Enriched gas production system and enriched gas production method

Abstract

This enriched gas production system has a gas synthesis reaction unit that generates a gas B by causing a raw material gas containing a gas A to react, and generates a synthesized gas containing the gas A and the gas B, and a gas separating unit that separates enriched gas of the gas B from the synthesized gas. The gas separating unit has a connected structure having one gas inlet, and a total of three or more permeated gas discharge ports and non-permeated gas discharge ports. The connected structure and the gas synthesis reaction unit are connected by a gas supply line, wherein: gas flows (i) to (iii) having different compositions are obtained from the permeated gas discharge ports and non-permeated gas discharge ports of the connected structure; the gas flow (i) having the highest concentration of the gas B is obtained as product gas; the gas flow (ii) having the highest concentration of the gas A is refluxed to the gas synthesis reaction unit; and a gas flow (iii) other than (i) and (ii) is refluxed to the gas supply line.

Description

A system for producing enriched gas and a method for producing enriched gas

[0001] The present invention relates to a system for producing enriched gas using a gas separation membrane unit and a method for producing enriched gas.

[0002] A known method for separating a mixed gas containing two or more different gases into individual gases is membrane separation, which utilizes the difference in the gas permeation rates through a membrane. In this method, by recovering the permeate gas and / or non-permeate gas, it is possible to obtain a target gas, which is a high-purity, high-permeability gas and / or a high-purity, low-permeability gas. For example, Patent Document 1 describes a method for producing methane, comprising a methanation step of generating a methane-containing gas by a methanation reaction in which hydrogen and carbon dioxide are reacted in the presence of a methanation catalyst or microorganisms, and a gas separation step of separating the hydrogen and carbon dioxide remaining in the methane-containing gas from the methane-containing gas to increase the methane concentration in the methane-containing gas and obtain a processed gas mainly composed of methane, wherein the method further comprises a step of circulating the hydrogen and carbon dioxide separated in the gas separation step back to the methanation step. In Document 1, it is not explicitly stated that the methane-containing gas produced by the methanation means is separated using two or more gas separation membrane units. An example of a configuration in which the above-mentioned methane production method is carried out using a single-stage gas separation membrane unit is the enriched gas production system 5 shown in Figure 6.

[0003] Japanese Patent Publication No. 2024-086395

[0004] In conventional methods for producing enriched gas, as shown in Figure 6, recycling the permeate gas from the separation membrane unit into the methanation reaction section to increase the recovery rate of the non-permeate gas (product gas) presented a problem: the high methane content in the permeate gas reduced the efficiency of the methane production reaction in methanation. Consequently, it was difficult to achieve both the required standards for the product gas, such as recovery rate and purity, and the efficiency of the methane production reaction.

[0005] The present invention provides the following configuration: [1] A system for producing enriched gas, comprising: a gas synthesis reaction unit that reacts a raw material gas containing gas A to produce at least gas B and produces a synthesis gas containing gas A and gas B; and a gas separation unit that separates the enriched gas of gas B from the synthesis gas produced in the gas synthesis reaction unit, wherein the gas separation unit has a connecting structure that has one gas inlet and a total of three or more permeate gas outlets and non-permeate gas outlets by connecting a plurality of gas separation membrane units having a gas inlet, a permeate gas outlet and a non-permeate gas outlet in series; the gas inlet of the connecting structure and the synthesis gas outlet of the gas synthesis reaction unit are connected by a gas supply line; a plurality of gas flows with different compositions can be obtained from a total of three or more permeate gas outlets and non-permeate gas outlets in the connecting structure; means for obtaining the gas flow (i) with the highest concentration of gas B among the plurality of gas flows as the product gas; and means for recycling the gas flow (ii) with the highest concentration of gas A to the gas synthesis reaction unit. [1] A system for producing enriched gas, comprising means for recycling gas flow (iii) other than (i) and (ii) to the gas supply line. [2] The system for producing enriched gas according to [1], wherein the raw material gas further contains gas C, gas A has a higher permeation rate to the gas separation membrane in each gas separation membrane unit than gas C, and the gas synthesis reaction unit reacts gas A and gas C to produce gas B. [3] The system for producing enriched gas according to [1] or [2], comprising a detection unit for detecting the amount or composition of gas flow (ii), and a control unit for adjusting the amount of gas A supplied to the gas synthesis reaction unit based on the detection result in the detection unit. [4] The system for producing enriched gas according to [1] or [2], wherein it is any of (a), (b), and (c) below. (a) The connecting structure comprises a first gas separation membrane unit, a second gas separation membrane unit, a permeate gas discharge line connecting the permeate gas outlet of the first gas separation membrane unit and the gas inlet of the second gas separation membrane unit, and a recirculation line that recirculates the exhaust gas from the non-permeate gas outlet of the second gas separation membrane unit back to the gas supply line.(b) The connecting structure comprises a first gas separation membrane unit, a second gas separation membrane unit, a non-permeable gas discharge line connecting the non-permeable gas outlet of the first gas separation membrane unit and the gas inlet of the second gas separation membrane unit, and a recirculation line that recirculates the exhaust gas from the permeable gas outlet of the second gas separation membrane unit back to the gas supply line. (c) The connecting structure comprises a first gas separation membrane unit, a second gas separation membrane unit, a third gas separation membrane unit, a non-permeable gas discharge line connecting the non-permeable gas outlet of the first gas separation membrane unit and the gas inlet of the second gas separation membrane unit, a permeable gas discharge line connecting the permeable gas outlet of the first gas separation membrane unit and the gas inlet of the third gas separation membrane unit, and a recirculation line that recirculates the exhaust gas from the permeable gas outlet of the second gas separation membrane unit back to the gas supply line, and a recirculation line that recirculates the exhaust gas from the non-permeable gas outlet of the third gas separation membrane unit back to the gas supply line. [5] A gas enrichment production system according to any one of [1] to [3], wherein the concentration of gas B in gas stream (i) is 90 mol% or more, and the concentration of gas A is 5000 volume ppm or less, the concentration of gas B in gas stream (ii) is 60 mol% or less, and the concentration of gas A is 40 mol% or more, and the concentration of gas B in gas stream (iii) is 50 to 99.8 mol%, and the concentration of gas A is 0.1 to 55 mol%. [6] A gas enrichment production system according to any one of [1] to [4], wherein in each of the gas separation membrane units, the permeation rate of gas A is greater than that of gas B. [7] (a) and the separation selectivity of gas A to gas B in the first gas separation membrane unit (P'). Ａ / P' Ｂ (b) is equal to or less than that of the second gas separation membrane unit, or (b) the separation selectivity of gas A to gas B in the first gas separation membrane unit (P' Ａ / P' Ｂ (c) is equal to or better than that of the second gas separation membrane unit, or the separation selectivity of gas A to gas B in the third gas separation membrane unit (P' Ａ / P' ＢA gas enrichment production system according to any one of items [3] to [5], wherein the flow rate F3 of gas (iii) is in the range of 10% to 300% with respect to the flow rate F0 of synthesis gas flowing into the structural assembly. [9] Each gas separation membrane unit has a separation selectivity of gas A to gas B at 30°C (P' Ａ / P' Ｂ A gas enrichment production system according to any one of items [1] to [7], wherein the ratio is 10 to 150.

[10] A gas enrichment production system according to any one of items [1] to [8], wherein the gas synthesis reaction section is a methanation reaction section, gas A is hydrogen, and gas B is methane.

[11] A gas enrichment production system according to any one of items [1] to [8], wherein the gas synthesis reaction section is a methanation reaction section, gas A is hydrogen, gas B is methane, and gas C is carbon dioxide.

[12] A method for producing an enriched gas, comprising: a gas synthesis reaction step of reacting a raw material gas containing gas A to produce at least gas B, thereby producing a synthesis gas containing gas A and gas B; and a gas separation step of separating a gas enriched gas of gas B from the synthesis gas produced in the gas synthesis reaction step, wherein the gas separation step uses a connected structure having one gas inlet and a total of three or more permeate gas outlets and non-permeate gas outlets by connecting a plurality of gas separation membrane units having a gas inlet, a permeate gas outlet and a non-permeate gas outlet in series; a gas supply line for supplying the synthesis gas obtained in the gas synthesis reaction step is connected to the gas inlet of the connected structure; a plurality of gas flows with different compositions are obtained from a total of three or more permeate gas outlets and non-permeate gas outlets in the connected structure; a step of obtaining the gas flow (i) with the highest concentration of gas B among the plurality of gas flows as the product gas; and a step of recycling the gas flow (ii) with the highest concentration of gas A to the gas synthesis reaction step. A method for producing enriched gas, comprising the step of recycling a gas flow (iii) other than (i) and (ii) into the gas supply line.

[0006] Figure 1 is a schematic diagram showing the configuration of a gas enrichment production system in a first embodiment of the present invention. Figure 2 is a schematic diagram showing the configuration of a gas separation membrane module of the present invention. Figure 3 is a schematic diagram showing the configuration of a gas enrichment production system in a second embodiment of the present invention. Figure 4 is a schematic diagram showing the configuration of a gas enrichment production system in yet another embodiment of the present invention. Figure 5 is a schematic diagram showing the configuration of a gas enrichment production system in yet another embodiment of the present invention. Figure 6 is a schematic diagram showing the configuration of a gas enrichment production system in a conventional form corresponding to Patent Document 1.

[0007] The present invention will be described below with reference to Figures 1 to 5, based on its preferred embodiments. The upper and lower limits of numerical values ​​in this specification can be combined in any way. Hereinafter, "upstream" and "downstream" refer to the flow direction of the gas discharged from the gas synthesis reaction unit 20. In this specification, the term "line" includes not only a single pipe but also a combination of multiple pipes, between which any configuration such as a compressor, cooling device, or heating device can be placed.

[0008] The embodiments shown in Figures 1, 3 to 5 relate to a system for producing enriched gas, comprising a gas synthesis reaction unit 20 that reacts a raw material gas containing gas A to produce at least gas B, thereby producing a synthesis gas containing gas A and gas B, and a gas separation unit 7 that separates the enriched gas, which is enriched with gas B, from the synthesis gas. The raw material gas for producing gas B may include other gases such as gas C in addition to gas A. Of the raw material gases for gas B, gas A has a higher permeation rate through the gas separation membrane in the gas separation unit 7 than other gases such as gas C. Figures 1 and 3 illustrate embodiments having two gas separation membrane units 11 and 12. Figures 4 and 5 illustrate embodiments having three gas separation membrane units 11, 12, and 13.

[0009] Each gas separation membrane unit 11 to 13 can be, for example, a module 40 in which a gas separation membrane 30 having selective gas permeability, made of a hollow fiber membrane or the like and housed in a casing 31, can be used as each gas separation membrane unit 11 to 13. Each gas separation membrane unit can be, for example, the gas separation membrane module 40 shown in Figure 2 as is, or multiple modules 40 can be connected in parallel. In the latter case, each of the multiple gas separation membrane modules 40 has a gas inlet 37, a non-permeable gas outlet 38, and a permeable gas outlet 39, and the gas inlet 37, non-permeable gas outlet 38, and permeable gas outlet 39 of each module are shared to form the gas inlet 11a (or 12a, 13a), non-permeable gas outlet 11b (or 12b, 13b), and permeable gas outlet 11c (or 12c, 13c) of the gas separation membrane unit.

[0010] In module 40, the casing 31 has two opposing sides that are open, forming openings 32. When the gas separation membrane 30 consists of a bundle of hollow fiber membranes, the gas separation membrane 30 is housed in the casing 31 such that, in its housed state, each end of the hollow fiber membrane is open near each opening 32 of the casing 31.

[0011] A hollow fiber gas separation membrane module, such as module 40, is obtained by bundling together, for example, about 100 to 1,000,000 (more preferably about 100 to 500,000) hollow fiber membranes of appropriate length, fixing both ends of the hollow fiber membrane bundle with a tube sheet made of thermosetting resin or the like so that at least one end of the hollow fiber remains open, and then housing and installing the resulting hollow fiber membrane bundle and hollow fiber membrane element made of the tube sheet or the like in a container equipped with at least a mixed gas inlet, a permeable gas outlet, and a non-permeable gas outlet, such that the space leading to the inside of the hollow fiber membrane and the space leading to the outside of the hollow fiber membrane are separated.

[0012] When the gas separation membrane 30 is housed in the casing 31, the gas separation membrane 30 is fixed to the inner wall of the casing 31 by tube sheets 33 and 34 at both ends in the Y direction, which is the direction in which the hollow fiber membrane extends. Each opening 32 of the casing 31 is closed by lids 35 and 36. A gas inlet 37 is provided in lid 35. On the other hand, a non-permeable gas outlet 38 is provided in lid 36. The mixed gas to be separated is introduced into the module from the gas inlet 37 of lid 35. Of the introduced gas, the gas that permeates through the gas separation membrane 30 is discharged outside the module from a permeable gas outlet 39 provided in the casing 31. On the other hand, the non-permeable gas that does not permeate through the gas separation membrane 30 is discharged outside the module from a non-permeable gas outlet 38 of lid 36. The above explanation has been given using the separation membrane module shown in Figure 2 as an example, but of course, the present invention can be applied to separation membrane modules with other configurations, for example, to shell-feed type modules.

[0013] The following explanation will be based on Figure 1. Figure 1 shows the configuration of (a) among (a) to (c) described above. In the explanation following Figure 1, when gas B is produced by reacting gas A and gas C in the synthesis reaction section 20, it is preferable that the gas stream (ii) with the highest concentration of gas A has a higher concentration of gas C as well as gas A, compared to the other gas streams (i) and (iii).

[0014] The system 1 shown in Figure 1 has a connecting structure 10 in which a plurality of gas separation membrane units (in this embodiment, a first gas separation membrane unit 11 and a second gas separation membrane unit 12) are connected in series. Each gas separation membrane unit 11 (12) has a gas inlet 11a (12a), a non-permeable gas outlet 11b (12b), and a permeable gas outlet 11c (12c). Series connection means connecting the non-permeable gas outlet or permeable gas outlet of one gas separation membrane unit to the gas inlet of another gas separation membrane unit with piping (also referred to as a "line" in this specification; in the configuration of Figure 1, the first permeable gas outlet line 18). The lines referred to here do not include reflux gas lines. A reflux gas line is a gas line that returns gas discharged downstream from the gas synthesis reaction unit 20, which will be described later, to the upstream.

[0015] In the following, the gas inlets, outlets, gases supplied to each unit, permeate gases discharged from each unit, and non-permeate gases of the first gas separation membrane unit 11 and the second gas separation membrane unit 12 may be described using the same terms as the units, "first" and "second." The same applies to the configuration of the third gas separation membrane unit 13, which will be described later.

[0016] In the connecting structure 10, among the gas inlets 11a, 12a, impermeable gas outlets 11b, 12b, and permeable gas outlets 11c, 12c of each unit, the gas inlets, impermeable gas outlets, and permeable gas outlets that are not involved in the aforementioned series connection become the gas inlets, impermeable gas outlets, and permeable gas outlets of the connecting structure, respectively. For this reason, the connecting structure 10 has one gas inlet 10a, and at least one permeable gas outlet 10c and at least three impermeable gas outlets 10b in total. In the configuration shown in Figure 1, the first gas inlet 11a corresponds to the gas inlet 10a of the connecting structure 10, the second permeable gas outlet 12c corresponds to the permeable gas outlet 10c of the connecting structure 10, and the first impermeable gas outlet 11b and the second impermeable gas outlet 12b correspond to the impermeable gas outlets 10b of the gas in the connecting structure 10.

[0017] As shown in Figures 1 and 3 to 5, the enriched gas production systems (hereinafter sometimes simply referred to as "systems") 1 to 4 of the present invention comprise a gas synthesis reaction unit 20 that reacts gas A with a raw material gas preferably containing gas C to produce at least gas B, and generates a synthesis gas comprising gas A, gas B, and preferably gas C. The system 1 has a gas supply line 26 connecting a synthesis gas outlet 20a of the gas synthesis reaction unit 20 and a gas inlet 10a of the connecting structure 10, and supplies the synthesis gas produced from the gas synthesis reaction unit 20 to the connecting structure 10. In addition, for example, another gas line (not shown, excluding the gas separation unit reflux lines 16 and 17) may be further joined to the gas supply line 26, so that a mixed gas obtained by mixing another gas from said another gas line into the synthesis gas is introduced into the connecting structure 10. Among the gas flow rate supplied to the connecting structure 10 (excluding the flow rate of reflux gas from the gas separation unit reflux line), the proportion of the flow rate of the synthesis gas is preferably 10% or more, more preferably 20% or more, still more preferably 30% or more, further preferably 40% or more, particularly preferably 50% or more, and even more preferably 60% or more. In the present specification, the unit of flow rate is Nm ３ / hr (standard conditions are based on 0°C and 1 atmosphere).

[0018] Gas A is a raw material gas for producing gas B. Gas B is a gas obtained by a reaction involving gas A, and is preferably a gas obtained by reacting gas C in the raw material gas with gas A. When there are a plurality of raw material gases for gas B, gas A in the raw material gas supplied to the gas synthesis reaction unit 20 is the gas having the highest permeation rate among the gas separation membranes constituting each gas separation membrane unit in the separation unit. For example, when any of the gas separation membrane units has a plurality of gas separation membrane modules, the permeation rate of gas A among the raw material gases for gas B is the highest in the gas separation membrane constituting any of the gas separation membrane modules. The level of the permeation rate referred to herein is determined by the permeation rate of each gas through the separation membrane at 30°C.

[0019] Examples of the gas production reaction performed in the gas synthesis reaction unit 20 include those in which both the raw material components and the product components contain gas components, for example, CO ２and H ２ From CH ４ Examples include methanation reactions that produce phosphate (CO2 + 4H2 → CH4 + 2H2O). These reactions may be catalyzed by microorganisms, enzymes, or chemical catalysts, and may also require the addition of energy such as heat or light.

[0020] Among the gas generation reactions, the gas generation reaction carried out in the gas synthesis reaction section 20 is CO ２ and H ２ From CH ４ It is preferable that the methanation reaction produces CH. In the system of the present invention, gas B is CH ４ (Methane), and gas A is H ２ And gas C is CO ２ It may also be the case that gas B is CH ４ (Methane), and gas A is CO ２ And gas C is H ２ It is also possible, but if gas B is CH ４ (Methane), and gas A is H ２ And gas C is CO ２ This is because it is excellent in that it can achieve both a high recovery rate and high purity of methane, which is product gas B, and reduces the methane content in the gas returned to the gas synthesis reaction unit 20 according to the present invention, and H ２ The content of H ２ and CO ２Increasing the content of is particularly preferable because it can effectively suppress the decrease in methanation reaction efficiency. When the methanation reaction is carried out in the gas synthesis reaction section 20, microorganisms such as methanogenic bacteria may be used, or a methanation catalyst such as a metal catalyst may be used. Examples of methanation catalysts include Ni catalysts and Ru catalysts. These catalysts may be supported on a carrier, and the carrier is preferably a porous carrier, for example. Specifically, examples include catalysts on which active components such as Rh / Mn / Al, Rh / Al, Ni / Al, Pd / Al, Pt / Al, and Ni are supported on a carrier such as alumina, or catalysts on which Ni / Ce and Ni / Zr active components are supported on a carrier such as ceria or zirconia. When the gas production reaction carried out in the gas synthesis reaction section 20 is a methanation reaction, H ２ Source and CO ２ The source is not particularly limited, and carbon dioxide and hydrogen produced by gasifying fossil fuels such as coal and oil may be used. Alternatively, CO ２ As a source, carbon dioxide recovered from exhaust gases of thermal power plants and steel mills can also be used. On the other hand, H ２ As a power source, hydrogen can also be produced by electrolyzing water using surplus renewable energy.

[0021] For example, in the methanation reaction, water is produced as a by-product, and it is desirable to reduce the amount of water in the synthesis gas before it is introduced into the connecting structure in order to reduce the impact on separation performance. For this reason, as shown in the configuration of Figure 5 described later, it is desirable to provide a compression means 21, a cooling device 44, a drain discharge device 45, and a heating device 46 in the gas supply line 26 between the gas synthesis reaction section 20 and the first gas separation membrane unit 11 in the configuration of Figure 1, to compress and cool the synthesis gas in the shell of the gas synthesis reaction section 20, remove water at the drain discharge section, and then reheat it. In this case, the compression means 14 may not be provided in the gas separation section reflux line 17, and the non-permeable gas from the second non-permeable gas outlet 12b may be refluxed to the suction side of the compression means 21.

[0022] The concentration of gas B in the synthesis gas supplied from the gas synthesis reaction unit 20 to the connecting structure 10 (synthesis gas before mixing with reflux gas (ii)) is preferably 50 mol% or more from the viewpoint of easily achieving both the purity and recovery rate of gas B in the resulting product gas, and more preferably 70 mol% to 90 mol, and particularly preferably 75 mol% to 90 mol, as the effects of applying the present invention become even clearer. The concentration of gas A in the synthesis gas supplied from the gas synthesis reaction unit 20 to the connecting structure 10 is preferably 40 mol% or less from the viewpoint of easily achieving both the purity and recovery rate of gas B in the resulting product gas, and more preferably 5 mol% to 40 mol, and particularly preferably 8 mol% to 20 mol, as the effects of applying the present invention become even clearer. The concentration of gas C in the synthesis gas is preferably 0.1 mol% to 15 mol, and more preferably 1 mol% to 10 mol. If the synthesis gas is a gas produced by methanation, then the CO in the synthesis gas ２ : H ２ The molar ratio is preferably 100:100 to 700, and more preferably 100:200 to 500. ４ : H ２ The molar ratio is preferably 100 to 1000:100, and more preferably 300 to 1000:100. In this specification, the product gas refers to the gas flow of (i). When the gas supplied to the connecting structure 10 is a mixed gas containing the above-mentioned synthesis gas, the preferred concentrations of gas B and gases A and C in the mixed gas are the same concentrations as those for gas B and gases A and C in the synthesis gas mentioned above.

[0023] In this embodiment and the embodiments described later, the gas separation membrane unit and gas separation membrane module used in the connected structure have a permeation rate P' of gas A. Ａ , permeation rate P' of gas B ＢHowever, the relationship is as shown in (1) below. Furthermore, when gas B is obtained by reacting multiple types of raw material gases such as gas A and C, it is preferable that each raw material gas (e.g., A and C) has a higher permeation rate than gas B in each gas separation membrane module that constitutes each gas separation membrane unit (see equations (1) and (2) below). Here, the permeation rate is the permeation rate at the temperature of the gas separation membrane in which gas separation is performed, and the temperature of the gas separation membrane can be said to be, for example, 30°C. P' Ａ > P' Ｂ (1) P' Ｃ > P' Ｂ (2) P' is the permeation rate (permeation volume per unit membrane area, unit time, and unit partial pressure difference relative to the membrane), and its unit is ×10 －５ cm ３ (STP) / cm ２ It is sec・cmHg.

[0024] Further explanation will be given based on Figure 1. Multiple gas flows with different compositions are obtained from the permeate gas outlet 10c (second permeate gas outlet 12c in the configuration of Figure 1) and the impermeable gas outlet 10b (first impermeable gas outlet 11b, second impermeable gas outlet 12b in the configuration of Figure 1) of the connecting structure 10. In this specification, the component concentrations in the gas flows (i) to (iii) below are determined by comparing the composition of the gas flows at the time they are discharged from outlets 10b (11b), 10b (12b), and 10c (12c).

[0025] The system of this embodiment has a product gas extraction line 15 connected to the first impermeable gas outlet 11b as a means of obtaining the gas stream (i) with the highest concentration of gas B among the plurality of gas streams as the product gas. It also has a synthesis reaction reflux line 24 connecting the second permeable gas outlet 12c and the gas inlet 20b of the gas synthesis reaction unit 20 as a means of recycling the gas stream (ii) with the highest concentration of gas A to the gas synthesis reaction unit 20. It also has a gas separation reflux line 17 that recycles the gas stream (iii) other than (i) and (ii) to the gas supply line 26. The gas separation reflux line 17 connects the second impermeable gas outlet 12b and the gas supply line 26. In this specification, "line A is connected to line B" includes both cases where line A and line B are separate components and cases where they are a single component. In the example shown in Figure 1, the gas separation reflux line 17 connects the gas supply line 26 to the position between the gas synthesis reaction section 20 and the connecting structure 10.

[0026] By configuring the system as described above, the second permeate gas, which is further enriched with gas A (preferably gases A and C, hereinafter simply referred to as "gas A, etc.") compared to the first permeate gas and has a lower concentration of product gas B, is refluxed to the gas synthesis reaction unit 20. As a result, a gas stream with a higher concentration of gas A, etc. and a lower product gas B content can be supplied to the gas synthesis reaction unit 20 compared to the conventional method. This makes it possible to lower the partial pressure of gas B in the reaction vessel in the gas synthesis reaction unit 20, while increasing the partial pressure of gas A, etc., thereby increasing the efficiency of the reaction that produces gas B from gas A, etc., shortening the processing time, and effectively increasing the amount of gas B produced. Furthermore, by performing gas separation in two or more stages, excellent separation performance can be achieved, and both the purity and recovery rate of the product gas can be improved.

[0027] As shown in Figure 1, the gas separation reflux line 17, the first permeate gas discharge line 18, and the synthesis reaction reflux line 24 are each provided with flow rate control valves 79, 84, and 87, respectively. In addition, truncation lines 80, 82, and 86 may be provided upstream of the gas separation reflux line 17, the first permeate gas discharge line 18, and the synthesis reaction reflux line 24, respectively. The truncation lines 80, 82, and 86 each have flow rate control valves 81, 83, and 85, respectively. These flow rate control valves allow some of the gas to be discharged through the respective truncation lines 80, 82, and 86 if a large amount of gas flows to each unit relative to the membrane area of ​​the gas separation membrane. With such a mechanism, even if the flow rate of the synthesis gas fluctuates during operation, the purity can be stabilized without stopping the operation to increase or decrease the membrane area. In this specification, the statement "line B is provided to line A" includes both cases where line A and line B are the same component and cases where they are different components.

[0028] As described above, if a large amount of synthesis gas flows relative to the membrane area, and the flow rate is adjusted using a truncation line, for example, if a truncation line 86 is provided on the line 24 that returns to methanation, in Comparative Example 1, because the proportion of gas B in the gas refluxed to the synthesis reaction section 20 in line 24 is large, a large amount of gas B is lost due to truncation, and the recovery rate of gas B as product gas decreases. On the other hand, in the present invention, since the concentration of gas B in line 24 is relatively low, the decrease in the recovery rate can be suppressed even when the flow rate is adjusted using a truncation line.

[0029] In the example shown in Figure 1, there is a detection unit 42 that detects the amount or composition of gas flow (ii) in the reflux line 24 of the synthesis reaction unit, an adjustment unit 41A that adjusts the amount of gas A supplied to the gas synthesis reaction unit 20 based on the detection result of the detection unit 42, and an adjustment unit 41C that adjusts the amount of gas C supplied to the gas synthesis reaction unit 20. A flow rate detection device or a gas component concentration sensor can be used as the detection unit 42. For the adjustment units 41A and 41C, an opening control valve, a blower with rotational speed control, etc., are preferably used. For example, a control means 135, which is composed of a computer equipped with a processing unit and a memory device, is electrically connected to the detection unit 42, the adjustment units 41A and 41C. The control means 135 adjusts the amount of gas A and / or gas C flowing into the reaction vessel based on the amount or composition of gas flow (ii) so that the concentrations of gas A and / or gas C in the gas phase in the reaction vessel of the gas synthesis reaction unit 20 are in a constant ratio. With this configuration, even if the amount or composition of the gas flow (ii) fluctuates, the amount and composition of gas supplied from the gas synthesis reaction unit 20 to the connecting structure 10 via the gas supply line 26 can be kept constant. As a result, this system 1 can stably maintain a state in which gas B can be recovered with high purity and high recovery rate. Note that in Figure 3 and later, the control means 135, detection unit 42, and adjustment units 41A and 41C are omitted from the description, but the same configuration can be adopted in the forms of Figures 3 and 4. Also, as shown in Figure 1, there are usually multiple supply ports for the raw material gas of gas B to the synthesis reaction unit 20 when there are multiple types of raw material gases. ２ and CO ２ ) If this is the case, two types of gas (H) return from the recycling line 24 ２ and CO ２ The ratio of gases A and C does not necessarily maintain the reaction ratio in the synthesis reaction section. Gases A and C flow into their respective synthesis reaction section 20 via lines (for example, H ２ Line, CO ２ The system has a line, and based on the amount or composition of the gas flow (ii) for each of the two types of gas, the detection unit 42 recognizes the excess or deficiency and the ratio of the amounts of two or more gases (for example, H) that flow into the synthesis reaction unit 20. ２ :CO ２It is preferable to adjust the ratio of these factors to remain constant.

[0030] In the configuration shown in Figure 1, the compression means 14 is interposed in the gas separation reflux line 17. In this configuration, the reflux rate (the ratio of the gas flow (iii) to the synthesis gas flow rate F0 supplied to the connecting structure 10) (F3 / F0) tends to be relatively high, but by using the compression means 14, gas separation can be performed efficiently in terms of time. In this specification, a compressor can be used as the compression means 14.

[0031] Next, an embodiment will be further described based on Figure 3 (the embodiment of (b) among (a) to (c) above). The connecting structure 10A in the embodiment of Figure 3 is the same as the embodiment of Figure 1 in that the first gas separation membrane unit 11 and the second gas separation membrane unit 12 are connected in series. However, unlike the embodiment of Figure 1, the connection between the two units in series in the connecting structure 10A is not through the first permeable gas outlet 11c, but through the first non-permeable gas outlet 11b and the second gas inlet 12a. As a result, multiple gas flows with different compositions can be obtained from the permeable gas outlet 10c (first permeable gas outlet 11c and second permeable gas outlet 12c in the embodiment of Figure 3) and the non-permeable gas outlet 10b (second non-permeable gas outlet 12b in the embodiment of Figure 3) of the connecting structure 10A.

[0032] The system 2 in the configuration shown in Figure 3 has a product gas extraction line 15 connected to the second impermeable gas outlet 12b as a means of obtaining the gas stream (i) with the highest concentration of gas B among the multiple gas streams as the product gas. It also has a synthesis reaction reflux line 24 connecting the first permeate gas outlet 11c and the gas inlet 20b of the gas synthesis reaction unit 20 as a means of recycling the gas stream (ii) with the highest concentration of gas A, etc., to the gas synthesis reaction unit 20. It also has a gas separation reflux line 17 that recycles the gas stream (iii) other than (i) and (ii) to the gas supply line 26. In the configuration shown in Figure 3, the gas separation reflux line 17 connects the second permeate gas outlet 12c to a position in the gas supply line 26 between the gas synthesis reaction unit 20 and the connecting structure 10. In the configuration shown in Figure 3, the separation reflux line 17 can also be provided with a cut-off line 90 and control valves 88, 89, similar to the separation reflux line 17 in Figure 1.

[0033] As described above, the concentration of gas A and other gases in the first permeate gas can be increased, and a gas flow with a higher concentration of gas A and other gases and a lower content of product gas B can be supplied to the gas synthesis reaction unit 20 compared to the conventional method. Therefore, in this embodiment as well, the partial pressure of gas B in the reaction vessel in the gas synthesis reaction unit 20 can be reduced, and the partial pressure of gas A and other gases can be increased, thereby increasing the reaction efficiency and shortening the reaction time. In addition, since the second permeate gas is recycled to the connecting structure 10 in the gas separation reflux line 17, the recovery rate of product gas B can be improved or its decrease can be suppressed. The second non-permeate gas is easier to improve the purity of the product gas compared to the first non-permeate gas. Therefore, in this embodiment as well, it is possible to balance the purity of the product gas with the recovery rate. Furthermore, this embodiment has the advantage of making it easier to reduce the reflux rate of the second permeate gas and to balance the membrane area with the compression power.

[0034] The configuration shown in Figure 4 will be described further. The configuration in Figure 4 corresponds to configuration (c) of the above (a) to (c). In the configuration of Figure 4, the connecting structure 10B has a first gas separation membrane unit 11, a second gas separation membrane unit 12, and a third gas separation membrane unit 13. In the configuration of Figure 4, the first gas separation membrane unit 11 and the second gas separation membrane unit 12 are connected in series. The first gas separation membrane unit 11 and the second gas separation membrane unit 12 are connected by a first non-permeable gas outlet 11b and a second gas inlet 12a, which are connected by a first non-permeable gas discharge line 28. The first gas separation membrane unit 11 and the third gas separation membrane unit 13 are also connected in series. The first gas separation membrane unit 11 and the third gas separation membrane unit 13 are connected by a first permeable gas outlet 11c and a third gas inlet 13a, which are connected by a first permeable gas discharge line 18.

[0035] Multiple gas flows with different compositions can be obtained from the permeate gas outlets 10c (second permeate gas outlet 12c and third permeate gas outlet 13c in the configuration of Figure 4) and non-permeate gas outlets 10b (second non-permeate gas outlet 12b and third non-permeate gas outlet 13b in the configuration of Figure 4) of the connecting structure 10B. The system of this embodiment has a product gas extraction line 15 connected to the second non-permeate gas outlet 12b as a means of obtaining the gas flow (i) with the highest concentration of gas B among the multiple gas flows as the product gas. It also has a synthesis reaction reflux line 24 connecting the third permeate gas outlet 13c and the gas inlet 20b of the gas synthesis reaction unit 20 as a means of recycling the gas flow (ii) with the highest concentration of gas A, etc., to the gas synthesis reaction unit 20. It also has gas separation reflux lines 16 and 17 that recycle gas flows (iii) other than (i) and (ii) to the gas supply line 26. The gas separation reflux line 16 connects the third impermeable gas outlet 13b to a position in the gas supply line 26 between the gas synthesis reaction unit 20 and the connecting structure 10. The gas separation reflux line 17 connects the second impermeable gas outlet 12c to a position in the gas supply line 26 between the gas synthesis reaction unit 20 and the connecting structure 10. In the configuration of Figure 4, a compression means 21 is interposed in the gas supply line 26 between the gas synthesis reaction unit 20 and the gas inlet 10a of the connecting structure 10, and the gas separation reflux lines 16 and 17 are connected to the gas supply line 26 at the suction side of the compression means 21. In the configuration of Figure 4, lines 16; 17; 18; 24 can also be provided with truncation lines 80; 90; 82; 86 and control valves 74, 81; 88, 89; 83, 84; 85, 87, similar to the separation reflux line 17 in Figure 1.

[0036] As described above, a third permeate gas, which has a higher concentration of gas A and other gases and a lower concentration of product gas B compared to the first permeate gas, can be supplied to the gas synthesis reaction unit 20. Therefore, in this embodiment as well, the partial pressure of gas B in the reaction vessel in the gas synthesis reaction unit 20 can be reduced, and the partial pressure of gas A and other gases can be increased, thereby increasing the efficiency of the reaction that produces gas B in the gas synthesis reaction unit 20. This effectively increases the production efficiency of gas B, shortens the processing time, and allows for a smaller reaction vessel. Furthermore, since the second permeate gas and the third non-permeate gas are refluxed to the connecting structure 10B via the gas separation reflux lines 16, 17 and the gas supply line 26, the recovery rate of product gas B can be improved or suppressed. In addition, since the second non-permeate gas, which is enriched with gas B compared to the first non-permeate gas, is used as the product gas, it is easier to improve the purity of the product gas. For this reason, in the present invention, it is possible to balance the purity and recovery rate of the product gas.

[0037] The configurations in Figures 1, 3, and 4 can be modified by adding or changing components as appropriate. For example, the configuration in Figure 4 may be modified to the configuration in Figure 5. For example, in the configuration in Figure 5, a cooling means 44 located downstream of the compression means 21, a drain discharge device 45 located downstream of the cooling means 44, and a heating device 46 located downstream of the drain discharge device 45 are interposed between the gas synthesis reaction section 20 in the gas supply line 26 and the connecting structure 10C. Similarly, in the first permeate gas discharge line 18, a compression means 22, a cooling means 54 located downstream of it, a drain discharge device 55 located downstream of it, and a heating device 56 located downstream of it are interposed. Heat exchangers can be used as the cooling means and heating means. The drain discharge device is a device that removes moisture flowing at the bottom of the pipe while maintaining the airtightness of the pipe, and conventionally known devices can be used. For example, a drain pan and drain port, a float-type drain discharge valve, a solenoid valve type drain discharge device, etc. can be used. According to the system in Figure 5, moisture and high-boiling-point substances contained in the synthesis gas or originating from the compression means 21 and 22 are liquefied by the cooling means 44 and 54. Since the liquefied substances remain in the piping, they are discharged out of the system by the drain discharge devices 45 and 55. To prevent the gas from being re-condensed and reducing the gas separation performance, the gas from which impurities have been removed by the drain discharge devices 45 and 55 is heated by the heating devices 46 and 56 and supplied to the first gas separation membrane unit 11 and the third gas separation membrane unit 13, respectively. Here, high-boiling-point substances refer to substances that are in a state of condensation under the supply gas pressure and temperature conditions introduced into the separation membrane. According to the above configuration, the amount of moisture mixed into the second non-permeable gas, which is the product gas, can be reduced, and the purity of the extracted product gas can be increased. In the configurations of Figures 1 and 3, the compression means, cooling means, drain discharge device, heating device, etc. may be arranged in the gas supply line 26 in the same manner as in Figure 5.

[0038] In the case of (a), the reflux rate (F3 / F0 × 100 (%)), which is the ratio of the flow rate F3 of gas flow (iii) to the flow rate F0 of synthesis gas supplied to the structural assembly (flow rate before merging with gas flow (iii)), is preferably 300% or less, more preferably 200% or less, even more preferably 150% or less, and particularly preferably 100% or less. It is also more preferably 10% or more, and particularly preferably 20% or more. In the case of (a), the reflux rate (F3 / F0 × 100 (%)) is preferably 80% or more and 300% or less, and more preferably 100% or more and 250% or less. In the case of (b), the reflux rate (F3 / F0 × 100 (%)) is preferably 10% or more and 150% or less, and more preferably 10% or more and 100% or less. In the case of form (c), the reflux rate (F3 / F0 × 100 (%)) is preferably 50% or more and 200% or less, and more preferably 50% or more and 150% or less.

[0039] The reflux rate (F2 / F0 × 100 (%)), which is the ratio of the flow rate F2 of gas flow (ii) to the flow rate F0 of synthesis gas supplied to the structural assembly (flow rate before joining with gas flow (iii)), is preferably 80% or less, more preferably 60% or less, even more preferably 40% or less, and particularly preferably 30% or less, from the viewpoint of balancing separation performance and reaction efficiency. It is also more preferably 5% or more, and particularly preferably 10% or more.

[0040] In the case of (a), the reflux rate (F3 / F0 × 100 (%)), which is the ratio of the flow rate F3 of gas flow (iii) to the flow rate F0 of synthesis gas supplied to the structural assembly (flow rate before merging with gas flow (iii)), is preferably 300% or less, more preferably 200% or less, even more preferably 150% or less, and particularly preferably 100% or less. It is also more preferably 10% or more, and particularly preferably 20% or more. In the case of (a), the reflux rate (F3 / F0 × 100 (%)) is preferably 80% or more and 300% or less, and more preferably 100% or more and 250% or less. In the case of (b), the reflux rate (F3 / F0 × 100 (%)) is preferably 10% or more and 150% or less, and more preferably 10% or more and 100% or less. In the case of form (c), the reflux rate (F3 / F0 × 100 (%)) is preferably 50% to 200%, and more preferably 50% to 150%. The unit of flow rate is Nm ３ The value is / hr. In this disclosure, the concentration of gas B in the product gas stream (i) is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, and particularly preferably 99.5 mol% or more. The concentration of gas A is preferably 5000 volume ppm or less, and more preferably 3000 volume ppm or less. The concentration of gas C is preferably 5000 volume ppm or less, more preferably 3000 volume ppm or less, and particularly preferably 1000 ppm or less. Furthermore, if the product gas is to be liquefied in the next process, it is preferable to set the concentration of gas C to 50 ppm or less to prevent blockage of the line.

[0041] In this disclosure, the concentration of gas B in the gas stream (ii) refluxed to the gas synthesis reaction section 20 is preferably 60 mol% or less, and more preferably 30 mol% or less. The concentration of gas A in the gas stream (ii) refluxed to the gas synthesis reaction section 20 is preferably 40 mol% or more, and more preferably 55 mol% or more. The concentration of gas C is preferably 5 mol% or more, and more preferably 9 mol% or more. When the synthesis gas is a gas produced by methanation, CO in the gas stream (ii) ２ : H ２ The molar ratio is preferably 100:300 to 600, and more preferably 100:350 to 550.

[0042] In this disclosure, the concentration of gas B in the gas flow (iii) returned to the gas supply line 26 is preferably 40 to 99 mol%, and more preferably 50 to 99 mol%. The concentration of gas A in the gas flow (iii) returned to the gas supply line 26 is preferably 0.1 to 55 mol%, and more preferably 0.1 to 45 mol%. The concentration of gas C in the gas flow (iii) returned to the gas supply line 26 is preferably 0.1 to 25 mol%, and more preferably 0.1 to 15 mol%. In particular, in the case of embodiment (a), the concentration of gas B in the gas flow (iii) is preferably 40 to 70 mol%, and more preferably 50 to 70 mol%. The concentration of gas A is preferably 15 to 55 mol%, and more preferably 20 to 45 mol%. The concentration of gas C is preferably 2 to 25 mol%, and more preferably 4 to 18 mol%. In particular, in the case of embodiment (b), the concentration of gas B in the gas flow (iii) is preferably 65 to 99 mol%, and more preferably 70 to 90 mol%. The concentration of gas A is preferably 1 to 30 mol%, and more preferably 2 to 25 mol%. The concentration of gas C is preferably 1 to 15 mol%, and more preferably 2 to 12 mol%. In particular, in the case of embodiment (c), the concentration of gas B in the gas flow (iii) is preferably 70 to 95 mol%, and more preferably 70 to 90 mol%. The concentration of gas A is preferably 5 to 30 mol%, and more preferably 5 to 25 mol%. The concentration of gas C is preferably 1 to 15 mol%, and more preferably 2 to 10 mol%. In the case of (c), the concentrations of gas A and gas B in gas flow (iii) are the average values ​​obtained by multiplying the concentrations of gas A and gas B in reflux gas in lines 16 and 17 by the flow rate ratio of these reflux gases. If the synthesis gas is a gas produced by methanation, the CO in gas flow (iii) ２ : H ２The molar ratio of gas A to gas B is preferably 100:100 to 500, and more preferably 100:300 to 400. The concentrations of gas A and gas B referred to here are the average values ​​obtained by multiplying the flow rates of two or more reflux gas flows by their respective flow rates.

[0043] The relationships between high and low permeation rates or high and low separation selectivity described below are acceptable at 30°C, but it is more preferable that they are also acceptable at the actual operating temperature of the gas separation membrane unit. Furthermore, the values ​​and ratios of permeation rates or separation selectivity described below are acceptable at 30°C, but it is more preferable that they are also acceptable at the actual operating temperature of the gas separation membrane unit.

[0044] In embodiment (a) of the present invention, the permeation rate P' for the gas separation membrane constituting the first gas separation membrane unit is １Ａ and P' １Ｂ Preferably, each of these values ​​is equal to or greater than that of the gas separation membrane constituting the second gas separation membrane unit, and the permeation rate P' １Ａ , P' １Ｂ and P' １Ｃ It is more preferable that all of them are equal to or better than the gas separation membrane constituting the second gas separation membrane unit (i.e., relation 1: P' １Ａ ≧P' ２Ａ And P' １B ≧P' ２Ａ It is preferable that this is the case, and furthermore, in addition to relation 1, relation 2: P' １C ≧P' ２C It is preferable that this is the case.) Furthermore, in the embodiment of (a), the permeation rate P' for the gas separation membrane constituting the first gas separation membrane unit is １Ａ and P' １Ｂ It is preferable that each of these values ​​exceeds that of the gas separation membrane constituting the second gas separation membrane unit (i.e., the "≧" in relation 1 becomes ">"), and the permeation rate P' １Ａ , P' １Ｂ and P' １Ｃ It is more preferable that all of these values ​​exceed those of the gas separation membranes constituting the second gas separation membrane unit (i.e., the "≧" in relations 1 and 2 becomes ">").

[0045] In the embodiment (b) of the present invention, it is preferable that the permeation rate P' of the gas separation membranes constituting the first gas separation membrane unit １Ａ and P' １Ｂ are each equal to or less than that of the gas separation membranes constituting the second gas separation membrane unit, and it is more preferable that all of the permeation rate P' １Ａ , P' １Ｂ and P' １Ｃ are equal to or less than that of the gas separation membranes constituting the second gas separation membrane unit. Furthermore, in the embodiment (b), it is preferable that the permeation rate P' of the gas separation membranes constituting the first gas separation membrane unit １Ａ and P' １Ｂ are each lower than that of the gas separation membranes constituting the second gas separation membrane unit, and it is more preferable that all of the permeation rate P' １Ａ , P' １Ｂ and P' １Ｃ are each lower than that of the gas separation membranes constituting the second gas separation membrane unit.

[0046] In the present invention, when using the connected structure 10B of (c), it is preferable that the permeation rate P' of the gas separation membranes constituting the third gas separation membrane unit ３Ａ and P' ３Ｂ are equal to or less than that of the gas separation membranes constituting the second gas separation membrane unit, and it is more preferable that all of the permeation rate P' ３Ａ , P' ３Ｂ and P' ３Ｃ are equal to or less than that of the gas separation membranes constituting the second gas separation membrane unit. Furthermore, in the embodiment (c), it is preferable that the permeation rate P' of the gas separation membranes constituting the third gas separation membrane unit ３Ａ and P' ３Ｂ is lower than that of the gas separation membranes constituting the second gas separation membrane unit, and it is more preferable that all of the permeation rate P' ３Ａ , P' ３Ｂ and P' ３Ｃ are lower than that of the gas separation membranes constituting the second gas separation membrane unit.

[0047] In the present invention, when using the connected structure 10B of (c), the permeation rate P' of the gas separation membranes constituting the first gas separation membrane unit １Ａ and P' １Ｂis preferably equal to or less than the gas separation membrane constituting the second gas separation membrane unit, and the permeation rate P' ３Ａ , P' ３Ｂ and P' ３Ｃ it is more preferable that all are equal to or less than the gas separation membrane constituting the second gas separation membrane unit. Further, in the embodiment of (c), the permeation rate P' of the gas separation membrane constituting the first gas separation membrane unit １Ａ and P' １Ｂ is preferably lower than that of the gas separation membrane constituting the second gas separation membrane unit, respectively, and the permeation rate P' １Ａ , P' １Ｂ and P' １Ｃ it is more preferable that all are lower than the gas separation membrane constituting the second gas separation membrane unit.

[0048] In the present invention, the permeation rate of gas A (P' Ａ (P' １Ａ～ P' ３Ａ )) is preferably 5×10 －５ cm ３ (STP) / cm ２ ·sec·cmHg or more, more preferably 10×10 －５ cm ３ (STP) / cm ２ ·sec·cmHg or more, still more preferably 15×10 －５ cm ３ (STP) / cm ２ ·sec·cmHg or more. Also, the permeation rate (P' Ａ ) may be 200×10 －５ cm ３ (STP) / cm ２ ·sec·cmHg or less, may be 150×10 －５ cm ３ (STP) / cm ２ ·sec·cmHg or less, and may be 100×10 －５ cm ３ (STP) / cm ２ ·sec·cmHg or less. The permeation rate of gas B (P' Ｂ (P'１Ｂ～ P' ３Ｂ )) is 10 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be 5 × 10⁻¹⁰ sec·cmHg or less. －５ cm ３ (STP) / cm ２ It is more preferable that the value be 3 × 10⁻¹⁰ or less, and sec·cmHg or less. －５ cm ３ (STP) / cm ２ It is even more preferable that the speed (P') is less than or equal to sec·cmHg. Ｂ ) is 0.01 × 10 －５ cm ３ (STP) / cm ２ - It may be sec·cmHg or higher, and 0.05 × 10 －５ cm ３ (STP) / cm ２ - It may be sec·cmHg or higher, and 0.1 × 10 －５ cm ３ (STP) / cm ２ - It may be sec·cmHg or higher. The permeation rate (P') of the gas separation membrane constituting each gas separation membrane unit. Ｃ (P' １Ｃ～ P' ３Ｃ )) is 3 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or higher, and 5 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the amount be sec·cmHg or higher, and 8 × 10 －５ cm ３ (STP) / cm ２ It is even more preferable that the speed (P') is 2000-10 Ｃ ) is 100 x 10 －５ cm ３ (STP) / cm ２ - It may be sec·cmHg or less, and 50 × 10 －５ cm ３ (STP) / cm ２ - It may be sec·cmHg or less, and 30 × 10 －５ cm３ (STP) / cm ２ - It may be sec・cmHg or less.

[0049] In the present invention, P' １Ａ P' ２Ａ If it exceeds P' １Ａ is 15 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or higher, and 25 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the amount be sec·cmHg or higher, and 35 × 10 －５ cm ３ (STP) / cm ２ It is even more preferable that the value be sec·cmHg or higher. Also, P' １Ｂ is 5 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or less, and 3 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the value be 2 × 10⁻¹⁰ sec·cmHg or less. －５ cm ３ (STP) / cm ２ It is even more preferable that it be sec·cmHg or less. Furthermore, P' １Ｃ is 10 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or higher, and 15 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the amount be sec·cmHg or higher, and 20 × 10 －５ cm ３ (STP) / cm ２ It is even more preferable that the level be sec·cmHg or higher.

[0050] In the present invention, P' １Ａ P' ２Ａ If it falls below P' ２Ａ is 15 x 10 －５ cm ３(STP) / cm ２ It is preferable that the value be sec·cmHg or higher, and 25 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the amount be sec·cmHg or higher, and 35 × 10 －５ cm ３ (STP) / cm ２ It is even more preferable that the transmission rate (P') is 2000-10 ２Ｂ ) is 5 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or less, and 3 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the value be 2 × 10⁻¹⁰ sec·cmHg or less. －５ cm ３ (STP) / cm ２ It is even more preferable that it be sec·cmHg or less. Furthermore, P' ２Ｃ is 10 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or higher, and 15 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the amount be sec·cmHg or higher, and 20 × 10 －５ cm ３ (STP) / cm ２ It is even more preferable that the level be sec·cmHg or higher.

[0051] In the present invention, P' ３Ａ P' ２Ａ If it falls below P' ３Ａ is 15 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or higher, and 25 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the amount be sec·cmHg or higher, and 35 × 10 －５ cm ３ (STP) / cm２ It is even more preferable that the value be sec·cmHgg or higher. Also, P' ３Ｂ is 5 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or less, and 3 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the value be 2 × 10⁻¹⁰ sec·cmHg or less. －５ cm ３ (STP) / cm ２ It is even more preferable that it be sec·cmHg or less. Furthermore, P' ３Ｃ is 10 x 10 －５ cm ３ (STP) / cm ２ It is preferable that the value be sec·cmHg or higher, and 15 × 10 －５ cm ３ (STP) / cm ２ It is more preferable that the amount be sec·cmHg or higher, and 20 × 10 －５ cm ３ (STP) / cm ２ It is even more preferable that the level be sec·cmHg or higher.

[0052] In embodiment (a) of the present invention, the separation selectivity of gas A to gas B in the first gas separation membrane unit is equal to or less than the separation selectivity of the second gas separation membrane unit ((P' １Ａ / P' １Ｂ )≦(P' ２Ａ / P' ２Ｂ It is preferable that relation 3) is met, and the separation selectivity of all raw material gases (e.g., gases A and C) is equal to or less than the separation selectivity of the second gas separation membrane unit (for example, relation 4 (P') in addition to relation 3 above). １Ｃ / P' １Ｂ )≦(P' ２Ｃ / P' ２Ｂ It is more preferable that the separation selectivity of gas A with respect to gas B in the first gas separation membrane unit is such that the separation selectivity of the second gas separation membrane unit (P' ２Ａ / P' ２ＢIt is preferable that the ratio is less than (i.e., the "≦" in relation 3 above becomes "<"), and it is preferable that the separation selectivity of each raw material gas (e.g., gas A, C) of gas B in the first gas separation membrane unit is lower than that of the second gas separation membrane unit (for example, in addition to relation 3 above, the ratio is also less than in relation 4). With this configuration, it is possible to further improve the content of raw material gases and further decrease the content of gas B in the gas flow (ii), and as a result, the reaction efficiency of the gas synthesis reaction unit 20 can be further improved. In addition, it is possible to further improve or suppress the decrease in the recovery rate of gas B, and this can be achieved in compatibility with high purity.

[0053] In embodiment (b) of the present invention, the ratio (P') of the separation selectivity of gas A to gas B in the first gas separation membrane unit to the separation selectivity of the second gas separation membrane unit is １Ａ / P' １Ｂ Preferably, the separation selectivity of all raw material gases for gas B (e.g., (P')) is equal to or better than that of the second gas separation membrane unit, and the separation selectivity of all raw material gases for gas B is (e.g., (P') １Ａ / P' １Ｂ ), (P' １Ｃ / P' １Ｂ )) is more preferably equal to or better than that of the second gas separation membrane unit. Furthermore, in the embodiment of (b), it is preferable that the separation selectivity of gas A relative to gas B in the first gas separation membrane unit is greater than that of the second gas separation membrane unit, and it is more preferable that the separation selectivity of all raw material gases relative to gas B in the first gas separation membrane unit is greater than that of the second gas separation membrane unit. With such a configuration, it is possible to further improve the content of gas A and further decrease the content of gas B in the gas flow (ii), and as a result, the reaction efficiency of the gas synthesis reaction unit 20 can be further improved. In addition, it is possible to further improve or suppress the decrease in the recovery rate of gas B, and this can be achieved in conjunction with high purity.

[0054] When the present invention uses the connecting structure 10B of (c), the separation selectivity of gas A to gas B in the third gas separation membrane unit (P' ３Ａ / P' ３ＢPreferably, the second gas separation membrane unit is equivalent to or better than the third gas separation membrane unit, and all the raw material gases (e.g., (P')) for gas B in the third gas separation membrane unit are also included. ３Ａ / P' ３Ｂ ), (P' ３Ｃ / P' ３Ｂ )) is more preferably equal to or better than that of the second gas separation membrane unit. Furthermore, in the embodiment of (c), it is preferable that the separation selectivity of gas A relative to gas B in the third gas separation membrane unit is greater than that of the second gas separation membrane unit, and it is more preferable that the separation selectivity of each raw material gas relative to gas B in the third gas separation membrane unit is greater than that of the second gas separation membrane unit. With such a configuration, it is possible to further improve the content of gas A (and preferably gas C, hereinafter the same) and further decrease the content of gas B in the gas flow (ii), thereby further improving the reaction efficiency of the gas synthesis reaction unit 20. In addition, it is possible to further improve or suppress the decrease in the recovery rate of gas B, and this can be achieved in compatibility with high purity.

[0055] When the present invention uses the connecting structure 10B (c), the separation selectivity of at least gas A to gas B in the first gas separation membrane unit (P' １Ａ / P' １Ｂ Preferably, the separation selectivity of all raw material gases for gas B in the first gas separation membrane unit is equal to or greater than that of the second gas separation membrane unit (for example, (P' １Ａ / P' １Ｂ ), (P' １Ｃ / P' １ＢIt is more preferable that the gas separation selectivity is equal to or greater than that of the second gas separation membrane unit. Furthermore, when the connecting structure 10B is used, it is preferable that the separation selectivity of gas A relative to gas B in the first gas separation membrane unit is greater than that of the second gas separation membrane unit, and it is more preferable that the separation selectivity of the raw material gas relative to gas B in the first gas separation membrane unit is greater than that of the second gas separation membrane unit. With such a configuration, it is possible to further improve the content of gas A, etc., in the gas flow (ii) and further reduce the content of gas B, thereby further improving the reaction efficiency of the gas synthesis reaction unit 20. In addition, it is possible to further improve or suppress the decrease in the recovery rate of gas B, and this can be achieved in conjunction with high purity.

[0056] In the present invention, if the separation selectivity of gas A to gas B in the first gas separation membrane unit is lower than that of the second gas separation membrane unit, the ratio of the separation selectivity of the two (P' of the second gas separation membrane unit) ２Ａ / P' ２Ｂ ) / (P' of the first gas separation membrane unit １Ａ / P' １Ｂ The ratio (P') is preferably 1.5 or higher, more preferably 2 or higher, particularly preferably 2.3 or higher, and most preferably 2.5 or higher. ２Ａ / P' ２Ｂ ) / (P' １Ａ / P' １Ｂ )) may be 5 or less, 4 or less, or 3 or less. The ratio of the separation selectivity of gas C (of the second gas separation membrane unit (P' ２Ｃ / P' ２Ｂ ) / (P' of the first gas separation membrane unit １Ｃ / P' １Ｂ It is also preferable that the ratio is 1.5 or more and 5 or less, more preferably 2 or more and 5 or less, particularly 2.3 or more and 4 or less, and especially 2.5 or more and 4 or less.

[0057] In the present invention, if the separation selectivity of gas A to gas B in the first gas separation membrane unit is greater than that of the second gas separation membrane unit, the ratio of the separation selectivity of the two (P' of the first gas separation membrane unit) １Ａ / P' １Ｂ ) / (P' of the second gas separation membrane unit ２Ａ / P'２Ｂ The ratio ((P')) is preferably 1.5 or higher, more preferably 2 or higher, particularly preferably 2.3 or higher, and most preferably 2.5 or higher. １Ａ / P' １Ｂ ) / (P' ２Ａ / P' ２Ｂ )) may be 5 or less, 4 or less, or 3 or less. The ratio of the separation selectivity of gas C (of the first gas separation membrane unit (P' １Ｃ / P' １Ｂ ) / (P' of the second gas separation membrane unit ２Ｃ / P' ２Ｂ It is also preferable that the ratio is 1.5 or more and 5 or less, more preferably 2 or more and 5 or less, particularly 2.3 or more and 4 or less, and especially 2.5 or more and 4 or less.

[0058] In the present invention, if the separation selectivity of gas A to gas B in the third gas separation membrane unit is greater than that of the second gas separation membrane unit, the ratio of the separation selectivity of the two (P' of the third gas separation membrane unit) ３Ａ / P' ３Ｂ ) / (P' of the second gas separation membrane unit ２Ａ / P' ２Ｂ The ratio ((P')) is preferably 1.5 or higher, more preferably 2 or higher, particularly preferably 2.3 or higher, and most preferably 2.5 or higher. ３Ａ / P' ３Ｂ ) / (P' ２Ａ / P' ２Ｂ )) may be 5 or less, 4 or less, or 3 or less. The ratio of the separation selectivity of gas C (of the third gas separation membrane unit (P') ３Ｃ / P' ３Ｂ ) / (P' of the second gas separation membrane unit ２Ｃ / P' ２Ｂ It is also preferable that the ratio is 1.5 or more and 5 or less, more preferably 2 or more and 5 or less, particularly 2.3 or more and 4 or less, and especially 2.5 or more and 4 or less.

[0059] Each gas separation membrane unit has a separation selectivity (P') for gas A and gas C relative to gas B at 30°C. Ａ / P' Ｂ ) and (P' Ｃ / P' ＢThe values ​​of these factors are preferably between 10 and 500, and more preferably between 10 and 300.

[0060] In particular, when the gas synthesis reaction unit 20 is a methanation reaction unit, each gas separation membrane unit has a hydrogen separation selectivity (P') at 30°C. Ｈ２ / P' ＣＨ４ The separation selectivity (P') is preferably 30 to 500, and more preferably 50 to 400. Ｈ２ / P' ＣＨ４ When there are two or more gas separation membrane units with different separation selectivity (P'), the separation selectivity of the unit with the highest separation selectivity is (P'). Ｈ２ / P' ＣＨ４ The separation selectivity (P') of the unit with the lowest separation selectivity is preferably 150 to 500, and more preferably 150 to 400. Ｈ２ / P' ＣＨ４ ) is preferably 30 to 300, and more preferably 50 to 200.

[0061] In particular, when the gas synthesis reaction unit 20 is a methanation reaction unit, each gas separation membrane unit is CO at 30°C ２ Separation selectivity (P' ＣＯ２ / P' ＣＨ４ ) is preferably 10 to 100, and more preferably 10 to 80. Among these, separation selectivity (P' ＣＯ２ / P' ＣＨ４ When there are two or more gas separation membrane units with different separation selectivity (P'), the separation selectivity of the unit with the highest separation selectivity is (P'). ＣＯ２ / P' ＣＨ４ The separation selectivity (P') of the unit with the lowest separation selectivity is preferably 30 to 100, and more preferably 40 to 80. ＣＯ２ / P' ＣＨ４ ) is preferably 10 to 50, and more preferably 10 to 40.

[0062] In the gas separation membrane module used in the present invention, a hollow fiber membrane made of polymer and having an asymmetric structure can be suitably used as the gas separation membrane. The hollow fiber membrane having an asymmetric structure has a skin layer and a porous layer. The skin layer is a thinner layer than the porous layer and is mainly responsible for gas separation performance. The skin layer is a very dense layer compared to the porous layer and is usually very thin, preferably with a thickness of 1 nm to 5 μm, and more preferably with a thickness of 10 nm to 200 nm. The porous layer is a relatively thick porous layer that supports the skin layer, preferably with a thickness of 10 μm to 2000 μm, and more preferably with a thickness of 20 μm to 200 μm. The diameter of the pores in the porous layer is not particularly limited, but is generally 0.01 to 100 μm, and more preferably 0.01 to 50 μm. Such a hollow fiber membrane has a large effective surface area, high pressure resistance, and is excellent as a gas separation membrane.

[0063] The hollow fiber membrane preferably has an inner diameter of approximately 10 to 3000 μm, with 30 to 500 μm being preferred. Furthermore, the outer diameter of the hollow fiber membrane preferably has an outer diameter of approximately 30 to 7000 μm, with 35 to 700 μm being more preferred. The thickness of the skin layer and porous layer, the inner and outer diameters of the hollow fiber membrane, and the pore diameter can be measured using an optical microscope or an electron microscope.

[0064] The material for the gas separation membrane constituting the gas separation membrane module of the present invention is not particularly limited, but examples include polyimide, polyamide, polysulfone, polyethersulfone, polyamideimide, polyetherimide, and polycarbonate. Of these, the gas separation membrane is preferably made of polyimide in terms of separation performance, durability, and heat resistance.

[0065] Furthermore, the preferred operating temperature range for the gas separation membrane units 11, 12, and 13 (temperature of the gas separation membrane during operation) is preferably 0 to 100°C, more preferably 5 to 80°C, and even more preferably 10 to 60°C. The preferred temperature range for the synthesis gas supplied to the connecting structure 10 (temperature of the synthesis gas flowing upstream of the reflux gas inflow point) is the same as the preferred operating temperature range mentioned above.

[0066] The operating pressure of the gas separation membrane units 11, 12, and 13 (the pressure of the gas flowing into each unit) is preferably 0.2 MPaG or higher, and more preferably 0.3 MPaG or higher. The pressure of the gas separation membrane units 11, 12, and 13 may be 2 MPaG or lower, or 1.6 MPaG or lower.

[0067] From the viewpoint of further improving the effects of the present invention, in embodiment (a), the ratio of the membrane area S1 of the gas separation membrane unit 11 to the membrane area S2 of the gas separation membrane unit 11 is preferably S1:S2 is 100:1 to 200, and more preferably 100:10 to 100. In embodiment (b), the ratio of the membrane area S1 of the gas separation membrane unit 11 to the membrane area S2 of the gas separation membrane unit 11 is preferably S1:S2 is 100:100 to 500, and more preferably 100:150 to 400. In embodiment (c), the ratio of the membrane area S1 of the gas separation membrane unit 11, the membrane area S2 of the gas separation membrane unit 11, and the membrane area S3 of the gas separation membrane unit 13 is preferably S1:S2:S3 is 100:10 to 200:10 to 200, and more preferably S1:S2:S3 is 100:40 to 130:40 to 100.

[0068] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in addition to the compression means in the above embodiments, a depressurization means may be provided on any one or two permeation sides of each gas separation membrane unit to provide power to the mixed gas supplied to each gas separation membrane unit to pass through the separation membrane. A known vacuum pump or the like can be used as such a depressurization means. Furthermore, gas separation membranes, which are not shown, may or may not be provided in the lines between each component of each gas separation system in each embodiment of the present invention.

[0069] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited by these examples.

[0070] <Gas Separation Membrane Modules> The following examples and comparative examples are cases in which the gas synthesis reaction section is a methanation reaction section. The gas separation characteristics of gas separation membrane modules A and B used in the examples and comparative examples are shown in Table 1. These gas separation membrane modules house a gas separation membrane composed of aromatic polyimide hollow fiber membranes within a case.

[0071]

[0072] (Comparative Examples 1, 2, Examples 1-5) Simulations were performed operating systems 1, 2, or 4 described in Table 2 under the conditions described in Tables 2 and 3, respectively. The simulations were performed using the model described in THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, VOLUME 90, 2011, pp. 1253-1268, and calculated using equations (1) to (20) described in the simulation method described above. P' at 30°C for each module ＣＯ is 0.3 to 2.0 x 10 －５ cm ３ (STP) / cm ２ • Within the range of sec·cmHg, P' at 30℃ Ｈ２Ｏ is 100-400 x 10 －５ cm ３ (STP) / cm ２ ・Calculations were performed within the range of sec・cmHg. In the simulation, the composition and pressure of the synthesis gas supplied to the connecting structure (synthesis gas before it merges with the reflux gas of (iii)) were kept constant regardless of the composition and flow rate of the gas flow (ii) flowing into the methanation reaction section, as shown in Tables 2 and 3 below. In Table 2, the temperature of the synthesis gas refers to the temperature of the synthesis gas supplied to the connecting structure (the temperature of the synthesis gas flowing upstream of the reflux gas inlet). The operating pressure refers to the pressure of the synthesis gas flowing into each gas separation membrane unit. The operating temperature refers to the temperature of the gas separation membrane in each gas separation membrane unit. The flow rates of the first to third supply gases refer to the flow rates supplied to the gas inlets of each gas separation membrane unit 11 to 13. The product gas obtained in the gas separation section (gas B (CH)) ４ The composition of (enriched gas) and CH ４Table 4 shows the recovery rate and the composition of the gas flow (ii) returned to the methanation synthesis reaction section. Note that gas was not discharged through the truncation line (see Figure 1).

[0073]

[0074]

[0075]

[0076] As can be seen from Table 4, the gas separation systems of each embodiment of the present invention show a higher rate of gas B (CH) in the product gas compared to the comparative example gas separation system which is a single stage. ４ While achieving both purity and recovery rate, the gas A (H) in the gas stream (ii) returned to the gas synthesis reaction section 20 is used. ２ ) and gas C (CO ２ The concentration of ) can be increased.

[0077] According to the present invention, a system and method for producing enriched gas, including a gas synthesis reaction section, is provided, which can improve the separation performance of the product gas and the reaction efficiency in the gas synthesis reaction section.

Claims

A gas enrichment gas production system comprising: a gas synthesis reaction unit that reacts a raw material gas containing gas A to produce at least gas B, thereby producing a synthesis gas containing gas A and gas B; and a gas separation unit that separates the enriched gas of gas B from the synthesis gas produced in the gas synthesis reaction unit, The gas separation unit has a connecting structure that has one gas inlet and a total of three or more permeable and non-permeable gas outlets, by connecting multiple gas separation membrane units, each having a gas inlet, a permeable gas outlet, and a non-permeable gas outlet, in series. The gas inlet of the aforementioned connecting structure and the synthesis gas outlet of the gas synthesis reaction section are connected by a gas supply line. In the aforementioned connecting structure, multiple gas flows of different compositions are obtained from a total of three or more permeable gas outlets and non-permeable gas outlets. Among the aforementioned multiple gas flows, A means for obtaining the gas stream (i) with the highest concentration of gas B as the product gas, A means for recycling the gas stream (ii) with the highest concentration of gas A into the gas synthesis reaction section, A gas enrichment production system comprising means for recycling gas flows other than (i) and (ii) (iii) to the gas supply line. 　 The enriched gas production system according to claim 1, wherein the raw material gas further contains gas C, gas A has a higher permeation rate through the gas separation membrane in each gas separation membrane unit compared to gas C, and the gas synthesis reaction unit reacts gas A and gas C to produce gas B. 　 A gas enrichment production system according to claim 1 or 2, comprising: a detection unit for detecting the amount or composition of gas flow (ii); and a control unit for adjusting the amount of gas A supplied to a gas synthesis reaction unit based on the detection result from the detection unit. 　 A gas enrichment production system according to claim 1 or 2, wherein (a), (b), and (c) are any of the following: (a) The aforementioned connecting structure First gas separation membrane unit, The second gas separation membrane unit, It has a permeate gas discharge line connecting the permeate gas outlet of the first gas separation membrane unit and the gas inlet of the second gas separation membrane unit. The second gas separation membrane unit has a recirculation line that recirculates the exhaust gas from the non-permeable gas outlet back into the gas supply line. (b) The aforementioned connecting structure First gas separation membrane unit, The second gas separation membrane unit, The first gas separation membrane unit has a non-permeable gas outlet, and the second gas separation membrane unit has a non-permeable gas outlet line connecting the non-permeable gas outlet and the gas inlet. The second gas separation membrane unit has a recirculation line that recirculates the exhaust gas from the permeate gas outlet back to the gas supply line. (c) The aforementioned connecting structure First gas separation membrane unit, The second gas separation membrane unit, Third gas separation membrane unit, A non-permeable gas discharge line connects the non-permeable gas outlet of the first gas separation membrane unit and the gas inlet of the second gas separation membrane unit, It has a permeate gas discharge line connecting the permeate gas outlet of the first gas separation membrane unit and the gas inlet of the third gas separation membrane unit, A recirculation line that recirculates the exhaust gas from the permeate gas outlet of the second gas separation membrane unit back to the gas supply line, The third gas separation membrane unit has a recirculation line that recirculates the exhaust gas from the non-permeable gas outlet back into the gas supply line. The concentration of gas B in gas stream (i) is 90 mol% or more, and the concentration of gas A is 5000 volume ppm or less. The concentration of gas B in gas flow (ii) is 60 mol% or less, and the concentration of gas A is 40 mol% or more. A gas enrichment production system according to claim 1 or 2, wherein the concentration of gas B in the gas stream (iii) is 50 to 99.8 mol%, and the concentration of gas A is 0.1 to 55 mol%. 　 The enriched gas production system according to claim 1 or 2, wherein in each of the gas separation membrane units, the permeation rate of gas A is greater than that of gas B. 　 (a) The separation selectivity of gas A to gas B in the first gas separation membrane unit (P' Ａ / P' Ｂ ) is equivalent to or less than the second gas separation membrane unit, (b) The separation selectivity of gas A to gas B in the first gas separation membrane unit (P' Ａ / P' Ｂ ) is equivalent to or better than the second gas separation membrane unit, (c) The separation selectivity of gas A to gas B in the third gas separation membrane unit (P' Ａ / P' Ｂ The enriched gas production system according to claim 3, wherein the second gas separation membrane unit is equivalent to or better than the second gas separation membrane unit. 　 A gas enrichment production system according to claim 1 or 2, wherein the flow rate F3 of gas (iii) is in the range of 10% to 300% of the flow rate F0 of synthesis gas flowing into the structural assembly. 　 Each gas separation membrane unit has a separation selectivity (P') for gas A relative to gas B at 30°C. Ａ / P' Ｂ A gas enrichment production system according to claim 1 or 2, wherein the ratio is 10 to 150. 　 The gas synthesis reaction section is the methanation reaction section. Gas A is hydrogen, A gas enrichment production system according to claim 1 or 2, wherein gas B is methane. 　 The gas synthesis reaction section is the methanation reaction section. Gas A is hydrogen, Gas B is methane, A gas enrichment production system according to claim 3, wherein gas C is carbon dioxide. 　 A method for producing an enriched gas, comprising: a gas synthesis reaction step of reacting a raw material gas containing gas A to produce at least gas B, thereby producing a synthesis gas containing gas A and gas B; and a gas separation step of separating the enriched gas of gas B from the synthesis gas produced in the gas synthesis reaction step, The gas separation process uses a connected structure that has one gas inlet and a total of three or more permeable and non-permeable gas outlets, by connecting multiple gas separation membrane units, each having a gas inlet, a permeable gas outlet, and a non-permeable gas outlet, in series. A gas supply line is connected to the gas inlet of the aforementioned connecting structure to supply the synthesis gas obtained in the gas synthesis reaction step. In the aforementioned connecting structure, multiple gas flows with different compositions are obtained from a total of three or more permeable gas outlets and non-permeable gas outlets. Among the aforementioned multiple gas flows, A process to obtain the gas stream (i) with the highest concentration of gas B as the product gas, A process to recycle the gas stream (ii) with the highest concentration of gas A into the gas synthesis reaction process, A method for producing enriched gas, comprising the step of recycling a gas flow (iii) other than (i) and (ii) into the gas supply line.

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