Method for separating / recovering / concentrating gas using a separation membrane.

Abstract

An object is to provide a method for separating / recovering / concentrating small-diameter molecules such as hydrogen from a mixed gas of small-diameter molecules / large-diameter molecules with high safety and high recovery rate. 【Solution means】A method for separating / recovering / concentrating a gas containing a target molecule from a supply mixed gas containing at least one kind each of a small-diameter molecule having a dynamic molecular diameter smaller than 0.3 nm and a large-diameter molecule having a dynamic molecular diameter of 0.3 nm or more, using a separation membrane, wherein at least one set of a small-diameter molecule and a large-diameter molecule in the supply mixed gas and the separation membrane satisfy the following formula 1, and is achieved by the separation / recovery / concentration method. Formula 1: 0.5 ≦ α w (S / L) / α d (S / L) ≦ 1.2 Here, Formula 2: α w (S / L) ≡ P w (S) / P w (L) Formula 3: α d (S / L) ≡ P d (S) / P d (L) is.

Description

[Technical Field]

[0001] The present invention relates to a method for separating, recovering, and concentrating a gas containing a target molecule from a supply mixed gas containing at least one small-diameter molecule and at least one large-diameter molecule, using a separation membrane. [Background technology]

[0002] Hydrogen is expected to be actively utilized as a next-generation energy source, and various hydrogen production methods have been proposed. In particular, regarding the production of so-called green hydrogen, methods such as electrolysis of water using renewable energy such as sunlight, and methods that generate hydrogen and oxygen simultaneously by the total decomposition of water using photocatalysis, and then separate and recover hydrogen, have been proposed. In electrolysis, oxygen and hydrogen are obtained from the positive and negative electrodes, but in reality, hydrogen and oxygen mix to some extent, so it is necessary to separate and recover the hydrogen from this mixture. In the case of total water decomposition by photocatalysis, 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 multiple gaseous components is brought into contact with a separation membrane, and the highly permeable component is allowed to pass through the mixed gas to separate the highly permeable component, or the less permeable component is concentrated by allowing the highly permeable component to pass through the mixed gas (see, for example, Patent Document 1). Furthermore, a porous support-zeolite membrane composite has been proposed as the separation membrane (see, for example, Patent Documents 2 and 3). Separation membranes having an amorphous silica network structure (see, for example, Non-Patent Document 1), organic-inorganic hybrid silica separation membranes (see, for example, Non-Patent Document 2), and zeolite membranes synthesized in contact with a tubular metal support have also been reported (see, for example, Non-Patent Document 3).

[0004] The differences in permeability of each gas in the aforementioned membrane separation are thought to be mainly due to differences in the dynamic molecular diameter of each gas. For example, Non-Patent Documents 1 and 2 state that the dynamic molecular diameters are 0.289 nm for hydrogen, 0.26 nm for helium, 0.346 nm for oxygen, 0.330 nm for carbon dioxide, 0.34 nm for argon, 0.364 nm for nitrogen, and 0.38 nm for methane.

[0005] The aforementioned hydrogen:oxygen 2:1 mixture is also called hydrogen detonation gas, and once ignited, it can cause a detonation phenomenon in which flames accompanied by shock waves propagate at speeds exceeding the speed of sound. Therefore, sufficient safety precautions must be taken when handling it. For example, the explosive and detonation ranges of a hydrogen-oxygen mixture at atmospheric pressure are described, with a hydrogen concentration of 3.9 vol% to 95.8 vol% being within the explosive range, and a hydrogen concentration of 15.5 vol% to 92.6 vol% being specifically within the detonation range (Shozo Yagyu, Explosive Limits of Gases and Vapors, Japan Safety Engineering Association, 1977.4).

[0006] The separation of multiple gaseous components using separation membranes is usually performed under pressure. However, in the case of membrane separation of the generated hydrogen-oxygen mixed gas, from a safety standpoint, it is preferable to avoid extreme pressurization and extreme heating, supply the mixed gas at atmospheric pressure or slight pressure, and perform gas separation by reducing the pressure on the permeate side.

[0007] Furthermore, for safety reasons, the hydrogen-oxygen mixed gas needs to be separated into hydrogen (or hydrogen-rich gas with a composition exceeding the appropriate level) and oxygen (or oxygen-rich gas with a composition exceeding the appropriate level) so that the hydrogen concentration falls outside the explosion and detonation ranges of hydrogen. Furthermore, in separating hydrogen and oxygen from the aforementioned hydrogen-oxygen mixed gas, there is a strong demand for a method that achieves a high recovery rate from an economic standpoint. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2015-44162 [Patent Document 2] Japanese Patent Publication No. 2015-44163 [Patent Document 3] Japanese Patent Publication No. 2020-131184 [Non-patent literature]

[0009] [Non-Patent Document 1] Masayoshi Kanazashi, Network Structure Control and Permeation Characteristics Evaluation of Silica-based Gas Separation Membranes, MEMBRANE 41(4), 183-188, 2016. [Non-Patent Document 2] Kanezashi et al, Organic-inorganic hybrid silica membranes with controlled silica network size for propylene / propane separation,(Ind. Eng. Chem. Res.) 2012, 51, 944-953 [Non-Patent Document 3] Halil Kalipcilar et al., Synthesis and Separation Performance of SSZ-13 Zeolite Membranes on Tubular Supports, Chem. Mater. 2002, 14, 3458-3464 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] A specific example is a separation process for a hydrogen-oxygen mixed gas in an artificial photosynthesis plant where the mixed gas flows. In an artificial photosynthesis plant, this process may include decomposing water into hydrogen and oxygen using a photocatalyst, then separating these into a hydrogen-rich gas and an oxygen-rich gas using a separation membrane or the like, and subsequently improving the purity of the hydrogen by various methods.

[0011] The hydrogen-oxygen mixed gas generated by photocatalytic panels in artificial photosynthesis plants contains water vapor corresponding to the saturated water vapor pressure. However, when separating and recovering hydrogen from this hydrogen-oxygen mixed gas containing water vapor using a separation membrane, water molecules exhibit permeation behavior through the separation membrane that cannot be explained solely by the dynamic molecular diameter of the gas, because their physical properties, such as polarity, differ significantly from those of hydrogen and oxygen.

[0012] Therefore, compared to the separation of dry mixed gases, when separating a mixed gas containing water vapor (hereinafter sometimes referred to as "wet mixed gas") using a separation membrane, the water vapor in the mixed gas may impair the performance of the separation membrane. Specifically, during gas separation of the aforementioned wet mixed gas using a separation membrane, the permeability of each gas molecule in the mixed gas to the membrane and the resulting decrease in the separation performance of each gas may occur, which could lead to a decrease in the process performance of the gas separation. Therefore, gas separation of wet gas mixtures using separation membranes has various limitations compared to the separation of dry gas mixtures, and achieving safe and highly efficient separation can sometimes be difficult.

[0013] Furthermore, in addition to hydrogen / oxygen, there are many other gases that can be separated by separation membranes as mixed gases accompanied by water vapor, such as hydrogen / carbon dioxide, hydrogen / argon, hydrogen / nitrogen, hydrogen / methane, and hydrogen / air.

[0014] Furthermore, from the perspective of constructing a safe and simplified experiment by not using hydrogen, it is possible to estimate the performance of the separation membrane using helium as a substitute gas for hydrogen. Therefore, in addition to helium / oxygen, other possible separation targets for the separation membrane include helium / carbon dioxide, helium / argon, helium / nitrogen, helium / methane, and helium / air. Further mixed gases are also possible.

[0015] Under the above circumstances, an object of the present invention is to provide a method for separating / recovering / concentrating small-diameter molecules such as hydrogen from a mixed gas of small-diameter molecules / large-diameter molecules such as hydrogen / oxygen, hydrogen / carbon dioxide, hydrogen / argon, hydrogen / nitrogen, hydrogen / methane, hydrogen / air, helium / oxygen, helium / methane, etc. safely and with a high recovery rate.

Means for Solving the Problems

[0016] In the present invention, as a result of intensive studies to solve the problem that the performance of the separation membrane is impaired including the case where water vapor is entrained in the separation of the mixed gas as exemplified above, a method for separating / recovering / concentrating the mixed gas safely and with high efficiency has been found, and the present invention has been achieved.

[0017] [1] A method for separating / recovering / concentrating a gas containing a target molecule using a separation membrane from a supply mixed gas containing at least one kind each of a small-diameter molecule having a dynamic molecular diameter smaller than 0.3 nm and a large-diameter molecule having a dynamic molecular diameter of 0.3 nm or more, wherein at least one set of a small-diameter molecule and a large-diameter molecule in the supply mixed gas and the separation membrane satisfy the following formula 1 separation / recovery / concentration method. Formula 1: 0.5≦α w (S / L) / α d (S / L)≦1.2 Herein, Formula 2: α w (S / L)≡P w (S) / P w (L) Formula 3: α d (S / L)≡P d (S) / P d (L) wherein, further P w (S): The permeability of one kind of small-diameter molecule contained in the supply mixed gas through the separation membrane, P w (L): The permeability of one kind of large-diameter molecule contained in the supply mixed gas through the separation membrane, P d(S): When the separation conditions are the same except that the supply mixed gas is a dry gas, P w (S) The permeance through which the small molecular diameter molecules selected during derivation pass through the separation membrane is P d (L): When the separation conditions are the same except that the supply mixed gas is a dry gas, P w (L) This is the permeance through which the large molecular weight molecules selected during derivation pass through the separation membrane. [2] The separation / recovery / concentration method according to [1], characterized in that the supply mixed gas contains water vapor. [3] The separation / recovery / concentration method according to [1] or [2], wherein the dew point of the supply mixed gas when it is in a dry state is -20°C or lower. [4] A separation / recovery / concentration method according to any one of [1] to [3] wherein all combinations of small and large molecular diameter molecules in the supply mixed gas satisfy formula 1. [5] The separation / recovery / concentration method according to any one of [1] to [4], wherein the separation membrane has a composite separation structure. [6] The separation / recovery / concentration method according to [5], wherein the composite separation structure is a zeolite membrane having a CHA-type skeletal structure with a silica layer formed on its surface. [7] The separation / recovery / concentration method according to any one of [1] to [6], wherein the small molecular weight molecules in the supply mixed gas are either hydrogen, helium, or both, and the large molecular weight molecules are any one or more of carbon dioxide, argon, oxygen, nitrogen, methane, or a combination of two or more of them. [8] The α of the separation membrane as defined by the hydrogen and oxygen contained in the supply mixed gas d The separation / recovery / concentration method described in [7], wherein the (S / L) is between 42 and 190. [9] The α of the separation membrane as defined by the hydrogen and nitrogen contained in the supply mixed gas d The separation / recovery / concentration method according to [7] or [8], wherein the (S / L) is 63 or greater and 475 or less.

[10] The α of the separation membrane as defined by the hydrogen and methane contained in the supply mixed gas d A separation / recovery / concentration method according to any one of [7] to [9], wherein the (S / L) is between 75 and 570.

[11] The separation / recovery / concentration method according to any one of claims [7] to

[10] , wherein the recovery rate of hydrogen molecules contained in the permeate mixed gas obtained by permeating the supply mixed gas through the separation membrane is 60% or more.

[12] A separation / recovery / concentration method according to any one of [7] to

[11] , wherein the concentration of hydrogen molecules in the permeate mixed gas obtained by permeating the supply mixed gas through the separation membrane is 93.6% by volume or more.

[13] A separation / recovery / concentration method according to any one of [7] to

[12] , wherein the concentration of hydrogen molecules in the impermeable mixed gas obtained from the supply mixed gas that does not permeate the separation membrane is 35.0 volume% or less.

[14] A separation / recovery / concentration method according to any one of [7] to

[10] , wherein the recovery rate of hydrogen molecules contained in the permeate mixed gas obtained by permeating the supply mixed gas through the separation membrane is 60% or more, the concentration of hydrogen molecules contained in the permeate mixed gas is 93.6% by volume or more, and the concentration of hydrogen molecules contained in the non-permeate mixed gas recovered from the supply mixed gas without permeating the separation membrane is 35.0% by volume or less.

[15] The α of the separation membrane as defined by the helium and carbon dioxide contained in the supply mixed gas. d The separation / recovery / concentration method described in [7], wherein the (S / L) is between 5 and 348.

[16] The α of the separation membrane as defined by the helium and argon contained in the supply mixed gas d The separation / recovery / concentration method according to [7] or

[15] , wherein (S / L) is 24 or greater and 389 or less.

[17] The α of the separation membrane as defined by the helium and oxygen contained in the supply mixed gas d A separation / recovery / concentration method according to any one of [7],

[15] , and

[16] , wherein (S / L) is 31 or greater and 305 or less.

[18] The α of the separation membrane as defined by the helium and nitrogen contained in the supply mixed gas. d A separation / recovery / concentration method according to any one of [7] and

[15] to

[17] , wherein (S / L) is 39 or greater and 855 or less.

[19] The α of the separation membrane is defined by the helium and methane contained in the aforementioned supply mixed gas.d A separation / recovery / concentration method according to any one of [7] and

[15] to

[18] , wherein (S / L) is 46 or more and 1026 or less.

[20] The separation / recovery / concentration method according to any one of [7] and

[15] to

[19] , wherein the recovery rate of helium contained in the permeate mixed gas obtained by permeating the supply mixed gas through the separation membrane is 30% or more.

[21] The separation / recovery / concentration method according to any one of [7] and

[15] to

[20] , wherein the concentration of helium in the permeate mixed gas obtained by permeating the supply mixed gas through the separation membrane is 50% by volume or more.

[22] The separation / recovery / concentration method according to any one of [7] and

[15] to

[21] , wherein the concentration of helium in the non-permeable mixed gas that is recovered from the supply mixed gas without passing through the separation membrane is 30% by volume or less.

[23] A separation / recovery / concentration method according to any one of [7] and

[15] to

[19] , wherein the recovery rate of helium contained in the permeate mixed gas is 30% or more, the concentration of helium contained in the permeate mixed gas is 50% by volume or more, and the concentration of helium contained in the non-permeate mixed gas is 30% by volume or less. [Effects of the Invention]

[0018] According to the present invention, it is possible to safely and efficiently separate small-diameter molecules having a dynamic molecular diameter smaller than 0.3 nm from large-diameter molecules having a dynamic molecular diameter of 0.3 nm or more, even when water vapor is present in the mixed gas. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram of the composite separation structure of the present invention. [Figure 2] This is a schematic diagram of the gas flow type apparatus used to form the second separation section. [Figure 3] This is a schematic diagram of the inside of the reaction tube of the gas flow type apparatus used to form the second separation section. [Modes for carrying out the invention]

[0020] The embodiments of the present invention will be described in more detail below, but the description of the constituent elements described below is just one example of an embodiment of the present invention, and the present invention is not limited to these contents, and can be implemented in various ways within the scope of its gist.

[0021] In the present invention, the gas obtained by permeating the separation membrane from the supplied mixed gas is called the "permeated mixed gas," and the gas obtained by not permeating the separation membrane from the supplied mixed gas is called the "impermeable mixed gas." Furthermore, in the present invention, "separation / recovery / concentration method" and "separation / recovery / concentration method" mean, respectively, "a method selected from at least one of the separation method, recovery method, and concentration method" and "a method selected from at least one of the separation method, recovery method, and concentration method." However, in this invention, since the above functions are realized by the separation membrane, all of these functions are realized simultaneously. For example, if the target molecule is molecule A, and a supply mixed gas consisting of molecules A, B, C, and D is supplied to the separation membrane, and the most abundant molecule A permeates to the permeate side, then the proportion of molecule A in the permeate mixed gas will be high, and the proportion of molecule A in the non-permeate mixed gas will be low. This means that molecule A has been separated from the other molecules, and its high proportion on the permeate side is equivalent to concentration. Furthermore, from the perspective of using molecule A in the permeate mixed gas, it can be said that molecule A has been recovered. Also, for example, if the target molecule is molecule Z, and a supply mixed gas consisting of molecules X, Y, and Z is supplied to the separation membrane, and molecule Z is the least likely to permeate to the permeate side, and the most abundant molecule Z remains on the non-permeate side, then the proportion of molecule Z in the non-permeate mixed gas will be high, and the proportion of molecule Z in the permeate mixed gas will be low. This means that molecule Z has been separated from the other molecules, and its high proportion on the non-permeate side is equivalent to concentration. Furthermore, from the perspective of using molecule Z in the impermeable mixed gas, it can be said that molecule Z was recovered.

[0022] The present invention provides a method for separating, recovering, and concentrating a gas containing a target molecule from a supply mixed gas containing at least one small-diameter molecule having a dynamic molecular diameter smaller than 0.3 nm (hereinafter also simply referred to as "small-diameter molecule") and at least one large-diameter molecule having a dynamic molecular diameter of 0.3 nm or more (hereinafter also simply referred to as "large-diameter molecule"), using a separation membrane. The gist of this method is that at least one pair of small-diameter molecules and large-diameter molecules in the supply mixed gas and the separation membrane satisfy the following formula 1. Equation 1: 0.5≦α w (S / L) / α d (S / L) ≤ 1.2 Here, Equation 2: α w (S / L) ≡ P w (S) / P w (L) Equation 3: α d (S / L) ≡ P d (S) / P d (L) And further P w (S): One small molecular weight molecule contained in the supply mixed gas is the permeance that permeates the separation membrane. P w (L): One large molecular weight molecule contained in the supply mixed gas is the permeance that permeates the separation membrane. P d (S): When the separation conditions are the same except that the supply mixed gas is a dry gas, P w (S) The permeance through which the small molecular diameter molecules selected during derivation pass through the separation membrane is P d (L): When the separation conditions are the same except that the supply mixed gas is a dry gas, P w (L) This is the permeance through which the large molecular weight molecules selected during derivation pass through the separation membrane.

[0023] [Supply mixed gas] The supply mixed gas in the present invention, including cases where water vapor is present, is a supply mixed gas containing at least one small molecular diameter molecule having a dynamic molecular diameter smaller than 0.3 nm and at least one large molecular diameter molecule having a dynamic molecular diameter of 0.3 nm or more, and is not particularly limited as long as it is possible to suitably separate / recover / concentrate small molecular diameter molecules having a dynamic molecular diameter smaller than 0.3 nm by the method of the present invention. In the present invention, when separating / recovering / concentrating small molecular diameter molecules from a supply mixed gas containing at least one small molecular diameter molecule and at least one large molecular diameter molecule, any number of gases that satisfy the requirement of being large molecular diameter molecules can be selected. Furthermore, the supplied mixed gas may be a humid gas or a dry gas.

[0024] [Small molecular weight molecules with a dynamic molecular diameter smaller than 0.3 nm] Examples of small molecular weight molecules with a dynamic molecular diameter smaller than 0.3 nm contained in the supply gas mixture of the present invention include helium (0.26 nm), hydrogen (0.289 nm), and water (0.265 nm). Needless to say, the term "small molecular weight molecules" here also includes monatomic molecules. Furthermore, as mentioned above, the dynamic molecular diameter of water is small, and since water is a polar molecule, adsorption on the separation membrane surface proceeds easily. Therefore, even when compared to small molecular weight molecules with similar dynamic molecular diameters, such as helium and hydrogen, the permeance of water during separation through the membrane is known to be very large. Although it depends on the constituent materials of the separation membrane and the shape of the separation membrane module, the permeance of water is 1 × 10⁻⁶. -6 (mol / m 2 It is thought to be around ∠Pa.

[0025] [Large molecular weight molecules with a dynamic molecular diameter of 0.3 nm or more] The large molecular diameter molecules having a dynamic molecular diameter of 0.3 nm or more contained in the supply gas mixture of the present invention are not particularly limited as long as they have a dynamic molecular diameter of 0.3 nm or more. Examples of such large molecular diameter molecules include carbon dioxide (0.33 nm), argon (0.34 nm), oxygen (0.346 nm), nitrogen (0.364 nm) and air as a mixture thereof, as well as methane (0.38 nm). Needless to say, the large molecular diameter molecules referred to here also include monatomic molecules.

[0026] Here, for example, consider a case where hydrogen, a small molecular weight molecule, is the target molecule to be separated / recovered / concentrated, and the supply mixture gas, consisting of air (a mixture of carbon dioxide, argon, oxygen, and nitrogen) as a large molecular weight molecule, is supplied to the separation membrane along with water vapor. First, if the membrane area of ​​the separation membrane is excessive, the following considerations apply. Because the permeance of water vapor accompanying the supply gas mixture is high, most of the water vapor permeates through the membrane portion near the supply side, i.e., only a small portion of the total membrane surface area. Therefore, the strong influence of water vapor does not extend to the entire separation membrane, and the permeation performance P of the separation membrane as a whole is not affected. w (S) and transmission performance P w The effect of water vapor on (L) will be limited. However, there is a concern that, especially in the membrane portion far from the supply side, molecules such as carbon dioxide, argon, oxygen, and nitrogen will permeate in considerable quantities along with hydrogen due to the excessive membrane surface area. Therefore, in order to achieve a proper separation process, a separation performance α equivalent to a state where the influence of water vapor is very small (dry state) between hydrogen and each large molecular weight molecule is required. d (S / L) is set too high (separation performance α) d The (S / L) value needs to be excessively large. However, there are limits to achieving a membrane with high separation performance, making it difficult to achieve a proper separation process. Specifically, in such cases, while the hydrogen recovery rate may be high, there is concern about a decrease in the hydrogen concentration on the permeate side.

[0027] On the other hand, if the membrane area of ​​the separation membrane is insufficient, the following can be considered. Because the influence of water vapor accompanying the supply mixed gas strongly affects the entire separation membrane, hydrogen, which has a similar dynamic molecular size to water vapor, is strongly affected, and the permeation performance P w (S) will decrease significantly. Furthermore, molecules such as carbon dioxide, argon, oxygen, and nitrogen are also affected to some extent, and the permeability P w (L) will also decrease. In other words, separation performance α in a wet state w (S / L) decreases, making it impossible to achieve a proper separation process. In the case of such insufficient membrane area, the permeation performance P w A significant decrease in (S) raises the hydrogen concentration on the non-permeable side, resulting in a higher hydrogen concentration on the permeable side, but there are concerns that this will lead to a substantial decrease in the hydrogen recovery rate.

[0028] Furthermore, let's consider the case where the membrane surface area of ​​the separation membrane is appropriate. In this case, some water vapor permeates through the membrane surface area near the supply side of the separation membrane, and although the strong effect of water vapor does not extend to the entire separation membrane, it is thought that some effect of water vapor remains in the latter half of the separation membrane. Therefore, in order to achieve proper separation process performance, the separation performance α should be measured under conditions where the effect of water vapor is minimal (dry conditions). d (S / L) is also the separation performance α measured under conditions where the influence of water vapor is present to some extent (humid conditions). w The (S / L) ratio also needs to be within an appropriate range.

[0029] The above study outlines the effects of different membrane areas on a supply gas mixture consisting of hydrogen (a small molecular weight molecule) as the target molecule to be separated, recovered, and concentrated, and air (a mixture of carbon dioxide, argon, oxygen, and nitrogen) as a large molecular weight molecule, when supplied to the separation membrane accompanied by water vapor. This situation is also true when the small molecular weight molecules are helium or when the large molecular weight molecules are other than those mentioned above. Furthermore, in order to achieve proper separation in an actual separation process, in addition to the above, the separation process conditions such as the composition of the supply gas mixture containing the target molecule, the dew point of the gas mixture supplied to the separation membrane, the temperature of the supply gas mixture, the total supply flow rate, the supply pressure, and the permeate pressure of the separation membrane must be appropriate, as well as the separation performance α d (S / L) also has separation performance α w It is necessary to adapt a separation membrane with an appropriate (S / L) ratio to the separation process. According to the present invention, in a method for separating, recovering, and concentrating a gas containing a target molecule from a supply mixed gas containing at least one small-diameter molecule having a dynamic molecular diameter smaller than 0.3 nm and at least one large-diameter molecule having a dynamic molecular diameter of 0.3 nm or more, if the method satisfies the above formula 1, the mixed gas can be safely and efficiently separated, recovered, and concentrated.

[0030] The index α in the above formula 1 w (S / L) / α d (S / L) is an index that indicates whether the separation process conditions, such as the composition of the feed gas mixture containing the target molecule, the dew point of the feed gas mixture supplied to the separation membrane, the temperature of the feed gas mixture, the total flow rate of the feed gas mixture, the pressure of the feed gas mixture, and the permeate pressure of the separation membrane, are appropriate for the membrane performance of the separation membrane. When this index is within the appropriate range, the target molecule in the feed gas mixture will be recovered at a high rate and / or concentrated at a high concentration after processing by the separation membrane. For example, index α w (S / L) / α d When (S / L) is within the appropriate range, the target molecule in the supply mixed gas is recovered at a high rate in the permeate mixed gas, and / or the target molecule is concentrated at a high concentration in the permeate mixed gas, and / or the target molecule is concentrated at a low concentration in the non-permeate mixed gas.

[0031] Above indicator α w (S / L) / α dThe closer (S / L) is to 1, the smaller the influence of water vapor tends to be on the separation membrane as a whole. α w (S / L) / α d The lower limit of (S / L) is 0.50 or higher, preferably 0.60 or higher, more preferably 0.70 or higher, even more preferably 0.75 or higher, and most preferably 0.80 or higher. On the other hand, the upper limit is 1.20 or lower, preferably 1.15 or lower, more preferably 1.10 or lower, even more preferably 1.05 or lower, and most preferably 1.00 or lower. The above-mentioned lower and upper limits can be combined in any way; for example, 0.50 to 1.2 is preferred, 0.6 to 1.15 is also preferred, 0.70 to 1.10 is more preferred, 0.75 to 1.05 is even more preferred, and 0.80 to 1.00 is most preferred. w (S / L) / α d When (S / L) is within the above range, the recovery rate of the target small molecular weight molecules contained in the permeate mixed gas can be increased, as can their concentration, while the concentration of the target small molecular weight molecules contained in the non-permeate mixed gas can be decreased.

[0032] Furthermore, in the present invention, it is preferable that at least one pair of small-diameter molecules and large-diameter molecules in the supply mixed gas satisfy the above range, more preferably that two or more pairs of small-diameter molecules and large-diameter molecules satisfy the above range, and even more preferably that all combinations of small-diameter molecules and large-diameter molecules satisfy the above range. Furthermore, in this case, all combinations of small and large molecular diameter molecules are 0.80 ≤ α w (S / L) / α d It is most preferable that (S / L) ≤ 1.00 be satisfied. In such cases, it is possible to achieve a high level of recovery rate and concentration of the target small molecular weight molecules contained in the permeate mixed gas, while simultaneously lowering the concentration of the target small molecular weight molecules contained in the non-permeate mixed gas.

[0033] The separation performance α in the above formula 3 d(S / L) can be defined not only as "a state with very little influence from water vapor," but also as "a state with little influence from water vapor." Therefore, the α d P used in the calculation of (S / L) d (S) and P d In the present invention, the dry mixed gas (dry gas) in (L) is not particularly limited, but the dew point of the dry mixed gas is, for example, -20°C or lower. Separation performance α d Regarding the dew point for (S / L), if it is excessively high, for example, exceeding 60°C, it will not reflect the situation where the influence of water vapor is minimal, which is undesirable. For this reason, the upper limit of the dew point is preferably -20°C or lower, more preferably -30°C or lower, even more preferably -35°C or lower, and most preferably -40°C or lower. On the other hand, if the dew point is excessively low, it may be difficult to achieve and measure the film performance, which is undesirable. Therefore, the lower limit is more preferably -70°C or higher, even more preferably -65°C or higher, and most preferably -60°C or higher. The above-mentioned lower and upper limits of the dew point can be combined arbitrarily.

[0034] The method of the present invention is suitably applicable when the supply mixed gas contains water vapor; therefore, it is preferable that the supply mixed gas contains water vapor. In the present invention, the component ratios of each individual gas excluding the water vapor component in the mixed gas are described as totaling 100%, and it is assumed that water vapor corresponding to the dew point is superimposed thereon. The dew point of the supply mixed gas can be arbitrarily determined according to various process conditions, such as the composition of the supply mixed gas containing the target molecule, the temperature of the supply mixed gas, the total flow rate of the supply mixed gas, the pressure of the supply mixed gas, and the permeate side pressure of the separation membrane. It can also be arbitrarily determined according to the membrane area, membrane performance, etc. However, separating a supply mixed gas with an excessively high dew point requires a separation membrane with an excessively large membrane area, raising concerns about malfunctions and increased costs due to decreased separation efficiency. For this reason, the upper limit of the dew point of the supply mixed gas is preferably 50°C or lower, more preferably 30°C or lower, even more preferably 20°C or lower, and most preferably 10°C or lower. In terms of the separation process configuration, it is preferable to include a dehumidification function before the separation membrane as needed to lower the dew point. While there are no particular restrictions on the lower limit of the dew point of the supply mixed gas, for feasibility reasons, it is more preferable that the lower limit be -70°C or higher, even more preferable that be -65°C or higher, and most preferable that be -60°C or higher.

[0035] As mentioned above, separation performance α d Regarding (S / L), if the dew point of the supply mixed gas in a dry state (dry gas) is excessively high, it is undesirable because it does not reflect the situation where the influence of water vapor is small. For this reason, the upper limit of the dew point of the supply mixed gas in a dry state is preferably -20°C or lower, more preferably -30°C or lower, even more preferably -35°C or lower, and most preferably -40°C or lower. On the other hand, if the dew point is excessively low, it may be difficult to achieve and is undesirable, so the lower limit is more preferably -70°C or higher, even more preferably -65°C or higher, and most preferably -60°C or higher. It goes without saying that the dry gas referred to in this invention is a gas that contains water vapor commensurate with that dew point, even if it has the above dew point.

[0036] As mentioned above, index α w (S / L) / α d (S / L) is an index that indicates whether the separation process conditions, such as the composition of the feed gas mixture containing the target molecule, the dew point of the feed gas mixture supplied to the separation membrane, the temperature of the feed gas mixture, the total flow rate of the feed gas mixture, the supply pressure of the feed gas mixture, and the permeate pressure of the separation membrane, are appropriate for the membrane performance of the separation membrane. When this is within the appropriate range, the target molecule in the feed gas mixture will be recovered at a high rate after processing by the separation membrane, and / or the target molecule will be concentrated to a high concentration. For example, index α w (S / L) / α d When (S / L) is within the appropriate range, the target molecule in the supply mixed gas is recovered at a high rate in the permeate mixed gas, and / or the target molecule is concentrated at a high concentration in the permeate mixed gas, and / or the target molecule is concentrated at a low concentration in the non-permeate mixed gas.

[0037] In the present invention, the composition ratio of the supply mixed gas containing the target molecule is not particularly limited, as long as at least one set of small-diameter molecules, large-diameter molecules, and separation membrane in the supply mixed gas satisfy the following formula 1. Equation 1: 0.5≦α w (S / L) / α d (S / L) ≤ 1.2 However, generally speaking, it is preferable that the proportion of the target molecule in the supply gas mixture be high. For example, the proportion of the target molecule in the supply gas mixture is preferably 10% by volume or more, more preferably 20% by volume or more, even more preferably 30% by volume or more, and most preferably 40% by volume or more. In addition, since the method of the present invention is also applicable to the separation / recovery / concentration of trace amounts of helium, etc., in this case, the lower limit of the proportion of the target molecule in the supply gas mixture is preferably 0.1% by volume or more, more preferably 1% by volume or more, even more preferably 3% by volume or more, and most preferably 5% by volume or more. Furthermore, from the viewpoint of whether separation by a separation membrane is required, the upper limit of the proportion of the target molecule in the supplied mixed gas is preferably 99.9% by volume or less, more preferably 99% by volume or less, even more preferably 95% by volume or less, and most preferably 90% by volume or less. In this invention, the mixed gas containing the target molecule may be recovered mainly from the permeate side of the separation membrane or mainly from the non-permeable side. The former is preferred when the target molecule is a small molecular diameter molecule such as hydrogen or helium, while the latter is preferred when the target molecule is a large molecular diameter molecule with a dynamic molecular diameter of 0.3 nm or more, such as carbon dioxide, argon, oxygen, nitrogen, or methane. The lower and upper limits mentioned above can be combined in any way.

[0038] In the present invention, the temperature of the supply mixed gas, the temperature of the separation membrane, or the temperature of the separation membrane module are not particularly limited, as long as at least one set of small-diameter molecules and large-diameter molecules in the supply mixed gas and the separation membrane satisfy the above formula 1. However, separation performance α w (S / L) and separation performance α d Since (S / L) depends on the separation temperature, the supply mixed gas temperature, separation membrane temperature, or separation membrane module temperature will affect the separation performance α. w (S / L) and separation performance α dIt is preferable to adjust the (S / L) ratio to a suitable value. Furthermore, by doing so, it is possible to lower the relative humidity of the supply mixed gas when raising the supply mixed gas temperature, separation membrane temperature, or separation membrane module temperature by various heating methods, which is preferable. Moreover, in the case of a separation membrane in which a silica layer is formed on the surface of a zeolite membrane having a CHA-type skeletal structure, for example, a unique tendency is observed in the temperature dependence of the permeance performance of small and large molecular weight molecules, so it is preferable to raise the supply mixed gas temperature by various heating methods. This is because, for example, hydrogen, a small molecular weight molecule, has a positive activation energy for its permeance, and despite being a small molecular weight molecule, its value is larger than that of large molecular weight molecules such as carbon dioxide, argon, nitrogen, and methane, which is a unique characteristic. Therefore, by raising the temperature, both the permeance and separation performance α are affected. w (S / L) and separation performance α d This is because it can also improve the (S / L) ratio.

[0039] Specifically, a separation membrane having a silica layer formed on the surface of a zeolite membrane having the CHA-type skeletal structure described above (hereinafter also referred to as a "surface-modified CHA membrane") has a permeance P(S) (mol / (m³) for small molecules with a dynamic molecular diameter smaller than 0.3 nm and large molecules with a dynamic molecular diameter of 0.3 nm or more, which is derived within a temperature range Tam(°C) that satisfies the following formula 4 for small molecules with a dynamic molecular diameter smaller than 0.3 nm and large molecules with a dynamic molecular diameter of 0.3 nm or more. 2 The activation energy Ep(S)(kJ / mol) of the separation membrane is given by the same temperature range as the permeance P(L)(mol / (m) of large molecules in the separation membrane. 2 The activation energy Ep(L)(kJ / mol) of s·Pa satisfies the relationship shown in equation 5 below. Formula 4: 5(℃)≦Tam(℃)≦200(℃) Equation 5: |Ep(L)|<|Ep(S)| In other words, this separation membrane has the opposite characteristics of a typical separation membrane: within a specific temperature range, the absolute value of the activation energy of the permeance of small molecules is greater than the absolute value of the activation energy of the permeance of large molecules. A large absolute value of activation energy means a high degree of temperature dependence; that is, the gas permeance, i.e., the permeation characteristics of the target gas, changes significantly whether the temperature is raised or lowered. Here, we will explain using two typical cases as examples.

[0040] The first case is when diffusion is considered to be the dominant factor determining the gas permeance (gas permeability) of each gas to be separated. Normally, increasing the temperature improves the gas permeance of both small and large molecular weight molecules. However, large molecular weight molecules tend to have a relatively large temperature dependence, while small molecular weight molecules such as hydrogen tend to have a relatively small temperature dependence. Therefore, when the temperature is increased and small molecular weight molecules are recovered by permeating through the membrane, the gas permeability improves, but the gas separation performance decreases. Note that when the gas permeance improves with increasing temperature, the activation energy of the gas permeance will have a positive value. Therefore, 0 <Ep(S)<Ep(L)である。

[0041] The second case is when adsorption is considered to be the dominant factor determining the gas permeance (gas permeability) of each gas to be separated. Normally, lowering the temperature improves the gas permeance of both small and large molecular weight molecules. However, large molecular weight molecules tend to have a relatively large temperature dependence, while small molecular weight molecules like hydrogen tend to have a relatively small temperature dependence. Therefore, when lowering the temperature and recovering small molecular weight molecules by permeating through the membrane, the gas permeability improves, but the gas separation performance decreases. Furthermore, when lowering the temperature improves gas permeance, the activation energy of the gas permeance will have a negative value, so Ep(L) <Ep(S)<0である。

[0042] Combining the relationships between the first and second cases described above, we can write |Ep(S)|<|Ep(L)|. Furthermore, depending on the combination of gases to be separated, there may be cases where "adsorption is dominant" for one and "diffusion is dominant" for the other, but even in these cases, |Ep(S)|<|Ep(L)| is usually true. In contrast, the present invention uses a separation membrane with characteristics opposite to those of a typical separation membrane, namely, a large absolute value of the activation energy showing the temperature dependence of the permeance of small molecules such as hydrogen, and a small absolute value of the activation energy showing the temperature dependence of the permeance of large molecules. By changing the temperature, it is preferable to improve the permeation performance of small molecules such as hydrogen while also improving the separation performance. It is optional whether to improve both permeation performance and separation performance by raising the temperature, or by lowering the temperature, but in either case, it can be written as |Ep(L)|<|Ep(S)|.

[0043] Furthermore, it is preferable that the surface-modified CHA membrane, depending on the gas species selected, always has a permeance for small molecular weight molecules greater than the permeance for large molecular weight molecules. Having this property, the separation membrane can efficiently and safely separate small molecular weight molecules from the supplied gas mixture. In other words, it is preferable that the following formula 6 is satisfied. Equation 6: P(L) <P(S) Furthermore, the separation membrane of the present invention preferably satisfies the following formula 7 for small-molecule and large-molecule molecules. formula 7:0 <Ep(L)<Ep(S) Having such characteristics makes it possible to improve the permeance P(S) of small molecules while simultaneously improving the selectivity of hydrogen gas for large molecules α(S / L)=P(S) / P(L) by "heat separation," which involves heating the mixed gas to be separated, separation membrane, separation module or separation tower, hydrogen recovery system, etc., to an appropriate temperature, making it highly desirable. Note that P(S) is P w (S) is also the case, P d It could also be (S). Also, P(L) is Pw (L) is also P d It may also be (L). Similarly, α(S / L) is α w (S / L) d It could also be (S / L).

[0044] <Activation Energy> The above activation energy can be derived as follows. Within the range of 5°C to 200°C (Tam(°C) in Equation 4 above), an appropriate temperature range for deriving the activation energy of permeance can be set. Within this range, the permeance of each constituent gas in the supply mixed gas to be separated can be measured at multiple temperatures, and this can be derived by approximating it with the least squares formula using the Arrhenius equation. It is reasonable that the temperature range from which the activation energy is derived 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 is 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 lower, and high hydrogen permeance can be obtained by setting the temperature to 5°C or higher. Therefore, the lower limit of the temperature range from which the activation energy is derived is 5°C or higher, preferably 10°C or higher, while the upper limit of the temperature range from which the activation energy is derived is 200°C or lower, preferably 150°C or lower. Furthermore, a lower limit of 15°C or higher is more preferable, 20°C or higher is even more preferable, and 25°C or higher is particularly preferable. Similarly, for the upper limit, 140°C or lower is more preferable, 130°C or lower is even more preferable, and 120°C or lower is particularly preferable. The lower and upper limits mentioned above can be combined in any way.

[0045] The inventors measured the activation energies of the permeance of various small and large molecular weight molecules in a surface-modified CHA film prepared by the inventors at 30-100°C. They found that the activation energy of hydrogen permeance as a small molecular weight molecule was 7.0 kJ / mol, while the activation energies of nitrogen, carbon dioxide, argon, and methane permeance as large molecular weight molecules were -1.6-1.4 kJ / mol.

[0046] In separation membranes, the absolute value of the activation energy of the permeance of small molecular weight molecules is generally smaller (less temperature-dependent) compared to the absolute value of the activation energy of large molecular weight molecules. However, in the surface-modified CHA membrane described above, if the mixed gas is composed of hydrogen as a small molecular weight molecule and at least one gas selected from carbon dioxide, argon, oxygen, nitrogen, and methane as a large molecular weight molecule, it is expected that when separating and recovering hydrogen from the mixed gas, heating within an appropriate range will improve the hydrogen recovery rate while maintaining a high level of hydrogen concentration on the permeate side, and also reduce the hydrogen concentration on the non-permeate side.

[0047] From this perspective, the lower limit of the supply mixed gas temperature, separation membrane temperature, or separation membrane module temperature is preferably 10°C or higher, more preferably 30°C or higher, even more preferably 50°C or higher, and most preferably 70°C or higher. On the other hand, if the temperature of the supply mixed gas is excessively high, safety concerns may arise, such as in the case of a hydrogen-oxygen mixed gas. For this reason, the upper limit of the supply mixed gas temperature is preferably 200°C or lower, more preferably 170°C or lower, even more preferably 140°C or lower, and most preferably 110°C or lower. The lower and upper limits mentioned above can be combined in any way.

[0048] <Separation conditions> In the present invention, the total flow rate of the supply mixed gas containing the target molecule, the supply pressure of the supply mixed gas, and the permeate side pressure of the separation membrane are not particularly limited, as long as at least one set of small-diameter molecules and large-diameter molecules in the supply mixed gas and the separation membrane satisfy the above formula 1. In this invention, the total flow rate of the supplied mixed gas can be appropriately adjusted according to the membrane area of ​​the separation membrane being prepared.

[0049] On the other hand, the supply pressure of the supplied mixed gas and the permeate side pressure of the separation membrane can be appropriately selected depending on the types of gases constituting the supplied mixed gas, their characteristics, and composition. For example, if the supplied mixed gas is a mixture containing hydrogen and oxygen, and especially if its composition is hydrogen:oxygen = 2:1 (hydrogen explosive gas), then concerns about safety increase due to pressurizing the mixed gas, so a range from atmospheric pressure supply to a slightly pressurized supply considering piping pressure loss is preferable. Furthermore, in such cases, from the viewpoint of ensuring differential pressure in the separation membrane portion, it is preferable to reduce the pressure on the permeate side using a vacuum pump or the like.

[0050] Furthermore, if the supply mixed gas contains only a small amount of the target molecule, for example, if the mixed gas consists of about 3 volume% helium and about 97 volume% air, then because the amount of the target molecule is small, pressurizing the supply side will mostly contribute to increasing the pressure of gases other than the target molecule. For this reason, from the viewpoint of ensuring differential pressure in the separation membrane portion, it is efficient and preferable to reduce the pressure on the permeate side using a vacuum pump or the like.

[0051] On the other hand, when the supply gas mixture is a mixture of hydrogen and nitrogen, or when helium and air make up more than 50% by volume, it is preferable to pressurize the supply gas mixture from both a safety standpoint and a separation efficiency standpoint. In such cases, it is also preferable to set the permeate side to atmospheric pressure or slightly pressurized, as this makes it easier to ensure a sufficient separation differential pressure. However, excessive pressurization of the supply gas mixture can lead to problems such as the need to increase the strength of the piping that makes up the separation system.

[0052] Therefore, in the present invention, the lower limit value of the pressure of the supplied mixed gas is preferably atmospheric pressure, more preferably slightly pressurized at 15 kPa(G) (= 0.015 MPa(G)) or more considering the piping pressure loss, even more preferably 100 kPa(G) (= 0.1 MPa(G)) or more from the viewpoint of separation stability, and most preferably 300 kPa(G) (= 0.3 MPa(G)) or more from the viewpoint of separation efficiency. The upper limit value of the pressure of the supplied mixed gas is preferably set to a pressure less than 2 MPa(G) so as not to over-strengthen the piping of the separation system, more preferably a pressure less than 1 MPa(G) from the viewpoint of configuring the separation system in a so-called low-pressure region, even more preferably a pressure less than 0.8 MPa(G), and most preferably a pressure less than 0.6 MPa(G). The above lower limit value and upper limit value can be arbitrarily combined.

[0053] When the permeation side is depressurized with a vacuum pump or the like, the upper limit value of the permeation pressure of the separation membrane is preferably -50 kPa(G) (= -0.05 MPa(G)) or less, more preferably -70 kPa(G) (= -0.07 MPa(G)) or less, and most preferably -90 kPa(G) (= -0.09 MPa(G)) or less. By doing so, a sufficient differential pressure in the separation membrane part can be ensured. When the permeation side is depressurized with a vacuum pump or the like, the lower limit of the permeation pressure of the separation membrane is preferably -100 kPa(G) (= -0.1 MPa(G)) or more, more preferably -99 kPa(G) (= -0.099 MPa(G)) or more, even more preferably -98 kPa(G) (= -0.098 MPa(G)) or more, and most preferably -97 kPa(G) (= -0.097 MPa(G)) or more. This is to avoid the need for an excessive vacuum pump to achieve excessive depressurization because when the permeation side is depressurized, a vacuum pump or the like with a corresponding exhaust speed, airtightness, etc. is required to reduce the pressure.

[0054] Furthermore, the upper limit value of the permeation pressure of the separation membrane when the permeation side is not depressurized with a vacuum pump or the like is preferably 35 kPa(G) (= 0.035 MPa(G)) or less, more preferably 30 kPa(G) (= 0.030 MPa(G)) or less, even more preferably 25 kPa(G) (= 0.025 MPa(G)) or less, and most preferably 20 kPa(G) (= 0.020 MPa(G)) or less, from the viewpoint of ensuring the differential pressure across the separation membrane. Also, the lower limit value of the permeation pressure of the separation membrane when the permeation side is not depressurized with a vacuum pump or the like is preferably 5 kPa(G) (= 0.005 MPa(G)) or more, more preferably 8 kPa(G) (= 0.008 MPa(G)) or more, even more preferably 11 kPa(G) (= 0.011 MPa(G)) or more, and most preferably 14 kPa(G) (= 0.014 MPa(G)) or more, from the viewpoint of allowing the gas to flow against pipe pressure loss and the like. The above lower limit value and upper limit value can be arbitrarily combined.

[0055] The separation membrane applied to the present invention may be a separation membrane composed of an inorganic material, an organic material, a composite material (inorganic-organic composite material) of an inorganic material and an organic material, or a separation membrane composed of a metal-organic framework, and there is no restriction on its constituent material.

[0056] On the other hand, in the present invention, as the small molecule diameter molecules, it is preferable that either or both of hydrogen and helium are used. On the other hand, it is preferable that the large molecule diameter molecules may include any one or a combination of two or more of carbon dioxide, argon, oxygen, nitrogen, and methane, more preferably any one or a combination of two or more of carbon dioxide, argon, oxygen, and nitrogen, even more preferably any one or a combination of two of oxygen and nitrogen, and most preferably oxygen.

[0057] To properly separate these substances, it is preferable that the effective pore size of the separation membrane be larger than that of small molecules such as hydrogen and helium, and smaller than that of large molecules such as carbon dioxide, argon, oxygen, nitrogen, and methane. The effective pore size of such a membrane is thought to be about 0.3 nm, but in order to realize a separation membrane with such a narrow effective pore size uniformly, it is preferable that the separation membrane be made of inorganic materials, and it is even more preferable that the inorganic materials form a composite structure to improve its separation performance. In other words, it is preferable to make the original pore size uniform and even smaller (narrower) by combining the inorganic materials.

[0058] Specifically, it is more preferable that the inorganic composite material is formed by creating a zeolite film, silica film, carbon film, etc., in contact with an inorganic support material such as alumina or mullite, and further forming a thin layer of heterogeneous silica on the surface side of the film. The zeolite film is more preferably an 8-membered ring zeolite such as CHA type, AEI type, DDR type, LEV type, or AFX type, with a narrow pore diameter of about 0.4 nm, and most preferably has a CHA type or AEI type skeletal structure with a pore diameter of 0.38 nm. Of these two, the CHA type is more preferable because it allows for the formation of a homogeneous and high-density film. Therefore, in the present invention, it is best to use a separation membrane having the composite separation structure in which a silica layer is formed on the surface of a zeolite film having a CHA type skeletal structure. From this perspective, helium is more preferable as the small molecular size molecule. In a zeolite membrane having a CHA-type framework structure that does not normally have a composite separation structure (unmodified, with no silica layer formed on the surface), when comparing helium and hydrogen, the permeance of hydrogen, which has a relatively large dynamic molecular size, is greater than that of helium, which has a relatively small dynamic molecular size. This is thought to be due to the interaction between the quadrupole moment of hydrogen and the local polarity of the CHA-type zeolite. However, in the composite separation structure in which a silica layer is formed on the surface of the zeolite membrane having a CHA-type framework structure, this interaction is reduced, and the permeance of helium and hydrogen follows the order of their dynamic molecular sizes. That is, the permeance of helium, which has a relatively small dynamic molecular size, is greater than that of hydrogen, which has a relatively large dynamic molecular size. For this reason, in the present invention, helium is more preferable than hydrogen as the small molecular size molecule because it can achieve higher separation performance for large molecular size molecules.

[0059] [Composite separation structure] The composite separation structure only needs to have a base portion, a first separation portion arranged in contact with the base portion, and a second separation portion that is not in contact with the base portion but is in contact with the first separation portion, and its shape is not particularly limited. For example, it may be a sheet-like laminate in which the first separation portion and the second separation portion are stacked in this order on a sheet-like base portion. In the case of such a sheet-like laminate, the gas to be separated and concentrated (hereinafter sometimes referred to as "gas to be separated") is permeated from the second separation portion side, and in the process of permeating through the second separation portion and the first separation portion in order, a specific gas of the gas to be separated and concentrated is concentrated and permeated and separated. Alternatively, as shown in Figure 1, the structure may consist of a cylindrical base, a first separation section, and a second separation section stacked concentrically. Such a cylindrical structure is preferable because it allows for efficient concentration and separation of the target gas even in a small space.

[0060] The cylindrical composite separation structure shown in Figure 1 will be described in detail below. The composite separation structure 100 of the present invention comprises a base portion 101, a first separation portion 103 arranged in contact with the base portion, and a second separation portion 104 arranged not in contact with the base portion but in contact with the first separation portion. Preferably, the base portion 101 has a void portion 102 in the composite separation structure for recovering the target gas from the gas to be separated and concentrated. That is, the gas to be separated and concentrated is introduced from outside the second separation portion 104, concentration and separation occur as the gas permeates through the second separation portion and the first separation portion, and the target gas is recovered from the void portion 102. In the embodiment shown in Figure 1, the composite separation structure of the present invention has a base portion 101 at the center, a first separation portion 103 is arranged outside of the base portion 101 in contact with it, and a second separation portion 104 is arranged further outside of the first separation portion in contact with it. Here, the surface of the base portion 101 that is in contact with the first separation portion may be described as the "upper end," and the opposite side, i.e., the side with the void portion 102, may be described as the "lower end." Also, the end of the first separation portion 103 that is in contact with the second separation portion 104 may be described as the "upper end," and the end that is in contact with the base portion 101 may be described as the "lower end," and the end of the second separation portion 104 that is in contact with the first separation portion 103 may be described as the "lower end," and the opposite end may be described as the "upper end."

[0061] In addition, in the case of a cylindrical composite separation structure, it is also possible to form a first separation section inside the base section, and a second separation section further inside the first separation section. In this case as well, the surface of the base section that contacts the first separation section is defined as the "upper end," and the opposite side, i.e., the outer surface, is defined as the "lower end." Furthermore, the end of the first separation section that contacts the second separation section is defined as the "upper end," and the end that contacts the base section is defined as the "lower end." The end of the second separation section that contacts the first separation section is defined as the "lower end," and the opposite end, i.e., the side with the void, is defined as the "upper end." In this embodiment, the gas to be separated and concentrated is introduced from the inner surface side of the composite separation structure, i.e., from the central void, and concentration and separation occur as the gas permeates through the second separation section and the first separation section, and the target gas is extracted from the outer surface side.

[0062] The composite separation structure described above is characterized in that the second separation portion has an amorphous structure. More specifically, a single separation structure (consisting of a substrate portion and a first separation portion) made of a thin film body such as a polycrystalline zeolite by crystal growth, etc., is provided on a substrate portion such as a porous substrate, and the upper end of the single separation structure is treated with, for example, a gas derived from a Si compound and water vapor derived from water, etc., to form an amorphous layer (second separation portion) on the single separation structure. Here, by controlling factors related to manufacturing, such as the processing time conditions in manufacturing, a composite separation structure with desired permeation separation performance can be obtained.

[0063] The following describes a composite separation structure that is a feature of the present invention, having a base portion, a first separation portion arranged in contact with the base portion, and a second separation portion that is not in contact with the base portion but is in contact with the first separation portion. Figure 1 shows the structural relationship between the "first separation part," the "second separation part," and the "substrate part" in this specification. Furthermore, the composite of the "substrate part" and the "first separation part" is referred to as the "single separation structure."

[0064] <Base part> In the present invention, the base portion is not particularly limited as long as it can form a first separation portion at its upper end, but it is preferable that it is chemically stable for forming the first separation portion. Furthermore, it is preferable that it has mechanical strength in the separation process. From this viewpoint, examples include ceramics, ceramic sintered bodies, metals, metal sintered bodies, and various insulators, and it is preferable that it is an inorganic porous material. In particular, when the first separation portion is a zeolite having various structures, the substrate portion is preferably an inorganic porous material. The substrate portion may also be composed of multiple inorganic porous materials with different pore sizes. When the first separation portion 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, an inorganic porous substrate portion containing at least one of alumina, silica, or mullite is preferred. Using these inorganic porous substrate portions facilitates partial zeolization, resulting in a strong bond between the substrate portion and the zeolite, making it easier to form a dense film with high separation performance.

[0065] The shape of the inorganic porous substrate is not particularly limited as long as it can effectively separate the gas mixture (the gas to be separated). Specifically, examples include flat plates, tubular shapes, cylindrical shapes, honeycomb shapes with numerous cylindrical or prismatic pores, and monoliths. In the present invention, it is preferable to form a zeolite film on such an inorganic porous substrate, i.e., on the upper end of the substrate. The upper end of the inorganic porous substrate is defined as the surface that forms the first separation part as described above, and means the surface portion of the inorganic porous substrate where the zeolite crystallizes. Any surface of each shape may be used, and there may be multiple surfaces. For example, in the case of a cylindrical tube substrate, it may be the outer surface or the inner surface, and in some cases, it may be both the outer and inner surfaces. In this case, any of these surfaces is considered the upper end.

[0066] The average pore diameter at the upper end of the inorganic porous substrate is not particularly limited, but it is preferable that the pore diameter is controlled. The average pore diameter at the upper end of the inorganic porous substrate 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, and more preferably 5 μm or less. If the average pore diameter is 0.02 μm or more, sufficient permeability can be obtained, and if it is 20 μm or less, the strength of the substrate itself will be sufficient. In addition, the proportion of pores at the upper end of the inorganic porous substrate is appropriate, and a sufficiently dense zeolite individual separation structure is formed. It is also possible to change the average pore diameter of the substrate from the lower end to the upper end according to the purpose. In particular, at the upper end of the substrate where the first separation section is planned to be formed, it is preferable to make the average pore diameter smaller than that of other parts of the substrate in order to obtain a dense zeolite individual separation structure.

[0067] The average thickness (wall thickness) of the inorganic porous substrate 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 substrate is used to provide mechanical strength to the individual separation structure. When the average thickness of the inorganic porous substrate is 0.1 mm or more, the individual separation structure has sufficient strength and becomes resistant to impacts and vibrations. Furthermore, when the average thickness of the inorganic porous substrate is 7 mm or less, the diffusion of the permeated substance is good, and sufficient permeability is obtained.

[0068] The porosity of the inorganic porous substrate is typically 20% or more, preferably 25% or more, more preferably 30% or more, and typically 70% or less, preferably 60% or less, and more preferably 50% or less. The porosity of the inorganic porous substrate affects the permeate flow rate when separating gases; if it is 20% or more, sufficient diffusion of the permeate can be obtained. On the other hand, if it is 70% or less, sufficient strength can be obtained for the inorganic porous substrate. Furthermore, the upper end of the inorganic porous substrate may be polished with a file or the like as needed. By polishing with a file or the like, for example, if there are burrs on the surface, the surface can be smoothed, and conversely, by roughening a smooth surface, subsequent processes such as crystal support and crystal growth can be made more efficient.

[0069] <Separated structure> The individual separation structure 106 in the present invention consists of a substrate portion 101 and a first separation portion 103 (see Figure 1). The components of the first separation portion are not particularly limited, and for example, an inorganic porous thin layer made of ceramics, a silica film, etc. can be used, but it is preferable to use a zeolite polycrystalline thin film for the individual separation layer (first separation portion). It is preferable to obtain a zeolite individual separation structure by forming a zeolite polycrystalline thin film on the inorganic porous substrate portion by crystal growth. In addition to zeolite, the components constituting the zeolite individual separation structure may include, as necessary, inorganic binders such as silica and alumina, and organic compounds such as polymers. Furthermore, the zeolite individual separation structure before upper end treatment in the present invention may contain some amorphous components, but a zeolite individual separation structure composed substantially only of zeolite is preferred.

[0070] The thickness of the first separation layer 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 is usually in the range of 100 μm or less, preferably 60 μm or less, and more preferably 20 μm or less. If the film thickness is 100 μm or less, a sufficient amount of permeation can be obtained, and if it is 0.1 μm or more, good selectivity of the permeated gas and sufficient film strength can be obtained. The particle size of the zeolite is not particularly limited, but it is usually preferably 30 nm or more, more preferably 50 nm or more, still more preferably 100 nm or more, and the upper limit is not more than the thickness of the membrane. When the particle size of the zeolite is 30 nm or more, the grain boundaries do not become large, and sufficient permeation selectivity can be obtained. Therefore, the case where the particle size of the zeolite is the same as the thickness of the membrane is particularly preferable. When the particle size of the zeolite is the same as the thickness of the membrane, the grain boundaries of the zeolite are minimized. The zeolite single separation structure obtained by hydrothermal synthesis described later is particularly preferable because the particle size of the zeolite and the thickness of the membrane tend to be the same.

[0071] The shape of the zeolite single separation structure is not particularly limited, and any shape such as tubular, hollow fiber, monolith, honeycomb, etc. can be adopted. Also, the size is not particularly limited. For example, in the case of a tube, a length of usually 2 cm or more and 200 cm or less, an inner diameter of 0.05 cm or more and 2 cm or less, and a thickness of 0.5 mm or more and 4 mm or less are practical and preferable. One of the separation functions of the zeolite single separation structure is separation as a molecular sieve, and gas molecules having a size larger than the effective pore diameter of the zeolite used and gases smaller than that can be preferably separated. Although there is no upper limit to the molecules to be separated, the size of the molecules is usually about 10 nm or less.

[0072] The type of the main zeolite constituting the zeolite single separation structure is not particularly limited. All zeolite structure types defined by the International Zeolite Association are included. More preferably, it is a zeolite having a pore structure with an oxygen 12-membered ring or less, still more preferably a zeolite having a pore structure with an oxygen 8-membered ring or less, and it may be a zeolite having a pore structure with an oxygen 6-membered ring. The smaller the pore with an oxygen member ring, the higher the effect of pore narrowing by the modification reaction and the easier the occurrence of the molecular sieve effect. In the present invention, it is particularly preferably a zeolite having an oxygen 6-membered ring or oxygen 8-membered ring structure.

[0073] In this context, the value of n in zeolites having an n-membered oxygen ring indicates the largest number of oxygen atoms in the pores composed of oxygen and T elements (elements other than oxygen that make up the zeolite framework). For example, if pores with both 12-membered and 8-membered oxygen rings exist, as in MOR-type zeolites, it is considered a zeolite with a 12-membered oxygen ring.

[0074] Examples of zeolites having a pore structure of 8 or fewer oxygen rings 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.

[0075] Examples of zeolites having an oxygen 6-8 membered 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, and UFI. In this specification, the structure of zeolite is indicated by the code for defining zeolite structure as defined by the International Zeolite Association (IZA), as described above.

[0076] The oxygen n-membered ring structure determines the pore size of the zeolite. Zeolites with an oxygen n-membered ring structure smaller than six members have pores smaller than the kinetic diameter of the H2O molecule, resulting in low permeability and potentially making them impractical. Conversely, zeolites with an oxygen n-membered ring structure larger than eight members have larger pores, which can reduce separation performance for small gaseous components, limiting their applications.

[0077] The framework density (T / 1000Å) of the zeolite is not particularly limited, but is usually 17 or less, preferably 16 or less, more preferably 15.5 or less, and most preferably 15 or less, and is usually 10 or more, preferably 11 or more, and more preferably 12 or more. Framework density refers to the number of elements other than oxygen (T elements) that make up the framework of a zeolite per 1000 Å, and this value is determined by the structure of the zeolite. The relationship between framework density and zeolite structure is shown in ATLAS OF ZEOLITEFRAMEWORK TYPES Fifth Revised Edition 2001 ELSEVIER.

[0078] 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, AEI, and LEV; and the most preferred structure is CHA.

[0079] In this invention, CHA-type zeolite refers to a zeolite with a CHA structure, as defined by the International Zeolite Association (IZA) in its structural code. This zeolite has a crystal structure equivalent to that of naturally occurring chabasite. CHA-type zeolite is characterized by a three-dimensional pore consisting of an 8-membered oxygen ring with a diameter of 3.8 × 3.8 Å, and this structure is characterized by X-ray diffraction data.

[0080] The framework density (T / 1000Å) of CHA-type zeolite is 14.5. In the present invention, when the zeolite separation structure includes CHA-type zeolite, it is preferable that the intensity of the peak around 2θ = 17.9° in the X-ray diffraction pattern is 0.5 or greater than the intensity of the peak around 2θ = 20.8°.

[0081] Here, 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 higher, preferably 1 or higher, more preferably 1.2 or higher, and particularly preferably 1.5 or higher. There is no particular upper limit, but it is usually 1000 or lower.

[0082] Furthermore, in the case of a zeolite-only separation structure containing CHA-type zeolite, it is preferable that the intensity of the peak around 2θ = 9.6° in the X-ray diffraction pattern is at least twice as large as the intensity of the peak around 2θ = 20.8°. 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°), is usually 2 or higher, preferably 2.5 or higher, more preferably 3 or higher, more preferably 4 or higher, even more preferably 6 or higher, particularly preferably 8 or higher, and most preferably 10 or higher. There is no particular upper limit, but it is usually 1000 or lower.

[0083] The X-ray diffraction pattern referred to here is obtained by irradiating the surface on which the zeolite is mainly attached with X-rays from a CuKα source, with the scanning axis set to θ / 2θ. There are no particular restrictions on the shape of the sample to be measured, as long as it is a shape that allows X-rays to be irradiated onto the surface on which the zeolite individual separation structure is mainly attached. It is preferable to use the fabricated individual separation structure as is, or to cut it to an appropriate size that is constrained by the equipment, as it best represents the characteristics of the individual separation structure.

[0084] Here, the X-ray diffraction pattern may be measured by fixing the irradiation width using an automatic variable slit if the upper end of the zeolite isolation structure is curved. The X-ray diffraction pattern when using an automatic variable slit refers to the pattern after correcting from variable to fixed slit. Here, the peak around 2θ = 17.9° refers to the largest peak among those not originating from the substrate that are within the range of 17.9° ± 0.6°.

[0085] The peak around 2θ = 20.8° refers to the largest peak that does not originate from the substrate and is located within the range of 20.8° ± 0.6°. The peak around 2θ = 9.6° refers to the largest peak among those not originating from the substrate that are within the range of 9.6° ± 0.6°. According to the Collection of Simulated X-ray POWDER Patterns for Zeolite Third Revised Edition 1996 Elsevier (Non-Patent Literature 4), the peak around 2θ = 9.6° in the X-ray diffraction pattern corresponds to the space group in the rhomboheadral setting.

[0086]

number

[0087] When (No. 166) is used, the peak in the CHA structure originates from the (1,0,0) plane. Furthermore, according to Non-Patent Document 4, the peak around 2θ = 17.9° in the X-ray diffraction pattern indicates that the space group is determined by the rhomboheadral setting.

[0088]

number

[0089] When (No. 166) is used, the peak in the CHA structure originates from the (1,1,1) plane. According to Non-Patent Document 4, the peak around 2θ = 20.8° in the X-ray diffraction pattern corresponds to the space group in rhomboheadral setting.

[0090]

number

[0091] When (No. 166) is used, the peak in the CHA structure originates from the plane of (2, 0, -1) where the exponent is located. According to Halil Kalipcilar et al., "Synthesis and Separation Performance of SSZ-13 Zeolite Membranes on Tubular Supports", Chem. Mater. 2002, 14, 3458-3464 (Non-Patent Literature 3), the typical ratio (peak intensity ratio B) of the peak intensity originating from the (1,0,0) plane to the peak intensity originating from the (2,0,-1) plane in the isolated structure of CHA-type aluminosilicate zeolites is less than 2.

[0092] Therefore, a ratio of 2 or greater suggests that, for example, the zeolite crystals are growing oriented such that the (1,0,0) plane, when the CHA structure is set in a rhomboheadral setting, is nearly parallel to the upper end of the single-element separation structure. In a single-element separation structure, the oriented growth of zeolite crystals is advantageous in that it results in a dense film with high separation performance.

[0093] According to Non-Patent Document 4, the typical ratio (peak intensity ratio A) of the peak intensity originating from the (1,1,1) plane to the peak intensity originating from the (2,0,-1) plane in the isolated structure of CHA-type aluminosilicate zeolites is less than 0.5. Therefore, a ratio of 0.5 or higher suggests that, for example, the zeolite crystals are growing oriented such that the (1,1,1) plane, when the CHA structure is set to rhomboheadral orientation, is nearly parallel to the upper end of the single-element separation structure. In a single-element zeolite separation structure, the oriented growth of zeolite crystals is advantageous in that it results in a dense film with high separation performance.

[0094] Thus, the fact that either peak intensity ratio A or B falls within the specific range described above indicates that the zeolite crystals have grown in an oriented manner, forming a dense film with high separation performance. The peak intensity ratios A and B indicate that a higher value indicates a stronger degree of orientation, and generally, a stronger degree of orientation indicates the formation of a denser film. Generally, a stronger orientation tends to result in higher separation performance, but the optimal degree of orientation for high separation performance varies depending on the mixture (gas) to be separated. Therefore, it is desirable to select and use a zeolite separation structure with the optimal degree of orientation for the mixture to be separated.

[0095] <Manufacturing method for a single-unit separation structure> The method for manufacturing the individual separation structure is not particularly limited, as long as it can form the first separation portion on the substrate. Below, the method for manufacturing the individual separation structure will be described in detail, using the case where the first separation portion is zeolite as an example. In the present invention, the method for producing the zeolite-only separated structure is not particularly limited, but a preferred method is to form the zeolite on an inorganic porous substrate by hydrothermal synthesis. Specifically, for example, a zeolite-only separation structure can be prepared by adjusting the composition of a reaction mixture for hydrothermal synthesis (hereinafter sometimes referred to as "aqueous reaction mixture") to make it homogenized, placing it in a heat-resistant and pressure-resistant container such as an autoclave, in which an inorganic porous substrate is loosely fixed inside, sealing it, and heating it for a certain period of time.

[0096] The aqueous reaction mixture includes a Si element source, an Al element source, an alkali source, and water, and may further include an organic template as needed. Examples of Si element sources that can be used in aqueous reaction mixtures include amorphous silica, colloidal silica, silica gel, sodium silicate, amorphous aluminosilicate gel, tetraethoxysilane (TEOS), and trimethylethoxysilane.

[0097] As the Al element source, for example, sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum oxide, amorphous aluminosilicate gel, etc. may be used. In addition to the Al element source, other element sources such as Ga, Fe, B, Ti, Zr, Sn, Zn, etc. may also be included. In the crystallization of zeolites, organic templates (structure-controlling agents) can be used as needed, and those synthesized using organic templates are preferred. By synthesizing using organic templates, the ratio of silicon atoms to aluminum atoms in the crystallized zeolite increases, improving its acid resistance and water vapor resistance.

[0098] Any type of organic template is acceptable, as long as it can form the desired zeolite individual isolation structure. Furthermore, one type of template or a combination of two or more types may be used. When the zeolite is of the CHA type, amines and quaternary ammonium salts are typically used as organic templates. For example, the organic templates described in U.S. Patent No. 4,544,538 and U.S. Patent Publication No. 2008 / 0075656 are preferred.

[0099] Specifically, for example, cations derived from alicyclic amines such as cations derived from 1-adamantanamine, cations derived from 3- quinacridinyl, cations derived from 3-exo-aminonorbornene, etc. can be mentioned. Among these, cations derived from 1-adamantanamine are more preferable. When a cation derived from 1-adamantanamine is used as an organic template, a CHA-type zeolite capable of forming a dense film crystallizes. By forming a dense film, a CHA-type zeolite with high separation performance can be obtained.

[0100] Among the cations derived from 1-adamantanamine, N,N,N-trialkyl-1-adamantanium ammonium cations are more preferable. The three alkyl groups of the N,N,N-trialkyl-1-adamantanium ammonium cation are usually each an independent alkyl group, preferably a lower alkyl group, more preferably a methyl group. The most preferable compound among them is N,N,N-trimethyl-1-adamantanium ammonium cation.

[0101] Such cations are accompanied by anions that do not harm the formation of CHA-type zeolite. Representative examples of such anions include Cl - , Br - , I - and other halogen ions such as hydroxide ions, sulfate radicals, and carboxylate radicals such as acetate radicals. Among these, hydroxide ions are particularly preferably used. As other organic templates, N,N,N-trialkylbenzylammonium cations can also be used. In this case as well, the alkyl groups are each an independent alkyl group, preferably a lower alkyl group, more preferably a methyl group. The most preferable compound among them is N,N,N-trimethylbenzylammonium cation. Also, the anions accompanying this cation are the same as those described above.

[0102] As alkali sources used in aqueous reaction mixtures, hydroxide ions from the counteranions of organic templates, alkali metal hydroxides such as NaOH and KOH, and alkaline earth metal hydroxides such as Ca(OH)2 can be used. The type of alkali is not particularly limited, and typically Na, K, Li, Rb, Cs, Ca, Mg, Sr, and Ba are used. Among these, Li, Na, and K are preferred, with K being more preferred. Furthermore, two or more alkalis may be used in combination, and specifically, it is preferable to use Na and K, or Li and K in combination.

[0103] The ratio of Si element source to Al element source in aqueous reaction mixture is usually expressed as the molar ratio of the oxides of each element, i.e., the SiO2 / Al2O3 molar ratio. The SiO2 / Al2O3 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. Also, it is usually 10,000 or less, preferably 1,000 or less, more preferably 300 or less, and even more preferably 100 or less.

[0104] When the SiO2 / Al2O3 molar ratio is within this range, a dense zeolite separation structure is formed, resulting in a membrane with high separation performance. Furthermore, because an appropriate amount of Al atoms are present in the formed zeolite, the separation performance is improved for gaseous components that exhibit adsorption to Al. Also, when Al is within this range, a zeolite separation structure with high acid and water vapor resistance can be obtained. The ratio of silica source to organic template in the aqueous reaction mixture is typically 0.005 or higher, preferably 0.01 or higher, more preferably 0.02 or higher, and typically 1 or lower, preferably 0.4 or lower, more preferably 0.2 or lower, in terms of the molar ratio of organic template to SiO2 (organic template / SiO2 (molar ratio)).

[0105] When the organic template / SiO2 (molar ratio) is within the above range, a dense zeolite elemental separation structure can be formed, and the resulting zeolite becomes highly resistant to acids and water vapor. The ratio of Si element source to alkali source is M (2 / n)The molar ratio of O / SiO2 (where M represents an alkali metal or alkaline earth metal, and n represents its valency 1 or 2) is usually 0.02 or higher, preferably 0.04 or higher, more preferably 0.05 or higher, and usually 0.5 or lower, preferably 0.4 or lower, more preferably 0.3 or lower.

[0106] When forming a CHA-type zeolite individual separation structure, it is preferable to include potassium (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 containing K is usually 0.01 to 1, preferably 0.1 to 1, and more preferably 0.3 to 1. The addition of K to the aqueous reaction mixture, as described above, involves the space group in rhomboheadral setting.

[0107]

number

[0108] When (No. 166) is assumed, the ratio of the peak intensity around 2θ = 9.6°, which originates from the (1,0,0) plane, to the peak intensity around 2θ = 20.8°, which originates from the (2,0,-1) plane (peak intensity ratio B), or the ratio of the peak intensity around 2θ = 17.9°, which originates from the (1,1,1) plane, to the peak intensity around 2θ = 20.8°, which originates from the (2,0,-1) plane (peak intensity ratio A), tends to be increased.

[0109] The ratio of Si element source to water is, in terms of the molar ratio of water to SiO2 (H2O / SiO2 (molar ratio)), 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 element separation structure can be formed. The amount of water is particularly important in the formation of a dense zeolite element separation structure, and denser films tend to form when the water-to-silica ratio is higher than the general conditions for powder synthesis.

[0110] Generally, the amount of water used when synthesizing powdered CHA-type zeolite is around 15-50 in terms of H2O / SiO2 (molar ratio). By using a high H2O / SiO2 (molar ratio) (between 50 and 1000), i.e., a condition with a large amount of water, it is possible to obtain a zeolite-only separation structure with high separation performance in which CHA-type zeolite crystallizes into a dense film on an inorganic porous substrate. Furthermore, while it is not always necessary to have seed crystals in the reaction system during hydrothermal synthesis, adding seed crystals can promote the crystallization of zeolite on the inorganic porous substrate. The method of adding seed crystals is not particularly limited; methods such as adding seed crystals to the aqueous reaction mixture, as in the synthesis of powdered zeolite, or attaching seed crystals to the inorganic porous substrate can be used.

[0111] When manufacturing a zeolite-only separation structure, it is preferable to attach seed crystals to the inorganic porous substrate. By attaching seed crystals to the inorganic porous substrate in advance, it becomes easier to produce a dense zeolite-only separation structure with good separation performance. Any type of zeolite that promotes crystallization can be used as the seed crystal, but to efficiently crystallize it, it is preferable that the seed crystal be the same crystal type as the zeolite elemental separation structure to be formed. When forming a CHA-type zeolite elemental separation structure, it is preferable to use a seed crystal of CHA-type zeolite.

[0112] The particle size of the seed crystal is usually 0.5 nm or larger, preferably 1 nm or larger, more preferably 2 nm or larger, and usually 20 μm or smaller, preferably 15 μm or smaller, more preferably 10 μm or smaller. The method for attaching seed crystals to the inorganic porous substrate is not particularly limited. For example, a dipping method can be used, in which seed crystals are dispersed in a solvent such as water and the substrate is immersed in the dispersion to attach the seed crystals. Alternatively, a method can be used in which seed crystals are mixed with a solvent such as water to form a slurry, which is then applied to the inorganic porous substrate. The dipping method is preferable for controlling the amount of seed crystals attached and for producing zeolite individual separation structures with good reproducibility.

[0113] The solvent used to disperse the seed crystals is not particularly limited, but water is particularly preferred. The amount of seed crystals dispersed is also 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, relative to the total mass of the dispersion.

[0114] If the amount of dispersed seed crystals is above the lower limit, the amount of seed crystals adhering to the inorganic porous substrate is sufficient, so they are generated evenly on the substrate during hydrothermal synthesis, and there are no areas where zeolite is not generated, resulting in a defect-free film. With the dip method, the amount of seed crystals adhering to the inorganic porous substrate becomes almost constant once the amount of seed crystals in the dispersion is above a certain level, so if the amount of seed crystals in the dispersion is below the upper limit, there is no waste of seed crystals, which is advantageous in terms of cost.

[0115] It is desirable to attach seed crystals to the inorganic porous substrate by dipping or by applying a slurry, and then form a zeolite-only isolated structure after drying. The amount of seed crystals to be pre-attached to the inorganic porous substrate is not particularly limited, and the substrate is 1 m 2 The mass per unit is usually 0.01g or more, preferably 0.05g or more, more preferably 0.1g or more, and usually 100g or less, preferably 50g or less, more preferably 10g or less, and even more preferably 8g or less.

[0116] When the amount of seed crystals is above the lower limit, crystals are more easily formed, films grow sufficiently, and film growth tends to be more uniform. Conversely, when the amount of seed crystals is below the upper limit, surface irregularities are not amplified by the seed crystals, spontaneous nuclei do not grow more easily due to seed crystals falling from the substrate, and film growth on the substrate is not inhibited. Therefore, dense zeolite individual separation structures are more easily formed.

[0117] When forming a zeolite-only separation structure on an inorganic porous substrate by hydrothermal synthesis, there are no particular restrictions on the method of immobilizing the inorganic porous substrate; it can take any form, such as vertical or horizontal orientation. In this case, the zeolite-only separation structure may be formed by static standing, or the aqueous reaction mixture may be stirred to form the zeolite-only separation structure. The temperature for forming the zeolite individual separation structure is not particularly limited, but is usually 100°C or higher, preferably 120°C or higher, 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 more likely to crystallize, and if it is below the upper limit, the reaction temperature is too high, preventing the formation of a type of zeolite different from the desired zeolite.

[0118] The heating time is not particularly limited, but is usually 1 hour or more, preferably 5 hours or more, 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 above the lower limit, the zeolite will crystallize sufficiently. On the other hand, if it is below the upper limit, a type of zeolite different from the desired zeolite will not be produced.

[0119] The pressure required for the separation and formation of zeolite structures is not particularly limited; the self-sustaining pressure generated when the aqueous reaction mixture in a sealed container is heated to this temperature range is sufficient. Furthermore, an inert gas such as nitrogen may be added if necessary. The zeolite elemental separation structures obtained by hydrothermal synthesis are washed with water and then heat-treated. Here, heat treatment means drying the zeolite elemental separation structures by applying heat, or, if a template is used, removing the template by calcination.

[0120] The heat treatment temperature is typically 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, and typically 200°C or lower, preferably 150°C or lower, when the purpose is drying. When the purpose is to burn off the template, the temperature is typically 350°C or higher, preferably 400°C or higher, more preferably 430°C or higher, even more preferably 480°C or higher, and typically 900°C or lower, preferably 850°C or lower, even more preferably 800°C or lower, and even more preferably 750°C or lower.

[0121] When the purpose is to remove the template by calcination, if the heat treatment temperature is above the lower limit, the organic template can be sufficiently calcined and removed, leaving no residue. This results in sufficient pore size in the zeolite, ensuring adequate permeation flux during separation and concentration. On the other hand, if the heat treatment temperature is below the upper limit, the difference in thermal expansion coefficients between the substrate and the zeolite does not become large, and cracks do not occur in the zeolite separation structure. Therefore, sufficient density of the zeolite separation structure can be ensured, and sufficient separation performance can be obtained.

[0122] The heating time is not particularly limited as long as it is sufficient time for the zeolite individual structure to dry completely or for the template to be removed by calcination, but is preferably 0.5 hours or more, more preferably 1 hour or more. There is no particular upper limit, but is usually within 200 hours, preferably within 150 hours, and more preferably within 100 hours. When the purpose is to remove the template by calcination, the heat treatment may be carried out in an air atmosphere, but it may also be carried out in an atmosphere with an inert gas such as N2 or oxygen added.

[0123] When hydrothermal synthesis is performed in the presence of an organic template, it is appropriate to remove the organic template from the resulting zeolite elemental structure by washing it with water, and then, for example, by heat treatment or extraction, preferably by heat treatment, i.e., calcination. When performing heat treatment for the purpose of firing and removing the template, the heating rate should preferably be as slow as possible in order to reduce the occurrence of cracks in the zeolite single-separation structure due to the difference in the thermal expansion coefficients between the substrate part and the zeolite. The heating rate 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. Usually, it is 0.1 °C / min or more in consideration of workability.

[0124] In addition, the cooling rate after firing also needs to be controlled to avoid the occurrence of cracks in the zeolite single-separation structure. Similar to the heating rate, the slower the better. The cooling rate 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. Usually, it is 0.1 °C / min or more in consideration of workability. The zeolite single-separation structure may be ion-exchanged as necessary. When synthesized using a template, ion exchange is usually performed after removing the template. Examples of the ions for ion exchange include protons, alkali metal ions such as Na + 、K + 、Li + ; alkaline earth metal ions such as Ca 2+ 、Mg 2+ 、Sr 2+ 、Ba 2+ ; and ions of transition metals such as Fe, Cu, Zn. Among these, protons and alkali metal ions such as Na + 、K + 、Li + are preferred.

[0125] Ion exchange can be carried out by treating the zeolite single-separation structure after firing (such as when using a template) with an aqueous solution containing an ammonium salt such as NH4NO3 or NaNO3 or the ions to be exchanged, or in some cases, an acid such as hydrochloric acid, usually at a temperature from room temperature to 100 °C, followed by washing with water. Furthermore, firing may be performed at 200 °C to 500 °C as necessary. The air permeability [L / (m2 ·h) is typically 1400L / (m 2 • h) less than or equal to preferably 1000 L / (m 2 h) or less, more preferably 700 L / (m 2 h) less than or equal to 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 • h) or less. The lower limit of the transmission rate 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) is above.

[0126] <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 separation performance than the gas separation performance of the first separation section. For example, in order to exhibit high separation performance, it is preferable to use a material with a smaller pore diameter or a higher density than the first separation section (layer). Specifically, it is preferable that the main constituent elements are Si and O, and silica is particularly preferable.

[0127] As described above, by forming an amorphous layer with smaller pores on the upper end of a single-component separation structure (for example, a single-component zeolite separation structure), separation performance that cannot be achieved by the zeolite pore size alone is obtained. Furthermore, it is preferable that the density of the amorphous layer in the composite separation structure is 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 the relative density, if the relative density is too low, the separation performance of the amorphous layer may become indistinguishable from that of the zeolite, and practical separation performance cannot be obtained. On the other hand, if the relative density is too high, the porosity of the amorphous layer becomes excessively low, the pores become excessively narrowed, the permeability resistance increases, and the permeance of the expected permeable components decreases. Known amorphous silica (density = 2.2 g / cm³) 3Assuming a separation structure of CHA-type zeolite alone, the relative density is 1.46. On the other hand, considering the low permeability performance 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.

[0128] The second separation section preferably contains Si atoms, and in particular, the Si atoms are preferably supplied in the gas phase. The gas phase is advantageous because it allows for a more reactive supply of Si to the upper end of the first separation section, making it easier to achieve the desired separation performance. There are no particular limitations on the method of supplying in the gas phase; for example, a liquid Si compound such as a silicate oligomer can be supplied using a bubbler or the like. It is also possible to supply it in mist form.

[0129] In the composite separation structure described above, it is preferable that the thickness of the second separation portion from the end (lower end) in contact with the first separation portion to the opposite end (upper end) (thickness of the second separation portion) is 5 nm or more and 200 nm or less.

[0130] The second separation portion is preferably in the form of a film, and the lower limit of its film thickness is 5 nm or more, preferably 7 nm or more, more preferably 10 nm or more, and most preferably 12 nm or more. On the other hand, the second separation portion needs to be thinner than a certain thickness so that the gas permeation resistance does not become excessive, and the upper limit of its film thickness is 200 nm or less, preferably 100 nm or less, more preferably 50 nm or less, and most preferably 25 nm or less.

[0131] Furthermore, if the first separation portion is a porous ceramic or zeolite, it is preferable that the second separation portion has a different type of structure with adjustable thickness and high density. For example, an amorphous structure is preferable. Also, it is preferable that the second separation portion is a different type of material with high density, such as silica. Therefore, an amorphous silica having the above-mentioned film thickness is a more preferable embodiment. As described above, the second separation portion is most preferably a silica film with a thickness of 5 nm or more and 200 nm or less.

[0132] The absolute density of the second separation region is 1.58 g / cm³. 3 More than 1.96g / cm 3 Preferably, the absolute density of the second separation portion is 1.58 g / cm³. 3 The above conditions are advantageous in terms of the density and fineness required to achieve separation performance. On the other hand, the absolute density of the second separation section is 1.96 g / cm³. 3 The following conditions are advantageous in that the permeation resistance of the permeate gas is low, which narrows the pores and allows for improved separation performance. From this perspective, the absolute density of the second separation section should be 1.67 g / cm³. 3 More than 1.72g / cm 3 The following is more preferable:

[0133] The relative density of the second separation section relative 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 can be obtained as described above. On the other hand, when the relative density is 1.30 or less, the pores do not narrow and the permeation resistance is maintained. From the above viewpoint, it is even more preferable that the relative density of the second separation section with respect to the first separation section be 1.11 or higher and 1.15 or lower.

[0134] <Method for manufacturing a composite separation structure> A single-component separation structure is manufactured using the method described above, and a second separation section is formed by exposing the side opposite to the substrate portion of the first separation section (the upper end) to a gas containing a molecular compound having at least Si atoms. The following describes a case in which an amorphous second separation layer is formed at the upper end of a zeolite-only separation structure, with the first separation layer being zeolite. A Si compound containing Si atoms is supplied in gaseous form, and depending on the conditions, along with water vapor, to the upper end of the zeolite-only separation structure for a reaction treatment (exposure treatment). As a result, a thin layer of the Si compound is formed at the upper end of the zeolite-only separation structure, resulting in a separation layer with pores smaller than the pore diameter inherent to the zeolite, which is thought to improve separation performance.

[0135] For this upper end treatment, the molecular compounds (Si compounds) containing Si atoms can be used as liquid raw materials before the gaseous raw materials are vaporized. Examples include alkylalkoxysilanes such as methyltriethoxysilane, 3-aminopropyltriethoxysilane, and 1,1,3,3-tetramethoxy-1,3-dimethylpropanedisiloxane, organosilicon compounds having siloxanes such as hexamethyldisiloxane, organosilicon compounds having silazanes such as hexamethyldisilazane, silicates such as tetramethoxysilane and tetraethoxysilane, silicate oligomers such as methyl silicate oligomer and ethyl silicate oligomer, colloidal silica, sodium silicate, silica sol, etc.

[0136] Among these, silicates or silicate oligomers are preferred in terms of reactivity, with tetraethoxysilane and methyl silicate oligomers being particularly preferred. Furthermore, methyl silicate oligomers are preferred, and polymethoxysiloxanes are most preferred. These Si compounds may be used individually or in combination of two or more types.

[0137] The method for converting the Si compound into a gaseous state can be vaporization from a liquid Si compound by heating, or the gas generated by bubbling an inert gas such as nitrogen, helium, argon, xenon, or krypton into a container containing the liquid Si compound. The processing method is not particularly limited as long as the raw material gas is supplied to the upper end of the zeolite separation structure and the reaction is carried out. For example, there are two methods. One is to seal the zeolite separation structure together with the Si compound liquid and water in separate closed reactors, heat them, and react the gas produced by vaporization from the Si compound in the closed reaction vessel and the water vapor generated from the water at high temperature on the upper end of the zeolite separation structure (hereinafter sometimes referred to as the "closed reaction vessel method"). The other is to circulate gas through a bubbler (gas generator) containing the Si compound, carry the generated Si compound gas along with a transport gas, and supply it to a flow-through reaction tube where the zeolite separation structure is installed, and react it on the upper end of the zeolite separation structure (hereinafter sometimes referred to as the "flow-through reactor method").

[0138] First, we will explain the process using the closed-container reaction vessel method. The sealed reaction vessel method involves creating a sealed reaction vessel under desired temperature conditions in which a zeolite separation structure, gas generated from a Si compound, and water vapor generated from water coexist and react on the upper end of the zeolite separation structure. The sealed reaction vessel is not particularly limited; any container that can accommodate the shape and dimensions of the zeolite separation structure is acceptable. For example, a stainless steel autoclave with a Teflon inner cylinder can be used. By placing a stainless steel autoclave with a Teflon inner cylinder in a constant temperature bath at the desired temperature, the temperature and the saturated vapor pressure of the water vapor and gas generated from the Si raw material supply source at that temperature are achieved, and saturated vapor of gas and water vapor generated from the Si raw material is produced inside the vessel. The shape of the water vapor and Si raw material supply source is not limited as long as it is contained within the sealed reaction vessel. Water and liquid Si raw material may be placed in small containers, or they may be impregnated into a porous material.

[0139] The processing 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. If the temperature is above the lower limit, the dehydration condensation reaction and hydrolysis reaction that occur between the Si compound and the upper end of the first separated portion of the zeolite and the Si compound proceed sufficiently, the modification treatment by the Si compound is sufficiently performed, and the hydrophilicity of the upper end of the first separated portion of the zeolite is sufficiently improved. On the other hand, if the temperature is below the upper limit, the reaction at the upper end of the first separated portion of the zeolite does not proceed too much, resulting in a film sample with low permeation resistance and high permeability. In the manufacturing method of the present invention, it is preferable that all steps be carried out at a temperature of 200°C or lower.

[0140] The processing 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. If the processing time is above the lower limit, the reaction at the upper end of the first separation portion of the zeolite proceeds sufficiently, and a sufficient effect is obtained. On the other hand, if the processing time is below the upper limit, the reaction at the upper end of the first separation portion of the zeolite does not proceed too much, resulting in a film sample with low permeation resistance and high permeation performance.

[0141] Next, we will explain the treatment of the upper end portion of the zeolite separation structure using a flow-through reactor system. In this case, the gas generated from the Si compound and the water vapor generated from water are generated separately and supplied to a reaction tube equipped with a zeolite separation structure, thereby causing a reaction at the upper end of the zeolite separation structure. With this method, the gas generated from the Si compound and the water vapor generated from water can be supplied to the reaction tube separately or simultaneously at any time. Therefore, the process can be carried out in multiple stages. That is, there are stages in which the gas generated from the Si compound and the water vapor generated from water are supplied and circulated to the reaction tube simultaneously, or stages in which the gas generated from the Si compound or the water vapor generated from water are supplied and circulated to the reaction tube separately. The entire process can be constructed by arbitrarily combining these elementary stages.

[0142] For example, the treatment of the upper end of the zeolite separation structure in the reaction tube is carried out in three consecutive stages by controlling the supply gas. In the first stage, only water vapor generated from water is supplied to the reaction tube using an accompanying transport gas. In this stage, water components are adsorbed onto the upper end of the zeolite separation 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 an accompanying transport 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 an accompanying transport gas. In this stage, the reaction of organic group detachment of the Si compound proceeds.

[0143] The shape of the reaction tube for upper end modification treatment is not particularly limited. Any container that can accommodate zeolite individual separation structures of any shape and size, such as tubular, hollow fiber, monolithic, or honeycomb, is acceptable.

[0144] The processing 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. If the processing time is above the lower limit, the reaction at the upper end of the first separation portion of the zeolite proceeds sufficiently, and a sufficient effect is obtained. On the other hand, if the processing time is below the upper limit, the reaction at the upper end of the first separation portion of the zeolite does not proceed too much, resulting in a film sample with low permeation resistance and high permeation performance.

[0145] The composite separation structure of the first invention of this invention is obtained by forming an amorphous silica layer as the second separation part through the above reaction. Although amorphous silica separation membranes have been reported conventionally, there are no reports of widespread industrial use. This is because the performance of amorphous silica separation membranes is unstable, and in particular, they are not very stable with respect to moisture. It is presumed that the cause of this instability of amorphous silica separation membranes is that the material is produced under high temperature conditions of 300°C or higher, the formed amorphous silica is metastable and structurally unstable, has reactive activity with respect to moisture, reacts with moisture after film formation, the amorphous silica is altered, and its permeability performance changes. In other words, the instability of these amorphous silica separation membranes is thought to be caused by the high temperature conditions of film formation. In order to obtain a second separation part made of stable amorphous silica, it is possible to create a stable composite separation structure by avoiding the formation of amorphous silica at temperatures of 300°C or higher and forming the amorphous silica layer under lower temperature conditions of 200°C or lower. This makes it possible to create a water-resistant and stable composite separation structure.

[0146] The processing 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. Most preferably 100°C or lower. If the temperature is above the lower limit, the dehydration condensation reaction and hydrolysis reaction that occur between the Si compound and the upper end of the first separated portion of the zeolite and the Si compound proceed sufficiently, the modification treatment by the Si compound is sufficiently performed, and the hydrophilicity of the upper end of the first separated portion of the zeolite is sufficiently improved. On the other hand, if the temperature is below the upper limit, the reaction at the upper end of the first separated portion of the zeolite does not proceed too much, resulting in a film sample with low permeation resistance and high permeability.

[0147] In a flow-through reactor system (upper end treatment of a flow-through zeolite single-unit separation structure), the flow rate of the gas used to bubble or entrain the Si compound and water gas (hereinafter referred to as "supply flow rate") is not particularly limited, but in order to supply the amount of Si compound or water necessary for the reaction, it 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.

[0148] The upper end of the zeolite separation structure can be processed as follows, for example, using the apparatus schematically shown in Figure 2 (flow-through reactor system; raw material supply gas flow-through zeolite separation structure upper end reaction treatment apparatus). Specifically, in Figure 2, a container (bubbler) 1 for generating gas from Si compounds, a container (bubbler) 2 for generating steam from water, a tubular reaction tube 3, and a valve 8 are installed in a constant temperature bath 11 as part of the piping system. The constant temperature bath 11 is equipped with a temperature control device so that the temperature of the containers (bubblers), reaction tube, and gas can be adjusted. Outside the constant temperature bath 11, the piping system includes a gas flow controller 4, a steam repairer 5 for exhaust gas, a back pressure valve 6, and a gas flow meter 7. Figure 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-through reactor system (raw material supply gas flow type zeolite single-unit separation structure upper end reaction treatment device). In the example shown in Figure 3, the inner diameter of the tubular reaction tube 21 is 15 mm. A tubular zeolite single-unit separation structure 22 with an outer diameter of 12 mm is installed in the reaction tube and processed. The zeolite single-unit separation structure 22 is fixed inside the reaction tube by a zeolite membrane fixing jig 23 (hereinafter sometimes simply referred to as "jig"). This jig 23 has holes or notches so as not to hinder the flow of gas. Due to this zeolite membrane fixing jig 23, the distance between the upper end of the zeolite single-unit separation structure 22 and the inner wall of the reaction tube 21 is constant, and the supply gas for the reaction flows stably. After the installation of the zeolite single-unit separation structure 22, the reaction tube is sealed with a flange 24. The supplied gas enters the reaction tube from the supply gas introduction pipe 25, passes through the upper end of the tubular zeolite individual separation structure 22, and is discharged from the exhaust gas pipe 26. By changing the gas supply flow rate, the gas linear velocity and flow state at the upper end of the zeolite individual separation structure 22 can be controlled.

[0149] The procedure and convenience of supplying raw material gas in a flow-through reactor system (raw material supply gas flow-through zeolite single-element separation structure upper end treatment device) will be explained using Figure 2. The porous single-element zeolite membrane composite (zeolite single-element separation structure) to be processed is placed in the tubular reaction tube 3, and the valve 8 incorporated into the piping is closed. Furthermore, a container (bubbler) 1 for generating Si compound gas containing the Si compound raw material liquid and water, respectively, and a container (bubbler) 2 for generating water vapor from water are incorporated into the piping, and the valve 8 is closed. The temperature of the constant temperature bath 11 is set to the desired value to equalize the temperature inside the constant temperature bath. Then, by controlling the necessary valves and operating the gas flow rate controller, the gas containing Si compound gas and the gas containing water vapor are supplied to the tubular reaction tube 3. The type of gas supplied (gas containing Si compound raw material, gas containing water vapor), flow rate, and time can be adjusted arbitrarily. The gas supplied to the tubular reaction tube 3, after the processing step, is discharged outside the apparatus through the reaction tube, steam repair unit 5, back pressure valve 6, and flow meter 7. The pressure inside the tubular reaction tube 3 can be adjusted by controlling the back pressure valve 6.

[0150] It is not entirely clear why the aforementioned trend in the activation energy of gas permeance occurs when such processing is performed. However, it is possible that gas adsorption due to the inherent polarity of the CHA-type zeolite membrane is shielded to some extent by the siloxane network or silica-modified region formed on its surface, and conversely, gas diffusion becomes dominant in the modified region. In other words, it is possible that the aforementioned trend in the activation energy of gas permeance occurs due to a complex phenomenon that is not simply molecular sieving. Considering this, it is conceivable that similar properties may occur in separation membranes with complex structures, such as composite separation membranes having silica-modified regions 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 film-like structures produced by various CVD / sol-gel methods, and composite separation membranes having silica-modified regions formed on carbon films. In other words, it is presumed that such a trend in the activation energy of gas permeance may occur when the gas separation characteristics, such as gas adsorption characteristics, gas diffusion characteristics, and gas desorption characteristics, differ between the first and second separation sections, or when there is an interaction where the second separation section shields the characteristics of the first separation section.

[0151] P in the separation membrane of the present invention d (S) can take any value. However, if the small molecular weight molecules are hydrogen, helium, or both, and the large molecular weight molecules include carbon dioxide, argon, oxygen, nitrogen, methane, or a combination of two or more of these, then, as mentioned above, the effective pore size of the membrane is considered to be about 0.3 nm in order to separate / recover / concentrate them. In order to realize a separation membrane with such a narrow effective pore size uniformly, it is preferable that the separation membrane be made of inorganic material, and therefore its P d (S) is preferably large compared to organic membranes, etc. Assuming hydrogen as the target molecule, P d The lower limit of (S) is 5.00 × 10 -8 mol / (m 2It is preferable that it be 7.50 × 10⁻¹⁰ or higher. -8 mol / (m 2 It is more preferable that the pressure be 1.00 × 10⁻¹⁰ or higher. -7 mol / (m 2 It is even more preferable that it be 1.25 × 10⁻¹⁰ or higher. -7 mol / (m 2 It is most preferable that the value be above (·sec·Pa). Also, excessively large P d Separation membranes with (S) tend to have lower separation performance, therefore the upper limit is 1.00 × 10 -6 mol / (m 2 It is preferable that the pressure be less than or equal to 8.00 × 10⁻¹⁰ sec·Pa. -7 mol / (m 2 It is more preferable that the pressure be less than or equal to 6.00 × 10⁻¹⁰ sec·Pa. -7 mol / (m 2 It is even more preferable that it be less than or equal to 4.00 × 10⁻¹⁰ sec·Pa. -7 mol / (m 2 It is most preferable that it be less than or equal to (sec·Pa). And P w The preferred range for (S) is the same.

[0152] On the other hand, if we assume helium as the target molecule, P d The lower limit of (S) is 1.00 × 10 -8 mol / (m 2 It is preferable that the pressure be 3.00 × 10⁻¹⁰ or higher. -8 mol / (m 2 It is more preferable that the pressure be 7.00 × 10⁻¹⁰ or higher. -8 mol / (m 2 It is even more preferable that the pressure be 1.00 × 10⁻¹⁰ or higher. -7 mol / (m 2 It is most preferable that the value be above (·sec·Pa). Also, excessively large P d Separation membranes with (S) tend to have lower separation performance, therefore the upper limit is 6.00 × 10 -7 mol / (m2 It is preferable that the pressure be less than or equal to 5.00 × 10⁻¹⁰ sec·Pa. -7 mol / (m 2 It is more preferable that it be less than or equal to 4.00 × 10 -7 mol / (m 2 It is even more preferable that it be less than or equal to 3.00 × 10⁻¹⁰ sec·Pa. -7 mol / (m 2 It is most preferable that it be less than or equal to (sec·Pa). And P w The preferred range for (S) is the same.

[0153] In this invention, the small molecular weight molecules are preferably hydrogen, helium, or both, and the large molecular weight molecules are preferably carbon dioxide, argon, oxygen, nitrogen, methane, or a combination of two or more of these. In order to properly separate these, the effective pore size of the separation membrane should be larger than that of hydrogen and helium, and smaller than that of carbon dioxide, argon, oxygen, nitrogen, methane, etc., i.e., separation performance α d A higher (S / L) is preferable. On the other hand, α d If (S / L) is excessive, the transmission performance P d (S) / P d (L) decreases, which raises concerns that it may result in the need for excessive membrane surface area or excessive supply pressure. When the small molecular size molecule is hydrogen, according to the inventors' previous experiments and simulations, this can be separated into specific molecules with a specific separation performance α d When expressed as (S / L), it became clear that the following applies.

[0154] Separation performance α d Since a higher (S / L) ratio is preferable, the separation performance α of the separation membrane is defined as the small molecular weight molecules in the supply mixed gas being hydrogen and the large molecular weight molecules being oxygen. d The lower limit of (S / L) is preferably 42 or higher, more preferably 60 or higher, even more preferably 80 or higher, and most preferably 100 or higher. On the other hand, α d If (S / L) is excessive, the transmission performance P d (S) / Pd (L) decreases, which raises concerns that an excessive membrane surface area or excessive supply pressure may be required. Therefore, the separation performance α of the separation membrane is defined as hydrogen for small molecular weight molecules and oxygen for large molecular weight molecules in the supply gas mixture. d Regarding the upper limit of (S / L), it is preferably 190 or less, more preferably 170 or less, even more preferably 150 or less, and most preferably 130 or less. α w The preferred range for (S / L) is the same.

[0155] When the small molecular weight molecules are hydrogen and the large molecular weight molecules are nitrogen, the separation performance α of the separation membrane d The lower limit of (S / L) is preferably 63 or higher, more preferably 90 or higher, even more preferably 120 or higher, and most preferably 150 or higher. The upper limit is preferably 475 or lower, more preferably 425 or lower, even more preferably 375 or lower, and most preferably 325 or lower. α w The preferred range for (S / L) is the same.

[0156] When the small molecular weight molecules are hydrogen and the large molecular weight molecules are methane, the separation performance α of the separation membrane is d The lower limit of (S / L) is preferably 75 or higher, more preferably 108 or higher, even more preferably 144 or higher, and most preferably 180 or higher. The upper limit is preferably 570 or lower, more preferably 510 or lower, even more preferably 450 or lower, and most preferably 390 or lower. α w The preferred range for (S / L) is the same.

[0157] When the small molecular weight molecules are hydrogen and the large molecular weight molecules are carbon dioxide, the separation performance α of the separation membrane is... d The lower limit of (S / L) is preferably 3 or higher, more preferably 5 or higher, even more preferably 7 or higher, and most preferably 8 or higher. The upper limit is preferably 28 or lower, more preferably 25 or lower, even more preferably 23 or lower, and most preferably 20 or lower. α w The preferred range for (S / L) is the same.

[0158] When the small molecular weight molecules are hydrogen and the large molecular weight molecules are argon, the separation performance α of the separation membrane d The lower limit of (S / L) is preferably 32 or higher, more preferably 45 or higher, even more preferably 60 or higher, and most preferably 75 or higher. The upper limit is preferably 285 or lower, more preferably 254 or lower, even more preferably 225 or lower, and most preferably 194 or lower. α w The preferred range for (S / L) is the same.

[0159] In this invention, the small molecular weight molecules are preferably hydrogen, helium, or both, and the large molecular weight molecules are preferably carbon dioxide, argon, oxygen, nitrogen, methane, or a combination of two or more of these. Therefore, it can also be suitably used when hydrogen is selected as the target molecule among the small molecular weight molecules in the supplied mixed gas.

[0160] In this case, the hydrogen and oxygen mixture gas may cause explosions and detonations depending on its composition. For this reason, it is preferable that the compositions of the permeate mixture gas and the non-permeate mixture gas after separation be such that they avoid the detonation range (where detonation can occur when the hydrogen concentration of the hydrogen-oxygen mixture gas is greater than 15.5 volume% and less than 93.6 volume%), and it is even more preferable that they be such that they avoid the explosion range (where explosions, including detonations, can occur when the hydrogen concentration of the hydrogen-oxygen mixture gas is greater than 4 volume% and less than 95.8 volume%).

[0161] Even in the case of hydrogen mixed with other gases, the safety is considered sufficient if we assume the case of hydrogen-oxygen mixed gases. Therefore, the hydrogen concentration in the permeate mixed gas is preferably 93.6% by volume or higher, more preferably 95.8% by volume or higher, even more preferably 96.0% by volume or higher, and most preferably 97.0% by volume or higher. The hydrogen concentration in the non-permeate mixed gas is preferably 35.0% by volume or lower, more preferably 25.0% by volume or lower, even more preferably 15.5% by volume or lower, and most preferably 4.0% by volume or lower.

[0162] The hydrogen recovery rate, which correlates with the non-permeable concentration, is preferably high, preferably 60% or higher, more preferably 75% or higher, even more preferably 90% or higher, and most preferably 92% or higher. Furthermore, it is ideal and most preferable to separate the gases in a way that satisfies all of these conditions (hydrogen concentration in the permeable and non-permeable mixed gases, and the hydrogen recovery rate).

[0163] In this invention, the small molecular weight molecules are preferably hydrogen, helium, or both, and the large molecular weight molecules are preferably carbon dioxide, argon, oxygen, nitrogen, methane, or a combination of two or more of these. In order to properly separate these, the effective pore size of the separation membrane should be larger than that of hydrogen and helium, and smaller than that of carbon dioxide, argon, oxygen, nitrogen, methane, etc., i.e., separation performance α d A higher (S / L) is preferable. On the other hand, α d If (S / L) is excessive, the transmission performance P d (S) / P d (L) decreases, which raises concerns that it may result in the need for excessive membrane surface area or excessive supply pressure. In the case of small molecular weight molecules, according to the inventors' previous experiments and simulations, this can be separated by a specific separation performance α d When expressed as (S / L), it became clear that the following applies.

[0164] Separation performance α d Since a higher (S / L) ratio is preferable, the separation performance α of the separation membrane is defined as the small molecular weight molecules in the supply gas mixture being helium and the large molecular weight molecules being carbon dioxide. d The lower limit of (S / L) is preferably 5 or higher, more preferably 6 or higher, even more preferably 8 or higher, and most preferably 9 or higher. On the other hand, α d If (S / L) is excessive, the transmission performance P d (S) / P d(L) decreases, which raises concerns that an excessive membrane area or supply pressure may be required. Therefore, the α of the separation membrane is defined as the small molecular weight molecules in the supply gas mixture being helium and the large molecular weight molecules being carbon dioxide. d The upper limit of (S / L) is preferably 348 or less, more preferably 283 or less, even more preferably 216 or less, and most preferably 151 or less. α w The preferred range for (S / L) is the same.

[0165] When the small molecular weight molecules are helium and the large molecular weight molecules are argon, the separation performance α of the separation membrane is d The lower limit of (S / L) is preferably 24 or higher, more preferably 29 or higher, even more preferably 35 or higher, and most preferably 40 or higher. The upper limit is preferably 389 or lower, more preferably 316 or lower, even more preferably 242 or lower, and most preferably 169 or lower. α w The preferred range for (S / L) is the same.

[0166] When the small molecular weight molecules are helium and the large molecular weight molecules are oxygen, the separation performance α of the separation membrane is... d The lower limit of (S / L) is preferably 31 or higher, more preferably 38 or higher, even more preferably 46 or higher, and most preferably 53 or higher. The upper limit is preferably 305 or lower, more preferably 241 or lower, even more preferably 177 or lower, and most preferably 113 or lower. α w The preferred range for (S / L) is the same.

[0167] When the small molecular weight molecule is helium and the large molecular weight molecule is nitrogen, α d The lower limit of (S / L) is preferably 39 or higher, more preferably 48 or higher, even more preferably 57 or higher, and most preferably 66 or higher. The upper limit is preferably 855 or lower, more preferably 694 or lower, even more preferably 533 or lower, and most preferably 372 or lower. α w The preferred range for (S / L) is the same.

[0168] When the small molecular weight molecule is helium and the large molecular weight molecule is methane, α d The lower limit of (S / L) is preferably 46 or higher, more preferably 57 or higher, even more preferably 68 or higher, and most preferably 79 or higher. The upper limit is preferably 1026 or lower, more preferably 832 or lower, even more preferably 639 or lower, and most preferably 446 or lower. α w The preferred range for (S / L) is the same.

[0169] In the present invention, the small molecular weight molecules are preferably hydrogen, helium, or both, and the large molecular weight molecules are preferably carbon dioxide, argon, oxygen, nitrogen, methane, or a combination of two or more of these. Therefore, it can be suitably used even when helium is selected as the target molecule among the small molecular weight molecules in the supplied mixed gas.

[0170] In this case, a mixed gas of carbon dioxide, argon, oxygen, nitrogen, methane, or a combination of two or more of these with helium may require separation, recovery, or concentration of helium in various situations. For example, for safety reasons, a helium-oxygen mixed gas may be used as a simulated gas for hydrogen-oxygen mixed gas to evaluate the performance of separation membranes. Also, during helium recovery in a gas field, natural gas may be partially dehydrated, and then helium may be recovered using a separation membrane from a mixed gas of carbon dioxide, nitrogen, methane, water vapor, and trace amounts of helium. Alternatively, even in the above case, carbon dioxide and water vapor may be removed from the mixed gas of carbon dioxide, nitrogen, methane, water vapor, and trace amounts of helium, and then helium may be recovered using a separation membrane from a mixed gas of trace amounts of helium, nitrogen, and methane. Furthermore, a multi-stage process using a separation membrane may be constructed from a mixed gas of trace amounts of helium, nitrogen, and methane to separate methane, then nitrogen, and finally helium.

[0171] On the other hand, since helium is a scarce natural resource, it is sometimes recovered on-site after use. In such cases, helium may be recovered from a mixed gas of air (a mixture of carbon dioxide, argon, oxygen, nitrogen, and water vapor) and trace amounts of helium using a separation membrane. When separating / recovering / concentrating helium using a separation membrane in this way, the helium concentration in the supply mixed gas is expected to be low initially, and it is expected that the concentration will be increased by repeatedly concentrating it in multiple stages. In this case, the helium concentration in the supply mixed gas to the separation membrane will be higher in subsequent stages.

[0172] Therefore, it is preferable that the helium concentration in the permeate mixed gas after separation be high, preferably 50.0% by volume or more, more preferably 60.0% by volume or more, even more preferably 70.0% by volume or more, and most preferably 80.0% by volume or more.

[0173] The helium concentration in the impermeable mixed gas is preferably low, preferably 30.0% by volume or less, more preferably 25.0% by volume or less, even more preferably 20.0% by volume or less, and most preferably 15.0% by volume or less.

[0174] The helium recovery rate, which correlates with the non-permeable concentration, is preferably high, preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, and most preferably 60% or more. Furthermore, it is ideal and most preferable to separate the gases in such a way that all of these conditions (helium concentration in the permeable and non-permeable mixed gases, and helium recovery rate) are met.

[0175] In particular, in the separation / recovery / concentration of helium, due to its scarcity, it is ideal to achieve a helium recovery rate of 95% or more, and / or to have a helium concentration of 95% by volume or more in the permeate mixed gas, and / or to have a helium concentration of 10% by volume or less in the non-permeate mixed gas. Furthermore, it is even more ideal to achieve a helium recovery rate of 97% or more, and / or to have a helium concentration of 97% by volume or more in the permeate mixed gas, and / or to have a helium concentration of 5% by volume or less in the non-permeate mixed gas.

[0176] According to the processing method of the present invention, target small molecular diameter molecules can be safely and efficiently separated, recovered, and concentrated from a supply mixed gas containing at least one small molecular diameter molecule having a dynamic molecular diameter smaller than 0.3 nm and at least one large molecular diameter molecule having a dynamic molecular diameter of 0.3 nm or more. [Examples]

[0177] 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.

[0178] Example 1 A zeolite membrane having a CHA-type skeletal structure was fabricated as follows. The following reaction mixtures were prepared for hydrothermal synthesis. 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 together, and 0.975 g of aluminum hydroxide (containing 53.5% by mass of Al2O3, manufactured by Aldrich) was added and stirred to dissolve, resulting in a clear solution. To this, 12.15 g of TMADAOH (N,N,N-Trimethyl-1-adamantylammonium Hydroxide) aqueous solution (containing 25% by mass of TMADAOH, manufactured by Seichem Co., Ltd.) was added as an organic template, and then 54 g of colloidal silica (Nissan Chemical Corporation, Snowtec-40) was added and stirred for 30 minutes to obtain a reaction mixture.

[0179] The composition (molar ratio) of this reaction mixture is SiO2 / Al2O3 / NaOH / KOH / H2O / TMADAOH = 1 / 0.014 / 0.02 / 0.08 / 100 / 0.04, and SiO2 / Al2O3 = 70. As an inorganic porous support, an alumina tube (outer diameter 12 mm, inner diameter 9 mm) was cut to a length of 400 mm and used. As seed crystals, a CHA-type zeolite was used, which was crystallized by hydrothermal synthesis at 160°C for 2 days with a gel composition (molar ratio) of SiO2 / Al2O3 / NaOH / KOH / H2O / TMADAOH = 1 / 0.033 / 0.1 / 0.06 / 20 / 0.07. The above support was immersed in a dispersion of 1.0 mass% of this seed crystal in water for 30 seconds, then withdrawn, and the seed crystal was supported on the upper end of the inorganic porous support, which was then used for hydrothermal synthesis.

[0180] Three supports, one with seed crystals attached in this manner and two other supports with seed crystals attached in the same manner, were immersed vertically in a Teflon® inner cylinder containing the reaction mixture, the autoclave was sealed, and the autoclave was heated at 180°C for 18 hours under self-sustaining pressure to induce zeolite crystal growth on the upper end of the inorganic porous supports by hydrothermal synthesis. After cooling, the zeolite individual structures were removed from the reaction mixture, washed, and dried at 100°C for more than 2 hours.

[0181] The zeolite individual-unit separated structures were fired in an electric furnace at 500°C for 5 hours before template firing. 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 zeolite individual-unit separated structures after firing and the mass of the support, was 60 g / m². 2 The XRD of the generated film revealed the formation of CHA-type zeolite. In the X-ray diffraction pattern, the peak intensity around 2θ=9.6° was 2.5 times that of the peak intensity around 2θ=20.8°.

[0182] Next, the surface of the obtained zeolite film was modified according to the method described below. The 400 mm long CHA-type zeolite separation structure obtained by the synthesis method described above was divided into two 200 mm lengths and placed in series to form a total length of 400 mm sample. At 100°C, using the apparatus shown in Figure 2, 50 ml / min of supply gas was supplied to a reaction tube (Figure 3) containing the CHA-type zeolite separation structure via bubblers containing water vapor and polymethoxysiloxane (MKC® silicate, MS-51, manufactured by Mitsubishi Chemical Corporation), a methyl silicate oligomer, respectively. This process treated the upper end of the CHA-type zeolite separation structure (surface modification to form the second separation section) and prepared a composite separation membrane. In the supply of gases from the bubblers for each raw material, nitrogen gas was used for the water vapor supply and helium was used for the silica source supply. The reaction tube is 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 can be connected to the gas supply piping by flanges, allowing gas to flow through the reaction tube. For the first hour of the process, only gas containing water vapor was supplied and circulated through the reaction tube (first processing stage). For the next two hours, a mixture of gas containing water vapor and gas carrying polymethoxysisiloxane was supplied and circulated through the reaction tube (second processing stage). For the following hour, only gas containing water vapor was supplied and circulated through the reaction tube (third processing stage). After the processing, the inside of the reaction tube was allowed to cool, and the composite separation membrane was removed and further heat-treated at 130°C for one hour (fourth processing stage). At this point, two 200 mm long composite separation membranes were prepared. One of these was set to a membrane length of 17.5 cm and installed in the separation membrane module, completing the preparation for the gas separation experiment.

[0183] The resulting 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 mmφ, and a supply channel width of 2 mm on each side for the gas to be separated was formed between the modified surface of the mounted composite separation membrane (outer diameter of 12 mmφ) and the module. Due to connection with the connecting pipe for gas flow, the length of the surface of the composite separation membrane exposed within the separation module was 175 mm.

[0184] Using a module equipped with a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), the separation performance α of the said separation membrane was measured. d (S / L) was calculated as follows: The supplied gas mixture consisted of 66.6% hydrogen and 33.4% oxygen by volume, and hydrogen was separated, recovered, and concentrated as the target molecule. The dew point of the supplied gas mixture was -54.06°C, the total amount of hydrogen-oxygen gas supplied to the composite separation membrane was 75 mL / min, the supply pressure was 10 kPa(G), and the pressure on the depressurized separation membrane permeate side was -100 kPa(G). Furthermore, by heating, the temperature of the supplied gas mixture, the separation membrane temperature, and the separation membrane module temperature were all set to 90°C. Here, the permeance P of hydrogen, a small molecular weight molecule, was considered. d (S) is 1.40 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 2.15 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 65.1, which indicated more favorable separation performance (Table 1).

[0185] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed from -2.77°C to 21.39°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.32 × 10 -7 mol / (m 2 (·sec·Pa) from 1.20 × 10 -7 mol / (m 2 ·sec·Pa) and P w (L) is 2.03 × 10 -9 mol / (m 2 (·sec·Pa) from 1.85 × 10 -9 mol / (m 2It was (·sec·Pa). Therefore, α in this range w The change in (S / L) remained within the range of 63.6 to 65.2, α d Compared to (S / L), the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained at an extremely high level. As a result of maintaining the separation performance of the separation membrane at an extremely high level, the hydrogen recovery rate remained at an extremely high level of over 91% even under humidification conditions, the hydrogen permeation concentration remained at an extremely high level of over 97% by volume, and the hydrogen non-permeation concentration remained at an extremely low level of below 15.5% by volume (Table 1).

[0186] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 1, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.977 to 1.002. As a result, the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained at an extremely high level. Consequently, even under humidified conditions, the hydrogen recovery rate and permeate concentration were maintained at an extremely high level, and the non-permeate concentration of hydrogen was also maintained at an extremely low level, resulting in extremely ideal process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0187] [Table 1]

[0188] Example 2 The hydrogen-oxygen mixed gas was separated using a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 1, except that the separation process was carried out under different separation process conditions. The separation performance α of the separation membrane dWhen deriving (S / L), the permeance P of hydrogen, a small molecular weight molecule, was determined in the same manner as in Example 1, except that the dew point of the supplied mixed gas was set to -38.76°C and the total amount of hydrogen-oxygen mixed gas supplied to the composite separation membrane was 135 mL / min. d (S) Permeance P of oxygen, a large molecular weight molecule d (L), separation performance α d The (S / L) ratio was calculated. The permeance P of hydrogen, a small molecular weight molecule. d (S) is 1.49 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 2.21 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 67.3, which indicated more favorable separation performance (Table 2).

[0189] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was set to -65.93°C and then varied from -4.42°C to 13.76°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.46 × 10 ―7 mol / (m 2 (·sec·Pa) from 1.08 × 10 ―7 mol / (m 2 ·sec·Pa) and P w (L) is 2.26 × 10 ―9 mol / (m 2 (·sec·Pa) from 1.96 × 10 ―9 mol / (m 2 It was (·sec·Pa). Therefore, α in this range w The change in (S / L) is in the range of 64.6 to 55.2, α dCompared to (S / L), the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained at a high level. Furthermore, as a result of maintaining the high separation performance of the separation membrane, the hydrogen recovery rate remained high at over 60% even under humidified conditions, the hydrogen permeation concentration remained extremely high at over 98% by volume, and the hydrogen non-permeation concentration was below 45% by volume (Table 2).

[0190] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 2, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.821 to 1.000. As a result, the change in separation performance due to humidification was small, and the separation performance of the separation membrane was maintained at a high level. Consequently, even under humidified conditions, the hydrogen recovery rate remained high, the permeate concentration remained extremely high, and the non-permeable hydrogen concentration remained low, resulting in very good process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0191] [Table 2]

[0192] Example 3 The hydrogen-oxygen mixed gas was separated using a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 1, except that the separation process was carried out under different separation process conditions. The separation performance α of the separation membrane d When deriving (S / L), the permeance P of hydrogen, a small molecular weight molecule, was determined in the same manner as in Example 1, except that the dew point of the supplied mixed gas was set to -66.33°C and the total amount of hydrogen-oxygen mixed gas supplied to the composite separation membrane was 200 mL / min. d (S) Permeance P of oxygen, a large molecular weight molecule d (L), separation performance α d (S / L) was calculated. The permian group P of hydrogen, which is a small molecular weight molecule. d (S) is 1.45 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 2.39 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 60.6, which indicated more favorable separation performance (Table 3).

[0193] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed from -1.98°C to 18.36°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.19 × 10 -7 mol / (m 2 (·sec·Pa) from 9.62 × 10 -8 mol / (m 2 ·sec·Pa) and P w (L) is 2.15 × 10 -9 mol / (m 2 (·sec·Pa) from 1.97 × 10 -9 mol / (m 2 It was (·sec·Pa). Therefore, α in this range w The change in (S / L) is in the range of 55.2 to 48.8, α d Compared to (S / L), the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained. As a result of maintaining the separation performance of the separation membrane, the hydrogen recovery rate remained above 40% even under humidified conditions, the hydrogen permeation concentration remained extremely high at over 98% by volume, and the hydrogen non-permeation concentration was below 55% by volume (Table 3).

[0194] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 3, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.804 to 1.000. As a result, the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained. Consequently, even under humidified conditions, the hydrogen recovery rate was maintained, the permeate concentration remained extremely high, and the non-permeable hydrogen concentration was also maintained, resulting in good process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0195] [Table 3]

[0196] Example 4 A composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was fabricated in the same manner as in Example 1, except that the upper end treatment of the CHA-type zeolite single separation structure (surface modification to form the second separation section) was modified to process a 400 mm long CHA-type zeolite single separation structure as is, the time for the first processing stage was changed from 1 hour to 2 hours, and the time for the second processing stage was changed from 2 hours to 5 hours. Furthermore, the length of one membrane was changed to 37.5 cm and mounted in a separation membrane module, four such separation membrane modules were prepared, and these four modules were connected in series to create an effective membrane length of 150 cm. A separation membrane module equipped with the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was prepared in the same manner as in Example 1, except that the separation process was carried out under different separation process conditions as described below. Separation of a hydrogen-oxygen mixed gas was performed in the same manner as in Example 1 using the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) module prepared as described above. The separation performance α of the separation membrane dIn deriving (S / L), the dew point of the supply mixed gas was set to -26.15°C, the total amount of hydrogen-oxygen mixed gas supplied to the composite separation membrane was set to 600 mL / min, the pressure of the supply mixed gas was set to 7 kPa (G), and the permeation side pressure of the separation membrane was set to -99 kPa (G). The permeance P of hydrogen, a small molecular weight molecule, was calculated in the same manner as in Example 1. d (S) Permeance P of oxygen, a large molecular weight molecule d (L), separation performance α d (S / L) was calculated. Here, the permeance P of hydrogen, a small molecular size molecule, is used. d (S) is 1.33 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 1.39 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 95.6, which was an even more favorable separation performance (Table 4).

[0197] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed from 18.19°C to 28.19°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.26 × 10 -7 mol / (m 2 (·sec·Pa) from 1.15 × 10 -7 mol / (m 2 ·sec·Pa) and P w (L) is 1.40 × 10 -9 mol / (m 2 (·sec·Pa) from 1.20 × 10 -9 mol / (m 2 It was (·sec·Pa). Therefore, α in this range w The change in (S / L) is in the range of 89.9 to 95.8, α dCompared to (S / L), the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained at an extremely high level. As a result of maintaining the separation performance of the separation membrane at an extremely high level, the hydrogen recovery rate remained at an extremely high level of over 91% even under humidification conditions, the hydrogen permeation concentration remained at an extremely high level of over 98% by volume, and the hydrogen non-permeation concentration remained at an extremely low level of below 15.5% by volume (Table 4).

[0198] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 4, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.863 to 1.002. As a result, the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained at an extremely high level. Consequently, even under humidified conditions, both the hydrogen recovery rate and permeate concentration were maintained at an extremely high level, and the non-permeable hydrogen concentration was also maintained at an extremely low level, resulting in extremely ideal process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0199] [Table 4]

[0200] Example 5 The hydrogen-oxygen mixed gas was separated using a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 1, except that the separation process was carried out under different separation process conditions. The separation performance α of the separation membrane d In deriving (S / L), the permeance P of hydrogen, a small molecular weight molecule, was calculated in the same manner as in Example 1, except that the hydrogen composition of the supply gas mixture was changed to 40% by volume and the oxygen composition to 60% by volume, and the dew point of the supply gas mixture was set to -65.77°C. d (S) Permeance P of oxygen, a large molecular weight molecule d(L), separation performance α d (S / L) was calculated. Here, the permeance P of hydrogen, a small molecular size molecule, is used. d (S) is 1.25 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 1.73 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 72.3, which indicated more favorable separation performance (Table 5).

[0201] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed from 0.44°C to 17.17°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.15 × 10 -7 mol / (m 2 (·sec·Pa) from 1.08 × 10 -7 mol / (m 2 ·sec·Pa) and P w (L) is 1.79 × 10 -9 mol / (m 2 (·sec·Pa) from 1.74 × 10 -9 mol / (m 2 It was (·sec·Pa). Therefore, α in this range w The change in (S / L) is in the range of 64.2 to 61.9, α d Compared to (S / L), the change in separation performance due to humidification was small, and the separation performance of the separation membrane was maintained at a high level. Furthermore, as a result of maintaining the high separation performance of the separation membrane, the hydrogen recovery rate remained high at over 80% even under humidification conditions, the hydrogen permeation concentration remained extremely high at over 95% by volume, and the hydrogen non-permeation concentration was extremely low, at or below 10% by volume (Table 5).

[0202] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 5, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.855 to 1.000. As a result, the separation performance was not significantly affected by humidification, and the separation performance of the separation membrane was maintained at a high level. Consequently, even under humidified conditions, the hydrogen recovery rate and permeate concentration remained high, and the non-permeate concentration of hydrogen remained low, resulting in very good process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0203] [Table 5]

[0204] Example 6 Except for performing the separation process under different separation process conditions, a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 2 was used to separate the hydrogen-oxygen mixed gas. The separation performance α of the separation membrane d In deriving (S / L), the hydrogen composition of the supply gas mixture was changed to 40% by volume and the oxygen composition to 60% by volume, and the dew point of the supply gas mixture was set to -64.29°C. The permeance P of hydrogen, a small molecular weight molecule, was calculated in the same manner as in Example 2. d (S) Permeance P of oxygen, a large molecular weight molecule d (L), separation performance α d (S / L) was calculated. The permeance P of hydrogen, a small molecular weight molecule. d (S) is 1.42 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 2.16 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, αd The (S / L) ratio was 65.6, which indicated more favorable separation performance (Table 6).

[0205] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed from -2.80°C to 21.26°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.26 × 10 -7 mol / (m 2 (·sec·Pa) to 1.05 × 10 -7 mol / (m 2 (·sec·Pa) and P w (L) is 2.04 × 10 -9 mol / (m 2 (·sec·Pa) from 1.85 × 10 -9 mol / (m 2 It was (·sec·Pa). Therefore, α in this range w The change in (S / L) is in the range of 61.6 to 56.9, α d Compared to (S / L), the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained. As a result of maintaining the separation performance of the separation membrane, the hydrogen recovery rate remained above 55% under humidification conditions, the hydrogen permeation concentration remained extremely high at over 96% by volume, and the hydrogen non-permeation concentration was below 25% by volume (Table 6).

[0206] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α dAs shown in Table 6, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.867 to 1.000. As a result, the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained. Consequently, even under humidified conditions, the hydrogen recovery rate was maintained, the permeate concentration remained extremely high, and the non-permeable hydrogen concentration remained low, resulting in good process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0207] [Table 6]

[0208] Example 7 The hydrogen-oxygen mixed gas was separated using a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 3, except that the separation process was carried out under different separation process conditions. The separation performance α of the separation membrane d In deriving (S / L), the hydrogen composition of the supply gas mixture was changed to 40% by volume and the oxygen composition to 60% by volume, and the dew point of the supply gas mixture was set to -65.77°C. The permeance P of hydrogen, a small molecular weight molecule, was calculated in the same manner as in Example 3. d (S) Permeance P of oxygen, a large molecular weight molecule d (L), separation performance α d (S / L) was calculated. The permeance P of hydrogen, a small molecular weight molecule. d (S) is 1.39 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 2.11 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 65.7, which indicated more favorable separation performance (Table 7).

[0209] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed from 0.60°C to 22.92°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.15 × 10 -7 mol / (m 2 (·sec·Pa) from 9.24 × 10 -8 mol / (m 2 ·sec·Pa) and P w (L) is 1.91 × 10 -9 mol / (m 2 (·sec·Pa) from 1.71 × 10 -9 mol / (m 2 It was (·sec·Pa). Therefore, α in this range w The change in (S / L) is in the range of 60.0 to 53.9, α d Compared to (S / L), the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained. As a result of maintaining the separation performance of the separation membrane, the hydrogen recovery rate remained above 35% under humidification conditions, the hydrogen permeation concentration remained extremely high at over 96% by volume, and the hydrogen non-permeation concentration was below 30% by volume (Table 7).

[0210] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 7, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.821 to 1.000. As a result, the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained. Consequently, even under humidified conditions, the hydrogen recovery rate was maintained, the permeate concentration remained extremely high, and the non-permeable hydrogen concentration remained low, resulting in good process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0211] [Table 7]

[0212] Example 8 Except for performing the separation process under different separation process conditions, a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 4 was used to separate the hydrogen-oxygen mixed gas. The separation performance α of the separation membrane d In deriving (S / L), the hydrogen composition of the supply gas mixture was changed to 40% by volume and the oxygen composition to 60% by volume, and the dew point of the supply gas mixture was set to -22.43°C. The permeance P of hydrogen, a small molecular weight molecule, was calculated in the same manner as in Example 4. d (S) Permeance P of oxygen, a large molecular weight molecule d (L), separation performance α d (S / L) was calculated. The permian group P of hydrogen, which is a small molecular weight molecule. d (S) is 1.28 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 1.62 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 79.3, which indicated more favorable separation performance (Table 8).

[0213] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed from 6.27°C to 21.74°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, Pw (S) is 1.17 × 10 -7 mol / (m 2 (·sec·Pa) from 1.15 × 10 -7 mol / (m 2 ·sec·Pa) and P w (L) is 1.54 × 10 -9 mol / (m 2 (·sec·Pa) from 1.42 × 10 -9 mol / (m 2 It was (·sec·Pa). Therefore, α in this range w The change in (S / L) is in the range of 76.0 to 80.6, α d Compared to (S / L), the change in separation performance due to humidification was very small, and the separation performance of the separation membrane was maintained at a very high level. Furthermore, as a result of maintaining the separation performance of the separation membrane at a very high level, the hydrogen recovery rate remained very high at over 85% even under humidification conditions, the hydrogen permeation concentration remained extremely high at over 95% by volume, and the hydrogen non-permeation concentration was extremely low at less than 10% by volume (Table 8).

[0214] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 8, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.958 to 1.017. As a result, the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained at a very high level. Consequently, even under humidified conditions, both the hydrogen recovery rate and permeate concentration were maintained at a very high level, and the non-permeable hydrogen concentration was also maintained at a very low level, resulting in very good process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0215] [Table 8]

[0216] Example 9 Except for performing the separation process under different separation process conditions, a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 8 was used to separate the hydrogen-oxygen mixed gas. The separation performance α of the separation membrane d When deriving (S / L), the permeance P of hydrogen, a small molecular weight molecule, was calculated in the same manner as in Example 8, except that the total volume of the supplied mixed gas was set to 750 mL / min and the dew point of the supplied mixed gas was set to -23.76°C. d (S) Permeance P of oxygen, a large molecular weight molecule d (L), separation performance α d (S / L) was calculated. The permeance P of hydrogen, a small molecular weight molecule. d (S) is 1.37 × 10 -7 mol / (m 2 The permeance of oxygen, a large molecular weight molecule, is P(sec·Pa). d (L) is 1.57 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, α d The (S / L) ratio was 87.4, which indicated more favorable separation performance (Table 9).

[0217] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was changed to 17.94°C, the permeance P of hydrogen, a small molecular weight molecule, was measured. w (S) Permeance P of oxygen, a large molecular weight molecule w (L) is measured at each supply mixed gas dew point, and α at each dew point is measured. w (S / L) was calculated. As a result, P w (S) is 1.17 × 10 -7 mol / (m 2 ·sec·Pa) and P w (L) is 1.51 × 10 -9 mol / (m 2 The value was (·sec·Pa). Therefore, the α at this value w (S / L) is 77.1, α dCompared to (S / L), the change in separation performance due to humidification was very small, and the separation performance of the separation membrane was maintained at a very high level. Furthermore, as a result of maintaining the separation performance of the separation membrane at a very high level, the hydrogen recovery rate remained high at over 75% even under humidification conditions, the hydrogen permeation concentration remained very high at over 96% by volume, and the hydrogen non-permeation concentration was also very low at less than 15% by volume (Table 9).

[0218] Based on these results, the index α indicates whether the hydrogen-oxygen separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 9, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.882 to 1.000. As a result, the change in separation performance due to humidification was minimal, and the separation performance of the separation membrane was maintained at a very high level. Consequently, even under humidified conditions, the hydrogen recovery rate remained high, the permeate concentration remained very high, and the non-permeable hydrogen concentration remained very low, resulting in very good process performance. Overall, the method of separating / recovering / concentrating hydrogen from a hydrogen-oxygen mixed gas using the separation membrane in question and under these conditions is considered an appropriate method.

[0219] [Table 9]

[0220] Example 10 A composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was fabricated in the same manner as in Example 1, except that the upper end treatment of the CHA-type zeolite single separation structure (surface modification to form the second separation section) was modified to process a 400 mm long CHA-type zeolite single separation structure as is, and the time for the second processing stage was changed from 2 hours to 4 hours. A separation membrane module equipped with the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) was prepared in the same manner as in Example 1, except that the length of one membrane was changed to 37.5 cm and mounted inside the separation membrane module. The separation process was then carried out using the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) module prepared as described above, under the following separation process conditions.

[0221] First, using a module equipped with the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), the separation performance α of the separation membrane was evaluated. d The (S / L) ratio was determined as follows. The supply mixed gas was a helium-air mixture with the composition shown in Table 10 (either a mixture with a composition of 44.33 vol% helium, 11.64 vol% oxygen, 43.49 vol% nitrogen, 0.52 vol% argon, and 0.02 vol% carbon dioxide, or a mixture with a nearly identical composition of 44.42 vol% helium, 11.62 vol% oxygen, 43.42 vol% nitrogen, 0.52 vol% argon, and 0.02 vol% carbon dioxide), and helium was separated / recovered / concentrated as the target molecule. The dew point of the supply mixed gas was -58.54°C, the total amount of helium-air mixture supplied to the composite separation membrane was 90 mL / min, the supply pressure was 11 kPa (G), and the pressure on the permeate side of the reduced-pressure separation membrane was -100 kPa (G). Furthermore, by heating, the temperature of the supplied mixed gas, the separation membrane temperature, and the separation membrane module temperature were all set to 30°C. The permeance P of helium, a small molecular weight molecule. d (S) is 8.08 × 10 -8 mol / (m 2 The permeance of oxygen is (·sec·Pa), and it is a large molecular weight molecule. d (L) is 1.31 × 10-9 mol / (m 2 (·sec·Pa), nitrogen permeance P d (L) is 5.42 × 10 -10 mol / (m 2 (·sec·Pa), permeance of argon P d (L) is 1.01 × 10 -9 mol / (m 2 (·sec·Pa), permeance of carbon dioxide P d (L) is 1.36 × 10 -9 mol / (m 2 It was (·sec·Pa). From this, the α can be derived from the results for helium and oxygen. d (S / L) is 61.6, and α is derived from the results for helium and nitrogen. d (S / L) is 149.0, and α is derived from the results for helium and argon. d (S / L) is 80.0, and α is derived from the results for helium and carbon dioxide. d The (S / L) ratio was 59.4 (Table 10). These represented the most favorable separation performance.

[0222] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was set to 16.46°C, the permeance P of helium, which is a small molecular weight molecule, was measured. w (S), the permeance P of oxygen, a large molecular weight molecule. w (L), permeance of nitrogen P w (L), permeance P of argon w (L), Permeance P of carbon dioxide w (L) is measured at the dew point of the supply mixed gas, and α at that dew point is measured. w (S / L) was calculated. As a result, the P of helium w (S) is 3.93 × 10 -8 mol / (m 2 It was (·sec·Pa). Also, the P of oxygen w (L) is 6.25 × 10 -10 mol / (m 2 (·sec·Pa) and nitrogen P w (L) is 3.77 × 10 -10 mol / (m 2(·sec·Pa), and the P of argon w (L) is 4.24 × 10 -10 mol / (m 2 (·sec·Pa) and the P of carbon dioxide w (L) is 9.58 × 10 -10 mol / (m 2 It was ·sec·Pa). Therefore, the α derived from the results for helium and oxygen w (S / L) is 62.8, and α was derived from the results for helium and nitrogen. w (S / L) is 104.1, and α was derived from the results for helium and argon. w (S / L) is 92.5, and α was derived from the results for helium and carbon dioxide. w The (S / L) ratio was 41.0. These results are based on the respective α d Compared to (S / L), the change in separation performance due to humidification was small, and the separation performance of the separation membrane was maintained at a high level. Furthermore, as a result of maintaining the separation performance of the separation membrane at an extremely high level, the helium recovery rate remained high at over 65% even under humidified conditions, the helium permeation concentration remained extremely high at over 97% by volume, and the helium non-permeation concentration remained low at below 25.0% by volume (Table 10).

[0223] Based on these results, the index α indicates whether the helium-air separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d As shown in Table 10, the (S / L) ratio was within the appropriate range of 0.5 to 1.2 in all cases, ranging from 0.690 to 1.157. As a result, the change in separation performance due to humidification was not significant, and the separation performance of the separation membrane was maintained at a high level. Consequently, even under humidified conditions, the helium recovery rate remained high, the permeate concentration remained extremely high, and the helium non-permeation concentration remained low, resulting in good process performance. Overall, the method of separating / recovering / concentrating helium from a helium-air mixture using the separation membrane and under these conditions is considered appropriate.

[0224] [Table 10]

[0225] Example 11 Helium-air mixed gas was separated using a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 10, except that the separation process was carried out under different separation process conditions. First, using a module equipped with the composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane), the separation performance α of the separation membrane was evaluated. d The (S / L) ratio was determined as follows. The supply mixed gas was a helium-air mixed gas with the composition shown in Table 11 (either a mixed gas with a composition of 44.41 vol% helium, 11.62 vol% oxygen, 43.43 vol% nitrogen, 0.52 vol% argon, and 0.02 vol% carbon dioxide, or a mixed gas with a nearly identical composition of 44.43 vol% helium, 11.62 vol% oxygen, 43.41 vol% nitrogen, 0.52 vol% argon, and 0.02 vol% carbon dioxide, or a mixed gas with a nearly identical composition of 44.47 vol% helium, 11.61 vol% oxygen, 43.38 vol% nitrogen, 0.52 vol% argon, and 0.02 vol% carbon dioxide), and helium was separated / recovered / concentrated as the target molecule. The helium-air mixed gas was separated using a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) prepared in the same manner as in Example 10, except that the dew point of the supplied mixed gas was -56.05°C, the total amount of helium-air mixed gas supplied to the composite separation membrane was 225 mL / min, and the supply pressure was 19 kPa(G). The permeance P of helium, a small molecular weight molecule. d (S) is 1.21 × 10 -7 mol / (m 2 The permeance of oxygen is (·sec·Pa), and it is a large molecular weight molecule. d (L) is 1.07 × 10 -9 mol / (m 2 (·sec·Pa), nitrogen permeance P d (L) is 3.25 × 10-10 mol / (m 2 (·sec·Pa), permeance of argon P d (L) is 7.14 × 10 -10 mol / (m 2 (·sec·Pa), permeance of carbon dioxide P d (L) is 7.99 × 10 -10 mol / (m 2 It was (·sec·Pa). From this, the α can be derived from the results for helium and oxygen. d (S / L) is 112.6, and α is derived from the results for helium and nitrogen. d (S / L) is 371.4, and α is derived from the results for helium and argon. d (S / L) is 168.8, and α is derived from the results for helium and carbon dioxide. d The (S / L) ratio was 150.9. These represented the most favorable separation performance (Table 11).

[0226] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was set from 1.13°C to 7.17°C, the permeance P of helium, a small molecular weight molecule, was measured. w (S), the permeance P of oxygen, a large molecular weight molecule. w (L), permeance of nitrogen P w (L), permeance P of argon w (L), Permeance P of carbon dioxide w (L) is measured within the range of the dew point of the supply mixed gas, and α at these dew points is measured. w (S / L) was calculated. As a result, the P of helium w (S) is 4.48 × 10 -8 mol / (m 2 (·sec·Pa) from 3.67 × 10 -8 mol / (m 2 It was (·sec·Pa). Also, the P of oxygen w (L) is 7.09 × 10 -10 mol / (m 2 (·sec·Pa) from 6.24 × 10 -10 mol / (m 2 (·sec·Pa) and nitrogen P w(L) is 4.17 × 10 -10 mol / (m 2 (·sec·Pa) from 3.90 × 10 -10 mol / (m 2 (·sec·Pa) is the P of argon w (L) is 5.26 × 10 -10 mol / (m 2 (·sec·Pa) from 4.74 × 10 -10 mol / (m 2 (·sec·Pa) is the P of carbon dioxide w (L) is 1.64 × 10 -9 mol / (m 2 (·sec·Pa) from 1.20 × 10 -9 mol / (m 2 The result was (·sec·Pa). Therefore, the α derived from the results for helium and oxygen was w (S / L) is in the range of 63.3 to 58.7, and α was derived from the results for helium and nitrogen. w (S / L) is in the range of 107.6 to 94.0, and is derived from the α values ​​from the helium and argon results. w (S / L) is in the range of 85.2 to 77.3, and α was derived from the results for helium and carbon dioxide. w The (S / L) ranged from 27.3 to 30.5. These results are related to the respective α d Compared to (S / L), the change in separation performance due to humidification was not extreme, and the separation performance of the separation membrane was maintained. As a result of maintaining the separation performance of the separation membrane, the helium recovery rate exceeded 30% even under humidified conditions, the helium permeation concentration remained extremely high at over 98% by volume, and the helium non-permeation concentration was below 35.0% by volume (Table 11).

[0227] Based on these results, the index α indicates whether the helium-air separation conditions are appropriate for the composite separation membrane in question. w (S / L) / α d The (S / L) ratio ranges from 0.202 to 1.000, as shown in Table 11. However, if helium is selected as the small molecular weight molecule and oxygen as the large molecular weight molecule, the index α w (S / L) / α dThe (S / L) ratio ranged from 0.522 to 1.000, which was within the appropriate range of 0.5 to 1.2. As a result, it can be said that the change in separation performance due to humidification did not severely impair the separation performance of the separation membrane. Consequently, even under humidified conditions, the helium recovery rate was maintained within a reasonable range, the permeate concentration was maintained at a very high level, and the non-permeable helium concentration was maintained at a low level, with process performance within an acceptable range. Overall, the method of separating / recovering / concentrating helium from a helium-air mixture using the separation membrane and under these conditions is considered appropriate.

[0228] [Table 11]

[0229] Comparative Example 1 Helium-air mixed gas was separated using a composite separation membrane (surface-modified CHA-type zeolite membrane / surface-modified CHA membrane) in the same manner as in Example 11, except that the dew point of the supplied mixed gas was set to 13.23°C and the pressure of the supplied mixed gas was set to 20 kPa(G). As described in Example 11, the permeance P of helium, a small molecular weight molecule. d (S) is 1.21 × 10 -7 mol / (m 2 It is a large molecular weight molecule, and oxygen has a permeability of P (integer pulses). d (L) is 1.07 × 10 -9 mol / (m 2 (·sec·Pa), nitrogen permeance P d (L) is 3.25 × 10 -10 mol / (m 2 (·sec·Pa), permeance of argon P d (L) is 7.14 × 10 -10 mol / (m 2 (·sec·Pa), permeance of carbon dioxide P d (L) is 7.99 × 10 -10 mol / (m 2 It was (·sec·Pa). From this, the α can be derived from the results for helium and oxygen. d(S / L) is 112.6, and α is derived from the results for helium and nitrogen. d (S / L) is 371.4, and α is derived from the results for helium and argon. d (S / L) is 168.8, and α is derived from the results for helium and carbon dioxide. d The (S / L) ratio was 150.9. These represented the most favorable separation performance (Table 11).

[0230] Next, under the same conditions except that the dew point of the supplied mixed gas to the composite separation membrane was set to 13.23°C, the permeance P of helium, a small molecular weight molecule, was measured. w (S), the permeance P of oxygen, a large molecular weight molecule. w (L), permeance of nitrogen P w (L), permeance P of argon w (L), Permeance P of carbon dioxide w (L) is measured at the dew point of the supply mixed gas, and α at this dew point is measured. w (S / L) was calculated. As a result, the P of helium w (S) is 3.22 × 10 -8 mol / (m 2 It was (·sec·Pa). Also, the P of oxygen w (L) is 5.76 × 10 -10 mol / (m 2 (·sec·Pa) and nitrogen P w (L) is 3.83 × 10 -10 mol / (m 2 (·sec·Pa), and the P of argon w (L) is 4.45 × 10 -10 mol / (m 2 (·sec·Pa) and the P of carbon dioxide w (L) is 1.08 × 10 -9 mol / (m 2 The result was (·sec·Pa). Therefore, the α derived from the results for helium and oxygen was w (S / L) is 55.9, and α was derived from the results for helium and nitrogen. w (S / L) is 84.2, and α was derived from the results for helium and argon. w(S / L) is 72.4, and α was derived from the results for helium and carbon dioxide. w The (S / L) ratio was 29.8. These results are, d Compared to (S / L), the change in separation performance due to humidification was significant, and it could not be said that the separation performance of the separation membrane was maintained. Furthermore, as a result of the separation performance of the separation membrane not being maintained, the helium recovery rate did not reach 30% even under humidified conditions, and the helium non-permeation concentration also exceeded 35.0 volume% (Table 12).

[0231] These results, when combined, indicate whether the helium-air separation conditions are appropriate for the composite separation membrane, α is an index that shows whether these conditions are suitable. w (S / L) / α d The (S / L) ratio is between 0.197 and 0.497, as shown in Table 12, and regardless of whether we focus on helium as a small molecular weight molecule or oxygen, nitrogen, argon, or carbon dioxide as large molecular weight molecules, the index α w (S / L) / α d The (S / L) ratio was less than 0.5 and outside the appropriate range. Therefore, it is considered that the change in separation performance due to humidification impaired the separation performance of the separation membrane. Therefore, it can be said that using the separation membrane in question and under these conditions to separate / recover / concentrate helium from helium-air is not an appropriate method.

[0232] [Table 12] [Industrial applicability]

[0233] According to the present invention, it is possible to safely and efficiently separate small-molecule molecules such as hydrogen and helium from large-molecule molecules present in a mixed gas, including in cases where it is conventionally difficult to separate small-molecule molecules and large-molecule molecules due to the presence of water vapor. Therefore, by separating the hydrogen from the hydrogen-oxygen mixture, which was previously thought to be difficult to separate due to the presence of water vapor, the oxygen concentration after permeation through the separation membrane is sufficiently reduced, moving it out of the detonation range, thus making separation safer. The section where hydrogen-oxygen separation takes place is where hydrogen-oxygen mixed gases from many hydrogen-oxygen gas generators (for example, water decomposition devices using photocatalysts for artificial photosynthesis) gather. By applying the present invention here, the large amount of mixed gas to be separated is removed from the detonation range after passing through the separation process, thereby enabling the safe separation and recovery of hydrogen from the mixed gas containing hydrogen and oxygen. This technology can efficiently separate and recover so-called green hydrogen by combining, for example, a method of electrolyzing water using renewable energy such as sunlight, and a method of simultaneously generating hydrogen and oxygen through the complete decomposition of water using a photocatalyst. Therefore, the present invention is a technically and environmentally useful invention and represents a technology of high industrial value. [Explanation of Symbols]

[0234] 1. A container (bubbler) that generates gas from Si compounds. 2. A container that generates water vapor from water (bubbler) 3. Tubular reaction tube 4. Gas flow control meter 5. Water vapor collector in exhaust gas 6. Back pressure valve 7. Gas flow meter 8. Valve 9. Supply gas 10. Exhaust gas 11.Thermostat 21. Tubular reaction tube 22. Zeolite Separation Structure 23. Fixed Jig 24. Flange 25. Supply gas introduction piping 26. Piping for exhaust gases 100.Composite separation membrane (composite separation structure) 101. Base part 102.Void area 103.First separation section 104.Second separation section 105. Separation active part 106. Separation structure

Claims

1. A method for separating, recovering, and concentrating a gas containing a target molecule from a supply mixed gas containing at least one small-diameter molecule having a dynamic molecular diameter smaller than 0.3 nm and at least one large-diameter molecule having a dynamic molecular diameter of 0.3 nm or more, using a separation membrane, wherein at least one set of small-diameter molecules and large-diameter molecules in the supply mixed gas and the separation membrane satisfy the following formula 1. Equation 1: 0.5≦α ｗ (S / L) / α ｄ (S / L) ≤ 1.2 Here, Equation 2: α ｗ (S / L)≡P ｗ (S) / P ｗ (L) Equation 3: α ｄ (S / L)≡P ｄ (S) / P ｄ (L) And further P ｗ (S): The permeability of one small-diameter molecule contained in the supplied mixed gas through the separation membrane, P ｗ (L): One large molecular weight molecule contained in the supply mixed gas is the permeance that permeates the separation membrane. P ｄ (S): When the separation conditions are the same except that the supply mixed gas is a dry gas, P ｗ (S) The permeance through which the small molecular weight molecules selected during derivation pass through the separation membrane. P ｄ (L): P ｗ (L) is the permeance through which the large molecular weight molecules selected during derivation pass through the separation membrane.

2. The separation / recovery / concentration method according to claim 1, characterized in that the supply mixed gas contains water vapor.

3. The separation / recovery / concentration method according to claim 1, wherein the dew point of the supply mixed gas when it is in a dry state is -20°C or lower.

4. The separation / recovery / concentration method according to claim 1, wherein all combinations of small and large molecular diameter molecules in the supply mixed gas satisfy formula 1.

5. The separation / recovery / concentration method according to claim 1, wherein the separation membrane has a composite separation structure.

6. The separation / recovery / concentration method according to claim 5, wherein the composite separation structure has a silica layer formed on the surface of a zeolite membrane having a CHA-type skeletal structure.

7. The separation / recovery / concentration method according to claim 1, wherein the small molecular weight molecules in the supply mixed gas are either hydrogen, helium, or both, and the large molecular weight molecules include any one or more of carbon dioxide, argon, oxygen, nitrogen, and methane.

8. The α of the separation membrane is defined by the hydrogen and oxygen contained in the aforementioned supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 42 or more and 190 or less.

9. The α of the separation membrane is defined by the hydrogen and nitrogen contained in the aforementioned supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 63 or more and 475 or less.

10. The α of the separation membrane is defined by the hydrogen and methane contained in the aforementioned supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 75 or more and 570 or less.

11. The separation / recovery / concentration method according to any one of claims 7 to 10, wherein the recovery rate of hydrogen molecules contained in the permeate mixed gas obtained by the supply mixed gas permeating through the separation membrane is 60% or more.

12. The separation / recovery / concentration method according to any one of claims 7 to 10, wherein the concentration of hydrogen molecules contained in the permeate mixed gas obtained by the supply mixed gas permeating through the separation membrane is 93.6% by volume or more.

13. The separation / recovery / concentration method according to any one of claims 7 to 10, wherein the concentration of hydrogen molecules contained in the non-permeable mixed gas obtained from the supply mixed gas without permeating the separation membrane is 35.0% by volume or less.

14. The separation / recovery / concentration method according to any one of claims 7 to 10, wherein the recovery rate of hydrogen molecules contained in the permeate mixed gas obtained by the supply mixed gas permeating through the separation membrane is 60% or more, the concentration of hydrogen molecules contained in the permeate mixed gas is 93.6% by volume or more, and the concentration of hydrogen molecules contained in the non-permeate mixed gas recovered from the supply mixed gas without permeating through the separation membrane is 35.0% by volume or less.

15. The α of the separation membrane is defined by the helium and carbon dioxide contained in the aforementioned supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 5 or more and 348 or less.

16. The α of the separation membrane is defined by the helium and argon contained in the aforementioned supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 24 or more and 389 or less.

17. The α of the separation membrane is defined by the helium and oxygen contained in the supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 31 or more and 305 or less.

18. The α of the separation membrane is defined by the helium and nitrogen contained in the aforementioned supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 39 or more and 855 or less.

19. The α of the separation membrane is defined by the helium and methane contained in the aforementioned supply mixed gas. ｄ The separation / recovery / concentration method according to claim 7, wherein (S / L) is 46 or more and 1026 or less.

20. The separation / recovery / concentration method according to any one of claims 7 and 15 to 19, wherein the recovery rate of helium contained in the permeate mixed gas obtained by the supply mixed gas permeating through the separation membrane is 30% or more.

21. The separation / recovery / concentration method according to any one of claims 7 and 15 to 19, wherein the concentration of helium contained in the permeate mixed gas obtained by the supply mixed gas permeating through the separation membrane is 50% by volume or more.

22. The separation / recovery / concentration method according to any one of claims 7 and 15 to 19, wherein the concentration of helium contained in the non-permeable mixed gas that is recovered from the supply mixed gas without passing through the separation membrane is 30% by volume or less.

23. A separation / recovery / concentration method according to any one of claims 7 and 15 to 19, wherein the recovery rate of helium contained in the permeate mixed gas is 30% or more, the concentration of helium contained in the permeate mixed gas is 50% by volume or more, and the concentration of helium contained in the non-permeate mixed gas is 30% by volume or less.

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