Separation membrane composite treatment method and separation membrane composite treatment device

Abstract

This method for processing a separation membrane composite includes a step of preparing a separation membrane composite comprising a porous support and a separation membrane provided on the support (step S11), and a step of causing a washing fluid comprising supercritical or subcritical carbon dioxide having a density of 600-1000 kg / m3 to contact the separation membrane of the separation membrane composite (step S13). This enables removal of organic compounds adsorbed onto the separation membrane, and appropriate restoration of the membrane performance of the separation membrane.

Description

[Technical Field]

[0001] The present invention relates to a technique for treating a separation membrane composite. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2021-147815, filed on September 10, 2021, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] Zeolite membranes have traditionally been used as separation membranes that utilize molecular sieving. Zeolite membranes are typically provided on porous supports and treated as separation membrane composites (zeolite membrane composites). Japanese Patent Application Laid-Open Publication No. 2016-175063 (Reference 1) discloses a method for restoring the performance of a DDR-type zeolite membrane used to separate a specific component from a mixed fluid. In this restoration method, the DDR-type zeolite membrane is heated to a predetermined temperature of 100°C or higher and 550°C or lower. Japanese Patent Application Laid-Open Publication No. 2017-148741 (Reference 2) discloses a method for restoring the performance of a used zeolite membrane composite by permeating dry carbon dioxide gas through the used zeolite membrane composite. International Publication No. 2020 / 136718 (Reference 3) discloses a method for restoring the performance of a zeolite membrane by supplying carbon dioxide gas containing water to the zeolite membrane and then supplying dry natural gas.

[0003] Japanese Patent Laid-Open No. 2010-125394 (Document 4) and Japanese Patent Laid-Open No. 2012-232310 (Document 5) disclose systems for cleaning a filter housed in a cleaning chamber by injecting either a supercritical or subcritical cleaning fluid into the cleaning chamber. The filter is an air filter or liquid filter that includes a filter medium in which an adsorbent such as granular zeolite is interposed between fibers such as synthetic resin fibers.

[0004] However, when a separation membrane composite is exposed to air during storage after production or during installation of the separation membrane composite in a housing (casing), it adsorbs not only moisture in the air but also organic compounds such as volatile organic compounds (VOCs), which can clog the pores. Therefore, if the separation membrane composite is used directly for gas separation in a separation device, it cannot exhibit sufficient membrane performance. In particular, when the separation membrane is a zeolite membrane, many organic compounds are easily adsorbed by the membrane, which has a significant impact on membrane performance.

[0005] While the method in Reference 1 may restore the performance of the separation membrane, in this case, heating may cause the membrane to deteriorate. Furthermore, if the separation membrane is attached to a housing, it may affect components such as gaskets. Furthermore, the methods in References 2 and 3 make it difficult to sufficiently remove organic compounds from the separation membrane. Furthermore, the systems in References 4 and 5 are designed for granular zeolite adsorbents, and do not disclose what kind of cleaning fluid should be used for dense zeolite membranes. Summary of the Invention

[0006] The present invention is directed to a method for treating a separation membrane composite, and aims to properly restore the membrane performance of the separation membrane.

[0007] A first aspect of the invention is a method for treating a separation membrane composite, comprising the steps of: (a) preparing a separation membrane composite comprising a porous support and a separation membrane disposed on the support and having an average pore size of 1 nm or less; and (b) forming a porous support having a density of 600 to 1000 kg / m 3 and contacting the separation membrane of the separation membrane composite with a cleaning fluid comprising supercritical or subcritical carbon dioxide, In the step b), the separation membrane composite is accommodated in a container, and the container is filled with the cleaning fluid and maintained in this state for a predetermined time, whereby the organic compounds adsorbed to the separation membrane are dissolved in the cleaning fluid, The gas permeation amount of the predetermined gas through the separation membrane after the step b) is greater than the gas permeation amount before the step b).

[0008] According to the present invention, the organic compounds adsorbed to the separation membrane can be removed, and the membrane performance of the separation membrane can be appropriately restored.

[0010] Aspects 2 The invention is 1 of A method for treating a separation membrane composite, wherein the separation membrane is a zeolite membrane.

[0011] Aspects 3 The invention of the present invention is or 2 In the method for treating a separation membrane composite of the above, the predetermined gas is carbon dioxide.

[0012] Aspects 4 The invention is as follows: 3 In the step b), the temperatures of the separation membrane composite and the washing fluid are less than 100°C.

[0013] Aspects 5 The invention is as follows: 4 In the step b), the cleaning fluid contacts both the surface of the separation membrane facing the support and the surface opposite to the support.

[0014] Aspects 6 The invention is as follows: 5 The separation membrane composite treatment method according to any one of the above, wherein the separation membrane composite is contained in a housing, the housing is provided with a fluid supply port, a permeate fluid discharge port, and a non-permeate fluid discharge port, and in step b), the cleaning fluid is supplied into the housing from one port of the housing.

[0015] A seventh aspect of the invention is a separation membrane composite treatment device, comprising: a porous support; a composite accommodation unit that accommodates a separation membrane composite provided on the support and including a separation membrane having an average pore size of 1 nm or less; and a porous support having a density of 600 to 1000 kg / m 3 a cleaning fluid supply unit that supplies a cleaning fluid made of supercritical or subcritical carbon dioxide into the composite storage unit, thereby performing a cleaning process in which the cleaning fluid is brought into contact with the separation membrane of the separation membrane composite, In the cleaning process, the state in which the cleaning fluid is filled inside the composite container is maintained for a predetermined time, so that the organic compounds adsorbed on the separation membrane are dissolved in the cleaning fluid,The gas permeation amount of the predetermined gas through the separation membrane after the cleaning treatment is greater than the gas permeation amount before the cleaning treatment.

[0016] 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. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a treatment flow for a separation membrane composite. [Figure 2] FIG. 2 is a cross-sectional view of a separation membrane composite. [Figure 3] FIG. 2 is an enlarged cross-sectional view showing a part of the separation membrane composite. [Figure 4] FIG. 2 is a cross-sectional view of a housing to which a separation membrane composite is attached. [Figure 5] FIG. [Figure 6] FIG. 1 is a diagram showing the flow of separation of a mixed substance. DETAILED DESCRIPTION OF THE INVENTION

[0018] Fig. 1 is a diagram showing the flow of treatment for a separation membrane composite. The treatment in Fig. 1 is a treatment for removing organic compounds adsorbed within the separation membrane of the separation membrane composite and restoring the membrane performance of the separation membrane.

[0019] In the treatment of the separation membrane composite, first, a separation membrane composite before treatment is prepared (Step S11). FIG. 2 is a cross-sectional view of the separation membrane composite 1. FIG. 3 is a cross-sectional view showing an enlarged portion of the separation membrane composite 1. The separation membrane composite 1 includes a porous support 11 and a zeolite membrane 12 provided on the support 11. A zeolite membrane 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. The zeolite membrane 12 may also contain two or more types of zeolite with different structures or compositions. In FIG. 2, the zeolite membrane 12 is depicted with a thick line. In FIG. 3, the zeolite membrane 12 is depicted with parallel diagonal lines. In FIG. 3, the thickness of the zeolite membrane 12 is depicted thicker than it actually is.

[0020] The treatment of FIG. 1 may be performed on a separation membrane composite 1 other than a zeolite membrane composite. That is, instead of the zeolite membrane 12, an inorganic membrane formed of an inorganic substance other than zeolite, or a membrane other than an inorganic membrane, may be formed on the support 11 as a separation membrane. In addition to a zeolite membrane, for example, a silica membrane, a carbon membrane, a metal-organic framework (MOF) membrane, or the like may be used as the separation membrane. Also, a separation membrane in which particles such as zeolite are dispersed in an organic membrane may be used. In the following description, the separation membrane is assumed to be a zeolite membrane 12.

[0021] The support 11 is a porous member that is permeable to gases and liquids. In the example shown in FIG. 2, 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. 2). In the example shown in FIG. 2, 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. 2, 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 circumferential surfaces of the through-holes 111, and covers the inner circumferential surfaces of the through-holes 111 over substantially the entire surfaces.

[0022] The length of the support 11 (i.e., the length in the left-right direction in FIG. 2) 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 plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal pillar 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.

[0023] The material of the support 11 can be various substances (for example, 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 that can be 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 contains at least one of alumina, silica, and mullite.

[0024] 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.

[0025] The average pore size of the support 11 is, for example, 0.01 μm to 70 μm, and preferably 0.05 μm to 25 μm. The average pore size 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. The average pore size can be measured, for example, by a mercury porosimeter, a perm porometer, or a nanoperm porometer. Regarding the pore size 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%.

[0026] 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 particle 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 particle 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.

[0027] The zeolite membrane 12 is a porous membrane having pores. The zeolite membrane 12 can be used as a separation membrane that separates a specific substance from a mixture of multiple substances by utilizing molecular sieving action. The zeolite membrane 12 is less permeable to other substances than to 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.

[0028] 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 amount. 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.

[0029] The average pore diameter of the zeolite membrane 12 is, for example, 1 nm or less. The average pore diameter of the zeolite membrane 12 is preferably 0.2 nm or more and 0.8 nm or less, more preferably 0.3 nm or more and 0.5 nm or less, and even more preferably 0.3 nm or more and 0.4 nm or less. If the average pore diameter is larger than 1 nm, the separation performance may decrease. If the average pore diameter is smaller than 0.2 nm, the permeation amount may decrease. 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.

[0030] When the maximum number of rings in the zeolite constituting the zeolite membrane 12 is n, the average pore size is the arithmetic mean of the minor and major axes of the n-ring pores. An n-ring pore is a pore in which the number of oxygen atoms in the portion where an oxygen atom is bonded to a T atom (described later) to form a ring structure is n. When a zeolite has multiple types of n-ring pores with the same n, the arithmetic mean of the minor and major axes of all types of n-ring pores is the average pore size of the zeolite. In this way, the average pore size of a zeolite membrane is uniquely determined by the skeletal structure of the zeolite, and is listed in the "Database of Zeolite Structures" [online] of the International Zeolite Society, the Internet, and other sources.<URL:http: / / www.iza-structure.org / databases / > The values can be obtained from the values disclosed in

[0031] The type of zeolite constituting the zeolite membrane 12 is not particularly limited, and may be, for example, AEI type, AEN type, AFN type, AFV type, AFX type, BEA type, CHA type, DDR type, ERI type, ETL type, FAU type (X type, Y type), GIS type, LEV type, LTA type, MEL type, MFI type, MOR type, PAU type, RHO type, SAT type, SOD type, etc. The zeolite constituting the zeolite membrane 12 may be one type or two or more types.

[0032] From the viewpoint of increasing the CO2 permeation amount and improving separation performance, the maximum number of rings in the zeolite is preferably 8 or less (e.g., 6 or 8). The zeolite membrane 12 is, for example, a DDR-type zeolite. In other words, the zeolite membrane 12 is a zeolite membrane composed of zeolite whose structure code is "DDR" as defined by the International Zeolite Association. In this case, 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.

[0033] 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 a zeolite in which the atom (T atom) located at the center of the oxygen tetrahedron (TO4) constituting the zeolite is only Si or is composed of Si and Al; an AlPO-type zeolite in which the T atom is composed of Al and P; a SAPO-type zeolite in which the T atom is composed of Si, Al, and P; a MAPSO-type zeolite in which the T atom is composed of magnesium (Mg), Si, Al, and P; or a ZnAPSO-type zeolite in which the T atom is composed of zinc (Zn), Si, Al, and P. Some of the T atoms may be substituted with other elements.

[0034] 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 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. The zeolite membrane 12 may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K).

[0035] When the separation membrane is not a zeolite membrane, the pore size can be determined by well-known methods such as a nanoperm porometer or gas adsorption method, and when the pore size has a distribution, the median size (D50) is taken as the average pore size.

[0036] The separation membrane composite 1 before treatment may be prepared by a known method. In one example, first, DDR-type zeolite powder is attached to a support 11 as seed crystals. Next, the support 11 is immersed in a raw material solution containing a Si source, a structure-directing agent, and the like. DDR-type zeolite is grown by hydrothermal synthesis using the seed crystals as nuclei, thereby forming a DDR-type zeolite membrane 12 on the support 11. The zeolite membrane 12 is then heat-treated to almost completely burn off the structure-directing agent in the zeolite membrane 12 and open the micropores in the zeolite membrane 12. This results in the above-described separation membrane composite 1 before treatment. The zeolite membrane 12 may be a type other than the DDR type.

[0037] Next, the separation membrane composite 1 is placed in a predetermined container (step S12). Here, since the separation membrane composite 1 is used in a separation device 4 (see FIG. 5) described below, the separation membrane composite 1 is attached in a housing 22, which is a container for the separation device 4. FIG. 4 is a cross-sectional view of the housing 22 to which the separation membrane composite 1 is attached. In FIG. 4, a wash fluid supply unit 36 described below is shown as a block, and a first discharge pipe 37 and a second discharge pipe 38 are also shown.

[0038] When the separation membrane composite 1 is attached to the housing 22, sealing portions 13 are provided at both longitudinal ends of the support 11 as a preliminary preparation (for example, before forming the zeolite membrane 12 on the support 11). The sealing portions 13 are members that cover and seal both longitudinal end faces of the support 11 and the outer surfaces near these end faces. The sealing portions 13 prevent gas from flowing in or out from these end faces of the support 11. The sealing portions 13 are formed of, for example, glass, resin, or metal. The material and shape of the sealing portions 13 may be changed as appropriate. Note that both longitudinal ends of each through-hole 111 are not covered by the sealing portions 13, and gas can flow in and out of the through-hole 111 from these ends.

[0039] The shape of the housing 22 is not limited, but may be, for example, a substantially cylindrical tubular member. The housing 22 is formed, for example, from stainless steel or carbon steel. The longitudinal direction of the housing 22 is substantially parallel to the longitudinal direction of the separation membrane composite 1. A fluid supply port 221 is provided at one longitudinal end of the housing 22 (i.e., the left end in FIG. 4 ), and a non-permeated fluid discharge port 222 is provided at the other end. A permeated fluid discharge port 223 is provided on the side of the housing 22. The internal space of the housing 22 is a sealed space isolated from the space surrounding the housing 22.

[0040] In the example shown in FIG. 4 , the housing 22 includes a housing main body 224 and two lid portions 226. The housing main body 224 is a substantially cylindrical member having openings at both longitudinal ends. Two flange portions 225 are provided on the housing main body 224. Each of the two flange portions 225 is a substantially annular plate-shaped portion that extends radially outward from the housing main body 224 around the two openings of the housing main body 224. The housing main body 224 and the two flange portions 225 are a continuous member. The two lid portions 226 are fixed to the two flange portions 225 by bolting or the like while covering the two openings of the housing main body 224. This hermetically seals the two openings of the housing main body 224. The above-mentioned fluid supply port 221 is provided on the lid portion 226 on the left side in FIG. 4 . The non-permeated fluid discharge port 222 is provided on the lid portion 226 on the right side in FIG. 4 . The permeate fluid discharge port 223 is provided at approximately the center of the housing body 224 in the longitudinal direction.

[0041] The separation membrane composite 1 is fixed to the housing 22 via two seal members 23. The two seal members 23 are arranged around the entire circumference between the outer circumferential surface of the separation membrane composite 1 and the inner circumferential surface of the housing 22 (housing main body 224) near both longitudinal ends of the separation membrane composite 1. Each seal member 23 is a substantially annular member made of a gas-impermeable material. The seal member 23 is, for example, an O-ring made of a flexible resin. The seal member 23 closely contacts the outer circumferential surface of the separation membrane composite 1 and the inner circumferential surface of the housing 22 around the entire circumference. In the example shown in FIG. 4, the seal member 23 closely contacts the outer circumferential surface of the sealing portion 13 and indirectly contacts the outer circumferential surface of the separation membrane composite 1 via the sealing portion 13. A seal is formed between the seal member 23 and the outer circumferential surface of the separation membrane composite 1, and between the seal member 23 and the inner circumferential surface of the housing 22, so that gas hardly or completely passes through.

[0042] In FIG. 4, a separation membrane module 20 is configured with the separation membrane composite 1, a housing 22, and two sealing members 23. The separation membrane module 20 may include other components. As described below, the separation membrane module 20 is attached to a separation device 4 for use. Incidentally, the zeolite membrane 12 is usually exposed to air during storage of the separation membrane composite 1 after production, during attachment of the separation membrane composite 1 to the housing 22, and the like. In this case, the zeolite membrane 12 adsorbs not only moisture in the air but also organic compounds such as volatile organic compounds (VOCs), and the pores are clogged with the organic compounds. In the separation membrane module 20 of FIG. 4, the zeolite membrane 12 also adsorbs organic compounds such as VOCs. If the separation membrane module 20 were used as is in the separation device 4, sufficient membrane performance would not be achieved.

[0043] Next, a wash fluid supply unit 36 is connected to the fluid supply port 221 of the housing 22. The wash fluid supply unit 36 includes, for example, a pump that supplies wash fluid into the housing 22. The pump includes a pressure adjustment unit that adjusts the pressure of the wash fluid supplied to the housing 22. A first discharge pipe 37 is connected to the non-permeate fluid discharge port 222 of the housing 22, and a second discharge pipe 38 is connected to the permeate fluid discharge port 223. A valve 371 is provided on the first discharge pipe 37, and a valve 381 is provided on the second discharge pipe 38. As will be described later, the separation membrane composite 1 accommodated in the housing 22 is washed with the wash fluid supplied from the wash fluid supply unit 36 into the housing 22. Therefore, it can be said that the wash fluid supply unit 36 and the housing 22, which serves as the composite accommodation unit, constitute a treatment device 3 for the separation membrane composite 1. The treatment device 3 may include other components.

[0044] Here, the cleaning fluid is a fluid made of supercritical or subcritical carbon dioxide (CO2). Carbon dioxide has a small molecular diameter and can easily diffuse into the pores of the zeolite membrane 12. The density of carbon dioxide in the cleaning fluid is 600 to 1000 kg / m 3Carbon dioxide in this density range has a solubility parameter value similar to that of organic compounds such as VOCs, and is therefore compatible with the organic compounds. The cleaning fluid may contain substances other than CO2 (e.g., nitrogen, etc.). In this case, the density of CO2 is 600 to 1000 kg / m 3 That's fine.

[0045] Thereafter, with the valve 371 of the first discharge pipe 37 and the valve 381 of the second discharge pipe 38 closed, the wash fluid supply unit 36 supplies the wash fluid to the internal space of the housing 22 via the fluid supply port 221. The wash fluid fills the internal space of the housing 22 near the fluid supply port 221, and is introduced into each of the through-holes 111 of the support 11 from the left end of the separation membrane composite 1 in the drawing, as indicated by arrow 241. As a result, the wash fluid comes into contact with the surface of the zeolite membrane 12 provided on the inner circumferential surface of the through-hole 111 (i.e., the surface opposite to the support 11) (step S13).

[0046] A portion of the wash fluid diffuses into the pores of the zeolite membrane 12. The wash fluid that has permeated the zeolite membrane 12 and the support 11 is discharged from the outer peripheral surface of the support 11. As a result, the wash fluid fills the space between the outer peripheral surface of the support 11 and the inner peripheral surface of the housing body 224, and the permeated fluid discharge port 223. The wash fluid that has permeated the zeolite membrane 12 may be in the form of a gas or liquid. The remainder of the wash fluid introduced into the through-holes 111 is discharged from the right end of the separation membrane composite 1 in the figure without permeating the zeolite membrane 12. As a result, the wash fluid also fills the internal space of the housing 22 near the non-permeated fluid discharge port 222.

[0047] In the processing device 3, the cleaning fluid in the housing 22 is maintained at a constant temperature and pressure for a predetermined time. As described above, the organic compounds in the pores of the zeolite membrane 12 are highly compatible with the cleaning fluid, so the organic compounds dissolve in the cleaning fluid. The cleaning fluid in the pores of the zeolite membrane 12 is discharged to the outside, as described below. Therefore, the process of bringing the cleaning fluid into contact with the zeolite membrane 12 is a cleaning process for removing organic compounds in the zeolite membrane 12. In this case, if the Si / Al ratio (molar ratio) in the zeolite membrane 12 is 5 or more, the affinity between the zeolite membrane 12 and the cleaning fluid is high, thereby facilitating the removal of the organic compounds. Note that the cleaning fluid supply unit 36 may be configured to supply liquefied CO2 into the housing 22 and then pressurize or heat the CO2 in the housing 22 to bring it to a supercritical or subcritical state.

[0048] The density of the cleaning fluid in the housing 22 is 600 to 1000 kg / m 3 As long as the temperature and pressure of the cleaning fluid are within the above range, there are no particular limitations. From the viewpoint of suppressing deterioration of the zeolite membrane 12 and the seal member 23 due to the cleaning treatment, the temperature of the cleaning fluid in the housing 22 is preferably less than 100°C, more preferably less than 80°C, and even more preferably less than 60°C. As long as the above density range of the cleaning fluid is satisfied, the lower limit of the temperature of the cleaning fluid in the housing 22 is not particularly limited, but is, for example, 0°C. Furthermore, from the viewpoint of avoiding an increase in the manufacturing cost of the housing 22, it is preferable that the pressure of the cleaning fluid in the housing 22 is not excessively high. The pressure of the cleaning fluid in the housing 22 is, for example, 100 MPa or less, preferably 60 MPa or less, and more preferably 40 MPa or less. As long as the above density range of the cleaning fluid is satisfied, there are no particular limitations on the lower limit of the pressure of the cleaning fluid in the housing 22, but is, for example, 5 MPa. The cleaning treatment time is, for example, 1 to 100 hours.

[0049] In the housing 22, a wash fluid supply unit 36 may be connected to the non-permeated fluid discharge port 222 or the permeated fluid discharge port 223, and the wash fluid may be supplied into the housing 22. Alternatively, the wash fluid may be supplied into the housing 22 from both the fluid supply port 221 and the permeated fluid discharge port 223. In this case, the wash fluid that has not permeated the zeolite membrane 12 can be brought into contact with both the surface of the zeolite membrane 12 facing the support 11 and the surface opposite to the support 11, thereby more effectively removing organic compounds. In the housing 22, the wash fluid is supplied into the interior from at least one port.

[0050] When the cleaning process is completed, the housing 22 is depressurized by opening the valve 371 of the first discharge pipe 37 and the valve 381 of the second discharge pipe 38 in FIG. 4. This also discharges the cleaning fluid, which is present in the pores of the zeolite membrane 12 and contains dissolved organic compounds, to the outside. Thereafter, the cleaning fluid supply unit 36, the first discharge pipe 37, and the second discharge pipe 38 are removed from the housing 22, completing the process of FIG. 1 for the separation membrane composite 1. Note that the cleaning fluid supply unit 36, the first discharge pipe 37, and the second discharge pipe 38 do not need to be removed from the housing 22. Furthermore, it is preferable that cap members be attached to the fluid supply port 221, the non-permeated fluid discharge port 222, and the permeated fluid discharge port 223 of the housing 22 to prevent outside air from entering the housing 22.

[0051] Here, when the gas permeation rate of a predetermined gas through the separation membrane composite 1 immediately before the cleaning process in step S13 (i.e., immediately after installation in the housing 22) and the gas permeation rate of the same gas through the separation membrane composite 1 immediately after the cleaning process are measured, the gas permeation rate immediately after the cleaning process is greater than the gas permeation rate immediately before the cleaning process. The type of predetermined gas used to measure the gas permeation rate is not particularly limited as long as it can permeate the zeolite membrane 12. For example, the predetermined gas is a molecule whose kinetic molecular diameter is smaller than the average pore diameter of the zeolite membrane 12, preferably He, H2, HO, N2, O2, or CO2, and more preferably CO2. Because CO2 has a small molecular diameter and can easily diffuse into the pores of the zeolite membrane 12, using CO2 as the predetermined gas allows for more accurate evaluation of the degree of clogging of the pores of the zeolite membrane 12. In this embodiment, CO2 is used as the predetermined gas.

[0052] The ratio of the CO2 permeation amount immediately after the cleaning treatment to the CO2 permeation amount immediately before the cleaning treatment (i.e., (CO2 permeation amount immediately after the cleaning treatment) / (CO2 permeation amount immediately before the cleaning treatment), hereinafter referred to as the "CO2 recovery ratio") is, for example, 3 or more, preferably 4 or more, and more preferably 5 or more. There is no particular upper limit to the CO2 recovery ratio. In this way, it is believed that the increase in the CO2 permeation amount of the separation membrane composite 1 by the cleaning treatment appropriately removes organic compounds adsorbed to the zeolite membrane 12. The treatment method of Figure 1 may also be performed on the separation membrane composite 1 after use in the separation device 4.

[0053] Next, separation of a mixed substance using the separation membrane complex 1 will be described with reference to Figures 5 and 6. Figure 5 is a diagram showing the separation device 4. Figure 6 is a diagram showing the flow of separation of a mixed substance by the separation device 4.

[0054] In the separation device 4, a mixed substance containing multiple types of fluids (i.e., gases or liquids) is supplied to the separation membrane composite 1, and highly permeable substances in the mixed substance are separated from the mixed substance by permeating through the separation membrane composite 1. Separation in the separation device 4 may be performed, for example, for the purpose of extracting highly permeable substances from the mixed substance, or for the purpose of concentrating less permeable substances.

[0055] The mixed substance (i.e., mixed fluid) may be a mixed gas containing multiple types of gases, a mixed liquid containing multiple types of liquids, or a gas-liquid two-phase fluid containing both gas and liquid.

[0056] The mixture may include one or more of the following substances: hydrogen (H2), helium (He), nitrogen (N2), oxygen (O2), water (H2O), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides, ammonia (NH3), sulfur oxides, hydrogen sulfide (H2S), sulfur fluoride, mercury (Hg), arsine (AsH3), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1 to C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes.

[0057] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of the nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (also called dinitrogen monoxide) (N2O), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5), etc. X It is a gas called NOX.

[0058] Sulfur oxides are compounds of sulfur and oxygen. Examples of sulfur oxides include sulfur dioxide (SO2), sulfur trioxide (SO3), and other sulfur compounds. X It is a gas called SOX.

[0059] Sulfur fluoride is a compound of fluorine and sulfur. The sulfur fluoride may be, for example, disulfur difluoride (FSSF, S=SF), sulfur difluoride (SF), sulfur tetrafluoride (SF), sulfur hexafluoride (SF), or disulfur decafluoride (SF). 10 ) etc.

[0060] C1-C8 hydrocarbons are hydrocarbons with one or more carbon atoms and eight or less. C3-C8 hydrocarbons may be straight-chain compounds, branched-chain compounds, or cyclic compounds. C2-C8 hydrocarbons may be saturated hydrocarbons (i.e., those without double or triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those with double and / or triple bonds in the molecule). Examples of C1-C4 hydrocarbons include methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), propylene (C3H6), normal butane (CH3(CH2)2CH3), isobutane (CH(CH3)3), 1-butene (CH2=CHCH2CH3), 2-butene (CH3CH=CHCH3), and isobutene (CH2=C(CH3)2).

[0061] The organic acid may be a carboxylic acid or a sulfonic acid. Examples of the carboxylic acid include formic acid (CHO), acetic acid (CHO), oxalic acid (CHO), acrylic acid (CHO), or benzoic acid (CHCOOH). Examples of the sulfonic acid include ethanesulfonic acid (CHOS). The organic acid may be a chain compound or a cyclic compound.

[0062] The alcohols mentioned above are, for example, methanol (CH3OH), ethanol (C2H5OH), isopropanol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)) or butanol (C4H9OH).

[0063] Mercaptans are organic compounds with hydrogenated sulfur (SH) at the end, also known as thiols or thioalcohols. Examples of the mercaptans include methyl mercaptan (CHSH), ethyl mercaptan (CHSH), and 1-propanethiol (CHSH).

[0064] The esters mentioned above are, for example, formates or acetates.

[0065] The above-mentioned ethers are, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3) or diethyl ether ((C2H5)2O).

[0066] The ketone may be, for example, acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3), or diethyl ketone ((C2H5)2CO).

[0067] The aldehydes mentioned above are, for example, acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO) or butanal (butyraldehyde) (C3H7CHO).

[0068] In the following description, it is assumed that the mixed substance separated by the separation device 4 is a mixed gas containing a plurality of types of gases.

[0069] The separation device 4 includes a separation membrane module 20, a supply unit 46, a first recovery unit 47, and a second recovery unit 48. As described above, the separation membrane module 20 includes a separation membrane composite 1, a housing 22, and two seal members 23. The separation membrane composite 1 and the seal members 23 are housed in the housing 22. In the separation membrane composite 1, organic compounds have been removed from the zeolite membrane 12 by the process shown in FIG. 1. The supply unit 46, the first recovery unit 47, and the second recovery unit 48 are disposed outside the housing 22 and connected to the housing 22. Specifically, the supply unit 46 is connected to a fluid supply port 221. The first recovery unit 47 is connected to a non-permeated fluid discharge port 222. The second recovery unit 48 is connected to a permeated fluid discharge port 223.

[0070] The supply unit 46 supplies the mixed gas to the internal space of the housing 22 via the fluid supply port 221. The supply unit 46 is, for example, a blower or a pump that pressure-feeds the mixed gas toward the housing 22. The blower or pump includes a pressure adjustment unit that adjusts the pressure of the mixed gas supplied to the housing 22. The first recovery unit 47 and the second recovery unit 48 are, for example, storage containers that store the gas drawn out from the housing 22, or blowers or pumps that transport the gas.

[0071] When separating a mixed gas, the separation membrane composite 1 is prepared by preparing the separation device 4 described above (step S21). Next, a mixed gas containing multiple types of gases with different permeabilities through the zeolite membrane 12 is supplied to the internal space of the housing 22 by the supply unit 46. For example, the main components of the mixed gas are CO2 and CH4. The mixed gas may contain gases other than CO2 and CH4. The pressure of the mixed gas supplied from the supply unit 46 to the internal space of the housing 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.

[0072] The mixed gas supplied from the supply unit 46 to the housing 22 is introduced into each through-hole 111 of the support 11 from the left end of the separation membrane composite 1 in the drawing, as indicated by arrow 251. Highly permeable gases in the mixed gas (e.g., CO2, hereinafter referred to as "highly permeable substances") permeate through the zeolite membrane 12 provided on the inner circumferential surface of each through-hole 111 and the support 11, and are discharged from the outer circumferential surface of the support 11. As a result, the highly permeable substances are separated from lowly permeable gases in the mixed gas (e.g., CH4, hereinafter referred to as "lowly permeable substances") (step S22). The gas discharged from the outer circumferential surface of the support 11 (hereinafter referred to as "permeated substances") is recovered by the second recovery unit 48 via the permeated fluid discharge port 223, as indicated by arrow 253. The pressure of the gas recovered by the second recovery section 48 via the permeate fluid discharge port 223 (ie, the permeate pressure) is, for example, about 1 atmosphere (0.101 MPa).

[0073] Furthermore, gases (hereinafter referred to as "non-permeating substances") in the mixed gas excluding the gas that has permeated the zeolite membrane 12 and the support 11 pass through each through-hole 111 of the support 11 from left to right in the figure, and are recovered by the first recovery section 47 via the non-permeating fluid discharge port 222, as indicated by arrow 252. The pressure of the gas recovered by the first recovery section 47 via the non-permeating fluid discharge port 222 is, for example, approximately the same as the introduction pressure. In addition to the above-mentioned low-permeability substances, the non-permeating substances may also include highly permeable substances that did not permeate the zeolite membrane 12.

[0074] Next, Examples 1 to 5 and Comparative Examples 1 to 3 for treating the separation membrane composite will be described.

[0075] Example 1 A DDR-type zeolite membrane was synthesized on a porous alumina substrate by hydrothermal synthesis, and the structure-directing agent was removed by heating to obtain a separation membrane composite. The separation membrane composite was then stored at 25°C in air for one week.

[0076] CO2 gas was supplied to the separation membrane composite at 0.3 MPa, and the permeation pressure was set at 0.1 MPa. The CO2 permeation amount (Permeance) was calculated from the amount of CO2 gas that permeated the zeolite membrane. The separation membrane composite was then placed in a pressure vessel, liquefied CO2 was injected, and the mixture was maintained at 40°C and 9.7 MPa for 50 hours (cleaning treatment). The density of CO2 at this time was 600 kg / m 3 It was.

[0077] After releasing the pressure in the pressure vessel, the separation membrane composite was removed and the CO2 permeation amount was determined in the same manner as above. The CO2 recovery factor was calculated by dividing the CO2 permeation amount after treatment by the CO2 permeation amount before treatment, and was found to be 7.5.

[0078] Example 2 The conditions for the cleaning treatment were the same as in Example 1, except that the temperature was 40°C and the pressure was 25 MPa. The density of CO2 at this time was 880 kg / m 3 The CO2 recovery ratio in Example 2 was 7.7.

[0079] Example 3 The conditions for the cleaning treatment were the same as in Example 1, except that the temperature was 10°C and the pressure was 25 MPa. The density of CO2 at this time was 1000 kg / m 3 The CO2 recovery ratio in Example 3 was 6.8.

[0080] Example 4 The procedure was the same as in Example 1, except that a CHA-type zeolite membrane was used instead of the DDR-type zeolite membrane. The CHA-type zeolite membrane was produced with reference to Comparative Example 2 of JP 2014-198308 A. The CO2 recovery ratio in Example 4 was 10.3.

[0081] Example 5 The procedure was the same as in Example 1, except that a carbon membrane was used instead of the DDR-type zeolite membrane. The carbon membrane was produced with reference to Example 3 of JP 2011-201753 A. The CO2 recovery ratio in Example 5 was 5.1.

[0082] (Comparative Example 1) The conditions for the cleaning treatment were the same as in Example 1, except that the temperature was 40°C and the pressure was 1 MPa. The density of CO2 at this time was 18 kg / m 3 The CO2 in the pressure vessel was neither supercritical nor subcritical. The CO2 recovery factor in Comparative Example 1 was 2.4.

[0083] (Comparative Example 2) The conditions for the cleaning treatment were the same as in Example 4, except that the temperature was 40°C and the pressure was 1 MPa. The density of CO2 at this time was 18 kg / m 3 The CO2 recovery factor in Comparative Example 2 was 1.5, and the CO2 in the pressure vessel was neither supercritical nor subcritical.

[0084] (Comparative Example 3) The conditions for the cleaning treatment were the same as in Example 5, except that the temperature was 40°C and the pressure was 1 MPa. The density of CO2 at this time was 18 kg / m 3 The CO2 recovery ratio in Comparative Example 3 was 1.2, and the CO2 in the pressure vessel was neither supercritical nor subcritical.

[0085] In Examples 1 to 5, a high CO2 recovery rate was obtained, which suggests that the organic compounds adsorbed on the separation membrane were effectively removed. On the other hand, in Comparative Examples 1 to 3, the CO2 recovery rate was significantly lower than in Examples 1 to 5. Therefore, the CO2 recovery rate was significantly lower in Comparative Examples 1 to 3 than in Examples 1 to 5. 3 It can be said that CO2 that is not a zeolite membrane cannot effectively remove the organic compounds adsorbed on the separation membrane. In addition, in Examples 1 and 4 where the separation membrane is a zeolite membrane, the CO2 recovery ratio is higher than in Example 5 where the separation membrane is a carbon membrane. Therefore, it is necessary to use a carbon membrane with a density of 600 to 1000 kg / m 3 Treatment using CO2, which is more suitable for zeolite membranes, is considered.

[0086] As described above, the method for treating the separation membrane composite 1 includes a step (step S11) of preparing the separation membrane composite 1 including the porous support 11 and the separation membrane (zeolite membrane 12 in the above treatment example) provided on the support 11, and a step of treating the separation membrane composite 1 with a porous support 11 having a density of 600 to 1000 kg / m 3 and a step (step S13) of contacting the separation membrane with a cleaning fluid consisting of supercritical or subcritical CO2. The CO2 in the cleaning fluid easily diffuses into the pores of the separation membrane, and because the cleaning fluid is highly compatible with the organic compounds adsorbed on the separation membrane, the organic compounds can be effectively removed. As a result, the gas permeation rate of the predetermined gas through the separation membrane after the cleaning treatment in step S13 is significantly higher than the gas permeation rate before the cleaning treatment, and the membrane performance of the separation membrane can be appropriately restored.

[0087] Preferably, the separation membrane composite 1 is housed in a housing 22, which is provided with a fluid supply port 221, a permeate fluid discharge port 223, and a non-permeate fluid discharge port 222. In the cleaning treatment in step S13, a cleaning fluid is supplied into the housing 22 from one port of the housing 22. This makes it possible to easily perform the cleaning treatment.

[0088] Preferably, the separation membrane has an average pore size of 1 nm or less. Organic compounds adsorbed to a separation membrane having such a small average pore size can also be appropriately removed by the present treatment method. Preferably, the temperatures of the separation membrane composite 1 and the cleaning fluid during the cleaning treatment are less than 100°C. This makes it possible to prevent the separation membrane from deteriorating during the cleaning treatment. Furthermore, when the cleaning treatment is performed on a separation membrane composite 1 housed in a housing 22, it is possible to prevent the seal member 23 from deteriorating.

[0089] The treatment device 3 for the separation membrane composite 1 includes a composite accommodation unit (housing 22 in the example of FIG. 4) for accommodating the separation membrane composite 1, and a membrane separator having a density of 600 to 1000 kg / m 3and a cleaning fluid supply unit 36 that supplies a cleaning fluid consisting of supercritical or subcritical CO2 into the composite storage unit to perform a cleaning process in which the cleaning fluid comes into contact with the separation membrane of the separation membrane composite 1. As described above, the cleaning process can effectively remove organic compounds adsorbed to the separation membrane, so that the gas permeation rate of a predetermined gas through the separation membrane after the cleaning process is significantly higher than the gas permeation rate before the cleaning process. In this way, the treatment device 3 can appropriately restore the membrane performance of the separation membrane.

[0090] The treatment method for the separation membrane complex 1 and the treatment device 3 described above can be modified in various ways.

[0091] The average pore size of the separation membrane may be greater than 1 nm depending on the type of separation membrane provided in the separation membrane composite 1. In addition, in the cleaning treatment of step S13, the temperatures of the separation membrane composite 1 and the cleaning fluid may be 100°C or higher.

[0092] The separation membrane composite 1 for which the treatment method of FIG. 1 is performed does not necessarily have to be housed in the housing 22. For example, the separation membrane composite 1 may be placed in a predetermined container, and the container may be filled with a cleaning fluid during the cleaning treatment. In this case, the container serves as the composite housing portion of the treatment device 3. In the container, the cleaning fluid that has not permeated the zeolite membrane 12 can be brought into contact with both the surface of the zeolite membrane 12 facing the support 11 and the surface opposite the support 11, allowing for more effective removal of organic compounds.

[0093] In addition to the support 11 and the zeolite membrane 12, the separation membrane composite 1 may further include a functional membrane or a protective membrane laminated on the zeolite membrane 12. Such functional membranes or protective membranes may be inorganic membranes such as zeolite membranes, silica membranes, or carbon membranes, or organic membranes such as polyimide membranes or silicone membranes. Furthermore, the functional membranes or protective membranes laminated on the zeolite membrane 12 may contain added substances that easily adsorb specific molecules such as CO2.

[0094] The configurations of the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0095] 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. [Industrial Applicability]

[0096] The separation membrane composite treatment method and treatment device of the present invention can be used for separation membrane composites used in a variety of fields. [Explanation of symbols]

[0097] 1 Separation membrane complex 3 Processing equipment 11 Support 12 Zeolite membrane 22 Housing 36 Cleaning fluid supply unit 221 fluid supply port 222 Non-permeable fluid discharge port 223 Permeate fluid discharge port S11~S13, S21, S22 steps

Claims

1. A method for treating a separation membrane composite, comprising: a) preparing a separation membrane composite including a porous support and a separation membrane provided on the support and having an average pore diameter of 1 nm or less; b) Density is 600 to 1000 kg / m ３ contacting the separation membrane of the separation membrane composite with a cleaning fluid comprising supercritical or subcritical carbon dioxide, Equipped with In the step b), the separation membrane composite is accommodated in a container, and the container is maintained in a state where the cleaning fluid is filled therein for a predetermined time, whereby the organic compounds adsorbed to the separation membrane are dissolved in the cleaning fluid, The method for treating a separation membrane composite, wherein the gas permeation amount of a predetermined gas through the separation membrane after the step b) is greater than the gas permeation amount before the step b).

2. The method for treating the separation membrane composite according to claim 1, The method for treating a separation membrane composite, wherein the separation membrane is a zeolite membrane.

3. The method for treating the separation membrane composite according to claim 1, The method for treating a separation membrane composite, wherein the predetermined gas is carbon dioxide.

4. The method for treating the separation membrane composite according to claim 1, The method for treating a separation membrane composite, wherein in step b), the temperatures of the separation membrane composite and the cleaning fluid are less than 100°C.

5. The method for treating the separation membrane composite according to claim 1, In the step b), the cleaning fluid contacts both the surface of the separation membrane facing the support and the surface opposite to the support.

6. A method for treating a separation membrane composite according to any one of claims 1 to 5, the separation membrane composite is accommodated in a housing, the housing being provided with a fluid supply port, a permeate fluid discharge port, and a non-permeate fluid discharge port; In the step b), the cleaning fluid is supplied into the housing from one port of the housing.

7. A treatment device for a separation membrane composite, a composite housing portion that houses a separation membrane composite including a porous support and a separation membrane provided on the support and having an average pore diameter of 1 nm or less; Density: 600 to 1000 kg / m ３ a cleaning fluid supply unit that supplies a cleaning fluid made of supercritical or subcritical carbon dioxide into the composite storage unit, thereby performing a cleaning process in which the cleaning fluid is brought into contact with the separation membrane of the separation membrane composite; Equipped with In the cleaning process, the state in which the cleaning fluid is filled inside the composite container is maintained for a predetermined time, so that the organic compounds adsorbed on the separation membrane are dissolved in the cleaning fluid, The treatment device for a separation membrane composite, wherein the gas permeation amount of a predetermined gas through the separation membrane after the cleaning treatment is larger than the gas permeation amount before the cleaning treatment.

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