition ratio (volume ratio) of hydrogen to oxygen is 2:1 or more, with an excess of hydrogen. Furthermore, the mixed gas M supplied to the separation and recovery process may be within the explosion range, or the detonation range. The explosion range of the mixed gas M is a hydrogen-oxygen mixed gas with a hydrogen concentration of 3.9% to 95.8% by volume, and the detonation range is a hydrogen concentration range of 15.5% to 92.6% by volume. The mixed gas may be a wet gas, but is preferably a dry gas. In particular, in a separation and recovery method using a separation membrane, the small amount of water vapor in the mixed gas M suppresses adsorption of water vapor to the membrane, allowing the separation membrane to fully demonstrate its performance.

[0170] The method for separating and recovering hydrogen in the present invention (second embodiment) is not particularly limited as long as it is a technique that can achieve the effects of the present invention, and examples thereof include cryogenic separation, pressure swing adsorption (PSA), a method using a separation membrane, etc. In the present invention, a method using a separation membrane is efficient and preferable.

[0171] <Separation membrane> The separation membrane that can be used in the present invention is not particularly limited as long as it exhibits the effects of the present invention, and may be an organic membrane or an inorganic membrane. Specific examples include inorganic separation membranes such as ceramic membranes and carbon membranes, such as zeolite membranes, silica membranes, alumina membranes, zirconia membranes, and titania membranes; and organic separation membranes such as fluororesin membranes, such as PTFE (polytetrafluoroethylene) membranes and PVDF (polyvinylidene fluoride) membranes, and polymer membranes, such as polyamide membranes, cellulose acetate membranes, polyimide membranes, and polyethylene membranes. Furthermore, the structure of the membrane may be such that it has the necessary structure to exhibit the separation ability essential for separating the mixed gas M, specifically, the part having separation activity (in other words, the part having the ability to separate hydrogen and oxygen), and may include, for example, a support function part for maintaining the shape of the membrane, a protective part for maintaining the separation ability, etc. For example, a porous support is generally used as the support function part for maintaining the shape of the membrane. Furthermore, a structure that combines support, protection, and separation functions can also be used, in which a portion having separation ability, such as zeolite, is dispersed in a porous support that maintains the membrane shape, allowing the separation section to function as a membrane while protecting the portion having separation ability. Of these, from the viewpoint of hydrogen separation and recovery performance, polyimide or polyamide membranes are preferred as organic membranes, and membranes using zeolite are preferred as inorganic membranes, and more preferably separation membranes in which a zeolite membrane is provided on a support, and particularly surface-modified zeolite membranes are preferred.

[0172] <Polyimide Film, Polyamide Film> The polyimide constituting the polyimide film is not particularly limited as long as the effects of the present invention are achieved. For example, polyimide can be obtained by condensation polymerization of an m-phenylenediamine compound and a tetracarboxylic dianhydride. Polyimide synthesis can be performed by conventional methods. Furthermore, the polyamide constituting the polyamide film is not particularly limited as long as the effects of the present invention are achieved. For example, polyamide can be obtained by condensation polymerization of an m-phenylenediamine compound and a dicarboxylic acid compound. Polyamide synthesis can be performed by conventional methods. The molecular weight of the polyimide and polyamide is preferably 10,000 or more and 1,000,000 or less, more preferably 15,000 or more and 500,000 or less, and even more preferably 20,000 or more and 200,000 or less, in terms of weight average molecular weight. Polyimide and polyamide membranes can be produced, for example, by applying polyimide or polyamide together with a solvent or the like onto a gas-permeable support layer that provides mechanical strength, thereby forming a thin film.

[0173] <Zeolite membrane> As the zeolite membrane, as described above, a structure in which a zeolite membrane exists on a support is preferred, and a surface-modified zeolite membrane is more preferred. More specifically, a composite separation membrane described below is preferred.

[0174] <Composite separation membrane> The separation membrane of the present invention is not particularly limited as long as it has the ability to separate oxygen and hydrogen, but a specific structure thereof is preferably a composite separation membrane 100 having a support 101, a first separation section 103 arranged in contact with the support, and a second separation section 104 having an amorphous structure that is not in contact with the support but is arranged in contact with the first separation section, as shown in Figure 1. The composite separation membrane will be described in detail below.

[0175] (Support) The support is the same as the support of the separation membrane laminate in the first embodiment. Specifically, the pores such as the average pore diameter at the upper end of the inorganic porous support, the average thickness (wall thickness) of the inorganic porous support, the porosity of the inorganic porous support, and polishing with a file or the like are also the same as those in the first embodiment.

[0176] The shape of the inorganic porous support is not particularly limited as long as it can effectively separate the target gas mixture M. Specific examples include flat, tubular, honeycomb, and monolithic structures with a large number of cylindrical, columnar, or prismatic holes. In the present invention, it is preferable to form a membrane of zeolite on such an inorganic porous support, i.e., on the upper end of the support. The upper end of the inorganic porous support is defined as the surface that forms the first separation section, and refers to the surface portion of the inorganic porous support where the zeolite is crystallized. As long as it is a surface, it may be any surface of each shape, or multiple surfaces. For example, in the case of a cylindrical support, it may be either the outer surface or the inner surface, or in some cases, both the outer and inner surfaces. In this case, either surface is considered to be the upper end.

[0177] (First Separation Section) The configuration of the first separation section is the same as that of the first separation section in the separation membrane stack of the first embodiment, and therefore description thereof will be omitted here.

[0178] The shape of the zeolite liberation structure, which has only the zeolite membrane (first separation section) formed on the support, is not particularly limited, and any shape can be used, such as tubular, hollow fiber, monolith, or honeycomb. The size is also not particularly limited. For example, in the case of a tubular structure, a length of 2 cm to 200 cm, an inner diameter of 0.05 cm to 2 cm, and a thickness of 0.5 mm to 4 mm are practical and preferred. The inner diameter here refers to the equivalent circle diameter. One of the separation functions of the zeolite liberation structure is its ability to function as a molecular sieve, effectively separating gas molecules larger than the effective pore size of the zeolite used from gas molecules smaller than that. While there is no upper limit to the molecules used for separation, the molecular size is typically approximately 100 Å or less. The main zeolite constituting the zeolite liberation structure is the same as the zeolite described in the first embodiment, and therefore will not be described here.

[0179] <Method for Manufacturing the Liberation Structure> The method for manufacturing the liberation structure is the same as that described in the first embodiment above, and therefore will not be described here.

[0180] (Second Separation Section) The second separation section formed at the upper end of the first separation section is similar to that in the first embodiment, and therefore will not be described here.

[0181] As described above, the separation membrane of the present invention has an amorphous layer with smaller pores formed at the upper end of the liberation structure (e.g., zeolite liberation structure) to achieve separation performance that cannot be achieved by the function of the zeolite pore size alone. Furthermore, in the separation membrane of the present invention, the density of the amorphous layer of the composite separation membrane is preferably higher than that of the underlying zeolite. When the ratio of the density of the amorphous layer to the density of the underlying zeolite is defined as the relative density, increasing the relative density makes the separation performance of the amorphous layer higher than that of the zeolite, and thus makes it easier to achieve practically sufficient separation performance.

[0182] On the other hand, by setting the relative density to a certain value or less, the porosity of the amorphous layer becomes appropriately dense, and the pores are not excessively narrowed to prevent an increase in permeation resistance, and the expected permeance of the permeating component is not reduced, which is preferable. ３ ) and a CHA-type zeolite free separation structure, the relative density is 1.46. On the other hand, considering the low permeability reported for amorphous silica separation membranes, a relative density of 1.46 is considered to be the upper limit. Therefore, the relative density is 1.46 or less, preferably 1.30 or less, and more preferably 1.15 or less. The thickness of the second separation section is the same as in the first embodiment, so it will not be described here.

[0183] <Method for producing composite separation membrane> The method for producing the composite separation membrane is the same as the method for producing the separation membrane laminate in the first embodiment, and therefore the description thereof will be omitted.

[0184] This separation membrane can be suitably used to separate and recover hydrogen from a mixed gas M containing hydrogen and oxygen, and is similar to that described in the first embodiment. Therefore, a detailed description will be omitted here.

[0185] In addition, when any of the zeolite membrane, silica membrane, and carbon membrane is formed on a tubular support, the inner diameter of the support and the like are the same as those described in the first embodiment, and the method of supplying the feed gas and the like are also the same as those described in the first embodiment, and therefore will not be described here.

[0186] (Pressure F of mixed gas M Ｍ ) The pressure F of the mixed gas M in the second embodiment Ｍ is the pressure F of the mixed gas M in the first embodiment Ｍ The relative humidity (RH) of the mixed gas M in the hydrogen separation and recovery method using the separation membrane of the present invention is the same as that of the mixed gas M. Ｍ ) are the same as those described in the first embodiment, and therefore will not be described here. It is preferable to supply the mixed gas M so that the maximum Reynolds number on the supply side and / or the maximum Reynolds number on the permeation side is 5 or more and 2000 or less.

[0187] Furthermore, it is preferable that the gas mixture M is passed through a separation membrane after passing through the flame propagation suppression mechanism, so that hydrogen is separated and recovered. By adopting such an embodiment, flame propagation can be more easily suppressed.

[0188] [Separation Module or Separation Tower] The separation module or separation tower of the present invention separates and recovers hydrogen from a mixed gas M containing at least hydrogen and oxygen. The separation module or separation tower of the present invention is characterized by having a temperature adjustment mechanism. The temperature adjustment mechanism can heat the mixed gas M, the separation module, and the separation tower, allowing hydrogen to be separated and recovered from the hydrogen-oxygen mixed gas M safely and efficiently.

[0189] <Temperature Control Mechanism> The temperature control mechanism may be, for example, a tubular flow path through which a heat transfer medium flows, and may be installed so as to be in contact with the outer wall surface of the outer cylinder of the separation module or separation tower. It may also be a mechanism for efficiently applying hot air to the outer wall surface of the outer cylinder, or a heating element directly wrapped around the outer wall surface of the outer cylinder. Among these, a tubular flow path through which a heat transfer medium flows is preferred. For example, when water is used as the heat transfer medium, a mechanism for heating / cooling water may be provided in a location separate from the separation module or separation tower to control the temperature. Furthermore, when the heating element is directly wrapped around the outer wall surface, it is preferable for safety reasons that the heating element itself be covered with a metal sheath or the like. By using such a heating mechanism to heat the separation module or separation tower, the separation membrane of the present invention can simultaneously achieve higher separation performance and higher permeability.

[0190] The temperature control mechanism may also include a heat insulating section, which can keep the temperature of the heated mixed gas M. Therefore, by providing a heat insulating section, it is possible to reduce energy consumption for heating and improve the temperature uniformity of the parts that require heating. Furthermore, the heat insulating section can easily keep the temperature Tos of the separation module or separation column, which will be described in detail later, within a desired range.

[0191] The temperature Tos of the separation module or separation column preferably satisfies the following formula (2-VII): 51 (°C)≦Tos(°C)≦220 (°C) (2-VII) By setting Tos to 51°C or higher, the hydrogen permeability is excellent during separation and recovery, and the effects of the present invention are easily achieved, which is preferable. This configuration is particularly preferable when separation and recovery are performed using a separation membrane. It is further preferable that Tos satisfies the following formula (2-VIII): 70 (°C)≦Tos(°C)≦200 (°C) (2-VIII)

[0192] The higher Tos is, the higher the permeance of hydrogen that permeates the separation membrane is, and therefore, preferable. It is more preferably 60°C or higher, even more preferably 70°C or higher, particularly preferably 80°C or higher, and most preferably 90°C or higher. Meanwhile, the upper limit of Tos depends on the resistance, such as heat resistance, of the separation membrane, for example, when a separation membrane is used. Specifically, Tos may be 220°C or lower, ensuring the heat resistance of the separation membrane and ensuring flame-extinguishing performance. From the above viewpoints, the upper limit of Tos is preferably 200°C or lower. Furthermore, for example, when an inorganic membrane is used as the separation membrane, the resistance of the membrane is sufficiently ensured, and resistance, such as heat resistance, can also be ensured for the structure of the connecting parts of components such as the separation membrane.

[0193] Furthermore, the upper limit is more preferably 150°C or less. If the upper limit is 150°C or less, when an inorganic membrane is used as the separation membrane, long-term membrane denaturation of the separation membrane can be suppressed by removing water during membrane regeneration. Furthermore, the upper limit is preferably 120°C or less. If Tos is 120°C or less, flame quenching performance can be ensured. From the above viewpoints, Tos is particularly preferably 95°C or less. Furthermore, when an organic membrane is used as the separation membrane, for example, the upper limit of Tos is preferably 100°C or less from the viewpoint of preventing thermal degradation of the organic membrane.

[0194] The separation module or separation tower of the present invention preferably includes a separation membrane. The separation membrane is as described above, and similar separation membranes can be suitably used in the separation module or separation tower of the present invention. In particular, inorganic membranes are preferred in terms of resistance, such as heat resistance, and zeolite membranes are preferred in terms of permeability. It is most preferred that the separation membrane include a surface-modified zeolite membrane. Furthermore, when the separation membrane has a tubular support, the inner diameter φi (mm) of the support preferably satisfies the following formula (2-IX): 6≦φi≦16 (2-IX) By satisfying formula (IX), the strength of the separation module or separation tower can be sufficiently obtained, and a certain degree of resistance can be obtained, for example, even when ignition and subsequent detonation occur. Furthermore, the separation membrane can be mounted on an outer cylinder, modularized, and configured as a separation module or an even larger separation tower, making it suitable for use in separation and recovery processes.

[0195] When separating a mixed gas M using a separation module or separation tower equipped with the separation membrane of the present invention, it is preferable that the gas flow within the separation module or separation tower be laminar. In particular, when separating a mixed gas of hydrogen and oxygen, it is desirable to accurately determine the hydrogen to oxygen composition ratio in the direction of gas flow for the mixed gas M (feed gas), the mixed gas M after permeation through the separation membrane (permeation gas), and the portion of the mixed gas M that did not permeate the separation membrane (non-permeation gas). This is to determine whether the flowing hydrogen-oxygen mixed gas is in the explosive or detonation range in the direction of the mixed gas flow. Generally, the viscosity of gas increases with increasing temperature, so that, other conditions being equal, a higher temperature makes it easier to achieve a laminar flow of the mixed gas. From this perspective, performing heated separation within an appropriate temperature range using the separation membrane and separation module or separation tower of the present invention not only improves both the permeation performance and separation performance of the separation membrane, but also has the synergistic effect of maintaining a laminar flow of the mixed gas within the separation module or separation tower, which is highly preferable.

[0196] Furthermore, from this viewpoint, the lower limit of the distance between the inner wall of the separation membrane module or separation tower and the surface of the separation membrane closest to the inner wall is preferably 0.1 cm or more, taking into consideration the assembly tolerances required during actual module production. It is more preferably 0.2 cm or more, even more preferably 0.5 cm or more, and most preferably 1 cm or more. On the other hand, it is preferable to keep the distance between the inner wall of the separation membrane module or separation tower and the surface of the separation membrane closest to the inner wall within a reasonable range, as this makes it easier to maintain a laminar flow as the flow of the mixed gas. From this viewpoint, the upper limit of the distance is preferably 50 cm or less, more preferably 25 cm or less, even more preferably 10 cm or less, and most preferably 2 cm or less.

[0197] The material of the outer cylinder constituting the separation module or separation tower can be selected from any material, and those described in the first embodiment can be used, and the preferred range is also the same. The outer cylinder preferably has other additional functions, such as a built-in dehumidifying mechanism, a heating mechanism, and a flame propagation function.

[0198] <Dehumidifying mechanism> The dehumidifying mechanism is the same as that of the first embodiment, including the preferred range, and therefore will not be described here. In addition, the dehumidifying mechanism and the heating mechanism may be used in combination, as described in the first embodiment.

[0199] <Flame Propagation Suppression Mechanism> The flame propagation suppression mechanism is also similar to that described in the first embodiment, and therefore a description thereof will be omitted here.

[0200] In the system for separating and recovering hydrogen from a gas mixture using the separation membrane, separation module, or separation column of the present invention, there are no particular restrictions on the type of gas mixture containing the hydrogen. Here, the gas mixture preferably contains oxygen and includes at least one gas selected from carbon dioxide, argon, nitrogen, and methane. Furthermore, the gas mixture preferably contains oxygen in addition to the hydrogen to be recovered, and is more preferably composed of a gas selected from carbon dioxide, argon, nitrogen, and methane, excluding impurities. Furthermore, the gas mixture more preferably contains a gas selected from oxygen and nitrogen in addition to the hydrogen to be recovered. Furthermore, the gas mixture most preferably contains oxygen in addition to the hydrogen to be recovered. Furthermore, the gas mixture may be a wet gas, but is more preferably a dry gas.

[0201] In the system for separating and recovering hydrogen from a mixed gas using the separation membrane, separation module, or separation tower of the present invention, the temperature Tgm of at least one of the separation module or separation tower for the mixed gas is preferably 45 ° C or higher and 200 ° C or lower. In particular, since the separation membrane of the present invention can be suitably used for separating and recovering hydrogen from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen = 2:1 ratio, it is preferable from the viewpoint of safety to set the temperature to 200 ° C or lower. In addition, in the studies of the present inventors, a separation module or separation tower of 45 ° C or higher was appropriate, particularly for increasing the permeance of hydrogen gas within an appropriate range. However, in addition to this, it was effective to preheat the temperature of the mixed gas to be separated in the same manner as the separation module or separation tower. Therefore, the lower limit of the temperature range of at least one of the mixed gas, separation module, or separation tower is 45 ° C or higher, preferably 51 ° C or higher, more preferably 60 ° C or higher, even more preferably 70 ° C or higher, and most preferably 80 ° C or higher. The upper limit of the temperature range of at least one of the mixed gas, separation module, or separation column is 200°C or less, preferably 150°C or less, more preferably 140°C or less, even more preferably 130°C or less, and most preferably 120°C or less. Studies by the inventors have shown that for separation of a hydrogen-oxygen mixed gas having a stoichiometric composition of hydrogen:oxygen = 2:1, a temperature range of 85°C to 115°C is preferred, and it is most preferable and effective to preheat the mixed gas to be separated and also heat the outer casing of the separation module for heated separation. Furthermore, particularly when water is used as the heat medium for the heating mechanism, it is most preferable and effective to preheat the mixed gas to be separated to 85°C to 95°C and also heat the outer casing of the separation module for heated separation.

[0202] [Hydrogen Recovery System] The hydrogen recovery system of the present invention is a hydrogen recovery system that separates and recovers hydrogen from a mixed gas M containing at least hydrogen and oxygen, and is characterized by having a separation unit, which has a temperature adjustment mechanism. In the present invention, it is preferable to use the above-mentioned separation module or separation tower as the separation unit. Furthermore, the temperature adjustment mechanism is the same as that described for the above-mentioned separation module or separation tower. That is, the temperature adjustment mechanism may be a tubular flow path through which a heat transfer medium flows, or may include an insulating part. The heated mixed gas M can be kept warm by the insulating part.

[0203] In the hydrogen recovery system of the present invention, it is preferable that the temperature Tgm of the separation section satisfies the following formula (2-I): 45 (°C)≦Tgm(°C)≦200 (°C) (2-I) Here, Tgm is the temperature of the separation section, and specifically, is the temperature of the mixed gas or the temperature of the separation membrane inside at least one of the separation module or the separation tower. It is also preferable that Tgm further satisfies the following formula (2-II): 70 (°C)≦Tgm(°C)≦200 (°C) (2-II)

[0204] The separation section in the hydrogen recovery system of the present invention preferably has a separation membrane. As the separation membrane, as described above, an inorganic membrane is preferable in terms of durability such as heat resistance, and a zeolite membrane is preferable in terms of permeability.

[0205] The hydrogen recovery system of the present invention preferably has a mechanism for adjusting the pressure of the mixed gas supplied to the separation membrane, separation membrane module, or separation column according to the purpose. Figure 4 shows a schematic diagram of the device (hydrogen recovery system) used for separating the mixed gas M of the present invention.

[0206] <Pressure Mechanism> The pressure mechanism is the same as that described in the first embodiment, and therefore a description thereof will be omitted here.

[0207] <Pressure reduction mechanism> The hydrogen recovery system of the present invention preferably has a pressure reduction mechanism downstream of the separation module or separation column. Details are as described in the first embodiment, and will not be described here. The vacuum pump is also the same as that described in the first embodiment.

[0208] Furthermore, it is preferable that the recovery system of the present invention additionally has other functions, such as a built-in dehumidification mechanism, a heating mechanism, and a flame propagation function.

[0209] <Dehumidifying mechanism> The dehumidifying mechanism is the same as that described in the first embodiment, so a description thereof will be omitted here. <Warming mechanism> The heating mechanism is also the same as that described in the first embodiment, so a description thereof will be omitted here.

[0210] <Flame Propagation Suppression Mechanism> The flame propagation suppression mechanism is the same as that described in the first embodiment, and therefore will not be described here.

[0211] In the hydrogen recovery system of the present invention, when a separation module or separation tower equipped with the above-described separation membrane is included, as described above, the distance between the inner wall of the separation membrane module or separation tower and the surface of the separation membrane closest to the inner wall is preferably 0.1 cm or more and 50 cm or less. A distance of 0.1 cm or more widens the assembly tolerance required during module manufacture, while a distance of 50 cm or less makes it easier to maintain laminar gas flow. From the above viewpoints, the distance is more preferably 0.2 cm or more, even more preferably 0.5 cm or more, and most preferably 1 cm or more. Furthermore, a distance of 25 cm or less is more preferable, even more preferably 10 cm or less, and most preferably 2 cm or less.

[0212] Furthermore, when the separation membrane has a tubular support, the inner diameter φi (mm) of the support is preferably 6 mm or more and 16 mm or less. That is, it is preferable to satisfy the following formula (2-IX): 6≦φi≦16 (2-IX) By satisfying formula (2-IX), the strength of the separation module or separation tower can be sufficiently obtained, and a certain degree of resistance can be obtained, for example, even when ignition and subsequent detonation occur.

[0213] In the hydrogen separation and recovery method using the separation membrane of the present invention, the hydrogen permeance P(S) (mol / (m ２The activation energy Ep(S) (kJ / mol) of the separation membrane is calculated from the activation energy Ep(S) (kJ / mol) of the separation membrane. The permeance P(L) of the gas L (e.g., oxygen) for ... ２ It is preferable to use a separation membrane in which the activation energy Ep(L) (kJ / mol) of the hydrogen permeation rate (kJ / mol) satisfies |Ep(L)| < |Ep(S)|. Furthermore, in the hydrogen separation and recovery method using the separation membrane of the present invention, hydrogen is preferably separated and recovered using a separation membrane that also satisfies 0 < Ep(L) < Ep(S) for hydrogen with a relatively small kinetic molecular diameter and gas L with a relatively large kinetic molecular diameter. When separating and recovering hydrogen gas from a mixed gas M containing hydrogen gas, having such characteristics makes it possible to improve the permeance P(S) of hydrogen gas while simultaneously improving the selectivity α(S / L) of hydrogen gas relative to gas L, α(S / L) = P(S) / P(L), by "heat separation," in which the mixed gas M to be separated, the separation membrane, the separation membrane module, the hydrogen recovery system, etc., are heated to an appropriate temperature. This is highly preferable.

[0214] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0215] Example 1-1 The following reaction mixture for hydrothermal synthesis was prepared. 7.2 g of 1 mol / L NaOH aqueous solution, 28.8 g of 1 mol / L KOH aqueous solution, and 570.05 g of water were mixed, to which 0.975 g of aluminum hydroxide (containing 53.5% by mass of Al2O3, manufactured by Aldrich Chemical Co.) was added and stirred to dissolve, forming a clear solution. 12.15 g of an organic template TMADAOH (N,N,N-trimethyl-1-adamantylammonium hydroxide) aqueous solution (containing 25% by mass of TMADAOH, manufactured by Seichem Co., Ltd.) was added, followed by 54 g of colloidal silica (Nissan Chemical Industries, Ltd., Snowtec-40) and stirring for 30 minutes to form a reaction mixture.

[0216] The composition (molar ratio) of this reaction mixture was: SiO ２ / Al ２ O ３ / NaOH / KOH / H ２O / TMADAOH=1 / 0.014 / 0.02 / 0.08 / 100 / 0.04, SiO ２ / Al ２ O ３ = 70. An alumina tube (outer diameter 12 mm, inner diameter 9 mm) was cut to a length of 400 mm and used as the inorganic porous support. SiO ２ / Al ２ O ３ / NaOH / KOH / H ２ CHA-type zeolite was used, which had a gel composition (molar ratio) of 0.033 / 0.1 / 0.06 / 20 / 0.07 and was crystallized by hydrothermal synthesis for 2 days at 160° C. The support was immersed in a dispersion of 1.0 mass % of this seed crystal in water for 30 seconds and then pulled out, so that the seed crystal was supported on the upper end of the inorganic porous support, and the support was used for hydrothermal synthesis.

[0217] The support with the seed crystals attached in this way and two other supports with seed crystals attached in the same way, a total of three supports, were immersed vertically in the Teflon (registered trademark) inner tube containing the reaction mixture, the autoclave was sealed, and the support was heated in a stationary state at 180°C for 18 hours under autogenous pressure to carry out zeolite crystal growth at the upper end of the inorganic porous support by hydrothermal synthesis. After cooling, the zeolite liberation structure was removed from the reaction mixture, washed, and then dried at 100°C for 2 hours or more.

[0218] The zeolite liberation structure before calcining the template was calcined in an electric furnace at 500°C for 5 hours. The mass per unit area of ​​CHA-type zeolite crystallized on the upper end of the support, calculated from the difference between the mass of the calcined zeolite liberation structure and the mass of the support, was 60 g / m. ２ The XRD of the produced membrane was measured, and it was found that CHA-type zeolite was produced. In the X-ray diffraction pattern, the peak intensity around 2θ = 9.6° was 2.5 times the peak intensity around 2θ = 20.8°.

[0219] The 400 mm long CHA-type zeolite liberation structure obtained by this synthesis method was divided into two 200 mm long pieces and installed in series to form a 400 mm long sample. Using the apparatus shown in Figure 2, at 100°C, feed gases were supplied at 50 ml / min each to the reaction tube (Figure 3) in which the CHA-type zeolite liberation structure was installed via bubblers containing water vapor and polymethoxysiloxane (MKC (registered trademark) Silicate, MS-51, manufactured by Mitsubishi Chemical Corporation), a methyl silicate oligomer, as a silica source. This supplied gas at 50 ml / min each to the reaction tube (Figure 3) in which the CHA-type zeolite liberation structure was installed, thereby treating the upper end of the CHA-type zeolite liberation structure (surface modification to form a second separation section), and preparing a composite separation membrane. In the gas supply from the bubblers for each raw material, nitrogen gas was used to supply water vapor, and helium was used to supply the silica source. The reaction tube was a stainless steel tube with an inner diameter of 15 mm, an outer diameter of 20 mm, and a total length of 440 mm. Both ends could be connected to gas supply pipes with flanges, allowing gas to flow through the reaction tube. The treatment consisted of supplying only a gas carrying water vapor through the reaction tube for the first hour (treatment stage 1). Over the next two hours, the gas carrying water vapor and the gas carrying polymethoxysiloxane were mixed and supplied through the reaction tube (treatment stage 2). Over the next hour, only the gas carrying water vapor was supplied through the reaction tube (treatment stage 3). After the treatment, the reaction tube was allowed to cool, and the composite separation membrane was removed and further heat-treated at 130°C for 1 hour (treatment stage 4). Two 200 mm-long composite separation membranes were prepared. One of these was installed in a separation membrane module with a membrane length of 17.5 cm, completing preparations for the gas separation experiment.

[0220] The obtained composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was modularized. The separation module was cylindrical with an inner diameter of 16 mm, and a supply flow path width of 2 mm on each side for the gas to be separated was formed between the module and the modified surface of the mounted composite separation membrane with an outer diameter of 12 mm. The exposed length of the surface of the composite separation membrane within the separation module was 175 mm for connection to the connecting pipe for gas circulation.

[0221] The measurement temperatures Tam (°C) were set to 16°C, 50°C, 70°C, 80°C, and 90°C, and the membrane performance evaluation and hydrogen / oxygen separation experiments of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) were carried out. Based on the results, the hydrogen permeance P (H ２ ) (mol / (m ２ Activation energy Ep(H ２ ) (kJ / mol) and oxygen permeance P (O ２ ) (mol / (m ２ Activation energy Ep(O ２ ) were derived. In the experiment, the target gas to be separated was a mixture of hydrogen and oxygen supplied from a cylinder. The former was supplied at 133.3 ml / min and the latter at 66.7 ml / min, for a total of 200.0 ml / min, to the separation membrane and separation membrane module. The target gas mixture had a stoichiometric hydrogen:oxygen ratio of 2:1. This represents the hydrogen and oxygen generated from the total decomposition of water in artificial photosynthesis plants equipped with photocatalytic materials. Figure 4 shows a schematic diagram of the measurement system used for the evaluation. This measurement system can be scaled up to be used as a hydrogen recovery system in artificial photosynthesis plants. In this experiment, pressurization mechanism A was not used, and a dehumidification module equipped with silica gel was used as dehumidification mechanism A. As a result, the relative humidity of the mixed gas introduced into the separation module was below 0.1% under all conditions. Temperature control mechanism A was not used, and flame propagation suppression mechanism A consisted of a filling pipe filled with zircon beads and a rupture disc connected by an elbow pipe. A temperature-adjustable water tank was used as the temperature adjustment mechanism B, and the separation module was placed inside it to evaluate the membrane performance of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) at 16°C, 50°C, 70°C, 80°C, and 90°C, as well as to conduct hydrogen / oxygen separation experiments. The separation module was not integrated with a dehumidifying mechanism B or a flammable propagation suppression mechanism B. The supply pressure was set to 20 kPa (G) by controlling the exhaust valve as the pressurizing mechanism B in the figure. Furthermore, a scroll pump with a maximum pumping speed of 580 L / min was provided as a pressure reduction mechanism on the permeation side of the separation membrane module, which reduced the pressure on the permeation side to approximately -99 kPa (G).

[0222] The membrane performance (separation module performance) at each temperature is shown in Table 1, and the process performance as a hydrogen recovery system is shown in Table 2. Figure 5 shows the Arrhenius plot results for the activation energies of hydrogen permeance and oxygen permeance derived from the experiment.

[0223]

[0224]

[0225] From these results, as shown in Table 1, the following membrane performance was revealed in the range of 16 (°C) ≤ Tam (°C) ≤ 90 (°C). By heating from 16°C to 90°C, the hydrogen permeance P (H ２ ) was approximately doubled, improving the membrane performance or separation module performance. ２ ) was only about 1.6 times. As a result, by heating from 16°C to 90°C, the hydrogen-oxygen separation performance α (H ２ / O ２ ) was increased by about 1.3 times, and the membrane performance or separation module performance was improved. ２ ) activation energy Ep(H ２ ) is 8.9 kJ / mol, oxygen permeance P(O ２ ) activation energy Ep(O ２ ) was 5.51 kJ / mol. Therefore, 0 < Ep(O ２ ) <Ep(H ２ ) at each temperature. ２ ) and oxygen permeance P(O ２ ) is P(O ２ ) < P(H ２ ) was.

[0226] Furthermore, from these results, as shown in Table 2, between 16 (°C) ≦ Tos (°C) ≦ 90 (°C) or between 16 (°C) ≦ Tgm (°C) ≦ 90 (°C), the following became clear as a hydrogen recovery system or separation / recovery process performance. By heating from 16 °C to 90 °C, the hydrogen recovery rate improved by approximately 1.7 times. Accordingly, by heating from 16 °C to 90 °C, the non-permeate side hydrogen concentration was reduced from 52.8 vol% to 32.4 vol%, reducing the detonation power in the event of ignition and improving safety. Therefore, even when heated from 16 °C to 90 °C, the permeate side hydrogen concentration was stable at approximately 98 vol%, and the stoichiometric hydrogen-oxygen mixed gas (hydrogen detonation gas) outside the explosive range (over 95.8 vol%) was stably achieved over the entire temperature range.

[0227] Thus, the improvement in the performance of the hydrogen recovery system or separation / recovery process is due to the unique temperature dependence of the permeance of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), which is significantly different from the membrane performance widely known to date. In separation membranes, the absolute value of the activation energy of the permeance of molecules with small kinetic molecular diameters is generally smaller (less temperature-dependent) than the absolute value of the activation energy of molecules with large kinetic molecular diameters. However, it was confirmed that the opposite was true for this composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane). As a result, it was confirmed that when separating and recovering molecules with relatively small kinetic molecular diameters from a mixed gas, heating within an appropriate range can improve the hydrogen recovery rate while roughly maintaining the hydrogen concentration on the permeate side, and also reduce the hydrogen concentration on the non-permeate side.

[0228] In the separation module equipped with this composite separation membrane, the maximum supply-side Reynolds number of the gas to be separated at the module inlet was as shown in Table 3, which was sufficiently smaller than 2000, which is the boundary between laminar flow and turbulent flow, confirming that the supply gas or non-permeate gas was supplied as a stable laminar flow on the zeolite membrane side of the surface-modified composite separation membrane. Furthermore, the maximum permeate-side Reynolds number of the gas to be separated at the module permeate outlet was also as shown in Table 3, which was sufficiently smaller than 2000, which is the boundary between laminar flow and turbulent flow, confirming that the permeate gas flowed as a stable laminar flow on the support side of the composite separation membrane.

[0229]

[0230] Example 1-2 Six composite separation membranes (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) similar to those described in Example 1-1 were prepared as follows. Each of these membranes had a length of 170 mm and was mounted on six separation modules equipped with a heating mechanism. Figure 6 is a schematic diagram of the separation module equipped with the heating mechanism. The separation module was similar to Example 1-1 except that a tubular flow path was provided on the outside of the module, through which water, a fluorine-based inert liquid, or the like could flow as a heat transfer medium, and a heat insulating section was provided surrounding the flow path.

[0231] These six separation modules were then connected in series to create a configuration equivalent to a separation module with a membrane length of 102 cm. The tubular flow paths of each separation module were also connected and heated. After this preparation, a hydrogen recovery system capable of separating and recovering hydrogen from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was constructed using the series-connected separation modules. A conceptual diagram is shown in Figure 4. When scaled up, this recovery system can also be used as a hydrogen recovery system in artificial photosynthesis plants, etc. In Figure 4, in this example, pressurization mechanisms A and B were not used, and two dehumidification modules equipped with silica gel were used as dehumidification mechanism A. As a result, the relative humidity of the mixed gas introduced into the separation module was 0.1% or less under all conditions. Furthermore, a temperature adjustment mechanism A was not used, and a commercially available dry safety device (manufactured by Nippon Sanso Tanaka Corporation / model number: FA-510-H) was used as the flame propagation suppression mechanism A. The temperature adjustment mechanism B was realized by supplying hot water from a thermostatic chamber to a tubular flow path integrated with the separation module shown in FIG. 6. The separation module did not incorporate a dehumidification mechanism B or a flame propagation suppression mechanism B. The supply pressure of the hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was set to 0 kPa (G) without using any pressure mechanism B shown in the figure. Furthermore, a commercially available dry safety device (manufactured by Nippon Sanso Tanaka Corporation / model number: FA-510-H) was further installed downstream of the pressure mechanism B to ensure safety. A diaphragm pump with a maximum pumping speed of 120 L / min was also prepared as a pressure reduction mechanism on the permeate side of the separation membrane module, reducing the pressure on the permeate side to less than -92 kPa (G). A commercially available dry safety device (manufactured by Nippon Sanso Tanaka Corporation / model number: FA-510-H) was also installed downstream of the pressure reduction mechanism to ensure safety. Here, the temperature Tos of the separation module was set to 90°C, and a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was supplied at 900 ml / min to evaluate the process performance as a hydrogen recovery system. The results are shown in Table 4. The hydrogen concentration on the permeate side, sucked by the diaphragm pump used as a pressure reduction mechanism, was 98.2% by volume, outside the explosive range, and hydrogen was safely separated from the hydrogen detonation gas. In addition, the hydrogen recovery rate was high at 75.8%, confirming highly efficient hydrogen recovery.The supply pressure at this time was 0 kPa (G), which was sufficiently low, and was ideal as a supply condition for hydrogen detonation gas.

[0232] Example 1-3: Process performance was evaluated using the hydrogen recovery system of Example 1-2, except that the supply rate of the hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was set to 510 ml / min. The results are shown in Table 4. The pressure on the permeate side was reduced to -92.5 kPa (G) by a diaphragm pump with a movable part prepared as a pressure reduction mechanism. Furthermore, the hydrogen concentration on the permeate side sucked by the diaphragm pump with a movable part was 96.8 vol%, outside the explosive range, and hydrogen could be safely separated from the hydrogen detonation gas. The hydrogen recovery rate was also very high at 93.7%, confirming ultra-efficient hydrogen recovery. Furthermore, the hydrogen concentration on the non-permeate side, which did not have a movable part downstream, was low at 12.1 vol%, outside the explosive range. Thus, safe and ultra-efficient hydrogen-oxygen separation was achieved. The supply pressure at this time was sufficiently low at 0 kPa (G), which was ideal as a supply condition for hydrogen detonation gas.

[0233] Example 1-4 Process performance was evaluated using the hydrogen recovery system of Example 1-2, except that the separation module temperature was set to 70°C and the supply rate of the hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was set to 450 ml / min. The results are shown in Table 4. The pressure on the permeate side was reduced to -94.5 kPa (G) by a diaphragm pump with a movable part prepared as a pressure reduction mechanism. Furthermore, the hydrogen concentration on the permeate side sucked by the diaphragm pump with a movable part was 96.6 vol%, outside the explosive range, and hydrogen was safely separated from the hydrogen detonation gas. The hydrogen recovery rate was also very high at 94.8 vol%, confirming ultra-efficient hydrogen recovery. Furthermore, the hydrogen concentration on the non-permeate side without a movable part downstream was also low at 10.0 vol%, outside the explosive range. In this way, safe and ultra-efficient hydrogen-oxygen separation was achieved. Note that the supply pressure at this time was sufficiently low at 0 kPa (G), which was ideal as a supply condition for hydrogen detonation gas.

[0234] Example 1-5: Process performance was evaluated using the hydrogen recovery system of Example 1-2, except that the separation module temperature was set to 50°C and the supply rate of the hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was set to 300 ml / min. The results are shown in Table 4. The pressure on the permeate side was reduced to -95.5 kPa (G) by a diaphragm pump with a movable part prepared as a pressure reduction mechanism. Furthermore, the hydrogen concentration on the permeate side sucked by the diaphragm pump with a movable part was 95.9 vol%, outside the explosive range, and hydrogen was safely separated from the hydrogen detonation gas. The hydrogen recovery rate was also very high at 97.3%, confirming ultra-efficient hydrogen recovery. Furthermore, the hydrogen concentration on the non-permeate side, which did not have a movable part downstream, was also very low at 7.0 vol%, outside the explosive range. In this way, safe and ultra-efficient hydrogen-oxygen separation was achieved. Note that the supply pressure at this time was sufficiently low at 0 kPa (G), which was ideal as a supply condition for hydrogen detonation gas.

[0235]

[0236] Example 1-6 The following reaction mixture for hydrothermal synthesis was prepared. 1.44 g of a 1 mol / L NaOH aqueous solution, 5.76 g of a 1 mol / L KOH aqueous solution, and 114.01 g of water were mixed, and aluminum hydroxide (Al ２ O ３ 0.195 g of TMADAOH (containing 53.5% by mass, manufactured by Aldrich) was added and stirred to dissolve, forming a transparent solution. 2.43 g of an aqueous TMADAOH solution (containing 25% by mass, manufactured by Seichem Co.) was added as an organic template, and 10.8 g of colloidal silica (Snowtec-40, manufactured by Nissan Chemical Industries, Ltd.) was then added and stirred for 30 minutes to form a reaction mixture.

[0237] The composition (molar ratio) of this reaction mixture was: SiO ２ / Al ２ O ３ / NaOH / KOH / H ２ O / TMADAOH=1 / 0.014 / 0.02 / 0.08 / 100 / 0.04, SiO ２ / Al ２ O ３= 70. An alumina tube (outer diameter 12 mm, inner diameter 9 mm) was cut to a length of 400 mm and used as the inorganic porous support. SiO ２ / Al ２ O ３ / NaOH / KOH / H ２ CHA-type zeolite was used, which had a gel composition (molar ratio) of 0.033 / 0.1 / 0.06 / 20 / 0.07 and was crystallized by hydrothermal synthesis for 2 days at 160° C. The support was immersed in a dispersion of 1.0 mass % of this seed crystal in water for 30 seconds and then pulled out, so that the seed crystal was supported on the upper end of the inorganic porous support, and the support was used for hydrothermal synthesis.

[0238] The support with the seed crystals attached in this way and two other supports with seed crystals attached in the same way, a total of three supports, were immersed vertically in the Teflon (registered trademark) inner tube containing the reaction mixture, the autoclave was sealed, and the support was heated in a stationary state at 180°C for 18 hours under autogenous pressure to carry out zeolite crystal growth at the upper end of the inorganic porous support by hydrothermal synthesis. After cooling, the zeolite liberation structure was removed from the reaction mixture, washed, and then dried at 100°C for 2 hours or more.

[0239] The zeolite liberation structure before the template calcination was calcined in an electric furnace at 500°C for 5 hours. XRD analysis of the resulting membrane revealed that CHA-type zeolite had been produced. In the X-ray diffraction pattern, the peak intensity near 2θ = 9.6° was 2.5 times that near 2θ = 20.8°.

[0240] The 80 mm-long CHA-type zeolite liberation structure obtained by this synthesis method was treated at 100°C using the apparatus shown in Figure 2. Gases were supplied at 50 ml / min each to a reaction tube (Figure 3) containing a CHA-type zeolite liberation structure via bubblers containing water vapor and polymethoxysiloxane (MKC (registered trademark) Silicate, MS-56, manufactured by Mitsubishi Chemical Corporation), a methyl silicate oligomer, as a silica source. This supplied gas was then passed through bubblers. The upper end of the zeolite liberation structure was then treated to prepare a composite separation membrane. In this treatment, a total of four CHA-type zeolite liberation structures, including the 80 mm-long CHA-type zeolite liberation structure and three other 80-100 mm-long CHA-type zeolite liberation structures, were installed in series. In the gas supply from the bubblers for each raw material, nitrogen gas was used to supply water vapor, and helium was used to supply the silica source. The reaction tube was a stainless steel tube with an inner diameter of 15 mm, an outer diameter of 20 mm, and a total length of 440 mm. Both ends were connected to gas supply pipes with flanges, allowing gas to flow through the reaction tube. The treatment consisted of supplying only a gas carrying water vapor through the reaction tube for the first hour (treatment stage 1). Over the next five hours, a mixture of the water vapor-carrying gas and a gas carrying polymethoxysiloxane was supplied and allowed to flow through the reaction tube (treatment stage 2). Over the next hour, only the water vapor-carrying gas was supplied and allowed to flow through the reaction tube (treatment stage 3). Following treatment, the reaction tube was allowed to cool, and the composite separator was removed and further heat-treated at 130°C for one hour (treatment stage 4).

[0241] The resulting composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) with a support length of 80 mm was used to prepare a module. The separation module was cylindrical with an inner diameter of 15 mm, and a supply flow path width of 1.5 mm on one side for the gas to be separated was formed between the modified surface of the mounted composite separation membrane with an outer diameter of 12 mm. The exposed length of the surface of the composite separation membrane within the separation module was 59 mm for connection to the gas flow connecting pipe.

[0242] The membrane performance of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was evaluated, and hydrogen / oxygen separation experiments were carried out. Based on the results, the hydrogen permeance P (H２ ) (mol / (m ２ Activation energy Ep(H ２ ) (kJ / mol) and oxygen permeance P (O ２ ) (mol / (m ２ Activation energy Ep(O ２ ) were derived. In this derivation, two methods were performed: one in which the supply gas was hydrogen and oxygen as single gases, and the other in which a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was used. First, using the measurement system shown in Figure 4, 200 ml / min of hydrogen single gas and oxygen single gas were each supplied to the separation membrane and separation membrane module, and the activation energy of each permeance was determined. In this case, the membrane performance (separation module performance) for hydrogen single gas and oxygen single gas was determined in the same manner as in Example 1-1, except that the temperature of the temperature-adjustable water tank used as temperature adjustment mechanism B was set to a range of 16°C to 80°C, and the supply pressure was set to 19 kPa (G) by controlling the exhaust valve as pressure adjustment mechanism B in the figure. The results are summarized in Table 5. Note that Figure 7 shows the Arrhenius plot results from which the activation energies of hydrogen permeance and oxygen permeance were derived. The hydrogen permeance P (H ２ ) activation energy Ep(H ２ ) is 13.4 kJ / mol, oxygen permeance P(O ２ ) (mol / (m ２ Activation energy Ep(O ２ ) was 7.1 kJ / mol.

[0243]

[0244] Comparing the results of this Example 1-6 with those of Example 1-1, in the zeolite liberation structure upper end treatment (surface modification treatment), if the second treatment stage in producing the composite separation membrane is long, the activation energy Ep(S) or Ep(H ２ ) also corresponds to the activation energy of oxygen permeance Ep(L) or Ep(O ２) also increased (temperature dependency became stronger). However, in the range of 5 (°C) ≤ Tam (°C) ≤ 200 (°C) under each processing condition, |Ep(L)| < |Ep(S)| or |Ep(O ２ ) | < | Ep (H ２ ) | relationship remained unchanged.

[0245] Example 1-7: The supply pressure was set to 19 kPa (G) by controlling the exhaust valve as the pressurizing mechanism B in FIG. 4. The gas to be separated was a mixture of hydrogen and oxygen supplied from a cylinder, and the former was 133.3 ml / min and the latter 66.7 ml / min, for a total of 200.0 ml / min, as in Example 1-6. The hydrogen permeance P (H ２ ) activation energy Ep(H ２ ) and oxygen permeance P(O ２ ) (mol / (m ２ Activation energy Ep(O ２ The results are summarized in Table 6. FIG. 8 shows the Arrhenius plot results from which the activation energies of hydrogen permeance and oxygen permeance were derived. The hydrogen permeance P(H ２ ) activation energy Ep(H ２ ) is 13.5 kJ / mol, oxygen permeance P(O ２ ) (mol / (m ２ Activation energy Ep(O ２ ) was 7.2 kJ / mol.

[0246]

[0247] The results derived from the membrane performance for hydrogen and oxygen gases alone, and the results derived from the hydrogen-oxygen mixed gas (hydrogen:oxygen = 133.3:66.7 = 2:1) are common to the range of 16 (°C) ≦ Tam (°C) ≦ 80 (°C), and the following became clear regarding the membrane performance and separation module performance. By heating from 16°C to 80°C, the hydrogen permeance P(H ２The oxygen permeance P(O ２ ) was only about 1.7 times when the single gas shown in Table 5 was supplied, and only about 1.7 times when the mixed gas shown in Table 6 was supplied. As a result, by heating from 16°C to 80°C, the hydrogen-oxygen separation performance α(H ２ / O ２ ) was increased by approximately 1.6 to 1.7 times, improving the membrane performance or separation module performance. ２ ) activation energy Ep(H ２ ) is 13.4 kJ / mol when a single gas is supplied, and 13.5 kJ / mol when a mixed gas is supplied. ２ ) activation energy Ep(O ２ ) was 7.1 kJ / mol when a single gas was supplied and 7.2 kJ / mol when a mixed gas was supplied. Therefore, under all measurement conditions, |Ep(L)| < |Ep(S)| or |Ep(O ２ ) | < | Ep (H ２ ) | The hydrogen permeance P(H ２ ) and oxygen permeance P(O ２ ) is P(L)<P(S) or P(O) whether a single gas or a mixed gas is supplied. ２ ) < P(H ２ On the other hand, Table 7 shows the process performance of the hydrogen recovery system when the mixed gas was supplied at 50°C and 90°C.

[0248]

[0249] These results revealed the following about the hydrogen recovery system and separation / recovery process performance. By heating from 50°C to 90°C, the hydrogen recovery rate increased by approximately 1.5 times. Even when heated from 50°C to 90°C, the permeate-side hydrogen concentration remained stable at approximately 98% by volume, consistently achieving a concentration outside the explosion range (over 95.8% by volume) of the stoichiometric hydrogen-oxygen mixed gas (hydrogen detonation gas). The improvement in performance as a hydrogen recovery system or separation / recovery process is attributed to the unique temperature dependence of the permeance of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), which is significantly different from the widely known membrane performance. In separation membranes, the absolute value of the activation energy of the permeance of molecules with small kinetic molecular diameters is generally smaller (less temperature-dependent) than the absolute value of the activation energy of molecules with large kinetic molecular diameters. However, it was confirmed that the opposite was true for this composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane).As a result, it was confirmed that when separating and recovering molecules with relatively small dynamic molecular diameters from a mixed gas, by heating within an appropriate range, it is possible to improve the hydrogen recovery rate while roughly maintaining the hydrogen concentration on the permeate side, and also to reduce the hydrogen concentration on the non-permeate side.

[0250] Example 1-8 One 400 cm long CHA type zeolite liberation structure obtained in the same manner as in Example 1-1 was divided into two 200 mm long pieces, and one of the 200 mm long CHA type zeolite liberation structures was placed in the reaction tube of the raw material supply gas flow type zeolite liberation structure upper end treatment device shown in Figure 2. The treatment (surface modification treatment) in the reaction tube was carried out in the same manner as in Example 1-1, except that the number of 200 cm long membrane samples was one and nitrogen gas was also used to supply the silica source. After the treatment process, the reaction tube was allowed to cool, and then the composite separation membrane was removed. One 200 mm long composite separation membrane was prepared. This composite separation membrane was installed in a separation membrane module with a membrane length of 17.5 cm, and preparation for a gas separation experiment was completed. The membrane performance of the composite separation membrane (surface-modified CHA type zeolite membrane / surface-modified CHA membrane) was evaluated, and a hydrogen / nitrogen separation experiment was also carried out. Based on the results, the hydrogen permeance P (H ２) (mol / (m ２ Activation energy Ep(H ２ ) (kJ / mol) and nitrogen permeance P (N ２ ) (mol / (m ２ Activation energy Ep(N ２ In this derivation, the supply gas was a hydrogen-nitrogen mixed gas with a hydrogen:nitrogen ratio of 2:1, and the measurement system shown in FIG.

[0251] The membrane performance (separation module performance) for a hydrogen-nitrogen mixed gas was determined in the same manner as in Example 1-1, except that the temperature control mechanism B used was an oven with an adjustable temperature range of 30°C to 130°C, the supply pressure was set to 100 kPa (G) by controlling the exhaust valve as the pressurization mechanism B in Figure 4, and no pressure reduction mechanism was used. The results are summarized in Table 8. Figure 9 shows the Arrhenius plot results from which the activation energies of hydrogen permeance and nitrogen permeance were derived. The hydrogen permeance P(H ２ ) activation energy Ep(H ２ ) is 10.0 kJ / mol, oxygen permeance P(O ２ ) (mol / (m ２ Activation energy Ep(O ２ ) was 0.8 kJ / mol.

[0252]

[0253] When the results of this Example 1-8 and the results of Example 1-1 are considered together, the following can be seen. In separation membranes, the absolute value of the activation energy of the permeance of molecules with small kinetic molecular diameters is generally smaller (less temperature dependent) than the absolute value of the activation energy of molecules with large kinetic molecular diameters. However, in this composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), it was confirmed that this is the opposite between diatomic molecules of hydrogen, oxygen, and nitrogen. That is, the kinetic molecular diameter of hydrogen is 2.89 A, the kinetic molecular diameter of oxygen is 3.46 A, and the kinetic molecular diameter of nitrogen is 3.64 A. From conventional knowledge, it is thought that the activation energy of hydrogen permeance is the smallest, followed by the activation energy of oxygen permeance and the activation energy of nitrogen permeance. However, in this composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), this result was reversed. Specifically, the activation energy of hydrogen permeance was the highest at 8.9 to 10.0 kJ / mol, followed by the activation energy of oxygen permeance at 5.5 kJ / mol, and the activation energy of nitrogen permeance was the lowest at 0.8 kJ / mol.

[0254] As a result, it was confirmed that when separating and recovering molecules with relatively small dynamic molecular diameters from a mixed gas, heating within an appropriate range can improve the hydrogen recovery rate while maintaining the hydrogen concentration on the permeate side, and can also reduce the hydrogen concentration on the non-permeate side. Furthermore, from these results, it is believed that, for example, when considering air separation, such as separating oxygen and nitrogen from air, it is possible to separate oxygen and nitrogen highly efficiently by heating separation using a composite separation membrane. That is, similar characteristics may be exhibited in separation membranes with composite structures such as composite separation membranes having a silica-modified portion formed on a CHA-type zeolite membrane, composite separation membranes having a silica-modified portion formed on various zeolite membranes other than CHA-type, composite separation membranes having a carbon network formed on a zeolite membrane, composite separation membranes having a carbon network formed on a silica membrane prepared by various CVD / sol-gel methods, and composite separation membranes having a silica-modified portion formed on a carbon membrane, etc., which may exhibit the above-mentioned tendency in the activation energy of gas permeance due to complex phenomena other than simple molecular sieves. In other words, it is presumed that such a tendency in the activation energy of gas permeance may occur when the first and second separation sections have different gas separation characteristics, such as gas adsorption characteristics, gas diffusion characteristics, and gas desorption characteristics, or when there is an interaction between them, such as when the second separation section shields the characteristics of the first separation section. In the separation of oxygen and nitrogen or air using such separation membranes, it is presumed that appropriate heating separation can achieve highly selective and high-recovery separation.

[0255] Example 1-9 The membrane performance (separation module performance) of the composite separation membrane was measured in the same manner as in Example 1-7, except that the supply gas was changed from a hydrogen / nitrogen mixed gas with a hydrogen:nitrogen ratio of 2:1 to simple hydrogen gas, carbon dioxide gas, argon gas, nitrogen gas, and methane gas, and the temperature of the temperature-controllable oven used as temperature control mechanism B was changed to a range of 30° C. to 100° C. The results are summarized in Table 9.

[0256]

[0257] Considering the results of this Example 1-9 together with the results of Examples 1-1 and 1-6, the following can be seen. In a separation membrane, the absolute value of the activation energy of the permeance of molecules with a small kinetic molecular diameter is generally smaller (less temperature dependent) than the absolute value of the activation energy of molecules with a large kinetic molecular diameter. However, in this composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), when hydrogen is included as a molecule with a relatively small kinetic molecular diameter and at least one gas selected from carbon dioxide, argon, oxygen, nitrogen, and methane is included as a molecule with a relatively large kinetic molecular diameter, and the mixed gas is composed of the gas, when heated within an appropriate range when separating and recovering hydrogen from the mixed gas, it is expected that the hydrogen recovery rate can be improved while maintaining the hydrogen concentration on the permeate side at a high level, and the hydrogen concentration on the non-permeate side can also be reduced.

[0258] Example 1-10 As shown below, a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) having the same performance as in Example 1-7 was assumed, except that the membrane length was set to 1 m, and the expected separation process performance for hydrogen-nitrogen mixed gas at 30 ° C, 80 ° C, and 130 ° C was derived by calculation as follows. A so-called two-sided plug flow model was used for the calculation, with the hydrogen-nitrogen mixed gas supply flow rate set to 900 mL / min, hydrogen:nitrogen = 1:1, the composite separation membrane length set to 1 m, the supply pressure set to 0.1 MPa (G) using the pressurization mechanism B in Figure 4, and -0.09 MPa (G) on the permeate side using a vacuum pump as a pressure reduction mechanism. The results are summarized in Table 10.

[0259]

[0260] These results show that even with a 1:1 hydrogen:nitrogen mixed gas, if a separation process is configured using a composite separation membrane, the hydrogen recovery rate can be improved while maintaining a high hydrogen concentration on the permeate side by increasing the set temperature for thermal separation. At the same time, it was also found that the hydrogen concentration on the non-permeate side can be reduced by increasing the set temperature for thermal separation.

[0261] Examples 1-11 The following reaction mixture for hydrothermal synthesis was prepared. 21.6 g of a 1 mol / L NaOH aqueous solution, 86.4 g of a 1 mol / L KOH aqueous solution, and 1710.2 g of water were mixed, and aluminum hydroxide (Al ２ O ３ 2.925 g of TMADAOH (N,N,N-Trimethyl-1-adamantylammonium Hydroxide) aqueous solution (TMADAOH 25% by mass, manufactured by Seichem Co., Ltd.) was added as an organic template, and 162 g of colloidal silica (Nissan Chemical Industries, Ltd., Snowtec-40) was added and stirred for 30 minutes to form a reaction mixture.

[0262] The composition (molar ratio) of this reaction mixture was: SiO ２ / Al ２ O ３ / NaOH / KOH / H ２ O / TMADAOH=1 / 0.014 / 0.02 / 0.08 / 100 / 0.04, SiO ２ / Al ２ O ３ = 70. An alumina tube (outer diameter 12 mm, inner diameter 9 mm) was cut into a length of 1000 mm and used as the inorganic porous support. SiO ２ / Al ２ O ３ / NaOH / KOH / H ２ CHA-type zeolite was used, which had a gel composition (molar ratio) of 0.033 / 0.1 / 0.06 / 20 / 0.07 and was crystallized by hydrothermal synthesis for 2 days at 160° C. The support was immersed in a dispersion of 1.0 mass % of this seed crystal in water for 30 seconds and then pulled out, so that the seed crystal was supported on the upper end of the inorganic porous support, and the support was used for hydrothermal synthesis.

[0263] The support with the seed crystals attached in this way and two other supports with seed crystals attached in the same way, a total of three supports, were immersed vertically in the Teflon (registered trademark) inner tube containing the reaction mixture, the autoclave was sealed, and the support was heated in a stationary state at 180°C for 18 hours under autogenous pressure to carry out zeolite crystal growth at the upper end of the inorganic porous support by hydrothermal synthesis. After cooling, the zeolite liberation structure was removed from the reaction mixture, washed, and then dried at 100°C for 2 hours or more.

[0264] The zeolite liberation structure before calcining the template was calcined in an electric furnace at 500°C for 5 hours. The mass per unit area of ​​CHA-type zeolite crystallized on the upper end of the support, calculated from the difference between the mass of the calcined zeolite liberation structure and the mass of the support, was 60 g / m. ２ The XRD of the produced membrane was measured, and it was found that CHA-type zeolite was produced. In the X-ray diffraction pattern, the peak intensity around 2θ = 9.6° was 2.5 times the peak intensity around 2θ = 20.8°.

[0265] The 1000 mm long CHA-type zeolite liberation structure obtained by this synthesis method was cut into 400 mm lengths, and at 100°C, using the apparatus shown in Figure 2, feed gases were supplied at 100 ml / min each to a reaction tube (Figure 3) equipped with a CHA-type zeolite liberation structure via bubblers containing water vapor and polymethoxysiloxane (MKC (registered trademark) Silicate, MS-51, manufactured by Mitsubishi Chemical Corporation), a methyl silicate oligomer, as a silica source. This performed upper end treatment of the CHA-type zeolite liberation structure (surface modification to form a second separation section), thereby preparing a composite separation membrane. In the gas supply from the bubblers for each raw material, nitrogen gas was used to supply water vapor and the silica source. The reaction tube was a stainless steel tube with an inner diameter of 15 mm, an outer diameter of 20 mm, and a total length of 440 mm. Both ends could be connected to gas supply pipes with flanges, allowing gas to flow through the reaction tube. During the first two hours of treatment, only the gas carrying water vapor was supplied and allowed to flow through the reactor (first treatment stage). Over the next six hours, the gas carrying water vapor and the gas carrying polymethoxysiloxane were mixed and supplied and allowed to flow through the reactor (second treatment stage). Over the next hour, only the gas carrying water vapor was supplied and allowed to flow through the reactor (third treatment stage). After the treatment, the reactor was allowed to cool, and the composite separation membrane was removed and further heat-treated at 130°C for one hour (fourth treatment stage). A 400 mm long composite separation membrane was then prepared. This composite separation membrane was installed in a separation membrane module with a membrane length of 375 mm, completing preparations for the gas separation experiment.

[0266] The obtained composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was modularized. The separation module was cylindrical with an inner diameter of 16 mm, and a supply flow path width of 2 mm on each side for the gas to be separated was formed between the module and the modified surface of the mounted composite separation membrane with an outer diameter of 12 mm. The exposed length of the surface of the composite separation membrane within the separation module was 375 mm for connection to the connecting pipe for gas circulation.

[0267] The measurement temperatures Tam (°C) were set to 50°C, 70°C, and 90°C, and the membrane performance evaluation of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) and hydrogen / oxygen separation experiments were carried out. Based on the results, the hydrogen permeance P (H ２ ) (mol / (m2 s Pa)) activation energy Ep(H ２ ) (kJ / mol) and oxygen permeance P (O ２ ) (mol / (m ２ Activation energy Ep(O ２) were derived. In the membrane performance evaluation experiment, the target gas to be separated was a mixture of hydrogen and oxygen supplied from a cylinder. The former was supplied at 100 ml / min and the latter at 50 ml / min, for a total of 150 ml / min, to the separation membrane and separation membrane module. The target gas had a stoichiometric composition of hydrogen:oxygen = 2:1. This simulates the hydrogen and oxygen generated from the total decomposition of water in an artificial photosynthesis plant equipped with a photocatalytic material. Meanwhile, in the hydrogen / oxygen separation experiment (process performance confirmation experiment), the target gas to be separated was a mixture of hydrogen and oxygen supplied from a cylinder, but the former was set at 60 ml / min and the latter at 30 ml / min, for a total supply flow rate of 90 ml / min, supplied to the separation membrane and separation membrane module. A schematic diagram of the measurement system used in the evaluation is shown in Figure 4. This measurement system can be expanded to be used as a hydrogen recovery system in an artificial photosynthesis plant. In this experiment, pressurization mechanism A was not used, and a dehumidification module equipped with silica gel was used as dehumidification mechanism A. As a result, the relative humidity of the mixed gas introduced into the separation module was 0.1% or less under all conditions. Temperature control mechanism A was not used, and a filled pipe filled with zircon beads and a rupture disc connected with an elbow pipe was used as flame propagation suppression mechanism A. A temperature-controllable water tank was used as temperature control mechanism B, and the separation module was installed inside it to evaluate the membrane performance of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) at 50°C, 70°C, and 90°C, and to conduct hydrogen / oxygen separation experiments. Note that dehumidification mechanism B, flammable propagation suppression mechanism B, etc. were not integrated into the separation module. The supply pressure was set to 20 kPa (G) by controlling the exhaust valve as pressurization mechanism B in the figure. Furthermore, a scroll pump with a maximum pumping speed of 580 L / min was provided as a pressure reducing mechanism on the permeate side of the separation membrane module, and the pressure on the permeate side was reduced to about -99 kPa (G).

[0268] The membrane performance (separation module performance) at each temperature is shown in Table 11, and the process performance as a hydrogen recovery system is shown in Table 12. Fig. 11 also shows the Arrhenius plot results for the activation energies of hydrogen permeance and oxygen permeance derived from the experiment.

[0269]

[0270]

[0271] As shown in Table 12, when a separation membrane module equipped with the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared as described above was used and Tam = 90 °C, the process performance during hydrogen-oxygen separation was as follows. The permeate side hydrogen concentration was approximately 97.7 vol.%. At the same time, the non-permeate side hydrogen concentration was approximately 3.4 vol.%. Here, the explosion range of hydrogen-oxygen mixed gas is considered to be 3.9 vol.% to 95.8 vol.%, but it was confirmed that both the permeate side hydrogen concentration and the non-permeate side hydrogen concentration were outside the upper and lower limits of the explosion range. In other words, hydrogen detonation gas (gas of hydrogen:oxygen = 2:1) was successfully separated into a hydrogen-oxygen mixed gas of a non-explosive composition on both the permeate and non-permeate sides. In other words, the permeate side was approximately 97.7 vol.% hydrogen, and the non-permeate side contained approximately 3.4 vol.% hydrogen, but approximately 96.6 vol.% oxygen. Furthermore, it was confirmed that the hydrogen recovery rate was an extremely high 98.3%.

[0272] Comparative Example 1-1: A zeolite liberation structure (unmodified CHA membrane) was used without surface modification, the length of the exposed surface of the zeolite liberation structure in the separation module was 57 mm, hydrogen gas and nitrogen gas were used instead of a mixed gas of hydrogen and oxygen from the viewpoint of safety, and the temperature range for measurement was 50°C to 140°C. The hydrogen permeance P(H ２ ) (mol / (m ２ Activation energy Ep(H ２ ) (kJ / mol) and nitrogen permeance P (N ２ ) (mol / (m ２ Activation energy Ep(N ２ ) was derived.

[0273]

[0274] In a separation membrane, the absolute value of the activation energy of the permeance of molecules with small kinetic molecular diameters is generally smaller (less temperature dependent) than the absolute value of the activation energy of molecules with large kinetic molecular diameters, and this behavior was observed in the zeolite free separation structure (unmodified CHA membrane) of this separation structure. That is, the derived hydrogen permeance P(H ２ ) activation energy Ep(H ２ ) is -4.1 kJ / mol when single gas is supplied, and nitrogen permeance P (N ２ ) activation energy Ep(N ２ ) was -9.5 kJ / mol when the single gas was supplied. ２ ) <Ep(H ２ ) < 0, and |Ep(H ２ ) | < | Ep(N ２ As a result, when heating is applied to separate and recover molecules with relatively small dynamic molecular diameters from a mixed gas, selectivity improves, but the amount of hydrogen on the permeate side was confirmed.

[0275] Example 2-1 (Relative Temperature Dependence of Explosion / Detonation Power of Hydrogen-Oxygen Mixed Gas) Figure 12 shows a schematic diagram of the experimental apparatus used to determine the critical extinction pressure. An explosion experiment vessel 200 made of SUS was prepared, which had a cylindrical interior space with a diameter of approximately 6 cm and a height of approximately 15.5 cm, and in which a cell loaded with small-diameter inorganic particles could be placed in the middle. The inorganic particle-loaded cell 201 in the vessel has a certain degree of flame propagation suppression function, and its flame-extinguishing ability is determined by the hydrogen-oxygen mixture ratio, temperature, pressure, and particle size, packing density, shape, etc. of the hydrogen-oxygen mixed gas filled in the vessel. Here, in evaluating the relative temperature dependence of explosion / detonation power, the hydrogen-oxygen mixture ratio is set to the strictest stoichiometric composition (hydrogen:oxygen = 2:1), and the particle size, packing density, shape, etc. of the inorganic particles are kept constant to provide the inorganic particle-loaded cell with fixed flame quenching performance. Furthermore, the temperature is fixed, and the pressure of the hydrogen-oxygen mixed gas is varied. This makes it possible to determine the upper limit of the temperature at which flame quenching is possible for the inorganic particle-loaded cell 201 and its temperature. This pressure is designated as the "extinction pressure limit" at that temperature. Next, using an inorganic particle-loaded cell 201 equivalent to the above, the "extinction pressure limit" at that temperature is determined at a different temperature. By repeating this process, the extinction pressure limit at multiple temperature levels can be obtained. Here, if the extinction pressure limit is high, the explosive power of the hydrogen-oxygen mixed gas at that temperature is low, and therefore, it can be understood that flame quenching is possible even if the pressure is increased. On the other hand, when the flame-extinction limit pressure is low, the explosive power of the hydrogen-oxygen mixed gas at that temperature is high, so the pressure cannot be increased, and it can be understood that the flame can only be extinguished at a relatively low pressure.

[0276] Zirconia with an average particle size of 0.22 mm was filled into an inorganic particle-loaded cell to a height of 3.5 cm and placed in the SUS explosion test vessel. The vessel was then degassed, and a gas adjusted to a hydrogen:oxygen ratio of 2:1 was introduced into the vessel. The SUS explosion test vessel was then controlled to the desired temperature. After confirming that both the introduced gas temperature and the vessel temperature had reached a constant temperature, the first combustion chamber 202 (lower space) was ignited and an intentional explosion occurred. The presence or absence of flame propagation was determined by the presence or absence of an increase in temperature / pressure in the second combustion chamber 203 (upper space), and the flame-extinction limit pressure was calculated as a function of temperature. The experimental temperatures were 20°C, 80°C, and 120°C. The results are shown in Table 14.

[0277]

[0278] If we assume that the explosive power of hydrogen detonation gas depends on 1 / √Tab, we obtain the results shown in Figure 13. Figure 13 shows both the calculation results and the experimental results, and it is possible to explain the increasing trend in the extinction limit pressure.

[0279] In plants that handle hydrogen-oxygen mixed gases, such as artificial photosynthesis plants, safety designs for various components, including piping, preferably have a safety factor of about 200% relative to the expected explosive potential at room temperature. However, because excessive safety factors can cause various problems, such as increased piping thickness and increased costs, a safety factor of about 180% is more preferable, about 160% is even more preferable, and about 140% is most preferable. Therefore, it is desirable to keep the increase in detonation potential due to temperature smaller than this, preferably within 30%, more preferably within 20%, even more preferably within 15%, and most preferably within 12%. Roughly converting this to temperature from Figure 6, the respective values ​​are preferably 220°C or less, more preferably 150°C or less, even more preferably 120°C or less, and most preferably 95°C or less.

[0280] Example 2-2 The following reaction mixture for hydrothermal synthesis was prepared. 7.2 g of 1 mol / L NaOH aqueous solution, 28.8 g of 1 mol / L KOH aqueous solution, and 570.05 g of water were mixed, to which 0.975 g of aluminum hydroxide (containing 53.5% by mass of Al2O3, manufactured by Aldrich) was added and stirred to dissolve, forming a clear solution. 12.15 g of an organic template TMADAOH (N,N,N-trimethyl-1-adamantylammonium hydroxide) aqueous solution (containing 25% by mass of TMADAOH, manufactured by Seichem Co., Ltd.) was added, followed by 54 g of colloidal silica (Nissan Chemical Industries, Ltd., Snowtec-40). The mixture was stirred for 30 minutes to form a reaction mixture.

[0281] The composition (molar ratio) of this reaction mixture was: SiO ２ / Al ２ O ３ / NaOH / KOH / H ２ O / TMADAOH=1 / 0.014 / 0.02 / 0.08 / 100 / 0.04, SiO ２ / Al ２ O ３ = 70. An alumina tube (outer diameter 12 mm, inner diameter 9 mm) was cut to a length of 400 mm and used as the inorganic porous support. SiO ２ / Al ２ O ３ / NaOH / KOH / H ２ CHA-type zeolite was used, which had a gel composition (molar ratio) of 0.033 / 0.1 / 0.06 / 20 / 0.07 and was crystallized by hydrothermal synthesis for 2 days at 160° C. The support was immersed in a dispersion of 1.0 mass % of this seed crystal in water for 30 seconds and then pulled out, so that the seed crystal was supported on the upper end of the inorganic porous support, and the support was used for hydrothermal synthesis.

[0282] The support with seed crystals attached in this manner and two other supports with seed crystals attached in the same manner, a total of three supports, were immersed vertically in a Teflon (registered trademark) inner tube containing the reaction mixture, the autoclave was sealed, and the support was heated in a stationary state at 181°C for 18 hours under autogenous pressure to perform zeolite crystal growth at the upper end of the inorganic porous support by hydrothermal synthesis. The support was then cooled, and the zeolite liberation structure was removed from the reaction mixture, washed, and dried at 100°C for 2.5 hours or more.

[0283] The zeolite liberation structure before calcining the organic template was calcined in an electric furnace at 500°C for 5 hours. The mass per unit area of ​​the CHA-type zeolite crystallized on the upper end of the support, calculated from the difference between the mass of the calcined zeolite liberation structure and the mass of the support, was 60 g / m. ２ The XRD of the produced membrane was measured, and it was found that CHA-type zeolite was produced. In the X-ray diffraction pattern, the peak intensity around 2θ = 9.6° was 2.5 times the peak intensity around 2θ = 20.8°.

[0284] The 400 mm long CHA-type zeolite liberation structure obtained by this synthesis method was divided into two 200 mm long pieces and installed in series to form a 400 mm long sample. Using the apparatus shown in Figure 2, at 100°C, feed gases were supplied at 50 ml / min each to the reaction tube (Figure 3) in which the CHA-type zeolite liberation structure was installed via bubblers containing water vapor and polymethoxysiloxane (MKC (registered trademark) Silicate, MS-51, manufactured by Mitsubishi Chemical Corporation), a methyl silicate oligomer, as a silica source. This supplied gas at 50 ml / min each to the reaction tube (Figure 3) in which the CHA-type zeolite liberation structure was installed, thereby treating the upper end of the CHA-type zeolite liberation structure (surface modification to form a second separation section), and preparing a composite separation membrane. In the gas supply from the bubblers for each raw material, nitrogen gas was used to supply water vapor, and helium was used to supply the silica source. The reaction tube was a stainless steel tube with an inner diameter of 15 mm, an outer diameter of 20 mm, and a total length of 440 mm. Both ends could be connected to gas supply pipes with flanges, allowing gas to flow through the reaction tube. The treatment consisted of supplying only a gas carrying water vapor through the reaction tube for the first hour (treatment stage 1). Over the next three hours, the gas carrying water vapor and the gas carrying polymethoxysiloxane were mixed and supplied through the reaction tube (treatment stage 2). Over the next hour, only the gas carrying water vapor was supplied through the reaction tube (treatment stage 3). After the treatment, the reaction tube was allowed to cool, and the composite separation membrane was removed and further heat-treated at 130°C for one hour (treatment stage 4). Two 200 mm-long composite separation membranes were prepared. One of these was installed in a separation membrane module with a membrane length of 17.5 cm, completing preparations for the gas separation experiment.

[0285] The obtained composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was modularized. The separation module was cylindrical (tubular) with an inner diameter of 16 mm, and a supply flow path width of 2 mm on each side for the gas to be separated was formed between the module and the modified surface of the mounted composite separation membrane with an outer diameter of 12 mm. The exposed length of the surface of the composite separation membrane within the separation module was 175 mm for connection to the connecting pipe for gas circulation.

[0286] The measurement temperatures Tam (°C) were set to 20°C, 51°C, 70°C, 80°C, and 90°C, and the membrane performance evaluation and hydrogen / oxygen separation experiments of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) were carried out. Based on the results, the hydrogen permeance P (H ２ ) (mol / (m ２ s Pa) and oxygen permeance P(O ２ ) (mol / (m ２ The temperature dependence of the relative humidity (H2O) (s·Pa) was derived. In the experiment, a mixture of hydrogen and oxygen was supplied from a cylinder as the target gas for separation. The former was supplied at 133.3 ml / min and the latter at 66.7 ml / min, for a total of 200.0 ml / min, to the separation membrane and separation membrane module. The target gas had a stoichiometric hydrogen:oxygen ratio of 2:1. This represents the hydrogen and oxygen generated from the total decomposition of water in artificial photosynthesis plants equipped with photocatalytic materials. A schematic diagram of the measurement system used for the evaluation is shown in Figure 4. This measurement system can be scaled up and used as a hydrogen recovery system in artificial photosynthesis plants. In this experiment, pressurization mechanism A was not used, and a dehumidification module equipped with silica gel was used as dehumidification mechanism A. As a result, the relative humidity of the mixed gas introduced into the separation module was below 0.1% under all conditions. No temperature control mechanism A was used, and a flame propagation suppression mechanism A was a filled pipe filled with zircon beads and a rupture disc connected by an elbow pipe. A temperature-controllable water tank was used as the temperature control mechanism B, and the separation module was installed in it to evaluate the membrane performance of the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) at 20°C, 51°C, 70°C, 80°C, and 90°C, as well as conduct hydrogen / oxygen separation experiments. The separation module was not integrated with a dehumidifying mechanism B or a flammable propagation suppression mechanism B. The supply pressure was set to 20 kPa (G) by controlling the exhaust valve as pressurizing mechanism B in the figure. Furthermore, a scroll pump with a maximum pumping speed of 580 L / min was prepared as a pressure reduction mechanism on the permeation side of the separation membrane module, which reduced the pressure on the permeation side to approximately -99 kPa (G).

[0287] Table 15 shows the membrane performance (separation module performance) at each temperature, and Table 16 shows the process performance as a hydrogen recovery system.

[0288]

[0289]

[0290] From these results, we first consider the effect of heating from 20°C to 90°C. ２ ) increased by about three times, improving the membrane performance or separation module performance. On the other hand, by heating from 20°C to 90°C, the oxygen permeance P(O ２ ) was only about 1.7 times. As a result, by heating from 20°C to 90°C, the hydrogen-oxygen separation performance α (H ２ / O ２ ) was increased by about 1.9 times, improving the membrane performance or separation module performance. ２ ) and oxygen permeance P(O ２ ) is P(O ２ ) < P(H ２ ) was.

[0291] Furthermore, from these results, as shown in Table 16, between 20 (°C) ≦ Tos (°C) ≦ 90 (°C) or between 20 (°C) ≦ Tgm (°C) ≦ 90 (°C), the following was clarified as a hydrogen recovery system or separation / recovery process performance. Considering 20°C as the standard, heating to 90°C improved the hydrogen recovery rate by approximately 2.7 times. Accordingly, by heating from 20°C to 90°C, the non-permeate side hydrogen concentration was reduced from 60.3 vol% to 40.1 vol%, reducing the detonation power in the event of ignition and improving safety. Even when heated from 20°C to 90°C, the permeate side hydrogen concentration was stable at approximately 98 vol%, and a stoichiometric hydrogen-oxygen mixed gas (hydrogen detonation gas) outside the explosive range (over 95.8 vol%) was stably achieved over the entire temperature range. When heating from 20°C to 90°C in this way, the explosive power in the event of ignition of the supply-side hydrogen-oxygen mixed gas is estimated to increase by about 6 to 7% from the results of Example 2-1, but the impact can be said to be sufficiently small. Therefore, when considering the above-mentioned advantages of heating and separating within the appropriate range, its effectiveness is clear.

[0292] Furthermore, regarding these results, the influence of heating from 20°C to 51°C will be considered. From these results, it can be seen that heating from 20°C to 51°C increases the hydrogen permeance P(H ２ ) was approximately doubled, improving the membrane performance or separation module performance. On the other hand, by heating from 20°C to 51°C, the oxygen permeance P(O ２ ) was only about 1.3 times. As a result, by heating from 20°C to 51°C, the hydrogen-oxygen separation performance α (H ２ / O ２ ) was increased by about 1.6 times, improving the membrane performance or separation module performance. ２ ) and oxygen permeance P(O ２ ) is P(O ２ ) < P(H ２ ) was.

[0293] Furthermore, from these results, as shown in Table 16, the following became clear as a hydrogen recovery system or separation / recovery process performance when the temperature range was 20 (°C) ≦ Tos (°C) ≦ 51 (°C), or when the temperature range was 20 (°C) ≦ Tgm (°C) ≦ 51 (°C). Considering 20°C as the standard, heating to 51°C improved the hydrogen recovery rate by approximately 1.9 times. Accordingly, heating from 20°C to 51°C reduced the non-permeate side hydrogen concentration from 60.3 vol% to 51.8 vol%, reducing the detonation power in the event of ignition and improving safety. Even when heated from 20°C to 51°C, the permeate side hydrogen concentration remained stable at approximately 98 vol%, and a stoichiometric hydrogen-oxygen mixed gas (hydrogen detonation gas) outside the explosive range (over 95.8 vol%) was stably achieved over the entire temperature range. When heating from 20°C to 51°C in this way, the explosive power in the event of ignition of the supply-side hydrogen-oxygen mixed gas is estimated to increase by about 2 to 3% from the results of Example 2-1, but the impact can be said to be sufficiently small. Therefore, when considering the above-mentioned advantages of heating and separation, its effectiveness is clear.

[0294] As such, improving the characteristics of a hydrogen recovery system or separation / recovery process performance comes down to the temperature dependency of the separation membrane, and at least when separating and recovering hydrogen from a mixed gas containing both hydrogen and oxygen, it is important to heat the target hydrogen-oxygen mixed gas within a range that does not excessively increase the explosive power of the target hydrogen-oxygen mixed gas.

[0295] Six composite separation membranes (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) similar to those described in Example 2-2 were prepared as follows. Each membrane had a length of 170 mm and was mounted on six separation modules equipped with heating mechanisms.

[0296] These six separation modules were then connected in series to create a configuration equivalent to a separation module with a membrane length of 102 cm. After this preparation, the series-connected separation modules were used to construct a hydrogen recovery system capable of separating and recovering hydrogen from a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 containing saturated water vapor. A conceptual diagram is shown in Figure 4. This recovery system can also be used as a hydrogen recovery system in artificial photosynthesis plants, etc., if scaled up. In Figure 4, in this example, pressurization mechanisms A and B were not used, and two dehumidification modules equipped with silica gel were used as dehumidification mechanism A. As a result, the relative humidity of the mixed gas introduced into the separation module was below 0.1% under all conditions.

[0297] Further, a temperature adjustment mechanism A was not used, and a commercially available dry safety device (manufactured by Nippon Sanso Tanaka Corporation / model number: FA-510-H) was used as the flame propagation suppression mechanism A. The temperature adjustment mechanism B was realized by supplying hot water from a thermostatic chamber to a tubular flow path integrated with the separation module. Note that the separation module was not integrated with a dehumidification mechanism B or a flame propagation suppression mechanism B. Furthermore, the supply pressure of the hydrogen-oxygen mixed gas (hydrogen detonation gas) containing saturated water vapor at a hydrogen:oxygen = 2:1 ratio was set to 0 kPa (G) without using any pressure mechanism B in the figure. Furthermore, to ensure safety, a commercially available dry safety device (manufactured by Nippon Sanso Tanaka Corporation / model number: FA-510-H) was further installed downstream of the pressure mechanism B. Furthermore, a diaphragm pump with a maximum pumping speed of 120 L / min was prepared as a pressure reduction mechanism on the permeation side of the separation membrane module, and the permeation side was reduced in pressure to less than -96 kPa (G). To ensure safety even downstream of the pressure reduction mechanism, a commercially available dry safety device (manufactured by Nippon Sanso Tanaka Co., Ltd., model number: FA-510-H) was also installed. Here, the temperature Tos of the separation module was set to 90°C, and a hydrogen-oxygen mixed gas (hydrogen detonation gas) with a hydrogen:oxygen ratio of 2:1 was supplied at 480 ml / min to evaluate the process performance as a hydrogen recovery system.

[0298] The permeate flow rate, drawn by the diaphragm pump used as a pressure reducing mechanism, was 315 ml / min, and the hydrogen concentration was 95.9 vol%, outside the explosive range. This allowed for safe separation of hydrogen from the detonation gas. Furthermore, the hydrogen recovery rate was as high as 94.3 vol%, confirming highly efficient hydrogen recovery. The supply pressure was 0 kPa (G), a sufficiently low value, providing ideal conditions for supplying hydrogen from the detonation gas. Meanwhile, the non-permeate flow rate was 165 ml / min, and the hydrogen concentration was 8.4 vol%, within the explosive range but outside the explosive range. Therefore, hydrogen could be safely separated from the detonation gas. Based on the results of Example 2-1, when heated to 90°C, the explosive power is estimated to increase by approximately 6-7% compared to the explosive power generated when the supply-side hydrogen-oxygen mixed gas is ignited at room temperature. This effect is considered sufficiently small. Therefore, considering the advantages of heating and separating the hydrogen within the appropriate range, its effectiveness is clear.

[0299] According to the present invention, hydrogen can be efficiently separated from other gases, enabling efficient separation of hydrogen from large amounts of hydrogen-oxygen mixtures obtained, for example, by artificial photosynthesis. Furthermore, according to the present invention, hydrogen-oxygen mixtures, which were previously considered dangerous when heated, are separated using a high-temperature separation membrane, which has not been used in the past. This allows hydrogen to be sufficiently separated from the hydrogen-oxygen mixture, resulting in a sufficiently low oxygen concentration after permeation through the separation membrane, which is outside the detonation range, making the separation safer. The hydrogen-oxygen separation area is where hydrogen-oxygen mixtures from many hydrogen-oxygen mixture generators (e.g., photocatalytic water splitting devices using artificial photosynthesis) gather. By applying the present invention here, the large amount of mixture to be separated is outside the detonation range after passing through the separation process, allowing hydrogen to be safely separated and recovered from the hydrogen-oxygen mixture. Combining this technology with, for example, a method of electrolyzing water using renewable energy such as sunlight, or a method of simultaneously generating hydrogen and oxygen through photocatalytic water splitting, allows for efficient separation and recovery of so-called green hydrogen. Therefore, the present invention is useful from both a technical and environmental perspective, and is a technology of great industrial value.

[0300] 1. Container (bubbler) for generating gas from Si compound 2. Container (bubbler) for generating water vapor from water 3. Tubular reaction tube 4. Gas flow controller 5. Water vapor collector in exhaust gas 6. Back pressure valve 7. Gas flow meter 8. Valve 9. Supply gas 10. Exhaust gas 11. Thermostatic chamber 21. Tubular reaction tube 22. Zeolite liberation structure 23. Fixing jig 24. Flange 25. Supply gas inlet piping 26. Exhaust gas piping 100. Composite separation membrane 101. Support 102. Void portion 103. First separation section 104. Second separation section 105. Separation activation section 106. Liberation structure 200. Limit quenching pressure measuring device 201. Inorganic particle-loaded cell 202. First combustion chamber 203. Second combustion chamber 204. Pressure detector 205. Thermocouple 206. Ignition neon transformer

Claims

1. The hydrogen permeance P(S) (mol / (m) of the separation membrane, calculated within the temperature range Tam (°C) that satisfies the following formula (1-I): ２ The activation energy Ep(S) (kJ / mol) of the separation membrane is expressed as the activation energy Ep(S) (kJ / mol) of the separation membrane. The permeance P(L) (mol / (m ２ and the activation energy Ep(L) (kJ / mol) of |Ep(S)| (s·Pa) satisfies the following formula (1-II): 5 (° C.)≦Tam(° C.)≦200 (° C.) (1-I) |Ep(L)|<|Ep(S)| (1-II) 2. The separation membrane according to claim 1, which satisfies the following formula (1-III): P(L)<P(S)...(1-III) 3. The separation membrane according to claim 1, which satisfies the following formula (1-IV): 0<Ep(L)<Ep(S) ... (1-IV) 4. The separation membrane according to claim 1, which is an inorganic membrane.

5. The separation membrane according to claim 1, which has a surface-modified zeolite membrane.

6. A separation membrane laminate comprising a separation membrane on a support, the separation membrane being the separation membrane according to any one of claims 1 to 5, the support being tubular, and the inner diameter φi (mm) of the support satisfying the following formula (1-VI): 6 (mm)≦φi (mm)≦16 (mm) ... (1-VI) 7. A separation module or a separation tower equipped with a separation membrane, the separation membrane being the separation membrane according to any one of claims 1 to 5, and the temperature Tos (°C) of the separation module or the separation tower satisfies the following formula (1-VII): 45 (°C) ≦ Tos (°C) ≦ 200 (°C) ... (1-VII) 8. The separation module or separation column according to claim 7, wherein the distance between the inner wall of the separation module or separation column and the separation membrane closest to the inner wall is 0.1 cm or more and 50 cm or less.

9. A separation module or a separation tower equipped with the separation membrane laminate according to claim 6, wherein the temperature Tos (°C) of the separation module or the separation tower satisfies the following formula (1-VII): 45 (°C) ≦ Tos (°C) ≦ 200 (°C) ... (1-VII) 10. The separation module or separation tower according to claim 7, further comprising at least one of a dehumidification mechanism, a heating mechanism, and a flame propagation suppression mechanism.

11. A hydrogen recovery system equipped with a separation membrane, the separation membrane being the separation membrane according to any one of claims 1 to 5, and at least one of the temperatures Tgm (°C) of the mixed gas M to be separated and recovered in the hydrogen recovery system or the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C) ≦ Tgm (°C) ≦ 200 (°C) ... (1-IX) 12. A hydrogen recovery system comprising the separation membrane laminate according to claim 6, wherein at least one of the temperatures Tgm (°C) of the mixed gas M to be separated and recovered in the hydrogen recovery system and the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) ... (1-IX) 13. The hydrogen recovery system according to claim 11, wherein the separation membrane is mounted in a separation module or separation tower, and the distance between the inner wall of the separation membrane module or separation tower and the separation membrane closest to the inner wall is 0.1 cm or more and 50 cm or less.

14. The hydrogen recovery system according to claim 11, further comprising a pressurizing mechanism for the mixed gas M supplied to the separation membrane.

15. The hydrogen recovery system according to claim 11, further comprising at least one of a dehumidifying mechanism, a heating mechanism, and a flame propagation suppression mechanism.

16. The hydrogen recovery system according to claim 11, further comprising a pressure reducing mechanism on the permeation side of the separation membrane.

17. A method for separating and recovering hydrogen from a mixed gas M of hydrogen and a gas L1 having a larger kinetic molecular diameter than hydrogen, using a separation membrane, the separation membrane being the separation membrane according to any one of claims 1 to 5, and at least one of the temperatures Tgm (°C) of the mixed gas M and the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) ... (1-IX) 18. Pressure F of the mixed gas M supplied to the separation membrane Ｍ The method for separating and recovering hydrogen according to claim 17, wherein 0.0 (MPa(G))≦F satisfies the following formula (1-XI): Ｍ (MPa(G))≦0.2(MPa(G))...(1-XI) 19. The method for separating and recovering hydrogen according to claim 17, wherein the permeation side of the separation membrane is subjected to a reduced pressure.

20. The method for separating and recovering hydrogen according to claim 19, wherein the pressure on the permeation side of the separation membrane is −0.101 MPa (G) or more and −0.065 MPa (G) or less.

21. Relative humidity RH of a gas mixture M Ｍ The method for separating and recovering hydrogen according to claim 17, wherein 0.0(%)≦RH satisfies the following formula (1-XIII): Ｍ (%)≦5(%)...(1-XIII) 22. The method for separating and recovering hydrogen according to claim 18, wherein heating is performed so that at least one of the temperature Tgm (°C) of the mixed gas M or the temperature of the separation membrane satisfies the following formula (1-IX): 45 (°C)≦Tgm (°C)≦200 (°C) ... (1-IX) 23. A method for separating and recovering hydrogen as described in claim 17, in which the mixed gas M passes through a separation membrane after passing through the flame propagation suppression mechanism.

24. A method for separating and recovering hydrogen as described in claim 17, which has a separation membrane module or separation tower equipped with the separation membrane, and supplies mixed gas M so that the maximum Reynolds number on the supply side in the separation membrane module or separation tower is 5 or more and 2,000 or less and / or the maximum Reynolds number on the permeation side is 5 or more and 2,000 or less.

25. A method for separating and recovering hydrogen as described in claim 17, in which the gas L is oxygen and the hydrogen-oxygen mixed gas is supplied so that the hydrogen concentration of the hydrogen-oxygen mixed gas on the permeation side after the separation and recovery step exceeds 95.8 volume %.

26. A method for separating and recovering hydrogen as described in claim 25, in which a hydrogen-oxygen mixed gas is supplied so that the hydrogen concentration of the hydrogen-oxygen mixed gas on the permeate side after the separation and recovery step is 96.0 volume % or more, and the hydrogen concentration of the hydrogen-oxygen mixed gas on the non-permeate side is 15.5 volume % or less.

27. The hydrogen permeance P(S) (mol / (m) of the separation membrane, calculated within the temperature range Tam (°C) that satisfies the following formula (1-I): ２ The activation energy Ep(S) (kJ / mol) of the separation membrane, and the permeance P(L) (mol / (m ２ and the activation energy Ep(L) (kJ / mol) of |Ep(S)| (s·Pa) satisfies the following formula (1-II): 5 (° C.)≦Tam(° C.)≦200 (° C.) (1-I) |Ep(L)|<|Ep(S)| (1-II) 28. A method for separating and recovering hydrogen from a mixed gas M containing at least hydrogen and oxygen, in which the temperature Tgm (°C) in the separation and recovery step satisfies the following formula (2-I): 45 (°C) ≦ Tgm (°C) ≦ 200 (°C) ... (2-I) 29. The separation and recovery method according to claim 28, wherein the composition ratio of hydrogen to oxygen in the mixed gas M supplied to the separation and recovery step is 2:1 or more, with hydrogen in excess.

30. The separation and recovery method according to claim 28, wherein the mixed gas M supplied to the separation and recovery step is within the explosive range.

31. The separation and recovery method according to claim 28, wherein a separation membrane is used in the separation and recovery step.

32. The separation and recovery method according to claim 31, wherein the separation membrane is an inorganic membrane.

33. The separation and recovery method according to claim 32, wherein the separation membrane has a surface-modified zeolite membrane.

34. The separation and recovery method according to claim 31, wherein the separation membrane is a polyimide membrane or a polyamide membrane.

35. Pressure F of the mixed gas M supplied to the separation membrane Ｍ The separation and recovery method according to claim 31, wherein (MPa(G)) satisfies the following formula (2-III): 0.0(MPa(G))≦F Ｍ (MPa(G))≦0.2(MPa(G))...(2-III) 36. The separation and recovery method according to claim 31, wherein the permeate side of the separation membrane is subjected to a reduced pressure.

37. The separation and recovery method according to claim 36, wherein the pressure on the permeate side of the separation membrane is lower than -0.9 MPa (G).

38. Relative humidity RH in the mixed gas M Ｍ The separation and recovery method according to claim 31, wherein 0.0(%)≦RH satisfies the following formula (2-V): Ｍ (%)≦5.0(%)...(2-V) 39. The separation and recovery method according to claim 31, wherein at least one of the mixed gas M and the separation membrane is heated so that the temperature Tgm satisfies the above formula (2-I).

40. The separation and recovery method according to claim 31, in which the mixed gas M passes through a separation membrane after passing through the flame propagation suppression mechanism.

41. The separation and recovery method according to claim 31, wherein the mixed gas M is supplied so that the maximum Reynolds number on the supply side and / or the maximum Reynolds number on the permeation side is 5 or more and 2,000 or less.

42. The separation and recovery method according to claim 31, in which the mixed gas M is supplied so that the hydrogen concentration of the mixed gas after permeation in the separation and recovery step is greater than 95.8 volume %.

43. A separation and recovery method as described in claim 42, in which mixed gas M is supplied so that the hydrogen concentration of the mixed gas on the permeation side after the separation and recovery step is 96.0 volume % or more and the hydrogen concentration of the mixed gas on the non-permeation side is 15.5 volume % or less.

44. A separation module or separation tower for separating and recovering hydrogen from a mixed gas M containing at least hydrogen and oxygen, the separation module or separation tower having a temperature control mechanism.

45. The separation module or separation column according to claim 44, wherein the temperature adjustment mechanism includes a tubular flow path through which a heat transfer medium flows and / or an insulating section.

46. ​​The separation module or separation column according to claim 44, wherein the temperature Tos (°C) of either the separation module or the separation column satisfies the following formula (2-VII): 51 (°C)≦Tos (°C)≦220 (°C) ... (2-VII) 47. The separation module or column of claim 44, wherein the separation module or column is equipped with a separation membrane.

48. The separation module or column of claim 47, wherein the separation membrane is an inorganic membrane.

49. The separation module or column of claim 47, wherein the separation membrane comprises a surface-modified zeolite membrane.

50. The separation module or column according to claim 47, wherein the distance between the inner wall of the separation module or column and the separation membrane closest to the inner wall is 0.1 cm or more and 50 cm or less.

51. The separation module or separation column according to claim 47, wherein the separation membrane has a tubular support, and the inner diameter φi (mm) of the support satisfies the following formula (2-IX): 6≦φi≦16... (2-IX) 52. A hydrogen recovery system for separating and recovering hydrogen from a mixed gas M containing at least hydrogen and oxygen, comprising a separation module or separation tower according to any one of claims 44 to 51.

53. The hydrogen recovery system according to claim 52, further comprising a pressurizing mechanism for the mixed gas M supplied to the separation module or separation column.

54. A hydrogen recovery system as described in claim 52, comprising a section for dehumidifying the mixed gas M and / or a section for heating the mixed gas M.

55. A hydrogen recovery system as described in claim 52, comprising a flame propagation suppression portion.

56. The hydrogen recovery system according to claim 52, further comprising a pressure reducing mechanism downstream of the separation module or separation column.

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