Zeolite membrane complex, separation apparatus, separation method and method of producing zeolite membrane complex

Abstract

A zeolite membrane complex (1) includes a porous support (11), and a zeolite membrane (12) formed on the support (11) and composed of an 8-membered ring zeolite. The zeolite membrane (12) is selectively permeable to hydrogen sulfide rather than nitrogen for a gas containing nitrogen and hydrogen sulfide. It is therefore possible to provide a zeolite membrane complex (1) that is stably permeable to hydrogen sulfide.

Description

Zeolite membrane composite, separation device, separation method, and method for manufacturing zeolite membrane composite

[0001] The present invention relates to a zeolite membrane composite and a separation technique using the zeolite membrane composite. [Reference to Related Applications] This application claims the benefit of priority from International Patent Application PCT / JP2020 / 012910, filed March 24, 2020, the entire disclosure of which is incorporated herein by reference.

[0002] Japanese Patent Laid-Open Publication No. 2006-112488 (Reference 1) and "Development of a Methane Recovery System from Biogas Using a DDR Zeolite Membrane" by Takemi Tomohiro and three others (31st Research and Survey Presentation Meeting of the Niigata Committee of the Kanto Branch of the Japan Society of Civil Engineers, 2014, pp. 484-485) (Reference 2) disclose an apparatus that uses a DDR zeolite membrane to separate methane from biogas such as digester gas. Because biogas contains hydrogen sulfide in addition to methane and carbon dioxide, in References 1 and 2, sulfur is removed from the biogas in advance using a desulfurization device.

[0003] Furthermore, Japanese Patent Laid-Open No. 2014-46267 (Document 3) discloses a method for separating hydrogen sulfide from a mixed gas containing hydrogen sulfide using an eight-membered ring zeolite membrane (i.e., a zeolite membrane including a zeolite structure having an eight-membered oxygen ring). Japanese Patent Laid-Open No. 2019-171234 (Document 4) discloses a method for recovering the separation performance of a zeolite membrane for separating hydrogen sulfide, which has deteriorated separation performance, by heat-treating the membrane at a temperature of 30°C or higher and 500°C or lower under vacuum to remove sulfur from the zeolite.

[0004] However, as described in Literature 2, when the zeolite membrane of Literature 3 is used for a long period of time, hydrogen sulfide accumulates in the membrane, reducing the hydrogen sulfide permeation rate and the separation performance of the zeolite membrane, as is believed to be the case. While it is possible to provide a desulfurization device to remove hydrogen sulfide from the mixed gas, this increases the cost required for separating hydrogen sulfide. Furthermore, even when the method of Literature 4, in which the separation performance of the zeolite membrane is regenerated by heating, increases the cost required for separating hydrogen sulfide and complicates the separation process. Therefore, there is a need for a zeolite membrane that can stably transmit hydrogen sulfide even when the hydrogen sulfide concentration is high.

[0005] The present invention is directed to a zeolite membrane composite, and an object of the present invention is to provide a zeolite membrane composite including a zeolite membrane that can stably permeate hydrogen sulfide.

[0006] The zeolite membrane composite according to the present invention comprises a porous support and a zeolite membrane formed on the support and made of an eight-membered ring zeolite, the zeolite membrane containing protons, and selectively allowing hydrogen sulfide to permeate more than nitrogen in a gas containing nitrogen and hydrogen sulfide.

[0007] According to the present invention, a zeolite composite membrane capable of stably permeating hydrogen sulfide can be provided.

[0008] Preferably, in ammonia temperature programmed desorption measurement of the zeolite membrane, the amount of ammonia desorbed in a peak temperature region where the amount of ammonia desorbed is maximum is 1 μmol / cm ３ That's all.

[0009] Preferably, in the zeolite membrane, the ratio of alkali metal atoms to oxygen atoms is 1 atm % or less.

[0010] The present invention is also directed to a separation apparatus, which comprises the above-described zeolite composite membrane and a supply unit for supplying a mixed gas containing at least hydrogen sulfide to the zeolite composite membrane.

[0011] Preferably, the mixed gas contains a hydrocarbon.

[0012] Preferably, the concentration of hydrogen sulfide in the mixed gas is 3 mol % or more.

[0013] The present invention is also directed to a separation method, which comprises the steps of preparing the above-described zeolite composite membrane and supplying a mixed gas containing at least hydrogen sulfide to the zeolite composite membrane.

[0014] Preferably, the mixed gas contains a hydrocarbon.

[0015] Preferably, the concentration of hydrogen sulfide in the mixed gas is 3 mol % or more.

[0016] The present invention is also directed to a method for producing a zeolite composite membrane. The method for producing a zeolite composite membrane according to the present invention comprises the steps of forming a zeolite membrane made of an eight-membered ring zeolite on a porous support using a raw material solution containing a structure-directing agent, removing the structure-directing agent from the zeolite membrane, and immersing the zeolite membrane in an alkaline treatment solution that is substantially free of ammonium ions for one hour or more to obtain the zeolite membrane that contains protons and selectively permeates hydrogen sulfide over nitrogen when gases containing nitrogen and hydrogen sulfide are present.

[0017] Preferably, the pH of the treatment liquid is 9.5 to 12.

[0018] Preferably, the alkali metal ion concentration in the treatment liquid is 0.1 mol / L or less.

[0019] Preferably, the treatment liquid contains at least one of silicon and aluminum.

[0020] In this case, the total concentration of silicon atoms and aluminum atoms in the treatment liquid is preferably 0.001 mol / L or more, and is less than the concentration in the raw material solution and 1 mol / L or less.

[0021] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings.

[0022] Fig. 1 is a cross-sectional view of a zeolite composite membrane. Fig. 2 is a cross-sectional view showing an enlarged portion of the zeolite composite membrane. Fig. 3 is a diagram showing a flow of manufacturing the zeolite composite membrane. Fig. 4 is a diagram showing a separation device. Fig. 5 is a diagram showing a flow of separation of a mixed gas by the separation device.

[0023] FIG. 1 is a cross-sectional view of a zeolite membrane composite 1. FIG. 2 is an enlarged cross-sectional view of a portion of the zeolite membrane composite 1. The zeolite membrane composite 1 includes a porous support 11 and a zeolite membrane 12 provided on the support 11. The zeolite membrane 12 is at least a membrane of zeolite formed on the surface of the support 11, and does not include a membrane in which zeolite particles are simply dispersed in an organic film. In FIG. 1, the zeolite membrane 12 is depicted with a thick line. In FIG. 2, the zeolite membrane 12 is depicted with parallel diagonal lines. Furthermore, in FIG. 2, the thickness of the zeolite membrane 12 is depicted thicker than it actually is.

[0024] The support 11 is a porous member that is permeable to gases and liquids. In the example shown in FIG. 1 , the support 11 is a monolithic support having a single, continuous columnar body formed integrally with the support 11, and a plurality of through-holes 111 extending in the longitudinal direction (i.e., the left-right direction in FIG. 1 ). In the example shown in FIG. 1 , the support 11 is substantially cylindrical. The cross section perpendicular to the longitudinal direction of each through-hole 111 (i.e., cell) is, for example, substantially circular. In FIG. 1 , the diameter of the through-holes 111 is drawn larger than in reality, and the number of through-holes 111 is drawn smaller than in reality. The zeolite membrane 12 is formed on the inner surfaces of the through-holes 111 and covers the inner surfaces of the through-holes 111 over substantially the entire surfaces.

[0025] The length of the support 11 (i.e., the length in the left-right direction in FIG. 1 ) is, for example, 10 cm to 200 cm. The outer diameter of the support 11 is, for example, 0.5 cm to 30 cm. The distance between the central axes of adjacent through holes 111 is, for example, 0.3 mm to 10 mm. The surface roughness (Ra) of the support 11 is, for example, 0.1 μm to 5.0 μm, and preferably 0.2 μm to 2.0 μm. The shape of the support 11 may be, for example, a honeycomb shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal columnar shape. When the shape of the support 11 is tubular or cylindrical, the thickness of the support 11 is, for example, 0.1 mm to 10 mm.

[0026] The material of the support 11 can be various substances (e.g., ceramic or metal) as long as they are chemically stable in the process of forming the zeolite membrane 12 on the surface. In this embodiment, the support 11 is formed of a ceramic sintered body. Examples of ceramic sintered bodies selected as the material of the support 11 include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide. In this embodiment, the support 11 includes at least one of alumina, silica, and mullite.

[0027] The support 11 may contain an inorganic binder, which may be at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite.

[0028] The average pore diameter of the support 11 is, for example, 0.01 μm to 70 μm, and preferably 0.05 μm to 25 μm. The average pore diameter of the support 11 near the surface on which the zeolite membrane 12 is formed is 0.01 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. With regard to the pore diameter distribution throughout the support 11, including the surface and interior, D5 is, for example, 0.01 μm to 50 μm, D50 is, for example, 0.05 μm to 70 μm, and D95 ​​is, for example, 0.1 μm to 2000 μm. The porosity of the support 11 near the surface on which the zeolite membrane 12 is formed is, for example, 20% to 60%.

[0029] The support 11 has, for example, a multilayer structure in which multiple layers with different average pore sizes are stacked in the thickness direction. The average pore size and sintered grain size in the surface layer, including the surface on which the zeolite membrane 12 is formed, are smaller than the average pore size and sintered grain size in the layers other than the surface layer. The average pore size in the surface layer of the support 11 is, for example, 0.01 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. When the support 11 has a multilayer structure, the materials described above can be used for each layer. The materials of the multiple layers forming the multilayer structure may be the same or different.

[0030] The zeolite membrane 12 is a porous membrane having fine pores (micropores). The zeolite membrane 12 can be used as a separation membrane that separates a specific substance from a mixture of multiple types of substances by utilizing the molecular sieve effect. The zeolite membrane 12 is less permeable to other substances than the specific substance. In other words, the amount of the other substances that permeates the zeolite membrane 12 is smaller than the amount of the specific substance that permeates the zeolite membrane 12. As will be described later, the zeolite membrane 12 has a high permeability to nitrogen (N ２ ) and hydrogen sulfide (H ２ The membrane selectively allows hydrogen sulfide to permeate through the membrane over nitrogen when gases containing hydrogen sulfide are present.

[0031] The thickness of the zeolite membrane 12 is, for example, 0.05 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.5 μm to 10 μm. Increasing the thickness of the zeolite membrane 12 improves separation performance. Increasing the thickness of the zeolite membrane 12 increases the permeation rate. The surface roughness (Ra) of the zeolite membrane 12 is, for example, 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less.

[0032] The maximum number of rings in the zeolite constituting the zeolite membrane 12 is 8. That is, the zeolite membrane 12 is an 8-membered ring zeolite membrane made of 8-membered ring zeolite, the maximum number of rings of which is 8. The zeolite membrane 12 is typically made of only 8-membered ring zeolite, but depending on the manufacturing method, etc., the zeolite membrane 12 may contain a small amount (for example, 1 mass % or less) of a substance other than the 8-membered ring zeolite.

[0033] The type of zeolite constituting the zeolite membrane 12 is not particularly limited as long as it is an 8-membered ring zeolite, and may be, for example, AEI type, AFN type, AFV type, AFX type, CHA type, DDR type, ERI type, ETL type, GIS type, IHW type, LEV type, LTA type, LTJ type, RHO type, SAT type, or other zeolite. More preferably, it is, for example, AEI type, AFN type, AFV type, AFX type, CHA type, DDR type, ERI type, ETL type, GIS type, LEV type, RHO type, or SAT type zeolite. The zeolite membrane 12 is, for example, a DDR type zeolite. In other words, the zeolite membrane 12 is a zeolite membrane composed of a zeolite whose structure code defined by the International Zeolite Society is "DDR."

[0034] In this embodiment, the average pore size of the zeolite is the arithmetic mean of the minor axis and major axis of the 8-membered ring pores. The 8-membered ring pores are micropores in which the number of oxygen atoms in the ring structure formed by bonding with a T atom (described later) is eight. When the zeolite has multiple types of 8-membered ring pores, the average pore size of the zeolite is the arithmetic mean of the minor axis and major axis of all types of 8-membered ring pores. In this way, the average pore size of the zeolite membrane is uniquely determined by the skeletal structure of the zeolite, and can be determined from the values ​​disclosed in the "Database of Zeolite Structures" [online] of the International Zeolite Society, available on the Internet at <URL: http: / / www.iza-structure.org / databases / >.

[0035] The average pore diameter of the zeolite membrane 12 is, for example, 0.2 nm or more and 0.5 nm or less, and preferably 0.3 nm or more and 0.5 nm or less. The average pore diameter of the zeolite membrane 12 is smaller than the average pore diameter of the support 11 near the surface on which the zeolite membrane 12 is formed. When the zeolite membrane 12 is composed of DDR-type zeolite, the intrinsic pore diameter of the zeolite constituting the zeolite membrane 12 is 0.36 nm × 0.44 nm, and the average pore diameter is 0.40 nm.

[0036] The zeolite membrane 12 contains, for example, silicon (Si). The zeolite membrane 12 may contain, for example, any two or more of Si, aluminum (Al), and phosphorus (P). In this case, the zeolite constituting the zeolite membrane 12 may be an oxygen tetrahedron (TO) constituting the zeolite. ４ Zeolites in which the atom (T atom) located at the center of the zeolite (T atom) is composed of only Si or Si and Al, AlPO zeolites in which the T atoms are composed of Al and P, SAPO zeolites in which the T atoms are composed of Si, Al, and P, MAPSO zeolites in which the T atoms are composed of magnesium (Mg), Si, Al, and P, and ZnAPSO zeolites in which the T atoms are composed of zinc (Zn), Si, Al, and P can be used. Some of the T atoms may be substituted with other elements.

[0037] When the zeolite membrane 12 contains Si atoms and Al atoms, the Si / Al ratio in the zeolite membrane 12 is, for example, 1 or more and 100,000 or less. The Si / Al ratio is preferably 5 or more, more preferably 20 or more, and even more preferably 100 or more, and the higher the Si / Al ratio, the better. The Si / Al ratio in the zeolite membrane 12 can be adjusted by adjusting the blending ratio of the Si source and the Al source in the raw material solution, which will be described later. Furthermore, when the zeolite membrane 12 contains Al atoms and P atoms, the P / Al ratio in the zeolite membrane 12 is preferably 0.7 or more and 1.5 or less. The P / Al ratio in the zeolite membrane 12 can be adjusted by adjusting the blending ratio of the P source and the Al source in the raw material solution, which will be described later.

[0038] It is preferable that the zeolite constituting the zeolite membrane 12 does not substantially contain P as a T atom. In other words, it is preferable that the zeolite does not substantially contain P as a framework element. This can improve the heat resistance of the zeolite membrane 12. Note that "not substantially containing P as a framework element" means that the proportion of P in all T atoms is 3 mol % or less.

[0039] The zeolite membrane 12 may contain a small amount of alkali metal. The alkali metal may be, for example, sodium (Na) or potassium (K). In the zeolite membrane 12, the smaller the ratio of alkali metal atoms to oxygen atoms, the better, e.g., 1 atm% or less. This ratio is preferably 0.7 atm% or less, and more preferably 0.5 atm% or less. The ratio of alkali metal atoms (including alkali metal ions) to oxygen atoms is an atomic percentage calculated by (number of alkali metal atoms / number of oxygen atoms) and can be determined, for example, by X-ray photoelectron spectroscopy (XPS). Note that the composition of the zeolite membrane 12 can be measured by XPS after etching the membrane surface by approximately 1 nm with argon to remove the influence of surface contamination. When the zeolite membrane 12 contains multiple types of alkali metals, the above ratio refers to the ratio of the total number of alkali metal atoms to oxygen atoms.

[0040] The zeolite membrane 12 may contain a small amount of a structure-directing agent (hereinafter also referred to as "SDA"). That is, the zeolite constituting the zeolite membrane 12 may contain an SDA. The SDA is used in the formation of the zeolite membrane 12. As described below, a preferred zeolite membrane 12 contains almost no SDA.

[0041] The zeolite membrane 12 contains protons. In a preferred zeolite membrane 12, when ammonia temperature-programmed desorption measurement is performed, the amount of ammonia desorbed in the peak temperature range is 1 μmol / cm ３That's all. The higher the proton concentration in the zeolite membrane 12, the higher the amount of ammonia desorption in the peak temperature range in ammonia temperature programmed desorption measurement. In ammonia temperature programmed desorption measurement, ammonia is adsorbed onto a zeolite membrane composite 1 cut to a predetermined size, followed by steam treatment. Thereafter, the zeolite membrane 12 is heated at 10°C / min, and the amount of ammonia desorbed at each temperature is measured. The steam treatment removes ammonia adsorbed other than protons. The desorption amount in the peak temperature range is the peak temperature at which the amount of ammonia desorption is maximized within the range of 300 to 550°C, and is the ammonia desorption amount integrated within a range of 50°C (100°C) around the peak temperature. The volume of the zeolite membrane 12 used in the ammonia temperature programmed desorption measurement is calculated by multiplying the thickness of the zeolite membrane 12 (the thickness of the zeolite membrane formed on the surface of the support 11) measured using an electron microscope (SEM) or the like by the area of ​​the zeolite membrane 12 contained in the cut-out zeolite membrane composite 1. The desorption amount in the peak temperature range is preferably 1.5 μmol / cm ３ More preferably, 2 μmol / cm ３ The upper limit of the amount of desorption in the peak temperature range is not particularly limited, but is, for example, 100 μmol / cm ３ is.

[0042] Zeolite membrane 12 selectively allows hydrogen sulfide to permeate over nitrogen in a gas containing nitrogen and hydrogen sulfide in a molar ratio of 1:1 (hereinafter referred to as "evaluation gas"). That is, in the evaluation gas, the permeation amount (number of molecules) of hydrogen sulfide permeating through zeolite membrane 12 is greater than the permeation amount of nitrogen permeating through zeolite membrane 12. Specifically, the evaluation gas at a temperature of 25°C is supplied to zeolite membrane 12 at a pressure of 0.9 MPa, and the flow rate of the permeated gas (pressure of approximately 0.1 MPa) that permeates and exits zeolite membrane 12 is measured using a mass flow meter, and its composition is measured using gas chromatography. Then, based on the flow rate and composition of the permeated gas, the permeation rates (permeance) of hydrogen sulfide and nitrogen per unit membrane area and unit pressure difference are calculated. When the ratio of hydrogen sulfide permeance to nitrogen permeance (i.e., hydrogen sulfide permeance / nitrogen permeance) is greater than 1, the zeolite membrane 12 can be said to selectively permeate hydrogen sulfide over nitrogen. Such a zeolite membrane 12 can stably permeate hydrogen sulfide even in a mixed gas containing hydrogen sulfide, such as biogas (hereinafter referred to as the "gas to be separated"). The reason for this is not clear, but is presumed to be as follows.

[0043] Because nitrogen and hydrogen sulfide have nearly the same molecular diameter, the pore size of a zeolite membrane alone is not sufficient to selectively permeate one of the test gases. Furthermore, hydrogen sulfide tends to remain and accumulate within the zeolite pores, making it difficult to permeate the zeolite membrane. Therefore, a typical eight-membered ring zeolite membrane selectively allows nitrogen to permeate more readily than hydrogen sulfide for a test gas containing nitrogen and hydrogen sulfide. On the other hand, the zeolite membrane 12, which selectively allows hydrogen sulfide to permeate more readily than nitrogen for a test gas, is thought to allow hydrogen sulfide to permeate without remaining within the zeolite pores, making pore clogging by hydrogen sulfide less likely to occur. Therefore, hydrogen sulfide can be stably permeated through the target gas. As a result, degradation of hydrogen sulfide separation performance is suppressed during long-term use of the zeolite membrane composite 1 in the separation device 2 (see Figure 4) described below.

[0044] The zeolite membrane 12, which selectively allows hydrogen sulfide to permeate the test gas more than nitrogen, can be obtained, for example, by increasing the proton concentration in the membrane to a certain level or higher. This is thought to be because protons interact appropriately with hydrogen sulfide without inhibiting the permeation of hydrogen sulfide. The ammonia temperature-programmed desorption measurement described above can be used to evaluate the proton concentration in the zeolite membrane 12. When the amount of ammonia desorbed in the peak temperature range is, for example, 1 μmol / cm ３ If the proton concentration in the membrane is higher than this, the zeolite membrane 12 that selectively permeates hydrogen sulfide over nitrogen can be obtained. ３ If the proton concentration in the membrane is not too high, the zeolite membrane 12 having a high hydrogen sulfide permeability rate can be obtained.

[0045] Furthermore, the ratio of alkali metal atoms to oxygen atoms in the zeolite membrane 12 is preferably 1 atm % or less. This is thought to be because alkali metal ions strongly interact with hydrogen sulfide, and therefore the presence of an excess of alkali metal ions in the membrane inhibits the permeation of hydrogen sulfide. In other words, a small amount of alkali metal ions suppresses the inhibition of hydrogen sulfide permeation.

[0046] Next, an example of a flow of manufacturing the zeolite membrane composite 1 will be described with reference to Fig. 3 . The manufacturing of the zeolite membrane composite 1 in Fig. 3 also includes the manufacturing of the zeolite membrane 12. In the manufacturing of the zeolite membrane composite 1, first, seed crystals to be used for forming the zeolite membrane 12 are prepared (step S11). In one example of forming the DDR-type zeolite membrane 12, DDR-type zeolite powder is produced by hydrothermal synthesis, and the seed crystals are obtained from the zeolite powder. The zeolite powder may be used as the seed crystals as is, or the seed crystals may be obtained by processing the powder by pulverization or the like.

[0047] Next, the porous support 11 is immersed in the dispersion liquid in which the seed crystals are dispersed, and the seed crystals are attached to the support 11 (step S12). Alternatively, the dispersion liquid in which the seed crystals are dispersed is brought into contact with the portion of the support 11 where the zeolite membrane 12 is to be formed, thereby attaching the seed crystals to the support 11. In this way, a seed crystal-attached support is produced. The seed crystals may also be attached to the support 11 by other methods.

[0048] The support 11 with the seed crystals attached thereto is immersed in a raw material solution. The raw material solution is prepared by dissolving or dispersing raw materials for the zeolite membrane 12, an SDA, and the like in a solvent. In an example for forming a DDR-type zeolite membrane 12, the raw material solution contains a Si source, an SDA, and water as a solvent. Of course, the raw material solution may contain other raw materials such as an Al source, and the composition of the DDR-type zeolite membrane 12 can be adjusted by adjusting the blending ratios in the raw material solution. A water-soluble solvent such as alcohol or a water-insoluble solvent may be used as the solvent for the raw material solution. The SDA contained in the raw material solution is, for example, an organic substance (organic SDA). For example, 1-adamantanamine, ethylenediamine, or the like can be used as the SDA.

[0049] Thereafter, zeolite is grown by hydrothermal synthesis using the seed crystals on the support 11 as nuclei, thereby forming a zeolite membrane 12 made of 8-membered ring zeolite on the support 11 (step S13). The temperature during hydrothermal synthesis is, for example, 110 to 200° C. The hydrothermal synthesis time is, for example, 5 to 100 hours.

[0050] After the hydrothermal synthesis is completed, the support 11 and the zeolite membrane 12 are washed with pure water. The washed support 11 and the zeolite membrane 12 are dried, for example, at 100°C. After the support 11 and the zeolite membrane 12 are dried, the zeolite membrane 12 is heat-treated in an oxidizing gas atmosphere, thereby burning and removing the SDA in the zeolite membrane 12 (step S14). This penetrates the micropores in the zeolite membrane 12. Preferably, the SDA is almost completely removed. The heating temperature for removing the SDA is, for example, 400 to 1000°C, preferably 400 to 900°C, and more preferably 450 to 800°C. The heating time is, for example, 10 to 200 hours. The oxidizing gas atmosphere is an atmosphere containing oxygen, for example, air.

[0051] Subsequently, an alkaline processing liquid (hereinafter referred to as "alkaline processing liquid") is prepared by dissolving an alkali source in water. Examples of alkali sources that can be used include organic amines and quaternary ammonium hydroxides. The pH of the alkaline processing liquid is, for example, 9.5 to 12, preferably 10 to 12, and more preferably 10 to 11.5. Use of an alkaline processing liquid allows for more effective removal of alkali metals, as described below.

[0052] The alkaline processing solution also contains ammonium ions (NH ４ ＋) is substantially free of ammonium ions. If the treatment solution contains ammonium ions, the ammonium ions may penetrate into the zeolite pores of the zeolite membrane 12, resulting in a decrease in the permeation rate of the zeolite membrane 12. Complete removal of ammonium ions from the zeolite membrane 12 requires heating at a temperature higher than 500°C (e.g., 600°C). Therefore, thermal damage (defects, etc.) may reduce the separation performance of the zeolite membrane 12. Therefore, alkali sources that produce ammonium ions, such as ammonia, are not suitable. Note that the alkaline treatment solution being substantially free of ammonium ions means that the ammonium ion concentration in the alkaline treatment solution is 1 μmol / L or less. Furthermore, the aforementioned ammonium ions do not include organic ammonium ions. This is because organic ammonium ions are large and therefore difficult to penetrate into the zeolite pores.

[0053] In addition, when removing alkali metals from zeolite powder, an aqueous solution of an inorganic ammonium salt such as ammonium nitrate or ammonium chloride is used as a treatment liquid. However, because the inorganic ammonium salt aqueous solution is acidic or neutral, it is difficult to effectively remove alkali metals from the zeolite membrane 12, unlike the case of zeolite powder. In addition, because the inorganic ammonium salt aqueous solution contains ammonium ions, when used as a treatment liquid, the ammonium ions penetrate into the pores of the zeolite membrane 12, as described above. Therefore, in the ammonia temperature-programmed desorption measurement described below, the amount of ammonia desorption is reduced to 1 μmol / cm. ３ It cannot be more than that.

[0054] The alkaline processing liquid may contain alkali metals as impurities. The alkaline processing liquid preferably contains a small amount of alkali metal. The alkali metal ion concentration in the alkaline processing liquid is preferably 0.1 mol / L or less, more preferably 0.05 mol / L or less. The alkali metal ion concentration can be determined, for example, by inductively coupled plasma (ICP) atomic emission spectrometry. When the alkaline processing liquid contains multiple types of alkali metal ions, the alkali metal ion concentration is the total concentration of the multiple types of alkali metal ions.

[0055] Once the alkaline treatment solution is prepared, the support 11 and the zeolite membrane 12 are immersed in a sufficient amount of the alkaline treatment solution for at least one hour (step S15). For example, by immersing the support 11 and the zeolite membrane 12 in an alkaline treatment solution containing 1-adamantanamine or the like for at least one hour, the alkali metal ions contained in the zeolite membrane 12 are gradually replaced with hydronium ions, thereby removing the alkali metals from the zeolite membrane 12. In other words, an immersion time of less than one hour may not be sufficient to remove the alkali metals from the zeolite membrane 12. Furthermore, if an alkaline treatment solution is applied to the surface of the zeolite membrane 12 instead of immersion, a sufficient amount of the alkaline treatment solution may not be brought into contact with the zeolite membrane 12, and therefore the alkali metals may not be sufficiently removed. The immersion time is, for example, 1 to 100 hours, preferably 2 to 50 hours. The alkaline treatment solution is preferably heated, which promotes the exchange of alkali metal ions with hydronium ions. The heating temperature is, for example, 60 to 250°C, preferably 80 to 200°C.

[0056] In the treatment using an alkaline treatment liquid (alkaline treatment), to prevent dissolution of the zeolite in the zeolite membrane 12, the alkaline treatment liquid preferably contains at least one of silicon or aluminum, or both silicon and aluminum. The total concentration of silicon atoms and aluminum atoms in the alkaline treatment liquid (when only one of silicon or aluminum is contained, this refers to the concentration of the selected atom; the same applies below) is, for example, 0.001 mol / L or more, preferably 0.002 mol / L or more, and more preferably 0.005 mol / L or more. Furthermore, in order to prevent a decrease in the permeation rate of the zeolite membrane 12, the total concentration of silicon atoms and aluminum atoms in the alkaline treatment liquid is preferably less than the concentration in the raw material solution used to synthesize the zeolite membrane 12 (i.e., the total concentration of silicon atoms and aluminum atoms) and 1 mol / L or less.

[0057] Thereafter, the support 11 and the zeolite membrane 12 are washed with pure water. The washed support 11 and the zeolite membrane 12 are dried, for example, at 100°C. After the support 11 and the zeolite membrane 12 are dried, the zeolite membrane 12 is subjected to a heat treatment in the atmosphere (step S16). This removes adsorbed water and the like in the zeolite membrane 12, and converts hydronium ions into protons. The heating temperature is, for example, 300 to 500°C, preferably 350 to 500°C. The heating time is, for example, 10 to 100 hours, preferably 15 to 50 hours. Through the above treatment, a zeolite membrane 12 is obtained that selectively permeates hydrogen sulfide over nitrogen in an evaluation gas containing nitrogen and hydrogen sulfide, and the zeolite membrane composite 1 is completed.

[0058] In the alkaline treatment, the zeolite membrane 12 is immersed in the alkaline treatment solution together with the support 11, but the immersion method may also be a method in which the alkaline treatment solution is brought into contact with the zeolite membrane 12 by pouring and retaining the alkaline treatment solution only in the through-holes 111. As described above, in the alkaline treatment, the zeolite membrane 12 may be immersed in the alkaline treatment solution by various methods.

[0059] As described above, the zeolite membrane composite 1 includes the zeolite membrane 12 made of an eight-membered ring zeolite, and the zeolite membrane 12 selectively allows hydrogen sulfide to permeate over nitrogen in a test gas containing nitrogen and hydrogen sulfide. This makes it possible to provide a zeolite membrane composite 1 that allows hydrogen sulfide to stably permeate. As a result, during separation of hydrogen sulfide from a target gas, accumulation of hydrogen sulfide in the zeolite membrane 12 is suppressed, and the zeolite membrane composite 1 can be used stably (over a long period of time) for separating hydrogen sulfide.

[0060] In the ammonia temperature-programmed desorption measurement for the zeolite membrane 12, the ammonia desorption amount in the peak temperature range where the ammonia desorption amount is maximum is 1 μmol / cm ３This makes it possible to more reliably achieve selective permeation of hydrogen sulfide through the zeolite membrane 12. Furthermore, even when the ratio of alkali metal atoms to oxygen atoms in the zeolite membrane 12 is 1 atm % or less, selective permeation of hydrogen sulfide can be more reliably achieved.

[0061] In the production of the zeolite membrane composite 1, a zeolite membrane 12 made of an eight-membered ring zeolite is formed on a support 11 using a raw material solution containing SDA. Subsequently, the SDA is removed from the zeolite membrane 12. The zeolite membrane 12 is then immersed in an alkaline treatment solution to obtain a zeolite membrane 12 that selectively permeates hydrogen sulfide over nitrogen when an evaluation gas containing nitrogen and hydrogen sulfide is used. This allows the zeolite membrane composite 1 to be easily produced.

[0062] The alkaline treatment liquid has a pH of 9.5 to 12, which makes it possible to more reliably produce a zeolite membrane 12 that selectively allows hydrogen sulfide to permeate. The alkaline treatment liquid has an alkali metal ion concentration of 0.1 mol / L or less, which makes it possible to more reliably reduce the amount of alkali metal atoms contained in the zeolite membrane 12.

[0063] The alkaline treatment liquid contains at least one of silicon and aluminum, which can prevent dissolution of the zeolite membrane 12 during alkaline treatment. The total concentration of silicon atoms and aluminum atoms in the alkaline treatment liquid is 0.001 mol / L or more, which can more reliably prevent dissolution of the zeolite membrane 12. Furthermore, the total concentration of silicon atoms and aluminum atoms in the alkaline treatment liquid is less than the respective concentrations in the raw material solution used to synthesize the zeolite membrane 12 and is 1 mol / L or less, which can prevent a decrease in the permeation rate of the zeolite membrane 12.

[0064] Next, an example of the production of the zeolite membrane composite 1 will be described.

[0065] Example 1 First, DDR-type zeolite powder obtained by hydrothermal synthesis was used as seed crystals, and the seed crystals were added to pure water at a predetermined mixing ratio, and the support was brought into contact with the solution to attach the seed crystals to each through-hole. The mixing ratio was, for example, 0.001% by mass to 0.36% by mass.

[0066] Next, a raw material solution for the zeolite membrane was prepared by adding 1-adamantanamine (manufactured by Aldrich) as an SDA, sodium hydroxide (manufactured by Aldrich), 30 mass% colloidal silica (manufactured by Nissan Chemical Industries, trade name: Snowtex S), and sodium aluminate (manufactured by Wako Pure Chemical Industries) to pure water (e.g., ion-exchanged water) and mixing them. The weights of 1-adamantanamine, sodium hydroxide, colloidal silica, sodium aluminate, and pure water when the raw material solution was prepared were 1.32 g, 0.35 g, 52.6 g, 0.36 g, and 152.4 g, respectively.

[0067] After the raw material solution was prepared, a support with seed crystals attached was immersed in the raw material solution and subjected to hydrothermal synthesis at 160°C for 48 hours to form a DDR-type zeolite membrane on the support. The support on which the zeolite membrane was formed was then thoroughly washed with pure water and completely dried at 100°C. Next, the support on which the zeolite membrane was formed was heated in the atmosphere at 450°C for 50 hours to burn off the SDA and penetrate the pores in the zeolite membrane.

[0068] Next, an alkaline treatment solution was prepared by dissolving 0.31 g of 1-adamantanamine in 207 g of pure water. The prepared alkaline treatment solution had a pH of 11. The support on which the zeolite membrane was formed was immersed in the alkaline treatment solution and heated at 130°C for 24 hours, thereby subjecting the zeolite membrane to an alkaline treatment. The support on which the alkali-treated zeolite membrane was formed was then thoroughly washed with pure water and completely dried at 100°C. Next, the support on which the alkali-treated zeolite membrane was formed was heated in the atmosphere at 450°C for 50 hours, thereby obtaining a zeolite membrane composite.

[0069] A hydrogen sulfide / nitrogen separation test was conducted on the zeolite membrane composite of Example 1 using a separation device 2 described below and a mixed gas of hydrogen sulfide and nitrogen (molar ratio 1:1). The mixed gas introduction pressure was 0.9 MPa, the permeation pressure was 0.1 MPa, and the temperature was 25°C. The resulting (hydrogen sulfide permeance / nitrogen permeance) was 1.2. Thus, it was found that the zeolite membrane composite of Example 1 is a membrane that selectively allows hydrogen sulfide to permeate over nitrogen.

[0070] When ammonia temperature-programmed desorption measurement was performed on the zeolite membrane composite of Example 1, the desorption amount in the peak temperature range was 1 μmol / cm ３ Furthermore, when XPS measurement was carried out, the ratio of alkali metal atoms to oxygen atoms in the zeolite membrane was 1 atm % or less.

[0071] Comparative Example 1 The production of a zeolite membrane composite in Comparative Example 1 was substantially the same as in Example 1, except that the operations after the alkali treatment were not carried out.

[0072] A hydrogen sulfide / nitrogen separation test was performed on the zeolite membrane composite of Comparative Example 1 in the same manner as in Example 1. The result was that the (hydrogen sulfide permeance / nitrogen permeance) was 0.3. Thus, it was found that the zeolite membrane composite of Comparative Example 1 is a membrane that selectively allows nitrogen to permeate over hydrogen sulfide.

[0073] When ammonia temperature-programmed desorption measurement was performed on the zeolite membrane composite of Comparative Example 1, the amount of desorption in the peak temperature range was 1 μmol / cm ３ Furthermore, when XPS measurement was carried out, the ratio of alkali metal atoms to oxygen atoms in the zeolite membrane was greater than 1 atm %.

[0074] <Comparative Example 2> The production of a zeolite membrane composite in Comparative Example 2 was substantially the same as in Example 1, except that an aqueous solution prepared by dissolving 0.17 g of ammonium nitrate in 207 g of pure water was used instead of the alkaline treatment liquid. The pH of the prepared ammonium nitrate aqueous solution was 5.6.

[0075] A hydrogen sulfide / nitrogen separation test was performed on the zeolite membrane composite of Comparative Example 2 in the same manner as in Example 1. The result was that the (hydrogen sulfide permeance / nitrogen permeance) was 0.5. Thus, it was found that the zeolite membrane composite of Comparative Example 2 is a membrane that selectively allows nitrogen to permeate over hydrogen sulfide.

[0076] When ammonia temperature-programmed desorption measurement was performed on the zeolite membrane composite of Comparative Example 2, the amount of desorption in the peak temperature range was 1 μmol / cm ３ Furthermore, when XPS measurement was carried out, the ratio of alkali metal atoms to oxygen atoms in the zeolite membrane was greater than 1 atm %.

[0077] Next, separation of a mixed gas (gas to be separated) using the zeolite membrane composite 1 will be described with reference to Figures 4 and 5. Figure 4 is a diagram showing the separation device 2. Figure 5 is a diagram showing the flow of separation of a mixed gas by the separation device 2.

[0078] In the separation device 2, a mixed gas containing multiple types of gases is supplied to the zeolite membrane composite 1, and a highly permeable gas in the mixed gas is separated from the mixed gas by permeating through the zeolite membrane composite 1. The separation device 2 is a gas separation device. Separation in the separation device 2 may be performed, for example, for the purpose of extracting a highly permeable gas from the mixed gas, or for the purpose of concentrating a less permeable gas.

[0079] As described above, a typical example of a gas that has high permeability through the zeolite membrane composite 1 is hydrogen sulfide (H ２ S). The mixed gas to be separated contains at least hydrogen sulfide. The concentration of hydrogen sulfide in the mixed gas may be relatively high, for example, 3 mol% or more. The concentration of hydrogen sulfide in the mixed gas may be even higher (10 mol% or more), for example, 50 mol% or less. The concentration of hydrogen sulfide in the mixed gas can be measured, for example, using a commercially available hydrogen sulfide concentration meter. The mixed gas may further contain other gases with high permeability.

[0080] The gas with low permeability through the zeolite membrane composite 1 is not particularly limited. A preferred example of a gas with low permeability is hydrocarbon. That is, it is preferred that the mixed gas further contains hydrocarbon. For example, the mixed gas contains C1 to C8 hydrocarbons. C1 to C8 hydrocarbons are hydrocarbons having 1 to 8 carbon atoms. C3 to C8 hydrocarbons may be any of straight-chain compounds, branched-chain compounds, and cyclic compounds. Furthermore, C2 to C8 hydrocarbons may be either saturated hydrocarbons (i.e., those having no double or triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those having double and / or triple bonds in the molecule). C1 to C4 hydrocarbons include, for example, methane (CH ４ ), ethane (C ２ H ６ ), ethylene (C ２ H ４ ), propane (C ３ H ８ ), propylene (C ３ H ６ ), normal butane (CH ３ (CH ２ ) ２ CH ３ ), isobutane (CH(CH ３ ) ３ ), 1-butene (CH ２ =CHCH ２ CH ３ ), 2-butene (CH ３ CH=CHCH ３ ) or isobutene (CH ２ =C(CH ３ ) ２ )

[0081] The separation device 2 includes a zeolite membrane composite 1, a plugging section 21, an outer cylinder 22, two seal members 23, a supply section 26, a first recovery section 27, and a second recovery section 28. The zeolite membrane composite 1, the plugging section 21, and the seal members 23 are housed in the outer cylinder 22. The supply section 26, the first recovery section 27, and the second recovery section 28 are disposed outside the outer cylinder 22 and connected to the outer cylinder 22.

[0082] The sealing portion 21 is attached to both longitudinal end portions of the support 11 (i.e., the left-right direction in FIG. 4 ) and is a member that covers and seals both longitudinal end faces of the support 11 and the outer surfaces near these end faces. The sealing portion 21 prevents gas from flowing in and out from these end faces of the support 11. The sealing portion 21 is, for example, a plate-like member formed of glass or resin. The material and shape of the sealing portion 21 may be changed as appropriate. Note that the sealing portion 21 has multiple openings that overlap with the multiple through holes 111 of the support 11, and therefore both longitudinal ends of each through hole 111 of the support 11 are not covered by the sealing portion 21. Therefore, gas and the like can flow in and out of the through holes 111 from these ends.

[0083] The shape of the outer cylinder 22 is not limited, but may be, for example, a substantially cylindrical tubular member. The outer cylinder 22 is formed of, for example, stainless steel or carbon steel. The longitudinal direction of the outer cylinder 22 is substantially parallel to the longitudinal direction of the zeolite membrane composite 1. A supply port 221 is provided at one longitudinal end of the outer cylinder 22 (i.e., the left end in FIG. 4 ), and a first discharge port 222 is provided at the other longitudinal end. A second discharge port 223 is provided on the side surface of the outer cylinder 22. A supply unit 26 is connected to the supply port 221. A first recovery unit 27 is connected to the first discharge port 222. A second recovery unit 28 is connected to the second discharge port 223. The internal space of the outer cylinder 22 is a sealed space isolated from the space surrounding the outer cylinder 22.

[0084] Two seal members 23 are disposed around the entire circumference between the outer surface of the zeolite membrane composite 1 and the inner surface of the outer cylinder 22 near both longitudinal ends of the zeolite membrane composite 1. Each seal member 23 is a substantially annular member made of a gas-impermeable material. The seal members 23 are, for example, O-rings made of a flexible resin. The seal members 23 are in close contact with the outer surface of the zeolite membrane composite 1 and the inner surface of the outer cylinder 22 around the entire circumference. In the example shown in FIG. 4 , the seal member 23 is in close contact with the outer surface of the sealing portion 21 and indirectly with the outer surface of the zeolite membrane composite 1 via the sealing portion 21. The seal members 23 are sealed between the outer surface of the zeolite membrane composite 1 and the inner surface of the outer cylinder 22, so that gas hardly or completely passes through.

[0085] The supply unit 26 supplies the mixed gas to the internal space of the outer cylinder 22 via the supply port 221. The supply unit 26 is, for example, a blower or a pump that pressure-feeds the mixed gas toward the outer cylinder 22. The blower or pump includes a pressure adjustment unit that adjusts the pressure of the mixed gas supplied to the outer cylinder 22. The first recovery unit 27 and the second recovery unit 28 are, for example, storage containers that store the gas drawn out from the outer cylinder 22, or blowers or pumps that transport the gas.

[0086] When a mixed gas is to be separated, the above-described separation device 2 is prepared, thereby preparing the zeolite membrane composite 1 (step S21). Subsequently, a mixed gas containing multiple types of gases having different permeabilities through the zeolite membrane 12 is supplied to the internal space of the outer casing 22 by the supply unit 26. The pressure of the mixed gas supplied from the supply unit 26 to the internal space of the outer casing 22 (i.e., the introduction pressure) is, for example, 0.1 MPa to 20.0 MPa. The temperature at which the mixed gas is separated is, for example, 10°C to 150°C.

[0087] The mixed gas supplied from the supply unit 26 to the outer cylinder 22 is introduced into each through-hole 111 of the support 11 from the left end of the zeolite membrane composite 1 in the drawing, as indicated by arrow 251. A highly permeable gas in the mixed gas (typically hydrogen sulfide, hereinafter referred to as "highly permeable gas") permeates through the zeolite membrane 12 provided on the inner surface of each through-hole 111 and the support 11, and is discharged from the outer surface of the support 11. This separates the highly permeable gas from a less permeable gas in the mixed gas (e.g., methane, hereinafter referred to as "lowly permeable gas") (step S22). The gas discharged from the outer surface of the support 11 (hereinafter referred to as "permeated gas") is recovered by the second recovery unit 28 via the second discharge port 223, as indicated by arrow 253. The pressure (i.e., permeation pressure) of the gas recovered by the second recovery section 28 via the second discharge port 223 is, for example, about 1 atmosphere (0.101 MPa).

[0088] Furthermore, the gas mixture excluding the gas that has permeated the zeolite membrane 12 and the support 11 (hereinafter referred to as "non-permeating gas") passes through each through-hole 111 of the support 11 from left to right in the figure and is recovered by the first recovery unit 27 via the first discharge port 222, as indicated by arrow 252. The pressure of the gas recovered by the first recovery unit 27 via the first discharge port 222 is, for example, approximately the same as the introduction pressure. In addition to the low-permeability gas described above, the non-permeating gas may also include a high-permeability gas that has not permeated the zeolite membrane 12. The non-permeating gas recovered by the first recovery unit 27 may be circulated to the supply unit 26 and supplied again into the outer casing 22, for example.

[0089] A hydrogen sulfide / methane separation test was conducted on the zeolite membrane composite of Example 1 using separation device 2 and a mixed gas of hydrogen sulfide and methane (molar ratio 1:1). The mixed gas introduction pressure was 0.9 MPa, the permeation pressure was 0.1 MPa, and the temperature was 25°C. The resulting (hydrogen sulfide permeance / methane permeance) was 5.3. Furthermore, the (hydrogen sulfide permeance / methane permeance) value remained almost constant over the separation test period of 5 hours or more. Thus, the zeolite membrane composite of Example 1 was found to be a membrane that stably allows hydrogen sulfide to permeate. On the other hand, when the hydrogen sulfide / methane separation test was conducted on the zeolite membrane composites of Comparative Examples 1 and 2, the (hydrogen sulfide permeance / methane permeance) value gradually decreased over the test period.

[0090] As described above, the separation device 2 shown in Fig. 4 separates a highly permeable gas (i.e., hydrogen sulfide) from a mixed gas using the zeolite membrane composite 1, which selectively allows hydrogen sulfide to permeate. This prevents a decrease in hydrogen sulfide separation performance due to accumulation of hydrogen sulfide in the membrane during long-term use of the zeolite membrane composite 1 in the separation device 2. As a result, a low-permeability gas (e.g., methane) can be stably concentrated. Furthermore, the separation device 2 can appropriately separate hydrogen sulfide from a mixed gas even when the concentration of hydrogen sulfide in the mixed gas is relatively high (e.g., 3 mol % or more).

[0091] The zeolite membrane composite 1, the method for producing the zeolite membrane composite 1, the separation device 2, and the separation method can be modified in various ways.

[0092] In the production of the zeolite membrane composite 1, it is possible to omit the process of attaching seed crystals to the support 11 (steps S11 and S12 in FIG. 3 ) and directly form the zeolite membrane 12 on the support 11 in the process of step S13. On the other hand, in order to easily form the zeolite membrane 12 having densely packed zeolite crystal grains, it is preferable to attach seed crystals to the support 11 before forming the zeolite membrane 12.

[0093] In addition to the support 11 and the zeolite membrane 12, the zeolite membrane composite 1 may further include a functional membrane or a protective membrane laminated on the zeolite membrane 12. Such a functional membrane or protective membrane may be an inorganic membrane such as a zeolite membrane, a silica membrane, or a carbon membrane, or an organic membrane such as a polyimide membrane or a silicone membrane. Furthermore, a substance that easily adsorbs specific molecules may be added to the functional membrane or protective membrane laminated on the zeolite membrane 12.

[0094] The separation device 2 and separation method are particularly suitable for separating hydrogen sulfide from a gas mixture containing hydrogen sulfide and hydrocarbons, such as biogas, but may also be used for separating hydrogen sulfide from a gas mixture containing hydrogen sulfide and other gases, or for separations other than biogas.

[0095] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0096] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention.

[0097] The zeolite membrane composite of the present invention can be used in various fields in which zeolites are used, such as as separation membranes for various substances or adsorption membranes for various substances.

[0098] REFERENCE SIGNS LIST 1 Zeolite membrane composite 2 Separation device 11 Support 12 Zeolite membrane 26 Supply section S11 to S16, S21, S22 Steps

Claims

A zeolite membrane complex, comprising: a porous support; and a zeolite membrane provided on said support, said zeolite membrane being composed of an 8-membered ring zeolite, wherein said zeolite membrane contains protons, and said zeolite membrane is selectively permeable to hydrogen sulfide rather than nitrogen for a gas containing nitrogen and hydrogen sulfide.The zeolite membrane complex according to claim 1, wherein            in temperature-programmed desorption of ammonia measurement for said zeolite membrane, an amount of desorbed ammonia in a peak temperature range in which said amount of desorbed ammonia is maximum is 1 µmol / cm3 or more.The zeolite membrane complex according to claim 1, wherein in said zeolite membrane, a ratio of alkali metal atoms to oxygen atoms is 1 atm% or less.A separation apparatus, comprising: a zeolite membrane complex according to any one of claims 1 to 3; and a supply part for supplying a mixed gas containing at least hydrogen sulfide to said zeolite membrane complex. The separation apparatus according to claim 4, wherein said mixed gas contains hydrocarbon.The separation apparatus according to claim 4, wherein a concentration of hydrogen sulfide in said mixed gas is 3 mol% or more.A separation method comprising: preparing a zeolite membrane complex according to any one of claims 1 to 3; andsupplying a mixed gas containing at least hydrogen sulfide to said zeolite membrane complex.The separation method according to claim 7, wherein said mixed gas contains hydrocarbon.The separation method according to claim 7, wherein a concentration of hydrogen sulfide in said mixed gas is 3 mol% or more.A method of producing a zeolite membrane complex, comprising:forming a zeolite membrane on a porous support with use of a starting material solution containing a structure-directing agent, said zeolite membrane being composed of an 8-membered ring zeolite;removing said structure-directing agent from said zeolite membrane; andimmersing said zeolite membrane in a treatment solution for one hour or more to obtain said zeolite membrane which contains protons and which is selectively permeable to hydrogen sulfide rather than nitrogen for a gas containing nitrogen and hydrogen sulfide, said treatment solution being alkaline, whereinsaid treatment solution contains organic amine or quaternary ammonium hydroxide, and a concentration of ammonium ions in said treatment solution is 1 µmol / L or less. The method of producing a zeolite membrane complex according to claim 10, wherein a pH of said treatment solution is in the range of 9.5 to 12.The method of producing a zeolite membrane complex according to claim 10, wherein a concentration of alkali metal ions in said treatment solution is 0.1 mol / L or less.The method of producing a zeolite membrane complex according to any one of claims 10 to 12, wherein said treatment solution contains at least one of silicon and aluminum.The method of producing a zeolite membrane complex according to claim 13, wherein a total concentration of silicon and aluminum atoms in said treatment solution is 0.001 mol / L or more, and said total concentration is less than the concentration in said starting material solution and 1 mol / L or less.

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