Composite zeolite membranes and gas separation membranes

Abstract

To provide a material that can be used in a gas separation membrane for separation of a lower hydrocarbon.SOLUTION: A gas separation membrane is composed of a composite zeolite membrane that contains a porous support and a zeolite membrane formed on the porous support, the zeolite membrane composed of an MFI-type zeolite, the zeolite membrane surface being surface-treated with an Si-containing compound represented by general formula (1) or general formula (11), where R1 is a halogenated aryl group, R11 is a halogenated alkyl group, m is an integer of 1-3, n is an integer of 0-8, and R2 is a C1-4 alkyl group.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a composite zeolite membrane, which is a zeolite membrane-attached porous support surface-treated with a Si-containing compound, and also to a gas separation membrane comprising the composite zeolite membrane. [Background technology]

[0002] Distillation has traditionally been used in the refining process of lower hydrocarbons. However, distillation separation, especially of hydrocarbons with low relative volatility, consumes a lot of energy. Energy-saving alternative refining methods to distillation include methods using adsorbents, as well as methods using gas separation membranes such as polymer membranes and zeolite membranes. Zeolites, which have heat resistance, pressure resistance, and high mechanical strength, are crystalline inorganic materials with unique pore sizes, and when made into membranes, separation is possible using their molecular sieving and adsorption properties.

[0003] Patent Document 1 discloses that a zeolite membrane-attached porous support, in which the surface of an MFI type zeolite membrane has been treated with a Si-containing compound such as phenyltrimethoxysilane, selectively allows nitrogen to permeate when contacted with a gas containing nitrogen and a hydrocarbon. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-131184 A Summary of the Invention [Problem to be solved by the invention]

[0005] In petrochemical plants, a variety of hydrocarbons, such as methane, ethane, ethylene, propane, propylene, and butane, can be obtained through the thermal cracking of raw materials such as naphtha. In order to refine each product, gas separation membranes that can separate these various hydrocarbons are required. It is an object of the present invention to provide a material which can be used in gas separation membranes for the separation of lower hydrocarbons. [Means for solving the problem]

[0006] While conducting research to solve the above problems, the inventors discovered that it is possible to adjust the selectively permeable hydrocarbons by using a compound containing a halogen as the Si-containing compound used for surface modification of the zeolite membrane-attached porous support described in Patent Document 1. After further research, they completed the present invention. Specifically, the present invention is as follows.

[0007] <1> A composite zeolite membrane comprising a porous support and a zeolite membrane formed on the porous support, The zeolite membrane is composed of MFI type zeolite, A composite zeolite membrane, the surface of which is treated with a Si-containing compound represented by general formula (1);

[0008] [ka]

[0009] In the formula, R 1 represents a halogenated aryl group, m represents an integer of 1 to 3, n represents an integer of 0 to 8, R 2 represents an alkyl group having 1 to 4 carbon atoms. <2> R 1 is a fluoroaryl group <1> The composite zeolite membrane according to claim 1. <3> R 1 is a pentafluorophenyl group <1> The composite zeolite membrane according to claim 1. <4> m is 1 and n is 0 <1> ~ <3> 13. The composite zeolite membrane according to claim 12 . <5> The Si-containing compound is pentafluorophenyltrimethoxysilane. <1> The composite zeolite membrane according to claim 1. <6> The porous support is an alumina porous support made of alumina. <1> ~ <5> 13. The composite zeolite membrane according to claim 12 . <7> The MFI type zeolite is silicalite-1. <1> ~ <6> 13. The composite zeolite membrane according to claim 12 .

[0010] <8> <1> ~ <7> A gas separation membrane comprising the composite zeolite membrane according to any one of claims 1 to 4. <9> Used to selectively permeate ethane over propane <8> The gas separation membrane according to claim 1. <10> Used to selectively permeate ethylene over propylene <8> The gas separation membrane according to claim 1.

[0011] <11> 1. A gas separation membrane for selectively permeating methane over ethane, comprising: A porous support and a zeolite membrane formed on the porous support, The zeolite membrane is composed of MFI type zeolite, a gas separation membrane, the surface of which is treated with a Si-containing compound represented by general formula (11);

[0012] [ka]

[0013] In the formula, R 11 represents a halogenated alkyl group, m represents an integer of 1 to 3, R 2 represents an alkyl group having 1 to 4 carbon atoms. <12> The Si-containing compound is 3,3,3-trifluoropropyltrimethoxysilane. <11> The gas separation membrane according to claim 1. <13> The porous support is an alumina porous support made of alumina. <11> or <12> The gas separation membrane according to claim 1. <14> The MFI type zeolite is silicalite-1. <11> ~ <13> 2. The gas separation membrane according to claim 1 . Effect of the Invention

[0014] The present invention provides a novel composite zeolite membrane that can be used as a gas separation membrane. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an apparatus used in the surface treatment by a liquid phase method performed in the examples. [Diagram 2] FIG. 1 is a schematic diagram showing an apparatus used in a surface treatment by a gas phase method performed in an example. [Diagram 3] FIG. 1 is a graph showing the gas permeability evaluation of a porous support with a zeolite membrane that was surface-treated with 3,3,3-trifluoropropyltrimethoxysilane, prepared in an example. [Figure 4] FIG. 1 is a graph showing the gas permeability evaluation of a porous support with a zeolite membrane that was surface-treated with pentafluorophenyltrimethoxysilane, prepared in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described in detail below. The following description of the components may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0017] <<Composite zeolite membrane: Porous support with zeolite membrane surface-treated with Si-containing compound>> In this specification, the composite zeolite membrane means a porous support with a zeolite membrane that has been surface-treated with a Si-containing compound. In the composite zeolite membrane, the porous support, the zeolite membrane, and the surface-treated surface with the Si-containing compound are arranged in this order. The zeolite membrane is formed on the porous support, and the zeolite membrane surface is surface-treated.

[0018] The shape of the composite zeolite membrane is assumed to be tubular, flat plate, honeycomb, etc., but is not particularly limited, and can take a shape along the shape of the porous support described later. For example, when it is tubular or cylindrical, the surface treatment surface may be inside or outside.

[0019] <Si-containing compound> The present inventors have found that a gas separation membrane capable of separating hydrocarbons having 1 to 3 carbon atoms from each other can be provided by a porous support with a zeolite membrane surface-treated with a Si-containing compound containing a halogen. In the present invention, as the Si-containing compound containing a halogen, a Si-containing compound represented by the general formula (1) or a Si-containing compound represented by the general formula (11) is used. As the Si-containing compound, two or more Si-containing compounds represented by the general formula (1) or two or more Si-containing compounds represented by the general formula (11) may be used in combination, or both the Si-containing compound represented by the general formula (1) and the Si-containing compound represented by the general formula (11) may be used in combination. As the Si-containing compound, another Si-containing compound (for example, a Si-containing compound not containing a halogen) may be used together with the Si-containing compound represented by the general formula (1) or the Si-containing compound represented by the general formula (11). However, the Si-containing compound represented by the general formula (1) or the Si-containing compound represented by the general formula (11) is preferably 50% by mass or more, more preferably 80% by mass or more, based on the total mass of the Si-containing compounds used. It is even more preferable that substantially all of the Si-containing compound used for the surface treatment is the Si-containing compound represented by the general formula (1) or the Si-containing compound represented by the general formula (11).

[0020] [Si-containing compound represented by general formula (1)]

Chemical formula

[0021] In general formula (1), R 1 represents a halogenated aryl group, m represents an integer of 1 to 3, n represents an integer of 0 to 8, and R 2 represents an alkyl group having 1 to 4 carbon atoms.

[0022] R 1 Examples of the halogen group in the halogenated aryl group represented by the formula (I) include a fluoro group, a chloro group, a bromo group, and an iodo group. Among these, a fluoro group is preferably used because it is easy to adjust the number of substitutions and to synthesize the group. That is, R 1 is preferably a fluorinated aryl group. Examples of the aryl group include a naphthyl group and a phenyl group, and a phenyl group is preferred. All or some of the substitutable hydrogen atoms in the aryl group may be halogenated. For example, when the aryl group is a phenyl group, it is sufficient that 1 to 5 hydrogen atoms are substituted with halogen groups, preferably 3 to 5 hydrogen atoms are substituted with halogen groups, and more preferably 5 hydrogen atoms are substituted with halogen groups. R 1 is most preferably a pentafluorophenyl group.

[0023] m is an integer of 1 to 3, preferably 1 or 2, and more preferably 1. When m is 2 or 3, multiple R 1 and each of the multiple n's may be the same or different. n represents an integer of 0 to 8, preferably 0 to 4, more preferably 0 to 2, and even more preferably 0.

[0024] R 2 represents an alkyl group having 1 to 4 carbon atoms, and preferably an alkyl group having 1 or 2 carbon atoms. When (4-m) is 2 or 3, multiple R 2 may be the same or different from each other.

[0025] In general formula (1), R 1 , R 2 , m and n can be selected depending on the application of the composite zeolite membrane, for example, the type of gas to be separated by the gas separation membrane, and availability.

[0026] Specific examples of the Si-containing compound represented by the general formula (1) include 2,4-difluorophenyltrimethoxysilane, 2,4-difluorophenyltriethoxysilane, 3,4,5-trifluorophenyltrimethoxysilane, 3,4,5-trifluorophenyltriethoxysilane, 4-(2,3,4,5-tetrafluorophenyl)phenyltrimethoxysilane, 4-(2,3,4,5-tetrafluorophenyl)phenyltriethoxysilane, pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilane, pentafluorobenzyltrimethoxysilane, pentafluorobenzyltriethoxysilane, 2-(pentafluorophenyl)ethyltrimethoxysilane, and 2-(pentafluorophenyl)ethyltriethoxysilane. Of these, pentafluorophenyltrimethoxysilane is preferred.

[0027] The Si-containing compound represented by the general formula (1) can be synthesized by a known method. As the Si-containing compound represented by the general formula (1), a commercially available product may be used.

[0028] [Si-containing compound represented by general formula (11)] [ka]

[0029] In the general formula (11), R 11 is a halogenated alkyl group, m is an integer of 1 to 3, n is an integer of 0 to 8, R 2 represents an alkyl group having 1 to 4 carbon atoms.

[0030] R 11 Examples of the halogen group in the halogenated alkyl group represented by the formula (I) include a fluoro group, a chloro group, a bromo group, and an iodo group. Among these, a fluoro group is preferably used because it is easy to adjust the number of substitutions and to synthesize the group. That is, R 1is preferably a fluorinated alkyl group. Examples of the alkyl group include alkyl groups having 1 to 16 carbon atoms. An alkyl group having 1 to 6 carbon atoms is preferred. The alkyl group having 3 to 16 carbon atoms may be either linear or branched, but is preferably a linear alkyl group. Specific examples include methyl, ethyl, n-propyl, and n-butyl groups, and of these, n-propyl is preferred. All or some of the substitutable hydrogen atoms in the alkyl group may be halogenated. It is preferred that three hydrogen atoms in the alkyl group are halogenated so that the terminal methyl group in the alkyl group becomes a trifluoromethyl group. 1 Most preferably, m is a 3,3,3-trifluoropropyl group. When m is 2 or 3, the plurality of R 11 may be the same or different from each other.

[0031] R in general formula (11) 2 and m is R in general formula (1). 2 and m have the same meanings and preferred ranges as well.

[0032] Specific examples of the Si-containing compound represented by the general formula (11) include 3,3,3-trifluoropropylmethyldimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, perfluorooctylethyltriethoxysilane, etc. Among these, 3,3,3-trifluoropropyltrimethoxysilane is preferred.

[0033] The Si-containing compound represented by the general formula (11) can be synthesized by a known method. As the Si-containing compound represented by the general formula (11), a commercially available product may be used.

[0034] <Zeolite membrane> Zeolite is a porous crystalline aluminosilicate. The zeolite membrane in the composite zeolite membrane of the present invention is a membrane composed of MFI type zeolite, and is formed by densely assembling MFI type zeolite crystals. Due to the skeletal structure of MFI type zeolite (specifically, 10-membered oxygen ring), fine pores (molecular level pores) are formed, and it can function as a separation membrane. It is considered that the type of gas that can be transmitted is adjusted by surface-treating the surface of this zeolite membrane with a Si-containing compound.

[0035] In the composite zeolite membrane of the present invention, the presence of MFI zeolite in the zeolite membrane can be determined by comparison with an X-ray diffraction (hereinafter referred to as "XRD") pattern having the structure code MFI according to the classification by the International Zeolite Society. As long as the zeolite membrane has the framework structure of MFI zeolite, it may contain other components, such as silica and alumina.

[0036] In the composite zeolite membrane of the present invention, the MFI zeolite constituting the zeolite membrane is preferably silicalite-1. Silicalite-1 is an MFI zeolite whose crystal framework is composed of silicon and oxygen and does not substantially contain aluminum in the crystal framework. This makes the zeolite membrane have high permeability to low molecular weight gases and excellent durability.

[0037] The thickness of the zeolite membrane is not particularly limited, but can be, for example, 0.1 μm or more and 100 μm or less.

[0038] Here, "on the porous support" refers to the outer surface of the porous support (the surface of the porous support excluding the surfaces of the holes provided in the porous support) and the openings of the holes leading to the outside of the porous support (the openings of the holes exposed on the outer surface of the porous support). In other words, the zeolite membrane formed on the porous support covers the outer surface of the porous support and closes the pores leading to the outside of the porous support.

[0039] The zeolite membrane may be formed on a porous support, and a part of the zeolite membrane may penetrate into the inside of the pores in the porous support and be formed on the surface of the pores (i.e., on the inner surface). That is, there may be an area between the porous support and the zeolite membrane where both are mixed. The zeolite membrane may be formed on the entire area of ​​the porous support, or may be formed on only a part of the area of ​​the porous support.

[0040] <Porous support> The porous support in the composite zeolite membrane of the present invention is not particularly limited as long as it has the strength to withstand a pressure difference and heat resistance, and examples thereof include inorganic porous supports and inorganic-organic hybrid porous supports.

[0041] The inorganic porous support is not particularly limited as long as it is porous, and for example, a ceramic sintered body such as silica, alumina, mullite, zirconia, titania, silicon nitride, or silicon carbide, or a sintered metal such as stainless steel, glass, or a carbon molded body can be used. The inorganic-organic hybrid porous support is not particularly limited, and for example, a mixture or laminate of the inorganic porous support and an organic support such as cellulose acetate can be used. In terms of strength, heat resistance, and corrosion resistance, an inorganic porous support is preferred, and an alumina porous support composed of alumina is more preferred.

[0042] The pore size of the porous support surface layer can be, for example, 0.05 μm to 4.0 μm, more preferably 0.08 μm to 2.0 μm, and even more preferably 0.10 μm to 1.5 μm. The pore size of the support can be evaluated by bubble point method, mercury intrusion method, or the like. The porous support surface layer refers to the surface portion of the porous support capable of forming a zeolite membrane, for example, a portion from the outer surface of the porous support to about 25% of the thickness of the porous support. The pore size of the portion other than the support surface layer forming the zeolite membrane is not particularly limited, but can be exemplified as 0.05 μm to 4.0 μm, and further 0.30 μm to 1.5 μm. The porosity of the porous support affects the strength and permeation flow rate when separating mixed gas, so that it is preferable to have a porosity of 20% to 60%.

[0043] The shape of the porous support is not limited as long as it can effectively separate the mixed gas, and examples thereof include flat plate, corrugated plate, tubular, cylindrical, conical, truncated conical, cylindrical, prismatic, rectangular tube, pyramidal, truncated pyramidal, honeycomb with many cylindrical or rectangular prismatic holes, etc. Corrugated plate, tubular, cylindrical, conical, truncated conical, cylindrical, prismatic, rectangular tube, pyramidal, truncated pyramidal, or cylindrical porous support is preferably a tube with a hollowed-out center, and the tube may be a through-hole or a test tube-like non-through-hole.

[0044] <<Method of manufacturing composite zeolite membrane>> <Method of manufacturing a porous support with a zeolite membrane> The porous support on which the zeolite membrane is formed (the porous support on which the zeolite membrane is formed) can be produced by a known method. Examples of known methods include the method described in JP 2015-150527 A and the method described in WO 2017 / 221761 A. One example includes a method in which seed crystals of MFI zeolite are attached to the outer surface of a porous support, and the porous support to which the seed crystals are attached is immersed in a raw material composition for zeolite membrane synthesis (a solution containing the constituent components of MFI zeolite) to perform hydrothermal synthesis.

[0045] <Surface treatment> In the composite zeolite membrane of the present invention, the zeolite membrane surface is surface-treated with the above-mentioned Si-containing compound. In this specification, the term "surface treatment" refers to a treatment for fixing the Si-containing compound on the surface of the zeolite membrane, and "surface-treated" refers to the Si-containing compound being fixed on the surface of the zeolite membrane. The Si-containing compound may be fixed on the zeolite membrane surface by a covalent bond, a hydrogen bond, a van der Waals bond, or the like.

[0046] The Si-containing compound may have a structure represented by the above-described general formula (1) or general formula (11) before the surface treatment of the zeolite membrane, and may have a partially different structure after the surface treatment by bonding to the zeolite membrane. For example, the OR in each structure may be 2 R 2 may be desorbed and bonded to the zeolite membrane. Specifically, it may be covalently bonded to Si in the zeolite membrane to form a partial structure of "Si-O-Si."

[0047] The fact that the zeolite membrane surface has been treated with a Si-containing compound can be confirmed by thermogravimetry of the surface-treated product or elemental mapping using a scanning electron microscope equipped with an energy dispersive X-ray analyzer. For example, the weight loss of surface-treated zeolite is slower than that of untreated zeolite, and a multi-stage weight loss that is thought to be due to the elimination of substituents is observed. Surface treatment can also be confirmed by detecting halogens such as fluorine through elemental mapping.

[0048] The surface treatment method of the zeolite membrane can be, for example, the following liquid phase method or gas phase method. The surface treatment method to be used may be selected mainly depending on the Si-containing compound. For example, when performing surface treatment with pentafluorophenyltrimethoxysilane, it is preferable to use the gas phase method.

[0049] (liquid phase method) The liquid phase method is a method in which a porous support on which a zeolite membrane has been formed is immersed in a solution containing a Si-containing compound, thereby fixing the Si-containing compound on the surface of the zeolite membrane.

[0050] The solution containing the Si-containing compound is a solution containing at least the Si-containing compound and a solvent. The solvent can be diluted with a solvent such as ethanol or hexane. The solution containing the Si-containing compound can be, for example, a solution in which 1 mole of the Si-containing compound is diluted with 300 moles of ethanol.

[0051] The temperature when the porous support on which the zeolite membrane is formed is immersed in the solution containing the Si-containing compound is preferably 20°C or higher, more preferably 50°C or higher. Also, 200°C or lower is preferable. By setting the temperature at 20°C or higher, it is possible to prevent the treatment from taking a long time. Also, by setting the temperature at 200°C or lower, it is possible to prevent defects from occurring due to the difference in thermal expansion coefficient between the zeolite membrane and the porous support. The immersion may be performed under atmospheric pressure or under reduced pressure. The immersion time is not particularly limited, but may be, for example, 2 hours to 24 hours.

[0052] After immersion, it is preferable to wash with water or a solvent, and then dry by heating in an electric furnace or the like. The heating temperature during drying is preferably 300°C or less. This is because, within this temperature range, defects caused by the difference in thermal expansion coefficient between the zeolite membrane and the porous support can be prevented. In addition, the temperature increase and decrease rates are preferably 5°C / min or less, and more preferably 3°C / min or less.

[0053] (Gas phase method) The gas-phase method is a method in which a Si-containing compound is vaporized at high temperature and fixed on the surface of the zeolite membrane. Specifically, the Si-containing compound is introduced into a sealed container (heat-resistant and pressure-resistant) together with the zeolite membrane and then subjected to high-temperature treatment.

[0054] Considering the heat resistance of the zeolite membrane, the heating temperature may be 100 to 500° C., preferably 130 to 300° C., and more preferably 150 to 200° C. Heating may be carried out in an electric furnace or the like.

[0055] The partial pressure of the Si-containing compound in the closed vessel may be, for example, 0.7 MPa or less, preferably 0.1 MPa or less, and more preferably 0.05 MPa or less.

[0056] The Si-containing compound is liquid or solid at room temperature, and in the gas phase method, it is placed in a closed container so as not to come into direct contact with the zeolite membrane. The Si-containing compound volatilizes in the closed container and reacts with the zeolite membrane, so the placement method is not particularly specified.

[0057] <<Gas separation membrane>> The composite zeolite membrane can be used as a gas separation membrane. A gas separation membrane is a membrane that can selectively permeate and separate a desired gas component from a mixed gas containing multiple types of gases. The gas separation membrane of the present invention is preferably used so that a mixed gas containing multiple types of gases to be treated (a gas to be treated) is permeated through the composite zeolite membrane from the surface-treated side (the zeolite membrane side with respect to the porous support). At this time, it is sufficient that a gas in which the concentration of the desired gas component is increased compared to the concentration in the gas to be treated is obtained from the opposite side. For example, a tubular composite zeolite membrane having a surface-treated surface on the outside is preferably used so that a gas to be treated can be introduced from the outside and the gas after treatment can be discharged from the inside.

[0058] The zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (1) has a remarkably high C2H6 / C3H8 permeability ratio and a C2H4 / C3H6 permeability ratio, as shown in the examples described later. Therefore, the zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (1) can be preferably used as a separation membrane for selectively permeating ethane (C2H6) over propane (C3H8), or a separation membrane for selectively permeating ethylene (C2H4) over propylene (C3H6). In this specification, a separation membrane for selectively permeating B over A may be one that increases the (concentration of B) / (concentration of A) in the mixed gas before permeation. The zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (1) can be used, for example, as a separation membrane for selectively permeating ethane from a mixed gas containing at least ethane and propane, or a separation membrane for selectively permeating ethylene from a mixed gas containing at least ethylene and propylene.

[0059] The zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (1) can be used to separate gases whose substantial molecular size during membrane permeation is larger than that of propane and propylene, and gases whose substantial molecular size during membrane permeation is smaller than that of ethane and ethylene. For example, the zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (1) can also be used as a separation membrane for selectively permeating methane over butane.

[0060] The ethane permeability of the porous support with a zeolite membrane that has been surface-treated with the Si-containing compound represented by the general formula (1) is 1×10 -8 mol / m 2 / s / Pa or more is preferable, and 3×10 -8 mol / m 2 The propane permeability of the zeolite membrane-attached porous support, the surface of which is treated with the Si-containing compound represented by the general formula (1), is preferably 3×10 -9 mol / m 2 / s / Pa or less is preferable, and more preferably 1×10 -9 mol / m 2 It is preferable that the viscosity is 1 / s / Pa or less.

[0061] The ethylene permeability of the porous support with a zeolite membrane that has been surface-treated with the Si-containing compound represented by the general formula (1) is 1×10 -8 mol / m 2 / s / Pa or more is preferable, and 3×10 -8 mol / m 2 The propylene permeability of the zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by the general formula (1) is preferably 5×10 -9 mol / m 2 / s / Pa or less is preferable, and more preferably 2×10 -9 mol / m 2 It is preferable that the viscosity is 1 / s / Pa or less.

[0062] The gas to be treated with the gas separation membrane made of a porous support with a zeolite membrane whose surface is treated with the Si-containing compound represented by the general formula (1) may contain one or more selected from the group consisting of methane, ethane, propane, butane, pentane, ethylene, acetylene, propylene, propadiene, butene, and butadiene. It may also contain hydrogen, nitrogen, carbon dioxide, water, oxygen, rare gases, and the like. The gas separation membrane made of a porous support with a zeolite membrane whose surface is treated with the Si-containing compound represented by the general formula (1) can be used to separate a gas to be treated containing at least nitrogen, carbon dioxide, methane, ethane, ethylene, propane, propylene, and butane into a mixed gas containing nitrogen, methane, ethane, and ethylene, and a mixed gas containing propane, propylene, and butane.

[0063] The zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (11) has a significantly high CH4 / C2H6 permeability ratio, as shown in the examples described later. Therefore, the zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (11) can be preferably used as a separation membrane for selectively permeating methane (CH4) relative to ethane. The zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (11) can be used, for example, as a separation membrane for selectively permeating ethane from a mixed gas containing at least methane and ethane.

[0064] The zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (11) can be used to separate gases whose substantial molecular size during membrane permeation is larger than that of ethane and gases whose substantial molecular size during membrane permeation is smaller than that of methane. For example, the zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by general formula (1) can also be used as a separation membrane for selectively permeating nitrogen relative to ethane.

[0065] The methane permeability of the porous support with a zeolite membrane that has been surface-treated with the Si-containing compound represented by the general formula (11) is 2×10-8 mol / m 2 / s / Pa or more is preferable, and 5×10 -8 mol / m 2 The ethane permeability of the zeolite membrane-attached porous support surface-treated with the Si-containing compound represented by the general formula (11) is preferably 5×10 -9 mol / m 2 / s / Pa or less is preferable, and more preferably 3×10 -9 mol / m 2 It is preferable that the viscosity is 1 / s / Pa or less.

[0066] The gas to be treated with the gas separation membrane made of a porous support with a zeolite membrane whose surface has been treated with the Si-containing compound represented by general formula (11) may contain, in addition to the above-mentioned components, one or more selected from the group consisting of propane, butane, pentane, ethylene, acetylene, propylene, propadiene, butene, and butadiene. It may also contain hydrogen, nitrogen, carbon dioxide, water, oxygen, rare gases, etc. The gas separation membrane made of a porous support with a zeolite membrane whose surface has been treated with the Si-containing compound represented by general formula (11) can be used to separate a gas to be treated containing at least nitrogen, carbon dioxide, methane, ethane, propane, and butane into a mixed gas containing nitrogen and methane and a mixed gas containing ethane, propane, and butane.

[0067] Methane, carbon dioxide, ethane, ethylene, propane, and propylene are the main components of natural gas, and the gas separation membrane of the present invention is industrially useful.

[0068] The gas separation membrane of the present invention is preferably used at a temperature at which hydrocarbons do not condense. For example, methane is at -89°C or higher, ethane at -89°C or higher, propane at -42°C or higher, and butane at 0°C or higher. By using the membrane at such temperatures, condensation of hydrocarbons such as methane is suppressed in the pores of the zeolite membrane and the pores of the porous support, and separation can be performed more efficiently. The membrane temperature is preferably 500°C or lower, and more preferably 200°C or lower. The gas separation membrane of the present invention is preferably used under temperature conditions of 0°C or higher and 200°C or lower.

[0069] In gas separation using the gas separation membrane of the present invention, the pressure of the gas to be treated on the gas separation membrane is not particularly limited, but is preferably 0.10 MPa or more. Such a pressure increases the permeation flow rate of the gas to be treated, making it possible to reduce the required membrane area. In other words, the required zeolite membrane area can be reduced, which is economically advantageous and allows the device to be simplified. The pressure is more preferably 0.20 MPa or more.

[0070] The gas separation membrane of the present invention can be used, for example, by being appropriately installed in a gas separation module. The gas separation module may be configured to include at least the gas separation membrane of the present invention, a housing made of metal such as stainless steel for housing the gas separation membrane of the present invention, a seal material made of rubber or the like for connecting the housing and the separation membrane, a means for supplying the gas to be treated to the surface treatment side of the gas separation membrane, and a means for recovering the treated gas from the side opposite to the surface treatment side of the gas separation membrane. EXAMPLES

[0071] The present invention will be described in more detail below with reference to examples. The materials, reagents, amounts of substances and their ratios, operations, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following examples.

[0072] <Production of composite zeolite membrane> [Seed crystal preparation] 1g of sodium hydroxide (special grade, manufactured by Kanto Chemical), 58.3g of distilled water, 16.2g of colloidal silica (SI-30, manufactured by Nissan Chemical) and 5.5g of tetrapropylammonium bromide (special grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed and stirred at room temperature for 1 hour, and then hydrothermal synthesis was carried out at 130°C for 20 hours. Next, the synthesis solution was filtered and washed with distilled water, then dried at 100°C for 15 hours, and calcined at 500°C for 15 hours. The constituent phases of the obtained seed crystals were identified by X-ray diffraction measurement (XRD, device name: RINT UltimaIII, manufactured by Rigaku Denki), and it was confirmed that the crystal phase of the seed crystals was silicalite-1.

[0073] [Preparation of porous support with silicalite-1 membrane] 0.4 g of the above seed crystals were dispersed in 50 ml of ethanol, and a cylindrical porous support (material: α-alumina, average pore size: 0.7 μm (surface side: 0.15 μm), porosity: 35 to 45%, length: 3 cm, outer diameter: 1 cm, inner diameter: 0.7 cm) was immersed in the dispersion, which was then dried at 100°C to support the seed crystals on the outer surface of the support.

[0074] 1g of sodium hydroxide (special grade, manufactured by Kanto Chemical Co., Ltd.), 655.5g of distilled water, 74.6g of tetramethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.66g of tetrapropylammonium bromide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed and stirred at room temperature for 1 hour, and then the seed crystal-attached porous support was immersed therein and hydrothermal synthesis was carried out at 180°C for 24 hours. Next, the support was taken out of the synthesis solution, washed with distilled water, and then fired at 500°C for 15 hours. The constituent phases of the membrane portion of the obtained porous support were identified by XRD, and it was confirmed that the crystalline phase of the zeolite membrane portion was silicalite-1.

[0075] [Preparation of porous support with silicalite-1 membrane surface-treated with 3,3,3-trifluoropropyltrimethoxysilane] As shown in FIG. 1, the silicalite-1 membrane-attached porous support (1) was immersed in a solution (2) prepared by dissolving 3.16 g of 3,3,3-trifluoropropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.) in 200 g of ethanol (Fujifilm Wako Pure Chemical Industries, Ltd.), refluxed at 80° C. for 10 hours, washed with ethanol, and heated at 220° C. for 24 hours to obtain a silicalite-1 membrane-attached porous support surface-treated with 3,3,3-trifluoropropyltrimethoxysilane.

[0076] [Preparation of porous support with silicalite-1 membrane surface-treated with pentafluorophenyltrimethoxysilane] As shown in FIG. 2, four of the silicalite-1 membrane-attached porous supports (1) were placed in a 100 ml sealed container (heat-resistant and pressure-resistant) (10). Furthermore, 0.11 g (concentration in the container after vaporization of about 0.004 mol / L) of pentafluorophenyltrimethoxysilane (2) was introduced into the pressure-resistant container. Pentafluorophenyltrimethoxysilane was synthesized by a known procedure. The pressure-resistant container was heated in an electric furnace at 170° C. for 3 hours. A silicalite-1 membrane-attached porous support surface-treated with pentafluorophenyltrimethoxysilane was obtained.

[0077] (Gas permeability evaluation) The resulting porous support with a surface-treated silicalite membrane was evaluated for various gas permeabilities. The evaluation procedure was as follows. Each gas was supplied to the surface of the surface-treated silicalite membrane, and the pressure was set to 0.2 MPa using the pressure regulating valve. The membrane temperature was kept at 20°C, and the flow rate of the gas that had permeated the porous support with the surface-treated silicalite-1 membrane was evaluated using a soap film flowmeter and a pressure change method. The permeabilities and ideal separation coefficients were calculated using the following formulas. The permeabilities were obtained based on the tests under the above-mentioned conditions. Permeability = (permeation flow rate (mol / s)) / (membrane area (m 2 )) / (Pressure difference (Pa)) The results for each gas are shown in Figures 3 and 4.

[0078] As can be seen from Figure 3, the surface treatment with 3,3,3-trifluoropropyltrimethoxysilane increased the C2H6 transmittance by 63.9 × 10 -9 molm -2 s -1 Pa -1 From 2.52 × 10 -9 molm -2 s -1 Pa -1 As a result, the CH4 / C2H6 transmittance ratio improved from 4.1 to 25.3.

[0079] As can be seen from Figure 4, the C3H6 transmittance increased by 4.94 × 10 after surface treatment with pentafluorophenyltrimethoxysilane. -9 molm -2 s -1 Pa -1 to 1.38 × 10 -9 molm -2 s -1 Pa -1 As a result, the C2H4 / C3H6 transmittance ratio improved from 15.0 to 34.5, and the C2H6 / C3H8 transmittance ratio improved from 22.3 to 42.7. [Industrial Applicability]

[0080] The gas separation membrane made of the composite zeolite membrane of the present invention can separate low-grade hydrocarbons. By using the gas separation membrane of the present invention, it is possible to highly selectively permeate and separate desired gases without adding a large amount of heat energy from outside the system, and it is possible to provide an energy-saving production process for highly purified hydrocarbons. [Explanation of symbols]

[0081] 1. Silicalite-1 membrane-coated porous support 2 Si compounds 10. Airtight containers

Claims

1. A composite zeolite membrane comprising a porous support and a zeolite membrane formed on the porous support, The zeolite membrane is made of MFI zeolite, A composite zeolite membrane, the surface of which is treated with a Si-containing compound represented by general formula (1); 【Chemistry 1】 In the formula, R １ represents a halogenated aryl group, m represents an integer of 1 to 3, n represents an integer of 0 to 8, R ２ represents an alkyl group having 1 to 4 carbon atoms.

2. R １ 2. The composite zeolite membrane according to claim 1, wherein is a fluoroaryl group.

3. R １ 2. The composite zeolite membrane according to claim 1, wherein is a pentafluorophenyl group.

4. 4. The composite zeolite membrane according to claim 1, wherein m is 1 and n is 0.

5. 2. The composite zeolite membrane according to claim 1, wherein the Si-containing compound is pentafluorophenyltrimethoxysilane.

6. The composite zeolite membrane according to any one of claims 1 to 5, wherein the porous support is an alumina porous support made of alumina.

7. The composite zeolite membrane according to any one of claims 1 to 6, wherein the MFI type zeolite is silicalite-1.

8. A gas separation membrane comprising the composite zeolite membrane according to any one of claims 1 to 7.

9. 9. The gas separation membrane of claim 8, which is used to selectively permeate ethane over propane.

10. 9. The gas separation membrane of claim 8, which is used to selectively permeate ethylene relative to propylene.

11. 1. A gas separation membrane for selectively permeating methane over ethane, comprising: A zeolite membrane formed on a porous support, The zeolite membrane is made of MFI zeolite, a gas separation membrane, the zeolite membrane surface of which is surface-treated with a Si-containing compound represented by general formula (11); 【Chemistry 2】 In the formula, R １１ represents a halogenated alkyl group, m represents an integer of 1 to 3, R ２ represents an alkyl group having 1 to 4 carbon atoms.

12. The gas separation membrane according to claim 11, wherein the Si-containing compound is 3,3,3-trifluoropropyltrimethoxysilane.

13. The gas separation membrane according to claim 11 or 12, wherein the porous support is an alumina porous support made of alumina.

14. The gas separation membrane according to any one of claims 11 to 13, wherein the MFI zeolite is silicalite-1.

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