Methods for separating ammonia

Abstract

This invention provides a method for separating ammonia gas from a mixed gas containing ammonia gas by making the permeation side of the zeolite membrane below atmospheric pressure, thereby allowing ammonia gas to permeate the zeolite membrane with high permeability and high separation selectivity. [Solution] A method for separating ammonia from a mixed gas consisting of at least ammonia using an ammonia separation membrane, comprising an ammonia separation step of supplying the mixed gas to an ammonia separation membrane and separating ammonia from the mixed gas by the ammonia separation membrane, wherein the pressure on the permeate side of the ammonia separation membrane is less than atmospheric pressure, and the ammonia separation membrane is a zeolite membrane, and the Si / Al2 molar ratio of the zeolite constituting the zeolite membrane is 40 or less.

Description

Technical Field

[0001] The present invention relates to a method for separating ammonia gas by using a zeolite membrane as an ammonia separation membrane, making the permeate side of the membrane less than atmospheric pressure, and selectively permeating ammonia gas from a mixed gas composed of a plurality of components containing ammonia gas.

Background Art

[0002] In recent years, as a method for separating a mixture of gases, membrane separation and concentration methods using membranes such as polymer membranes and zeolite membranes have been proposed. Among these methods, polymer separation membranes have the characteristic of excellent processability, but have a problem in that they are flammable. On the other hand, inorganic membranes such as zeolite membranes have good chemical resistance, oxidation resistance, heat stability, and pressure resistance, and various inorganic membranes have been proposed. Among them, zeolite membranes have regularly arranged pores of sub-nanometers and function as a molecular sieve. Therefore, not only can specific molecules be selectively permeated, but they are also expected to be highly durable separation membranes capable of separation and concentration in a wide temperature and pressure range.

[0003] In addition to existing uses such as fertilizers, industrial raw materials, and denitration applications, ammonia is recently expected to be a carbon-free fuel because it does not emit carbon even when burned. Therefore, it is expected that the uses of ammonia will increase in the future.

[0004] The separation method for separating ammonia gas from a mixed gas composed of a plurality of components containing ammonia gas of the present invention can be applied, for example, to an ammonia production process (Non-Patent Document 1), an ammonia decomposition process, and a process for recovering ammonia contained in exhaust gas.

[0005] In ammonia production processes, for example, membrane separation is expected to be applied to the Haber-Bosch process, which is one of the industrially important processes. A characteristic of the Haber-Bosch process is that the ammonia production reaction is an equilibrium reaction, and thermodynamically, the reaction is preferred under high pressure and low temperature conditions. However, in order to ensure the catalytic reaction rate, high pressure and high temperature production conditions are generally required. In addition, since unreacted hydrogen gas and nitrogen gas coexist with ammonia gas in the generated mixed gas, the process of recovering the ammonia gas as a product from the generated mixed gas requires cooling the mixed gas to about -20°C to -5°C to condense and separate the ammonia. On the other hand, a process has been proposed to efficiently recover high concentrations of ammonia gas by replacing the cooling condensation separation method in the purification process with a separation method using inorganic membranes (Patent Documents 1 and 2). In recent years, research has been progressing on reducing the energy required for the ammonia synthesis process by lowering the temperature and pressure of catalytic reactions through the development of highly active catalysts (Non-Patent Literature 1). Therefore, there is a need for a method that can efficiently separate ammonia under low-pressure conditions.

[0006] In ammonia decomposition processes, membrane separation is expected, for example, in the step of decomposing ammonia to extract hydrogen. The ammonia decomposition reaction is the reverse reaction of the ammonia production reaction described above, and to increase the conversion rate of ammonia, the reaction is preferably carried out under low pressure and high temperature conditions. However, the ammonia decomposition reaction is an endothermic reaction, and in order to maintain the reaction at high temperatures, it is necessary to continuously supply high heat. Furthermore, there is the challenge that the reactor and other equipment must be made of expensive materials to carry out the reaction at high temperatures. Therefore, in commercial machines, a method is considered in which the ammonia decomposition reaction is carried out at a relatively low temperature, and the undecomposed ammonia contained in the reactor outlet gas is recovered using a separation membrane and reused.

[0007] In the process of recovering ammonia contained in exhaust gas, ammonia is usually an air pollutant, and when ammonia is present in factory exhaust gas, it is absorbed with acid or water in a scrubber, or burned with a catalyst, etc., to detoxify the ammonia before releasing the exhaust gas into the atmosphere (Non-Patent Literature 2). For example, in nitride furnaces, much of the ammonia used as raw material is contained in the exhaust gas, and it is generally detoxified by combustion (Non-Patent Literature 3). However, these methods dispose of ammonia in a different form, so it is not possible to recover and reuse the ammonia. Membrane separation is expected to be applicable as a method for recovering ammonia that is being disposed of in this way.

[0008] Regarding the ammonia separation membrane used in the separation method for separating ammonia gas from a mixed gas consisting of multiple components including the ammonia gas described above, Patent Document 2 proposes an efficient ammonia separation method for separating ammonia gas from a mixed gas of ammonia gas, hydrogen gas, and / or nitrogen gas using a specific zeolite having an 8-membered oxygen ring.

[0009] Patent Document 3 proposes a zeolite membrane that exhibits high ammonia separation selectivity under high-temperature conditions of approximately 0.3 MPa and 100-325°C.

[0010] Non-patent document 4 describes ammonia separation using silicalite membranes, reporting that ammonia selectively permeates through them at temperatures below 100°C. Similarly, non-patent document 5 reports that a membrane made of silicalite in the form of nanosheets, with a permeability of 10 bar or less and a temperature below 100°C, exhibits very high ammonia permeability. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2008-247654 [Patent Document 2] Japanese Patent Publication No. 2014-058433 [Patent Document 3] Japanese Patent Publication No. 2022-95749 [Patent Document 4] Japanese Patent Publication No. 2001-333639 [Patent Document 5] Patent No. 7532871 [Non-patent literature]

[0012] [Non-Patent Document 1] ACS Sustainable Chem. Eng. 2023, 11, 9880-9899 [Non-Patent Document 2] Sumitomo Electric Industries, Technical Review (2012), January issue, No. 180, Development of Ammonia Abatement System, p. 93. [Non-Patent Document 3] Special Steel Club, Special Steel (2012), Vol. 61 No. 3, p. 18 [Non-Patent Document 4] AIChE Journal June 2006 Vol. 52, No. 6, 2055-2065 [Non-Patent Document 5] Chem. Commun., 2021, 57, 580-582 [Non-Patent Document 6] JXTG Technical review Volume 60, Issue 3 (November 2018) [Non-Patent Document 7] Mitsubishi Heavy Industries Technical Journal Vol. 60 No. 3 (2023) [Overview of the project] [Problems that the invention aims to solve]

[0013] However, membrane separation typically involves a dependence between the pressure of the gas supplied to the membrane and the flux of the permeated component; it is known that the flux increases with increasing pressure (Non-Patent Literature 6, the ammonia flux measured in the present example is shown in Figure 1). Therefore, the amount of ammonia that permeates through the membrane and is recovered requires a larger membrane area as the supply gas pressure decreases, and there is a problem that an economically viable process cannot be established under low pressure conditions.

[0014] To address these challenges, the system described in Patent Document 4 involves compressing the gas supplied to the membrane using a booster to increase its pressure. However, compressing the gas supplied to the membrane to achieve an economically viable membrane area results in a significant waste of energy during the compression process.

[0015] Patent Document 5 reports a method for separating gases containing CO2 by reducing the pressure on the permeate side. At 40°C, as shown in Comparative Examples 2 and 3, the separation coefficient improved, but the CO2 permeance remained almost unchanged. On the other hand, at 0°C, Examples 7 and 8 showed that the CO2 permeance increased slightly and the separation coefficient improved significantly, reporting that the effect of reduced pressure is greater at lower separation temperatures. However, when separating a mixed gas containing ammonia using this method, if the temperature of the gas supplied to the membrane is cooled to 0°C, the ammonia liquefies, making stable separation difficult. Furthermore, there is the problem of wasting a lot of energy to cool to 0°C.

[0016] The present invention has been made in view of the above-mentioned conventional circumstances, and aims to provide a membrane separation method for efficiently separating ammonia gas from a mixed gas consisting of multiple components including ammonia gas. [Means for solving the problem]

[0017] In order to solve the above problems, the inventors of the present invention investigated a method for separating ammonia from a mixed gas containing ammonia using a zeolite membrane, and found that by using a zeolite membrane with a specific composition and lowering the pressure on the permeate side of the membrane to below atmospheric pressure, ammonia can be efficiently separated with high ammonia permeability and high separation selectivity. As mentioned above, reducing the membrane area usually requires a high flux, and methods such as increasing the pressure of the supply gas are used. However, since ammonia exhibits separation selectivity through the adsorption / desorption mechanism to zeolite, increasing the pressure of the supply gas strengthens the adsorption interaction between ammonia and zeolite, and tends to decrease the permeience of ammonia. However, in the separation method of the present invention, by reducing the pressure of the permeate gas to below atmospheric pressure and using a zeolite membrane with an adjusted Si / Al 2 molar ratio that serves as the ammonia adsorption site, we have found that the adsorption interaction between ammonia and the zeolite adsorption site can be controlled, enabling the separation of ammonia with high permeience and high separation selectivity, thus completing the present invention.

[0018] Embodiments of the present invention have been achieved based on these findings and provide the following:

[0019] [1] A method for separating ammonia from a mixed gas consisting of at least ammonia and several other components using an ammonia separation membrane, The system includes an ammonia separation step in which the mixed gas is supplied to an ammonia separation membrane, and ammonia is separated from the mixed gas by the ammonia separation membrane. The pressure on the permeate side of the ammonia separation membrane is less than atmospheric pressure. A method for separating ammonia, characterized in that the ammonia separation membrane is a zeolite membrane, and the Si / Al2 molar ratio of the zeolite constituting the zeolite membrane is 40 or less. [2] The method for separating ammonia according to [1], characterized in that the temperature of the ammonia separation step is 20°C or higher. [3] The ammonia separation method according to [1] or [2], characterized in that the pressure on the supply side of the mixed gas is 8.1 MPaA or less. [4] The method for separating ammonia according to any one of [1] to [3], characterized in that the mixed gas contains hydrogen and / or nitrogen. [5] The ammonia separation method according to any one of [1] to [4], characterized in that the ammonia separation membrane is a zeolite membrane having a pore structure of 10 or fewer oxygen rings. [6] The ammonia separation method according to [1] to [5], characterized in that the ammonia separation membrane has an ammonia / nitrogen separation coefficient of 30 or more when measured under the following conditions. <Condition> The mixed gases used for measurement are ammonia gas, nitrogen, and hydrogen. ·Separation temperature: 30℃~200℃ • Supply gas pressure: 0.1~5.1 MPaA • Permeation gas pressure: Below atmospheric pressure (20 kPaA) • Ammonia concentration in the supply gas: 2% by volume or more [7] The ammonia separation method according to [1] or [2], characterized in that the ammonia separation membrane has an ammonia / nitrogen separation coefficient of 30 or more when measured under the following conditions. <Condition> The mixed gases used for measurement are ammonia gas, nitrogen, and hydrogen. ·Separation temperature: 20℃ or more and 500℃ or less • Supply gas pressure: 0.3 MPaA to 8.1 MPaA • Permeated gas pressure: Below atmospheric pressure • Ammonia concentration of supply gas: 1.0% by volume or higher [Effects of the Invention]

[0020] According to embodiments of the present invention, even gas supplied to the separation membrane at a low pressure can permeate through the zeolite membrane at a high ammonia permeation rate, and high ammonia separation selectivity can be obtained. As a result, ammonia can be recovered at a high concentration with a small membrane area, thus providing an economically viable ammonia recovery process.

[0021] As a specific example of the application of the ammonia separation method of the present invention, ammonia separation can be used in the following processes. (1) Ammonia production process (2) Ammonia water production process (3) Reaction-separation type ammonia producer (4) Ammonia decomposition process (5) Ammonia recovery process from exhaust gas

[0022] (1) Ammonia production process In ammonia production processes such as the Haber-Bosch process, when recovering ammonia from a mixed gas consisting of multiple components including ammonia gas, hydrogen gas, and nitrogen gas recovered from a reactor, applying the ammonia separation method of the present invention allows for more efficient separation of ammonia gas than conventional cooling condensation separation methods, thereby reducing the cooling energy required for ammonia condensation. When the ammonia separation method of the present invention is applied to the above ammonia production process, the gas containing a high concentration of ammonia after permeating the membrane may be recovered as liquefied ammonia by pressurizing, cooling, or a combination of pressurizing and cooling. This increases the purity of the ammonia. Furthermore, hydrogen and nitrogen that are not liquefied in the cooling process may be discarded or recycled as raw materials for ammonia synthesis. Furthermore, while ammonia synthesis reactions are typically carried out at 5-20 MPa, lower pressures consume more energy for cooling, condensation, and separation. However, using the separation method of the present invention, ammonia can be efficiently separated even at low pressures, thus suppressing the increase in energy consumption for cooling, condensation, and separation even when the pressure of the ammonia synthesis reaction is reduced. Specifically, it is possible to design an ammonia production process with a pressure of less than 0.3-5 MPa for the ammonia synthesis reaction.

[0023] (2) Ammonia water production process In ammonia production processes such as the Haber-Bosch process, aqueous ammonia is produced by re-gasifying liquefied ammonia and absorbing it with water in an absorption tower, or by absorbing ammonia contained in gas purged from an unreacted gas recycling line into water in an absorption tower. The reason for this process configuration is that if an absorption tower is installed at the outlet gas of the ammonia synthesis reactor and absorbed with water, when the unreacted gas is recycled and returned to the ammonia synthesis reactor, water vapor equivalent to the vapor pressure in the absorption tower is included in the recycled gas, reducing the performance of the ammonia synthesis catalyst. However, in the ammonia separation method of the present invention, if the gas with a high concentration of ammonia after permeating through a membrane is supplied to an absorption tower and the ammonia is absorbed with water, aqueous ammonia can be efficiently produced without water entering the ammonia synthesis reactor.

[0024] (3) Reaction-separation type ammonia producer According to the ammonia separation method of the present invention, a reaction-separation type ammonia producer can also be designed in which a zeolite membrane is installed in the reactor and ammonia gas is generated while simultaneously recovering the generated ammonia gas.

[0025] (4) Ammonia decomposition process Ammonia is expected to play a role as a hydrogen carrier because it contains 1.5 molecules of hydrogen per molecule. In this case, hydrogen gas is obtained by decomposing ammonia through a decomposition reaction at the site where the hydrogen is used. However, since the ammonia decomposition reaction is an equilibrium reaction, the reactor outlet gas contains hydrogen gas, nitrogen gas, and ammonia gas. By applying the ammonia separation method of the present invention to the outlet of the decomposition reactor, it becomes possible to realize a hydrogen production process in which unreacted ammonia gas is recovered and reused. A typical process is shown in Figure 2. If the pressure in the ammonia decomposition reaction is lower than the pressure required for ammonia separation, a booster may be installed after the ammonia decomposition process to boost the ammonia decomposition gas before separating the ammonia with an ammonia separation membrane. The recovered ammonia may be recycled back into the ammonia decomposition process and used as a raw material, or it may be burned as fuel to generate the heat supplied in the ammonia decomposition process. Alternatively, after the ammonia decomposition process, the mixed gas containing ammonia may be pressurized using a booster or the like before being separated using an ammonia separation membrane.

[0026] (5) Ammonia recovery process from exhaust gas In plants that use ammonia gas as a reaction material, exhaust gas containing unreacted ammonia is generally detoxified before disposal. For example, as shown in Non-Patent Document 3, in nitriding treatment, a large portion of the raw material ammonia remains unreacted in the exhaust gas and is detoxified using an ammonia removal device before disposal. Furthermore, as mentioned above, ammonia is being considered for use as a clean fuel, and for example, as shown in Figure 4 of Non-Patent Document 7, when ammonia is present in the exhaust gas from synthesis plants, storage facilities, or transporters, it is usually detoxified using an ammonia removal device. Typical treatment methods include absorbing ammonia gas with water, such as using a scrubber, and disposing of it as ammonia water, or neutralizing it with sulfuric acid and disposing of it as ammonium sulfate, or decomposing it into harmless substances using a catalyst before exhausting it (Non-Patent Document 2). However, these methods dispose of ammonia in a different form, making reuse impossible. The ammonia separation method of the present invention allows for the recovery and reuse of ammonia from exhaust gas, thereby improving ammonia raw material costs and waste disposal costs. Typical processes for recovering ammonia are shown in Figures 3 and 4. If the pressure of the mixed gas containing ammonia is low, the exhaust gas containing ammonia may be pressurized using a booster or the like, and then separated using an ammonia separation membrane. The recovered ammonia may be recycled as a raw material for the reaction, or it may be temporarily stored in a tank and used as a raw material in another process. Alternatively, it may be used for other purposes such as denitrification. Furthermore, even if ammonia is not used as a raw material, ammonia generated in the reaction process may be included in the reactor outlet gas. [Brief explanation of the drawing]

[0027] [Figure 1] Pressure dependence of ammonia flux [Figure 2]A specific application example of the ammonia separation method of the present invention is the ammonia decomposition process. [Figure 3] A specific application example of the ammonia separation method of the present invention is an ammonia recovery process from the exhaust gas outlet of a reactor using ammonia as a raw material. [Figure 4] A specific application example of the ammonia separation method of the present invention is an ammonia recovery process from the exhaust gas at the outlet of a reactor where ammonia is produced. [Figure 5] A schematic diagram showing the configuration of the apparatus used in the ammonia gas separation test in the example. [Figure 6] Two-stage separation process using the ammonia separation method of the present invention [Modes for carrying out the invention]

[0028] 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. In this specification, zeolite refers to zeolite as defined by the International Zeolite Association (IZA). Its structure is characterized by X-ray diffraction data. In this specification, a "porous support-zeolite membrane composite in which a zeolite membrane is formed on a porous support" may be referred to as a "zeolite membrane composite" or simply a "membrane composite." A "porous support" may be simply abbreviated as "support." Furthermore, in this specification, "hydrogen gas," "nitrogen gas," and "ammonia gas" may be simply referred to as "hydrogen," "nitrogen," and "ammonia," respectively. On the other hand, ammonia separation in this invention means obtaining a mixed gas containing a higher concentration of ammonia gas from a mixed gas containing ammonia gas.

[0029] An embodiment of the ammonia separation method of the present invention is a method for separating ammonia from a mixed gas consisting of at least ammonia and a plurality of components using a zeolite membrane, characterized in that the pressure on the permeate side of the zeolite membrane is less than atmospheric pressure and the SAR (Si / Al2 molar ratio) of the zeolite membrane is 40 or less. The details are explained below.

[0030] <Method 1 for producing ammonia> The ammonia separation method according to this embodiment can be effectively used to efficiently separate ammonia from a mixed gas containing ammonia, and is therefore effective when used in combination with a method for producing ammonia that yields such a mixed gas. That is, in addition to an ammonia production method that includes a first step of producing ammonia from hydrogen and nitrogen, and a second step of separating the ammonia obtained in the first step by an ammonia separation method described later, and separating the ammonia obtained in the first step in the second step, a method for producing ammonia in which the first and second steps proceed in a single reactor is also one of the preferred embodiments of the present invention. The fact that the first and second steps proceed in a single reactor means that the first and second steps proceed simultaneously. In other words, in one embodiment of the present invention, ammonia gas can be produced from hydrogen gas and nitrogen gas in a container, and ammonia can be efficiently produced in the container while separating ammonia from a mixed gas containing the produced ammonia gas. There are no particular restrictions on the industrial production method of ammonia, but one example is the Haber-Bosch process. In this method, iron oxide is basically used as a catalyst, and nitrogen and hydrogen gases are reacted on the catalyst at high temperature and high pressure of 300°C to 500°C and 10 to 40 MPaA to produce ammonia. The produced ammonia contained in the reactor outlet gas is cooled and condensed to be recovered as a product, while the unreacted nitrogen and hydrogen gases are separated and recycled as raw material gases. Furthermore, as an improved method of the Haber-Bosch process, Ru-based supported catalysts that enable ammonia production under lower pressure conditions were developed in the 1980s, and processes that combine the above Haber-Bosch process with these catalysts, as well as processes with even lower reaction pressures, have been industrialized. More recently, studies are being conducted on industrializing processes with even lower pressures using highly active Ru catalysts, but the basic structure of the production process has remained unchanged for 100 years. Thus, ammonia production industrial catalysts are generally broadly classified into iron-based catalysts and Ru-based catalysts. While the molar ratio of the raw material gases used in ammonia production is preferably the theoretical ratio of hydrogen / nitrogen = 3, catalyst poisoning by hydrogen is likely to occur with Ru-based catalysts, so production conditions with a lower molar ratio are preferred. Considering this point, although there are no particular limitations, a process using a Ru-based catalyst is preferred as the ammonia production catalyst process to be combined with the ammonia separation technology of the present invention, because it approaches the preferred volume ratio of hydrogen gas / nitrogen gas contained in the supply gas in the ammonia separation described later. This combination makes it possible to reduce the amount of hydrogen permeated during the separation of the generated ammonia.

[0031] <2 methods for producing ammonia> The ammonia separation method according to this embodiment is most effective when used in combination with another ammonia production method described above. Specifically, by using it in a so-called membrane reactor, in which ammonia gas is produced from hydrogen gas and nitrogen gas using a catalyst in the reactor, and a zeolite membrane is installed in the reactor to efficiently produce and recover ammonia while allowing the produced ammonia gas to permeate, it is possible to achieve an ammonia conversion rate higher than the equilibrium value of ammonia.

[0032] <Method for producing hydrogen by decomposing ammonia> The ammonia separation method according to this embodiment can be effectively used to efficiently separate ammonia from a mixed gas containing ammonia, and is therefore effective when used in combination with a production method that decomposes the ammonia obtained from such a mixed gas to obtain hydrogen. Specifically, the method includes a first step of producing hydrogen and nitrogen from ammonia, and a second step of separating unreacted ammonia that did not react in the first step by an ammonia separation method described later, and the ammonia recovered in the second step is recycled back into the first step, or the heat source obtained by burning the recovered ammonia is used as the heat supplied in the decomposition step.

[0033] <Reactions using ammonia as a raw material> The ammonia separation method according to this embodiment can be effectively used to efficiently separate ammonia from a mixed gas containing ammonia. Therefore, it is effective to use it in combination with a process in which a reaction is carried out using the ammonia obtained from such a mixed gas as a raw material, and exhaust gas containing unreacted ammonia is discharged. Specifically, the method includes a first step of carrying out a reaction using ammonia as a raw material, and a second step of separating the unreacted ammonia that did not react in the first step by an ammonia separation method described later, and the ammonia recovered in the second step is recycled back into the first step or used as a raw material for another purpose.

[0034] <Method for separating ammonia> An embodiment of the ammonia separation method of the present invention is characterized by using a zeolite membrane to bring a mixed gas containing ammonia into contact with the zeolite membrane and selectively permeating the mixed gas to separate the ammonia. Furthermore, the ammonia separation method of the present invention is characterized by using a specific zeolite membrane, contacting a mixed gas containing ammonia with the zeolite membrane, and selectively permeating the mixed gas to separate the ammonia.

[0035] In embodiments of the present invention, as described above, the adsorption of ammonia onto zeolite is utilized, and the separation of ammonia is characterized by a hopping mechanism of ammonia within the zeolite pores. Therefore, it is preferable to control the ammonia gas concentration in the mixed gas (supply gas) containing ammonia gas to a specific amount or higher. This concentration is preferably 1.0 volume% or more as the ammonia gas concentration in the supply gas. This is because the ammonia adsorbed onto the zeolite is in adsorption equilibrium with the ammonia gas in the gas phase, and the adsorption capacity of ammonia onto the zeolite largely depends on the ammonia gas concentration in the supply gas. Among the above, the ammonia gas concentration in the supply gas is preferably 2.0 volume% or more, more preferably 3.0 volume% or more, even more preferably 5.0 volume% or more, particularly preferably 6.0 volume% or more, especially preferably 8.0 volume% or more, and most preferably 10.0 volume% or more. On the other hand, the lower the ammonia gas concentration in the supply gas, the less interference the adsorbed ammonia has on the permeation of ammonia in the supply gas. Therefore, the ammonia gas concentration in the supply gas is usually preferably less than 80% by volume, more preferably less than 60% by volume, more preferably less than 50% by volume, even more preferably less than 40% by volume, and particularly preferably less than 30% by volume. The ammonia concentration in the supply gas is determined by taking a sample of the supply gas, analyzing its components, and considering the mole fraction of ammonia as equivalent to the volume percentage. Similarly, the volume percentages of other gases are also considered as volume percentages using their mole fractions.

[0036] The mixed gas used in the ammonia separation method of the present invention is not particularly limited as long as it consists of multiple components, including at least ammonia. A mixed gas containing hydrogen and / or nitrogen is more preferable. Because the ammonia separation method of the present invention exhibits excellent selectivity for separating ammonia from the mixed gas, it can be suitably applied, for example, to the processes described above.

[0037] In the present invention, the mixed gas containing ammonia may also contain water. Normally, water is adsorbed to zeolite acid sites, and in membrane separation using zeolite adsorption sites as in the present invention, it is a factor that reduces membrane performance. However, by reducing the permeation side of the membrane to below atmospheric pressure, water adsorbed on the zeolite can also permeate the membrane. When the permeation side is atmospheric pressure, for example, the permeation of ammonia may decrease significantly compared to when water is not present, but by reducing the pressure on the permeation side of the membrane, it may be possible to suppress the decrease in permeation even in such cases. The amount of water contained in the mixed gas containing ammonia is usually 5% by weight or less, preferably 4% by weight or less, more preferably 3% by weight or less, particularly preferably 2% by weight or less, and especially preferably 1% by weight or less.

[0038] In the present invention, the mixed gas containing ammonia may also contain hydrocarbons such as methane, ethane, propane, butane, ethylene, propylene, butene, butadiene, and acetylene, oxygen-containing compounds such as carbon monoxide, carbon dioxide, and oxygen, and chlorine gas. As described above, ammonia exhibits separation selectivity by adsorption to zeolite sites, but the adsorption of hydrocarbons and oxygen-containing compounds to zeolite sites is weak, and they can permeate the membrane when the permeation side of the membrane is below atmospheric pressure. The amount of hydrocarbons such as methane, ethane, propane, butane, ethylene, propylene, butene, butadiene, and acetylene, oxygen-containing compounds such as carbon monoxide, carbon dioxide, and oxygen, and chlorine gas in the mixed gas containing ammonia is usually 5% by weight or less, preferably 4% by weight or less, more preferably 3% by weight or less, more preferably 2% by weight or less, particularly preferably 1% by weight or less, and especially preferably 0.5% by weight or less.

[0039] In the present invention, the ammonia separation temperature is one of the important factors for improving the ammonia permeability of the zeolite membrane. It is usually between 20°C and 500°C, but may also be between 10°C and 500°C. Generally, the higher the pressure, the more the adsorption and desorption equilibrium of ammonia with respect to the acid sites of the zeolite membrane shifts towards the adsorption direction, and the lower the ammonia permeability. However, within the above temperature range, the acidic properties of the acid sites weaken, and the adsorption reaction rate decreases, so high permeability can be achieved even under high pressure conditions. The temperature range between 20°C and 500°C is a temperature range in which the ammonia production reaction, in which a mixed gas is generated, proceeds suitably, and therefore can be said to be sufficiently high. In addition to permeability, the separation temperature also greatly affects the long-term durability of the zeolite membrane used, as well as the overall production energy balance of the process using the ammonia separation membrane. From these perspectives, in the present invention, the temperature during ammonia separation is preferably 450°C or lower, more preferably 400°C or lower, particularly preferably 350°C or lower, especially preferably 300°C or lower, and most preferably 250°C or lower. On the other hand, in terms of the adsorption interaction between ammonia and zeolite acid sites, adsorption weakens as the temperature increases, and the permeability of ammonia improves. Also, ammonia has the property of liquefying at low temperatures. Therefore, the separation temperature is usually 20°C or higher, but may also be 10°C or higher, preferably 30°C or higher, more preferably 50°C or higher, even more preferably 80°C or higher, particularly preferably 100°C or higher, especially preferably 150°C or higher, and most preferably 200°C or higher. When ammonia is separated under these preferred temperature conditions, the desorption rate of ammonia adsorbed in the zeolite pores improves, and as a result, the ammonia permeability rate of the zeolite membrane improves. Note that the separation temperature refers to the temperature of the atmosphere in which the zeolite membrane is installed, and specifically refers to the temperature inside the module on which the zeolite membrane is mounted.

[0040] In this invention, the pressure of the supplied gas (mixed gas) is important because a higher pressure provides a partial pressure difference, which is the driving force for membrane separation, thus increasing the amount of ammonia that permeates per unit area. Therefore, the pressure of the mixed gas is usually 0.3 MPaA or higher, but may also be normal pressure (atmospheric pressure: 0.1 MPaA), preferably 0.1 MPaA or higher, more preferably 0.4 MPaA or higher, even more preferably 0.5 MPaA or higher, particularly preferably 0.6 MPaA or higher, even more preferably 0.8 MPaA or higher, even more preferably 0.9 MPaA or higher, especially particularly preferably 1.0 MPaA or higher, most preferably 1.1 MPaA or higher, and most preferably 1.2 MPaA or higher. On the other hand, when the permeation side of the membrane is below atmospheric pressure, a lower pressure of the supplied gas makes it easier to promote the desorption of ammonia adsorbed at the zeolite adsorption site, thus increasing the permeability of ammonia. From this perspective, the pressure of the mixed gas is usually 8.1 MPaA or less, preferably 6.1 MPaA or less, more preferably 5.1 MPaA or less, even more preferably 4 MPaA or less, particularly preferably 3.0 MPaA or less, especially preferably 2.5 MPaA or less, and most preferably 2.0 MPaA or less. If the pressure of the gas supplied to the membrane is less than the above preferred range, a step of increasing the pressure of the supplied gas using a booster or the like may be provided before membrane separation.

[0041] The pressure on the membrane permeation side is preferably below atmospheric pressure, typically 0.09 MPaA or less, preferably 0.08 MPaA or less, more preferably 0.06 MPaA or less, even more preferably 0.05 MPaA or less, particularly preferably 0.03 MPaA or less, especially preferably 0.02 MPaA or less, and most preferably 0.01 MPaA or less.

[0042] The differential pressure between the supply gas and the permeate gas on the membrane side is such that increasing the differential pressure requires increasing the supply pressure, while reducing the influence of adsorption interactions between ammonia and zeolite acid sites. Therefore, it is usually 8.1 MPa or less, preferably 6.1 MPa or less, more preferably 5.1 MPa or less, even more preferably 4.1 MPa or less, particularly preferably 3.1 MPa or less, especially preferably 2.1 MPa or less, and most preferably 1.1 MPa or less. Furthermore, since the differential pressure is the driving force for membrane separation, a larger differential pressure is preferable to reduce the membrane area. Therefore, it is usually 0.1 MPa or more, preferably 0.3 MPa or more, more preferably 0.5 MPa or more, even more preferably 0.6 MPa or more, particularly preferably 0.7 MPa or more, especially preferably 0.8 MPa or more, and most preferably 0.9 MPa or more.

[0043] Here, differential pressure refers to the difference between the pressure on the supply side of the gas and the pressure on the permeation side within the membrane (supply gas pressure - permeation gas pressure within the membrane). Also, pressure [PaA] refers to absolute pressure unless otherwise specified.

[0044] In the separation method of the present invention, the ammonia / nitrogen (NH3 / N2) separation coefficient (permeability coefficient ratio) of the zeolite membrane is 30 or higher. For example, the zeolite membrane used in the separation method of the present invention may have an ammonia / nitrogen (NH3 / N2) separation coefficient of 30 or more under the following conditions. By setting the NH3 / N2 separation coefficient within this range, ammonia can be permeated and separated from a mixed gas containing nitrogen and ammonia with high permeability. From the viewpoint of further improving selective permeability in separation, the NH3 / N2 separation coefficient is preferably 100 or more, more preferably 150 or more, particularly preferably 200 or more, especially preferably 500 or more, particularly preferably 1000 or more, and most preferably 10000 or more. The upper limit of the NH3 / N2 separation coefficient is not particularly limited, and is usually 1,000,000 or less. <Condition> The mixed gases used for measurement are ammonia gas, nitrogen, and hydrogen. ·Separation temperature: 30℃~200℃ • Supply gas pressure: 0.1~5.1 MPaA • Permeation gas pressure: Below atmospheric pressure (20 kPaA) • Ammonia concentration in the supply gas: 2% by volume or more

[0045] In the separation method of the present invention, the ammonia / hydrogen (NH3 / H2) separation coefficient (permeability coefficient ratio) of the zeolite membrane is 30 or higher. For example, the zeolite membrane used in the separation method of the present invention may have an ammonia / hydrogen (NH3 / H2) separation coefficient of 30 or more under the following conditions. By setting the NH3 / H2 separation coefficient within this range, ammonia can be permeated and separated from a mixed gas containing hydrogen and ammonia with high permeability. From the viewpoint of further improving selective permeability in separation, the NH3 / H2 separation coefficient is preferably 50 or more, more preferably 120 or more, particularly preferably 200 or more, especially preferably 1000 or more, particularly preferably 4300 or more, and most preferably 5000 or more. The upper limit of the NH3 / H2 separation coefficient is not particularly limited, and is usually 1,000,000 or less. <Condition> The mixed gases used for measurement are ammonia gas, nitrogen, and hydrogen. ·Separation temperature: 30℃~200℃ • Supply gas pressure: 0.1~5.1 MPaA • Permeation gas pressure: Below atmospheric pressure (20 kPaA) • Ammonia concentration in the supply gas: 2% by volume or more

[0046] The separation coefficient described above refers to the ratio of the permeance (transmission rate) of two gases under the operating conditions of the separation method according to one embodiment of the present invention. Specifically, the ammonia / nitrogen separation coefficient means ammonia permeance / nitrogen permeance, and the ammonia / hydrogen separation coefficient means ammonia permeance / hydrogen permeance. Permeance (also called "transmission rate") is the amount of substance that permeates divided by the product of the membrane area, time, and the partial pressure difference between the supply side and the permeation side of the substance, and its unit is [mol / (m³]. 2The value is [s·Pa]. In embodiments in which a zeolite membrane composite, in which a zeolite membrane is formed on a porous support, is mounted on a membrane module, the permeance value measured using the membrane composite is adopted. Permeance can be measured, for example, using the method of the embodiments described later. Flux (also called "permeation flux") is the amount of substance that permeates divided by the membrane area and time, and its unit is [mol / (m²). 2 This is (s). In embodiments in which a zeolite membrane composite, in which a zeolite membrane is formed on a porous support, is mounted on a membrane module, the flux value measured using the membrane composite is adopted. The flux can be measured, for example, using the method of the embodiments described later.

[0047] The separation coefficient can be adjusted to the above range by appropriately setting various conditions in the separation method, as long as the pressure of the mixed gas and the separation temperature meet the above ranges. Examples of conditions that can be set include, but are not limited to, the gas linear velocity of the mixed gas, the zeolite membrane, the composition of the mixed gas (composition ratio of hydrogen gas and nitrogen gas, ammonia concentration), the pressure on the permeate side of the membrane, and whether or not a sweep gas is used on the permeate side.

[0048] The linear velocity of the mixed gas (supply gas) should be sufficient to compensate for the decrease in permeable gas, and also sufficient to mix the supply gas so that the concentration of the less permeable gas in the immediate vicinity of the membrane matches the concentration of the gas in the whole. From the viewpoint of further improving the NH3 / H2 separation coefficient and the NH3 / N2 separation coefficient, the linear velocity of the gas depends on the tube diameter of the zeolite membrane and the separation performance of the membrane, but is usually 0.3 cm / sec or higher, preferably 0.5 cm / sec or higher, more preferably 0.7 cm / sec or higher, particularly preferably 0.8 cm / sec or higher, especially preferably 0.9 cm / sec or higher, and most preferably 1.0 cm / sec or higher. While there is no particular upper limit, if the amount of supplied gas is low, vibrations will occur in the membrane module and damage to the membrane can be avoided. Therefore, the gas linear velocity is usually 10 m / sec or less, preferably 5 m / sec or less, more preferably 1 m / sec or less, even more preferably 0.8 m / sec or less, particularly preferably 0.5 m / sec or less, especially preferably 0.3 m / sec or less, and most preferably 0.1 m / sec or less. In this specification, gas linear velocity refers to the gas linear velocity on the supply side within the membrane module on which the zeolite membrane is mounted.

[0049] There are no particular restrictions on the gas composition in the supply gas (mixed gas), but the volume ratio of hydrogen gas / nitrogen gas contained in the supply gas is usually 3.0 or less, preferably 2.9 or less, more preferably 2.8 or less, even more preferably 2.5 or less, particularly preferably 2.3 or less, especially preferably 2.0 or less, and most preferably 1.8 or less. By adjusting to this volume ratio, the amount of hydrogen permeate during ammonia separation is reduced, and the separation selectivity of ammonia is improved. For this reason, it is preferable to combine this embodiment with a Ru-based ammonia production catalyst process in which the volume ratio of hydrogen gas / nitrogen gas in the raw material gas is low. On the other hand, there are no particular restrictions on the lower limit of the volume ratio of hydrogen gas / nitrogen gas, but the lower the ratio, the better the separation selectivity of ammonia, so it is usually 0.2 or more, preferably 0.3 or more, and more preferably 0.5 or more. Here, the upper and lower limits are valid within the range of significant figures; that is, an upper limit of 3 or less means 2.5 or more and less than 3.5, while 0.2 or more means 0.15 or more and less than 0.25, and 1.0 or more means 0.95 or more and less than 1.05.

[0050] In the ammonia separation method from a mixed gas of the present invention, a sweep gas may be used. A sweep gas is a gas supplied to efficiently recover ammonia permeated through the separation membrane. It is not a gas introduced to the supply gas side before separation permeation, but rather a gas supplied to the permeation side of the separation membrane. In other words, the sweep gas is a gas supplied separately from the supply gas before separation permeation, and a different type of gas is flowed to the permeation side to recover the gas that has permeated through the membrane. However, if the ammonia on the permeation side is to be recovered at a high concentration, the sweep gas will dilute the ammonia, so it should not be used. Therefore, the sweep gas is used for the purpose of membrane separation. The sweep gas used in this invention refers, for example, to the gas 9 supplied from line 12 shown in Figure 5. The pressure of the sweep gas is usually atmospheric pressure, but is not particularly limited to atmospheric pressure, and is preferably 20 MPaA or less, more preferably 10 MPaA or less, and even more preferably 1 MPaA or less, with a lower limit of preferably 0.09 MPaA or more, and more preferably 0.1 MPaA or more.

[0051] There are no particular restrictions on the linear velocity of the sweep gas, but it is usually 0.5 mm / sec or more, preferably 1 mm / sec or more, and there are no particular upper limits, but it is usually 1 m / sec or less, preferably 0.5 m / sec or less.

[0052] The apparatus used for gas separation is not particularly limited, but typically a zeolite membrane is used as a membrane module (hereinafter, "zeolite membrane and / or separation apparatus using a zeolite membrane" may be simply referred to as "membrane module"). The membrane module may be, for example, an apparatus like the one schematically shown in Figure 5, or a membrane module exemplified in, for example, "Gas Separation and Purification Technology" (Toray Research Center, Inc., 2007, p. 22), may be used. In the membrane module, the zeolite membrane may be used in the form of a zeolite membrane composite, in which the zeolite membrane is formed on a porous support. The separation operation of the mixed gas in the apparatus shown in Figure 5 will be explained in the section on examples.

[0053] When separating ammonia from a mixed gas via membrane, multiple membrane modules may be used. In this case, the gas to be separated may be supplied to the first membrane module, and the non-permeable gas that did not permeate the membrane may be supplied to the second membrane module, or the permeable gas may be supplied to the second membrane module. In the former method, the concentration of the less permeable component on the non-permeable side can be further increased, while in the latter method, the concentration of the more permeable component in the permeable gas can be further increased. Methods combining these methods can also be suitably used. When separating using multiple membrane modules, the pressure of the supplied gas may be adjusted as needed using a booster or similar device when supplying gas to the subsequent membrane modules.

[0054] Furthermore, when using multiple membrane modules, membranes with different performance characteristics may be installed in each stage. Generally, membranes with high permeability tend to have low separation performance, and conversely, membranes with high separation performance tend to have low permeability. Therefore, when processing until the gas components to be separated or concentrated reach a predetermined concentration, a highly permeable membrane requires a smaller membrane area, but less permeable components also permeate more easily to the permeation side, resulting in a lower concentration of highly permeable components in the permeation gas. Conversely, a highly separation membrane makes it difficult for less permeable components to permeate to the permeation side, resulting in a higher concentration of highly permeable components in the permeation gas, but requiring a larger membrane area. With separation using a single type of membrane, it is difficult to control the relationship between the required membrane area and the permeation / blockage rates of the gas to be concentrated or separated, but this can be easily controlled by using membranes with different performance characteristics. By setting the membranes to achieve the optimal relationship between membrane area and the permeation / blockage rates of the gas to be concentrated or separated, based on membrane costs and the price of the gas to be separated and recovered, the overall benefits can be maximized.

[0055] For example, if ammonia cannot be sufficiently separated by a single membrane separation stage, the non-permeable gas can be separated by several additional membrane stages. Also, if the ammonia / hydrogen separation of the membrane is insufficient with a single membrane separation stage, and a large amount of hydrogen is present along with ammonia on the permeate side, the permeate gas can be separated by a membrane with high ammonia and hydrogen separation performance.

[0056] The zeolite membrane used in this invention preferably has excellent chemical resistance, oxidation resistance, thermal stability, and pressure resistance, as well as exhibiting high ammonia permeability and separation performance, and possessing excellent durability.

[0057] The high ammonia permeability referred to here means that it indicates a sufficient processing capacity, and the higher the ammonia permeance, the greater the amount of ammonia that passes through per unit membrane area, making it possible to install a membrane area that is economically viable when using the membrane in a commercial plant. For example, the permeance of the ammonia component that permeates the membrane under the following conditions [mol / (m³)] 2 (Ammonia transmittance) (s·Pa) is typically 0.5 × 10-7 Above, preferably 0.9×10 -7 Above, more preferably 1.0×10 -7 Above, even more preferably 1.5×10 -7 Above, particularly preferably 2.0×10 -7 Above, especially preferably 3.0×10 -7 Above, most preferably 4.0×10 -7 Above. The upper limit is not particularly limited and is usually 3.0×10 -4 Below. <Condition> · The mixed gas used for measurement is ammonia gas, nitrogen, and hydrogen. · Separation temperature: 30°C to 200°C · Pressure of the supply gas: 0.1 to 5.1 MPaA · Pressure of the permeated gas: less than atmospheric pressure (20 KPaA) · Ammonia concentration of the supply gas: 2% by volume or more

[0058] Also, the permselectivity [mol / (m 2 · s·Pa)] (nitrogen permeability) of the zeolite membrane used in the present invention, for example, when the membrane is permeated under the following conditions, is usually 5.0×10 -9 Below, preferably 1.0×10 -10 Below, more preferably 5.0×10 -11 Below, particularly preferably 1.0×10 -11 Below, most preferably 1.0×10 -12 Below, and ideally the permselectivity is 0, but in practical use, it may be on the order of 1×10 -10 ~1×10 -14 Degree. <Condition> · The mixed gas used for measurement is ammonia gas, nitrogen, and hydrogen. · Separation temperature: 30°C to 200°C · Pressure of the supply gas: 0.1 to 5.1 MPaA · Pressure of the permeated gas: less than atmospheric pressure (20 KPaA) · Ammonia concentration of the supply gas: 2% by volume or more

[0059] Furthermore, the hydrogen component permeance [mol / (m³) of the zeolite membrane used in this invention is 2 (Hydrogen permeability) (s·Pa) is typically 5.0 × 10 when the membrane is permeated under the following conditions. -9 The following is preferably 1.0 × 10 -10 More preferably 5.0 × 10 -11 The following is particularly preferred: 1.0 × 10 -11 The following is most preferably 5.0 × 10 -12 The following is true, and ideally the permience is 0, but in practice it is 1 × 10⁻⁶ -10 ~1 × 10 -14 It may be on the order of a certain degree. <Condition> The mixed gases used for measurement are ammonia gas, nitrogen, and hydrogen. ·Separation temperature: 30℃~200℃ • Supply gas pressure: 0.1~5.1 MPaA • Permeation gas pressure: Below atmospheric pressure (20 kPaA) • Ammonia concentration in the supply gas: 2% by volume or more

[0060] Here, permeance (also called "transmission rate") is the amount of substance that permeates divided by the product of the membrane area, time, and the partial pressure difference between the supply side and the permeation side of the substance, and its unit is [mol / (m³]. 2 (·s·Pa). In embodiments in which a zeolite membrane composite, in which a zeolite membrane is formed on a porous support, is mounted on a membrane module, the permeance value measured using the membrane composite is adopted.

[0061] Flux of ammonia components permeating the membrane [mol / (m³)] 2 The ammonia permeation rate (s) is typically 0.2 × 10 when ammonia is permeated through a membrane under the following conditions. -2 Preferably 0.5 × 10 -2 The above is a comfortable 1.0 × 10 -2 More preferably 2.0 × 10 -2 In particular, 3.0 × 10 -2 The above is particularly preferable to 5.0 × 10-2 In summary, the most preferred size is 9.0 × 10 -2 That's all. There is no particular upper limit, and it is usually 1.0 or less. <Condition> The mixed gases used for measurement are ammonia gas, nitrogen, and hydrogen. ·Separation temperature: 30℃~200℃ • Supply gas pressure: 0.1~5.1 MPaA • Permeation gas pressure: Below atmospheric pressure (20 kPaA) • Ammonia concentration in the supply gas: 2% by volume or more

[0062] (Zeolite) In the present invention, the zeolite constituting the zeolite film is preferably an aluminosilicate. Aluminosilicates mainly consist of oxides of Si and Al, but other elements may be included as long as they do not impair the effects of the present invention. The cation species to be included in the zeolite of the present invention is preferably a cation species that easily coordinates to the ion exchange sites of the zeolite, for example, a cation species selected from the elements of Group 1, Group 2, Group 8, Group 9, Group 10, Group 11, and Group 12 of the periodic table, NH4 + , and two or more of these cation species, more preferably cation species selected from the elements of Group 1 and Group 2 of the periodic table, NH4 + , as well as two or more of these cation species.

[0063] The Si / Al2 molar ratio of the zeolite constituting the zeolite membrane used in the present invention is not particularly limited, but is usually 5 or higher, preferably 6 or higher, more preferably 7 or higher, even more preferably 8 or higher, even more preferably 10 or higher, particularly preferably 15 or higher, especially preferably 18 or higher, and most preferably 20 or higher. On the other hand, it is usually 40 or lower, preferably 38 or lower, more preferably 35 or lower, even more preferably 33 or lower, particularly preferably 30 or lower, even more preferably 28 or lower, and most preferably 27 or lower. By using zeolites with a Si / Al2 molar ratio in such a specific range, the interaction between ammonia and the zeolite adsorption sites can be suitably controlled. From the viewpoint of separation performance for permeating ammonia from a mixed gas containing ammonia, it is preferable to use zeolites containing more Al because, as mentioned above, the acid sites of the Al element become ammonia adsorption sites. However, if the Al content is too high, the adsorption becomes strong and affects the permeability. Therefore, by using zeolites exhibiting the above Si / Al2 molar ratios, ammonia can be separated with high permeability and high selectivity. Furthermore, this is preferable because it can improve the density of the zeolite film as well as its durability, such as its resistance to chemical reactivity and heat resistance. The Si / Al2 molar ratio of the zeolite can be adjusted by the reaction conditions of the hydrothermal synthesis described later.

[0064] Examples of zeolite structures used in this invention, as defined by the International Zeolite Association (IZA), include ABW, ACO, AEI, AEN, AFI, AFT, AFX, ANA, ATN, ATT, ATV, AWO, AWW, BIK, CHA, DDR, DFT, EAB, EPI, ERI, ESV, GIS, GOO, ITE, JBW, KFI, LEV, LTA, MER, MON, MTF, OWE, PAU, PHI, RHO, RTE, RWR, SAS, SAT, SAV, SIV, TSC, UFI, VNI, YUG, AEL, AFO, AHT, DAC, FER, HEU, IMF, ITH, MEL, MFS, MWW, OBW, RRO, SFG, STI, SZR, TER, TON, TUN, WEI, MFI, MOR, FAU, and others. More preferably AEI, AFX, CHA, DDR, ERI, LEV, LTA, RHO, MOR, MFI, FAU, and even more preferably AEI, AFX, CHA, DDR, LTA, RHO, MOR, MFI, FAU, particularly preferably CHA, LTA, RHO, MOR, MFI, or FAU, especially preferably CHA, LTA, RHO or MFI, and most preferably RHO or MFI.

[0065] The preferred type of zeolite used to constitute the zeolite membrane in this invention is one having a pore structure with 10 or fewer oxygen rings, more preferably one having a pore structure with 8 or fewer oxygen rings, and may also have a pore structure with 6 oxygen rings. The smaller the oxygen ring size, the greater the effect of pore narrowing by the modification reaction, and the more likely a molecular sieving effect is to occur.

[0066] 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.

[0067] The oxygen n-membered ring structure determines the pore size of the zeolite. Zeolites with smaller oxygen n-membered rings have pore diameters smaller than the kinetic diameter of ammonia molecules, resulting in low permeability and potentially making them impractical. Therefore, zeolites with six or more oxygen n-membered rings are preferable.

[0068] Furthermore, the framework density of the zeolite film used in this invention is 19.5 T / nm 3 Zeolites with the following characteristics are preferred, and more preferably 19.0 T / nm 3 The zeolite is as follows, and more preferably 18.5T / nm 3 The zeolite is one of the following, and is particularly preferably CHA, RHO, or MFI, most preferably RHO or MFI. On the other hand, to achieve high separation performance, a higher framework density is preferable, typically 13.0 T / nm. 3 Preferably 14.0 T / nm 3 More preferably, 14.5 T / nm 3 The above, particularly preferred, is 15.0 T / nm 3 In particular, 16.0 T / nm is preferred. 3 In summary, the most preferred value is 17.0 T / nm. 3 Zeolites meeting the above criteria are preferred. A higher framework density makes it easier to obtain the effect of preventing the permeation of hydrogen and nitrogen by ammonia adsorbed on the zeolite.

[0069] Here, framework density (unit: T / nm) 3 ) refers to the unit volume (1 nm) of zeolite. 3 Framework density refers to the number of T atoms (atoms other than oxygen that make up the zeolite framework) present per unit area, and this value is determined by the structure of the zeolite. The relationship between framework density and zeolite structure is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Sixth Revised Edition 2007 ELSEVIER.

[0070] In the ammonia separation method of the present invention, the zeolite membrane exhibits a reduced effective pore size when ions in the zeolite are exchanged with monovalent ions with a large ionic radius. Conversely, when ions are exchanged with monovalent ions with a small ionic radius, the effective pore size becomes close to the pore size inherent in the zeolite structure. Furthermore, the permeation rate can be controlled by controlling the molecular adsorption performance.

[0071] Silylation treatment can also reduce the effective pore size of zeolites. For example, by silylation of the terminal silanols on the outer surface of a zeolite film and then stacking a silylated layer, the effective pore size of the pores facing the outer surface of the zeolite can be reduced.

[0072] The separation function of the zeolite membrane used in this invention is not particularly limited, but it is achieved by controlling the affinity and adsorption of gas molecules to the zeolite membrane by controlling the surface properties of the zeolite. In other words, by controlling the polarity of the zeolite, the adsorption of ammonia to the zeolite can be controlled, making it easier for the gas to permeate.

[0073] By substituting Si atoms in the zeolite framework with Al atoms, the polarity can be increased, allowing highly polar gas molecules such as ammonia to be actively adsorbed and permeated into the zeolite pores. Furthermore, the polarity of the resulting zeolite can be controlled by adding other atomic sources besides Al, such as Ga, Fe, B, Ti, Zr, Sn, and Zn, to the aqueous reaction mixture in hydrothermal synthesis.

[0074] (Zeolite membrane) In the present invention, a zeolite membrane is a membrane-like material composed of zeolite, preferably formed by crystallizing zeolite on the surface of a porous support. In addition to zeolite, the membrane may optionally contain inorganic binders such as silica and alumina, organic substances such as polymers, or silylation agents that modify the zeolite surface. The preferred zeolite to be included in the zeolite membrane used in the present invention is as described above, but the zeolite membrane may contain one type of zeolite or multiple types. In addition, zeolites that are easily formed in a multiphase, such as ANA, GIS, and MER, and amorphous components other than crystals may also be included.

[0075] The zeolite film used in the present invention may be a zeolite film characterized by having a molar ratio of nitrogen to Al, determined by X-ray photoelectron spectroscopy, of 0.01 or more and 4 or less. The zeolite film is preferably a zeolite film having a surface in which the molar ratio of nitrogen atoms to Al atoms, as determined by X-ray photoelectron spectroscopy (XPS), falls within a specific range. Here, the surface of the zeolite film as used herein refers to the surface of the zeolite film on the side to which the mixed gas containing ammonia is supplied for ammonia separation, and when the zeolite film composite is used in a form deposited on a porous support, it refers to the surface that is not in contact with the porous support. In this specification, the molar ratio of nitrogen atoms to Al atoms contained in the zeolite film is a value determined by X-ray photoelectron spectroscopy (XPS) under the following measurement conditions.

[0076] (Measurement conditions) X-ray source used for measurement: Monochromatic Al-Kα rays, output 16kV-34W Method for determining background during quantitative calculations: Shirley method

[0077] The zeolite membrane used in the present invention has a nitrogen atom content on its surface determined by the above-mentioned XPS measurement, which is typically 0.01 or more, preferably 0.05 or more, more preferably 0.10 or more, even more preferably 0.20 or more, particularly preferably 0.30 or more, and especially preferably 0.50 or more, relative to the Al atoms on the surface of the zeolite membrane, in molar ratio. The upper limit is not particularly limited as it depends on the structure of the nitrogen atom-containing cation species in the zeolite contained in the zeolite membrane and, if necessary, the amount of residual nitrate ions when the zeolite membrane is subjected to nitrate treatment, but is typically 4 or less, preferably 3 or less, and more preferably 1 or less. By using a zeolite having such a specific nitrogen atom / Al atom ratio surface composition, the density of the zeolite membrane and its durability, such as chemical reactivity resistance and heat resistance, can be improved, and ammonia can be separated from a mixed gas containing ammonia with high permeability and high selectivity. Here, the upper and lower limits are valid within the range of significant figures. In other words, "upper limit of 4 or less" means less than 4.5, while "0.01 or more" means 0.005 or more.

[0078] The nitrogen atoms contained in the zeolite membrane used in this invention are ammonium ions (NH4) contained in the zeolite, as described later. + These include nitrogen atoms derived from protonated cation species of organic amines having 1 to 20 carbon atoms, such as tetrapropylammonium ions, tetraethylammonium ions, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine; nitrogen atoms derived from organic templates (structure-correcting agents) containing nitrogen atoms when manufacturing zeolite films; and nitrogen atoms derived from nitrate ions remaining during nitrate treatment of zeolite films, which may be performed as needed as described later.

[0079] In this embodiment, further controlling the content of alkali metal atoms contained on the zeolite membrane surface, as determined by XPS measurement, to a specific range tends to improve ammonia permeability when separating ammonia from a mixed gas consisting of multiple components including ammonia, hydrogen, and / or nitrogen. Therefore, controlling their content as needed is one preferred embodiment. Examples of alkali metal atoms that can be present on the zeolite membrane surface as needed include Li, Na, K, Rb, Cs, and two or more of these metal atoms. Among these, Li, Na, and Cs are preferred, and Na is more preferred because it exhibits excellent ammonia separation performance and is a commonly used alkali metal. These alkali metal atoms exist in the form of cations as ion pairs at Al sites in the zeolite constituting the zeolite membrane, and are usually introduced into the zeolite by ion exchange treatment of the synthesized zeolite membrane, as described later. If alkali metal atoms are present on the zeolite film surface as needed, the content of alkali metal atoms is 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, even more preferably 0.04 or more, and particularly preferably 0.05 or more, relative to the Al atoms on the zeolite film surface, in molar ratio. The upper limit is usually 0.10 or less, preferably 0.070 or less, more preferably 0.065 or less, even more preferably 0.060 or less, and particularly preferably 0.055 or less. Controlling the alkali metal atom content within the above range tends to improve ammonia permeability while maintaining ammonia separation selectivity, which is preferable.

[0080] Furthermore, the zeolite film of the present invention is a zeolite film containing zeolite, and the molar ratio of alkali metal elements to Al elements, as determined by X-ray photoelectron spectroscopy, may be 0.01 or more and 0.070 or less. The zeolite film of the present invention is preferably a zeolite film having a surface in which the molar ratio of alkali metal atoms to Al atoms, as determined by X-ray photoelectron spectroscopy (XPS), falls within a specific range. In this specification, the molar ratio of alkali metal atoms to Al atoms contained in the zeolite film is a value determined by X-ray photoelectron spectroscopy (XPS) under the following measurement conditions.

[0081] In this embodiment, examples of alkali metal atoms contained on the zeolite film surface as determined by the above XPS measurement include Li, Na, K, Rb, Cs, and two or more of these metal atoms. Among these, Li, Na, and Cs are preferred, and Na is more preferred because it has excellent ammonia separation performance and is a general-purpose alkali metal. These alkali metal atoms exist in the form of cations as ion pairs at Al sites in the zeolite constituting the zeolite film, and are usually introduced into the zeolite by ion exchange treatment of the synthesized zeolite film, as will be described later.

[0082] In this embodiment, it is important to control the content of alkali metal atoms contained in the zeolite film surface as determined by the above XPS measurement. The content is 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, even more preferably 0.04 or more, and particularly preferably 0.05 or more, in molar ratio with respect to Al atoms on the zeolite film surface. The upper limit is usually 0.10 or less, preferably 0.070 or less, more preferably 0.065 or less, even more preferably 0.060 or less, and particularly preferably 0.055 or less. By controlling the content of alkali metal elements within the above range, it is possible to improve the permeability of ammonia while maintaining the separation selectivity of ammonia.

[0083] Furthermore, the zeolite membrane used in the present invention is a zeolite membrane composite for ammonia separation comprising a porous support and a zeolite membrane containing zeolite on its surface, wherein the rate of change of the thermal expansion coefficient of the zeolite at 300°C and 400°C relative to the thermal expansion coefficient at 30°C falls within a specific range. Specifically, the rate of change of the thermal expansion coefficient of the zeolite at 30°C relative to the thermal expansion coefficient at 30°C may be within ±0.25%, and the rate of change of the thermal expansion coefficient at 400°C relative to the thermal expansion coefficient at 30°C may be within ±0.35%. The thermal expansion coefficient defined for the zeolite in this embodiment is a value calculated under the following conditions. In this specification, a positive value for the thermal expansion coefficient indicates that the zeolite has expanded, and a negative value indicates that the zeolite has contracted.

[0084] (Method for measuring the rate of change in thermal expansion coefficient) In the present invention, the rate of change of the thermal expansion coefficient of zeolite at a predetermined temperature relative to the thermal expansion coefficient at 30°C can be determined by obtaining the crystallite constants measured at 30°C and the predetermined temperature using the heating XRD measurement method under the conditions shown in Tables 1 and 2 below, and then using the following formula (1).

[0085] (Specifications of the temperature-increasing XRD measurement device)

[0086] [Table 1]

[0087] (Measurement conditions)

[0088] [Table 2] Measurement atmosphere: Air Heating conditions: 20℃ / min Measurement method: XRD measurement is performed after holding the sample at the measurement temperature for 5 minutes. The measurement data is corrected for a fixed slit using a variable slit.

[0089] Change rate of thermal expansion coefficient = (Crystal lattice constant measured at a given temperature) ÷ (Crystal lattice constant measured at 30°C) - 1 ···(1)

[0090] The rate of change in the thermal expansion coefficient of the zeolite used in the present invention from the thermal expansion coefficient at 30°C to the thermal expansion coefficient at 30°C is, in absolute value, 0.25% or less, preferably 0.20% or less, more preferably 0.15% or less, particularly preferably 0.10% or less, and most preferably 0.05% or less. That is, the rate of change in the thermal expansion coefficient of the zeolite from the thermal expansion coefficient at 30°C to the thermal expansion coefficient at 30°C is within ±0.25%, preferably within ±0.20%, more preferably within ±0.15%, particularly preferably within ±0.10%, and most preferably within ±0.05%. On the other hand, the rate of change in the thermal expansion coefficient of zeolite at 400°C relative to the thermal expansion coefficient at 30°C is, in absolute value, 0.35% or less, preferably 0.30% or less, more preferably 0.25% or less, particularly preferably 0.20% or less, especially preferably 0.15% or less, and most preferably 0.10% or less. In other words, the rate of change in the thermal expansion coefficient of zeolite at 400°C relative to the thermal expansion coefficient at 30°C is within ±0.35%, preferably within ±0.30%, more preferably within ±0.25%, particularly preferably within ±0.20%, especially preferably within ±0.15%, and most preferably within ±0.10%.

[0091] This is thought to be because, although not yet fully understood and not particularly limited, even if the zeolite undergoes thermal contraction or expansion during the heating process, it moves favorably on the support without generating cracks, forming a dense zeolite membrane composite that exhibits high separation performance suitable for high-temperature conditions. Therefore, when stably separating ammonia under high-temperature conditions, a zeolite exhibiting nonlinear thermal expansion / contraction behavior during the heating process may be used. There are no particular restrictions on the zeolite used in this invention, but examples include RHO (DRCorbin.etaL.J.Am.Chem.Soc,112,4821-4830), MFI, AFI, and DDR (ParkS.H.etaL.Stud.Surf.Sci.Catal.1997,105,1989-1994).

[0092] Furthermore, the ratio of the change in the thermal expansion coefficient at 400°C to the change in the thermal expansion coefficient at 30°C to the change in the thermal expansion coefficient at 300°C of the zeolite in this embodiment is, in absolute value, usually 120% or less, preferably 115% or less, more preferably 110% or less, particularly preferably 105% or less, and most preferably 103% or less. A zeolite film composite formed on a porous support using a zeolite exhibiting such a specific ratio of the change in thermal expansion coefficient between specific temperatures can suppress the occurrence of grain boundary cracks due to local thermal expansion (contraction) of the zeolite, even when heterogeneous exothermic reaction occurs in the reactor in the initial stages of ammonia production, for example. Therefore, ammonia can be stably and efficiently separated to the permeate side with high permeability.

[0093] The zeolite membrane composite of this embodiment is preferable because, when prepared by attaching a zeolite with a rate of change of thermal expansion coefficient within a specific range as a seed crystal onto a porous support during membrane synthesis, it is often possible to stably separate ammonia with high selectivity even under high-temperature conditions. The rate of change of thermal expansion coefficient of the zeolite used as a seed crystal in the preparation of such a zeolite membrane composite is, as an absolute value of the rate of change of thermal expansion coefficient at 300°C relative to the thermal expansion coefficient at 30°C, 0.25% or less, preferably 0.20% or less, more preferably 0.15% or less, particularly preferably 0.10% or less, and most preferably 0.05% or less. On the other hand, the rate of change of thermal expansion coefficient at 400°C relative to the thermal expansion coefficient at 30°C is, as an absolute value, usually 0.30% or less, preferably 0.25% or less, more preferably 0.20% or less, particularly preferably 0.15% or less, and most preferably 0.10% or less.

[0094] The rate of change in the thermal expansion coefficient of the zeolite at a specific temperature, which is a characteristic of this embodiment, can be controlled by appropriately selecting the cation species of the zeolite used, as will be described later. For example, regarding the relationship between the cation species and thermal expansion coefficient of RHO-type zeolite, it is known that the thermal expansion coefficient changes depending on the cation species contained in the zeolite, as described in Chemical Communications, 2000, 2221-2222. Therefore, in order to obtain a zeolite membrane that stably separates ammonia with high selectivity even under the high-temperature conditions of this embodiment, it is particularly important to select a specific cation species among the RHO-type zeolites. On the other hand, regarding the thermal expansion coefficient of the MFI zeolite described in the examples of this embodiment, similar to the case of the RHO-type zeolite, a zeolite membrane exhibiting the characteristics of this embodiment can be manufactured by selecting an appropriate cation species in the zeolite. The cation species contained in the zeolite of this embodiment is preferably one that readily coordinates to the ion exchange sites of the zeolite, such as cation species selected from the elements of Groups 1, 2, 8, 9, 10, 11, and 12 of the periodic table, and NH4. +, and two or more of these cation species, more preferably cation species selected from the elements of Group 1 and Group 2 of the periodic table, NH4 + , as well as two or more of these cation species.

[0095] The thickness of the zeolite film used in the present invention is not particularly limited, but is usually 0.01 μm or more, preferably 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.7 μm or more, even more preferably 1.0 μm or more, and particularly preferably 1.5 μm or more. It is also usually 100 μm or less, preferably 60 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 5 μm or less. If the thickness of the zeolite film is above the lower limit, defects are less likely to occur, and separation performance tends to be good. Furthermore, if the thickness of the zeolite film is below the upper limit, permeability tends to improve, and in the high-temperature range, cracks are less likely to occur in the zeolite film as the temperature rises, thus suppressing the decrease in separation selectivity at high temperatures.

[0096] The average primary particle size of the zeolite forming the zeolite film is not particularly limited, but is usually 5 nm or larger, preferably 10 nm or larger, more preferably 20 nm or larger, and even more preferably 30 nm or larger, with its upper limit being less than or equal to the film thickness. If the average primary particle size of the zeolite is greater than or equal to the lower limit mentioned above, the grain boundaries of the zeolite can be made smaller, thus obtaining good separation selectivity. Therefore, it is most preferable that the average primary particle size of the zeolite is the same as the thickness of the zeolite film. In this case, the grain boundaries of the zeolite can be made the smallest. Zeolite films obtained by hydrothermal synthesis, which will be described later, are preferable because the particle size of the zeolite and the film thickness may be the same. In this invention, the average primary particle diameter is determined by measuring the primary particle diameter of 30 or more arbitrarily selected particles when observing the surface or fracture surface of the zeolite film of the present invention with a scanning electron microscope, and then calculating the average value.

[0097] The shape of the zeolite membrane is not particularly limited, and any shape can be adopted, such as tubular, hollow fiber, monolithic, or honeycomb. Furthermore, the size of the zeolite membrane is not particularly limited; for example, it can be formed as a zeolite membrane composite on a porous support of a size described later.

[0098] (Porous support) In the present invention, the zeolite film is preferably formed on the surface of a porous support. Preferably, the zeolite crystallizes in a film-like manner on the porous support.

[0099] The porous support used in the present invention preferably has chemical stability that allows zeolite to crystallize into a film on its surface. Suitable porous supports include gas-permeable porous polymers such as polysulfone, cellulose acetate, aromatic polyamide, vinylidene fluoride, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, polytetrafluoroethylene, and polyimide; ceramic sintered bodies such as silica, α-alumina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide; sintered metals such as iron, bronze, and stainless steel, and mesh-like molded bodies; and inorganic porous materials such as glass and carbon molded bodies. Among these, for porous supports used for ammonia separation in high-temperature regions, inorganic porous supports such as ceramic sintered bodies, metal sintered bodies, glass, and carbon molded bodies are preferred due to their excellent mechanical strength, deformation resistance, thermal stability, and reactivity resistance at high temperatures. The inorganic porous support is preferably made by sintering ceramics, which are solid materials whose basic components or the majority thereof are inorganic nonmetallic substances.

[0100] Preferred ceramic sintered bodies include, as mentioned above, ceramic sintered bodies containing α-alumina, γ-alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide, etc. These may be sintered bodies of a single material or mixed and sintered bodies of multiple materials. In these ceramic sintered bodies, a portion of the surface may become zeolite during zeolite film synthesis, which increases the adhesion between the porous support and the zeolite film, thereby improving the durability of the zeolite film composite. In particular, an inorganic porous support containing at least one of alumina, silica, and mullite is more preferable because it facilitates partial zeolization of the inorganic porous support, resulting in a strong bond between the inorganic porous support and the zeolite, and making it easier to form a dense zeolite film with high separation performance.

[0101] In the present invention, it is preferable that the porous support used has a surface (hereinafter also referred to as the "porous support surface") that causes the zeolite formed on the porous support to crystallize.

[0102] The porous support surface described above preferably has a controlled pore size. The average pore size of the porous support near the surface is usually 0.02 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, more preferably 0.15 μm or more, even more preferably 0.5 μm or more, particularly preferably 0.7 μm or more, most preferably 1.0 μm or more, and usually 20 μm or less, preferably 10 μm or less, even more preferably 5 μm or less, and especially preferably 2 μm or less. By using a porous support having a pore size within this range, a dense zeolite membrane can be formed that improves the separation selectivity of ammonia. The surface of the porous support is preferably smooth, and may be polished with sandpaper or the like if necessary.

[0103] In the present invention, the pore diameter of the porous support other than the area near the surface of the porous support is not limited and does not need to be particularly controlled, however the porosity of the other areas is usually 10% or more, preferably 20% or more, more preferably 30% or more, usually 60% or less, preferably 50% or less, and more preferably 40% or less. The porosity of the area other than the area near the surface of the porous support affects the permeate flow rate when separating gases and liquids, and if it is above the lower limit, the permeate tends to diffuse more easily, and if it is below the upper limit, it tends to prevent a decrease in the strength of the porous support. As a method of controlling the permeate flow rate, a porous support made by combining porous materials with different porosities in layers may be used.

[0104] The shape of the porous support used in this invention is not limited as long as it can effectively separate the mixed gas or liquid mixture. Specifically, examples include flat plates, tubular shapes, cylindrical shapes, honeycomb shapes with numerous through-holes, and monoliths. Furthermore, the size of the porous support is arbitrary and can be appropriately selected and adjusted to obtain the desired zeolite membrane composite. Among these, a tubular porous support may be preferred in some cases.

[0105] There are no particular restrictions on the length of the tubular porous support, but it is usually 2 cm or more, preferably 4 cm or more, more preferably 5 cm or more, even more preferably 8 cm or more, particularly preferably 10 cm or more, especially preferably 20 cm or more, most preferably 40 cm or more. On the other hand, it is usually 200 cm or less, preferably 150 cm or less, more preferably 130 cm or less, even more preferably 120 cm or less, particularly preferably 100 cm or less. When the length of the porous support is greater than or equal to the lower limit above, the amount of mixed gas separated per support can be increased, thereby reducing equipment costs. Furthermore, when it is less than or equal to the upper limit above, the manufacturing of the zeolite membrane composite can be simplified, and problems such as breakage due to vibration during use can be prevented.

[0106] The inner diameter of the tubular porous support is usually 0.1 cm or more, preferably 0.2 cm or more, more preferably 0.3 cm or more, particularly preferably 0.4 cm or more, and usually 2 cm or less, preferably 1.5 cm or less, more preferably 1.2 cm or less, particularly preferably 1.0 cm or less. The outer diameter is usually 0.2 cm or more, preferably 0.3 cm or more, more preferably 0.6 cm or more, particularly preferably 1.0 cm or more, and usually 2.5 cm or less, preferably 1.7 cm or less, more preferably 1.3 cm or less. The wall thickness of the tubular porous support is usually 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, even more preferably 0.7 mm or more, even more preferably 1.0 mm or more, particularly preferably 1.2 mm or more, and usually 4 mm or less, preferably 3 mm or less, more preferably 2 mm or less. If the inner diameter, outer diameter, and wall thickness of the tubular porous support are each above the lower limit values, the strength of the support can be improved and it can be made less prone to breakage. Furthermore, if the inner and outer diameters of the tubular support are below the above-mentioned upper limits, the size of the equipment required for ammonia separation can be reduced, which can be economically advantageous. Also, if the wall thickness of the tubular support is below the above-mentioned upper limits, the permeation performance tends to improve.

[0107] (Zeolite membrane complex) In the present invention, it is preferable to use a zeolite membrane composite comprising at least zeolite and a support. In the present invention, the zeolite membrane composite is a composite in which the zeolite is preferably crystallized and fixed in a membrane-like manner to the surface of the porous support described above, and in some cases, it is preferable that a portion of the zeolite is fixed into the interior of the support. As a zeolite membrane composite, for example, one in which zeolite is crystallized into a membrane on the surface of a porous support by hydrothermal synthesis is preferred.

[0108] The position of the zeolite membrane on the porous support is not particularly limited. When a tubular support is used, the zeolite membrane may be formed on the outer surface, the inner surface, or even on both sides depending on the system to which it is applied. It may also be formed by laminating it onto the surface of the support, or it may be crystallized to fill the pores in the surface layer of the support. In this case, it is important that there are no cracks or continuous micropores inside the crystallized membrane layer, and forming a so-called dense membrane is preferable in terms of improving separation performance.

[0109] Furthermore, there are no particular restrictions on the zeolite and support constituting the zeolite membrane composite, and it is preferable to use any combination of the above-mentioned zeolite and support. Among these, particularly preferred combinations of zeolite and porous support include MFI-type zeolite-porous alumina support, RHO-type zeolite-porous alumina support, DDR-type zeolite-porous alumina support, AFI-type zeolite-porous alumina support, CHA-type zeolite-porous alumina support, and AEI-type zeolite-porous alumina support. Preferably, the CHA-type zeolite-porous alumina support, MFI-type zeolite-porous alumina support, and RHO-type zeolite-porous alumina support are used, and more preferably, the MFI-type zeolite-porous alumina support and RHO-type zeolite-porous alumina support are used. In one embodiment of the present invention, preferably, an MFI-type zeolite-porous alumina support, a RHO-type zeolite-porous alumina support, and more preferably, an MFI-type zeolite-porous alumina support.

[0110] <Method for producing zeolite membrane composites> The method for forming the zeolite membrane composite that can be used in the present invention is not particularly limited as long as it is a method that can form the above-described zeolite membrane on a porous support, and can be manufactured by known methods. For example, any of the following methods can be used: (1) a method of crystallizing zeolite into a membrane on a support, (2) a method of fixing zeolite to a support with an inorganic binder or an organic binder, (3) a method of fixing a polymer in which zeolite is dispersed to a support, or (4) a method of fixing zeolite to a support by impregnating the support with a zeolite slurry and, in some cases by suction.

[0111] Among these methods, the method of crystallizing zeolite in a film-like manner on a porous support is particularly preferred. There are no particular restrictions on the crystallization method, but a preferred method is to place the support in a reaction mixture for hydrothermal synthesis used in zeolite production (hereinafter sometimes referred to as the "aqueous reaction mixture") and directly perform hydrothermal synthesis to crystallize the zeolite on the surface of the support. In this case, the zeolite membrane composite can be manufactured, for example, by adjusting the composition of a homogenized aqueous reaction mixture, sealing it in a heat-resistant and pressure-resistant container such as an autoclave containing a porous support, and heating it for a certain period of time.

[0112] The aqueous reaction mixture comprises a Si atom source, an Al atom source, an alkali source, and water, and optionally an organic template (structural modifier). To further enhance understanding of the manufacturing method of zeolite membrane composites, the manufacturing methods of RHO-type zeolite membrane composites and MFI-type zeolite membrane composites are described in detail below as representative examples. However, the zeolite membranes and manufacturing methods of the present invention are not limited to these.

[0113] (MFI-type zeolite membrane) The MFI-type zeolite used in the present invention refers to those having an MFI structure in the code that defines the structure of zeolite determined by the International Zeolite Association (IZA). The MFI-type zeolite has a structure characterized by three-dimensional pores composed of 10-membered oxygen rings with a diameter of 5.1×5.5 Å or 5.3×5.6 Å, and its structure is characterized by X-ray diffraction data. The framework density of the MFI-type zeolite used in the present invention is 17.9 T / 1000 Å 3 is. The framework density means the number of atoms other than oxygen that make up the framework per 1000 Å of zeolite, and this value is determined by the structure of the zeolite. The relationship between the framework density and the structure of the zeolite is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007 ELSEVIER. 3

[0114] <Method for Producing MFI-Type Zeolite Membrane> (Silicon Atom Source) Examples of the silicon (Si) atom source used in the aqueous reaction mixture include aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxides such as trimethylethoxysilane, tetraethyl orthosilicate, aluminosilicate gel, etc. Preferably, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxide, aluminosilicate gel are mentioned. These may be used alone or in combination of two or more.

[0115] The Si atom source is used so that the usage amounts of other raw materials with respect to the Si atom source are within the preferred ranges described above or below.

[0116] (Aluminum Atom Source) ​The aluminum (Al) atom source used in the production of porous support-MFI type zeolite membrane composites is not particularly limited, but examples include aluminosilicate zeolites, amorphous aluminum hydroxide, aluminum hydroxide with a gibbsite structure, aluminum hydroxide with a Bayerlite structure, aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, and aluminosilicate gel. Amorphous aluminum hydroxide, sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, and aluminosilicate gel are preferred, and amorphous aluminum hydroxide, sodium aluminate, and aluminosilicate gel are particularly preferred. These may be used individually or in combination of two or more.

[0117] The preferred range for the amount of aluminum atom source (including the aforementioned aluminosilicate zeolite and other aluminum atom sources) used relative to silicon (Si atoms) in the raw material mixture other than the seed crystal (Al atom / Si atom ratio) is, as a molar ratio, usually 0.001 or more, preferably 0.005 or more, more preferably 0.01 or more, even more preferably 0.015 or more, particularly preferably 0.02 or more, usually 1.0 or less, preferably 0.7 or less, more preferably 0.5 or less, even more preferably 0.4 or less, particularly preferably 0.35 or less, and most preferably 0.2 or less. By controlling the amount used within this range, it becomes easier to control the content of nitrogen atoms and alkali metal elements in the zeolite to the preferred range of the present invention. To increase the Al atom / Si atom ratio, the amount of silicon atom source used relative to the aluminum atom source should be reduced, while to decrease the ratio, the amount of silicon atom source used relative to the aluminum atom source should be increased.

[0118] Furthermore, the aqueous reaction mixture may contain other atomic sources in addition to the Si and Al sources, such as Ga, Fe, B, Ti, Zr, Sn, and Zn.

[0119] The type of alkali used as the alkali source is not particularly limited; alkali metal hydroxides and alkaline earth metal hydroxides can be used.

[0120] Specifically, examples of metal hydroxides that can be used include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide; and alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, strontium hydroxide, and barium hydroxide.

[0121] Furthermore, the hydroxide ions of the counteranions of the organic templates described below can be used as the alkali source for the aqueous reaction mixture.

[0122] In the crystallization of the zeolite according to the present invention, an organic template is not necessarily required. However, it is preferable to use an organic template (structure-controlling agent) of a type appropriate to each structure, as this increases the ratio of silicon atoms to aluminum atoms in the crystallized zeolite, thereby improving its crystallinity.

[0123] Any type of organic template is acceptable as long as it can form the desired zeolite film. Furthermore, one type of template or a combination of two or more types may be used.

[0124] The type of organic template suitable for the reaction depends on the zeolite structure to be synthesized; any organic template that yields the desired zeolite structure should be used. Specifically, for example, if an MFI structure is desired, tetrapropylammonium hydroxide may be used.

[0125] When the organic template is a cation, it is accompanied by anions that do not harm zeolite formation. A representative example of such anion is Cl - , Br - , I -These include halogen ions, hydroxide ions, acetates, sulfates, and carboxylates. Of these, hydroxide ions are particularly preferred, and in the case of hydroxide ions, they function as an alkali source as described above.

[0126] The ratio of Si atom source to organic template in the aqueous reaction mixture is the molar ratio of organic template to SiO2 (organic template / SiO2 ratio), which is usually 0.005 or higher, preferably 0.01 or higher, more preferably 0.02 or higher, particularly preferably 0.05 or higher, and especially preferably 0.1 or higher, and usually 1 or lower, preferably 0.5 or lower, more preferably 0.3 or lower, particularly preferably 0.25 or lower, and especially preferably 0.2 or lower. When the organic template / SiO2 ratio of the aqueous reaction mixture is within this range, a dense zeolite film can be formed, and a zeolite with excellent acid resistance and low Al elimination can be obtained. Furthermore, under these conditions, a particularly dense and acid-resistant MFI-type aluminosilicate zeolite can be formed.

[0127] By using an appropriate amount of alkali metal atom source, the organic structure-determining agent described later can be more easily coordinated to aluminum, thereby facilitating the formation of a crystalline structure. The molar ratio R / Si of alkali metal atom source (R) to silicon (Si) contained in the hydrothermal synthesis raw material mixture other than the seed crystal is usually 0.01 or higher, preferably 0.1 or higher, more preferably 0.2 or higher, even more preferably 0.3 or higher, particularly preferably 0.4 or higher, more preferably 0.5 or higher, usually 1.0 or lower, preferably 0.8 or lower, more preferably 0.7 or lower, even more preferably 0.6 or lower, and particularly preferably 0.55 or lower.

[0128] If the molar ratio of alkali metal atoms to silicon (R / Si) is greater than the upper limit mentioned above, the resulting zeolite may dissolve easily, resulting in no zeolite being obtained or a significantly low yield. If R / Si is less than the lower limit mentioned above, the raw material Al and Si atoms may not dissolve sufficiently, resulting in an inability to obtain a uniform mixture of raw materials for hydrothermal synthesis, and making it difficult to produce MFI-type zeolite.

[0129] (Amount of water) The amount of water in the raw material mixture for hydrothermal synthesis is usually 10 or more, preferably 20 or more, more preferably 40 or more, even more preferably 50 or more, most preferably 60 or more, and most preferably 70 or more, in terms of molar ratio to silicon (Si) contained in the raw material mixture other than the seed crystal. It is usually 500 moles or less, preferably 300 or less, more preferably 200 or less, even more preferably 150 or less, and most preferably 100 or less. If it is greater than the above upper limit, the reaction mixture may be too dilute, making it difficult to form a dense film without defects. If it is less than 10, the reaction mixture is too concentrated, which may lead to the formation of spontaneous nuclei, inhibiting the growth of MFI-type zeolite from the support and making it difficult to form a dense film.

[0130] (seed crystal) In the present invention, a seed crystal may be used as one component of the raw material (raw material compound) for producing "zeolite". While it is not always necessary to include seed crystals in the reaction system during hydrothermal synthesis, their presence can promote the crystallization of zeolite on a porous support. The method for including seed crystals in the reaction system is not particularly limited; methods such as adding seed crystals to an aqueous reaction mixture, as in the synthesis of powdered zeolite, or pre-attaching seed crystals to the support can be used. However, in this invention, pre-attaching seed crystals to the support is preferable. Pre-attaching seed crystals to the support facilitates the formation of a dense zeolite film with high separation performance.

[0131] Any type of zeolite that promotes crystallization can be used as the seed crystal, but to ensure efficient crystallization, it is preferable that the seed crystal be of the same crystal type as the zeolite film to be formed. For example, when forming an MFI-type aluminosilicate zeolite film, it is preferable to use an MFI-type zeolite seed crystal.

[0132] If the seed crystal contains an organic structural modifier within the zeolite pores, it may be used as is (uncalcined). The presence of the organic structural modifier within the zeolite pores prevents the alkaline hydrothermal raw material solution from penetrating the zeolite pores, thereby slowing down the dissolution rate of the seed crystal. On the other hand, if the solubility of the seed crystal is to be accelerated, the organic structural modifier can be removed by calcination, or even partially by calcination. Depending on the synthesis conditions of the zeolite film, it is preferable to use calcined or uncalcined seed crystals.

[0133] The particle size of the seed crystal is preferably close to the pore size of the support, and may be crushed as needed. The particle size is usually 1 nm or larger, preferably 10 nm or larger, more preferably 50 nm or larger, even more preferably 0.1 μm or larger, particularly preferably 0.5 μm or larger, especially preferably 0.7 μm or larger, most preferably 0.8 μm or larger, usually 5 μm or smaller, preferably 3 μm or smaller, more preferably 2 μm or smaller, most preferably 1.5 μm or smaller, particularly preferably 1.2 μm or smaller. Depending on the pore size of the support material, a smaller seed crystal particle size may be preferable, and the seed crystal may be crushed as needed. 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 5 μm or smaller, preferably 3 μm or smaller, more preferably 2 μm or smaller.

[0134] The method for attaching seed crystals to the support 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 support is immersed in the dispersion to attach the seed crystals to the surface. A suction method can be used, in which seed crystals are dispersed in a solvent such as water, and the support, sealed at one end, is immersed in the dispersion, and then the support is sucked from the other end to firmly attach the seed crystals to the surface of the support. Another method is to mix seed crystals with a solvent such as water to form a slurry, which is then applied to the support. To control the amount of seed crystals attached and to produce a zeolite film with good reproducibility, the dipping method and the suction method are preferable. To ensure that the seed crystals adhere closely to the support, the method of applying seed crystals in slurry and the suction method are preferable. Furthermore, for the purpose of ensuring that the seed crystals adhere closely to the support and / or to remove excess seed crystals, it is also preferable to rub and press the support to which the seed crystals have adhered using fingers wearing latex gloves after the dipping method or the suction method.

[0135] The solvent used to disperse the seed crystals is not particularly limited, but water and alkaline aqueous solutions are particularly preferred. The type of alkaline aqueous solution is not particularly limited, but sodium hydroxide aqueous solution and potassium hydroxide aqueous solution are preferred. These alkaline species may also be mixed. The alkali concentration of the alkaline aqueous solution is not particularly limited, but is usually 0.0001 mol% or more, preferably 0.0002 mol% or more, more preferably 0.001 mol% or more, and even more preferably 0.002 mol% or more. It is also usually 1 mol% or less, preferably 0.8 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.2 mol% or less.

[0136] The solvent used to disperse the seed crystals is not particularly limited, but water is particularly preferred. The amount of seed crystals to be dispersed is not particularly limited, and is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.12% by mass or more, even more preferably 0.15% by mass or more, particularly preferably 0.18% by mass or more, and most preferably 0.2% by mass or more, relative to the total weight of the dispersion. Alternatively, it is usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, particularly preferably 1% by mass or less, especially preferably 0.5% by mass or less, and most preferably 0.3% by mass or less.

[0137] If the amount of dispersed seed crystals is too small, the amount of seed crystals adhering to the support will be small, potentially resulting in areas where zeolite does not form on the support during hydrothermal synthesis, leading to a defective film. On the other hand, for example, the amount of seed crystals adhering to a porous support by the dip method becomes almost constant once the amount of seed crystals in the dispersion exceeds a certain level. Therefore, if the amount of seed crystals in the dispersion is too large, a lot of seed crystals will be wasted, which is disadvantageous in terms of cost.

[0138] It is desirable to attach seed crystals to the support by dipping, suction, or slurry application, and then form a zeolite film after drying. The drying temperature is usually 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, and usually 200°C or lower, preferably 180°C or lower, more preferably 150°C or lower. The drying time is not a problem as long as it is sufficiently dry, but is usually 10 minutes or more, preferably 30 minutes or more, and there is no particular upper limit, but from an economic standpoint it is usually 5 hours or less.

[0139] For the dried support to which the seed crystals are attached, it is also preferable to rub and press the support to which the seed crystals are attached using fingers wearing latex gloves, in order to make the seed crystals adhere to the support and / or to remove excess seed crystals.

[0140] The amount of seed crystals to be pre-attached to the porous support is not particularly limited, and the film-forming surface of the porous support is 1 m 2The mass per unit is typically 0.1g or more, preferably 0.3g or more, more preferably 0.5g or more, even more preferably 0.80g or more, most preferably 1.0g or more, and typically 50g or less, preferably 20g or less, more preferably 10g or less, even more preferably 5g or less, most preferably 3g or less.

[0141] If the amount of seed crystals attached is below the lower limit mentioned above, crystal formation becomes difficult, and film growth tends to be insufficient or uneven. Conversely, if the amount of seed crystals exceeds the upper limit mentioned above, surface irregularities may be amplified by the seed crystals, or spontaneous nuclei may grow more easily due to seed crystals falling from the support, inhibiting film growth on the support. In either case, it tends to become difficult to form a dense zeolite film.

[0142] When forming a zeolite film on a porous support by hydrothermal synthesis, there are no particular restrictions on the method of immobilizing the support; it can be placed vertically, horizontally, or in any other configuration. In this case, the zeolite film may be formed by static methods, or it may be formed under stirring of an aqueous reaction mixture.

[0143] Hydrothermal synthesis is carried out by placing a support bearing the seed crystal as described above, along with the prepared hydrothermal synthesis mixture or the aqueous gel obtained by maturing it, into a pressure-resistant container, and maintaining a predetermined temperature under self-generated pressure or under gas pressure that does not inhibit crystallization, while stirring, rotating or oscillating the container, or in a static state. Hydrothermal synthesis in a static state is desirable because it does not inhibit crystal growth from the seed crystal on the support.

[0144] The reaction temperature for forming a zeolite film by hydrothermal synthesis is not particularly limited and should be any temperature suitable for obtaining a film with the desired zeolite structure. However, it is usually 100°C or higher, preferably 120°C or higher, more preferably 140°C or higher, especially preferably 150°C or higher, particularly preferably 160°C or higher, and most preferably 170°C or higher, and usually 200°C or lower, preferably 195°C or lower, more preferably 190°C or lower, and particularly preferably 185°C or lower. If the reaction temperature is too low, the zeolite may not crystallize easily. Also, if the reaction temperature is too high, a type of zeolite different from the desired zeolite may be easily produced.

[0145] The heating (reaction) time for forming a zeolite film by hydrothermal synthesis is not particularly limited and should be any time suitable for obtaining a film with the desired zeolite structure. However, it is usually 3 hours or more, preferably 5 hours or more, more preferably 8 hours or more, particularly preferably 9 hours or more, particularly preferably 10 hours or more, and usually 10 days or less, preferably 5 days or less, more preferably 1 day or less, even more preferably 18 hours or less, particularly preferably 15 days or less. If the reaction time is too short, the zeolite may not crystallize easily. If the reaction time is too long, a type of zeolite different from the desired zeolite may be easily formed.

[0146] The pressure during hydrothermal synthesis is not particularly limited; the self-sustaining pressure generated when the aqueous reaction mixture in a sealed container is heated to the above-mentioned temperature range is sufficient. Furthermore, an inert gas such as nitrogen may be added if necessary.

[0147] The zeolite membrane composite obtained by hydrothermal synthesis is washed with water, then heat-treated and dried. Here, heat treatment means drying the zeolite membrane composite by applying heat, and if an organic template is used, removing the organic template by calcination.

[0148] The heat treatment temperature, when intended for drying, is usually 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, usually 200°C or lower, preferably 150°C or lower. The heat treatment temperature, when intended for calcination removal of the organic template, is usually 350°C or higher, preferably 400°C or higher, more preferably 450°C or higher, even more preferably 500°C or higher, usually 900°C or lower, preferably 800°C or lower, even more preferably 700°C or lower, and particularly preferably 600°C or lower.

[0149] When the purpose is to remove the organic template by calcination, if the heat treatment temperature is too low, the proportion of the organic template tends to increase, reducing the pore size of the zeolite and potentially decreasing the permeability when used for ammonia separation. If the heat treatment temperature is too high, the difference in thermal expansion coefficients between the support and the zeolite becomes large, which can easily cause cracks in the zeolite film, leading to a loss of density and reduced separation performance. When using tetrapropylammonium hydroxide as the organic template, the nitrogen atom content in the zeolite can be controlled by adjusting the heat treatment temperature.

[0150] The heating time is not particularly limited as long as the zeolite film is sufficiently dried and the organic template is removed by firing. When the purpose is drying, it is preferably 0.5 hours or more, more preferably 1 hour or more. When the purpose is to remove the organic template by firing, it varies depending on the heating rate and cooling rate, but is preferably 1 hour or more, more preferably 5 hours or more. The upper limit of the heating time is not particularly limited, but is usually 200 hours or less, preferably 150 hours or less, and more preferably 100 hours or less.

[0151] When the purpose is to fire a template, the heat treatment can be carried out in an air atmosphere, but it may also be carried out in an atmosphere with an inert gas such as nitrogen or oxygen added.

[0152] When hydrothermal synthesis is performed in the presence of an organic template, it is appropriate to remove the organic template from the resulting zeolite membrane composite by washing it with water, and then, for example, by heat treatment or extraction, preferably by the heat treatment described above, i.e., calcination.

[0153] When performing a heat treatment for the purpose of removing organic templates by firing, it is desirable to keep the heating rate as slow as possible to prevent cracking in the zeolite film due to the difference in thermal expansion coefficients between the porous support 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, particularly preferably 0.5°C / min or less, and most preferably 0.3°C / min or less. The lower limit of the heating rate is usually 0.1°C / min or more, taking workability into consideration.

[0154] Furthermore, in heat treatment aimed at removing organic templates by firing, the cooling rate after heat treatment must also be controlled to avoid cracking of the zeolite film, and like the heating rate, the slower the cooling rate, 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, particularly preferably 0.5°C / min or less, and most preferably 0.3°C / min or less. The lower limit of the cooling rate is usually 0.1°C / min or more, considering workability.

[0155] (RHO-type zeolite membrane) In this invention, the RHO-type zeolite refers to a zeolite with an RHO structure, as defined by the International Zeolite Association (IZA) in its structural code. RHO-type zeolites are characterized by a three-dimensional pore consisting of an 8-membered oxygen ring with a diameter of 3.6 × 3.6 Å, and this structure is characterized by X-ray diffraction data. The framework density of the RHO-type zeolite used in this invention is 14.1T / 1000Å. 3 Framework density is defined as 1000 Å of zeolite. 3It means the number of atoms that constitute the framework other than oxygen around, and this value is determined by the structure of the zeolite. The relationship between the framework density and the structure of the zeolite is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007 ELSEVIER.

[0156] <Method for Producing RHO-Type Zeolite Membrane> (Silicon atom source) The silicon (Si) atom source used in the aqueous reaction mixture is not particularly limited. Examples thereof include aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxide such as trimethylethoxysilane, tetraethyl orthosilicate, aluminosilicate gel, etc. Preferably, aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxide, aluminosilicate gel are mentioned. These may be used alone or in combination of two or more.

[0157] The Si atom source is used so that the usage amounts of other raw materials with respect to the Si atom source are within the preferred ranges described above or below.

[0158] (Aluminum atom source) The aluminum (Al) atom source used in the production of porous support-RHO type zeolite membrane composites is not particularly limited, but examples include aluminosilicate zeolite, amorphous aluminum hydroxide, aluminum hydroxide with a gibbsite structure, aluminum hydroxide with a Bayerlite structure, aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, and aluminosilicate gel. Aluminosilicate zeolite, amorphous aluminum hydroxide, sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, and aluminosilicate gel are preferred, and aluminosilicate zeolite, amorphous aluminum hydroxide, sodium aluminate, and aluminosilicate gel are particularly preferred. These may be used individually or in combination of two or more.

[0159] Aluminosilicate zeolite may be used alone or in a mixture of two or more types. When aluminosilicate zeolite is used as an Al atom source, it is preferable that 50% or more by mass of the total Al atom source, particularly 70-100% by mass, and especially 90-100% by mass, be the aforementioned aluminosilicate zeolite. Similarly, when aluminosilicate zeolite is used as a Si atom source, it is preferable that 50% or more by mass of the total Si atom source, particularly 70-100% by mass, and especially 90-100% by mass, be the aforementioned aluminosilicate zeolite. When the proportion of aluminosilicate zeolite is within this range, the Si atom / Al atom molar ratio of the RHO-type zeolite film becomes high, resulting in a zeolite film with excellent acid and water resistance and a wide range of applications.

[0160] The preferred range for the amount of Al atom source (including the aforementioned aluminosilicate zeolite and other Al atom sources) used relative to silicon (Si atoms) in the raw material mixture other than the seed crystal (Al atom / Si atom ratio) is usually 0.001 or higher, preferably 0.002 or higher, more preferably 0.004 or higher, even more preferably 0.006 or higher, and usually 1.0 or lower, preferably 0.5 or lower, more preferably 0.2 or lower, and even more preferably 0.1 or lower. By controlling the amount used within this range, it becomes easier to control the content of nitrogen atoms and alkali metal elements in the zeolite to the preferred range of the present invention. Furthermore, in order to increase the Al atom / Si atom ratio, the amount of silicon atom source used relative to the aluminum atom source should be reduced, while in order to decrease the ratio, the amount of silicon atom source used relative to the aluminum atom source should be increased.

[0161] Furthermore, in the zeolite film used in this invention, if the Al atom / Si atom ratio is greater than 1.0, the resulting RHO-type zeolite film may have low water resistance and acid resistance, limiting its applications as a zeolite film. If the Al atom / Si atom ratio is less than 0.001, it may be difficult to obtain an RHO-type zeolite film.

[0162] Furthermore, the aqueous reaction mixture may contain other atomic sources in addition to the silicon and aluminum atomic sources, such as gallium (Ga), iron (Fe), boron (B), titanium (Ti), zirconium (Zr), tin (Sn), and zinc (Zn).

[0163] The type of alkali used as the alkali source is not particularly limited; alkali metal hydroxides and alkaline earth metal hydroxides can be used.

[0164] The metal species of these metal hydroxides are typically sodium (Na), potassium (K), lithium (Li), rubidium (Rb), cesium (Cs), calcium (Ca), magnesium (Mg), strontium (Sr), and barium (Ba), preferably Na, K, and Cs, more preferably Na and Cs. Furthermore, two or more metal species of metal oxides may be used in combination; specifically, the combination of Na and Cs is preferred. Specifically, examples of metal hydroxides that can be used include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide; and alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, strontium hydroxide, and barium hydroxide.

[0165] Furthermore, the hydroxide ions of the counteranions of the organic templates described below can be used as the alkali source for the aqueous reaction mixture.

[0166] In the crystallization of the zeolite according to the present invention, an organic template (structure-determining agent) is not necessarily required. However, it is preferable to use an organic template because using an organic template of a type appropriate to each structure increases the ratio of silicon atoms to aluminum atoms in the crystallized zeolite, thereby improving its crystallinity.

[0167] Any type of organic template is acceptable as long as it can form the desired zeolite film. Furthermore, one type of template or a combination of two or more types may be used.

[0168] The type of organic template suitable for the reaction depends on the zeolite structure to be synthesized; any organic template that yields the desired zeolite structure should be used. Specifically, for example, if the RHO structure is desired, 18-crown-6-ether may be used.

[0169] When the organic template is a cation, it is accompanied by anions that do not harm zeolite formation. A representative example of such anion is Cl - , Br - , I - These include halogen ions, hydroxide ions, acetates, sulfates, and carboxylates. Of these, hydroxide ions are particularly preferred, and in the case of hydroxide ions, they function as an alkali source as described above.

[0170] The ratio of Si atom source to organic template in the aqueous reaction mixture, expressed as the molar ratio of organic template to SiO2 (organic template / SiO2 ratio), is typically 0.005 or higher, preferably 0.01 or higher, more preferably 0.02 or higher, even more preferably 0.05 or higher, particularly preferably 0.08 or higher, most preferably 0.1 or higher, and typically 1 or lower, preferably 0.5 or lower, more preferably 0.4 or lower, even more preferably 0.35 or lower, particularly preferably 0.30 or lower, most preferably 0.25 or lower. When the organic template / SiO2 ratio of the aqueous reaction mixture is within this range, a dense zeolite film can be formed, and a zeolite with excellent acid resistance and in which Al atoms are less likely to be removed can be obtained. Furthermore, under these conditions, a particularly dense and acid-resistant RHO-type aluminosilicate zeolite can be formed.

[0171] By using an appropriate amount of alkali metal atom source, the organic structure-determining agent described later can be more easily coordinated to aluminum in a suitable state, thereby facilitating the formation of a crystalline structure. The molar ratio (R / Si atoms) of alkali metal atom source (R) to silicon (Si atoms) contained in the mixture of hydrothermal synthesis raw materials other than seed crystals is usually 0.1 or more, preferably 0.15 or more, more preferably 0.20 or more, even more preferably 0.25 or more, particularly preferably 0.30 or more, especially preferably 0.35 or more, and usually 2.0 or less, preferably 1.5 or less, more preferably 1.0 or less, even more preferably 0.8 or less, particularly preferably 0.6 or less, and most preferably 0.5 or less.

[0172] If the molar ratio of alkali metal atoms to silicon (R / Si atoms) is greater than the upper limit mentioned above, the resulting zeolite may dissolve easily, resulting in no zeolite being obtained or a significantly low yield. If the R / Si atom ratio is smaller than the lower limit mentioned above, the raw material Al and Si atoms may not dissolve sufficiently, resulting in an inability to obtain a uniform mixture of raw materials for hydrothermal synthesis, and making it difficult to produce RHO-type zeolite.

[0173] (Amount of water) The amount of water in the hydrothermal synthesis raw material mixture is usually 10 or more, preferably 20 or more, more preferably 30 or more, even more preferably 40 or more, and particularly preferably 50 or more, in terms of molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystal, and is usually 200 or less, preferably 150 or less, more preferably 100 or less, even more preferably 80 or less, and particularly preferably 60 or less. If it is greater than the above upper limit, the reaction mixture may be too dilute, making it difficult to form a dense film without defects. If it is less than 10, the reaction mixture is too concentrated, which may lead to the formation of spontaneous nuclei, inhibiting the growth of RHO-type zeolite from the support and making it difficult to form a dense film.

[0174] (seed crystal) In the present invention, a seed crystal may be used as one component of the raw material (raw material compound) for producing "zeolite". While it is not always necessary to include seed crystals in the reaction system during hydrothermal synthesis, their presence can promote the crystallization of zeolite on a porous support. The method for including seed crystals in the reaction system is not particularly limited; methods such as adding seed crystals to an aqueous reaction mixture, as in the synthesis of powdered zeolite, or pre-attaching seed crystals to the support can be used. However, in this invention, pre-attaching seed crystals to the support is preferable. Pre-attaching seed crystals to the support facilitates the formation of a dense zeolite film with high separation performance.

[0175] Any type of zeolite that promotes crystallization can be used as the seed crystal, but to ensure efficient crystallization, it is preferable that the seed crystal be of the same crystal type as the zeolite film to be formed. For example, when forming a zeolite film of RHO-type aluminosilicate, it is preferable to use a seed crystal of RHO-type zeolite.

[0176] The particle size of the seed crystal is preferably close to the pore size of the support, and may be crushed as needed. The particle size is usually 20 nm or larger, preferably 50 nm or larger, more preferably 100 nm or larger, even more preferably 0.15 μm or larger, particularly preferably 0.5 μm or larger, most preferably 0.7 μm or larger, and usually 5 μm or smaller, preferably 3 μm or smaller, more preferably 2 μm or smaller, particularly preferably 1.5 μm or smaller. Depending on the pore size of the support material, a smaller seed crystal particle size may be preferable, and the seed crystal may be crushed as needed. The particle size of the seed crystal is usually 5 nm or larger, preferably 10 nm or larger, more preferably 20 nm or larger, and usually 5 μm or smaller, preferably 3 μm or smaller, more preferably 2 μm or smaller.

[0177] The method for attaching seed crystals to the support 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 support is immersed in the dispersion to attach the seed crystals to the surface. A suction method can be used, in which seed crystals are dispersed in a solvent such as water, and the support, sealed at one end, is immersed in the dispersion, and then the support is sucked from the other end to firmly attach the seed crystals to the surface of the support. Another method is to mix seed crystals with a solvent such as water to form a slurry, which is then applied to the support. To control the amount of seed crystals attached and to produce a zeolite film with good reproducibility, the dipping method and the suction method are preferable. To ensure that the seed crystals adhere closely to the support, the method of applying seed crystals in slurry and the suction method are preferable. Furthermore, for the purpose of ensuring that the seed crystals adhere closely to the support and / or to remove excess seed crystals, it is also preferable to rub and press the support to which the seed crystals have adhered using fingers wearing latex gloves after the dipping method or the suction method.

[0178] The solvent used to disperse the seed crystals is not particularly limited, but water and alkaline aqueous solutions are particularly preferred. The type of alkaline aqueous solution is not particularly limited, but sodium hydroxide aqueous solution and potassium hydroxide aqueous solution are preferred. These alkaline species may also be mixed. The alkali concentration of the alkaline aqueous solution is not particularly limited, but is usually 0.0001 mol% or more, preferably 0.0002 mol% or more, more preferably 0.001 mol% or more, and even more preferably 0.002 mol% or more. It is also usually 1 mol% or less, preferably 0.8 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.2 mol% or less.

[0179] The solvent used to disperse the seed crystals is not particularly limited, but water is particularly preferred. The amount of seed crystals dispersed is not particularly limited, but is usually 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and most preferably 3.0% by mass or more, relative to the total weight of the dispersion. It is also usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less.

[0180] If the amount of dispersed seed crystals is too small, the amount of seed crystals adhering to the support will be small, potentially resulting in areas where zeolite does not form on the support during hydrothermal synthesis, leading to a defective film. On the other hand, for example, the amount of seed crystals adhering to a porous support by the dip method becomes almost constant once the amount of seed crystals in the dispersion exceeds a certain level. Therefore, if the amount of seed crystals in the dispersion is too large, a lot of seed crystals will be wasted, which is disadvantageous in terms of cost.

[0181] It is desirable to attach seed crystals to the support by dipping, suction, or slurry application, and then form a zeolite film after drying. The drying temperature is usually 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, and usually 200°C or lower, preferably 180°C or lower, more preferably 150°C or lower. The drying time is not a problem as long as it is sufficiently dry, but is usually 10 minutes or more, preferably 30 minutes or more, and there is no particular upper limit, but from an economic standpoint it is usually 5 hours or less.

[0182] For the dried support to which the seed crystals are attached, it is also preferable to rub and press the support to which the seed crystals are attached using fingers wearing latex gloves, in order to make the seed crystals adhere to the support and / or to remove excess seed crystals.

[0183] The amount of seed crystals to be pre-attached to the porous support is not particularly limited, and the film-forming surface of the porous support is 1 m 2 The mass per unit is usually 0.1g or more, preferably 0.3g or more, more preferably 0.5g or more, even more preferably 0.8g or more, and most preferably 1.0g or more, and usually 100g or less, preferably 50g or less, more preferably 10g or less, even more preferably 8g or less, and most preferably 5g or less.

[0184] If the amount of seed crystals attached is below the lower limit mentioned above, crystal formation becomes difficult, and film growth tends to be insufficient or uneven. Conversely, if the amount of seed crystals exceeds the upper limit mentioned above, surface irregularities may be amplified by the seed crystals, or spontaneous nuclei may grow more easily due to seed crystals falling from the support, inhibiting film growth on the support. In either case, it tends to become difficult to form a dense zeolite film.

[0185] When forming a zeolite film on a porous support by hydrothermal synthesis, there are no particular restrictions on the method of immobilizing the support; it can be placed vertically, horizontally, or in any other configuration. In this case, the zeolite film may be formed by static methods, or it may be formed under stirring of an aqueous reaction mixture.

[0186] Hydrothermal synthesis is carried out by placing a support bearing the seed crystal as described above, along with the prepared hydrothermal synthesis mixture or the aqueous gel obtained by maturing it, into a pressure-resistant container, and maintaining a predetermined temperature under self-generated pressure or under gas pressure that does not inhibit crystallization, while stirring, rotating or oscillating the container, or in a static state. Hydrothermal synthesis in a static state is desirable because it does not inhibit crystal growth from the seed crystal on the support.

[0187] The reaction temperature for forming a zeolite film by hydrothermal synthesis is not particularly limited and should be any temperature suitable for obtaining a film with the desired zeolite structure. However, it is usually 100°C or higher, preferably 110°C or higher, more preferably 120°C or higher, particularly preferably 130°C or higher, especially preferably 140°C or higher, most preferably 150°C or higher, and usually 200°C or lower, preferably 190°C or lower, more preferably 180°C or lower, and even more preferably 170°C or lower. If the reaction temperature is too low, the zeolite may not crystallize easily. Also, if the reaction temperature is too high, a type of zeolite different from the desired zeolite may be easily produced.

[0188] The heating (reaction) time for forming a zeolite film by hydrothermal synthesis is not particularly limited and should be any time suitable for obtaining a film with the desired zeolite structure. However, it is usually 3 hours or more, preferably 8 hours or more, more preferably 12 hours or more, and especially preferably 15 hours or more. It is usually 10 days or less, preferably 5 days or less, more preferably 3 days or less, even more preferably 2 days or less, and especially preferably 1.5 days or less. If the reaction time is too short, the zeolite may not crystallize easily. If the reaction time is too long, a type of zeolite different from the desired zeolite may be easily formed.

[0189] The pressure during hydrothermal synthesis is not particularly limited; the self-sustaining pressure generated when the aqueous reaction mixture in a sealed container is heated to the above-mentioned temperature range is sufficient. Furthermore, an inert gas such as nitrogen may be added if necessary.

[0190] The density of the zeolite membrane can also be improved by repeating the hydrothermal synthesis multiple times. When repeating the hydrothermal synthesis multiple times, the zeolite membrane composite obtained in the first hydrothermal synthesis should be washed with water, heated and dried, and then immersed again in a newly prepared aqueous reaction mixture for hydrothermal synthesis. It is not always necessary to wash or dry the zeolite membrane composite obtained after the first hydrothermal synthesis, but washing and drying it will help maintain the composition of the aqueous reaction mixture to the intended composition. When synthesizing multiple times, the number of synthesis steps is usually two or more, usually 10 or less, preferably 5 or less, and more preferably 3 or less. Washing with water may be repeated once or multiple times.

[0191] The zeolite membrane composite obtained by hydrothermal synthesis is washed with water, then heat-treated and dried. Here, heat treatment means drying the zeolite membrane composite by applying heat, and if an organic template is used, removing the organic template by calcination.

[0192] The heat treatment temperature, when intended for drying, is usually 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, usually 200°C or lower, preferably 150°C or lower. The heat treatment temperature, when intended for calcination removal of the organic template, is usually 250°C or higher, preferably 300°C or higher, more preferably 350°C or higher, even more preferably 400°C or higher, usually 800°C or lower, preferably 600°C or lower, even more preferably 550°C or lower, and particularly preferably 500°C or lower.

[0193] When the purpose is to remove the organic template by calcination, if the heat treatment temperature is too low, the proportion of the organic template tends to remain high, reducing the pore size of the zeolite and potentially decreasing the permeability when used for ammonia separation. If the heat treatment temperature is too high, the difference in thermal expansion coefficients between the support and the zeolite becomes large, which can make the zeolite film more prone to cracking, leading to a loss of density in the zeolite film and a decrease in separation performance.

[0194] The heating time is not particularly limited as long as the zeolite film is sufficiently dried and the organic template is removed by firing. When the purpose is drying, it is preferably 0.5 hours or more, more preferably 1 hour or more. When the purpose is to remove the organic template by firing, it varies depending on the heating rate and cooling rate, but is preferably 1 hour or more, more preferably 5 hours or more. The upper limit of the heating time is not particularly limited, but is usually 200 hours or less, preferably 150 hours or less, and more preferably 100 hours or less.

[0195] When the purpose is to fire a template, the heat treatment can be carried out in an air atmosphere, but it may also be carried out in an atmosphere with an inert gas such as nitrogen or oxygen added.

[0196] When hydrothermal synthesis is performed in the presence of an organic template, it is appropriate to remove the organic template from the resulting zeolite membrane composite by washing it with water, and then, for example, by heat treatment or extraction, preferably by the heat treatment described above, i.e., calcination.

[0197] When performing a heat treatment for the purpose of removing organic templates by firing, it is desirable to keep the heating rate as slow as possible to prevent cracking of the zeolite film due to the difference in thermal expansion coefficients between the porous support 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, even more preferably 0.5°C / min or less, and particularly preferably 0.3°C / min or less. The lower limit of the heating rate is usually 0.1°C / min or more, taking workability into consideration.

[0198] Furthermore, in heat treatments aimed at removing organic templates by firing, the cooling rate after the heat treatment must also be controlled to avoid cracking of the zeolite film, and like the heating rate, the slower the cooling rate, 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, even more preferably 0.5°C / min or less, and particularly preferably 0.3°C / min or less. The lower limit of the cooling rate is usually 0.1°C / min or more, taking workability into consideration.

[0199] (Ion exchange) The synthesized zeolite membrane may be subjected to ion exchange as needed. Since the thermal expansion characteristics of the zeolite and the thermal stability of ammonia separation are greatly influenced by the cation species in the zeolite, this ion exchange is an important control method. Furthermore, the ammonia permeability and / or separation performance of the zeolite membrane may be improved depending on the cation species used. In other words, the cation species used in this invention are appropriately selected while taking into account the ammonia permeability and separation performance, while ensuring the thermal expansion characteristics of the zeolite and the thermal stability of ammonia separation as described above.

[0200] Ion exchange is usually performed after removing the organic template when synthesizing a zeolite membrane using an organic template. In this invention, NH4 is used as the ion to be exchanged in order to increase the nitrogen content on the surface of the zeolite membrane. + Preferably, any of the protonated cation species of organic amines having 1 to 20 carbon atoms, such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine, are used. In addition, protons and Na are also preferred. + , K + Li + , Rb + , Cs + Alkali metal ions such as Ca 2+ Mg 2+ Sr 2+ Ba 2+ Alkaline earth metal ions such as those listed above, as well as transition metal ions such as Fe, Cu, Zn, Ga, and La, may be present in the same environment. Among these, protons and NH4 + kaNa + Li + , Cs +Fe ions, Ga ions, and La ions are preferred. Multiple types of these ions may be present in the zeolite, and this method of mixing the ions is suitably employed to balance the thermal expansion characteristics and ammonia permeability of the zeolite. By controlling the cation species that undergo ion exchange and their amounts in this way, it is possible to control the ammonia affinity of the zeolite and the effective pore size within the zeolite pores, thereby improving the separation selectivity of ammonia and increasing the ammonia permeation rate. Among these, NH4 is an ion species that improves the separation selectivity of ammonia. + Preferably, the protonated cation species of organic amines having 1 to 20 carbon atoms, such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine, are preferred, among which NH4 + For the reasons mentioned above, cation species in which amines with small molecular sizes, such as organic amines with 1 to 6 carbon atoms, are protonated are more preferred, and among them, NH4 is particularly preferred. + This is preferable. On the other hand, as ion species that improve the ammonia permeation rate, protons and Na are preferred. + Li + , Cs + Fe ions, Ga ions, and La ions are preferred, and Na + Li + , Cs + Ions are particularly preferred, Na + It is most preferable to have ions coexisting. In this invention, the molar ratio of nitrogen atoms to Al atoms in the zeolite film can be controlled by adjusting the amount of ion exchange, which requires ion species containing nitrogen atoms.

[0201] Furthermore, in this invention, Na is added to the zeolite. +When ions are contained, the content is usually 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, still more preferably 0.04 or more, particularly preferably 0.05 or more, in terms of molar ratio with respect to Al atoms in the zeolite. The upper limit is not particularly limited, but is usually 0.10 or less, preferably 0.070 or less, more preferably 0.065 or less, still more preferably 0.060 or less, particularly preferably 0.055 or less. Zeolites with a Na + / Al atomic ratio within such a specific range can be used to separate ammonia from a mixed gas composed of a plurality of components including ammonia, hydrogen and / or nitrogen with a high permeability.

[0202] Ion exchange can be carried out by treating the zeolite membrane after firing (such as when an organic template is used) with nitrates, sulfates, phosphates, organic acid salts, hydroxides of the above-mentioned cations, as well as halogen salts of Cl and Br, and in some cases acids such as hydrochloric acid, usually at a temperature from room temperature to 100 °C, followed by washing with water or hot water washing with hot water at 40 °C to 100 °C. The solvent used for the ion exchange treatment may be water or an organic solvent as long as the salt for the ion exchange dissolves. The concentration of the salt to be treated is usually 10 mol / L or less, and the lower limit is 0.1 mol / L or more, preferably 0.5 mol / L or more, more preferably 1 mol / L or more. These treatment conditions may be appropriately set according to the salt and solvent species used. When using an acid such as hydrochloric acid, since the acid may destroy the crystal structure of the zeolite, usually the concentration of the acid to be treated is set to 5 mol / L or less, and the temperature and time may be appropriately set. Also, since the ion exchange rate increases by performing the ion exchange treatment repeatedly, the number of times of the ion exchange treatment is not particularly limited, and the treatment may be repeated until the desired effect is obtained. Furthermore, since the remaining substances derived from the ion exchange treatment raw material may exist in the zeolite pores after the ion exchange treatment and hinder the gas permeability of the ion-exchanged zeolite membrane, if necessary, the remaining substances after the ion exchange treatment may be removed by firing at 200 to 500 °C.

[0203] (Nitrate treatment) In certain embodiments of the zeolite membrane composite used in the present invention, as a method for adjusting the nitrogen atom content in the zeolite membrane, it is preferable to use nitrate treatment in combination. Therefore, nitrate treatment will be described below.

[0204] In the zeolite membrane composite used in the present invention, the synthesized zeolite membrane may be subjected to nitrate treatment as necessary. The nitrate treatment may be carried out in a state containing an organic template or after removing the organic template by firing. The nitrate treatment is performed by immersing the zeolite membrane composite in a solution containing, for example, nitrate. This may be preferable because the nitrate can block the fine defects present on the membrane surface. Further, when nitrate is present in the zeolite pores, it has the effect of improving the affinity of the zeolite membrane with ammonia and is preferably adopted as a method for improving the ammonia permeability. The solvent used for the nitrate treatment may be water or an organic solvent as long as the salt dissolves, and there is no limitation on the nitrate used. For example, magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate, gallium nitrate, indium nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, zinc nitrate, etc. may be mentioned. These may be used alone or in combination of two or more. Among these, magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate, gallium nitrate, indium nitrate are more preferable, and among them, magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate are even more preferable. Particularly, aluminum nitrate is preferable because it has a remarkable effect of blocking the fine defects present on the zeolite membrane surface and increases the ammonia separation performance. The concentration of nitrate is usually 10 mol / L or less, and the lower limit is 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. The treatment temperature is usually from room temperature to 150 °C or less, and the treatment may be carried out for about 10 minutes to 48 hours. These treatment conditions may be appropriately set according to the nitrate and solvent species used. The zeolite membrane after nitrate treatment may be washed with water, and by repeating the water washing, the nitrogen atom content of the zeolite membrane can be adjusted to a preferable range.

[0205] (Aluminum salt treatment) In the zeolite membrane composite used in the present invention, the synthesized zeolite membrane may be subjected to aluminum salt treatment as needed. The aluminum salt treatment may be performed while the organic template is still present, or after the organic template has been removed by calcination. The aluminum salt treatment is carried out by immersing the zeolite membrane composite, for example, in a solution containing aluminum salt. This may result in the aluminum salt sealing fine defects present on the membrane surface. Furthermore, if aluminum salt is present in the zeolite pores, it has the effect of attracting ammonia, and is therefore a suitable method for improving ammonia permeability. The solvent used for the aluminum salt treatment may be water or an organic solvent as long as the salt dissolves, and there are no restrictions on the aluminum salt used, but examples include aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum acetate, aluminum carbonate, and aluminum hydroxide. These may be used individually or in mixtures of two or more. The concentration of the aluminum salt is usually 10 mol / L or less, with a lower limit of 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. The processing temperature is usually from room temperature to 150°C or less, and the processing can be carried out for 10 minutes to 48 hours. These processing conditions can be appropriately set depending on the aluminum salt and solvent used. The zeolite film after aluminum salt treatment may be washed with water, and the Al atom content of the zeolite film can be adjusted by repeating the washing process. To increase the Si atom / Al atom ratio of the present invention, it is preferable to reduce the concentration and amount of aluminum salt to be treated, or to increase the number of washes after aluminum salt treatment. On the other hand, to decrease the ratio, it is preferable to increase the concentration and amount of aluminum salt to be treated, or to decrease the number of washes after aluminum salt treatment.

[0206] (Silylation treatment) In the zeolite membrane composite used in the present invention, the synthesized zeolite membrane may be subjected to silylation treatment as needed. Silylation treatment is carried out by immersing the zeolite membrane composite in a solution containing, for example, a Si compound. This modifies the surface of the zeolite membrane with the Si compound, making it possible to give it specific physicochemical properties. For example, by reliably forming a layer containing a large amount of Si-OH on the surface of the zeolite membrane, the polarity of the membrane surface can be improved, and the separation performance of polar molecules can be improved. In addition, modifying the surface of the zeolite membrane with the Si compound may have the effect of sealing fine defects present on the membrane surface. Furthermore, the pore size of the zeolite can be controlled by silylation treatment, and a method of improving the separation selectivity of ammonia by performing this treatment is also suitably employed.

[0207] The solvent used for the silylation treatment may be water or an organic solvent. The solution may also be acidic or basic, in which case the silylation reaction is catalyzed by the acid or base. There are no restrictions on the silylation agent used, but alkoxysilanes are preferred. The treatment temperature is usually from room temperature to 150°C or below, and the treatment can be carried out for about 10 minutes to 30 hours. These treatment conditions can be appropriately set depending on the silylation agent and solvent used.

[0208] In the zeolite membrane composite used in the present invention, the nitrogen atom content contained on the surface of the zeolite membrane can be controlled by, as described above, selecting a cation species containing nitrogen atoms in the zeolite contained in the zeolite membrane to adjust the Al atom / Si atom ratio of the zeolite, adjusting the nitrogen atom content by adjusting the amount of ion exchange by the ion exchange method, using an organic template (structure-determining agent) containing nitrogen atoms when manufacturing the zeolite membrane as needed and adjusting the amount added, the heating temperature and heating time when removing the organic template by calcination, treating the zeolite membrane with nitrate, adjusting the number of water washes when washing the nitric acid-treated zeolite membrane with water, and combining these methods as appropriate. The Al atom content in the zeolite film surface of the zeolite film composite used in the present invention can be controlled as described above by adjusting the Al atom / Si atom ratio in the zeolite contained in the zeolite film, treating the zeolite film with an aluminum salt, adjusting the number of water washes when washing the aluminum salt-treated zeolite film with water, and by appropriately combining these methods.

[0209] The zeolite membrane composite produced in this manner possesses excellent properties and can be suitably used as a membrane separation method for ammonia from a mixed gas in the present invention. [Examples]

[0210] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples unless it exceeds its gist. The various manufacturing conditions and evaluation result values ​​in the following examples are meant as preferred upper or lower limits in embodiments of the present invention, and the preferred range may be defined by a combination of the upper or lower limit value and the values ​​in the following examples or between examples. In the following, "RHO-type silicate zeolite" will be simply referred to as "RHO-type zeolite," and "MFI-type silicate zeolite" will be simply referred to as "MFI-type zeolite."

[0211] [Measurement of separation performance] The separation performance of the zeolite membrane composite was measured as follows:

[0212] (1) Ammonia separation test An ammonia separation test was performed in the apparatus schematically shown in Figure 5 as follows. In Figure 5, the cylindrical zeolite membrane composite 1 is housed in a stainless steel pressure vessel 2 and placed in a constant temperature bath (not shown). The constant temperature bath is equipped with a temperature control device to allow temperature adjustment of the sample gas. The tip of the support of the cylindrical zeolite membrane composite 1 is sealed with a sealing part (circular end pin) 3. The other end is connected by a joint 4, and the other end of the joint 4 is connected to the pressure vessel 2. The inside of the cylindrical zeolite membrane composite and a pipe (permeate gas recovery pipe) 11 for discharging permeate gas 8 are connected via the joint 4, and the permeate gas recovery pipe 11 extends to the outside of the pressure vessel 2. In addition, a pipe (sweep gas supply pipe) 12 for supplying sweep gas 9 is inserted into the zeolite membrane composite 1 via the permeate gas recovery pipe 11. Furthermore, a pressure gauge 5 for measuring the pressure on the supply side of the sample gas, and a back pressure valve 6 for controlling the discharge of the impermeable gas 10 from the pressure vessel 2 and adjusting the pressure on the supply side are connected to one of the points leading to the pressure vessel 2. Each connection is airtight. In the apparatus shown in Figure 5, a mixed gas containing ammonia gas (NH3), nitrogen gas (N2), and hydrogen (H2) with adjusted flow rates was supplied as the supply gas between the pressure vessel 2 and the zeolite membrane composite 1. The back pressure valve 6 was adjusted so that the pressure difference between the supply gas 7 and the permeate gas 8 that had permeated through the membrane remained constant. The exhaust gas 8 discharged from the piping 11 was analyzed using a microgas chromatograph to calculate the concentration and flow rate of the permeate gas. In the test where the permeate side was reduced to below atmospheric pressure, a vacuum pump (not shown) was installed in the exhaust gas 8 line, and the permeate side of the membrane was evaluated at below atmospheric pressure. The gas linear velocity inside the pressure vessel 2 was calculated by subtracting the cross-sectional area of ​​the zeolite membrane composite (the area obtained by cutting the zeolite membrane composite 1 perpendicular to the direction from the joint 4 to the sealing part 3) from the cross-sectional area of ​​the pressure vessel 2 (the area obtained by cutting the pressure vessel 2 perpendicular to the direction from the joint 4 to the sealing part 3) and dividing this result by the flow rate of the mixed gas.

[0213] In the ammonia separation test, to remove moisture and air from the pressure vessel 2, the sample gas was purged to dry and evacuate at a temperature above the measurement temperature. After purging, the sample gas temperature and the differential pressure between the supply gas 7 and permeate gas 8 sides of the zeolite membrane composite were kept constant. After the permeate gas flow rate stabilized, the flow rate of the sample gas (permeate gas) 8 that permeated through the zeolite membrane composite 1 was measured. From the measured value, the gas permeance [mol / (m³] was calculated. 2 (·s·Pa) or flux [mol / (m³)] 2 The following values ​​(s) were calculated. The pressure used when calculating these permeance and flux values ​​was the pressure difference (differential pressure) between the supply side and the permeate side of supply gas 7. In the case of mixed gases, the partial pressure difference was used. The permeance ratio for each gas was determined by calculating the permeance of each gas and then deriving the ratio from that calculation.

[0214] [Measurement of Si / Al molar ratio] The Si / Al molar ratio of the zeolite film described in the manufacturing example was measured under the following conditions. EDS mapping analysis conditions Detector: XFlash 6 / 60 (Bruker) Measurement software: Esprit 2.3 (Bruker) Measurement conditions • Magnification = 1200x, 3500x (Field of view: 107x80, 37x27μm) Image resolution = 512 x 384 pixels Acceleration voltage = 6.0 kV • WD (Working Distance) = 10 ± 1 mm • Spot intensity = 50 • Pulse throughput = 60 kcps (per detector element; 4 elements are used for analysis) • Total time = 180s EDS Object Analysis Conditions Detector: XFlash 6 / 60 (Bruker) Measurement software: Esprit 2.3 (Bruker) Measurement conditions ·Measurement magnification = 6000 times (observation field of view: 21×16 μm) ·Image resolution = 512×384 pixels ·Acceleration voltage = 6.0 kV ·WD (working distance) = 10±1 mm ·Spot intensity = 50 ·Pulse throughput = 60 kcps ·Integration time = 180 s Object analysis conditions Analysis software: Esprit 2.3 (Bruker) Method: Object analysis Map display settings ·EDS calibration: Calibrated to satisfy 10 Kcps in the Cu-Kα line when using a copper standard at an acceleration voltage of 15 kV. ·Method: Quantitative analysis (Phi-Rho-Z method) SAR calculation formula = (atomic number concentration of Si) / {(atomic number concentration of Al) / 2}

[0215] [Production Example A1: Production of MFI-type zeolite membrane composite 1] (Raw material mixture for hydrothermal synthesis) The raw material mixture for hydrothermal synthesis was prepared by the following method. 4.4 g of NaOH (granular, manufactured by Wako) and 266 g of water were mixed, and 0.75 g of sodium aluminate (containing 62.2 mass% Al2O3) was added thereto, followed by stirring at room temperature. 34 g of colloidal silica (Snowtech-40, manufactured by Nissan Chemical Industries, Ltd.) was added thereto, and the mixture was stirred at 50 °C for 4 hours to obtain a raw material mixture for hydrothermal reaction. The composition (molar ratio) of this reaction raw material mixture was SiO2 / Al2O3 / NaOH / H2O = 1.0 / 0.02 / 0.54 / 70.

[0216] (Porous support) As the porous support, an alumina tube (outer diameter 12 mm, inner diameter 9 mm, tubular) manufactured by Iwao Porcelain Industry Co., Ltd. with a length of 8 cm was washed with running deionized water and then dried before use.

[0217] (Seed crystal dispersion) A seed crystal dispersion was prepared by grinding MFI-type zeolite in a mortar and pestle, and then dispersing the seed crystals in water to a concentration of 0.2% by mass.

[0218] (Manufacturing of membrane composites) One end of the porous support was sealed tightly, and the other end was subjected to internal suction using a vacuum pump. The support was then immersed in the aforementioned seed crystal dispersion for 5 seconds, and dried at 100°C for more than 2 hours to allow the seed crystals to adhere to it. Subsequently, the seed crystals attached to the support surface were fixed to the support surface by the rubbing method, and any unwanted seed crystals were removed. Three porous supports with attached seed crystals were prepared using this method. The mass of the attached seed crystals was approximately 0.004 to 0.005 g. Three porous supports with seed crystals attached were immersed vertically in a Teflon® inner cylinder containing the above-mentioned hydrothermal synthesis raw material mixture. The autoclave was sealed, and the temperature was raised from room temperature to 160°C for 3 hours, then from 160°C to 180°C for 2 hours, followed by 15 hours of standing heating under self-synthesis pressure. After the predetermined time had elapsed, the porous support-zeolite membrane composite was allowed to cool, removed from the reaction mixture, washed with desalinated water, and dried at 100°C for more than 2 hours to obtain MFI-type zeolite membrane composite 1. The mass of the MFI-type zeolite crystallized on the porous support was 0.09 to 0.10 g, and the air permeability was 0.0 to 0.1 ml / min. The Si / Al2 molar ratio measured by irradiating the zeolite layer with an electron beam from the fracture surface of the obtained zeolite membrane composite was 19.

[0219] [Manufacturing Example A2: Manufacturing of MFI-type zeolite membrane composite 2] (Raw material mixture for hydrothermal synthesis) A mixture of raw materials for hydrothermal synthesis was prepared by the following method. 3.0 g of NaOH (Wako, granular) and 250 g of water were mixed, and 0.5 g of sodium aluminate (containing Al2O3-62% by mass) was added and the mixture was stirred at room temperature. 47 g of colloidal silica (Nissan Chemical, Snowtec-XS) was added to this mixture and stirred at 50°C for 4 hours to obtain a hydrothermal reaction raw material mixture. The composition (molar ratio) of this reaction raw material mixture was SiO2 / Al2O3 / NaOH / H2O = 1.0 / 0.02 / 0.54 / 70.

[0220] (Porous support) As the porous support, we used an 8cm alumina tube (outer diameter 12mm, inner diameter 9mm, tubular) manufactured by Iwao Porcelain Industry Co., Ltd., which was washed with desalinated water and then dried.

[0221] (Seed crystal dispersion) MFI-type zeolite was calcined at 500°C for 6 hours under air circulation to remove the organic structural regulator from the zeolite. The calcined MFI-type zeolite was then ground in a mortar and pestle to prepare a seed crystal dispersion. This seed crystal dispersion was then dispersed in water to a concentration of 0.2% by mass.

[0222] (Manufacturing of membrane composites) One end of the porous support was sealed, and the other end was subjected to internal suction using a vacuum pump. The support was then immersed in the aforementioned seed crystal dispersion for 5 seconds, and dried at 100°C for more than 2 hours to allow the seed crystals to adhere to it. Subsequently, the seed crystals attached to the support surface were fixed to the support surface by the rubbing method, and any unwanted seed crystals were removed. Three porous supports with attached seed crystals were prepared using this method. The mass of the attached seed crystals was approximately 0.002 to 0.005 g. Three porous supports with seed crystals attached were each immersed vertically in a Teflon® inner cylinder containing the above-mentioned hydrothermal synthesis raw material mixture. The autoclave was sealed, and the temperature was raised from room temperature to 160°C for 3 hours, then from 160°C to 180°C for 2 hours, followed by 15 hours of standing heating under self-synthesis pressure. After the predetermined time had elapsed, the porous support-zeolite membrane composite was allowed to cool, removed from the reaction mixture, washed with desalinated water, and dried at 100°C for more than 2 hours to obtain MFI-type zeolite membrane composite 1. The mass of the MFI-type zeolite crystallized on the porous support was 0.06 to 0.09 g, and the air permeability was 0.0 to 0.2 ml / min. The Si / Al2 molar ratio measured by irradiating the zeolite layer with an electron beam from the fracture surface of the obtained zeolite membrane composite was 26.

[0223] [Manufacturing Example A3: Manufacturing of MFI-type zeolite membrane composite 3] (Raw material mixture for hydrothermal synthesis) A mixture of raw materials for hydrothermal synthesis was prepared by the following method. 2.9 g of NaOH (Wako, granular) and 250 g of water were mixed, and 0.52 g of sodium aluminate (containing Al2O3 - 62.2% by mass) was added and the mixture was stirred at room temperature. 47 g of colloidal silica (Nissan Chemical, Snowtec-XS) was added to this mixture and stirred at 50°C for 4 hours to obtain a hydrothermal reaction raw material mixture. The composition (molar ratio) of this reaction raw material mixture was SiO2 / Al2O3 / NaOH / H2O = 1.0 / 0.02 / 0.54 / 100.

[0224] (Porous support) As the porous support, we used an 8cm alumina tube (outer diameter 12mm, inner diameter 9mm, tubular) manufactured by Iwao Porcelain Industry Co., Ltd., which was washed with desalinated water and then dried.

[0225] (Seed crystal dispersion) A seed crystal dispersion was prepared by grinding MFI-type zeolite in a mortar and pestle, and then dispersing the seed crystals in water to a concentration of 0.2% by mass.

[0226] (Manufacturing of membrane composites) One end of the porous support was sealed tightly, and the other end was subjected to internal suction using a vacuum pump. The support was then immersed in the seed crystal dispersion described above for 5 seconds, and dried at 100°C for more than 2 hours to allow the seed crystals to adhere to the porous support. Subsequently, the seed crystals attached to the support surface were fixed to the support surface by the rubbing method, and any unwanted seed crystals were removed. Three porous supports with attached seed crystals were prepared using this method. The mass of the attached seed crystals was approximately 0.003 to 0.004 g. Three porous supports with seed crystals attached were each immersed vertically in a Teflon® inner cylinder containing the above-mentioned hydrothermal synthesis raw material mixture. The autoclave was then sealed and heated in a constant temperature bath from room temperature to 160°C for 3 hours, then from 160°C to 180°C for 2 hours, and finally left to stand for 15 hours under self-synthesis pressure. After the predetermined time had elapsed, the porous support-zeolite membrane composite was allowed to cool, removed from the reaction mixture, washed with desalinated water, and dried at 100°C for more than 2 hours to obtain MFI-type zeolite membrane composite 3. The mass of the MFI-type zeolite crystallized on the porous support was 0.06-0.07 g, and the air permeability was 0.0-0.2 ml / min. The Si / Al2 molar ratio measured by irradiating the zeolite layer with an electron beam from the fracture surface of the obtained zeolite membrane composite was 26.

[0227] [Manufacturing Example B1: Manufacturing of CHA-type zeolite membrane composite 1] (Raw material mixture for hydrothermal synthesis) The composition (molar ratio) of the reaction raw material mixture was SiO2 / Al2O3 / NaOH / KOH / H2O / TMADAOH* = 1.0 / 0.014 / 0.02 / 0.08 / 95 / 0.04. *N,N,N-trimethyl-1-adamantanammonium hydroxide is referred to as "TMADAOH".

[0228] (Porous support) As the porous support, we used an 8cm alumina tube (outer diameter 12mm, inner diameter 9mm, tubular) manufactured by Iwao Porcelain Industry Co., Ltd., which was washed with desalinated water and then dried.

[0229] (Seed crystal dispersion) CHA-type zeolite was calcined at 500°C for 6 hours under air circulation to remove the organic structural regulator from the zeolite. The calcined CHA-type zeolite was then ground in a mortar and pestle to prepare a seed crystal dispersion. This seed crystal dispersion was then dispersed in water to a concentration of 0.1% by mass.

[0230] (Manufacturing of membrane composites) One end of the porous support was sealed tightly, and the other end was subjected to internal suction using a vacuum pump. The support was then immersed in the aforementioned seed crystal dispersion for 5 seconds, and dried at 100°C for more than 2 hours to allow the seed crystals to adhere to the porous support. Subsequently, the seed crystals attached to the support surface were fixed to the support surface by the rubbing method, and any unwanted seed crystals were removed. A porous support with seed crystals attached was immersed vertically in a Teflon® inner cylinder containing the above-mentioned hydrothermal synthesis raw material mixture. The autoclave was sealed, and the temperature was raised from room temperature to 180°C over 2 hours in a constant temperature bath. After that, it was left to stand for 18 hours and heated under self-synthesis pressure. After the predetermined time had elapsed, the porous support-zeolite membrane composite was allowed to cool, removed from the reaction mixture, washed with desalinated water, dried at 100°C for more than 2 hours, and then calcined to remove the organic structure-regulating material to obtain CHA-type zeolite membrane composite 1. The Si / Al2 molar ratio measured by irradiating the zeolite layer with an electron beam from the fracture surface of the obtained zeolite membrane composite was 54.

[0231] [Examples 1-13, Comparative Examples 1-8] <Evaluation of membrane separation performance> Using MFI-type zeolite membrane composite 1, MFI-type zeolite membrane composite 2, MFI-type zeolite membrane composite 3, and CHA-type zeolite membrane composite 1, an ammonia separation test from a mixed gas of ammonia / hydrogen / nitrogen was performed using the apparatus shown in Figure 5.

[0232] The conditions used for the separation evaluation in Examples 1-13 and Comparative Examples 1-8 are as follows, and the specific conditions are shown in Table 3. Supply gas pressure: 0.1 MPaA ~ 5.1 MPaA Permeated gas pressure: Atmospheric pressure, below atmospheric pressure (20 kPa) Separation temperature: 30℃~200℃ Ammonia concentration of the gas supplied to the zeolite membrane: 2-20% by volume

[0233] [Table 3]

[0234] Table 3 shows the results of calculating the ammonia flux, ammonia permeance (NH3 permeability), ammonia / hydrogen permeance ratio (NH3 / H2 separation coefficient), and ammonia / nitrogen permeance ratio (NH3 / N2 separation coefficient) from the gas composition and permeation rate of the obtained permeated and non-permeated gases.

[0235] As shown in Example 1 and Comparative Example 1, or Example 2 and Comparative Example 2, or Example 3 and Comparative Example 4, it was found that when the permeatement side of the zeolite membrane is depressurized under the same conditions of supply gas pressure, temperature, and ammonia concentration, the ammonia flux, ammonia permience, ammonia / hydrogen permience ratio (NH3 / H2 separation coefficient), and ammonia / nitrogen permience ratio (NH3 / N2 separation coefficient) are greatly improved.

[0236] When the supply gas pressure is constant, reducing the pressure on the permeate side of the membrane to below atmospheric pressure increases the pressure difference by 0.1 MPa compared to when the permeate side is at atmospheric pressure. Therefore, by adjusting the supply gas pressure so that the pressure difference between the supply gas and the permeate gas (hereinafter referred to as "pressure difference") is the same in both the case where the permeate side is at atmospheric pressure and the case where the pressure is reduced, the effect of reducing the pressure on the permeate side of the membrane to below atmospheric pressure can be clarified. In Comparative Example 2, the membrane performance was evaluated with a supply gas pressure of 1.1 MPaA and the permeate side at atmospheric pressure (differential pressure of 1.0 MPa). In Comparative Example 3, the supply gas pressure was 1.2 MPaA and the permeate side at atmospheric pressure (differential pressure of 1.1 MPa). In Example 2, the supply gas pressure was 1.1 MPaA and the permeate side was reduced pressure (differential pressure of 1.1 MPa). From Comparative Examples 2 and 3, it was found that increasing the pressure difference slightly improved the ammonia flux, but the ammonia permeance, the ammonia / hydrogen permeance ratio (NH3 / H2 separation coefficient), and the ammonia / nitrogen permeance ratio (NH3 / N2 separation coefficient) decreased. Surprisingly, in Example 2, where the permeate side of the membrane was set below atmospheric pressure, a significant improvement in membrane performance was obtained despite having the same pressure difference as Comparative Example 3. From this, it can be seen that reducing the pressure on the permeate side of the membrane to below atmospheric pressure has a different effect than simply increasing the pressure difference by 0.1 MPa. Normally, increasing the supply pressure increases the pressure difference, which is the driving force, and improves the ammonia flux. However, since ammonia exhibits separation selectivity through the adsorption / desorption mechanism to zeolite, the ammonia strongly adsorbs to the adsorption sites on the zeolite, reducing permeance and consequently decreasing separation selectivity. However, it has been found that the present invention, which involves reducing the pressure on the permeate side of the membrane to below atmospheric pressure, has the effect of promoting the desorption of ammonia adsorbed on the zeolite. In other words, in the conventional method of increasing the ammonia flux by increasing the pressure of the supply gas, the desorption of adsorbed ammonia becomes the rate-limiting step, and membrane performance other than the ammonia flux does not improve. However, by reducing the pressure on the permeate side of the membrane and promoting the desorption of ammonia, it was possible to obtain an improvement in membrane performance that would not normally be considered possible.

[0237] This mechanism can also be considered from the membrane separation temperature results of Comparative Example 5 and Example 4, for example. In Comparative Example 5, at a low separation temperature of 30°C, ammonia was strongly adsorbed at the zeolite adsorption site, resulting in a slow desorption rate, which is thought to have led to poor ammonia separation and permeation performance. However, in Example 4, by reducing the pressure on the permeation side of the membrane to promote the desorption of ammonia, which was the rate-limiting step, high ammonia separation and permeation performance was obtained.

[0238] Next, it can be seen that the improvement in membrane performance obtained by reducing the permeation side of the membrane of the present invention to below atmospheric pressure depends on the pressure of the gas supplied to the membrane. For example, from Example 4 and Comparative Example 2, where the supply gas pressure is 1.1 MPaA, and Example 3 and Comparative Example 4, where the supply gas pressure is 5.1 MPaA, the effect of reducing the pressure on the permeation side of the membrane on increasing the ammonia concentration of the gas that permeates through the membrane can be calculated as follows. Performance improvement effect of supply gas pressure of 1.1 MPaA: 85.8% (Example 4) ÷ 48.7% (Comparative Example 2) × 100 = 176% Performance improvement effect of supply gas pressure of 5.1 MPaA: 94.9% (Example 3) ÷ 91.8% (Comparative Example 4) × 100 = 103% Thus, it can be seen that the lower the pressure of the supply gas, the greater the effect of reducing the pressure on the permeate side. This is true for ammonia permeance (NH3 permeability), hydrogen permeance (H2 permeability), nitrogen permeance (N2 permeability), ammonia / hydrogen permeance ratio (NH3 / H2 separation coefficient), ammonia / nitrogen permeance ratio (NH3 / N2 separation coefficient), and ammonia flux.

[0239] These results suggest that reducing the pressure on the permeate side of the membrane is less effective in promoting the desorption rate because higher supply gas pressures increase the adsorption of ammonia adsorbed at the adsorption site of the zeolite on the membrane inlet side (supply gas side). Therefore, it was revealed that the supply gas pressure is related to the effect of reducing the pressure on the permeate side of the membrane to below atmospheric pressure in order to promote ammonia desorption, and that there is an optimal range.

[0240] The method of controlling the desorption rate of ammonia adsorbed on such zeolite adsorption sites becomes more effective as the number of adsorption sites in the zeolite increases. In other words, the more adsorption sites there are, the more ammonia is repeatedly adsorbed from the supply side to the permeate side of the membrane, and therefore becomes more susceptible to the effect of promoting desorption by reducing the pressure on the permeate side of the membrane. Comparative Example 8 shows the results of evaluating the performance using a CHA-type membrane with a Si / Al 2 molar ratio of 54. In this case, even with reduced pressure on the permeate side of the membrane, the separation coefficient of NH3 / H2 was 2 and the separation coefficient of NH3 / N2 was 6, indicating low separation performance despite the reduced pressure on the permeate side. Therefore, it can be seen that in order to improve membrane performance by reducing the pressure on the permeate side of the membrane, it is necessary to design a zeolite membrane with adsorption sites below a specific Si / Al 2 molar ratio.

[0241] Based on the above results, the inventors believe that the mechanism by which the effects of the present invention manifest is, although this is a hypothesis, that by using a zeolite membrane with a specific composition and making the permeable side of the membrane below atmospheric pressure, the desorption of ammonia adsorbed on the zeolite is promoted, thereby improving the ammonia separation performance.

[0242] The ammonia separation method of the present invention is also effective in multi-stage separation processes. Figure 6 shows an example of a two-stage separation process. Because the gas supplied to the membrane uses pressure when it permeates through the membrane, the pressure of the gas on the membrane permeation side is lower than that of the supply side. In a separation method that achieves high ammonia separation performance by reducing the pressure on the membrane permeation side, as in the present invention, it is possible to recover ammonia at a higher concentration by reducing the pressure on the membrane permeation side rather than increasing the pressure in a later stage and then permeating through the membrane again. [Industrial applicability]

[0243] The ammonia separation method of the present invention can efficiently separate ammonia from a mixed gas containing ammonia. Therefore, it can efficiently recover ammonia in processes such as ammonia production, ammonia decomposition, and ammonia recovery, and thus has high industrial applicability from the viewpoint of efficient energy production. [Explanation of symbols]

[0244] 1. Zeolite membrane complex 2. Pressure vessel 3. Sealing portion at the tip of the support 4. The joint between the zeolite membrane composite and the permeate gas recovery tube. 5. Pressure gauge 6. Back pressure valve 7. Supply gas (sample gas) 8 Permeable gas 9 Sweep gas 10 Impermeable gases 11 Permeate gas recovery pipe 12 Sweep gas supply pipe

Claims

1. A method for separating ammonia from a mixed gas consisting of at least ammonia-containing multiple components using an ammonia separation membrane, The system includes an ammonia separation step in which the mixed gas is supplied to an ammonia separation membrane, and ammonia is separated from the mixed gas by the ammonia separation membrane. The pressure on the permeate side of the ammonia separation membrane is less than atmospheric pressure. The ammonia separation membrane is a zeolite membrane, and the zeolite constituting the zeolite is Si / Al ２ A method for separating ammonia, characterized in that the molar ratio is 40 or less.

2. The method for separating ammonia according to claim 1, characterized in that the temperature of the ammonia separation step is 20°C or higher.

3. The ammonia separation method according to claim 1 or 2, characterized in that the pressure on the supply side of the mixed gas is 8.1 MPaA or less.

4. The method for separating ammonia according to claim 1 or 2, characterized in that the mixed gas contains hydrogen and / or nitrogen.

5. The method for separating ammonia according to claim 1 or 2, characterized in that the ammonia separation membrane is a zeolite membrane having a pore structure of 10 or fewer oxygen rings.

6. The ammonia separation method according to claim 1 or 2, characterized in that the ammonia separation membrane has an ammonia / nitrogen separation coefficient of 30 or more when measured under the following conditions. <Conditions> The mixed gas used for measurement is ammonia gas, nitrogen, and hydrogen. ・Separation temperature: 30℃~200℃ • Supply gas pressure: 0.1–5.1 MPaA • Permeation gas pressure: Below atmospheric pressure • Ammonia concentration in the supply gas: 2% by volume or higher

7. The ammonia separation method according to claim 1 or 2, characterized in that the ammonia separation membrane has an ammonia / nitrogen separation coefficient of 30 or more when measured under the following conditions. <Conditions> The mixed gas used for measurement is ammonia gas, nitrogen, and hydrogen. ・Separation temperature: 20℃ or higher and 500℃ or lower • Supply gas pressure: 0.3 MPaA or higher and 8.1 MPaA or lower • Permeation gas pressure: Below atmospheric pressure - Ammonia concentration in the supply gas: 1.0 volume% or higher

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