Separation membrane system

Abstract

Provided is a separation membrane system including a separation membrane that preferentially transmits and separates a flammable gas or a non-flammable gas from a mixed gas of the flammable gas and the non-flammable gas, and in which the separation membrane yields a gas that contains the non-flammable gas in an increased concentration (enriched with the non-flammable gas) and that can be effectively utilized or burned.　The separation membrane system according to an embodiment of the present invention separates a mixed gas of a flammable gas and a non-flammable gas on the basis of permeability, and includes a separation membrane that preferentially transmits the flammable gas or the non-flammable gas to separate the mixed gas into a flammable-gas-enriched gas and a non-flammable-gas-enriched gas. The non-flammable-gas-enriched gas is combustible.

Description

Separation Membrane System

[0001] The present invention relates to a separation membrane system.

[0002] Various methods have been studied for separating useful gases from mixed gases. For example, a method using a separation membrane that can selectively permeate specific gases is known. In a mixed gas of a flammable gas and a non-flammable gas, in order to increase the concentration of each of the flammable gas and the non-flammable gas, a separation membrane system that allows the specific gases to permeate often has no use for the concentrated non-flammable gas, and is therefore discarded, which is uneconomical.

[0003] International Publication No. 2011 / 105511

[0004] The main object of the present invention is to provide a separation membrane system that includes a separation membrane that preferentially permeates and separates a flammable gas or a non-flammable gas from a mixed gas of a flammable gas and a non-flammable gas, and that enables the effective use of gas in which the non-flammable gas has been highly concentrated (enriched) by the separation membrane.

[0005] [1] A separation membrane system according to an embodiment of the present invention is a separation membrane system that separates a mixed gas of a flammable gas and a non-flammable gas based on permeability, and includes a separation membrane that preferentially allows the flammable gas or the non-flammable gas to permeate and separates the mixed gas into a flammable-gas-enriched gas and a non-flammable-gas-enriched gas, the non-flammable-gas-enriched gas being combustible. [2] The separation membrane system of [1] above may have a mechanism for removing impurities upstream of the separation membrane. [3] In the separation membrane system of [1] above, the non-flammable-gas-enriched gas may contain nitrogen. [4] In the separation membrane system of [2] above, the non-flammable-gas-enriched gas may contain nitrogen. [5] In any of the separation membrane systems described in [1] to [4] above, the main component of the non-flammable gas in the non-flammable-gas-enriched gas may be nitrogen. [6] In any of the separation membrane systems described in [1] to "5" above, the non-flammable gas-enriched gas may be used to adjust the temperature of the separation membrane. [7] In any of the separation membrane systems described in [1] to "6" above, the non-flammable gas-enriched gas may be used to heat another separation membrane. [8] In any of the separation membrane systems described in [1] to [7] above, a portion of the mixed gas may be used to adjust the temperature of the separation membrane. [9] In any of the separation membrane systems described in [1] to [8] above, the flammable gas-enriched gas may be used to adjust the temperature of the separation membrane.

[0006] According to an embodiment of the present invention, a separation membrane system can be provided that includes a separation membrane that preferentially permeates and separates flammable gas or non-flammable gas from a mixed gas of flammable gas and non-flammable gas, and that enables effective use of gas in which the non-flammable gas has been highly concentrated (enriched) by the separation membrane.

[0007] Fig. 1 is an explanatory diagram showing an overview of a separation membrane system according to one embodiment of the present invention. Fig. 2 is an explanatory diagram showing an overview of a separation membrane system according to one embodiment of the present invention. Fig. 3 is an explanatory diagram showing an outline of the configuration of a separation membrane composite in one embodiment of the present invention. Fig. 4 is a schematic cross-sectional view showing the configuration of a separation membrane composite in one embodiment of the present invention.

[0008] A. Overview of Separation Membrane System FIG. 1 is an explanatory diagram showing an overview of a separation membrane system according to one embodiment of the present invention. Separation membrane system 100 is configured to separate a mixed gas of a flammable gas and a non-flammable gas based on permeability. The separation membrane system 100 includes a separation membrane. The separation membrane preferentially allows the flammable gas or the non-flammable gas to permeate, separating the mixed gas into a flammable-gas-enriched gas and a non-flammable-gas-enriched gas. In one embodiment, the separation membrane can constitute a separation membrane composite 10.

[0009] In one embodiment, a separation membrane that preferentially allows non-flammable gas to permeate is used as the separation membrane ( FIG. 1( a) ). In this embodiment, the non-flammable gas concentration in the gas that permeates the separation membrane (hereinafter also referred to as permeating gas) is higher than the non-flammable gas concentration in the mixed gas before contacting the separation membrane (hereinafter also referred to as the gas to be treated). On the other hand, in the separation membrane system, the non-flammable gas concentration in the gas that does not permeate the separation membrane (hereinafter also referred to as the non-permeating gas) is lower than the non-flammable gas concentration in the gas to be treated. Also, in this embodiment, in the separation membrane system, the flammable gas concentration in the non-permeating gas is higher than the flammable gas concentration in the gas to be treated. Note that the non-permeating gas may be flammable. In this specification, a gas that has a higher non-flammable gas concentration than the gas to be treated (a mixed gas of a flammable gas and a non-flammable gas before contacting the separation membrane) is referred to as a "non-flammable gas concentrated gas." In this embodiment, the permeating gas is a "non-flammable gas concentrated gas." Furthermore, a gas with a high concentration of flammable gas is referred to as a “flammable gas concentrated gas.” In this embodiment, the non-permeable gas is the “flammable gas concentrated gas.”

[0010] In another embodiment, a separation membrane that preferentially allows combustible gas to permeate is used as the separation membrane (FIG. 1(b)). In this embodiment, the non-permeable gas concentration is higher than the non-combustible gas concentration in the gas to be treated. On the other hand, the non-combustible gas concentration in the permeable gas is lower than the non-combustible gas concentration in the gas to be treated. Also, in this embodiment, the combustible gas concentration in the permeable gas is higher than the combustible gas concentration in the gas to be treated. Note that the permeable gas may be flammable. In this embodiment, the non-permeable gas is a "non-combustible gas concentrated gas." Also, the permeable gas is a "combustible gas concentrated gas."

[0011] In one embodiment, the separation membrane system has a mechanism for removing impurity components as pretreatment equipment upstream of the separation membrane. The impurity components may be solid components, liquid components, or gas components. When a heating device is provided as described below, the removal mechanism may be provided upstream or downstream of the heating device.

[0012] The gas to be treated is a mixed gas containing, for example, hydrogen, helium, nitrogen, oxygen, carbon monoxide, carbon dioxide, nitrogen oxides, ammonia, sulfur oxides, hydrogen sulfide, sulfur fluoride, mercury, arsine, hydrogen cyanide, carbonyl sulfide, C1 to C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, aldehydes, etc. In this specification, a flammable gas refers to a gas that becomes flammable in the presence of oxygen. Examples of flammable gases include hydrocarbon gases (methane, ethane, propane, butane, ethylene, etc.), hydrogen, and carbon monoxide. Examples of non-flammable gases include nitrogen and carbon dioxide. In one embodiment, nitrogen is used as the non-flammable gas. Alternatively, a non-flammable gas containing nitrogen as a main component may be used. In this specification, the term "main component" refers to the component with the highest concentration among the non-flammable gas components. In the mixed gas, the mixing ratio of the flammable gas to the non-flammable gas may be any appropriate ratio. In one embodiment, the separation membrane system is used as a means for purifying natural gas (for example, a mixture of nitrogen and hydrocarbon gas).

[0013] In the above separation membrane system, the non-flammable gas-enriched gas is a combustible gas. In an embodiment of the present invention, the non-flammable gas-enriched gas is generated while being configured to be combustible, thereby enabling effective utilization of the non-flammable gas. Typically, the non-flammable gas-enriched gas as exhaust gas can be combusted, thereby reducing the disposal cost of the non-flammable gas. The non-flammable gas-enriched gas can also be used to adjust the temperature of the separation membrane (details will be described later). In one embodiment, the non-flammable gas-enriched gas is a combustible gas based on the configuration of the separation membrane itself. That is, the non-flammable gas-enriched gas is a combustible gas without introducing a combustible gas separate from the non-flammable gas. Note that a gas being combustible means that it can be in the flammable range at atmospheric pressure and room temperature in the presence of a combustion-supporting gas (without introducing additional combustible gas). Preferably, it means that it can be in the flammable range at atmospheric pressure and room temperature by mixing with air.

[0014] The non-flammable gas-enriched gas may be stored and used outside the separation membrane system, or may be used within the separation membrane system. In one embodiment, the separation membrane system includes combusting the non-flammable gas-enriched gas.

[0015] In one embodiment, the non-combustible gas-enriched gas is used to adjust the temperature of the separation membrane ( FIG. 1( c) ). The temperature-adjusted separation membrane of this embodiment may be a separation membrane used to generate a non-combustible gas-enriched gas. Because the separation accuracy of a separation membrane varies depending on the temperature, the composition of the non-combustible gas-enriched gas can be controlled within the flammable range by appropriately adjusting the temperature. In one embodiment, the heated non-combustible gas-enriched gas heats the gas to be treated, thereby adjusting the temperature of the separation membrane. Preferably, the gas to be treated is heated using the heat obtained by burning the non-combustible gas-enriched gas in the presence of a combustion-supporting gas. All or a portion of the generated non-combustible gas-enriched gas may be used for the temperature adjustment. A separate heating device (such as an electric heater) may also be provided upstream of the separation membrane. In this case, the load on the heating device can be reduced by also using the heat obtained by burning the non-combustible gas-enriched gas.

[0016] In one embodiment, the temperature of the separation membrane is adjusted using the gas to be treated (a mixed gas of combustible and non-combustible gases before contacting the separation membrane) and / or a combustible-gas-enriched gas. Typically, as shown in FIG. 2 , the gas to be treated and / or a portion of the combustible-gas-enriched gas is heated to heat the gas, thereby adjusting the temperature of the separation membrane. Preferably, the gas to be treated is heated using heat obtained by burning a portion of the gas to be treated and / or a portion of the combustible-gas-enriched gas in the presence of a combustion-supporting gas. FIG. 2( a ) shows an embodiment in which a portion of the gas to be treated is combusted to heat the gas to be treated. FIG. 2( b ) shows an embodiment in which a portion of the combustible-gas-enriched gas serving as a non-permeable gas is combusted to heat the gas to be treated. FIG. 2( c ) shows an embodiment in which a portion of the combustible-gas-enriched gas serving as a permeable gas is combusted to heat the gas to be treated. Furthermore, as shown in Figures 2(a') to (c'), the temperature of the separation membrane may be adjusted using a gas obtained by mixing a non-combustible gas enriched gas with the gas to be treated and / or a combustible gas enriched gas.

[0017] In one embodiment, the non-combustible gas-enriched gas is used to heat another separation membrane (FIG. 1(d)). In this embodiment, the non-combustible gas-enriched gas can be used not only to regulate the temperature of the separation membrane when separation performance is expressed, but also when starting up (heating up) an apparatus equipped with the separation membrane. The other separation membrane may be a separation membrane within the separation membrane system, or may be a separation membrane outside the separation membrane system. For example, Japanese Patent Laid-Open No. 2009-039654 discloses a system that prevents condensation on the membrane surface by heating the separation membrane when it is started up, and Japanese Patent No. 6,500,499 discloses a system that dries the separation membrane by heating. All of the generated non-combustible gas-enriched gas may be used to heat another separation membrane, or a portion of it may be used to heat another separation membrane.

[0018] In one embodiment, the separation membrane system includes combusting the non-combustible gas-enriched gas after it has been used to heat the separation membrane (or another separation membrane) as described above. The separation membrane may be heated by supplying the heated non-combustible gas-enriched gas to the separation membrane, or by using the heat generated by burning a portion of the non-combustible gas-enriched gas in the presence of a combustion-supporting gas. This embodiment allows for more effective use of the non-combustible gas.

[0019] In one embodiment, the non-flammable gas-enriched gas contains nitrogen. The non-flammable gas contained in the non-flammable gas-enriched gas may contain nitrogen as a main component. In this specification, the term "main component" refers to the component with the highest concentration among the components in the non-flammable gas.

[0020] Although not shown, the heating of the separation membrane does not necessarily have to be performed at the most upstream of the series of separation membranes, but may be performed at any point in the series.

[0021] The separation membrane composite can be configured in a cylindrical shape. When a gas to be treated is introduced into the inside of the cylindrical structure of the separation membrane composite at a predetermined gas introduction pressure (e.g., 0.5 MPa or more), gas that permeates the separation membrane composite (essentially the separation membrane) is discharged from the surface of the separation membrane composite, while gas that does not permeate can be passed in the longitudinal direction of the cylindrical separation membrane composite, resulting in the separation of mixed gases. The separation membrane composite may be configured with a single cylindrical structure or multiple cylindrical structures. Preferably, the separation membrane composite has multiple cylindrical cells that penetrate in the longitudinal direction.

[0022] FIG. 3 is an explanatory diagram showing an outline of the configuration of a separation membrane composite according to one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing the configuration of a separation membrane composite according to one embodiment of the present invention. A separation membrane composite 10 has a plurality of cells 11 formed therein. The cells 11 are formed in a cylindrical shape so as to penetrate the separation membrane composite 10 in the longitudinal direction. The cells 11 can serve as flow paths for the gas to be treated. The separation membrane composite 10 includes a porous substrate 1 and a separation membrane 2 provided on the porous substrate 1. The separation membrane 2 can be provided so as to cover substantially the entire inner surface of the porous substrate 1. Of the gas to be treated passing through the cells 11, gases having high permeability to the separation membrane 2 (permeating gases) permeate the separation membrane composite 10 and are delivered from a side surface 13 of the separation membrane composite 10. On the other hand, gases having low permeability to the separation membrane 2 (non-permeating gases) pass through the flow paths of the cells 11 and are delivered. Although not shown, the separation membrane composite can be housed in any suitable outer cylinder for use.

[0023] The length of the separation membrane composite is, for example, 10 cm to 200 cm. The outer diameter of the separation membrane composite is, for example, 0.5 cm to 30 cm. The distance between the central axes of adjacent cells is, for example, 0.3 mm to 10 mm. The inner diameter of the cell is, for example, 1 mm to 10 mm.

[0024] The separation membrane system 100 may include a plurality of separation membrane assemblies 10. The plurality of separation membrane assemblies 10 may be arranged in series, in parallel, or in a combination of series and parallel. When the separation membrane assemblies 10 are arranged in parallel, the parallel separation membrane assemblies 10 may or may not operate simultaneously. In one embodiment, a separation membrane assembly operated for gas separation and a separation membrane assembly used for separation membrane regeneration as described above are arranged in parallel. Furthermore, combustible gas may be obtained individually from a plurality of separation membrane assemblies 10, or a combustible gas may be obtained by combining a plurality of separation membrane assemblies 10 as shown in FIG. 1.

[0025] In one embodiment, there is provided a method for separating a mixed gas of a flammable gas and a non-flammable gas using the separation membrane system described above. The method is a gas separation method for separating a mixed gas of a flammable gas and a non-flammable gas based on permeability, which includes separating the mixed gas into a flammable-gas-enriched gas and a non-flammable-gas-enriched gas using the separation membrane that preferentially allows the flammable gas or the non-flammable gas to permeate, and the non-flammable-gas-enriched gas is combustible.

[0026] B. Separation Membrane As described above, a separation membrane preferentially allows either a flammable gas or a non-flammable gas to permeate from a gas to be treated (a mixed gas of a flammable gas and a non-flammable gas). Typically, the mixed gas is separated by the difference in permeability through a separation membrane having micropores. For example, the gas to be treated is separated into a permeable gas and a non-permeable gas by the action of a so-called molecular sieve, which controls gas permeability depending on the molecular size of the gas and the pore diameter of the separation membrane.

[0027] Preferably, the separation membrane is an inorganic membrane. Examples of materials constituting the separation membrane include zeolite, alumina, titania, silica, cordierite, zirconia, and mullite.

[0028] In one embodiment, a zeolite membrane is used as the separation membrane. The zeolite membrane is formed by forming a film of zeolite on the surface of a porous substrate. The zeolite membrane may contain two or more types of zeolite with different structures or compositions.

[0029] The zeolite constituting the zeolite membrane is an oxygen tetrahedron (TO ４ Zeolites in which the atom (T atom) located at the center of the zeolite (T atom) is composed of only Si or Si and Al, AlPO zeolites in which the T atoms are composed of Al and P, SAPO zeolites in which the T atoms are composed of Si, Al, and P, MAPSO zeolites in which the T atoms are composed of magnesium (Mg), Si, Al, and P, and ZnAPSO zeolites in which the T atoms are composed of zinc (Zn), Si, Al, and P can be used. Some of the T atoms may be substituted with other elements.

[0030] Examples of the zeolite include 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, and SOD type zeolites. The maximum number of rings in the zeolite is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. Also, it is preferably 6 or more, and even more preferably 8 or more.

[0031] The zeolite membrane contains, for example, Si. The zeolite membrane may contain, for example, any two or more of Si, Al, and P. The zeolite membrane may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K). When the zeolite membrane contains Si atoms and Al atoms, the Si / Al ratio in the zeolite membrane is, for example, 1 or more and 100,000 or less. The Si / Al ratio is the molar ratio of Si to Al contained in the zeolite membrane. The Si / Al ratio is preferably 5 or more, more preferably 20 or more, and even more preferably 100 or more, and the higher the Si / Al ratio, the better. The Si / Al ratio in the zeolite membrane can be adjusted by adjusting the compounding ratio of the Si source and the Al source in the raw material solution, which will be described later.

[0032] The average pore diameter of the separation membrane is, for example, 0.2 nm to 1 nm, and more preferably 0.3 nm to 0.5 nm. The pore diameter of the separation membrane can be adjusted depending on the desired composition of the permeation gas. Reducing the average pore diameter of the separation membrane increases selectivity. The average pore diameter of the separation membrane is smaller than the average pore diameter of the porous substrate. When the separation membrane is a zeolite membrane, the maximum number of rings in the zeolite is n, and the average pore diameter is the arithmetic mean of the minor and major axes of the n-membered ring pores. An n-membered 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 to form a ring structure is n. When there are multiple n-membered ring pores with the same n, the arithmetic mean of the minor and major axes of all the n-membered ring pores is the average pore diameter of the zeolite. The average pore size of a zeolite membrane is determined by the framework structure of the zeolite, and can be determined from the values ​​disclosed in the "Database of Zeolite Structures" [online] of the International Zeolite Society, available on the Internet at <URL: http: / / www.iza-structure.org / databases / >.

[0033] The thickness of the separation membrane 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. A thicker separation membrane increases selectivity. A thinner separation membrane increases permeation rate.

[0034] The surface roughness (Ra) of the separation membrane 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. In this specification, the surface roughness (Ra) is the arithmetic surface roughness Ra measured in accordance with JIS B 0601.

[0035] The separation membrane can be formed by any appropriate method depending on the material constituting the membrane. For example, a zeolite membrane can be obtained by applying zeolite as seed crystals to a porous substrate, immersing the porous substrate with the attached seed crystals in a raw material solution, and growing zeolite using the seed crystals as nuclei by hydrothermal synthesis. The raw material solution contains, for example, a silica source, an alumina source, an organic substance, an alkali source, water, etc. The heating temperature in the hydrothermal synthesis is, for example, 60°C to 200°C. The heating time is, for example, 1 hour to 240 hours. Alternatively, the separation membrane may be formed using a raw material slurry obtained by mixing an organic binder, a ceramic raw material, and a solvent.

[0036] In one embodiment, the combustibility of the non-combustible gas-enriched gas, i.e., the composition of the permeable gas and non-permeable gas, can be controlled, for example, by using a separation membrane configured according to the gas to be treated and adjusting the separation accuracy (gas selectivity) by the temperature of the separation membrane. In one embodiment, the non-combustible gas concentration of the non-combustible gas-enriched gas as the permeable gas can be reduced by increasing the temperature of the separation membrane. For example, when the DDR-type zeolite membrane described in WO 2011 / 105511 is used, the carbon dioxide concentration of the permeable gas containing carbon dioxide (non-combustible gas) can be reduced.

[0037] Alternatively, a combustible non-combustible gas-enriched gas may be obtained by using a plurality of separation membrane composites each having different gas permeability characteristics and mixing the non-combustible gas-enriched gas as permeable gas or non-permeable gas delivered from each separation membrane composite. When a plurality of separation membrane composites are used, the combustible non-combustible gas-enriched gas may be obtained by mixing the permeable gas or non-permeable gas delivered from some of the separation membrane composites (FIGS. 1(e) and 1(f)), or the combustible non-combustible gas-enriched gas may be obtained by mixing the permeable gas or non-permeable gas delivered from all of the separation membrane composites.

[0038] C. Porous Substrate The porous substrate is configured to be gas permeable. In the example shown in FIG. 3, the porous substrate 1 is a so-called monolithic substrate in which a plurality of through holes extending in the longitudinal direction are provided in an integrally molded, continuous columnar body. In the example shown in FIG. 3, the porous substrate 1 is approximately cylindrical. The cross section perpendicular to the longitudinal direction of the through holes is, for example, approximately circular. A separation membrane can be formed on the inner surface of the through holes to obtain a separation membrane composite (porous substrate / separation membrane) in which cells are formed. The shape of the porous substrate is not limited to the above example, and may be, for example, a honeycomb shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal columnar shape. In one embodiment, a separation membrane may be formed on the outer surface of a tubular porous substrate.

[0039] The length of the porous substrate is, for example, 10 cm to 200 cm. The outer diameter of the porous substrate is, for example, 0.5 cm to 30 cm. When the porous substrate has through holes, the distance between the central axes of adjacent through holes is, for example, 0.3 mm to 10 mm. When the porous substrate is tubular or cylindrical, the thickness of the porous substrate is, for example, 0.1 mm to 10 mm.

[0040] The porous substrate may be made of any suitable material. In one embodiment, the porous substrate is made of a sintered ceramic body. Examples of sintered ceramic bodies that can be used as the porous substrate material include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide.

[0041] The porous substrate may contain an inorganic binder, which may be at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite.

[0042] The porous substrate may have a single layer structure or a multilayer structure. In one embodiment, the porous substrate has a multilayer structure with layers having different pore sizes, as shown in Figure 4. It is preferable that the pore size is smaller as it approaches the inside (i.e., the separation membrane side).

[0043] The average pore diameter of the porous substrate is, for example, 0.01 μm to 70 μm, preferably 0.05 μm to 25 μm. The average pore diameter of the porous substrate on the separation membrane side is 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. With regard to the pore size distribution throughout the porous substrate, 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 porous substrate on the separation membrane side is, for example, 25% to 50%. The average pore diameter of the porous substrate can be measured using a mercury porosimeter, perm porometer, nanoperm porometer, or the like.

[0044] The separation membrane system of the present invention can be suitably used in a process for separating components in a mixed gas.

[0045] 1 Porous base material 2 Separation membrane 10 Separation membrane composite

Claims

1. A separation membrane system that separates a mixed gas of a flammable gas and a non-flammable gas based on permeability, a separation membrane that allows the flammable gas or the non-flammable gas to pass through preferentially and separates the mixed gas into a flammable gas-enriched gas and a non-flammable gas-enriched gas; The non-flammable gas-enriched gas is combustible, The non-flammable gas-enriched gas is used to adjust the temperature of the separation membrane. Separation membrane system.

2. A separation membrane system that separates a mixed gas of a flammable gas and a non-flammable gas based on permeability, a separation membrane that allows the flammable gas or the non-flammable gas to pass through preferentially and separates the mixed gas into a flammable gas-enriched gas and a non-flammable gas-enriched gas; The non-flammable gas-enriched gas is combustible, The non-flammable gas-enriched gas is used to heat another separation membrane. Separation membrane system.

3. A separation membrane system that separates a mixed gas of a flammable gas and a non-flammable gas based on permeability, a separation membrane that allows the flammable gas or the non-flammable gas to pass through preferentially and separates the mixed gas into a flammable gas-enriched gas and a non-flammable gas-enriched gas; The non-flammable gas-enriched gas is combustible, The flammable gas-enriched gas is used to adjust the temperature of the separation membrane. Separation membrane system.

4. A separation membrane system that separates a mixed gas of a flammable gas and a non-flammable gas based on permeability, a separation membrane that allows the flammable gas or the non-flammable gas to pass through preferentially and separates the mixed gas into a flammable gas-enriched gas and a non-flammable gas-enriched gas; The non-flammable gas-enriched gas is combustible, A mechanism for removing impurities (excluding a mechanism for removing impurities by contact with water) is provided upstream of the separation membrane. Separation membrane system.

5. The separation system according to claim 1 , further comprising a mechanism for removing impurity components upstream of the separation membrane.

6. 5. The separation system according to claim 1, wherein the non-flammable gas-enriched gas contains nitrogen.

7. 5. The separation membrane system according to claim 1, wherein the main component of the non-flammable gas in the non-flammable gas concentrated gas is nitrogen.

8. 5. The separation membrane system according to claim 2, wherein the non-flammable gas-enriched gas is used to adjust the temperature of the separation membrane.

9. 2. The separation membrane system according to claim 1, wherein the non-flammable gas-enriched gas is used to heat another separation membrane.

10. The separation membrane system according to claim 1 , wherein a part of the mixed gas is used to adjust the temperature of the separation membrane.

11. 3. The separation membrane system according to claim 1, wherein the flammable gas-enriched gas is used to adjust the temperature of the separation membrane.