Zeolite membrane composite

Abstract

To provide a zeolite membrane composite, even when made long, enabling separation and recovery of desired gas from mixed gas.SOLUTION: Provided is a zeolite membrane composite 10 having a zeolite membrane on a porous support, with a tubular structure, in which a sodium / silicon (mole ratio) in a moiety (A) 12, a sodium / silicon (mole ratio) in a moiety (B) 13 and a sodium / silicon (mole ratio) in a moiety (B') 13' are all 0.2 or less, and each moiety is defined as follows: moiety (A): portion of 4 cm width to both sides from a center 11 in a length direction of zeolite membrane composite tube, moiety (B): portion of 8-12 cm from one end of zeolite membrane composite tube, and moiety (B'): portion of 8-12 cm from the other end of zeolite membrane composite tube.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a zeolite composite membrane. More specifically, the present invention relates to a zeolite composite membrane for separating a specific component from a mixed gas, and particularly to a long zeolite composite membrane. [Background technology]

[0002] 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. Of these methods, polymer separation membranes are characterized by their excellent processability, but have the problem of being flammable. On the other hand, inorganic membranes such as zeolite membranes have good chemical resistance, oxidation resistance, heat stability, and pressure resistance, so various inorganic membranes have been proposed. Among these, zeolite membranes have regular sub-nanometer pores and function as molecular sieves, so they are expected to be highly durable separation membranes that can not only selectively transmit specific molecules but also separate and concentrate molecules over a wide temperature range. Such zeolite membranes are usually used as zeolite membrane composites, in which zeolite is formed in a membrane shape on a support made of an inorganic material.

[0003] The application of membrane separation to the separation of ammonia gas from nitrogen gas in this invention has also been expected in recent years. For example, membrane separation has been applied to the ammonia production process using the Haber-Bosch process, an industrially important process. A characteristic of the Haber-Bosch process is that the ammonia production reaction is an equilibrium reaction, and although high-pressure, low-temperature conditions are thermodynamically favored, high-pressure, high-temperature production conditions are generally required to ensure catalytic reaction rates. Furthermore, because unreacted hydrogen gas and nitrogen gas coexist with ammonia gas in the resulting mixed gas, the process of recovering the product ammonia gas from the resulting mixed gas requires cooling the mixed gas to approximately -20°C to -5°C to condense and separate the ammonia. Meanwhile, a process has been proposed to efficiently recover high-concentration ammonia gas by replacing the cooling condensation separation method used in the purification process with a separation method using inorganic membranes (Patent Documents 1 and 2).

[0004] Patent Document 1 discloses a membrane separation process that includes a first separation step in which hydrogen is separated from crude ammonia using a gas separation membrane, and a second separation step in which ammonia is separated from the crude ammonia after the first separation step using another gas separation membrane. 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 also requires a step of separating ammonia gas from the high-concentration hydrogen mixed gas containing ammonia gas that has permeated through the first-stage separation membrane, and from the mixed gas of nitrogen gas and ammonia gas that has not permeated, in order to make it an economical process. However, the permeability of ammonia gas in the separation of nitrogen gas and ammonia gas by the second-stage membrane is insufficient, and there is a risk that the membrane area will become large. Furthermore, the method proposed in Patent Document 2 for separating ammonia gas from a mixed gas of ammonia gas and hydrogen gas and / or nitrogen gas using a specific zeolite having an eight-membered oxygen ring could be an effective method applicable to industrial processes. However, in the method for separating ammonia by molecular sieving using the pore size of zeolite proposed in Patent Document 2, the permeance ratio (ideal separation factor) of ammonia gas to nitrogen gas is about 14, and its permeation performance cannot necessarily be said to be sufficient.

[0005] In order to solve these problems, Patent Document 3 proposes a method for separating ammonia by using a zeolite membrane to selectively permeate ammonia gas from a mixed gas containing at least ammonia gas, hydrogen gas, and nitrogen gas, wherein the ammonia gas concentration in the mixed gas is 1.0% by volume or more, and discloses that RHO-type zeolite or MFI-type zeolite is preferable as the zeolite constituting the zeolite membrane. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-247654 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-058433 [Patent Document 3] International Publication No. 2018 / 230737 Brochure Summary of the Invention [Problem to be solved by the invention]

[0007] According to the technique disclosed in Patent Document 3, it is possible to efficiently separate and recover ammonia gas from a mixed gas containing at least ammonia gas and nitrogen gas (hereinafter, sometimes simply referred to as a "mixed gas"). A possible technique for separating and recovering ammonia gas more efficiently using this technique is to form a zeolite membrane composite, in which zeolite is formed in the form of a membrane on a support made of an inorganic material, into a tubular structure, and to elongate the tubular structure to increase the contact area with the mixed gas, thereby separating and recovering ammonia gas more efficiently from the mixed gas. However, it was found that elongating the zeolite composite membrane increases the amount of nitrogen permeation, resulting in a decrease in the ammonia gas separation capacity, i.e., the difference in permeability between nitrogen and ammonia. Investigation into the cause of this finding revealed that the increase in nitrogen permeation at both ends of the elongated zeolite composite membrane, or at least at one of the ends, significantly reduces the ammonia separation capacity of the composite as a whole. Therefore, an object of the present invention is to provide a zeolite composite membrane that can separate and recover a specific gas from a mixed gas without reducing the gas separation ability of the zeolite composite membrane, typically for ammonia gas, even when the zeolite composite membrane is lengthened. In the following description, the separation and recovery of ammonia and nitrogen will be taken as an example of a typical example of gas separation and recovery, but the present invention can also be applied to the separation and recovery of other gases. [Means for solving the problem]

[0008] As a result of extensive research to solve the above-mentioned problems, the inventors discovered that the cause is due to compositional irregularities, and that the reason for this is presumed to be, for example, that differences in composition cause microscopic breakdowns during thermal load, and that this can be confirmed by the ratio of Na to Si. They also found that the above-mentioned problems can be solved by using a specific zeolite membrane composite, and arrived at the present invention. As mentioned above, considering the principle of damage caused by compositional irregularities, similar problems arise not only in ammonia separation but also in methanol separation, for example, when synthesizing methanol from CO, CO2, H2, etc. as raw materials and separating it, or when separating methane from a mixture of CO, CO2, N2, etc. and CH4, such as natural gas or landfill gas, and the present invention can solve these problems. That is, the gist of the present invention lies in the following [1] to

[13] .

[0009] [1] A zeolite membrane composite having a zeolite membrane on a porous support, the zeolite membrane composite having a tubular structure, characterized in that the sodium / silicon (molar ratio) in the following region (A), the sodium / silicon (molar ratio) in the following region (B), and the sodium / silicon (molar ratio) in the following region (B') are all 0.2 or less. Section (A): 4 cm wide sections on both sides of the center of the zeolite membrane composite tube in the longitudinal direction Section (B): 8 to 12 cm from one end of the zeolite membrane composite tube Section (B'): 8 to 12 cm from the other end of the zeolite membrane composite tube [2] The zeolite composite membrane according to the above [1], wherein the length of the tube of the tubular structure is 40 cm or more. [3] The zeolite composite membrane according to the above [1], wherein the length of the tube of the tubular structure is 100 cm or more. [4] The zeolite composite membrane according to any one of the above [1] to [3], wherein the zeolite is any one of a CHA type, an FAU type, an MFI type, an LTA type, and an RHO type. [5] The zeolite composite membrane according to any one of the above [1] to [3], wherein the zeolite is any one of a CHA type, an MFI type, an LTA type, and an RHO type. [6] The zeolite composite membrane according to any one of the above [1] to [3], wherein the zeolite is either an MFI type or an RHO type. [7] The zeolite composite membrane according to any one of the above [1] to [3], wherein the zeolite is of MFI type. [8] The zeolite composite membrane according to any one of the above [1] to [7], wherein the sodium / silicon (molar ratio) is 0.18 or less. [9] The zeolite composite membrane according to any one of the above [1] to [7], wherein the sodium / silicon (molar ratio) is 0.16 or less.

[10] The zeolite composite membrane according to any one of the above [1] to [7], wherein the sodium / silicon (molar ratio) is 0.14 or less.

[11] A method for producing a zeolite membrane composite according to any one of [1] to

[10] 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.

[12] The method for producing a zeolite composite membrane according to the above

[11] , wherein the molar ratio of water to silicon is 60 or more and 200 or less.

[13] The method for producing a zeolite composite membrane according to the above

[11] or

[12] , wherein the molar ratio of water to silicon is 70 or more and 150 or less. [Effects of the Invention]

[0010] According to the present invention, a zeolite membrane composite can be provided that enables separation and recovery of gases, such as ammonia, from mixed gases without reducing the separation ability, even when the zeolite membrane composite is lengthened. Although the present invention will be described primarily using ammonia separation, as explained above, the problem of turbulence due to composition also occurs in, and can be prevented in, methanol separation, for example, when methanol is synthesized from CO, CO2, H2, or other raw materials and then separated, or when methane is separated from a mixture of CO, CO2, N2, or other raw materials and CH4, such as natural gas or landfill gas. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a zeolite membrane composite of the present invention. [Figure 2] 1 is a schematic diagram showing a cross-sectional structure of a zeolite membrane composite of the present invention. [Figure 3] FIG. 1 is a schematic diagram showing an ammonia gas separation test device. [Figure 4] FIG. 1 is a schematic diagram of the zeolite composite membrane produced in Example 1. [Figure 5] FIG. 1 is a diagram for explaining the state of a sample in SEM-EDS measurement. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes in more detail the embodiments of the present invention. However, the description of the constituent elements described below is an example of an embodiment of the present invention, and the present invention is not limited to these contents, and can be implemented in various modifications within the scope of its gist. In this specification, zeolite refers to a zeolite defined by the International Zeolite Association (IZA, hereinafter referred to as "IZA"). Its structure is characterized by X-ray diffraction data. In this specification, a "porous support-zeolite membrane composite in which a zeolite membrane is formed on a porous support" may be simply referred to as a "zeolite membrane composite." In addition, a "porous support" may be simply abbreviated as a "support," and an "aluminosilicate zeolite" may be simply abbreviated as a "zeolite." In this specification, "hydrogen gas," "nitrogen gas," and "ammonia gas" may be simply referred to as "hydrogen," "nitrogen," and "ammonia," respectively. Meanwhile, ammonia separation in this invention refers to obtaining a mixed gas containing a higher concentration of ammonia gas from a mixed gas containing ammonia gas.

[0013] [Zeolite membrane composite] The zeolite membrane composite of the present invention has a zeolite membrane on a porous support, which is preferably crystallized and fixed, and also includes a state in which part of the zeolite is fixed to the inside of the support. The zeolite membrane composite is preferably, for example, one in which zeolite is crystallized into a membrane on the surface of a porous support by hydrothermal synthesis.

[0014] 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 of a tubular support, or on the inner surface, or even on both surfaces depending on the application system. The zeolite membrane may also be formed by laminating it on the surface of the support, or may be crystallized so as to fill the pores in the surface layer of the support. In this case, it is important that the crystallized membrane layer does not have cracks or continuous micropores, and forming a so-called dense membrane is preferred in terms of improving separation performance.

[0015] The zeolite membrane composite of the present invention will be described in detail with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic diagram showing the 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 "tube") as shown in Fig. 1, and by definition, the length of the tube must be 28 cm, but the length of the tube is preferably 40 cm or more. 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 has a void 102 in the center. The cross-sectional structure in Fig. 2 shows an embodiment in which the zeolite membrane 103 is on the outer surface of the porous support 101, but the zeolite membrane may be on the inner surface of the porous support 101, or the zeolite membrane may be on both the outer and inner surfaces of the porous support. In Figure 1, the area 4 cm on either side of the center 11 in the longitudinal direction of the tube, i.e., ±2 cm in width from the center 11 in the left-right direction (plus on the right and minus on the left), is region (A) (12 in Figure 1). Also, the area 8 to 12 cm from one end is region (B) (13 in Figure 1), and the area 8 to 12 cm from the other end is region (B') (13' in Figure 1).

[0016] In the present invention, as described above, the length of the tube is preferably 40 cm or more. The longer the tube length, the greater the amount of mixed gas that can be separated and processed per tube, thereby reducing equipment costs. From the above viewpoints, 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. There is no particular upper limit to the length, but it is preferably 500 cm or less, more preferably 300 cm or less, and even more preferably 200 cm or less, in order to prevent problems such as breakage due to vibration during use.

[0017] 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, and particularly preferably 0.4 cm or more, and usually 2 cm or less, preferably 1.5 cm or less, more preferably 1.2 cm or less, and 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, and particularly preferably 1.0 cm or more, and usually 2.5 cm or less, preferably 1.7 cm or less, and more preferably 1.3 cm or less. If the inner diameter and outer diameter of the pipe are each equal to or less than the above upper limit, the size of the equipment required for separating ammonia, etc. can be reduced, which is economically advantageous.

[0018] <Porous support> The porous support used in the present invention preferably has chemical stability that allows zeolite to be crystallized into a membrane on its surface. Suitable porous supports include gas-permeable porous polymers such as polysulfone, cellulose acetate, aromatic polyamide, vinylidene fluoride, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, polytetrafluoroethylene, and polyimide; ceramic sinters such as silica, α-alumina, γ-alumina, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide; sintered metals and mesh-like molded bodies such as iron, bronze, and stainless steel; and inorganic porous bodies such as glass and carbon molded bodies. Among these, inorganic porous supports such as ceramic sinters, metal sinters, glass, and carbon molded bodies are preferred as porous supports for ammonia separation in high-temperature regions because of their excellent mechanical strength, deformation resistance, thermal stability, and reactivity resistance at high temperatures. The inorganic porous support is preferably a sintered ceramic, which is a solid material whose principal or majority components are inorganic non-metallic substances.

[0019] As described above, preferred ceramic sintered bodies include ceramic sintered bodies containing α-alumina, γ-alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, silicon carbide, etc., but these may be sintered bodies of a single material or a mixture of two or more materials sintered together. A part of the surface of these ceramic sintered bodies may be converted into zeolite during zeolite membrane synthesis, which increases the adhesion between the porous support and the zeolite membrane, thereby improving the durability of the zeolite membrane composite. In particular, inorganic porous supports containing at least one of alumina, silica, and mullite are more preferred because they can be easily partially zeoliteized, resulting in a stronger bond between the inorganic porous support and the zeolite, making it easier to form a dense zeolite membrane with high separation performance.

[0020] The porous support used in the present invention preferably has, on its surface (hereinafter also referred to as "porous support surface"), the action of crystallizing the zeolite formed on the porous support. The pore size of the porous support surface is preferably controlled. The average pore size of the porous support near the surface is usually 0.02 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, more preferably 0.15 μm or more, even more preferably 0.5 μm or more, particularly preferably 0.7 μm or more, most preferably 1.0 μm or more, and usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less, particularly preferably 2 μm or less. By using a porous support having a pore size in this range, a dense zeolite membrane that improves ammonia permeation selectivity can be formed. The surface of the porous support is preferably smooth, and the surface may be polished with a file or the like as needed.

[0021] The pore size of the porous support used in the present invention in the portion 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 portion is usually 20% or more, more preferably 30% or more, and usually 60% or less, preferably 50% or less. The porosity of the portion other than the vicinity of the surface of the porous support affects the permeation flow rate when separating gas or liquid, and when the porosity is above the above-mentioned lower limit, the permeate tends to diffuse easily, while when it is below the above-mentioned upper limit, it tends to be easier to prevent a decrease in the strength of the porous support. In addition, as a method of controlling the permeation flow rate, a porous support formed by combining porous bodies with different porosities in layers may be used.

[0022] The porous support used in the present invention has a tubular shape. The length of the tubular porous support may be any length that ensures the length of the above-mentioned zeolite membrane composite. Therefore, similar to the above-mentioned zeolite membrane composite, 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 particularly preferably 120 cm or more. Also, it is preferably 500 cm or less, more preferably 300 cm or less, and even more preferably 200 cm or less. If it is equal to or less than the above upper limit, there is no problem such as the above-mentioned tendency for the porous support to break due to vibration during use, and the production of the zeolite membrane composite can be simplified.

[0023] The inner diameter of the tubular porous support may also be any diameter that can ensure 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, more preferably 0.3 cm or more, and particularly preferably 0.4 cm or more, and usually 2 cm or less, preferably 1.5 cm or less, more preferably 1.2 cm or less, and 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, and particularly preferably 1.0 cm or more, and usually 2.5 cm or less, preferably 1.7 cm or less, and more preferably 1.3 cm or less. The wall thickness of the tubular porous support is usually 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, even more preferably 0.7 mm or more, even more preferably 1.0 mm or more, and particularly preferably 1.2 mm or more, and is 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 equal to or greater than the above-mentioned lower limit, the strength of the support can be improved, making it less likely to break. Furthermore, if the inner diameter and outer diameter of the tubular support are each equal to or less than the above-mentioned upper limit, the size of the equipment required for ammonia separation can be reduced, which can be economically advantageous. Furthermore, if the wall thickness of the tubular support is equal to or less than the above-mentioned upper limit, the permeation performance tends to be improved.

[0024] The absolute value of the rate of change in the thermal expansion coefficient of the porous support at 300°C relative to the thermal expansion coefficient at 30°C is 0.25% or less, preferably 0.20% or less, more preferably 0.15% or less, particularly preferably 0.10% or less, and most preferably 0.05% or less. That is, the rate of change in the thermal expansion coefficient of the porous support at 300°C relative to the thermal expansion coefficient at 30°C is within ±0.25%, preferably within ±0.20%, more preferably within ±0.15%, particularly preferably within ±0.10%, and most preferably within ±0.05%. Furthermore, the absolute value of the rate of change in the thermal expansion coefficient of the porous support at 400°C relative to the thermal expansion coefficient at 30°C is usually 0.30% or less, preferably 0.25% or less, more preferably 0.20% or less, particularly preferably 0.15% or less, and most preferably 0.10% or less. That is, the rate of change in the thermal expansion coefficient of the porous support at 400° C. relative to the thermal expansion coefficient at 30° C. is within ±0.30%, preferably within ±0.25%, more preferably within ±0.20%, particularly preferably within ±0.15%, and most preferably within ±0.10%. A zeolite membrane composite formed on a porous support exhibiting such a low thermal expansion coefficient is unlikely to develop cracks in the zeolite membrane due to the thermal expansion (contraction) of the porous support when the composite is heated, for example, at temperatures exceeding 200° C., even at temperatures exceeding 300° C., in order to allow ammonia to permeate from a mixed gas composed of multiple components containing at least ammonia and nitrogen. Therefore, ammonia can be stably and efficiently separated to the permeation side at high permeability even under high-temperature conditions.

[0025] Furthermore, the ratio of the rate of change in the thermal expansion coefficient of the porous support at 30°C to the rate of change in the thermal expansion coefficient at 300°C to the rate of change in the thermal expansion coefficient at 30°C to the rate of change in the thermal expansion coefficient at 400°C to the rate of change in the thermal expansion coefficient at 30°C is, in absolute terms, 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 formed on a porous support exhibiting such a specific ratio of thermal expansion coefficients between specific temperatures can suppress the occurrence of cracks in the zeolite membrane that would otherwise follow local thermal expansion (contraction) of the porous support, even when non-uniform heat generation occurs in a reactor during ammonia production, for example, and therefore can efficiently separate ammonia to the permeation side at high permeability stably even under high-temperature conditions.

[0026] (Method for measuring the rate of change in thermal expansion coefficient) In the present invention, the rate of change in the thermal expansion coefficient of the porous support at a predetermined temperature relative to the thermal expansion coefficient at 30°C can be calculated by the following formula (1) using the crystal lattice constants measured at 30°C and the predetermined temperature by a heating XRD measurement method under the following conditions.

[0027] (Temperature-raised XRD measurement device specifications) [Table 1]

[0028] (Measurement conditions) [Table 2]

[0029] Measurement atmosphere: air Temperature rise condition: 20℃ / min Measurement method: XRD measurement is carried out after holding at the measurement temperature for 5 minutes. The measurement data is subjected to fixed slit correction using a variable slit. Rate of change of thermal expansion coefficient = (crystal lattice constant measured at a given temperature) ÷ (crystal lattice constant measured at 30°C) - 1 (1)

[0030] <Zeolite> In the present invention, the zeolite constituting the zeolite membrane is preferably an aluminosilicate. The aluminosilicate is composed mainly 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 are preferably cationic species that are easily coordinated to the ion exchange sites of the zeolite, such as cationic species selected from the group consisting of elements of Groups 1, 2, 8, 9, 10, 11, and 12 of the periodic table, NH4 + and two or more of these cationic species, more preferably cationic species selected from the group of elements of Groups 1 and 2 of the periodic table, NH4 + and two or more cationic species thereof.

[0031] The SiO2 / Al2O3 molar ratio of the aluminosilicate is not particularly limited, but is usually 6 or more, preferably 7 or more, and more preferably 8 or more, and is usually 500 or less, preferably 100 or less, more preferably 80 or less, even 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 with an SiO2 / Al2O3 molar ratio in this specific range, the density of the zeolite membrane and its durability, such as chemical reactivity resistance and heat resistance, can be improved. Furthermore, from the viewpoint of separation performance for permeating ammonia from a mixed gas composed of multiple components containing at least ammonia and nitrogen, it is preferable to use a zeolite containing as much Al as possible within a range in which the zeolite structure can be easily maintained, because acid sites resulting from elements such as Al become adsorption sites for ammonia. By using a zeolite showing the above-mentioned SiO2 / Al2O3 molar ratio, ammonia can be separated with high selectivity and high permeability. The SiO2 / Al2O3 molar ratio of the zeolite can be adjusted by the reaction conditions of the hydrothermal synthesis, which will be described later.

[0032] In this specification, the SiO2 / Al2O3 molar ratio is a value determined by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), where the X-ray accelerating voltage is usually set to 10 kV to obtain information on only the zeolite membrane, which is several microns thick.

[0033] The structure of the zeolite used in the present invention, when expressed in terms of the codes specified by the IZA, includes, 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, TUN, WEI, MFI, MON, PAU, PHI, and MOR.

[0034] Among them, the framework density is 18.0T / nm 3 The following zeolites are preferred, more preferably CHA, FAU, MFI, LTA, and RHO, and even more preferably MFI and RHO. When permeating components other than ammonia are present in the ammonia-containing mixed gas, the use of a zeolite with a low framework density can reduce the resistance to permeation of these permeating components, making it easier to increase the amount of ammonia permeated.

[0035] Here, the framework density (unit: T / nm 3 ) is the unit volume of zeolite (1 nm 3It means the number of T atoms (atoms other than oxygen that make up the zeolite framework) present per 1000 sq m (1000 sq m), and this value is determined by the structure of the zeolite. The relationship between framework density and zeolite structure is shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007 ELSEVIER.

[0036] The membrane separation of ammonia and nitrogen in the present invention utilizes the adsorption of ammonia onto zeolite, and is characterized by the separation of ammonia based on the hopping mechanism of ammonia within the zeolite pores. Therefore, although not particularly limited, zeolites with pore sizes close to the molecular size of ammonia are sometimes preferred because they tend to improve ammonia separation selectivity. From the above perspective, zeolites with 8-membered oxygen ring pores are preferred. On the other hand, pores larger than the 8-membered oxygen ring are preferable because they increase ammonia permeability, but may result in reduced nitrogen separation performance. However, even when using a zeolite with pores larger than the 8-membered oxygen ring, if a zeolite with a reduced SiO2 / Al2O3 molar ratio is used, the pore size of the zeolite membrane is controlled by ammonia adsorbed on the Al site, allowing for high ammonia permeability and highly selective separation.

[0037] Therefore, the effective pore size of the zeolite used in membrane separation is an important design factor, as it significantly affects the pore size of the zeolite membrane when ammonia is adsorbed. The effective pore size of the zeolite can also be controlled by the type of metal introduced into the zeolite, ion exchange, acid treatment, silylation treatment, etc. It is also possible to improve separation performance by controlling the effective pore size using other methods. For example, the pore size of a zeolite is slightly affected by the atomic size of the metal species introduced into the zeolite framework. When a metal with an atomic size smaller than that of silicon, such as boron (B), is introduced, the pore size becomes smaller, while when a metal with an atomic size larger than that of silicon, such as tin (Sn), is introduced, the pore size becomes larger. In addition, the pore size may be affected by desorbing the metal introduced into the zeolite framework through acid treatment.

[0038] Furthermore, when the ions in zeolite are exchanged with monovalent ions having a large ionic radius, the effective pore size becomes smaller. On the other hand, when the ions are exchanged with monovalent ions having a small ionic radius, the effective pore size becomes close to the pore size inherent in the zeolite structure. Furthermore, the effective pore size of zeolite can also be reduced by silylation treatment. For example, by silylating the terminal silanols on the outer surface of a zeolite membrane and then laminating a silylated layer, the effective pore size of the pores facing the outer surface of the zeolite can be reduced.

[0039] The separation function of the zeolite membrane composite used in the present invention is not particularly limited, but is manifested 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 facilitating permeation. For example, the polarity of the zeolite can be controlled by the presence of nitrogen atoms, thereby controlling the affinity of ammonia to the zeolite and making it easier for ammonia to pass through.

[0040] In addition, the polarity of zeolite can be increased by substituting Al atoms for Si atoms in the zeolite framework, which allows highly polar gas molecules such as ammonia to be actively adsorbed and permeated through the zeolite pores. Furthermore, the polarity of the resulting zeolite can be controlled by adding other atom sources besides Al atoms, such as Ga, Fe, B, Ti, Zr, Sn, and Zn, to the aqueous reaction mixture for hydrothermal synthesis. In addition, ion exchange can be used to control not only the pore size of the zeolite but also its molecular adsorption performance, thereby controlling the permeation rate.

[0041] <Zeolite membrane> The zeolite membrane in the present invention refers to a membranous material made of zeolite, preferably formed by crystallizing zeolite on the surface of a porous support. The membrane may contain, as necessary, inorganic binders such as silica and alumina, organic substances such as polymers, or silylating agents for modifying the zeolite surface, in addition to zeolite. The preferred zeolite contained in the zeolite membrane used in the present invention is as described above, but the zeolite contained in the zeolite membrane may be one type or multiple types. Furthermore, the zeolite membrane may contain zeolites that tend to form in a mixed phase, such as ANA, GIS, and MER, or amorphous components other than crystals.

[0042] 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 zeolites and porous supports. Among these, particularly preferred combinations of zeolite and porous support include an MFI zeolite-porous alumina support, an RHO zeolite-porous alumina support, a DDR zeolite-porous alumina support, an AFI zeolite-porous alumina support, a CHA zeolite-porous alumina support, and an AEI zeolite-porous alumina support, and preferably a CHA zeolite-porous alumina support, an MFI zeolite-porous alumina support, and an RHO zeolite-porous alumina support, and more preferably an MFI zeolite-porous alumina support and an RHO zeolite-porous alumina support.

[0043] (molar ratio of alkali metal to aluminum) In the present invention, when the content of alkali metal atoms in the cross section of the zeolite membrane determined by SEM-EDS (scanning electron microscope energy dispersive X-ray analysis) measurement is controlled within a specific range, the ammonia permeability tends to improve when separating ammonia from a mixed gas consisting of multiple components including at least ammonia and nitrogen. Therefore, controlling the content of alkali metal atoms as needed is one of the preferred embodiments. In this way, when alkali metal atoms are present in the cross section of the zeolite membrane as needed, examples of the alkali metal atoms include Li, Na, K, Rb, Cs, and atoms of two or more of these metals. Among these, Li, Na, and Cs are preferred, and Na is more preferred because it has excellent ammonia separation performance and is a commonly used alkali metal. The measurement conditions for SEM-EDS are as follows: (Measurement conditions)

[0044] (Measurement conditions) (SEM-EDS measurement) Equipment: FE-SEM (JEOL JSM-7900F) EDS (Oxford ULTim MAX) Conditions: 5 kV (exposure current 500 pA, high vacuum mode) Observation magnification: 5000x, 10000x, 20000x

[0045] (Observation area for SEM-EDS measurement) An image was taken at 20,000x magnification, and the membrane portion was enclosed as shown in Figure 5 (a re-used example of an actual sample used in the Examples). Measurements were carried out for 120 seconds under the above conditions, and the Si / Al ratio and Na / Al ratio were calculated.

[0046] (Calculation of atomic concentration) The atomic concentration of each element was calculated using AZtec (Oxford Instruments) software. The Si / Al ratio was calculated by dividing the atomic concentration of Si by the atomic concentration of Al. The Na / Si ratio was calculated by dividing the atomic concentration of Na by the atomic concentration of Si.

[0047] Alkali metal atoms exist in the form of cations as ion pairs at the Al sites in the zeolite constituting the zeolite membrane, and are typically introduced into the zeolite by ion exchange treatment of the synthesized zeolite membrane, as described below. When alkali metal atoms are present on the zeolite membrane surface as needed, the content of alkali metal atoms, particularly sodium atoms, relative to the Al atoms on the zeolite membrane surface is preferably 2.0 or less, more preferably 1.8 or less, even more preferably 1.5 or less, and particularly preferably 1.0 or less. There is no particular restriction on the lower limit, but it is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more. Controlling the content of alkali metal atoms within the above range is preferred because it tends to improve the ammonia permeability while maintaining high ammonia separation selectivity. 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 will be described later.

[0048] Although the details of the present invention are not yet clear and are not particularly limited, the present invention is characterized by controlling the effective pore size of the zeolite used in membrane separation by utilizing the adsorption of ammonia onto the zeolite, and separating ammonia based on the hopping mechanism of ammonia within the zeolite pores. In this invention, which separates ammonia by primarily utilizing the intrapore hopping mechanism accompanied by the adsorption / desorption of ammonia onto the zeolite, an important design factor is how to increase the adsorption affinity of ammonia in the ammonia-containing feed mixed gas with the zeolite membrane surface compared to other gases such as hydrogen and nitrogen contained in the mixed gas. From this perspective, increasing the presence of Al atoms on the zeolite membrane surface changes the polarity of the zeolite membrane surface, increasing the adsorption affinity with ammonia in the feed gas, thereby improving ammonia separation performance. In addition, in the present invention, the content of Al atoms on the surface of the zeolite membrane is controlled by the SiO2 / Al2O3 ratio of the zeolite constituting the zeolite membrane and by aluminum salt treatment after the formation of the zeolite membrane, among other things. In particular, the latter aluminum salt treatment has the effect of sealing fine defects present on the surface of the zeolite membrane, thereby improving the density of the zeolite membrane and its durability, such as its resistance to chemical reactivity and heat resistance, and also greatly contributing to improving the thermal stability of the zeolite membrane for separation at high temperatures, which is one of the objectives of the present invention.

[0049] The selectivity of ammonia separation from a mixed gas containing at least ammonia and nitrogen is improved by the blocking effect of ammonia adsorption on the Al sites in the zeolite pores. Generally, ammonia tends to be highly adsorbed onto Al sites, resulting in impaired permeability (permeability). 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 onto the Al sites can be controlled, while the size of the alkali metal cations can maintain ammonia separation selectivity. These mechanisms enable the permeability to be improved while maintaining ammonia separation selectivity. In other words, it is preferable to control the molar ratio of alkali metal atoms (e.g., sodium) to Al atoms in the zeolite to 2.0 or less. It is also preferable that the molar ratio of alkali metal atoms to Al atoms in the zeolite be 0.01 or more.

[0050] (molar ratio of alkali metal to silicon) In the present invention, when the content of alkali metal atoms in the cross section of the zeolite membrane determined by SEM-EDS is controlled within a specific range, the ammonia permeability tends to improve when separating ammonia from a mixed gas consisting of multiple components including ammonia and nitrogen. Therefore, controlling the content of these atoms as needed is one of the preferred embodiments. In this way, when alkali metal atoms are present in the cross section of the zeolite membrane as needed, examples of the alkali metal atoms include Li, Na, K, Rb, Cs, and atoms of two or more of these metals. Among these, Li, Na, and Cs are preferred, and Na is more preferred because it has excellent ammonia separation performance and is a commonly used alkali metal. The measurement conditions are as described in the column (molar ratio of alkali metal to aluminum).

[0051] When alkali metal atoms are present on the zeolite membrane surface, the content of alkali metal atoms, preferably sodium, relative to silicon (Si atoms) on the zeolite membrane surface is, in molar ratio, 0.20 or less, preferably 0.18 or less, more preferably 0.16 or less, and even more preferably 0.14 or less. 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 content of alkali metal atoms within the above range is preferred because it tends to improve the ammonia permeability while maintaining high ammonia separation selectivity. 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 the ion exchange treatment of the zeolite or the amount of water during the production of the zeolite, as will be described later.

[0052] (nitrogen atom content on the zeolite membrane surface) In this embodiment, if the content of alkali metal atoms on the zeolite membrane surface is controlled and, if necessary, the content of nitrogen atoms contained in the zeolite membrane surface as determined by XPS measurement is controlled to a specific range, the separation selectivity when separating ammonia from a mixed gas tends to be significantly improved. Therefore, it is preferable to allow alkali metal atoms and nitrogen atoms to coexist on the zeolite membrane surface and appropriately control their contents. When nitrogen atoms are present on the zeolite membrane surface in this manner, the content of the nitrogen atoms, in terms of molar ratio relative to the Al atoms on the zeolite membrane surface, is usually 0.01 or more, preferably 0.05 or more, more preferably 0.10 or more, even more preferably 0.20 or more, particularly preferably 0.30 or more, and especially preferably 0.50 or more. The upper limit is not particularly limited because it depends on the structure of the cation species containing nitrogen atoms in the zeolite contained in the zeolite membrane and the amount of nitrate ions remaining when the zeolite membrane is subjected to nitrate treatment as needed, but is usually 4 or less, preferably 3 or less, and more preferably 1 or less. The use of a zeolite having a surface composition with such a specific nitrogen atom / Al atomic ratio is preferable because it can improve the denseness of the zeolite membrane and its durability, such as chemical reactivity resistance and heat resistance, and also enables highly selective separation of ammonia from a mixed gas consisting of ammonia and multiple components including hydrogen and / or nitrogen. The upper and lower limits are defined as being within the range of significant figures. That is, an upper limit of 4 or less means less than 4.5, while 0.01 or more means 0.005 or more.

[0053] In the present invention, when nitrogen atoms are contained in the zeolite membrane, the nitrogen atoms are ammonium ions (NH4 + ), nitrogen atoms derived from cationic species obtained by protonating organic amines having 1 to 20 carbon atoms, such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, as well as methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine; nitrogen atoms derived from an organic template when a nitrogen-containing organic template (structure-directing agent) is used in producing a zeolite membrane; and nitrogen atoms derived from nitrate ions remaining after the nitrate treatment of a zeolite membrane, which is performed as needed, as described below.

[0054] (Zeolite membrane thickness) 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, even more preferably 0.7 μm or more, even more preferably 1.0 μm or more, and particularly preferably 1.5 μm or more. It is also usually 100 μm or less, preferably 60 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 5 μm or less. When the thickness of the zeolite membrane is equal to or greater than the above lower limit, defects tend to be less likely to occur and separation performance tends to be improved. When the thickness of the zeolite membrane is equal to or less than the above upper limit, permeation performance tends to be improved. Furthermore, in the high-temperature region, cracks are less likely to occur in the zeolite membrane due to temperature rise, which tends to suppress a decrease in permeation selectivity at high temperatures.

[0055] The average primary particle size of the zeolite forming the zeolite membrane is not particularly limited, but is usually 30 nm or more, preferably 50 nm or more, and more preferably 100 nm or more, with the upper limit being equal to or less than the membrane thickness. If the average primary particle size of the zeolite is equal to or greater than the above-mentioned lower limit, the zeolite grain boundaries can be made small, resulting in good permeation selectivity. Therefore, it is most preferable that the average primary particle size of the zeolite is the same as the thickness of the zeolite membrane. In this case, the zeolite grain boundaries can be made the smallest. Zeolite membranes obtained by hydrothermal synthesis, which will be described later, are preferred because the zeolite particle size and membrane thickness may be the same. In the present invention, the average primary particle diameter is determined by measuring the primary particle diameters of 30 or more arbitrarily selected particles when observing the surface or fracture surface of the zeolite membrane composite of the present invention with a scanning electron microscope, and then averaging the measured values.

[0056] <Method of manufacturing zeolite membrane composite> In the present invention, the method for producing the zeolite membrane composite is not particularly limited as long as it is a method that can form the above-mentioned zeolite membrane on a porous support, and the zeolite membrane composite can be produced by any known method. For example, any of the following methods can be used: (1) a method of crystallizing zeolite into a membrane on a support, (2) a method of fixing zeolite to a support with an inorganic binder or an organic binder, (3) a method of fixing a polymer in which zeolite is dispersed to a support, and (4) a method of impregnating a support with a zeolite slurry and, in some cases, suctioning the zeolite to fix the zeolite to the support.

[0057] Among these, a method of crystallizing zeolite in a membrane form on a porous support is particularly preferred. Although there are no particular limitations on the crystallization method, a preferred method is to place the porous support in a reaction mixture for hydrothermal synthesis used to produce zeolite (hereinafter, this may be referred to as an "aqueous reaction mixture") and directly perform hydrothermal synthesis to crystallize zeolite on the surface of the porous support, etc. In this case, the zeolite membrane composite can be produced, for example, by placing an aqueous reaction mixture homogenized by adjusting the composition in a heat-resistant and pressure-resistant container such as an autoclave containing a porous support therein, sealing the container, and heating the container for a certain period of time.

[0058] 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) as needed. As particularly preferred examples of the method for producing a zeolite membrane composite, the methods for producing an RHO-type zeolite membrane composite and an MFI-type zeolite membrane composite will be described in detail below. However, the zeolite membrane and the method for producing the same of the present invention are not limited to these.

[0059] In the method for producing a zeolite membrane composite of the present invention, it is essential that the molar ratio of water to silicon in the raw material mixture for hydrothermal synthesis is 45 to 300. When the molar ratio of water to silicon is within this range, even when a long tube is formed, the sodium / silicon (molar ratio) can be easily maintained at 0.2 or less throughout the tube, i.e., in the regions (A), (B), and (B'). From the above viewpoints, 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.

[0060] (RHO type zeolite membrane) The RHO-type zeolite used in the present invention refers to a zeolite with an RHO structure, a code that specifies the structure of zeolites as defined by the IZA. RHO-type zeolite has a structure characterized by three-dimensional pores consisting of eight-membered oxygen rings with a diameter of 3.6 × 3.6 Å, and this structure is characterized by X-ray diffraction data. The framework density of the RHO-type zeolite used in the present invention is 14.1 (unit: T / nm 3 )

[0061] (MFI type zeolite membrane) The MFI zeolite used in the present invention refers to a zeolite with an MFI structure, a code for specifying the structure of zeolites as defined by the IZA. MFI zeolite has a structure characterized by three-dimensional pores consisting of 10-membered oxygen rings with diameters of 5.1 × 5.5 Å or 5.3 × 5.6 Å, and this structure is characterized by X-ray diffraction data. The framework density of the MFI zeolite used in the present invention is 17.9 (unit: T / nm 3 )

[0062] (CHA type zeolite membrane) The CHA-type zeolite used in the present invention refers to a zeolite having a CHA structure according to the code that defines the structure of zeolite determined by IZA. The CHA-type zeolite has a structure characterized by having a three-dimensional pore composed of an 8-membered oxygen ring with a diameter of 3.8 × 3.8 Å, and the 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 )

[0063] (FAU-type zeolite membrane) The FAU-type zeolite used in the present invention refers to a zeolite having a FAU structure according to the code that defines the structure of zeolite determined by IZA. The FAU-type zeolite has a structure characterized by having a three-dimensional pore composed of a 6-membered oxygen ring with a diameter of 7.4 × 7.4 Å, and the 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 )

[0064] (LTA-type zeolite membrane) The LTA-type zeolite used in the present invention refers to a zeolite having an LTA structure according to the code that defines the structure of zeolite determined by IZA. The LTA-type zeolite has a structure characterized by having a three-dimensional pore composed of an 8-membered oxygen ring with a diameter of 4.1 × 4.1 Å, and the 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 )

[0065] <<Method for producing RHO-type zeolite membrane>> (Silicon atom source) The silicon (Si) atom source used in the aqueous reaction mixture is not particularly limited, and examples thereof include aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxides such as trimethylethoxysilane, tetraethyl orthosilicate, and aluminosilicate gel, with aluminosilicate zeolite, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxides, and aluminosilicate gel being preferred. These may be used alone or in combination of two or more.

[0066] (Aluminum atom source) The aluminum (Al) atom source used in the production of the porous support-RHO-type zeolite membrane composite is not particularly limited, and examples thereof include aluminosilicate zeolite, amorphous aluminum hydroxide, aluminum hydroxide having a gibbsite structure, aluminum hydroxide having a bayerite structure, aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudo-boehmite, aluminum alkoxide, and aluminosilicate gel. Of these, aluminosilicate zeolite, amorphous aluminum hydroxide, sodium aluminate, boehmite, pseudo-boehmite, 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. The aluminosilicate zeolite may be used alone or in combination of two or more. When an aluminosilicate zeolite is used as the Al atom source, it is preferable that the aluminosilicate zeolite accounts for 50 mass% or more, particularly 70 to 100 mass%, and especially 90 to 100 mass% of the total Al atom source. When an aluminosilicate zeolite is used as the Si atom source, it is preferable that the aluminosilicate zeolite accounts for 50 mass% or more, particularly 70 to 100 mass%, and especially 90 to 100 mass% of the total Si atom source. When the proportion of the aluminosilicate zeolite is within this range, the Si atom / Al atom molar ratio of the RHO-type zeolite membrane is high, resulting in a zeolite membrane with excellent acid resistance and water resistance and a wide range of applications.

[0067] (Al atom / Si atomic ratio) The preferred range of the amount of Al atom source (including the above-mentioned aluminosilicate zeolite and other Al atom sources) used relative to the silicon (Si atoms) contained in the raw material mixture other than the seed crystals (Al atom / Si atom ratio) is usually 0.01 or more, preferably 0.02 or more, more preferably 0.04 or more, and even more preferably 0.06 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.2 or less, and even more preferably 0.1 or less. Controlling the amount used within this range makes it easier to control the contents of nitrogen atoms and alkali metal elements in the zeolite within the preferred ranges of the present invention. Furthermore, the Al atom / Si atom ratio can be increased by reducing the amount of silicon atom source used relative to the aluminum atom source, while the ratio can be decreased by increasing the amount of silicon atom source used relative to the aluminum atom source. If the Al atom / Si atomic ratio exceeds 1.0, the water resistance and acid resistance of the obtained RHO type zeolite membrane may be low, and the applications of the zeolite membrane may be limited. On the other hand, if the Al atom / Si atomic ratio is less than 0.01, it may be difficult to obtain an RHO type zeolite membrane. The aqueous reaction mixture may also contain, in addition to the silicon atom source and the aluminum atom source, other atom sources such as gallium (Ga), iron (Fe), boron (B), titanium (Ti), zirconium (Zr), tin (Sn), and zinc (Zn).

[0068] (Alkaline 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), and barium (Ba), preferably Na, K, and Cs, and more preferably Na and Cs. Two or more metal species of the metal oxides may be used in combination, and specifically, it is preferable to use Na and Cs in combination.

[0069] Specific examples of metal hydroxides that can be used include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide; and alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, strontium hydroxide, and barium hydroxide.

[0070] Additionally, hydroxide ions, which are counter anions of the organic template described below, can be used as the alkali source for the aqueous reaction mixture. In the crystallization of the zeolite according to the present invention, an organic template (structure-directing agent) is not necessarily required. However, by using a type of organic template corresponding to each structure, the ratio of silicon atoms to aluminum atoms in the crystallized zeolite increases, thereby improving the crystallinity, and therefore it is preferable to use an organic template.

[0071] (organic template) The organic template may be of any type as long as it can form the desired zeolite membrane, and one type of template may be used, or two or more types may be used in combination. The type of organic template suitable for the reaction varies depending on the zeolite structure to be synthesized, and an organic template that can obtain the desired zeolite structure may be used. Specifically, for example, in the case of the RHO structure, 18-crown-6-ether or the like may be used. When the organic template is a cation, it is accompanied by an anion that is not detrimental to the formation of the zeolite. Representative of such anions are Cl. - , Br - , I - These include halogen ions, hydroxide ions, acetates, sulfates, and carboxylates, etc. Among these, hydroxide ions are particularly preferred, and in the case of hydroxide ions, they function as an alkali source as described above.

[0072] The molar ratio of the Si atom source to the organic template in the aqueous reaction mixture (organic template / SiO ratio) is typically 0.005 or greater, preferably 0.01 or greater, more preferably 0.02 or greater, even more preferably 0.05 or greater, particularly preferably 0.08 or greater, and most preferably 0.1 or greater, and typically 1 or less, preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.35 or less, particularly preferably 0.30 or less, and most preferably 0.25 or less. When the organic template / SiO ratio of the aqueous reaction mixture is within this range, a dense zeolite membrane can be formed, and a zeolite with excellent acid resistance and reduced Al atom desorption can be obtained. Furthermore, under these conditions, a particularly dense and acid-resistant RHO-type aluminosilicate zeolite can be formed.

[0073] The use of an appropriate amount of alkali metal atom source facilitates the coordination of the organic structure-directing agent (described below) with aluminum in a suitable state, thereby facilitating the formation of a crystal structure. The molar ratio (R / Si atom) of the alkali metal atom source (R) to 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 or more, more preferably 0.20 or more, even more preferably 0.25 or more, particularly preferably 0.30 or more, and particularly preferably 0.35 or more, and is usually 2.0 or less, preferably 1.5 or less, more preferably 1.0 or less, even more preferably 0.8 or less, particularly preferably 0.6 or less, and most preferably 0.5 or less. If the molar ratio of the alkali metal atom source to silicon (R / Si atoms) is greater than the above upper limit, the produced zeolite tends to dissolve, which may result in failure to obtain zeolite or a significantly reduced yield. If the R / Si atoms is less than the above lower limit, the raw material Al atom source and Si atom source do not dissolve sufficiently, which may result in failure to obtain a uniform raw material mixture for hydrothermal synthesis, making it difficult to produce RHO-type zeolite.

[0074] (amount of water) The amount of water in the raw material mixture for hydrothermal synthesis is preferably larger than that in ordinary hydrothermal synthesis. By using a larger amount of water, it becomes easier to make the sodium / silicon (molar ratio) in each of the regions (A), (B), and (B') 0.2 or less. Specifically, the amount of water is preferably 45 or more, more preferably 50 or more, and even more preferably 60 or more, in terms of molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystals. The upper limit of the amount of water, expressed as a molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystals, is preferably 300 or less, more preferably 200 or less, and even more preferably 150 or less. By making the amount of water less than the upper limit, the concentration of the reaction mixture becomes sufficient, making it easier to form a defect-free, dense film.

[0075] (seed crystal) In the present invention, seed crystals may be used as one component of the raw material (raw material compound) for producing "zeolite." During hydrothermal synthesis, it is not necessary to have seed crystals present in the reaction system, but the presence of seed crystals can promote the crystallization of zeolite on the porous support. The method for having seed crystals present in the reaction system is not particularly limited, and methods such as adding seed crystals to the aqueous reaction mixture, as in the synthesis of powdered zeolite, or attaching seed crystals to the porous support can be used, but in the present invention, it is preferable to attach seed crystals to the porous support. Attaching seed crystals to the support in advance makes it easier to produce a dense zeolite membrane with high separation performance. The seed crystals to be used may be of any type as long as they are zeolite that promotes crystallization, but for efficient crystallization, they preferably have the same crystal type as the zeolite membrane to be formed. For example, when forming a zeolite membrane of RHO-type aluminosilicate, it is preferable to use seed crystals of RHO-type zeolite.

[0076] The particle size of the seed crystals is desirably close to the pore size of the porous support, and they may be crushed as 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, and most preferably 0.7 μm or more, and is usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less, and particularly preferably 1.5 μm or less. Depending on the pore size of the porous support, a smaller particle size of the seed crystals may be desirable, and they may be crushed as necessary. The particle size of the seed crystals is usually 5 nm or more, preferably 10 nm or more, and more preferably 20 nm or more, and usually 5 μm or less, preferably 3 μm or less, and more preferably 2 μm or less.

[0077] The method for attaching seed crystals to a porous support is not particularly limited. For example, a dipping method can be used, in which seed crystals are dispersed in a solvent such as water and the porous support is immersed in the dispersion to attach the seed crystals to the surface; a suction method can be used, in which seed crystals are dispersed in a solvent such as water and a support with one end sealed is immersed in the dispersion and then sucked from the other end to firmly attach the seed crystals to the surface of the porous support; or a method can be used in which seed crystals are mixed with a solvent such as water to form a slurry and then applied to the support. The dipping and suction methods are desirable for controlling the amount of seed crystal attachment and producing zeolite membranes with good reproducibility, while the suction and suction methods, in which seed crystals are applied in a slurry state, are desirable for adhering the seed crystals to the porous support. Furthermore, rubbing and pressing the support with the attached seed crystals with a latex gloved finger is also suitable following the dipping and suction methods to adhere the seed crystals to the porous support and / or remove excess seed crystals.

[0078] The solvent in which the seed crystals are dispersed is not particularly limited, but water or an alkaline aqueous solution is particularly preferred. The type of alkaline aqueous solution is not particularly limited, but a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferred. These alkaline species may also be mixed. The alkali concentration of the alkaline aqueous solution is not particularly limited, but is usually 0.0001 mol% or more, preferably 0.0002 mol% or more, more preferably 0.001 mol% or more, and even more preferably 0.002 mol% or more. The alkali concentration is also usually 1 mol% or less, preferably 0.8 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.2 mol% or less.

[0079] 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, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and most preferably 3% by mass or more, based on the total weight of the dispersion. Also, 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 dispersed seed crystals is too small, the amount of seed crystals attached to the porous support will be small, and therefore, there will be areas on the porous support where zeolite is not produced during hydrothermal synthesis, which may result in a defective membrane. On the other hand, for example, the amount of seed crystals attached to the porous support by the dipping method will be almost constant once the amount of seed crystals in the dispersion exceeds a certain level, so if the amount of seed crystals in the dispersion is too large, a lot of seed crystals will be wasted, which is disadvantageous in terms of cost.

[0080] It is desirable to attach seed crystals to a porous support by dipping, suction, or by applying a slurry, and then dry the resulting material before forming a zeolite membrane. The drying temperature is usually 50°C or higher, preferably 80°C or higher, and more preferably 100°C or higher, and usually 200°C or lower, preferably 180°C or lower, and more preferably 150°C or lower. The drying time is not limited as long as the material is sufficiently dry, but is usually 10 minutes or longer, preferably 30 minutes or longer. On the other hand, there is no particular upper limit, but from an economical standpoint, it is usually 5 hours or shorter. After drying, the support to which the seed crystals are attached is preferably rubbed and pressed with fingers or the like wearing latex gloves, in order to adhere the seed crystals to the support and / or to remove excess seed crystals.

[0081] The amount of seed crystals to be attached to the porous support in advance is not particularly limited, and the amount is determined by the number of crystals per 1 m of the membrane-forming surface of the porous support. 2 The mass per unit area is usually 0.1 g or more, preferably 0.3 g or more, more preferably 0.5 g or more, even more preferably 0.8 g or more, and most preferably 1.0 g or more, and is usually 100 g or less, preferably 50 g or less, more preferably 10 g or less, even more preferably 8 g or less, and most preferably 5 g or less. When the amount of seed crystals attached is equal to or greater than the lower limit, crystals tend to be easily formed, the film tends to grow sufficiently, and the film tends to grow uniformly. Furthermore, when the amount of seed crystals is equal to or less than the upper limit, the seed crystals do not increase the surface irregularities, and seed crystals that fall from the support do not easily grow spontaneous nuclei, thereby preventing the film growth on the support. Therefore, within the above range, a dense zeolite membrane tends to be produced.

[0082] (hydrothermal synthesis) When forming a zeolite membrane on a porous support by hydrothermal synthesis, there is no particular limitation on the method for immobilizing the porous support, and the support may be placed in any form, such as vertical or horizontal placement. In this case, the zeolite membrane may be formed by a static method, or may be formed while stirring the aqueous reaction mixture. Hydrothermal synthesis is carried out by placing the porous support carrying the seed crystals as described above and the prepared hydrothermal synthesis mixture or an aqueous gel obtained by aging the mixture in a pressure-resistant container, and maintaining the mixture at a predetermined temperature under self-generated pressure or under a gas pressure that does not inhibit crystallization, while stirring, rotating or rocking the container, or standing still. Hydrothermal synthesis in a stationary state is desirable because it does not inhibit crystal growth from the seed crystals on the support.

[0083] 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. The reaction temperature is usually 100°C or higher, preferably 110°C or higher, more preferably 120°C or higher, particularly preferably 130°C or higher, particularly preferably 140°C or higher, and most preferably 150°C or higher, and usually 200°C or lower, preferably 190°C or lower, more preferably 180°C or lower, and even more preferably 170°C or lower. If the reaction temperature is too low, the zeolite may be difficult to crystallize. If the reaction temperature is too high, a type of zeolite different from the desired zeolite may be easily 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. It is usually 3 hours or more, preferably 8 hours or more, more preferably 12 hours or more, and particularly preferably 15 hours or more, and usually 10 days or less, preferably 5 days or less, more preferably 3 days or less, even more preferably 2 days or less, and particularly preferably 1.5 days or less. If the reaction time is too short, the zeolite may be difficult to crystallize. If the reaction time is too long, a type of zeolite different from the desired zeolite may be easily produced.

[0084] The pressure during hydrothermal synthesis is not particularly limited, and the autogenous pressure that occurs when an aqueous reaction mixture placed in a sealed vessel is heated to the above-mentioned temperature range is sufficient. If necessary, an inert gas such as nitrogen may be added.

[0085] The density of the zeolite membrane can be improved by repeating the hydrothermal synthesis multiple times. When the hydrothermal synthesis is repeated multiple times, the zeolite membrane composite obtained in the first hydrothermal synthesis is washed with water, dried by heating, and then immersed again in a newly prepared aqueous reaction mixture for hydrothermal synthesis. The zeolite membrane composite obtained after the first hydrothermal synthesis does not necessarily need to be washed with water or dried, but washing with water and drying can maintain the intended composition of the aqueous reaction mixture. When the synthesis is performed multiple times, the number of synthesis times is usually two or more and usually ten or less, preferably five or less, and more preferably three or less. The water washing may be repeated once or multiple times.

[0086] (Washing, heat treatment, drying) The zeolite membrane composite obtained by hydrothermal synthesis is washed with water, then heat-treated, and dried. Here, heat treatment means drying the zeolite membrane composite by applying heat, and also means removing an organic template, if used, by calcining the organic template. When the purpose of the heat treatment is drying, the 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 150° C. or lower. When the purpose of the heat treatment is to remove the organic template by calcination, the temperature is usually 250° C. or higher, preferably 300° C. or higher, more preferably 350° C. or higher, even more preferably 400° C. or higher, and usually 800° C. or lower, preferably 600° C. or lower, even more preferably 550° C. or lower, particularly preferably 500° C. or lower. When the purpose is to remove the organic template by calcination, if the heat treatment temperature is too low, the proportion of the organic template remaining tends to be high, reducing the number of pores in the zeolite and potentially reducing the amount of permeation when used to separate ammonia. If the heat treatment temperature is too high, the difference in the thermal expansion coefficients between the support and the zeolite becomes large, which may lead to the likelihood of cracks occurring in the zeolite membrane, causing the zeolite membrane to lose its denseness and resulting in reduced separation performance.

[0087] The heat treatment time is not particularly limited as long as it is sufficient to sufficiently dry the zeolite membrane and remove the organic template by calcination, and is preferably 0.5 hours or more, more preferably 1 hour or more, for the purpose of drying, and is preferably 1 hour or more, more preferably 5 hours or more, for the purpose of removing the organic template by calcination, although this varies depending on the temperature increase rate and temperature decrease rate. The upper limit of the heating time is not particularly limited, and is usually 200 hours or less, preferably 150 hours or less, more preferably 100 hours or less. The heat treatment for calcining the template may be carried out in an air atmosphere, but may also be carried out in an atmosphere containing an inert gas such as nitrogen or oxygen.

[0088] When the hydrothermal synthesis is carried out in the presence of an organic template, it is appropriate to wash the obtained zeolite membrane composite with water and then remove the organic template by, for example, a heat treatment or extraction, preferably by the above-mentioned heat treatment, i.e., calcination. For the heat treatment aimed at firing and removing the organic template, the heating rate should preferably be as slow as possible in order to prevent the formation of cracks in the zeolite membrane due to the difference in the thermal expansion coefficients of the porous support and the zeolite. The heating rate is usually 5 °C / min or less, preferably 2 °C / min or less, more preferably 1 °C / min or less, still more preferably 0.5 °C / min or less, and particularly preferably 0.3 °C / min or less. The lower limit of the heating rate is usually 0.1 °C / min or more in consideration of workability. Also, in the heat treatment aimed at firing and removing the organic template, the cooling rate after the heat treatment also needs to be controlled to avoid the formation of cracks in the zeolite membrane. Similar to the heating rate, the slower the cooling rate, the more desirable. The cooling rate is usually 5 °C / min or less, preferably 2 °C / min or less, more preferably 1 °C / min or less, still more preferably 0.5 °C / min or less, and particularly preferably 0.3 °C / min or less. The lower limit of the cooling rate is usually 0.1 °C / min or more in consideration of workability.

[0089] <<Method for Producing MFI-Type Zeolite Membrane>> (Silicon Atom Source) Examples of the silicon (Si) atom source used in the aqueous reaction mixture include those described for the above-mentioned RHO-type zeolite. Among them, preferably, fumed silica, colloidal silica, amorphous silica, sodium silicate, methyl silicate, ethyl silicate, silicon alkoxide, and aluminosilicate gel can be mentioned. 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 are within the preferred ranges described above or below.

[0090] (Aluminum Atom Source) The aluminum (Al) atom source used in the production of the porous support-MFI zeolite membrane composite is not particularly limited, and examples thereof include those similar to those described above for the RHO zeolite. Among these, amorphous aluminum hydroxide, sodium aluminate, boehmite, pseudo-boehmite, aluminum alkoxide, and aluminosilicate gel are preferred, with amorphous aluminum hydroxide, sodium aluminate, and aluminosilicate gel being particularly preferred. These may be used alone or in combination of two or more.

[0091] (Al atom / Si atomic ratio) The preferred range of the amount of aluminum atom source (including the above-mentioned aluminosilicate zeolite and other aluminum atom sources) used relative to the silicon (Si atoms) contained in the raw material mixture other than the seed crystals (Al atom / Si atom ratio) is, in terms of molar ratio, usually 0.001 or more, preferably 0.002 or more, more preferably 0.003 or more, and even more preferably 0.004 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.2 or less, and even more preferably 0.1 or less. Controlling the amount used within this range makes it easier to control the contents of nitrogen atoms and alkali metal elements in the zeolite within the preferred ranges of the present invention. In order to increase the Al atom / Si atom ratio, the amount of silicon atom source used relative to the aluminum atom source can be reduced, while in order to decrease this ratio, the amount of silicon atom source used relative to the aluminum atom source can be increased. The aqueous reaction mixture may contain, in addition to the Si atom source and the Al atom source, other atom sources such as Ga, Fe, B, Ti, Zr, Sn, and Zn.

[0092] (Alkaline 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. Specific examples include those similar to those described above for the RHO-type zeolite. Additionally, hydroxide ions, which are counter anions of the organic template described below, can be used as the alkali source for the aqueous reaction mixture. In the crystallization of the zeolite according to the present invention, an organic template is not necessarily required. However, by using a type of organic template (structure-directing agent) corresponding to each structure, the ratio of silicon atoms to aluminum atoms in the crystallized zeolite increases, thereby improving the crystallinity, and therefore it is preferable to use an organic template.

[0093] (organic template) The organic template may be of any type as long as it can form the desired zeolite membrane, and one type of template may be used, or two or more types may be used in combination. The type of organic template suitable for the reaction varies depending on the zeolite structure to be synthesized, and an organic template that can obtain the desired zeolite structure may be used. Specifically, for example, tetrapropylammonium hydroxide may be used for the MFI structure. When the organic template is a cation, it is accompanied by an anion that is not detrimental to the formation of the zeolite. Representative of such anions are Cl. - , Br - , I - These include halogen ions, hydroxide ions, acetates, sulfates, and carboxylates, etc. Among these, hydroxide ions are particularly preferred, and in the case of hydroxide ions, they function as an alkali source as described above.

[0094] The molar ratio of the Si atom source to the organic template in the aqueous reaction mixture (organic template / SiO ratio) is typically 0.005 or greater, preferably 0.01 or greater, more preferably 0.02 or greater, particularly preferably 0.05 or greater, and particularly preferably 0.1 or greater, and typically 1 or less, preferably 0.5 or less, more preferably 0.3 or less, particularly preferably 0.25 or less, and particularly preferably 0.2 or less. When the organic template / SiO ratio of the aqueous reaction mixture is within this range, a dense zeolite membrane can be formed, and a zeolite with excellent acid resistance and low Al desorption can be obtained. Furthermore, under these conditions, a particularly dense and acid-resistant MFI-type aluminosilicate zeolite can be formed.

[0095] The use of an appropriate amount of alkali metal atom source facilitates the coordination of the organic structure-directing agent (described below) with aluminum in a suitable state, thereby facilitating the formation of a crystal structure. The molar ratio R / Si of the alkali metal atom source (R) to the silicon (Si) contained in the mixture of raw materials for hydrothermal synthesis other than the seed crystals is usually 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, even more preferably 0.04 or more, and particularly preferably 0.05 or more, and is usually 1.0 or less, preferably 0.6 or less, more preferably 0.4 or less, even more preferably 0.2 or less, and particularly preferably 0.1 or less.

[0096] If the molar ratio of the alkali metal atom source to silicon (R / Si) is greater than the upper limit, the produced zeolite is likely to dissolve, which may result in failure to obtain zeolite or a significantly reduced yield. If R / Si is less than the lower limit, the Al atom source and Si atom source as raw materials may not dissolve sufficiently, which may result in failure to obtain a uniform raw material mixture for hydrothermal synthesis, making it difficult to produce MFI zeolite.

[0097] (amount of water) The amount of water in the raw material mixture for hydrothermal synthesis is preferably larger than that in ordinary hydrothermal synthesis. A larger amount of water makes it easier to make the sodium / silicon (molar ratio) in the region (A), the region (B), and the region (B') all 0.2 or less. Specifically, the molar ratio of sodium 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. The upper limit of the amount of water, expressed as a molar ratio to silicon (Si atoms) contained in the raw material mixture other than the seed crystals, is preferably 300 or less, more preferably 200 or less, and even more preferably 150 or less. If the amount is greater than the upper limit, the reaction mixture may become too dilute, making it difficult to form a defect-free, dense film.

[0098] (seed crystal) In the present invention, seed crystals may be used as one component of the raw material (raw material compound) for producing "zeolite." The seed crystals are the same as those described above for RHO zeolite, and when a zeolite membrane of MFI aluminosilicate is to be formed, it is preferable to use seed crystals of MFI zeolite. The particle size of the seed crystals is desirably close to the pore size of the support, and they may be crushed before use as necessary. 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, especially preferably 0.7 μm or more, and most preferably 1 μm or more, and is usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less, most preferably 1.5 μm or less, and particularly preferably 1.2 μm or less. Depending on the pore size of the support, a smaller particle size of the seed crystal may be desirable, and the seed crystal may be crushed as necessary. The particle size of the seed crystal is usually 0.5 nm or more, preferably 1 nm or more, and more preferably 2 nm or more, and usually 5 μm or less, preferably 3 μm or less, and more preferably 2 μm or less.

[0099] The method for attaching seed crystals to a support is the same as that described for the RHO zeolite above. The solvent and concentration for dispersing the seed crystals are also the same as those described for the RHO zeolite above. Furthermore, the method for rubbing and pressing the support onto which the seed crystals are attached with a finger wearing a latex glove, the amount of seed crystals to be attached in advance to the porous support, and the method for immobilizing the support when a zeolite membrane is formed on the porous support by hydrothermal synthesis are also the same as those described for the RHO zeolite above.

[0100] (hydrothermal synthesis) The reaction temperature when forming a zeolite membrane by hydrothermal synthesis is not particularly limited, as long as it is a temperature suitable for obtaining a membrane with the desired zeolite structure, but is usually 100°C or higher, preferably 120°C or higher, more preferably 130°C or higher, particularly preferably 140°C or higher, particularly preferably 150°C or higher, and most preferably 160°C or higher, and is usually 210°C or lower, preferably 200°C or lower, more preferably 190°C or lower, and particularly preferably 180°C or lower. If the reaction temperature is too low, the zeolite may be difficult to crystallize. On the other hand, if the reaction temperature is too high, a type of zeolite different from the desired zeolite may be easily 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 at least 5 hours, and more preferably at least 10 hours, and usually at most 10 days, preferably at most 5 days, more preferably at most 3 days, even more preferably at most 2 days, and particularly preferably at most 1 day. If the reaction time is too short, the zeolite may be difficult to crystallize. If the reaction time is too long, a type of zeolite different from the desired zeolite may be easily produced.

[0101] The pressure during hydrothermal synthesis is not particularly limited, and the autogenous pressure that occurs when an aqueous reaction mixture placed in a sealed vessel is heated to the above-mentioned temperature range is sufficient. If necessary, an inert gas such as nitrogen may be added. The method for improving the density of the zeolite membrane by repeating the hydrothermal synthesis multiple times is the same as that described above for the RHO-type zeolite.

[0102] (Washing, heat treatment, drying) The zeolite membrane composite obtained by hydrothermal synthesis is washed with water, then heat-treated, and dried. Here, heat treatment means drying the zeolite membrane composite by applying heat, and also means removing an organic template, if used, by calcining the organic template. When the purpose of the heat treatment is drying, the 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 150° C. or lower. When the purpose of the heat treatment is to remove the organic template by calcination, the temperature 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, preferably 800° C. or lower, even more preferably 700° C. or lower, and particularly preferably 600° C. or lower.

[0103] If the purpose is to remove the organic template by calcination, a too low heat treatment temperature tends to increase the proportion of the organic template remaining, reducing the number of pores in the zeolite and potentially reducing the amount of permeation when used to separate ammonia. If the heat treatment temperature is too high, the difference in thermal expansion coefficient between the support and the zeolite becomes large, which may lead to the likelihood of cracking in the zeolite membrane, causing the zeolite membrane to lose its density and reduce its separation performance. When tetrapropylammonium hydroxide is used as the organic template, the content of nitrogen atoms in the zeolite can be controlled by adjusting the heat treatment temperature. The time, atmosphere, temperature increase rate, and temperature decrease rate of the heat treatment are the same as those described above for the RHO-type zeolite.

[0104] <<Ion exchange>> The synthesized zeolite membrane may be ion-exchanged as needed. The thermal expansion characteristics and thermal stability of ammonia separation of zeolite are significantly affected by the cation species in the zeolite, so this ion exchange is an important control method. Furthermore, as described below, the ammonia permeability and / or separation performance of the zeolite membrane may be improved depending on the cation species used. That is, the cation species used in the present invention are appropriately selected taking into account the ammonia permeability and separation performance while maintaining the thermal expansion characteristics and thermal stability of ammonia separation of the zeolite.

[0105] When a zeolite membrane is synthesized using an organic template, ion exchange is usually performed after removing the organic template. In the present invention, the ions to be exchanged are NH4 + or any of the cationic species obtained by protonating an organic amine having 1 to 20 carbon atoms, such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine, and other cationic species are also preferred. + , K. + , Li + , Rb + , Cs + Alkali metal ions such as Ca 2+ , Mg 2+ , Sr 2+ , Ba 2+ and ions of alkaline earth metals such as Fe, Cu, Zn, Ga, La, etc. may also be present. Among these, proton, NH4 + , 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 above ions is preferably adopted in order to balance the thermal expansion characteristics and ammonia permeability of the zeolite. By controlling the cation species and their amounts to be ion-exchanged in this way, it becomes possible to control the ammonia affinity of the zeolite and the effective pore size in the zeolite pores, thereby increasing the ammonia permeation selectivity and improving the ammonia permeation rate. Among these, the ion species that increase the ammonia permeation selectivity are NH4 + Cationic species obtained by protonating organic amines having 1 to 20 carbon atoms, such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine, aniline, methylaniline, benzylamine, methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine, and piperidine, are preferred, and among these, NH4 + For the above reasons, cationic species in which small molecular amines such as amines having 1 to 6 carbon atoms are protonated are more preferred, and among these, NH4 + is preferred. On the other hand, ionic species that improve the ammonia permeation rate include protons, Na + , Li + , Cs + , Fe ions, Ga ions, and La ions are preferred, and Na + , Li + , Cs + The ion is particularly preferred, Na + 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 ions exchanged, which essentially consist of ion species containing nitrogen atoms.

[0106] In addition, the zeolite of the present invention contains Na +When Na ions are contained, the content thereof is, in molar ratio relative to the Al atoms in the zeolite, usually 0.01 or more, preferably 0.02 or more, more preferably 0.03 or more, even more preferably 0.04 or more, and particularly preferably 0.05 or more. On the other hand, the upper limit is not particularly limited, but is usually 0.10 molar equivalents or less, preferably 0.070 molar equivalents or less, more preferably 0.065 molar equivalents or less, even more preferably 0.060 molar equivalents or less, and particularly preferably 0.55 molar equivalents or less. Na ions in such a specific range + By using a zeolite with a zeolite / Al atomic ratio, ammonia can be separated with high permeability from a mixed gas consisting of multiple components including ammonia and hydrogen and / or nitrogen.

[0107] Ion exchange can be performed by treating the calcined zeolite membrane (e.g., when an organic template is used) with nitrates, sulfates, phosphates, organic acid salts, hydroxides, and halogen salts of Cl and Br of the cations to be ion-exchanged, or with an acid such as hydrochloric acid, typically at room temperature to 100°C, followed by water washing or hot water washing at 40°C to 100°C. The solvent used for the ion exchange treatment can be water or an organic solvent as long as it dissolves the salt to be ion-exchanged. The concentration of the salt to be treated is typically 10 mol / L or less, with a lower limit of 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. These treatment conditions can be appropriately set depending on the salt and solvent used. When using an acid such as hydrochloric acid, the acid concentration is typically 5 mol / L or less, as the acid destroys the crystalline structure of the zeolite, and the temperature and time can be appropriately set. Furthermore, since the ion exchange rate increases when the ion exchange treatment is repeated, 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 achieved. Furthermore, since the ion-exchanged zeolite membrane may be calcined at 200 to 500°C as necessary to remove the residue from the ion exchange treatment, if any residue from the ion exchange treatment raw materials remains in the zeolite pores after the ion exchange treatment, this will hinder gas permeability.

[0108] <<Nitrate treatment>> In the zeolite membrane composite of the present invention, it is preferable to use a nitrate treatment in combination as a method for adjusting the nitrogen atom content in the zeolite membrane. Therefore, the nitrate treatment will be described below.

[0109] In the present invention, the synthesized zeolite membrane may be subjected to a nitrate treatment if necessary. The nitrate treatment may be carried out while the zeolite membrane contains the organic template or after the organic template has been removed by calcination. The nitrate treatment may be carried out by, for example, immersing the zeolite membrane composite in a solution containing nitrate. This may be preferable because the nitrate has the effect of sealing fine defects present on the membrane surface. Furthermore, when nitrate is present in the zeolite pores, it has the effect of improving the affinity of the zeolite membrane with ammonia, and is therefore preferably used as a method for improving ammonia permeability. The solvent used for the nitrate treatment may be water or an organic solvent as long as the salt dissolves therein, and the nitrate to be used is not limited, but examples thereof include magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate, gallium nitrate, 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, and indium nitrate are preferred, with magnesium nitrate, calcium nitrate, barium nitrate, and aluminum nitrate being more preferred, and aluminum nitrate being particularly preferred because it has a significant effect of sealing fine defects present on the surface of the zeolite membrane, thereby improving ammonia separation performance.

[0110] The nitrate concentration is usually 10 mol / L or less, with a lower limit of 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. The treatment temperature is usually from room temperature to 150°C or less, and the treatment may be carried out for approximately 10 minutes to 48 hours. These treatment conditions may be appropriately set depending on the type of nitrate and solvent used. The zeolite membrane after the nitrate treatment may be washed with water, and by repeating the water washing, the nitrogen atom content of the zeolite membrane can be adjusted to a preferred range.

[0111] <<Aluminum salt treatment>> The zeolite membrane composite of the present invention may be subjected to an aluminum salt treatment, if necessary. The aluminum salt treatment may be performed while the zeolite membrane composite contains the organic template, or after the organic template has been removed by calcination. The aluminum salt treatment may be performed, for example, by immersing the zeolite membrane composite in a solution containing an aluminum salt. This may have the effect of causing the aluminum salt to seal fine defects present on the membrane surface. Furthermore, when aluminum salt is present in zeolite pores, it has the effect of attracting ammonia gas, and is therefore preferably employed as a method for improving ammonia gas permeability. The solvent used in the aluminum salt treatment may be water or an organic solvent as long as the salt dissolves therein, and there is no limitation on the aluminum salt used, but examples include aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum acetate, aluminum carbonate, aluminum hydroxide, etc. These may be used alone or in combination of two or more.

[0112] The concentration of the aluminum salt is usually 10 mol / L or less, with a lower limit of 0.1 mol / L or more, preferably 0.5 mol / L or more, and more preferably 1 mol / L or more. The treatment temperature is usually from room temperature to 150°C or less, and the treatment may be carried out for about 10 minutes to 48 hours. These treatment conditions may be appropriately set depending on the aluminum salt and the type of solvent 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 the water washing. In order to increase the Si atom / Al atom ratio of the present invention, it is preferable to reduce the concentration or amount of aluminum salt used for treatment or to increase the number of water washings after the aluminum salt treatment. On the other hand, in order to decrease the ratio, it is preferable to increase the concentration or amount of aluminum salt used for treatment or to decrease the number of water washings after the aluminum salt treatment.

[0113] <<Silylation treatment>> The zeolite composite membrane of the present invention may be subjected to a silylation treatment, if necessary. The silylation treatment is carried out by immersing the zeolite composite membrane in a solution containing, for example, a Si compound. This modifies the zeolite membrane surface with the Si compound, thereby imparting specific physicochemical properties. For example, by reliably forming a layer containing a large amount of Si—OH on the zeolite membrane surface, the polarity of the membrane surface is improved, thereby improving the separation performance of polar molecules. In addition, modifying the zeolite membrane surface with a Si compound can sometimes have the effect of sealing fine defects present on the membrane surface. Furthermore, the pore size of zeolite can be controlled by silylation treatment, and this treatment can also be suitably used as a method for improving the ammonia permeation selectivity.

[0114] The solvent used for the silylation treatment may be water or an organic solvent. The solution may also be acidic or basic, in which case the silylation reaction is catalyzed by the acid or base. There are no limitations on the silylating agent used, but alkoxysilanes are preferred. The treatment temperature is usually from room temperature to 150°C or less, and the treatment may be carried out for approximately 10 minutes to 30 hours. These treatment conditions may be appropriately set depending on the silylating agent and solvent used.

[0115] <<Nitrogen atom content on 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 can be controlled by, as described above, adjusting the Al atom / Si atom ratio of the zeolite by selecting a cation species containing nitrogen atoms in the zeolite contained in the zeolite membrane, adjusting the content of nitrogen atoms by adjusting the amount of ion exchange by ion exchange, using an organic template (structure-directing agent) containing nitrogen atoms when producing the zeolite membrane as needed and adjusting the amount of the organic template added or the heating temperature and heating time when the organic template is removed by baking, treating the zeolite membrane with nitrate, adjusting the number of times of water washing when washing the nitric acid-treated zeolite membrane with water, or by an appropriate combination of these methods.

[0116] <<Aluminum atom content on the surface of zeolite membrane composite>> As described above, the content of Al atoms contained in the surface of the zeolite membrane composite of the present invention can be controlled by adjusting the Al atom / Si atom ratio in the zeolite contained in the zeolite membrane, treating the zeolite membrane with an aluminum salt, adjusting the number of times the aluminum salt-treated zeolite membrane is washed with water, or by appropriately combining these methods.

[0117] <<Content of alkali metal elements contained on the surface of zeolite membrane composite>> As described above, the content of alkali metal elements contained in the surface of the zeolite membrane composite of the present invention can be controlled by adjusting the Al atom / Si atom ratio in the zeolite contained in the zeolite membrane, adjusting the content of alkali metal elements by adjusting the amount of ion exchange by ion exchange, adjusting the number of times the zeolite membrane is washed with water, or by appropriately combining these methods. The zeolite composite membrane thus produced has excellent properties and can be suitably used as a membrane separation means for separating ammonia from a mixed gas in the present invention.

[0118] <Method for separating ammonia> The zeolite composite membrane of the present invention can selectively permeate and separate ammonia from a mixed gas containing at least nitrogen gas and ammonia gas. The method for separating ammonia 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 hydrogen, and therefore is effective when used in combination with an ammonia production method that produces such a mixed gas. That is, a preferred embodiment is an ammonia production method comprising a first step of producing ammonia from hydrogen and nitrogen, and a second step of separating the ammonia obtained in the first step. Furthermore, a preferred embodiment of the present invention is an ammonia production method in which the first step and the second step proceed in a single reactor. The first step and the second step proceed in a single reactor means that the first step and the second step proceed simultaneously. That is, one embodiment of the present invention is a method for efficiently producing ammonia by producing ammonia gas from hydrogen gas and nitrogen gas in a vessel and separating ammonia from a mixed gas containing the produced ammonia gas in the vessel.

[0119] There are no particular limitations on the industrial production method of ammonia, but the Haber-Bosch process is one example. This process essentially uses iron oxide as a catalyst. Nitrogen and hydrogen gas react over the catalyst at high temperatures and pressures of 300–500°C and 10–40 MPa to produce ammonia. The ammonia produced in the reactor outlet gas is cooled, condensed, and separated for recovery as a product, while unreacted nitrogen and hydrogen gas are separated and recycled as feed gas. In the 1980s, a Ru-based supported catalyst was developed as an improvement over the Haber-Bosch process, enabling ammonia production under lower pressures. A process combining this with the Haber-Bosch process has also been commercialized, but the basic production process has remained unchanged for over 100 years. Thus, industrial ammonia production catalysts are generally broadly divided into iron-based and Ru-based catalysts. The theoretical molar ratio of hydrogen to nitrogen (H / N) is ideal for ammonia production. However, because Ru-based catalysts are prone to catalyst poisoning by hydrogen, production conditions with a lower molar ratio are preferred. Considering this point, although not particularly limited, the ammonia production catalytic process to be combined with the ammonia separation technology according to the present invention is preferably a process using a Ru-based catalyst, since this approaches the preferred volume ratio of hydrogen gas / nitrogen gas contained in the feed gas in ammonia separation, which will be described later, and this combination makes it possible to reduce the amount of hydrogen permeating during separation of the produced ammonia.

[0120] The method for separating ammonia using the zeolite membrane composite of the present invention uses a specific zeolite membrane, and brings a mixed gas consisting of ammonia and multiple components including hydrogen and / or nitrogen into contact with the zeolite membrane, thereby selectively allowing ammonia to permeate and be separated from the mixed gas. As described above, according to the present invention, ammonia gas is produced from hydrogen gas and nitrogen gas in a reactor, and ammonia can be efficiently produced and recovered in the reactor while the produced ammonia gas is permeated through a zeolite membrane.

[0121] (mixed gas) In the present invention, the mixed gas is a gas containing at least ammonia gas and nitrogen gas, and preferably also hydrogen gas.

[0122] (ammonia concentration in mixed gas) The ammonia concentration in the mixed gas is not particularly limited, but from the viewpoint of the ammonia permeation rate, the ammonia gas concentration is preferably 1.0% by volume or more. If the ammonia gas concentration is 1.0% by volume or more, the ammonia gas permeation rate is improved. From the above viewpoint, the ammonia gas concentration in the feed gas is preferably 2.0% by volume or more, more preferably 3.0% by volume or more, and particularly preferably 5.0% by volume or more. On the other hand, the upper limit is not particularly limited, but since the higher the ammonia gas concentration in the feed gas, the better the separation performance, so it is usually less than 100% by volume. However, because of the need to separate ammonia, it is generally 80% by volume or less, preferably 60% by volume or less, and more preferably 40% by volume or less. The concentration of ammonia in the feed gas is determined by sampling the feed gas, analyzing its components, and using the molar fraction of ammonia as the equivalent of volume %. The volume % of other gases is also determined by molar fraction and volume %.

[0123] Furthermore, when ammonia is separated in combination with an ammonia production process, the ammonia concentration is equal to or lower than the equilibrium concentration of ammonia produced under the conditions of the production process. Compared to known methods of selectively permeating hydrogen gas and / or nitrogen gas from a mixed gas of hydrogen, nitrogen, and ammonia, the ammonia separation technology using the present invention is a process of separating ammonia from a feed gas, and is therefore advantageous for separating ammonia from a mixed gas containing a high concentration of ammonia. Furthermore, even if a subsequent step of recovering hydrogen gas from the non-permeated mixed gas that did not permeate the membrane is adopted as necessary, the design is such that hydrogen is recovered from the mixed gas in which the ammonia gas concentration has been sufficiently reduced, and therefore the above-mentioned problems that occur in known processes of separating hydrogen and / or nitrogen from a feed gas and concentrating ammonia are unlikely to occur. For example, compared to Patent Document 1, the ammonia separation performance is significantly improved, and the separation stability is also high during operation at high temperatures or long-term operation.

[0124] The reason why the permeation selectivity of ammonia permeating through a zeolite membrane is significantly improved when the ammonia gas concentration in a mixed gas containing at least ammonia and nitrogen exceeds a certain level is not yet clear. However, as the ammonia gas concentration in the mixed gas increases, adsorption to the zeolite becomes more likely due to the adsorption equilibrium between ammonia gas and zeolite, and a zeolite membrane is first formed in which ammonia is adsorbed within the pores. The zeolite membrane thus formed, with adsorbed ammonia, narrows the pore size within the zeolite membrane, thereby reducing the permeation rate of hydrogen, which has a small molecular size. This effect also occurs when a zeolite with a pore size larger than the molecular sizes of hydrogen, nitrogen, and ammonia narrows the pores of the zeolite membrane, significantly inhibiting hydrogen permeation. 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 the selective separation of ammonia.

[0125] That is, the present invention is a technology in which ammonia is first actively adsorbed onto zeolite, and the pore size of the zeolite membrane is controlled to increase the ammonia separation selectivity, while allowing ammonia to selectively permeate within the pores by hopping movement due to ammonia adsorption / desorption. In contrast, Patent Document 2 is significantly different in that it proposes a technology in which ammonia-adsorbed zeolite membranes such as this cause blockages in ammonia permeation, and therefore designs a zeolite that does not cause such adsorption, and separates ammonia using a molecular sieve that utilizes the pore size of the zeolite. Furthermore, in the silica film proposed in Patent Document 1, ammonia is unlikely to be adsorbed, and even if ammonia is adsorbed, the thermal stability is low, so the effect of the present invention is not achieved.

[0126] On the other hand, in the present invention, in which ammonia is separated mainly by the intrapore hopping mechanism accompanied by the adsorption / desorption of ammonia to the zeolite, the temperature during ammonia separation is an important design factor because it significantly affects the long-term durability of the zeolite membrane used, the ammonia separation performance of the zeolite membrane, and the production energy balance of the entire process when combined with an ammonia production facility. From these perspectives, 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, and the temperature during ammonia separation is the temperature inside the separator where ammonia separation is performed, i.e., the temperature of the mixed gas to be separated and the temperature of the separated ammonia gas. Furthermore, the temperature of the separation membrane can be considered to be approximately the same as the temperature inside the separator.

[0127] From the perspective of ammonia production process design, it is preferable to carry out separation at the same temperature as the synthesis temperature, since this eliminates the need to raise the temperature of the hydrogen and nitrogen recycled to the reactor. Therefore, the preferred temperature for ammonia separation, although it depends on the reaction temperature in the ammonia synthesis reaction, is usually 500°C or lower, preferably 450°C or lower, and more preferably 400°C or lower. When ammonia is separated using the zeolite membrane of the present invention under these temperature conditions, not only is continuous operation possible over a long period of time due to the high stability of the zeolite membrane, but high ammonia permeation selectivity is also exhibited.

[0128] On the other hand, the lower limit is usually a temperature above 50° C., preferably 100° C. or higher, more preferably 150° C. or higher, particularly preferably 200° C. or higher, among which, preferably 250° C. or higher, and particularly preferably 300° C. or higher. When ammonia separation is carried out under these temperature conditions, the desorption rate of ammonia adsorbed in the zeolite pores increases, and as a result, the ammonia permeation rate of the zeolite membrane increases. Furthermore, when recycling raw material gas in the ammonia production process, ammonia separation under higher temperature conditions is preferred because the energy required to raise the temperatures of hydrogen and nitrogen is reduced. From this viewpoint, the lower limit is preferably 250°C or higher, more preferably 300°C or higher.

[0129] The mixed gas (feed gas) may contain ammonia and nitrogen, and preferably contains hydrogen in consideration of the synthesis of ammonia. The volume ratio of hydrogen gas to nitrogen gas contained in the mixed gas is usually 3 or less, more preferably 2 or less. By adjusting the volume ratio to this value, the amount of hydrogen permeating during ammonia separation is reduced, and the separation selectivity of ammonia 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, it is preferable to combine it with a Ru-based ammonia production catalyst process in which the volume ratio of hydrogen gas to nitrogen gas in the feed gas is low, although this is not particularly limited. On the other hand, the lower limit of this ratio is not particularly limited, because the lower the ratio, the more improved the ammonia separation selectivity, but it is usually 0.2 or more, preferably 0.3 or more, and more preferably 0.5 or more. Here, the upper and lower limit values ​​are valid within the range of significant figures. That is, an upper limit of 3 or less means 2.5 or more and less than 3.5, whereas 0.2 or more means 0.15 or more and less than 0.25, and 1.0 or more means 0.95 or more and less than 1.05.

[0130] In the present invention, the pressure of the mixed gas (feed gas) is preferably higher because the separation performance of the zeolite membrane improves and the area of ​​the zeolite membrane used can be reduced, but there is no particular limitation as long as the pressure is equal to or higher than atmospheric pressure, and the pressure may be appropriately reduced and adjusted to the desired pressure. If the pressure of the gas to be separated is lower than the pressure used for separation, it can be increased using a compressor or the like. The pressure of the mixed gas (supply gas) is usually atmospheric pressure or higher, preferably 0.1 MPa or higher, more preferably 0.2 MPa or higher, and the upper limit is usually 20 MPa or lower, preferably 10 MPa or lower, more preferably 5 MPa or lower, and may be 3 MPa or lower.

[0131] The pressure on the permeation side is not particularly limited as long as it is lower than the pressure of the gas on the supply side, but is usually 10 MPa or less, preferably 5 MPa or less, more preferably 1 MPa or less, and even more preferably 0.5 MPa or less, and in some cases may be reduced to a pressure below atmospheric pressure. When separating ammonia until the concentration of ammonia in the supply gas becomes low, a low pressure on the permeation side is preferred, and reducing the pressure to below atmospheric pressure makes it possible to separate ammonia until the ammonia gas concentration in the supply gas becomes even lower. The pressure difference between the gas on the feed 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, and even more preferably 1 MPa or less, and 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. Furthermore, pressure [Pa] refers to absolute pressure unless otherwise specified.

[0132] The flow rate of the mixed gas (feed gas) should be such that it is possible to compensate for the decrease in the permeating gas and to mix the feed gas so that the concentration of the less permeable gas in the immediate vicinity of the membrane matches the concentration in the entire gas. Although it depends on the tube diameter of the zeolite membrane composite and the separation performance of the membrane, the linear velocity is usually 0.001 mm / sec or more, preferably 0.01 mm / sec or more, more preferably 0.1 mm / sec or more, and among these, preferably 0.5 mm / sec or more, more preferably 1 mm / sec or more. There is no particular upper limit, and it is usually 1 m / sec or less, preferably 0.5 m / sec or less.

[0133] 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. The sweep gas refers to a gas supplied to efficiently recover ammonia permeated by the separation membrane. It is not a gas introduced into the feed gas side before separation and permeation, but a gas supplied to the permeation side of the separation membrane. In other words, the sweep gas is a gas supplied separately from the feed gas before separation and permeation. A different type of gas than the feed gas is passed through the permeation side to recover the gas permeated through the membrane. The sweep gas used in the present invention refers, for example, to gas 39 supplied via line 342 shown in FIG. 3. The pressure of the sweep gas is usually atmospheric pressure, but is not particularly limited to atmospheric pressure. It is preferably 20 MPa or less, more preferably 10 MPa or less, and even more preferably 1 MPa or less. The lower limit is preferably 0.09 MPa or more, more preferably 0.1 MPa or more. In some cases, the sweep gas may be used at reduced pressure.

[0134] The flow rate of the sweep gas is not particularly limited, but is usually 0.5 mm / sec or more, preferably 1 mm / sec or more, in terms of linear velocity. There is no upper limit, but it is usually 1 m / sec or less, preferably 0.5 m / sec or less.

[0135] The apparatus used for gas separation is not particularly limited, but a zeolite membrane composite is usually used as a membrane module (hereinafter, "zeolite membrane composite and / or separation apparatus using a zeolite membrane composite" may be simply referred to as "membrane module"). The membrane module may be, for example, an apparatus as schematically shown in FIG. 3, or may be a membrane module exemplified in "Gas Separation and Purification Technology" (Toray Research Center, Inc., 2007, p. 22). 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 to be separated may be supplied to the first membrane module, and the non-permeated gas that does not permeate the membrane may be further supplied to the second membrane module, or the permeated gas may be supplied to the second membrane module. The former method can further increase the concentration of less permeable components in the non-permeated side, while the latter method can further increase the concentration of more permeable components in the permeated gas. A combination of these methods can also be used. When separation is performed using membrane modules provided in multiple stages, the pressure of the feed gas may be adjusted by a pressure booster or the like as necessary when the gas is supplied to the membrane module in the subsequent stage.

[0136] Furthermore, when using multiple membrane modules, membranes with different performance characteristics can be installed in each stage. Generally, membranes with high permeability have low separation performance, while membranes with high separation performance tend to have low permeability. Therefore, when processing gas components to be separated or concentrated to a desired concentration, membranes with high permeability require a smaller membrane area, but low-permeability components also easily permeate to the permeate side, resulting in a low concentration of highly permeable components in the permeate side gas. Conversely, membranes with high separation performance tend to limit the permeation of low-permeability components to the permeate side, resulting in a high concentration of highly permeable components in the permeate side gas, but require a larger membrane area. Separation using a single type of membrane makes it difficult to control the relationship between the required membrane area and the permeation and non-permeation amounts of the target gas for concentration or separation. However, using membranes with different performance characteristics makes this easier. By selecting the optimal membrane area and the permeation and non-permeation amounts of the target gas for concentration or separation, based on the membrane cost and the price of the gas to be separated and recovered, membranes can be installed to maximize overall benefits. For example, if ammonia cannot be sufficiently separated with one membrane separation stage, the non-permeate gas can be separated using several more membrane stages. Also, if the membrane's ammonia / hydrogen separation is not sufficient with one membrane separation stage and a large amount of hydrogen is contained along with ammonia on the permeate side, the permeate gas can be separated using a membrane with high ammonia and hydrogen separation performance.

[0137] The zeolite membrane used in the present invention has excellent chemical resistance, oxidation resistance, heat stability, and pressure resistance, and also exhibits high ammonia permeability and separation performance, and has excellent durability. The term "high permeability" used here refers to a sufficient throughput, for example, the permeance [mol / (m 2 ·s·Pa)], for example, when ammonia is passed through at a temperature of 200°C and a differential pressure of 0.3 MPa, it is usually 1×10 -9 or more, preferably 5 x 10 -9 or more, more preferably 1×10 -8 More preferably, 2 × 10 -8 More preferably, 5×10 -8 More preferably, 1×10 -7 or more, most preferably 2 x 10 -7 The upper limit is not particularly limited, and is usually 3 × 10 -4 The following is the result.

[0138] The permeance [mol / (m 2 ·s·Pa)] is typically 5×10 -8 Less than or equal to 3 x 10 -8 Less than 1×10, more preferably -8 Below, particularly preferably 5 × 10 -9 Below 1 × 10, most preferably -9 Ideally, the permeance is 0, but in practice it is 1×10 -10 ~1×10 -14 It may be on the order of about this. Here, permeance (also called "permeability") is the amount of permeating substance divided by the product of the membrane area, time, and the partial pressure difference between the supply side and permeation side of the permeating substance, and its unit is [mol / (m 2 ·s·Pa)] and is a value calculated by the method described in the Examples section.

[0139] The selectivity of a zeolite membrane is expressed by an ideal separation factor. The ideal separation factor and separation factor are indicators of selectivity generally used in membrane separation. The ideal separation factor is calculated by the method described in the Examples section, and the separation factor is calculated as follows: The separation factor α is calculated using the following formula. α=(Q'1 / Q'2) / (P'1 / P'2) [In the above formula, Q'1 and Q'2 represent the permeation amounts [mol / (m 2 s Pa), and P'1 and P'2 represent the partial pressures [Pa] of the highly permeable gas and the less permeable gas in the supply gas, respectively.

[0140] The separation factor α can also be determined as follows. α=(C'1 / C'2) / (C1 / C2) (In the above formula, C'1 and C'2 represent the concentrations [vol %] of the highly permeable gas and the less permeable gas in the permeating gas, respectively, and C1 and C2 represent the concentrations [vol %] of the highly permeable gas and the less permeable gas in the supply gas, respectively.)

[0141] 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 factor is usually 15 or more, preferably 20 or more, more preferably 25 or more, and most preferably 30 or more. When ammonia and hydrogen are permeated at a temperature of 200°C and a differential pressure of 0.3 MPa, the ideal separation factor is usually 2 or more, preferably 3 or more, more preferably 5 or more, even more preferably 7 or more, particularly preferably 8 or more, particularly preferably 10 or more, and most preferably 15 or more. The upper limit of the ideal separation factor is when only ammonia permeates, in which case the upper limit is infinite, but in practice the separation factor may be about 100,000 or less.

[0142] The separation factor of the zeolite membrane used in the present invention, for example, 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, is usually 2 or more, preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. The upper limit of the separation factor is when only ammonia permeates, in which case it is infinite, but in practice the separation factor may be about 100,000 or less.

[0143] As described above, the zeolite membrane used in the present invention has excellent chemical resistance, oxidation resistance, heat stability, and pressure resistance, and exhibits high permeability and separation performance and is highly durable. The ammonia separation method of the present invention using such a zeolite membrane can be applied to the separation of ammonia from the product of ammonia synthesis. Furthermore, the ammonia separation method of the present invention can also be used as a membrane reactor in which a zeolite membrane is provided in an ammonia synthesis reactor, and ammonia is selectively permeated and separated in the reactor, thereby shifting the equilibrium between hydrogen gas and nitrogen gas and ammonia gas in the reaction system, thereby synthesizing ammonia efficiently at a high conversion rate. [Example]

[0144] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples as long as it does not deviate from the gist of the invention. Note that the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limit values ​​in the embodiments of the present invention, and a preferred range may be defined by combining the above upper or lower limit values ​​with the values ​​of the following examples or values ​​of the examples themselves.

[0145] <Separation performance measurement> (1) Ammonia separation test An ammonia separation test was carried out as follows in the apparatus shown in Fig. 3. In the apparatus shown in Fig. 3, a mixed gas containing ammonia gas (NH3) and nitrogen gas (N2) was supplied as a feed gas at a flow rate of 126 SCCM between the pressure vessel 32 and the zeolite membrane composite 31, and the pressure difference between the gas on the feed side and the gas that had permeated through the membrane was adjusted to a constant value of 0.3 MPa using the back pressure valve 36. The exhaust gas discharged from the pipe 340 was analyzed by a micro gas chromatograph, and the concentration and flow rate of the permeated gas were calculated. In the ammonia separation test, the pressure vessel was purged with the sample gas to be used for drying and exhausting at temperatures above the measurement temperature in order to remove components such as moisture and air from the pressure vessel. After that, the sample gas temperature and the differential pressure between the supply gas side and the permeate gas side of the zeolite membrane composite were kept constant, and after the permeate gas flow rate had stabilized, the flow rate of the sample gas (permeate gas) that had permeated the zeolite membrane composite was measured, and the gas permeance [mol / (m 2 The pressure difference between the supply side and permeation side of the feed gas (differential pressure) was used as the pressure when calculating the permeance. In the case of a mixed gas, the partial pressure difference was used. Based on the measurement results, the ideal separation factor α' was calculated using the following formula (2). α'=(Q1 / Q2) / (P1 / P2) (2) [In equation (2), Q1 and Q2 are the permeation amounts [mol (m 2 ·s) -1 ], and P1 and P2 represent the pressure difference [Pa] between the supply side and the permeation side of the high-permeability gas and the low-permeability gas, respectively. This indicates the ratio of the 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 The zeolite membrane composites synthesized in Examples and Comparative Examples (see FIG. 4) were cut out with a diamond cutter at lengths of 8 to 12 cm (region B of zeolite membrane composite 1), 56 to 60 cm (region A of zeolite membrane composite 1), and 108 to 112 cm (region B' of zeolite membrane composite 1) from the bottom end to prepare samples for evaluating ammonia separation. FIG. 4 is a schematic diagram of the zeolite membrane composite produced in Example 1.

[0146] Example 1 [Production of MFI-type zeolite membrane composite] (Raw material mixture for hydrothermal synthesis) 32.7 g of 93% by mass sodium hydroxide (Wako, granular) and 2739.8 g of demineralized water were mixed, to which 5.3 g of sodium aluminate (Kishida Chemical, containing 62.2% by mass of Al2O3) was added and stirred at 50°C for 30 minutes. 238.5 g of colloidal silica (Nissan Chemical, Snowtex 40) was added, and the mixture was stirred at 50°C for 4 hours to prepare a raw material mixture for hydrothermal synthesis. The composition (molar ratio) of this raw material mixture for hydrothermal synthesis was SiO2 / Al2O3 / NaOH / H2O = 1 / 0.020 / 0.54 / 100.

[0147] (Porous support) The porous support used was a 120 cm alumina tube (outer diameter 12 mm, inner diameter 9 mm) manufactured by Iwao Porcelain Industries Co., Ltd., which had been washed by flowing demineralized water and then dried.

[0148] (Seed crystal dispersion) MFI type zeolite was ground in a mortar and prepared, and seed crystals were dispersed in the ground zeolite so that the seed crystal concentration was 0.1% by mass, to prepare a seed crystal dispersion.

[0149] (Production of Zeolite Membrane Composite) The porous support sucked with 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 attach the seed crystals to the porous support. The mass of the attached seed crystals was approximately 0.04 g. Four porous supports with attached seed crystals were prepared using this method. The four porous supports with the seed crystals attached were each immersed vertically in a Teflon (registered trademark) inner tube containing the above-mentioned mixture of raw materials for hydrothermal synthesis. The autoclave was then sealed and heated to 180°C in a thermostatic chamber over 3 hours, followed by 12 hours of static heating under autogenous pressure. After a predetermined time had passed, the porous support-zeolite membrane composite was removed from the reaction mixture, washed, and then refilled with demineralized water and heated in the autoclave at 120°C for 20 hours. After a predetermined time had passed, the porous support-zeolite membrane composite was removed from the demineralized water and dried at 100°C for 3 hours to obtain an MFI zeolite membrane composite. The mass of the MFI zeolite crystallized on the porous support was 1.3 g. The air permeability of the zeolite membrane composite after calcination was 4 cm. 3 / min.

[0150] Comparative Example 1 [Production of MFI-type zeolite membrane composite] (Raw material mixture for hydrothermal synthesis) 77.6 g of 93% by mass sodium hydroxide (Wako, granular) and 2398.3 g of demineralized water were mixed, to which 12.5 g of sodium aluminate (Kishida Chemical, containing 62.2% by mass of Al2O3) was added and stirred at 50°C for 30 minutes. 566.5 g of colloidal silica (Nissan Chemical, Snowtex 40) was added, and the mixture was stirred at 50°C for 4 hours to prepare a raw material mixture for hydrothermal synthesis. The composition (molar ratio) of this raw material mixture for hydrothermal synthesis was SiO2 / Al2O3 / NaOH / H2O = 1 / 0.020 / 0.54 / 40.

[0151] (Porous support) The porous support used was a 120 cm alumina tube (outer diameter 12 mm, inner diameter 9 mm) manufactured by Iwao Porcelain Industries Co., Ltd., which had been washed by flowing demineralized water and then dried.

[0152] (Seed crystal dispersion) MFI type zeolite was ground in a mortar and prepared, and seed crystals were dispersed in the ground zeolite so that the seed crystal concentration was 0.1% by mass, to prepare a seed crystal dispersion.

[0153] (Production of Zeolite Membrane Composite) The porous support sucked with 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 attach the seed crystals to the porous support. The mass of the attached seed crystals was approximately 0.038 g. Four porous supports with attached seed crystals were prepared using this method. The four porous supports with the seed crystals attached were each immersed vertically in a Teflon (registered trademark) inner tube containing the above-mentioned hydrothermal synthesis raw material mixture. The autoclave was then sealed and heated to 180°C in a thermostatic chamber over 3 hours, followed by 14 hours of static heating under autogenous pressure. After a predetermined time had passed, the porous support-zeolite membrane composite was removed from the reaction mixture, washed, and then refilled with demineralized water and heated in the autoclave at 120°C for 20 hours. After a predetermined time had passed, the porous support-zeolite membrane composite was removed from the demineralized water and dried at 100°C for 3 hours to obtain MFI zeolite membrane composite 2. The mass of the MFI zeolite crystallized on the porous support was 0.77 g. The air permeability of the calcined zeolite membrane composite 2 at 50 Torr was 1 cm. 3 / min.

[0154] (Evaluation results) The MFI type zeolite membrane composite produced above was subjected to an ammonia separation test under the condition that the temperature was 250°C, by the method described above. To simplify the experiment, a 9.5% by volume NH3 / 90.5% by volume N2 mixed gas was used. The ammonia concentration and ammonia / nitrogen (NH3 / N2) permeance ratio of the obtained permeable gas are shown in Table 1. In Table 1, the ammonia concentration of the permeable gas is rounded to one decimal place. Furthermore, the element ratios of each part were determined by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) described below, and the silicon / aluminum ratio and sodium / silicon ratio were measured five times (n = 5) and the average values ​​were recorded.

[0155] (Preparation of SEM-EDS analysis sample) (Pretreatment) The 4 cm zeolite membrane composite used for the NH3 separation measurement was cut into 5 mm square test pieces using a diamond cutter, and after further cutting the cross section, 2 nm of Pt was vapor-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 an ion beam was irradiated from the porous support side at an accelerating voltage of 4 kV to perform cross-sectional cutting for 4 hours. (SEM-EDS measurement) Equipment: FE-SEM (JEOL JSM-7900F) EDS (Oxford ULTim MAX) Conditions: 5 kV (exposure current 500 pA, high vacuum mode) Observation magnification: 5000x, 10000x, 20000x (Observation area for SEM-EDS measurement) An image was taken at 20,000x magnification, and the film portion was enclosed as shown in Figure 5. Measurements were carried out for 120 seconds under the above conditions, and the Si / Al ratio and Na / Al ratio were calculated. (Calculation of atomic concentration) The atomic concentration of each element was calculated using AZtec (Oxford Instruments) software. The Si / Al ratio was calculated by dividing the atomic concentration of Si by the atomic concentration of Al. The Na / Si ratio was calculated by dividing the atomic concentration of Na by the atomic concentration of Si.

[0156] [Table 3]

[0157] The zeolite composite membranes of the Examples of the present invention exhibit high ammonia and hydrogen separation capabilities at every site, with ammonia-to-nitrogen ratios of 100 or greater everywhere. On the other hand, the zeolite composite membrane of Comparative Example 1, which was manufactured by a conventional method, exhibits a significant decrease in separation performance at one end (site B). This indicates that although the zeolite composite membrane of Comparative Example 1 can be lengthened to increase its surface area and thereby increase the amount of gas that can pass through per unit time, a large amount of nitrogen is mixed into the separated gas, significantly reducing its ammonia separation capability. On the other hand, the zeolite composite membrane of Example 1 of the present invention, which was manufactured with a significantly higher water content than usual, exhibits a 100-fold or greater difference in ammonia and nitrogen permeability at every site, despite being over 1 meter long. This indicates that the membrane combines a large absolute amount of gas passing through due to its length with high ammonia separation capability. When these results are examined in relation to the composition, it is clear that the Na / Si molar ratio in the area where the ammonia and nitrogen separation ability is significantly reduced is significantly different from that in other areas. It is thought that this variation in composition somehow caused the reduction in separation ability. For example, when a thermal load is applied, the difference in composition at only this one end may have caused microscopic damage to one end of the tube, allowing both nitrogen and ammonia to pass through. This result is considered to indicate that a decrease in separation ability occurs when the Na / Si ratio exceeds 0.2. [Explanation of symbols]

[0158] 10. Zeolite membrane composite 11. Center of the tube length 12. Part (A) 13. Part (B) 13'. Part (B') 31. Zeolite membrane composite 32. Pressure-resistant vessel 33. Endpin 34. Connection 35. Pressure gauge 36. Back pressure valve 37. Supply gas (mixture of gases) 38. Permeable gas 39. Sweep Gas 340. Exhaust Gas 341. Piping 342. Piping 101.Porous support 102.Void 103. Zeolite membrane

Claims

1. A zeolite membrane composite for ammonia or methanol separation, comprising a zeolite membrane on a porous support, the zeolite membrane composite having a tubular structure, wherein the sodium / silicon (molar ratio) in site (A), the sodium / silicon (molar ratio) in site (B), and the sodium / silicon (molar ratio) in site (B') shown below are all 0.001 or more and 0.2 or less, and the SiO2 / Al2O3 molar ratio is 6 or more and 500 or less. Region (A): A region 4 cm wide on both sides of the center of the zeolite membrane composite tube in the longitudinal direction Region (B): A region 8 to 12 cm from one end of the zeolite membrane composite tube Region (B'): 8 to 12 cm from the other end of the zeolite membrane composite tube

2. A zeolite membrane composite for ammonia separation or methanol separation as described in claim 1, wherein the sodium / silicon (molar ratio) in the region (A), the sodium / silicon (molar ratio) in the region (B), and the sodium / silicon (molar ratio) in the region (B') are 0.03 or more and 0.2 or less.

3. 3. The zeolite membrane composite for ammonia separation or methanol separation according to claim 1, wherein the length of the tube of the tubular structure is 40 cm or more.

4. 4. The zeolite composite membrane for ammonia separation or methanol separation according to claim 1, wherein the length of the tube of the tubular structure is 100 cm or more.

5. 5. The zeolite membrane composite for ammonia separation or methanol separation according to claim 1, wherein the zeolite is any one of a CHA type, a FAU type, a MFI type, a LTA type, and a RHO type.

6. 5. The zeolite membrane composite for ammonia separation or methanol separation according to claim 1, wherein the zeolite is any one of a CHA type, an MFI type, an LTA type, and an RHO type.

7. 5. The zeolite membrane composite for ammonia separation or methanol separation according to claim 1, wherein the zeolite is either an MFI type or an RHO type.

8. 5. The zeolite membrane composite for ammonia separation or methanol separation according to claim 1, wherein the zeolite is an MFI type zeolite.

9. 9. The zeolite membrane composite for ammonia or methanol separation according to claim 1, wherein the sodium / silicon (molar ratio) is 0.18 or less.

10. 9. The zeolite membrane composite for ammonia or methanol separation according to claim 1, wherein the sodium / silicon (molar ratio) is 0.14 or less.

11. 11. A method for producing a zeolite membrane composite for ammonia separation or methanol separation according to claim 1, wherein the molar ratio of water to silicon in the raw material mixture for hydrothermal synthesis is 45 or more and 300 or less.

12. 12. The method for producing a zeolite membrane composite for ammonia or methanol separation according to claim 11, wherein the molar ratio of water to silicon is 60 or more and 200 or less.

13. 13. The method for producing a zeolite membrane composite for ammonia or methanol separation according to claim 11 or 12, wherein the molar ratio of water to silicon is 70 or more and 150 or less.

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