JP2023151632A - Zeolite membrane composite - Google Patents

Abstract

To provide a zeolite membrane composite, even when the zeolite membrane composite made long, enabling separation and recovery of desired gas from mixed gas without reducing permeation capacity of the gas to be separated.SOLUTION: Provided is a zeolite membrane composite having a zeolite membrane on a porous support, with a tubular structure, in which a sodium/silicon (mole ratio) in the zeolite membrane is 0.20 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a zeolite membrane composite. Specifically, the present invention relates to a zeolite composite membrane for separating specific components from a mixed gas. Particularly preferred is a long zeolite composite membrane.

In recent years, membrane separation and concentration methods using membranes such as polymer membranes and zeolite membranes have been proposed as methods for separating gas mixtures. Among these methods, polymer separation membranes are characterized by excellent processability, but have a problem in that they are flammable. On the other hand, various inorganic membranes such as zeolite membranes have been proposed because they have good chemical resistance, oxidation resistance, heat stability, and pressure resistance.
Among these, zeolite membranes have regular subnanometer pores and function as molecular sieves, so they not only allow specific molecules to permeate selectively, but also allow separation over a wide temperature range. It is expected to be a highly durable separation membrane capable of concentration. Such a zeolite membrane is usually used as a zeolite membrane composite in which zeolite is formed in the form of a membrane on a support made of an inorganic material.

The application of membrane separation to the separation of ammonia gas from nitrogen gas according to the present invention, for example, the application of membrane separation to the ammonia production process using the Haber-Bosch method, which is one of the industrially important processes, has recently been expected. There is. A characteristic of the Haber-Bosch process is that this ammonia production reaction is an equilibrium reaction, and thermodynamically it is said that reaction under high pressure and low temperature conditions is preferable, but in order to ensure the catalytic reaction rate, Generally, high pressure and high temperature manufacturing conditions are required. In addition, since unreacted hydrogen gas and nitrogen gas coexist with ammonia gas in the generated mixed gas, the process of recovering ammonia gas, which is a product, from the generated mixed gas requires a temperature range of -20°C to -5°C. It is necessary to cool the mixed gas to a certain degree to condense and separate ammonia. On the other hand, a process has been proposed in which a cooling condensation separation method during the purification process is replaced with a separation method using an inorganic membrane to efficiently recover high-concentration ammonia gas (Patent Documents 1 and 2).

Patent Document 1 discloses a first separation step in which hydrogen is separated from unpurified ammonia using a gas separation membrane, and a second separation step in which ammonia is separated from unpurified ammonia after the first separation step using another gas separation membrane. A membrane separation process is disclosed that includes a separation process. This method is not only a complicated process in which ammonia gas is separated from a mixed gas of hydrogen gas, nitrogen gas, and ammonia gas in at least two stages, but in order to make the process economical, it is necessary to separate the ammonia gas in the first stage. It is essential to separate ammonia gas from the highly concentrated hydrogen mixed gas containing ammonia gas that has permeated through the separation membrane and from the mixed gas of nitrogen gas and ammonia gas that has not permeated. Here, in the separation of nitrogen gas and ammonia gas by the second-stage membrane, the permeability of ammonia gas is not sufficient, and there is a possibility that the membrane area becomes large.
In addition, the method of separating ammonia gas from a mixed gas of ammonia gas, hydrogen gas, and/or nitrogen gas using a specific zeolite having an eight-membered oxygen ring proposed in Patent Document 2 is an effective method that can be applied to industrial processes. This can be a useful method. However, in the ammonia separation method using molecular sieve action using the pore size of zeolite proposed in Patent Document 2, the permeance ratio (ideal separation coefficient) between ammonia gas and nitrogen gas is about 14, and its permeation performance is sufficient. That is not necessarily true.

In order to solve these problems, Patent Document 3 discloses that a zeolite membrane is used to selectively permeate ammonia gas from a mixed gas containing at least ammonia gas, hydrogen gas, and nitrogen gas. An ammonia separation method is proposed in which the ammonia gas concentration in the mixed gas is 1.0% by volume or more, and the zeolite constituting the zeolite membrane is preferably RHO type zeolite or MFI type zeolite. This has been disclosed.

JP2008-247654A Japanese Patent Application Publication No. 2014-058433 International publication 2018/230737 pamphlet

According to the method disclosed in Patent Document 3, ammonia gas is efficiently separated and recovered from a mixed gas containing at least ammonia gas and nitrogen gas (hereinafter sometimes simply referred to as "mixed gas"). Is possible. In order to more efficiently separate and recover ammonia gas using this method, a zeolite membrane composite in which zeolite is formed in the form of a membrane on a support made of an inorganic material is formed into a tubular structure, and the tubular structure is extended into a long tube. A possible method is to separate and recover ammonia gas from the mixed gas more efficiently by increasing the area of contact with the mixed gas.
However, it has been found that by increasing the length of the zeolite membrane composite, the amount of nitrogen permeation increases, and as a result, the ammonia gas separation ability, that is, the difference in the permeation performance between nitrogen and ammonia becomes smaller. When we investigated the cause of this, we found that the amount of nitrogen permeation increased at both ends of the elongated zeolite membrane composite, or at least at one end of both ends, resulting in a significant decrease in the ammonia separation ability of the composite as a whole. I found out that there is.
Therefore, an object of the present invention is to separate a specific gas from a mixed gas without reducing the gas separation ability of the zeolite composite membrane, typified by ammonia gas, even when the zeolite membrane composite is lengthened. The object of the present invention is to provide a zeolite membrane composite that can be recovered.
In the following description, the separation and recovery of ammonia and nitrogen will be explained as a typical example of gas separation and recovery, but the present invention can of course be applied to the separation and recovery of other gases.

The inventors of the present invention have conducted intensive studies to solve the above problem, and have found that the cause of the problem is due to disordered composition, for example, micro-destruction occurs due to the difference in composition during heat load. We have found that this can be confirmed by ensuring that the Si/Al molar ratio is within a certain range, and have discovered that the above problem can be solved by a specific zeolite membrane composite, leading to the present invention. As mentioned above, considering the principle of damage caused by disturbances due to composition, it is possible to separate not only ammonia but also methanol, for example, when methanol is synthesized from raw materials such as CO, CO ₂ , H _{2 and} methanol is separated. A similar problem occurs when separating methane from a mixed gas of CO, _CO2 , _N2, etc. and _CH4 , such as natural gas or landfill gas, and can be solved by the present invention.
That is, the gist of the present invention resides in the following [1] to [12].

[1] A zeolite membrane composite having a zeolite membrane on a porous support, which has a tubular structure and has a Si/Al ratio in site (B) relative to the Si/Al ratio in site (A) shown below. and the ratio of Si/Al in the part (B') to the ratio of Si/Al in the part (A) are the same within a range of 20%.
Area (A): A partial area with a width of 4 cm on both sides from the longitudinal center of the zeolite membrane composite tube. Area (B): A partial area with a width of 8 to 12 cm from one end of the zeolite membrane composite tube (B). '): 8 to 12 cm from the other end of the tube of the zeolite membrane composite [2] The zeolite membrane composite according to the above [1], wherein the length of the tube of the tubular structure is 40 cm or more.
[3] The zeolite membrane composite according to the above [1], wherein the tube of the tubular structure has a length of 100 cm or more.
[4] The zeolite membrane composite according to any one of [1] to [3] above, wherein the zeolite is of any one of CHA type, FAU type, MFI type, LTA type, or RHO type.
[5] The zeolite membrane composite according to any one of [1] to [3] above, wherein the zeolite is of the CHA type, MFI type, LTA type, or RHO type.
[6] The zeolite membrane composite according to any one of [1] to [3] above, wherein the zeolite is either an MFI type or an RHO type.
[7] The zeolite membrane composite according to any one of [1] to [3] above, wherein the zeolite is an MFI type.
[8] The ratio of Si/Al in the site (B) to the Si/Al ratio in the site (A) and the Si/Al ratio in the site (B') to the Si/Al ratio in the site (A) are , the zeolite membrane composite according to any one of [1] to [7] above, in which the zeolite membrane composite matches within a range of 18%.
[9] The ratio of Si/Al in the site (B) to the Si/Al ratio in the site (A) and the Si/Al ratio in the site (B') to the Si/Al ratio in the site (A) are , the zeolite membrane composite according to any one of [1] to [7] above, wherein the zeolite membrane composite matches within a range of 15%.
[10] The method for producing a zeolite membrane composite according to any one of [1] to [9] above, wherein the molar ratio of water to silicon in the raw material mixture for hydrothermal synthesis is 45 or more and 300 or less. A method for producing a characteristic zeolite membrane composite.
[11] The method for producing a zeolite membrane composite according to the above [10], wherein the molar ratio of water to silicon is 60 or more and 200 or less.
[12] The method for producing a zeolite membrane composite according to [10] or [11] above, wherein the molar ratio of water to silicon is 70 or more and 150 or less.

According to the present invention, even when the zeolite membrane composite is lengthened, the zeolite enables separation and recovery of gas from a mixed gas without reducing the separation ability of gases represented by ammonia gas. A membrane complex can be provided.

FIG. 1 is a schematic diagram of a zeolite membrane composite of the present invention. FIG. 1 is a schematic diagram showing a cross-sectional structure of a zeolite membrane composite of the present invention. FIG. 2 is a schematic diagram showing an ammonia gas separation test device. 1 is a schematic diagram of a zeolite membrane composite produced in Example 1. FIG. FIG. 3 is a diagram for explaining the state of a sample in SEM-EDS measurement.

Hereinafter, the embodiments of the present invention will be described in more detail, but the explanation of the constituent elements described below is an example of the embodiments of the present invention, and the present invention is not limited to these contents. Various modifications can be made within the scope of the gist.
Note that the zeolite in this specification is a zeolite defined by the International Zeolite Association (IZA, hereinafter referred to as "IZA"). Its structure is characterized by X-ray diffraction data. Furthermore, in this specification, "a porous support-zeolite membrane composite in which a zeolite membrane is formed on a porous support" is sometimes simply referred to as a "zeolite membrane composite." Further, the "porous support" is sometimes simply referred to as "support", and the "aluminosilicate zeolite" is sometimes simply referred to as "zeolite". Furthermore, in this specification, "hydrogen gas,""nitrogengas," and "ammonia gas" may be simply referred to as "hydrogen,""nitrogen," and "ammonia," respectively. On the other hand, ammonia separation in the present invention means obtaining a mixed gas containing higher concentration of ammonia gas from a mixed gas containing ammonia gas.

[Zeolite membrane composite]
The zeolite membrane composite of the present invention has a zeolite membrane on a porous support, preferably crystallized and fixed, and a part of the zeolite is fixed to the inside of the support. Including those in the current state.
The zeolite membrane composite is preferably one in which zeolite is crystallized into a membrane on the surface of a porous support by hydrothermal synthesis.

The position of the zeolite membrane on the porous support is not particularly limited, and the zeolite membrane may be formed on the outer surface or the inner surface of the tubular support, and depending on the system to be applied, it may be formed on both sides. It may be formed into Further, it may be formed by laminating it on the surface of the support, or it may be crystallized so as to fill the pores of 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 it is preferable to form a so-called dense membrane in terms of improving separation performance.

The zeolite membrane composite of the present invention will be explained in detail using FIGS. 1 and 2. FIG. 1 is a schematic diagram showing a zeolite membrane composite of the present invention, and FIG. 2 is a schematic diagram showing a cross section of the zeolite membrane composite. The zeolite membrane composite 10 of the present invention has a tubular structure (hereinafter sometimes simply referred to as a "tube") as shown in FIG. 1, and by definition, the length of the tube must be 28 cm. However, it is preferable that the length of the tube is 40 cm or more.
Further, the zeolite membrane composite of the present invention has a cross-sectional structure as shown in FIG. 2, and has a zeolite membrane 103 on a porous support 101. The tube also has a cavity 102 in the center. Note that the cross-sectional structure in FIG. 2 shows an embodiment in which the porous support 101 has a zeolite membrane 103 on the outer surface, but the porous support 10 may have a zeolite membrane on the inner surface, The porous support may have a zeolite membrane on both the outer and inner surfaces.
In Fig. 1, the part (A) is 4 cm from the center 11 in the longitudinal direction of the tube, that is, the width of ±2 cm in the left and right directions from the center 11 (plus on the right side, minus on the left side) (12 in Fig. 1). It is. Also, the part 8 to 12 cm from one end is part (B) (13 in Figure 1), and the part 8 to 12 cm from the other end is part (B') (13' in Figure 1). ).

In the present invention, as mentioned above, the length of the tube is preferably 40 cm or more. The longer the length of the pipe, the greater the amount of mixed gas that can be separated and processed per pipe, and therefore the equipment cost can be reduced. From the above viewpoint, the length of the tube is preferably 80 cm or more, more preferably 100 cm or more, and even more preferably 120 cm or more.
The upper limit is not particularly limited, but it is preferably 500 cm or less, more preferably 300 cm or less, and even more preferably 200 cm or less, since this can prevent problems such as easy breakage due to vibrations during use.

The inner diameter of the tube 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. It is 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 is 1.3 cm or less.
If the inner diameter and outer diameter of the tube are each below the above upper limit values, the size of the equipment associated with the separation of ammonia etc. can be reduced, which is economically advantageous.

The zeolite membrane composite of the present invention has a Si/Al ratio in the site (B) to the Si/Al ratio in the site (A), and a Si/Al ratio in the site (B') to the Si/Al ratio in the site (A). /Al ratios are matched within a range of 20%. Note that the site (A), site (B), and site (B') are as described above.
The zeolite membrane composite of the present invention has a tubular structure, and even if it is long, it is important that it has a similar Si/Al ratio throughout regardless of the location of the tube. For this purpose, it is preferable that the fluctuation width of the Si/Al ratio at the center (site (A)) and at the ends (sites (B) and (B')) be within 20%. It is preferably within 18%, more preferably within 15%. Note that the range of variation of 20% or less is synonymous with the Si/Al ratio at the ends exhibiting a value of 80 to 120% of the Si/Al ratio at the center.

<Porous support>
The porous support used in the present invention preferably has chemical stability that allows zeolite to be crystallized in the form of a film on the surface. Suitable porous supports include gas permeable porous polymers such as polysulfone, cellulose acetate, aromatic polyamides, vinylidene fluoride, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, polytetrafluoroethylene, polyimide, etc. ; Ceramic sintered bodies such as silica, α-alumina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide; Sintered metals and mesh-shaped bodies such as iron, bronze, and stainless steel; Glass, Examples include inorganic porous materials such as carbon molded bodies. Among these, porous supports for ammonia separation in high-temperature ranges include ceramic sintered bodies and metals because of their excellent mechanical strength, deformation resistance, thermal stability, and reaction resistance at high temperatures. Inorganic porous supports such as sintered bodies, glass, and molded carbon bodies are preferred.
The inorganic porous support is preferably one obtained by sintering ceramics, which is a solid material whose basic component or most of it is composed of an inorganic nonmetallic substance.

As mentioned above, preferred ceramic sintered bodies include ceramic sintered bodies containing α-alumina, γ-alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide, etc. The sintered body may be a sintered body, or a mixture of a plurality of sintered bodies may be used. A part of the surface of these ceramic sintered bodies may turn into zeolite during zeolite membrane synthesis, which increases the adhesion between the porous support and the zeolite membrane, resulting in the formation of a zeolite membrane composite. Durability can be improved.
In particular, an inorganic porous support containing at least one of alumina, silica, and mullite can easily be partially converted into zeolite, so that the bond between the inorganic porous support and zeolite is strong. This is more preferable because it facilitates the formation of a dense zeolite membrane with high separation performance.

The porous support used in the present invention preferably has an effect on its surface (hereinafter also referred to as "porous support surface") to crystallize the zeolite formed on the porous support.
Moreover, it is preferable that the pore diameter of the surface of the porous support is controlled. The average pore diameter of the porous support near the surface of the porous support 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, and even more preferably 0. It is .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, more preferably 5 μm or less, particularly preferably 2 μm or less. By using a porous support having a pore size within such a range, a dense zeolite membrane that improves ammonia permselectivity can be formed.
Note that the surface of the porous support is preferably smooth, and if necessary, the surface may be polished with a file or the like.

The pore diameter of the porous support used in the present invention in areas other than the vicinity of the surface of the porous support is not limited and does not need to be particularly controlled, but the porosity of the other areas is usually 20. % or more, more preferably 30% or more, usually 60% or less, preferably 50% or less. The porosity of the part other than the vicinity of the surface of the porous support affects the permeation flow rate when separating gases and liquids, and if it is above the above lower limit, the permeate will tend to diffuse more easily, and if it is below the above upper limit. This tends to make it easier to prevent the strength of the porous support from decreasing. In addition, as a method of controlling the permeation flow rate, a porous support in which porous bodies having different porosities are combined in a layered manner may be used.

The shape of the porous support used in the present invention is tubular. The length of the tubular porous support may be any length that can ensure the length of the above-mentioned zeolite membrane composite. Therefore, the length of the tube of the porous support is preferably 40 cm or more, more preferably 80 cm or more, even more preferably 100 cm or more, and even more preferably 120 cm or more, similar to the above-mentioned zeolite membrane composite. It is particularly preferable that it is above. Further, the length is preferably 500 cm or less, more preferably 300 cm or less, and even more preferably 200 cm or less. When it is below the above upper limit, as mentioned above, there will be no problems such as easy breakage due to vibration during use, etc., and the production of the zeolite membrane composite can be simplified.

The inner diameter of the tubular porous support may be any diameter as long as it can maintain the inner diameter and outer shape of the zeolite membrane composite described above, and is usually 0.1 cm or more, preferably 0.2 cm or more, and more preferably 0.3 cm or more. , particularly preferably 0.4 cm or more, 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 is 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, still more preferably 1.0 mm or more, and particularly preferably is 1.2 mm or more, and usually 4 mm or less, preferably 3 mm or less, and more preferably 2 mm or less.
If the inner diameter, outer diameter, and wall thickness of the tubular porous support are each greater than or equal to the above lower limit values, the strength of the support can be improved and the support can be made less likely to break. Further, if the inner diameter and outer diameter of the tubular support are each equal to or less than the above-mentioned upper limit values, it may be economically advantageous because the size of the equipment for separating ammonia can be reduced. Furthermore, if the thickness of the tubular support is equal to or less than the above upper limit, the permeation performance tends to improve.

The rate of change in the coefficient of thermal expansion at 300°C relative to the coefficient of thermal expansion at 30°C of the porous support is, as an absolute value, 0.25% or less, preferably 0.20% or less, more preferably 0.15% or less. , particularly preferably 0.10% or less, most preferably 0.05% or less.
That is, the rate of change in the coefficient of thermal expansion at 300°C with respect to the coefficient of thermal expansion at 30°C of the porous support is within ±0.25%, preferably within ±0.20%, more preferably ±0.15. %, particularly preferably within ±0.10%, most preferably within ±0.05%.
Further, the rate of change in the coefficient of thermal expansion at 400°C relative to the coefficient of thermal expansion at 30°C of the porous support is usually 0.30% or less, preferably 0.25% or less, more preferably 0. .20% or less, particularly preferably 0.15% or less, most preferably 0.10% or less.
That is, the rate of change in the coefficient of thermal expansion at 400°C with respect to the coefficient of thermal expansion at 30°C of the porous support is within ±0.30%, preferably within ±0.25%, and more preferably within ±0.20%. It is particularly preferably within ±0.15%, most preferably within ±0.10%. A zeolite membrane composite film formed on a porous support exhibiting such a low coefficient of thermal expansion can absorb ammonia and nitrogen, for example, at temperatures exceeding 200°C, and even at temperatures exceeding 300°C. When the temperature of the composite is raised for the purpose of permeating ammonia from a mixed gas consisting of at least a plurality of components, cracks in the zeolite membrane are less likely to occur following the thermal expansion (contraction) of the porous support. Ammonia can be stably separated into the permeate side with high permeability even under high temperature conditions.

In addition, the rate of change in the coefficient of thermal expansion at 400°C with respect to the coefficient of thermal expansion at 30°C with respect to the rate of change in the coefficient of thermal expansion at 300°C with respect to the coefficient of thermal expansion at 30°C of the porous support is expressed as an absolute value as a ratio. , 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 membrane composite film formed on a porous support that exhibits a specific thermal expansion coefficient ratio between specific temperatures can be used, for example, even when heterogeneous heat generation occurs in a reactor during ammonia production. , it is possible to suppress the occurrence of cracks in the zeolite membrane that follows the local thermal expansion (contraction) of the porous support, so that ammonia can be stably and efficiently separated to the permeate side with high permeability even under high temperature conditions. I can do it.

(Method of measuring rate of change in coefficient of thermal expansion)
In the present invention, the rate of change in the coefficient of thermal expansion at a predetermined temperature with respect to the coefficient of thermal expansion at 30°C of the porous support is the crystal lattice constant measured at 30°C and a predetermined temperature by temperature-rising XRD measurement method under the following conditions. can be calculated using the following formula (1).

(Temperature rising XRD measuring device specifications)

(Measurement condition)

Measurement atmosphere: atmospheric temperature rising conditions: 20°C/min
Measurement method: Perform XRD measurement after holding at the measurement temperature for 5 minutes.
Fixed slit correction is performed on the measurement data using a variable slit.
Rate of change in thermal expansion coefficient = (crystal lattice constant measured at a given temperature) ÷ (crystal lattice constant measured at 30°C) -1... (1)

<zeolite>
In the present invention, the zeolite constituting the zeolite membrane is preferably an aluminosilicate. The aluminosilicate is mainly composed of oxides of Si and Al, and may contain other elements as long as the effects of the present invention are not impaired. The cationic species contained in the zeolite of the present invention is preferably a cationic species that easily coordinates to the ion exchange site of the zeolite, such as those belonging to Group 1, Group 2, Group 8, Group 9 of the periodic table, A cationic species selected from the element groups of Groups 10, 11, and 12, NH ₄ ⁺ , and two or more of these cationic species, more preferably cationic species from Group 1 of the periodic table, These include cationic species selected from the Group 2 element group, NH ₄ ⁺ , and two or more of these cationic species.

The SiO ₂ /Al ₂ O ₃ molar ratio of the aluminosilicate is not particularly limited, but is usually 6 or more, preferably 7 or more, more preferably 8 or more, while usually 500 or less, preferably 100 or less, It is more preferably 80 or less, still more preferably 50 or less, particularly preferably 45 or less, even more preferably 30 or less, and most preferably 25 or less. By using a zeolite having a SiO ₂ /Al ₂ O ₃ molar ratio in such a specific range, the denseness of the zeolite membrane and the durability such as chemical reaction resistance and heat resistance can be improved.
In addition, from the perspective of separation performance for permeating ammonia from a mixed gas consisting of multiple components containing at least ammonia and nitrogen, the structure of zeolite is maintained because acid points caused by Al elements become adsorption sites for ammonia. It is preferable to use a zeolite containing as much Al as possible, and by using a zeolite that exhibits the above SiO ₂ /Al ₂ O ₃ molar ratio, ammonia can be separated highly selectively with high permeability. be able to.
Note that the SiO ₂ /Al ₂ O ₃ molar ratio of the zeolite can be adjusted by the reaction conditions of hydrothermal synthesis described later.

In this specification, the SiO ₂ /Al ₂ O ₃ molar ratio is a value determined by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). In this case, in order to obtain information only on the zeolite membrane with a thickness of several microns, measurements are usually performed with the X-ray acceleration voltage set at 10 kV.

(Ratio of Si atoms to Al atoms in the zeolite composite membrane of the present invention)
The zeolite composite membrane of the present invention has been developed by discovering that the decrease in separation capacity of the entire composite membrane when lengthened as described above is due to a significant decrease in separation capacity at one end of the membrane. It has been discovered that, as a guideline, the ratio of Si atoms to Al atoms can be determined by having a constant value throughout the zeolite composite membrane. Specifically, we measured the ratio of Si atoms to Al atoms in each of the following parts, and compared the ratio of Si atoms to Al atoms in part A, that is, the central part, in parts B and B', which are the ends, both compared to the value in part A. The width is preferably within 20%, more preferably within 18%, even more preferably within 16%, and most preferably within 15%.
Area (A): A partial area with a width of 4 cm on both sides from the longitudinal center of the zeolite membrane composite tube. Area (B): A partial area with a width of 8 to 12 cm from one end of the zeolite membrane composite tube (B). '): 8 to 12 cm from the other end of the zeolite membrane composite tube

It is not clear why the above ratio is correlated with the separation ability when a long tube is used, but in the comparative example shown later, the ammonia permeation ability remains unchanged in the part where the composition differs greatly, while the nitrogen Since the transmittance of the material increased significantly, it is thought that this ratio of composition can be used to determine whether scratches occur when exposed to shocks such as temperature due to the difference in composition, and nitrogen also passes through. .
Note that the range of fluctuation of the Si/Al ratio within 20% is synonymous with the Si/Al ratio at the ends exhibiting a value of 80 to 120% of the Si/Al ratio at the center.

The structure of the zeolite used in the present invention is represented by the codes specified by IZA, for example, ABW, ACO, AEI, AEN, AFI, AFT, AFX, ANA, ATN, ATT, ATV, AWO, AWW, BIK, CHA, DDR, DFT, EAB, EPI, ERI, ESV, FAU, 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, Examples include TUN, WEI, MFI, MON, PAU, PHI, MOR, etc.

Among them, zeolites having a framework density of 18.0 T/nm ³ or less are preferred, more preferably CHA, FAU, MFI, LTA, and RHO, and still more preferably MFI and RHO. By using zeolite with a low framework density, when there are permeate components other than ammonia in a mixed gas containing ammonia, the resistance when those permeate components permeate can be reduced, and the amount of permeation of ammonia can be reduced. It becomes easier to make it bigger.

Here, the framework density (unit: T/nm ³ ) means the number of T atoms (atoms other than oxygen among the atoms constituting the zeolite skeleton) that exist per unit volume (1 nm ³ ) of the zeolite. However, this value is determined by the structure of the zeolite. Note that the relationship between the framework density and the structure of zeolite is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007 ELSEVIER.

The membrane separation of ammonia and nitrogen in the present invention utilizes adsorption of ammonia to zeolite, and is characterized by separation of ammonia based on a hopping mechanism of ammonia within zeolite pores. Therefore, although not particularly limited, a zeolite having a pore diameter close to the molecular diameter of ammonia may be preferable because the selectivity for ammonia separation tends to improve. From the above viewpoint, it is preferable that the zeolite has a structure having eight-membered oxygen ring pores.
On the other hand, pores with a size larger than the 8-membered oxygen ring are preferable because they increase ammonia permeability, but may result in poor nitrogen separation performance. However, even when using a zeolite with pores larger than the 8-membered oxygen ring, if a zeolite with a reduced SiO ₂ /Al ₂ O ₃ molar ratio is used, the ammonia adsorbed on the Al sites Since the pore size of the zeolite membrane is controlled, ammonia can be separated highly selectively with high permeability.

Therefore, the effective pore diameter of the zeolite used for membrane separation is one of the important design factors since it greatly influences the pore diameter of the zeolite membrane on which ammonia is adsorbed. The effective pore diameter of zeolite can also be controlled by the metal species introduced into the zeolite, ion exchange, acid treatment, silylation treatment, etc. It is also possible to improve the separation performance by controlling the effective pore diameter using other techniques.
For example, the pore size of the zeolite is slightly influenced by the atomic diameter of the metal species introduced into the zeolite skeleton. When a metal with an atomic diameter smaller than silicon, specifically, for example, boron (B), is introduced, the pore diameter becomes smaller, and when a metal with an atomic diameter larger than silicon, specifically, for example, tin (Sn ) etc., the pore diameter becomes larger. Furthermore, the pore diameter may be affected by removing metals introduced into the zeolite skeleton through acid treatment.

In addition, when ions in zeolite are exchanged with monovalent ions with a large ionic radius, the effective pore diameter becomes smaller, whereas when ions are exchanged with monovalent ions with a small ionic radius, the effective pore size becomes smaller. The pore diameter is close to the pore diameter of the zeolite structure.
Furthermore, the effective pore diameter of zeolite can also be reduced by silylation treatment. For example, by silylating the terminal silanol on the outer surface of the zeolite membrane and further laminating a silylated layer, the effective pore diameter of the pores facing the outer surface of the zeolite becomes smaller.

Although the separation function of the zeolite membrane composite used in the present invention is not particularly limited, it is expressed by controlling the surface properties of the zeolite to control the affinity and adsorption of gas molecules to the zeolite membrane. That is, by controlling the polarity of the zeolite, the adsorption of ammonia to the zeolite can be controlled, thereby making it easier to permeate ammonia.
For example, the affinity of ammonia to the zeolite can be controlled by controlling the polarity of the zeolite by the presence of a nitrogen atom, thereby making it easier to permeate ammonia.

In addition, it is possible to increase the polarity by replacing Si atoms in the zeolite skeleton with Al atoms, which allows highly polar gas molecules such as ammonia to be actively adsorbed and permeated into the zeolite pores. Can be done. It is also possible to control the polarity of the resulting zeolite by adding other atomic sources other than the Al atomic source, such as Ga, Fe, B, Ti, Zr, Sn, and Zn, to the aqueous reaction mixture for hydrothermal synthesis. It is.
In addition, through ion exchange, it is possible to control not only the pore size of the zeolite but also its ability to adsorb molecules, thereby controlling the permeation rate.

<Zeolite membrane>
The zeolite membrane in the present invention refers to a membrane-like material composed of zeolite, and is preferably formed by crystallizing zeolite on the surface of a porous support. In addition to zeolite, the membrane may optionally contain an inorganic binder such as silica or alumina, an organic substance such as a polymer, or a silylation agent that modifies the zeolite surface.
The preferred zeolite contained 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 of zeolite. In addition, zeolites such as ANA, GIS, and MER, which are easily generated in a mixed phase, and amorphous components other than crystals may be contained.

There are no particular restrictions on the zeolite and porous support that constitute the zeolite membrane composite, and it is preferable to use any combination of the above-mentioned zeolite and porous support, but among these, particularly preferred zeolites and porous supports are Specifically, the combinations of porous supports 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. Supports include CHA type zeolite-porous alumina support, AEI type zeolite-porous alumina support, preferably CHA type zeolite-porous alumina support, MFI type zeolite-porous alumina support, RHO Type zeolite-porous alumina support, more preferably MFI type zeolite-porous alumina support, RHO type zeolite-porous alumina support.

(Molar ratio of alkali metal and aluminum)
In the present invention, when the content of alkali metal atoms contained in the cross section of the zeolite membrane determined by SEM-EDS (scanning electron microscope energy dispersive X-ray analysis) is controlled within a specific range, ammonia and nitrogen can be reduced at least Ammonia permeability tends to improve when ammonia is separated from a mixed gas consisting of a plurality of components. Therefore, one of the preferred embodiments is to control the content of alkali metal atoms as necessary.
Examples of alkali metal atoms in the case where alkali metal atoms are present in the cross section of the zeolite membrane as necessary include Li, Na, K, Rb, Cs, and metal atoms of two or more of these. 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.
Note that the measurement conditions for SEM-EDS are as follows.

(Measurement condition)
(SEM-EDS measurement)
Equipment: FE-SEM (JEOL JSM-7900F)
EDS (Oxford ULTIM MAX)
Conditions: 5kV (irradiation current 500pA, high vacuum mode)
Observation magnification: 5000x, 10000x, 20000x

(Observation range for SEM-EDS measurement)
An image was acquired at a magnification of 20,000 times, the membrane part was enclosed as shown in Figure 5 (an example actually used in the example was reused), and measurements were performed for 120 seconds under the above conditions to determine the Si/Al ratio, Na/Al Calculate the ratio.

(Calculation of atomic concentration)
The atomic concentration of each element was calculated using software from AZtec (Oxford Instruments). The Si/Al ratio was calculated by dividing the Si atomic concentration by the Al atomic concentration. The Na/Si ratio is calculated by dividing the Na atomic concentration by the Si atomic concentration.

Alkali metal atoms exist in the form of cations as ion pairs of 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 below. If necessary, when alkali metal atoms are present on the zeolite membrane surface, the content of alkali metal atoms, particularly preferably sodium atoms, is 2.0 or less in molar ratio to Al atoms on the zeolite membrane surface. It is preferably at most 1.8, more preferably at most 1.5, even more preferably at most 1.0. The lower limit is not particularly limited, but is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more.
Controlling the alkali metal atom content within the above range tends to improve ammonia permeability while increasing ammonia separation selectivity, which is preferable.
Note that the molar ratio of alkali metal atoms to Al atoms in the zeolite membrane can be controlled by adjusting the amount of ions exchanged during the ion exchange treatment of the zeolite, as described later.

In the present invention, although the details are not yet clear and there are no particular limitations, the effective pore diameter of the zeolite used for membrane separation is controlled by utilizing the adsorption of ammonia to the zeolite, and the hopping mechanism of ammonia within the zeolite pores is controlled. It is characterized by separating ammonia based on In the present invention, which mainly utilizes the pore hopping mechanism that involves adsorption/desorption of ammonia onto zeolite to separate ammonia, first, the ammonia in the supplied mixed gas containing ammonia and the surface of the zeolite membrane are separated. An important design factor is how to increase the adsorption affinity with the mixed gas compared to other gases such as hydrogen and nitrogen contained in the mixed gas. From this point of view, when more Al atoms are present on the zeolite membrane surface, the polarity of the zeolite membrane surface changes, and the adsorption affinity with ammonia in the supplied gas increases, so that the ammonia separation performance improves. In addition, in the present invention, the content of Al atoms on the surface of the zeolite membrane is controlled by the SiO ₂ /Al ₂ O ₃ ratio of the zeolite constituting the zeolite membrane, the aluminum salt treatment after the zeolite membrane is formed, etc. The latter aluminum salt treatment has the effect of sealing minute defects existing on the surface of the zeolite membrane, improving the denseness of the zeolite membrane and durability such as chemical reaction resistance and heat resistance. This greatly contributes to improving the separation thermal stability of zeolite membranes at high temperatures, which is one of the challenges of the invention.

The selectivity for separating ammonia from a mixed gas containing at least ammonia and nitrogen is improved due to the blocking effect caused by adsorption of ammonia to Al sites within the zeolite pores.
Generally, since the adsorption power of ammonia to Al sites is high, permeation performance (permeability) tends to be impaired. In the present invention, by allowing a specific amount of alkali metal atoms to exist in the form of cations as ion pairs at Al sites in the zeolite constituting the zeolite membrane, the amount of ammonia adsorbed to the Al sites can be controlled; , the separation selectivity of ammonia can be maintained depending on the size of the alkali metal cation. These mechanisms make it possible to improve permeation performance while maintaining ammonia separation selectivity. That is, it is preferable to control the content of alkali metal atoms such as sodium to Al atoms in the zeolite to a molar ratio of 2.0 or less. Further, it is preferable that the content of alkali metal atoms to Al atoms in the zeolite is 0.01 or more.

(Molar ratio of alkali metal and silicon)
In the present invention, when the content of alkali metal atoms contained in the cross section of the zeolite membrane determined by SEM-EDS is controlled within a specific range, it is possible to separate ammonia from a mixed gas consisting of multiple components including ammonia and nitrogen. ammonia permeability tends to improve. Therefore, it is one of the preferred embodiments to control their content as necessary.
Examples of alkali metal atoms in the case where alkali metal atoms are present in the cross section of the zeolite membrane as necessary include Li, Na, K, Rb, Cs, and metal atoms of two or more of these. 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.
Note that the measurement conditions are as described in the column (molar ratio of alkali metal and aluminum).

When alkali metal atoms are present on the zeolite membrane surface, the content of alkali metal atoms, preferably sodium, is 0.20 or less in molar ratio to silicon (Si atoms) on the zeolite membrane surface, and 0.18 It is preferably at most 0.16, more preferably at most 0.14, even more preferably at most 0.14. There is no particular restriction on the lower limit, but it is preferably 0.001 or more, more preferably 0.005 or more, and even more preferably 0.01 or more.
Controlling the alkali metal atom content within the above range tends to improve ammonia permeability while increasing ammonia separation selectivity, which is preferable.
Note that the molar ratio of alkali metal atoms to Si atoms in the zeolite membrane can be controlled by adjusting the amount of ions exchanged during ion exchange treatment of zeolite and the amount of water during zeolite production, as described below. .

(Content of nitrogen atoms contained in the zeolite membrane surface)
In this embodiment, the content of alkali metal atoms on the surface of the zeolite membrane is controlled, and if necessary, the content of nitrogen atoms contained in the surface of the zeolite membrane determined by XPS measurement is adjusted to a specific region. If controlled, the separation selectivity when separating ammonia from a mixed gas tends to be significantly improved. preferable.
When nitrogen atoms are present on the zeolite membrane surface in this way, the content of the nitrogen atoms is usually 0.01 or more, preferably 0.05 or more in molar ratio to the Al atoms on the zeolite membrane surface. , more preferably 0.10 or more, still more preferably 0.20 or more, particularly preferably 0.30 or more, especially preferably 0.50 or more, and the upper limit is Although it is not particularly limited as it depends on the structure of the cationic species containing nitrogen atoms and the amount of nitrate ions remaining when nitrate treatment of the zeolite membrane is performed as necessary, it is usually 4 or less, preferably 3 or less, more preferably , is less than or equal to 1.
By using a zeolite having a surface composition with such a specific nitrogen atom/Al atomic ratio, it is possible to improve the denseness of the zeolite membrane and the durability such as chemical reaction resistance and heat resistance. This is preferable because ammonia can be separated with high selectivity from a mixed gas consisting of a plurality of components including/or nitrogen.
Note that the above upper and lower limits are valid within the range of significant figures. That is, the upper limit of 4 or less means less than 4.5, and the upper limit of 0.01 or more means 0.005 or more.

In the present invention, the nitrogen atoms used to contain nitrogen atoms in the zeolite membrane include ammonium ions (NH ₄ ⁺ ) contained in the zeolite, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, which will be described later. , tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, as well as methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine , and nitrogen atoms derived from cationic species in which organic amines having 1 to 20 carbon atoms such as piperidine are protonated. These include nitrogen atoms derived from the template, nitrogen atoms derived from nitrate ions remaining during the nitrate treatment of the zeolite membrane, which will be described later as necessary.

(Thickness of zeolite membrane)
The thickness of the zeolite membrane used in the present invention is not particularly limited, but is usually 0.1 μm or more, preferably 0.3 μm or more, more preferably 0.5 μm or more, and still more preferably 0.1 μm or more. The thickness is 7 μm or more, more preferably 1.0 μm or more, particularly preferably 1.5 μm or more. Further, it is usually 100 μm or less, preferably 60 μm or less, more preferably 20 μm or less, still 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 membrane is equal to or greater than the above lower limit, defects will be less likely to occur and separation performance will tend to be good. In addition, if the thickness of the zeolite membrane is below the above upper limit, the permeation performance tends to improve.Furthermore, in the high temperature range, the zeolite membrane is less likely to crack due to temperature rise, so the permeation performance at high temperatures is less likely to occur. There is a tendency to suppress a decrease in selectivity.

The average primary particle diameter of the zeolite forming the zeolite membrane is not particularly limited, but is usually 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more, and the upper limit is the thickness of the membrane or less. If the average primary particle diameter of the zeolite is equal to or larger than the above lower limit, the grain boundaries of the zeolite can be made small and good permeation selectivity can be obtained. Therefore, it is most preferable that the average primary particle diameter of the zeolite is the same as the thickness of the zeolite membrane. In this case, the grain boundaries of the zeolite can be made the smallest. A zeolite membrane obtained by hydrothermal synthesis, which will be described later, is preferable because the zeolite particle diameter and membrane thickness may be the same.
In the present 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 membrane composite of the present invention using a scanning electron microscope. and is calculated as the average value.

<Method for manufacturing zeolite membrane composite>
In the present invention, the method for producing the zeolite membrane composite is not particularly limited as long as the above-described zeolite membrane can be formed on a porous support, and any known method can be used. For example, (1) a method in which zeolite is crystallized in the form of a film on a support, (2) a method in which zeolite is fixed to a support with an inorganic binder or an organic binder, and (3) a method in which a polymer in which zeolite is dispersed is used as a support. (4) A method in which the zeolite is fixed to the support by impregnating the support with a slurry of zeolite and, if necessary, suctioning the zeolite.

Among these, a method in which zeolite is crystallized into a membrane on a porous support is particularly preferred. There are no particular restrictions on the crystallization method, but the porous support is placed in a reaction mixture for hydrothermal synthesis (hereinafter sometimes referred to as "aqueous reaction mixture") used for zeolite production, and then directly exposed to water. A method in which zeolite is crystallized on the surface of a porous support by thermal synthesis is preferred.
In this case, the zeolite membrane composite can be produced by, for example, placing an aqueous reaction mixture whose composition has been adjusted and homogenized into a heat-resistant and pressure-resistant container such as an autoclave containing a porous support inside, and then heating it for a certain period of time. It can be manufactured by

The aqueous reaction mixture contains a Si atom source, an Al atom source, an alkali source, and water, and further contains an organic template (structure directing agent) if necessary.
Regarding the manufacturing method of the zeolite membrane composite, the manufacturing method of the RHO type zeolite membrane composite and the MFI type zeolite membrane composite, which are particularly preferred examples, will be explained in detail. Note that the zeolite membrane and the manufacturing method of the present invention are not limited thereto.

In the method for producing a zeolite membrane composite of the present invention, it is important that the molar ratio of water to silicon in the raw material mixture for hydrothermal synthesis is 45 or more and 300 or less. When the molar ratio of water to silicon is within this range, even in a long zeolite membrane composite, fluctuations in the Si/Al ratio between the center and the ends can be easily suppressed.
From the above viewpoint, the molar ratio of water to silicon is preferably 60 or more and 200 or less, and more preferably 70 or more and 150 or less.

(RHO type zeolite membrane)
The RHO type zeolite used in the present invention refers to a zeolite having an RHO structure, which is a code defined by IZA that defines the structure of zeolite. RHO type zeolite has a structure characterized by having three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 3.6 x 3.6 Å, and its structure is characterized by X-ray diffraction data.
The framework density of the RHO type zeolite used in the present invention is 14.1 (unit: T/nm ³ ).

(MFI type zeolite membrane)
The MFI type zeolite used in the present invention refers to a zeolite having an MFI structure, which is a code defined by IZA that defines the structure of zeolite. MFI type zeolite has a structure characterized by having three-dimensional pores consisting of 10-membered oxygen rings with a diameter of 5.1 x 5.5 Å or 5.3 x 5.6 Å, and its structure can be determined by X-ray diffraction. Characterized by data.
The framework density of the MFI type zeolite used in the present invention is 17.9 (unit: T/nm ³ ).

(CHA type zeolite membrane)
The CHA type zeolite used in the present invention refers to a zeolite having a CHA structure, which is a code defined by IZA that defines the structure of zeolite. CHA type zeolite has a structure characterized by having three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 3.8×3.8 Å, and its structure is characterized by X-ray diffraction data.
The framework density of the CHA type zeolite used in the present invention is 14.5 (unit: T/nm ³ ).

(FAU type zeolite membrane)
The FAU type zeolite used in the present invention refers to a zeolite having an FAU structure, which is a code defined by IZA that defines the structure of zeolite. FAU type zeolite has a structure characterized by having three-dimensional pores consisting of six-membered oxygen rings with a diameter of 7.4 x 7.4 Å, and its structure is characterized by X-ray diffraction data.
The framework density of the FAU type zeolite used in the present invention is 12.7 (unit: T/nm ³ ).

(LTA type zeolite membrane)
The LTA type zeolite used in the present invention refers to a zeolite having an LTA structure, which is a code defined by IZA that defines the structure of zeolite. LTA type zeolite has a structure characterized by having three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 4.1×4.1 Å, and its structure is characterized by X-ray diffraction data.
The framework density of the LTA type zeolite used in the present invention is 12.9 (unit: T/nm ³ ).

<<Production method of RHO type zeolite membrane>>
(silicon atom source)
The silicon (Si) atom source used in the aqueous reaction mixture is not particularly limited, but includes silicones such as aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, and trimethylethoxysilane. Examples include alkoxide, tetraethylorthosilicate, aluminosilicate gel, etc., and preferred examples include aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxide, and aluminosilicate gel. . These may be used alone or in combination of two or more.

(Aluminum atomic source)
The aluminum (Al) atom source used for producing the porous support-RHO type zeolite membrane composite is not particularly limited, but includes aluminosilicate zeolite, amorphous aluminum hydroxide, aluminum hydroxide with a gibbsite structure, and bayerite structure. Aluminum hydroxide, aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, aluminosilicate gel etc., 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 alone or in combination of two or more.
Aluminosilicate zeolites may be used alone or in combination of two or more. When an aluminosilicate zeolite is used as an Al atom source, it is preferable that the above-mentioned aluminosilicate zeolite accounts for 50% by mass or more, particularly 70 to 100% by mass, particularly 90 to 100% by mass, of the total Al atom source. Further, when an aluminosilicate zeolite is used as a Si atom source, it is preferable that the above-mentioned aluminosilicate zeolite accounts for 50% by mass or more, particularly 70 to 100% by mass, particularly 90 to 100% by mass, of the total Si atom source. When the ratio of the aluminosilicate zeolite is within this range, the Si atom/Al atom molar ratio of the RHO type zeolite membrane becomes high, resulting in a zeolite membrane with excellent acid resistance and water resistance and a wide range of applications.

(Al atom/Si atomic ratio)
The preferred range of the amount (Al atoms/Si atomic ratio) of the Al atom source (including the aforementioned aluminosilicate zeolite and other Al atom sources) relative to the silicon (Si atoms) contained in the raw material mixture other than the seed crystal is , usually 0.01 or more, preferably 0.02 or more, more preferably 0.04 or more, even more preferably 0.06 or more, usually 1.0 or less, preferably 0.5 or less, more preferably It is 0.2 or less, more preferably 0.1 or less. By controlling the amount to be used within this range, it becomes easier to control the content of nitrogen atoms and alkali metal elements in the zeolite within the preferred range of the present invention. In addition, in order to increase the Al atom/Si atomic ratio, it is sufficient to reduce the amount of silicon atomic source used relative to the aluminum atomic source; on the other hand, in order to reduce the ratio, Just increase the amount you use.
Note that if the Al atom/Si atomic ratio exceeds 1.0, the resulting RHO type zeolite membrane may have low water resistance and acid resistance, and its use as a zeolite membrane may be limited. On the other hand, if the Al atom/Si atomic ratio is smaller than 0.01, it may become difficult to obtain an RHO type zeolite membrane.
In addition to the silicon atom source and aluminum atom source, other atom sources such as gallium (Ga), iron (Fe), boron (B), titanium (Ti), zirconium (Zr), tin ( Sn), zinc (Zn), and other atomic sources may be included.

(alkali source)
The type of alkali used as the alkali source is not particularly limited, and alkali metal hydroxides and alkaline earth metal hydroxides can be used.
The metal species of these metal hydroxides are usually sodium (Na), potassium (K), lithium (Li), rubidium (Rb), cesium (Cs), calcium (Ca), magnesium (Mg), strontium (Sr), Barium (Ba), preferably Na, K, and Cs, more preferably Na and Cs. Moreover, two or more types of metal species of the metal oxide may be used in combination, and specifically, it is preferable to use Na and Cs in combination.

Specific examples of metal hydroxides include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide; calcium hydroxide, magnesium hydroxide, and water. Alkaline earth metal hydroxides such as strontium oxide and barium hydroxide can be used.

Further, as an alkali source used in the aqueous reaction mixture, a hydroxide ion, which is a counter anion of an organic template described below, can be used.
Note that in the crystallization of zeolite according to the present invention, an organic template (structure directing agent) is not necessarily required, but by using a type of organic template according to each structure, the crystallized zeolite can be It is preferable to use an organic template because it increases the ratio of silicon atoms to aluminum atoms and improves crystallinity.

(organic template)
The organic template may be of any type as long as it can form the desired zeolite membrane. Further, one type of template or a combination of two or more types may be used.
The type of organic template suitable for the reaction varies depending on the zeolite structure to be synthesized, and any organic template that can provide the desired zeolite structure may be used. Specifically, for example, in the case of RHO structure, 18-crown-6-ether or the like may be used.
If the organic template is a cation, it is accompanied by an anion that does not harm the formation of the zeolite. Representative examples of such anions include halogen ions such as Cl ^- , Br ^- and I ^- , hydroxide ions, acetates, sulfates, and carboxylates. Among these, hydroxide ions are particularly preferably used, and in the case of hydroxide ions, they function as an alkali source as described above.

The ratio of the Si atom source to the organic template in the aqueous reaction mixture is the molar ratio of the organic template to SiO ₂ (organic template/SiO ₂ ratio), which is usually 0.005 or more, preferably 0.01 or more, and more preferably 0. .02 or more, more preferably 0.05 or more, particularly preferably 0.08 or more, most preferably 0.1 or more, and usually 1 or less, preferably 0.5 or less, more preferably 0.4 or less, and It is preferably 0.35 or less, particularly preferably 0.30 or less, and most preferably 0.25 or less. When the organic template/SiO ₂ ratio of the aqueous reaction mixture is within this range, not only can a dense zeolite film be produced, but also a zeolite with excellent acid resistance and from which Al atoms are difficult to desorb can be obtained. Further, under these conditions, it is possible to form a particularly dense RHO type aluminosilicate zeolite with excellent acid resistance.

By using an appropriate amount of the alkali metal atom source, it becomes easier to coordinate the organic structure directing agent described below to aluminum in a suitable state, thereby making it easier to form a crystal structure. The molar ratio (R/Si atom) between the alkali metal atom source (R) and the silicon (Si atom) contained in the raw material mixture for hydrothermal synthesis other than the seed crystal is usually 0.1 or more, preferably 0.15. Above, more preferably 0.20 or more, still more preferably 0.25 or more, particularly preferably 0.30 or more, particularly preferably 0.35 or more, and usually 2.0 or less, preferably 1.5 or less, It is more preferably 1.0 or less, further preferably 0.8 or less, particularly preferably 0.6 or less, and most preferably 0.5 or less.
If the molar ratio of the alkali metal atom source to silicon (R/Si atom) is larger than the above upper limit, the generated zeolite will be easily dissolved, and the zeolite may not be obtained or the yield may be extremely low. If the R/Si atom is smaller than the above lower limit, the raw material Al atom source and Si atom source will not be sufficiently dissolved, a uniform raw material mixture for hydrothermal synthesis will not be obtained, and RHO type zeolite will be difficult to produce. There are cases.

(amount of water)
It is preferable that the amount of water in the raw material mixture for hydrothermal synthesis is larger than that for normal hydrothermal synthesis. When the amount of water is large, the Si/Al (molar ratio) in site (A), site (B), and site (B') can all be easily set to 0.2 or less. Specifically, the molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystal is preferably 45 or more, more preferably 50 or more, and even more preferably 60 or more.
Regarding the upper limit of the amount of water, the molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystal is preferably 300 or less, more preferably 200 or less, and 150 or less. More preferred. If it is larger than the above upper limit, the reaction mixture may be too dilute and it may be difficult to form a dense film without defects.

(seed crystal)
In the present invention, seed crystals may be used as a component of the "zeolite" manufacturing raw material (raw material compound).
Although it is not necessarily necessary to have a seed crystal in the reaction system during hydrothermal synthesis, the presence of a seed crystal can promote crystallization of the zeolite on the porous support. The method of making seed crystals exist in the reaction system is not particularly limited, and may include adding seed crystals to an aqueous reaction mixture as in the synthesis of powdered zeolite, or attaching seed crystals to a porous support. In the present invention, it is preferable to attach seed crystals to the porous support. By attaching seed crystals to the support in advance, it becomes easier to produce a dense zeolite membrane with high separation performance.
The seed crystal to be used may be of any type as long as it is a zeolite that promotes crystallization, but in order to achieve efficient crystallization, it is preferably of the same crystal type as the zeolite membrane to be formed. For example, when forming a zeolite film of RHO type aluminosilicate, it is preferable to use seed crystals of RHO type zeolite.

It is desirable that the particle size of the seed crystal is close to the pore size of the porous support, and it may be pulverized and used if necessary. The particle size is usually 20 nm or more, preferably 50 nm or more, more preferably 100 nm or more, even more preferably 0.15 μm or more, particularly preferably 0.5 μm or more, most preferably 0.7 μm or more, and usually 5 μm or less, preferably is 3 μm or less, more preferably 2 μm or less, particularly preferably 1.5 μm or less.
Depending on the pore size of the porous support, it may be desirable for the seed crystal to have a smaller particle size, and the seed crystal may be pulverized and used if necessary. The particle size of the seed crystal is usually 5 nm or more, preferably 10 nm or more, more preferably 20 nm or more, and usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less.

The method of attaching the seed crystals onto the porous support is not particularly limited, and for example, a dip method in which the seed crystals are dispersed in a solvent such as water and the porous support is immersed in the dispersion to attach the seed crystals to the surface. Seed crystals are firmly attached to the surface of a porous support by dispersing seed crystals in a solvent such as water, immersing a support with one end sealed in the dispersion, and then sucking the support from the other end. A suction method in which seed crystals are deposited, a method in which a slurry made by mixing seed crystals with a solvent such as water and the like are applied onto a support can be used. In order to control the amount of seed crystals attached and to produce a zeolite membrane with good reproducibility, the dipping method and suction method are desirable.In order to bring the seed crystals into close contact with the porous support, the method of spreading the seed crystals on a slurry and the suction method are preferable. Law is preferable. In addition, in order to bring the seed crystals into close contact with the porous support and/or to remove excess seed crystals, following the dipping method or suction method, the support with the seed crystals attached may be rubbed with a finger wearing a latex glove. Pushing is also preferably carried out.

The solvent in which the seed crystals are dispersed is not particularly limited, but water and an alkaline aqueous solution are particularly preferred. The type of alkaline aqueous solution is not particularly limited, but a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution are preferred. Moreover, these alkali species may be mixed. The alkaline concentration of the alkaline aqueous solution is not particularly limited, and is usually at least 0.0001 mol%, preferably at least 0.0002 mol%, more preferably at least 0.001 mol%, even more preferably at least 0.002 mol%. Moreover, it is usually 1 mol% or less, preferably 0.8 mol% or less, more preferably 0.5 mol% or less, and still more preferably 0.2 mol% or less.

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 0.5% by mass or more, and even more preferably 0.5% by mass or more based on the total weight of the dispersion. is 1% by mass or more, particularly preferably 2% by mass or more, most preferably 3% by mass or more. Further, it is 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.
If the amount of seed crystals to be dispersed is too small, the amount of seed crystals that will adhere to the porous support will be small, resulting in areas on the porous support where no zeolite will be formed during hydrothermal synthesis, leading to defects. There is a possibility that it will become a certain film. On the other hand, for example, the amount of seed crystals deposited on a porous support by the dipping method becomes almost constant as long as the amount of seed crystals in the dispersion exceeds a certain level; therefore, the amount of seed crystals in the dispersion is too large. This increases the waste of seed crystals, which is disadvantageous in terms of cost.

It is desirable to form a zeolite membrane after seed crystals are attached to a porous support by a dipping method, a suction method, or by applying a slurry, and then dried. 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 limited as long as it is sufficiently dry, but it is usually 10 minutes or more, preferably 30 minutes or more. On the other hand, although no particular upper limit is specified, it is usually 5 hours or less from an economical point of view.
After drying, the seed crystal-attached support is rubbed with a finger wearing a latex glove in order to make the seed crystal adhere to the support and/or to remove excess seed crystals. Pushing is also preferably carried out.

The amount of seed crystals deposited on the porous support in advance is not particularly limited, and is usually 0.1 g or more, preferably 0.3 g or more, or more, based on the mass per 1 m ² of the film formation surface of the porous support. Preferably 0.5 g or more, more preferably 0.8 g or more, most preferably 1.0 g or more, and usually 100 g or less, preferably 50 g or less, more preferably 10 g or less, still more preferably 8 g or less, and most preferably 5 g. It is as follows.
When the amount of attached seed crystals is equal to or greater than the above lower limit, crystals are likely to be formed, the film will grow sufficiently, and the film will tend to grow uniformly. In addition, if the amount of seed crystals is below the above upper limit, the unevenness of the surface will not be increased by the seed crystals, and the seed crystals that have fallen from the support will facilitate the growth of spontaneous nuclei, which will cause the film on the support to grow. Growth is not inhibited. Therefore, within the above range, a dense zeolite film tends to be produced.

(hydrothermal synthesis)
When a zeolite membrane is formed on a porous support by hydrothermal synthesis, there is no particular restriction on the method of immobilizing the porous support, and it can take any form such as vertical or horizontal placement. In this case, the zeolite membrane may be formed by a standing method, or the zeolite membrane may be formed while stirring the aqueous reaction mixture.
In hydrothermal synthesis, the porous support supporting the seed crystal as described above and the prepared mixture for hydrothermal synthesis or the aqueous gel obtained by aging it are placed in a pressure-resistant container, and the mixture is heated under self-generated pressure. Alternatively, it may be carried out by maintaining a predetermined temperature under a gas pressure that does not inhibit crystallization, with stirring, while rotating or rocking the container, or in a stationary state. Hydrothermal synthesis under static conditions is desirable in that it does not inhibit crystal growth from seed crystals on a support.

The reaction temperature when forming a zeolite membrane by hydrothermal synthesis is not particularly limited and may be any temperature suitable for obtaining a membrane with the desired zeolite structure, but is usually 100°C or higher, preferably 110°C or higher, and The temperature is preferably 120°C or higher, particularly preferably 130°C or higher, particularly 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. , more preferably 170°C or lower. If the reaction temperature is too low, the zeolite may be difficult to crystallize. Furthermore, if the reaction temperature is too high, a type of zeolite different from the desired zeolite may be likely to be produced.
The heating (reaction) time when forming a zeolite membrane by hydrothermal synthesis is not particularly limited, and may be any time suitable for obtaining a membrane with the desired zeolite structure, but is usually 3 hours or more, preferably 8 hours. Above, more preferably 12 hours or more, particularly preferably 15 hours or more, usually 10 days or less, preferably 5 days or less, more preferably 3 days or less, still more preferably 2 days or less, particularly preferably 1. 5 days or less. If the reaction time is too short, the zeolite may become difficult to crystallize. If the reaction time is too long, a type of zeolite different from the desired zeolite may be likely to be produced.

The pressure during hydrothermal synthesis is not particularly limited, and the autogenous pressure generated when the aqueous reaction mixture placed in a closed container is heated to the above temperature range is sufficient. Furthermore, if necessary, an inert gas such as nitrogen may be added.

It is also possible to improve the compactness of the zeolite membrane by repeating hydrothermal synthesis multiple times. When repeating hydrothermal synthesis multiple times, the zeolite membrane composite obtained from the first hydrothermal synthesis is washed with water, heated and dried, and then immersed again in a newly prepared aqueous reaction mixture to perform hydrothermal synthesis. Just go. The zeolite membrane composite obtained after the first hydrothermal synthesis does not necessarily need to be washed with water or dried, but by washing with water and drying, the composition of the aqueous reaction mixture can be maintained at the intended composition. In the case of multiple synthesis, the number of synthesis is usually 2 or more and usually 10 or less, preferably 5 or less, and more preferably 3 or less. Washing with water may be repeated once or multiple times.

(Water washing, heat treatment, drying)
The zeolite membrane composite obtained by hydrothermal synthesis is washed with water, then heated and dried. Here, heat treatment means applying heat to dry the zeolite membrane composite, and when an organic template is used, baking and removing the organic template.
When the purpose of the heat treatment is drying, the temperature of the heat treatment is usually 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, and usually 200°C or lower, preferably 150°C or lower. The temperature of the heat treatment is usually 250°C or higher, preferably 300°C or higher, more preferably 350°C or higher, still more preferably 400°C or higher, and usually 800°C or lower, when the purpose is to remove the organic template by firing. The temperature is preferably 600°C or lower, more preferably 550°C or lower, particularly preferably 500°C or lower.
When the purpose is to remove the organic template by firing, if the temperature of the heat treatment is too low, the residual proportion of the organic template tends to increase, and the pores of the zeolite decrease, which makes it difficult to use for the separation of ammonia. The amount of permeation may be reduced. If the heat treatment temperature is too high, the difference in the coefficient of thermal expansion between the support and the zeolite will increase, which may cause the zeolite membrane to crack easily, causing the zeolite membrane to lose its compactness and reduce its separation performance. There is.

The time of the heat treatment is not particularly limited as long as the zeolite membrane is sufficiently dried and the organic template is removed by firing. If the purpose is drying, it is preferably 0.5 hours or more, more preferably If the purpose is to remove the organic template by firing, the heating time is preferably 1 hour or more, more preferably 5 hours or more, although it varies depending on the temperature increase rate and temperature fall rate. The upper limit of the heating time is not particularly limited, and is usually 200 hours or less, preferably 150 hours or less, and more preferably 100 hours or less.
The heat treatment for the purpose of firing the template may be performed in an air atmosphere, but may also be performed in an atmosphere to which an inert gas such as nitrogen or oxygen is added.

When hydrothermal synthesis is performed in the presence of an organic template, the resulting zeolite membrane composite is washed with water, and then the organic template is removed, for example, by heat treatment or extraction, preferably by the above-mentioned heat treatment, i.e., calcination. That is appropriate.
The temperature increase rate during heat treatment for the purpose of baking and removing the organic template should be kept as low as possible in order to prevent cracks from forming in the zeolite membrane due to the difference in thermal expansion coefficient between the porous support and the zeolite. It is preferable to slow down. The temperature increase 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, particularly preferably 0.3°C/min or less. It is. The lower limit of the temperature increase rate is usually 0.1° C./min or more in consideration of workability.
In addition, in heat treatment for the purpose of firing and removing the organic template, the rate of temperature drop after the heat treatment must be controlled to avoid cracks in the zeolite membrane, and the rate of temperature decrease, like the rate of temperature increase, must be slow. The later the better. The temperature decreasing 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, particularly preferably 0.3°C/min or less. be. The lower limit of the temperature decreasing rate is usually 0.1° C./min or more in consideration of workability.

<<Production method of MFI type zeolite membrane>>
(silicon atom source)
The silicon (Si) atom source used in the aqueous reaction mixture includes those described for the above-mentioned RHO type zeolite, and among them, preferably fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, silicic acid Examples include ethyl, silicon alkoxide, and aluminosilicate gel. These may be used alone or in combination of two or more.
The Si atom source is used such that the amounts of other raw materials relative to the Si atom source fall within the preferred ranges described above or below.

(Aluminum atomic source)
The aluminum (Al) atom source used for producing the porous support-MFI type zeolite membrane composite is not particularly limited, and examples include those similar to those described for the RHO type zeolite above. Among these, 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 alone or in combination of two or more.

(Al atom/Si atomic ratio)
The preferred range of the amount (Al atoms/Si atomic ratio) of the aluminum atom source (including the aforementioned aluminosilicate zeolite and other aluminum atom sources) relative to the silicon (Si atoms) contained in the raw material mixture other than the seed crystal is , the molar ratio is usually 0.001 or more, preferably 0.002 or more, more preferably 0.003 or more, even more preferably 0.004 or more, and usually 1.0 or less, preferably 0.5 or less. , more preferably 0.2 or less, still more preferably 0.1 or less. By controlling the usage amount 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. In order to increase the Al atom/Si atomic ratio, it is sufficient to reduce the amount of silicon atomic source used relative to the aluminum atomic source; on the other hand, to reduce the ratio, the amount of silicon atomic source used relative to the aluminum atomic source may be All you have to do is increase it.
Note that the aqueous reaction mixture may contain other atomic sources other than the Si atomic source and the Al atomic source, such as Ga, Fe, B, Ti, Zr, Sn, and Zn.

(alkali source)
The type of alkali used as the alkali source is not particularly limited, and alkali metal hydroxides and alkaline earth metal hydroxides can be used. Specifically, those similar to those described for the above-mentioned RHO type zeolite are used. Can be mentioned.
Further, as an alkali source used in the aqueous reaction mixture, a hydroxide ion, which is a counter anion of an organic template described below, can be used.
Note that in the crystallization of zeolite according to the present invention, an organic template is not necessarily required, but by using a type of organic template (structure directing agent) according to each structure, the crystallized zeolite can be It is preferable to use an organic template because it increases the ratio of silicon atoms to aluminum atoms and improves crystallinity.

(organic template)
The organic template may be of any type as long as it can form the desired zeolite membrane. Further, one type of template or a combination of two or more types may be used.
The type of organic template suitable for the reaction varies depending on the zeolite structure to be synthesized, and any organic template that can provide the desired zeolite structure may be used. Specifically, for example, if it has an MFI structure, tetrapropylammonium hydroxide or the like may be used.
If the organic template is a cation, it is accompanied by an anion that does not harm the formation of the zeolite. Representative examples of such anions include halogen ions such as Cl ^- , Br ^- and I ^- , hydroxide ions, acetates, sulfates, and carboxylates. Among these, hydroxide ions are particularly preferably used, and in the case of hydroxide ions, they function as an alkali source as described above.

The ratio of the Si atom source to the organic template in the aqueous reaction mixture is the molar ratio of the organic template to SiO ₂ (organic template/SiO ₂ ratio), which is usually 0.005 or more, preferably 0.01 or more, and more preferably 0. 0.02 or more, particularly preferably 0.05 or more, particularly preferably 0.1 or more, usually 1 or less, preferably 0.5 or less, more preferably 0.3 or less, particularly preferably 0.25 or less, especially Preferably it is 0.2 or less. When the organic template/SiO ₂ ratio of the aqueous reaction mixture is within this range, not only can a dense zeolite film be produced, but also a zeolite with excellent acid resistance and from which Al is hardly desorbed can be obtained. Further, under these conditions, it is possible to form an MFI type aluminosilicate zeolite which is particularly dense and has excellent acid resistance.

By using an appropriate amount of the alkali metal atom source, it becomes easier to coordinate the organic structure directing agent described below to aluminum in a suitable state, thereby making it easier to form a crystal structure. The molar ratio R/Si of the alkali metal atom source (R) and silicon (Si) contained in the raw material mixture for hydrothermal synthesis other than the seed crystal is usually 0.01 or more, preferably 0.02 or more, more preferably is 0.03 or more, more preferably 0.04 or more, particularly preferably 0.05 or more, and usually 1.0 or less, preferably 0.6 or less, more preferably 0.4 or less, still more preferably 0. 2 or less, particularly preferably 0.1 or less.

If the molar ratio of the alkali metal atom source to silicon (R/Si) is larger than the above upper limit, the produced zeolite will be easily dissolved, and the zeolite may not be obtained or the yield may be extremely low. If R/Si is smaller than the above lower limit, the raw material Al atom source and Si atom source will not be sufficiently dissolved, a uniform raw material mixture for hydrothermal synthesis will not be obtained, and MFI type zeolite will be difficult to produce. There is.

(amount of water)
It is preferable that the amount of water in the raw material mixture for hydrothermal synthesis is larger than that for normal hydrothermal synthesis. A large amount of water makes it easier to keep the Si/Al (molar ratio) in site (A), site (B), and site (B') all at 0.2 or less. Specifically, the molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystal is preferably 45 or more, more preferably 60 or more, and even more preferably 70 or more.
Regarding the upper limit of the amount of water, the molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystal is preferably 300 or less, more preferably 200 or less, and 150 or less. More preferred. If it is larger than the above upper limit, the reaction mixture may be too dilute and it may be difficult to form a dense film without defects.

(seed crystal)
In the present invention, seed crystals may be used as a component of the "zeolite" manufacturing raw material (raw material compound). The seed crystal is the same as that described for the above-mentioned RHO type zeolite, and when forming an MFI type aluminosilicate zeolite membrane, it is preferable to use an MFI type zeolite seed crystal.
It is desirable that the particle size of the seed crystal is close to the pore size of the support, and if necessary, it may be pulverized before use. The particle size is usually 1 nm or more, preferably 10 nm or more, more preferably 50 nm or more, even more preferably 0.1 μm or more, particularly preferably 0.5 μm or more, particularly preferably 0.7 μm or more, and most preferably 1 μm or more. It is usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less, most preferably 1.5 μm or less, particularly preferably 1.2 μm or less.
Depending on the pore size of the support, it may be desirable for the particle size of the seed crystal to be small, and the seed crystal may be pulverized and used if necessary. The particle size of the seed crystal is usually 0.5 nm or more, preferably 1 nm or more, more preferably 2 nm or more, and usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less.

The method for depositing seed crystals on the support is the same as that described for the RHO type zeolite described above. Further, the solvent and concentration in which the seed crystals are dispersed are also the same as those described for the above-mentioned RHO type zeolite. Furthermore, by rubbing and pushing the support with seed crystals attached with a finger wearing a latex glove, by applying the amount of seed crystals deposited on the porous support in advance, and by hydrothermal synthesis, the zeolite was added to the porous support. The method for immobilizing the support when forming a membrane is also the same as that described for the above-mentioned RHO type zeolite.

(hydrothermal synthesis)
The reaction temperature when forming a zeolite membrane by hydrothermal synthesis is not particularly limited and may be any temperature suitable for obtaining a membrane with the desired zeolite structure, but is usually 100°C or higher, preferably 120°C or higher, and The temperature is preferably 130°C or higher, particularly preferably 140°C or higher, particularly preferably 150°C or higher, most preferably 160°C or higher, and usually 210°C or lower, preferably 200°C or lower, even more preferably 190°C or lower, particularly preferably The temperature is 180°C or less. If the reaction temperature is too low, the zeolite may be difficult to crystallize. Furthermore, if the reaction temperature is too high, a type of zeolite different from the desired zeolite may be likely to be produced.
The heating (reaction) time when forming a zeolite membrane by hydrothermal synthesis is not particularly limited, and may be any time suitable for obtaining a membrane with the desired zeolite structure, but is usually at least 1 hour, preferably 5 hours. Above, more preferably 10 hours or more, usually 10 days or less, preferably 5 days or less, more preferably 3 days or less, still more preferably 2 days or less, particularly preferably 1 day or less. If the reaction time is too short, the zeolite may become difficult to crystallize. If the reaction time is too long, a type of zeolite different from the desired zeolite may be likely to be produced.

The pressure during hydrothermal synthesis is not particularly limited, and the autogenous pressure generated when the aqueous reaction mixture placed in a closed container is heated to the above temperature range is sufficient. Furthermore, if necessary, an inert gas such as nitrogen may be added.
Note that the method for improving the compactness of the zeolite membrane by repeating hydrothermal synthesis multiple times is the same as that described for the above-mentioned RHO type zeolite.

(Water washing, heat treatment, drying)
The zeolite membrane composite obtained by hydrothermal synthesis is washed with water, then heated and dried. Here, heat treatment means applying heat to dry the zeolite membrane composite, or, when an organic template is used, baking and removing the organic template.
When the purpose of the heat treatment is drying, the temperature of the heat treatment is usually 50°C or higher, preferably 80°C or higher, more preferably 100°C or higher, and usually 200°C or lower, preferably 150°C or lower. The temperature of the heat treatment is usually 350°C or higher, preferably 400°C or higher, more preferably 450°C or higher, even more preferably 500°C or higher, and usually 900°C or lower, when the purpose is to remove the organic template by firing. The temperature is preferably 800°C or lower, more preferably 700°C or lower, particularly preferably 600°C or lower.

When the purpose is to remove the organic template by firing, if the heat treatment temperature is too low, the residual proportion of the organic template tends to increase, and the pores of the zeolite decrease, which makes it difficult to use for ammonia separation. The amount of permeation may be reduced. If the heat treatment temperature is too high, the difference in the coefficient of thermal expansion between the support and the zeolite will increase, which may cause the zeolite membrane to crack easily, causing the zeolite membrane to lose its compactness and reduce its separation performance. There is. When using tetrapropylammonium hydroxide as the organic template, the content of nitrogen atoms in the zeolite can be controlled by adjusting the heat treatment temperature.
The heat treatment time, atmosphere, temperature increase rate, and temperature decrease rate are the same as those described for the above-mentioned RHO type zeolite.

<<Ion exchange>>
The synthesized zeolite membrane may be ion-exchanged if necessary. Since the thermal expansion characteristics of zeolite and the separation thermal stability of ammonia are greatly affected by the cation species in zeolite, this ion exchange is an important control method. Furthermore, as described below, the ammonia permeation performance and/or separation performance of the zeolite membrane may be improved depending on the cation species used. That is, the cationic species used in the present invention is appropriately selected in consideration of the ammonia permeability and separation performance while ensuring the thermal expansion characteristics of the zeolite and the thermal stability of ammonia separation.

When a zeolite membrane is synthesized using an organic template, ion exchange is usually performed after removing the organic template. In the present invention, in order to increase the nitrogen content on the surface of the zeolite membrane, ions to be ion-exchanged include NH ₄ ⁺ , methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, and tetramethylethylenediamine. , diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, piperidine, etc. Any of the cation species in which several 1 to 20 organic amines are protonated is preferable, and in addition, protons, alkali metal ions such as Na ⁺ , K + , Li ⁺ , Rb ⁺ , Cs ^{+ ,} Ca ²⁺ , Mg ²⁺ , Alkaline earth metal ions such as Sr ²⁺ and Ba ²⁺ and transition metal ions such as Fe, Cu, Zn, Ga, and La may coexist.
Among these, protons, NH ₄ ⁺ , Na ⁺ , Li ⁺ , Cs ⁺ , Fe ions, Ga ions, and La ions are preferred. A plurality of these ions may be mixed in the zeolite, and the method of mixing the ions is preferably adopted in order to balance the thermal expansion characteristics and ammonia permeation performance of the zeolite. By controlling the cation species to be ion-exchanged and their amounts, it is possible to control the ammonia affinity of the zeolite and the effective pore diameter within the zeolite pores, increasing ammonia permselectivity and The permeation rate can also be improved. Among these, the ionic species that increase the permselectivity of ammonia include NH ₄ ⁺ , methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, Organic amines having 1 to 20 carbon atoms such as aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylene diamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine. Preferably, cationic species in which amines with small molecular sizes such as NH ₄ ⁺ and organic amines having 1 to 6 carbon atoms are protonated are preferred for the above-mentioned reasons; Among them, NH ₄ ⁺ is particularly preferred.
On the other hand, the ion species that improve the permeation rate of ammonia are preferably protons, Na ⁺ , Li ⁺ , Cs ⁺ , Fe ions, Ga ions, and La ions, particularly preferably Na ⁺ , Li ⁺ , and Cs ⁺ ions, and Na It is most preferable to coexist with ⁺ ions. In the present invention, the molar ratio of nitrogen atoms to Al atoms in the zeolite membrane can be controlled by adjusting the amount of exchange of ions that require ion species containing nitrogen atoms.

In addition, when Na ⁺ ions are contained in the zeolite of the present invention, the content thereof is usually 0.01 or more, preferably 0.02 or more, or more, in molar ratio to Al atoms in the zeolite. Preferably it is 0.03 or more, more preferably 0.04 or more, particularly preferably 0.05 or more. On the other hand, the upper limit is not particularly limited, but is usually 0.10 molar equivalent or less, preferably 0.070 molar equivalent or less, more preferably 0.065 molar equivalent or less, still more preferably 0.060 molar equivalent or less, Particularly preferably, the amount is 0.055 molar equivalent or less. By using a zeolite having such a specific range of Na ⁺ /Al atomic ratio, ammonia can be separated with high permeability from a mixed gas consisting of ammonia and a plurality of components including hydrogen and/or nitrogen.

Ion exchange involves ion-exchanging the zeolite membrane after calcination (such as when an organic template is used) with nitrates, sulfates, phosphates, organic acid salts, and hydroxides of the above cations, as well as halogen salts of Cl and Br, Depending on the case, it may be treated with an acid such as hydrochloric acid, usually at a temperature of room temperature to 100°C, and then washed with water or with hot water of 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 to be ion exchanged is dissolved, and the concentration of the salt to be treated is usually 10 mol/L or less, and the lower limit is 0.1 mol/L. The amount is preferably 0.5 mol/L or more, more preferably 1 mol/L or more. These processing conditions may be appropriately set depending on the salt and solvent type used. When using an acid such as hydrochloric acid, the acid destroys the crystal structure of the zeolite, so the concentration of the acid to be treated is usually 5 mol/L or less, and the temperature and time may be set appropriately. Further, since the ion exchange rate increases by repeating the ion exchange treatment, the number of times the ion exchange treatment is performed is not particularly limited, and the treatment may be repeated until the desired effect is obtained. Furthermore, the ion-exchanged zeolite membrane should be calcined at 200 to 500°C as necessary, since if residues from the ion-exchange raw materials exist in the zeolite pores after the ion-exchange treatment, this will impede gas permeability. The residue after the ion exchange treatment may be removed by.

<<Nitrate treatment>>
In the zeolite membrane composite of the present invention, as a method for adjusting the content of nitrogen atoms in the zeolite membrane, it is preferable to use nitrate treatment in combination, so nitrate treatment will be explained below.

In the present invention, the synthesized zeolite membrane may be subjected to nitrate treatment if necessary. The nitrate treatment may be performed in a state where the organic template is included or after the organic template is removed by firing. The nitrate treatment is performed by, for example, immersing the zeolite membrane composite in a solution containing nitrate. This may be preferable because the nitrate has the effect of blocking minute defects present on the film surface.
Furthermore, when nitrate exists in the zeolite pores, it has the effect of improving the affinity of the zeolite membrane with ammonia, and is suitably employed as a method for improving ammonia permeability. The solvent used for nitrate treatment may be water or an organic solvent as long as the salt is dissolved, and there are no restrictions on the nitrate used, but examples include magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate, gallium nitrate, Examples include indium nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate, and zinc nitrate. 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, and among these, magnesium nitrate, calcium nitrate, barium nitrate, and aluminum nitrate are more preferable, and especially aluminum nitrate is present on the surface of the zeolite membrane. It is preferable because it has a remarkable effect of blocking minute defects and improves 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, 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, and these treatment conditions may be appropriately set depending on the nitrate used and the type of solvent. The zeolite membrane after the nitrate treatment may be washed with water, and by repeating water washing, the nitrogen atom content of the zeolite membrane can be adjusted to a preferable range.

<<Aluminum salt treatment>>
The zeolite membrane composite of the present invention may be subjected to aluminum salt treatment if necessary. The aluminum salt treatment may be performed in a state where the organic template is included or after the organic template is removed by firing. The aluminum salt treatment is performed by immersing the zeolite membrane composite in a solution containing aluminum salt, for example. As a result, the aluminum salt may have the effect of blocking minute defects present on the film surface. Furthermore, when an aluminum salt exists in the zeolite pores, it has the effect of attracting ammonia gas, and is suitably employed as a method for improving the permeability of ammonia gas.
The solvent used for the aluminum salt treatment may be water or an organic solvent as long as the salt is dissolved, and there are no restrictions on the aluminum salt used, but examples include aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, Examples include aluminum acetate, aluminum carbonate, and aluminum hydroxide. These may be used alone or in combination of two or more.

The concentration of the aluminum salt 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, and these treatment conditions may be appropriately set depending on the aluminum salt and solvent type used.
The zeolite membrane after the aluminum salt treatment may be washed with water, and the Al atom content of the zeolite membrane can be adjusted by repeating water washing. In order 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 increase the number of times of washing with water after aluminum salt treatment. In order to achieve this, it is preferable to increase the concentration and amount of aluminum salt to be treated, or to reduce the number of times of washing with water after aluminum salt treatment.

(Silylation treatment)
The zeolite membrane composite of the present invention may be subjected to silylation treatment if necessary. The silylation treatment is performed by immersing the zeolite membrane composite in, for example, a solution containing a Si compound. Thereby, the surface of the zeolite membrane can be modified with the Si compound to have specific physicochemical properties. For example, by reliably forming a layer containing a large amount of Si--OH on the surface of a zeolite membrane, the polarity of the membrane surface can be improved and the separation performance of polar molecules can be improved.
Furthermore, by modifying the zeolite membrane surface with a Si compound, the effect of closing minute defects present on the membrane surface may be obtained. Furthermore, the pore diameter of the zeolite can be controlled by silylation treatment, and a method of improving ammonia permeation selectivity by performing this treatment is also suitably employed.

The solvent used in the silylation treatment may be water or an organic solvent. Further, the solution may be acidic or basic, and in this case, the silylation reaction is catalyzed by the acid or base. Although there are no restrictions on the silylating agent used, alkoxysilanes are preferred. 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 30 hours, and these treatment conditions may be appropriately set depending on the silylating agent and solvent type used.

<<Content of nitrogen atoms contained in the zeolite membrane surface>>
In the present invention, the content of nitrogen atoms contained in the surface of the zeolite membrane of the present invention is determined by selecting the cation species containing nitrogen atoms in the zeolite contained in the zeolite membrane, as described above. A method of adjusting the atomic ratio, a method of adjusting the amount of ion exchange by the ion exchange method to adjust the content of nitrogen atoms, and an organic template containing nitrogen atoms (structure directing agent) when manufacturing a zeolite membrane as necessary. ), how to adjust the amount added, the heating temperature and heating time when removing the organic template by firing, the method to treat the zeolite membrane with nitrate, the number of times to wash the zeolite membrane treated with nitric acid with water. It can be controlled by adjusting methods and by appropriately combining these methods.

<<Content of Al atoms contained in the surface of the zeolite membrane composite>>
The content of Al atoms contained in the surface of the zeolite membrane composite of the present invention can be determined by adjusting the Al atom/Si atomic ratio in the zeolite contained in the zeolite membrane, or by treating the zeolite membrane with an aluminum salt, as described above. It can be controlled by a method of adjusting the number of times of water washing when washing a zeolite membrane treated with an aluminum salt, and by appropriately combining these methods.

<<Content of alkali metal elements contained in the surface of the zeolite membrane composite>>
The content of alkali metal elements contained in the surface of the zeolite membrane composite of the present invention can be determined by adjusting the Al atom/Si atomic ratio in the zeolite contained in the zeolite membrane, or by ion exchange using the ion exchange method. It can be controlled by adjusting the content of the alkali metal element by adjusting the amount, by adjusting the number of times the zeolite membrane is washed with water, and by appropriately combining these methods.
The zeolite membrane composite produced in this manner has excellent properties and can be suitably used as a membrane separation means for ammonia from a mixed gas in the present invention.

<Ammonia separation method>
The zeolite membrane composite of the present invention can selectively permeate and separate ammonia from a mixed gas containing at least nitrogen gas and ammonia gas.
Such an ammonia separation method using the zeolite membrane composite of the present invention can be effectively used to efficiently separate ammonia from a mixed gas containing at least ammonia, nitrogen, and even hydrogen. Therefore, it is effective to use it in combination with an ammonia production method that produces such a mixed gas.
That is, a preferred embodiment is a method for producing ammonia that includes a first step of producing ammonia from hydrogen and nitrogen, and a second step of separating ammonia obtained in the first step. Furthermore, a method for producing ammonia in which the first step and the second step proceed in one reactor is also one of the preferred embodiments to which the present invention is applied. The first step and the second step proceeding in one reactor means that the first step and the second step proceed simultaneously. That is, in one embodiment of the present invention, ammonia gas is produced from hydrogen gas and nitrogen gas in a container, and ammonia is efficiently produced in the container while separating ammonia from a mixed gas containing the produced ammonia gas. This is the way to do it.

Although there are no particular restrictions on the industrial production method of ammonia, the Haber-Bosch method may be mentioned. In this method, iron oxide is basically used as a catalyst, and nitrogen and hydrogen gas are reacted on the catalyst at 300°C to 500°C and 10 to 40 MPa to generate ammonia, and the reactor outlet gas is A process is adopted in which the produced ammonia contained therein is cooled, condensed and separated, and recovered as a product, while unreacted nitrogen and hydrogen gas are separated and recycled as raw material gas. Additionally, as an improved method of the Haber-Bosch process, a Ru-based supported catalyst that can produce ammonia under lower pressure conditions was developed in the 1980s, and a process that combines the Haber-Bosch process described above has also been industrialized, but its basics The manufacturing process has remained unchanged for 100 years. As described above, industrial catalysts for ammonia production are generally classified into iron-based catalysts and Ru-based catalysts. The molar ratio of the raw material gas used during ammonia production is preferably a theoretical ratio of hydrogen/nitrogen = 3, but since Ru-based catalysts are likely to be poisoned by hydrogen, production conditions that lower this molar ratio are preferably used. It will be done. Considering this point, although not particularly limited, the ammonia production catalytic process in combination with the ammonia separation technology according to the present invention is based on the preferred volume ratio of hydrogen gas/nitrogen gas contained in the feed gas in ammonia separation described below. Therefore, a process using a Ru-based catalyst is preferable, and this combination makes it possible to reduce the amount of permeation of hydrogen in the separation of produced ammonia.

A method for separating ammonia using the zeolite membrane composite of the present invention involves using a specific zeolite membrane to bring a mixed gas consisting of ammonia and a plurality of components including hydrogen and/or nitrogen into contact with the zeolite membrane, and then Ammonia is selectively permeated and separated from the gas.
As described above, according to the present invention, ammonia gas is produced from hydrogen gas and nitrogen gas in a reactor, and the ammonia gas produced using a zeolite membrane is permeated in the reactor and efficiently produced. Ammonia can be produced and recovered.

(mixed gas)
In the present invention, the mixed gas is a gas containing at least ammonia gas and nitrogen gas, and preferably also contains hydrogen gas.

(Ammonia concentration in mixed gas)
The ammonia concentration in the mixed gas is not particularly limited, but from the viewpoint of ammonia permeation rate, the ammonia gas concentration is preferably 1.0% by volume or more. When the content is 1.0% by volume or more, the permeation rate of ammonia gas is improved. From the above viewpoint, the ammonia gas concentration in the supplied gas is preferably 2.0% by volume or more, more preferably 3.0% by volume or more, particularly preferably 5.0% by volume or more.
On the other hand, the upper limit is not particularly limited, but is usually less than 100% by volume because the higher the ammonia gas concentration in the supplied gas, the better the separation performance. It is vol.% or less, preferably 60 vol.% or less, more preferably 40 vol.% or less. Note that the concentration of ammonia in the supplied gas is determined by sampling the supplied gas, analyzing its components, and assuming that the molar fraction of ammonia is the same as the volume %. Volume % of other gases are similarly considered to be volume % based on their mole fractions.

Furthermore, when ammonia is separated in combination with an ammonia production process, the ammonia equilibrium concentration produced under the production process conditions is lower than or equal to the equilibrium concentration of ammonia. The ammonia separation technology using the present invention separates ammonia from the feed gas, in contrast to the known method of selectively permeating hydrogen gas and/or nitrogen gas from a mixed gas of hydrogen, nitrogen, and ammonia. process, it is advantageous to separate ammonia from a mixed gas containing a high concentration of ammonia.
Furthermore, even if a process is adopted to recover hydrogen gas from the mixed gas on the non-permeable side that did not pass through the membrane as necessary, the design is designed to recover hydrogen from the mixed gas whose ammonia gas concentration has been sufficiently reduced. Therefore, the above-mentioned problem is unlikely to occur in the known process of separating hydrogen and/or nitrogen from a supply gas and concentrating ammonia.
Note that, for example, Patent Document 1 has the characteristics that the ammonia separation performance is significantly improved and the separation stability is also high during operation at high temperatures and during long-term operation.

The reason why the permeation selectivity of ammonia passing through a zeolite membrane increases significantly when the ammonia gas concentration in a mixed gas containing at least ammonia and nitrogen exceeds a certain amount is not yet clear, but the ammonia gas concentration in the mixed gas When the ammonia gas is increased, adsorption onto the zeolite becomes more likely to occur due to the above-mentioned adsorption equilibrium between ammonia gas and the zeolite, and a zeolite film in which ammonia is adsorbed within the pores is first formed. The zeolite membrane in which ammonia adsorbed in this manner narrows the pore diameter within the zeolite membrane, thereby reducing the permeation rate of hydrogen having a small molecular size. This effect similarly narrows the pores of the zeolite membrane even when a zeolite whose pore diameter is larger than the molecular size of hydrogen, nitrogen, or ammonia is used, so hydrogen permeation is significantly inhibited.
On the other hand, ammonia adsorbed within the zeolite pores can undergo hopping movement due to adsorption/desorption of ammonia within the pores due to the pressure difference between the inside and outside of the membrane, and this behavior results in selective separation of ammonia. .

That is, the present invention first actively adsorbs ammonia to zeolite, controls the pore diameter of the zeolite membrane, and increases the separation selectivity of ammonia. This is a technology that selectively transmits ammonia using hopping movement due to separation. On the other hand, in Patent Document 2, since such an ammonia-adsorbing zeolite membrane causes blockage during ammonia permeation, a zeolite that does not cause such adsorption is designed, and ammonia is removed using a molecular sieve that utilizes the pore size of the zeolite. They differ greatly in that they propose a technology to separate the two.
In addition, in the silica membrane proposed in Patent Document 1, adsorption of ammonia is difficult to occur, and even if ammonia is adsorbed, the thermal stability is low, so that the effect as in the present invention is not achieved.

On the other hand, in the present invention, in which ammonia is separated mainly by utilizing the pore hopping mechanism that involves adsorption/desorption of ammonia to zeolite, the temperature during ammonia separation is determined by the long-term durability of the zeolite membrane used. , is one of the important design factors because it greatly affects the ammonia separation performance of the zeolite membrane and the production energy balance of the entire process when combined with ammonia production equipment. From these viewpoints, in the present invention, when separating the product gas in ammonia synthesis, the temperature during ammonia separation is usually the same as or lower than the ammonia synthesis temperature, The temperature at this time is the temperature inside the separator that performs ammonia separation, that is, the temperature of the mixed gas subjected to separation and the temperature of separated ammonia gas. Further, the temperature of the separation membrane can be considered to be approximately the same as the temperature inside the separator.

From the viewpoint of ammonia manufacturing process design, it is preferable to perform separation at the same temperature as the synthesis temperature because it eliminates the need to raise the temperature of hydrogen and nitrogen that are recycled to the reactor. Therefore, the preferred temperature for ammonia separation depends on the reaction temperature in the ammonia synthesis reaction, but is usually 500°C or lower, preferably 450°C or lower, and more preferably 400°C or lower.
When ammonia is separated under these temperature conditions using the zeolite membrane of the present invention, since the zeolite membrane is highly stable, it not only enables continuous operation over a long period of time, but also allows for high ammonia permeation. Selectivity is expressed.

On the other hand, the lower limit is usually a temperature higher than 50°C, preferably 100°C or higher, more preferably 150°C or higher, particularly preferably 200°C or higher, particularly preferably 250°C or higher, particularly preferably 300°C or higher. When ammonia is separated under these temperature conditions, the rate of desorption of ammonia adsorbed within the zeolite pores increases, and as a result, the rate of ammonia permeation through the zeolite membrane increases.
In addition, when recycling raw material gas in the ammonia production process, it is preferable to separate ammonia under higher temperature conditions because the energy required to raise the temperature of hydrogen and nitrogen is reduced. The lower limit is preferably 250°C or higher, more preferably 300°C or higher.

The mixed gas (supply gas) only needs to contain ammonia and nitrogen, and in consideration of the synthesis of ammonia, preferably contains hydrogen. The volume ratio of hydrogen gas/nitrogen gas contained in the mixed gas is usually 3 or less, more preferably 2 or less. By adjusting the volume ratio to this level, the amount of permeation of hydrogen during ammonia separation is reduced, and the ammonia separation selectivity is improved.
For these reasons, when the feed gas for the ammonia separation process of the present invention is obtained from an ammonia production process, Ru-based ammonia production in which the volume ratio of hydrogen gas/nitrogen gas in the raw material gas is lowered is possible, although there is no particular limitation. Preferably, it is combined with a catalytic process. On the other hand, the lower limit is not particularly limited because the smaller the value, the better the ammonia separation selectivity is, but it is usually 0.2 or more, preferably 0.3 or more, and more preferably 0.5 or more.
Here, the stated values of the upper and lower limits are valid within the range of significant figures, that is, the upper limit of 3 or less means 2.5 or more and less than 3.5, and 0.2 or more means 0.15 or more. Less than 0.25 means 1.0 or more means 0.95 or more and less than 1.05.

In the present invention, the higher the pressure of the mixed gas (supply gas), the better the separation performance of the zeolite membrane and the reduction of the area of the zeolite membrane used, so it is a preferable embodiment, but if the pressure is higher than atmospheric pressure. There is no particular restriction, and the pressure may be adjusted to a desired pressure by reducing the pressure as appropriate. If the pressure of the gas to be separated is lower than the pressure used for separation, it can be used after increasing the pressure with a compressor or the like.
The pressure of the mixed gas (supplied gas) is usually atmospheric pressure or higher than atmospheric pressure, preferably 0.1 MPa or more, more preferably 0.2 MPa or more. Moreover, the upper limit is usually 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less, and may be 3 MPa or less.

The pressure on the permeation side is not particularly limited as long as it is lower than the gas pressure on the supply side, but it is usually 10 MPa or less, preferably 5 MPa or less, more preferably 1 MPa or less, even more preferably 0.5 MPa or less, and in some cases, atmospheric pressure or less. The pressure may be reduced to . When separating until the ammonia concentration in the feed gas reaches a low value, it is preferable that the pressure on the permeate side is low, and if the pressure is lowered to below atmospheric pressure, the ammonia gas concentration in the feed gas will be lower. It is possible to separate ammonia until the concentration is reached.
The pressure difference between the gas on the supply side and the gas on the permeation side is not particularly limited, but is usually 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less, even more preferably 1 MPa or less. Moreover, it is usually 0.001 MPa or more, preferably 0.01 MPa or more, and more preferably 0.02 MPa or more.
Here, the differential pressure refers to the difference between the partial pressure on the supply side and the partial pressure on the permeation side of the gas. Moreover, pressure [Pa] refers to absolute pressure unless otherwise specified.

The flow rate of the mixed gas (supply gas) is such that it can compensate for the decrease in permeated gas, and the concentration of the gas with low permeability in the supply gas in the immediate vicinity of the membrane matches the concentration in the entire gas. The flow rate may be sufficient to mix the supplied gas, and the linear velocity is usually 0.001 mm/sec or more, preferably 0.01 mm/sec, although it depends on the tube diameter of the zeolite membrane composite and the separation performance of the membrane. Above, it is more preferably 0.1 mm/sec or more, particularly preferably 0.5 mm/sec or more, more preferably 1 mm/sec or more, and the upper limit is not particularly limited, but usually 1 m/sec or less, preferably 0.5 mm/sec or more. It is 5m/sec or less.

In the method for separating ammonia from a mixed gas using the zeolite membrane composite of the present invention, a sweep gas may be used. Sweep gas refers to a gas supplied to efficiently recover ammonia permeated by a separation membrane, and is not a gas introduced to the supply gas side before separation and permeation, but a gas supplied to the permeation side of the separation membrane. be. In other words, the sweep gas is a gas that is supplied separately from the supply gas before separation and permeation, and is used to flow a different type of gas from the supply gas to the permeation side and recover the gas that has permeated through the membrane. The sweep gas used in the present invention refers to the gas 39 supplied from the line 342 shown in FIG. 3, for example. The pressure of the sweep gas is usually atmospheric pressure, but is not particularly limited to atmospheric pressure, and is preferably 20 MPa or less, more preferably 10 MPa or less, even more preferably 1 MPa or less, and the lower limit is preferably 0.09 MPa. More preferably, it is 0.1 MPa or more. Depending on the case, it may be used under reduced pressure.

The flow rate of the sweep gas is not particularly limited, but the linear velocity is usually 0.5 mm/sec or more, preferably 1 mm/sec or more, and the upper limit is not particularly limited, and is usually 1 m/sec or less, preferably 0.5 m/sec. It is less than sec.

The device used for gas separation is not particularly limited, but usually a zeolite membrane composite is used as a membrane module (hereinafter, "zeolite membrane composite and/or separation device using a zeolite membrane composite" will be simply referred to as "membrane module"). ). The membrane module may be, for example, a device as schematically shown in FIG. You can.
The operation of separating the mixed gas in the apparatus of FIG. 3 will be explained in the Examples section.
When performing membrane separation of ammonia from a mixed gas, membrane modules may be used in multiple stages. In this case, the gas for separation may be supplied to the first-stage membrane module, and the non-permeated gas that did not pass through the membrane may be further supplied to the second-stage membrane module, or the permeated gas may be supplied to the second-stage membrane module. It may also be supplied to the second stage membrane module. In the former method, the concentration of components with low permeability on the non-permeate side can be further increased, and in the latter method, the concentration of components with high permeability in the permeated gas can be further increased. Furthermore, a combination of these methods can also be suitably used.
In the case of separation using membrane modules provided in multiple stages, the pressure of the supplied gas may be adjusted using a booster or the like as necessary when supplying gas to the subsequent membrane module.

Furthermore, when using membrane modules in multiple stages, membranes with different performances may be installed in each stage. Generally, membranes with high permeability tend to have low separation performance, while membranes with high separation performance tend to have low permeation performance. For this reason, when processing gas components to be separated or concentrated to a predetermined concentration, a membrane with high permeability will require a smaller membrane area, while components with lower permeability will also more easily permeate to the permeate side. Therefore, the concentration of highly permeable components in the gas on the permeate side tends to be low. Conversely, in a membrane with high separation performance, it is difficult for components with low permeability to permeate to the permeate side, and therefore, although the concentration of components with high permeability in the gas on the permeate side is high, the required membrane area becomes large. Tend. In separation using one type of membrane, it is difficult to control the relationship between the required membrane area and the amount of permeation and non-permeation of the target gas for concentration or separation, but it becomes easier to control by using membranes with different performances. Depending on the membrane cost and the price of the gas to be separated and recovered, the membrane can be installed to achieve the optimal relationship between membrane area, concentration, permeation of the gas to be separated, and amount of non-permeation, thereby maximizing the overall benefits.
For example, if ammonia cannot be sufficiently separated by one stage of membrane separation, the gas on the non-permeate side can be further separated by several stages of membranes. In addition, if one-stage membrane separation does not sufficiently separate ammonia/hydrogen and the permeate side contains a large amount of hydrogen along with ammonia, the permeate gas should be separated using a membrane with high ammonia and hydrogen separation performance. You can also do it.

The zeolite membrane used in the present invention has excellent chemical resistance, oxidation resistance, thermal stability, and pressure resistance, and also exhibits high ammonia permeation performance and separation performance, and has excellent durability.
High permeation performance here refers to a sufficient throughput, for example, when the permeance [mol/(m ² s Pa)] of a gas component permeating through the membrane is such that, for example, ammonia is , when permeated at a differential pressure of 0.3 MPa, usually 1 x 10 ^-9 or more, preferably 5 x 10 ^-9 or more, more preferably 1 x 10 ^-8 or more, even more preferably 2 x 10 ^{-8 or} more, especially It is preferably 5×10 ⁻⁸ or more, particularly preferably 1×10 ⁻⁷ or more, and most preferably 2×10 ⁻⁷ or more. The upper limit is not particularly limited and is usually 3×10 ⁻⁴ or less.

Further, the permeance [mol/(m ² s Pa)] of the zeolite membrane composite used in the present invention is usually 5×10 ⁻⁸ or less, preferably 3× 10 ^-8 or less, more preferably 1 x 10 ^-8 or less, particularly preferably 5 x 10 ^-9 or less, most preferably 1 x 10 ^-9 or less, and ideally the permeance is 0, but in practice It may be on the order of 1×10 ⁻¹⁰ to 1×10 ⁻¹⁴ .
Here, permeance (also referred to as "permeability") is the amount of permeating substance divided by the product of the membrane area, time, and partial pressure difference between the supply side and permeation side of the permeating substance, and is expressed in units of is [mol/(m ² ·s · Pa)], which is a value calculated by the method described in the Examples section.

Further, the selectivity of a zeolite membrane is expressed by an ideal separation coefficient and a separation coefficient. The ideal separation coefficient and separation coefficient are indicators representing selectivity that are generally used in membrane separation, and the ideal separation coefficient is the value calculated below using the method described in the Examples section.
When determining the separation coefficient α, it is calculated using the following formula.
α=(Q'1/Q'2)/(P'1/P'2)
[In the above formula, Q'1 and Q'2 respectively represent the permeation amount [mol/(m ² · s · Pa)] of a gas with high permeability and a gas with low permeability, and P'1 and P '2 indicates the partial pressure [Pa] of a highly permeable gas and a low permeable gas in the feed gas, respectively. ]

The separation coefficient α can also be determined as follows.
α=(C'1/C'2)/(C1/C2)
[In the above formula, C'1 and C'2 respectively indicate the concentration [volume %] of a gas with high permeability and a gas with low permeability in the permeate gas, and C1 and C2 respectively It shows the concentration [volume %] of highly permeable gas and low permeable gas. ]

For example, when ammonia and nitrogen are permeated at a temperature of 200° C. and a differential pressure of 0.3 MPa, the ideal separation coefficient is usually 15 or more, preferably 20 or more, more preferably 25 or more, and most preferably 30 or more. Furthermore, when ammonia and hydrogen are permeated at a temperature of 200°C and a differential pressure of 0.3 MPa, it is usually 2 or more, preferably 3 or more, more preferably 5 or more, still more preferably 7 or more, particularly preferably 8 or more, particularly preferably It is 10 or more, most preferably 15 or more. The upper limit of the ideal separation coefficient is when only ammonia passes through completely, in which case it becomes infinite, but in practice, the separation coefficient may be about 100,000 or less.

The separation coefficient of the zeolite membrane used in the present invention is usually 2 or more, preferably 3 when a mixed gas of ammonia and nitrogen in a volume ratio of 1:1 is permeated at a temperature of 50°C and a differential pressure of 0.1 MPa. The number is preferably 4 or more, and even more preferably 5 or more. The upper limit of the separation coefficient is when only ammonia passes through completely, in which case it becomes infinite, but in practice, the separation coefficient may be about 100,000 or less.

As mentioned above, the zeolite membrane used in the present invention has excellent chemical resistance, oxidation resistance, thermal stability, and pressure resistance, and also exhibits high permeability and separation performance, and has excellent durability. The ammonia separation method of the present invention using such a zeolite membrane can be applied to the separation of ammonia from ammonia synthesis products. Furthermore, in the ammonia separation method of the present invention, a zeolite membrane is provided in an ammonia synthesis reactor, and ammonia is selectively permeated and separated in the reactor, thereby separating ammonia from hydrogen gas and nitrogen gas in the reaction system. It can also be used as a membrane reactor to efficiently synthesize ammonia at a high conversion rate by shifting the equilibrium with gas.

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. In addition, the values of various manufacturing conditions and evaluation results in the following examples have the meaning as preferable upper or lower limits in the embodiments of the present invention, and the preferable ranges are different from the above-mentioned upper or lower limits. It may be a range defined by the values of the following examples or a combination of values of the examples.

<Measurement of separation performance>
(1) Ammonia separation test In the apparatus schematically shown in FIG. 3, an ammonia separation test was conducted as follows. In the apparatus shown in FIG. 3, a mixed gas containing ammonia gas (NH ₃ ) and nitrogen gas (N ₂ ) is supplied between the pressure vessel 32 and the zeolite membrane composite 31 at a flow rate of 126 SCCM. The back pressure valve 36 is used to adjust the pressure difference between the gas on the supply side and the gas that has permeated through the membrane to be constant at 0.3 MPa, and the exhaust gas discharged from the piping 340 is analyzed using a micro gas chromatograph. The concentration and flow rate were calculated.
In addition, in the ammonia separation test, in order to remove components such as moisture and air from the pressure container, the sample gas temperature and After the permeate gas flow rate stabilizes by keeping the differential pressure between the supply gas side and the permeate gas side of the zeolite membrane composite constant, the flow rate of the sample gas (permeate gas) that has permeated through the zeolite membrane composite is measured, and the gas permeance [ mol/(m ² ·s · Pa)] was calculated. For the pressure when calculating permeance, the pressure difference (differential pressure) between the supply side and the permeation side of the supply gas was used. In the case of mixed gases, the partial pressure difference was used.
Furthermore, based on this measurement result, the ideal separation coefficient α' was calculated using the following equation (2).
α'=(Q1/Q2)/(P1/P2)...(2)
[In formula (2), Q1 and Q2 represent the permeation amount [mol・(m ²・s) ⁻¹ ] of a gas with high permeability and a gas with low permeability, respectively, and P1 and P2 are respectively, The pressure difference [Pa] between the supply side and the permeation side of a gas with high permeability and a gas with low permeability is shown. ]
This indicates the ratio of permeance of each gas, and therefore, the permeance of each gas can be calculated and determined from the ratio.

(2) Preparation of ammonia separation test sample 8 to 12 cm (part B of zeolite membrane composite 1) and 56 to 60 cm (zeolite membrane composite Part A) of body 1, 108 to 112 cm (part B' of zeolite membrane composite 1) was cut out with a diamond cutter and used as a sample for ammonia separation evaluation. Note that FIG. 4 is a schematic diagram of the zeolite membrane composite produced in Example 1.

Example 1
[Manufacture of MFI type zeolite membrane composite]
(Raw material mixture for hydrothermal synthesis)
A mixture of 32.7 g of 93% by mass sodium hydroxide (manufactured by Wako, granules) and 2739.8 g of demineralized water was mixed with sodium aluminate (manufactured by Kishida Chemical Co., Ltd., containing 62.2% by mass of Al ₂ O ₃ )5. .3g was added and stirred at 50°C for 30 minutes. 238.5 g of colloidal silica (Snowtex 40, manufactured by Nissan Chemical Co., Ltd.) was added to this and stirred at 50° C. for 4 hours to obtain a raw material mixture for hydrothermal synthesis. The composition (mole ratio) of this raw material mixture for hydrothermal synthesis was SiO ₂ /Al ₂ O ₃ /NaOH/H ₂ O=1/0.020/0.54/100.

(Porous support)
As the porous support, a 120 cm alumina tube (outer diameter 12 mm, inner diameter 9 mm) manufactured by Iwao Porcelain Industry Co., Ltd. was washed through circulation with demineralized water and then dried.

(Seed crystal dispersion)
A seed crystal dispersion was prepared by preparing MFI type zeolite ground in a mortar and dispersing the seed crystals so that the seed crystal concentration was 0.1% by mass.

(Manufacture of zeolite membrane composite)
The porous support, which was sucked by a vacuum pump, was immersed in the above-mentioned seed crystal dispersion for 10 seconds, and then dried at room temperature for 12 hours to adhere the seed crystals to the porous support. The mass of the attached seed crystal was about 0.04 g. Using this method, four porous supports to which seed crystals were attached were prepared.
Four porous supports with seed crystals attached were immersed vertically into Teflon (registered trademark) inner cylinders each containing the above-mentioned raw material mixture for hydrothermal synthesis, the autoclave was sealed, and the autoclave was sealed and placed in a constant temperature bath. After raising the temperature to 180° C. in a chamber for 3 hours, the mixture was left standing for 12 hours and heated under autogenous pressure. After a predetermined period of time had elapsed, the porous support-zeolite membrane composite was taken out from the reaction mixture after being allowed to cool, and after washing, demineralized water was added again and the mixture was heated in an autoclave at 120° C. for 20 hours. After a predetermined period of time had elapsed, the porous support-zeolite membrane composite was allowed to cool and then taken out from the demineralized water and dried at 100° C. for 3 hours to obtain an MFI type zeolite membrane composite. The mass of the MFI type zeolite crystallized on the porous support was 1.3 g. Further, the air permeation rate of the zeolite membrane composite after firing was 4 cm ³ /min.

Comparative example 1
[Manufacture of MFI type zeolite membrane composite]
(Raw material mixture for hydrothermal synthesis)
A mixture of 77.6 g of 93% by mass sodium hydroxide (manufactured by Wako, granular) and 2398.3 g of demineralized water was mixed with sodium aluminate (manufactured by Kishida Chemical Co., Ltd., containing 62.2% by mass of Al ₂ O ₃ )12 .5g was added and stirred at 50°C for 30 minutes. 566.5 g of colloidal silica (Snowtex 40, manufactured by Nissan Chemical Co., Ltd.) was added to this, and the mixture was stirred at 50° C. for 4 hours to obtain a raw material mixture for hydrothermal synthesis. The composition (mole ratio) of this raw material mixture for hydrothermal synthesis was SiO ₂ /Al ₂ O ₃ /NaOH/H ₂ O=1/0.020/0.54/40.

(Porous support)
As the porous support, a 120 cm alumina tube (outer diameter 12 mm, inner diameter 9 mm) manufactured by Iwao Porcelain Industry Co., Ltd. was washed through circulation with demineralized water and then dried.

(Seed crystal dispersion)
A seed crystal dispersion was prepared by preparing MFI type zeolite ground in a mortar and dispersing the seed crystals so that the seed crystal concentration was 0.1% by mass.

(Manufacture of zeolite membrane composite)
The porous support, which was sucked by a vacuum pump, was immersed in the above-mentioned seed crystal dispersion for 10 seconds, and then dried at room temperature for 12 hours to adhere the seed crystals to the porous support. The mass of the attached seed crystal was about 0.038 g. Using this method, four porous supports with seed crystals attached were prepared.
Four porous supports with seed crystals attached were immersed vertically into Teflon (registered trademark) inner cylinders each containing the above-mentioned raw material mixture for hydrothermal synthesis, the autoclave was sealed, and the autoclave was sealed and placed in a constant temperature bath. The temperature was raised to 180°C in a vacuum chamber for 3 hours, and the mixture was left standing for 14 hours and heated under autogenous pressure. After a predetermined period of time had elapsed, the porous support-zeolite membrane composite was taken out from the reaction mixture after being allowed to cool, and after washing, demineralized water was added again and the mixture was heated in an autoclave at 120° C. for 20 hours. After a predetermined period of time had elapsed, the porous support-zeolite membrane composite was allowed to cool, then taken out from the demineralized water, and dried at 100° C. for 3 hours to obtain MFI type zeolite membrane composite 2. The mass of the MFI type zeolite crystallized on the porous support was 0.77 g. Further, the air permeation amount of the zeolite membrane composite 2 after firing at 50 Torr was 1 cm ³ /min.

(Evaluation results)
An ammonia separation test was conducted by the method described above under the condition that the temperature of the MFI type zeolite membrane composite manufactured above was 250°C.
In addition, in order to conduct the experiment simply, a mixed gas of 9.5 volume % NH ₃ /90.5 volume % N ₂ was used as the mixed gas. Table 1 shows the ammonia concentration and ammonia/nitrogen (NH ₃ /N ₂ ) permeance ratio of the obtained permeate gas. In Table 1, the ammonia concentration of the permeated gas is a value rounded to the first decimal place.
Regarding the ratio of elements in each part, the silicon/aluminum ratio and sodium/silicon ratio were determined using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), which will be described later, and the number of measurements n = The average value of the measured values is shown as 5 times.

(Preparation of SEM-EDS analysis sample)
(Preprocessing)
The 4 cm zeolite membrane composite on which the NH ₃ separation measurement was performed was cut with a diamond cutter into a 5 mm square test piece, and after cutting the cross section, 2 nm of Pt was deposited and observed.
Equipment: Broad ion beam (JEOL IB-19520CCP)
Method: The support side was filed to a thickness of 1 mm or less, and cross-sectional cutting was carried out for 4 hours by irradiating the porous support side with an ion beam at an accelerating voltage of 4 kV.
(SEM-EDS measurement)
Equipment: FE-SEM (JEOL JSM-7900F)
EDS (Oxford ULTIM MAX)
Conditions: 5kV (irradiation current 500 pA, high vacuum mode)
Observation magnification: 5000x, 10000x, 20000x (observation range for SEM-EDS measurement)
An image was obtained at a magnification of 20,000 times, the membrane portion was enclosed as shown in FIG. 6, and measurement was performed for 120 seconds under the above conditions to calculate the Si/Al ratio and Na/Al ratio.
(Calculation of atomic concentration)
The atomic number concentration of each element was calculated using software from AZtec (Oxford Instruments). The Si/Al ratio was calculated by dividing the Si atomic concentration by the Al atomic concentration. The Na/Si ratio was calculated by dividing the Na atomic concentration by the Si atomic concentration.

The zeolite membrane composite of the example of the present invention exhibits high ammonia and nitrogen separation ability at every site, and the ammonia:nitrogen ratio is 100 or more at every site. On the other hand, the zeolite composite membrane of Comparative Example 1, which was manufactured by a typical conventional method, has a significantly reduced separation performance at one end (site B). As a result, although the zeolite composite membrane of Comparative Example 1 can be lengthened to increase the surface area and increase the amount of gas that can pass per unit time, the separated gas contains a large amount of nitrogen. It can be seen that the ability to separate ammonia is greatly reduced. On the other hand, the zeolite membrane composite of Example 1 of the present invention, which was manufactured with a considerably higher water content than usual, showed no difference in ammonia and nitrogen permeability at any part, even though it was longer than 1 m. It is more than 100 times larger, which shows that the longer length allows for an absolutely larger amount of gas to pass through, as well as a higher ammonia separation ability.
Looking at this result in relation to the composition, it can be seen that the Si/Al molar ratio differs greatly from the center in the region where the ability to separate ammonia and nitrogen is significantly reduced. It is thought that this fluctuation in composition was somehow responsible for the decrease in separation ability. For example, it is thought that when a heat load is applied, the difference in composition at only one end of the tube causes microscopic damage to one end of the tube, allowing both nitrogen and ammonia to pass through.
This result is considered to indicate that when the fluctuation range of the Si/Al ratio exceeds 20%, the separation ability decreases.

10. Zeolite membrane composite 11. Center of length of tube 12. Part (A)
13. Part (B)
13'. Part (B')
31. Zeolite membrane composite 32. Pressure-resistant container 33. End pin 34. Connection part 35. Pressure gauge 36. Back pressure valve 37. Supply gas (mixed gas)
38. Permeated gas39. Sweep gas 340. Exhaust gas 341. Piping 342. Piping 101. Porous support 102. Cavity part 103. zeolite membrane

Claims (12)

A zeolite membrane composite having a zeolite membrane on a porous support, which has a tubular structure and has the following ratio of Si/Al in part (B) to the ratio of Si/Al in part (A) and A zeolite membrane composite characterized in that the Si/Al ratio in the site (B') matches the Si/Al ratio in the site (A) within 20%.
Area (A): A partial area with a width of 4 cm on both sides from the longitudinal center of the zeolite membrane composite tube. Area (B): A partial area with a width of 8 to 12 cm from one end of the zeolite membrane composite tube (B). '): 8 to 12 cm from the other end of the zeolite membrane composite tube The zeolite membrane composite according to claim 1, wherein the length of the tube of the tubular structure is 40 cm or more. The zeolite membrane composite according to claim 1, wherein the length of the tube of the tubular structure is 100 cm or more. The zeolite membrane composite according to any one of claims 1 to 3, wherein the zeolite is of the CHA type, FAU type, MFI type, LTA type, or RHO type. The zeolite membrane composite according to any one of claims 1 to 3, wherein the zeolite is of the CHA type, MFI type, LTA type, or RHO type. The zeolite membrane composite according to any one of claims 1 to 3, wherein the zeolite is either an MFI type or an RHO type. The zeolite membrane composite according to any one of claims 1 to 3, wherein the zeolite is an MFI type. The ratio of Si/Al in the site (B) to the Si/Al ratio in the site (A) and the Si/Al ratio in the site (B') to the Si/Al ratio in the site (A) are 18%. The zeolite membrane composite according to any one of claims 1 to 7, wherein the zeolite membrane composites match within the range of . The ratio of Si/Al in the site (B) to the ratio of Si/Al in the site (A), and the ratio of Si/Al in the site (B') to the ratio of Si/Al in the site (A) is 15%. The zeolite membrane composite according to any one of claims 1 to 7, wherein the zeolite membrane composites match within the range of . The method for producing a zeolite membrane composite according to any one of claims 1 to 9, characterized in that the molar ratio of water to silicon in the raw material mixture for hydrothermal synthesis is 45 or more and 300 or less. Method for producing membrane composite. The method for producing a zeolite membrane composite according to claim 10, wherein the molar ratio of water to silicon is 60 or more and 200 or less. The method for producing a zeolite membrane composite according to claim 10 or 11, wherein the molar ratio of water to silicon is 70 or more and 150 or less.