Gas separation method and gas separation equipment

Abstract

The problem to be addressed by this disclosure is to provide a gas separation method or gas separation equipment that can suppress the degradation of a CO2 separation membrane and improve the membrane life of a CO2 separation membrane. [Solution] A gas separation method comprising an adjustment step of adjusting at least one of the NO2 concentration and water vapor partial pressure in a CO2-containing gas containing NO2 and water vapor, and a concentration step of concentrating the CO2 in the adjusted gas obtained in the adjustment step using a CO2 separation membrane, wherein the NO2 concentration and water vapor partial pressure in the adjusted gas satisfy formula (A). TIFF0007918379000015.tif10137 [In formula (A), C NO2 represents the NO2 concentration (ppm), and p H2O This represents the partial pressure of water vapor (kPa).

Description

[Technical Field]

[0001] This disclosure relates to a gas separation method and a gas separation apparatus. [Background technology]

[0002] In recent years, the importance of CCUS (Carbon Capture, Utilization, and Storage) technology, which involves capturing, utilizing, or storing carbon dioxide (CO2) contained in exhaust gases, has been increasing from the perspective of combating global warming. Known technologies for separating carbon dioxide from exhaust gases include absorption methods, adsorption methods, and membrane separation methods. Of these, membrane separation methods have the advantages of relatively simple equipment configurations and low energy consumption.

[0003] Patent Document 1 explains that exhaust gas (combustion exhaust gas) used as a raw material gas contains trace amounts of NOx and other components. Patent Document 2 discloses a technology related to gas separation using a CO2 separation membrane. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-188161 [Patent Document 2] Patent No. 7687504 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described in Patent Documents 1 and 2, exhaust gas may contain contaminants such as water vapor and nitrogen oxides (NOx). Our research has shown that contact with CO2 separation membranes can cause membrane degradation and a decrease in separation performance. In particular, nitrogen dioxide (NO2) and water vapor can easily accelerate the degradation of CO2 separation membranes, making it important to appropriately control these components before performing membrane separation operations.

[0006] The present disclosure has been made against the background of the above-mentioned conventional technical problems. That is, an object of the present disclosure to be solved is to provide a gas separation method or a gas separation facility capable of suppressing deterioration of a CO2 separation membrane and improving the membrane life of the CO2 separation membrane. Means for Solving the Problems

[0007] As a result of intensive studies, the present inventor has found that the above problems can be solved by the gas separation method or gas separation facility shown below. The present disclosure includes the following aspects. [1] An adjustment step of adjusting at least one of the NO2 concentration and the water vapor partial pressure in a CO2-containing gas containing NO2 and water vapor, a concentration step of concentrating CO2 in the adjusted gas obtained in the adjustment step using a CO2 separation membrane, wherein the NO2 concentration and the water vapor partial pressure in the adjusted gas satisfy Formula (A). [Math.]] [In Formula (A), C NO2 represents the NO2 concentration (ppm), and p H2O represents the water vapor partial pressure (kPa).] [2] The gas separation method according to [1], wherein the NO2 concentration and the water vapor partial pressure in the adjusted gas satisfy Formula (B). [Math.]] [In Formula (B), C NO2 and p H2O are the same as defined above.] [3] The gas separation method according to [1] or [2], wherein C NO2 in Formula (A) and Formula (B) is 6.0 ppm or less. [4] The gas separation method according to any one of [1] to [3], wherein p H2O in Formula (A) and Formula (B) is 5.0 kPa or less. [5] The gas separation method according to any one of [1] to [4], wherein the adjustment step includes a nitrogen oxide reduction step for reducing the NO2 concentration in the CO2-containing gas and / or a water vapor partial pressure reduction step for reducing the water vapor partial pressure in the CO2-containing gas. [6] The gas separation method according to [5], wherein the method for reducing the NO2 concentration in the nitrogen oxide reduction step is one or more methods selected from the group consisting of (a), (b), and (c). (a) Method by reduction of NO2 (b) Method by NO2 adsorption (c) Method by absorption of NO2 [7] The gas separation method according to [5] or [6], wherein the method for reducing the water vapor partial pressure in the water vapor partial pressure reduction step is one or more methods selected from the group consisting of (h), (i), and (j). (h) Method of removing water vapor by condensation (i) Method of adsorbing and removing water vapor using an adsorbent (j) Method of absorbing and removing water vapor using an absorbent solution [8] The gas separation method according to any one of [1] to [7], wherein the temperature of the regulating gas is 80°C or lower. [9] The gas separation method according to any one of [1] to [8], wherein the CO2-containing gas is combustion exhaust gas, cement exhaust gas, exhaust gas from a natural gas reforming plant, or exhaust gas from a hydrogen production plant.

[10] The gas separation method according to any one of [1] to [9], wherein the CO2 separation membrane comprises one or more selected from the group consisting of organic membranes, inorganic membranes and ionic liquid membranes.

[11] The gas separation method according to

[10] , wherein the CO2 separation membrane is an organic membrane having one or more bonds selected from the group consisting of amide bonds, ester bonds, ether bonds and carbonate bonds.

[12] An adjustment device for adjusting at least one of the NO2 concentration and water vapor partial pressure in a CO2-containing gas containing NO2 and water vapor, It includes a concentration device equipped with a CO2 separation membrane for concentrating CO2 in the adjusted gas discharged from the adjustment device, A gas separation facility, wherein the NO₂ concentration and the water vapor partial pressure in the adjusted gas satisfy formula (A).

Math

[13] The gas separation facility according to

[12] , wherein the NO₂ concentration and the water vapor partial pressure in the adjusted gas satisfy formula (B).

Math

[14] The gas separation facility according to

[12] or

[13] , wherein C in formula (A) and formula (B) NO2 is 6.0 ppm or less.

[15] The gas separation facility according to any one of

[12] to

[14] , wherein p in formula (A) and formula (B) H2O is 5.0 kPa or less.

[16] The gas separation facility according to any one of

[12] to

[15] , wherein the adjustment device includes at least one or both of a nitrogen oxide reduction device that reduces the NO₂ concentration in the CO₂-containing gas and a water vapor partial pressure reduction device that reduces the water vapor partial pressure in the CO₂-containing gas.

[17] The gas separation facility according to

[16] , wherein the nitrogen oxide reduction device includes one or more devices selected from the group consisting of a selective catalytic reduction device (SCR), a selective non-catalytic reduction device (SNCR), an adsorption device, and an absorption device.

[18] The gas separation facility according to

[16] or

[17] , wherein the water vapor partial pressure reduction device includes one or more devices selected from the group consisting of a condensing device, an adsorption device, and an absorption device.

[19] The gas separation facility according to any one of

[12] to

[18] , wherein the temperature of the adjusted gas is 80°C or lower.

[20] A gas separation apparatus according to any one of

[12] to

[19] , wherein the CO2-containing gas is combustion exhaust gas, cement exhaust gas, exhaust gas from a natural gas reforming plant, or exhaust gas from a hydrogen production plant.

[21] The gas separation apparatus according to any one of

[12] to

[20] , wherein the CO2 separation membrane is an organic membrane, an inorganic membrane, or an ionic liquid membrane.

[22] The gas separation apparatus according to

[21] , wherein the CO2 separation membrane is an organic membrane having one or more bonds selected from the group consisting of amide bonds, ester bonds, ether bonds and carbonate bonds. [Effects of the Invention]

[0008] According to the gas separation method or gas separation equipment of this disclosure, the deterioration of the CO2 separation membrane can be suppressed and the membrane life of the CO2 separation membrane can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a conceptual diagram showing an example of a gas separation facility according to this disclosure. [Figure 2] Figure 2 is a schematic diagram showing the configuration of a concentration apparatus equipped with a CO2 separation membrane. [Figure 3] Figure 3 is a conceptual diagram showing another example of the gas separation equipment of this disclosure. [Figure 4] Figure 4 is a schematic diagram showing the configuration of the CO2 concentration apparatus used in the examples and comparative examples. [Modes for carrying out the invention]

[0010] The following description concerns the gas separation equipment of this disclosure, and will be explained in detail with reference to the drawings illustrating the examples. However, this disclosure is not limited to the illustrated examples, and it is possible to implement the equipment with appropriate modifications to the extent that it conforms to the spirit of the preceding and following statements, and all such modifications are included within the technical scope of this disclosure. Furthermore, unless otherwise specified in this specification, "A~B" representing a numerical range means "greater than or equal to A, and less than or equal to B". Furthermore, unless otherwise specified herein, ppm refers to volume-based ppm (vol ppm).

[0011] [Embodiment 1: Gas Separation Method] The gas separation method provided in this disclosure includes an adjustment step of adjusting at least one of the NO2 concentration and water vapor partial pressure in a CO2-containing gas containing NO2 and water vapor, and a concentration step of concentrating the CO2 in the adjusted gas obtained in the adjustment step using a CO2 separation membrane, characterized in that the NO2 concentration and water vapor partial pressure in the adjusted gas satisfy equation (A). The inventors have found that membrane degradation of the CO2 separation membrane depends on both the NO2 concentration and water vapor partial pressure. In particular, the NO2 concentration in the adjusted gas C NO2 and water vapor partial pressure p H2O When equation (A) is satisfied, the degradation of the CO2 separation membrane is effectively suppressed. The following describes in detail each step of the gas separation method.

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[0012] [Adjustment process] The adjustment step in the gas separation method is a step of adjusting at least one of the NO2 concentration and water vapor partial pressure in a CO2-containing gas that includes NO2 and water vapor. The adjustment step generates an adjusted gas. By adjusting the gas properties in advance before the concentration step, membrane degradation of the CO2 separation membrane can be effectively suppressed. Other steps may be performed between the adjustment step and the concentration step.

[0013] In the adjustment step, each component is adjusted to satisfy equation (A). The adjustment step is a step of adjusting at least one of the NO2 concentration and the water vapor partial pressure in a CO2-containing gas containing NO2 and water vapor, preferably a step of adjusting both the NO2 concentration and the water vapor partial pressure. The adjustment step may include, for example, a nitrogen oxide reduction step to reduce the NO2 concentration in the CO2-containing gas and / or a water vapor partial pressure reduction step to reduce the water vapor partial pressure in the CO2-containing gas. This can suppress film degradation caused by NO2 and water vapor.

[0014] Figure 1 is a conceptual diagram showing an example of a gas separation facility according to this disclosure. In Figure 1, the gas separation facility 5 introduces a CO2-containing gas g and uses an adjustment device 4, which includes a water vapor partial pressure reduction device 1 and a nitrogen oxide reduction device 2, to remove C from the CO2-containing gas g. NO2 and / or p H2O The system has a configuration that supplies the adjusted gas to the concentration unit 3. The adjusting unit 4 may consist of either the water vapor partial pressure reducer 1 or the nitrogen oxide reducer 2, and if both are included, the arrangement order of these is not limited to that shown in the figure. In the figure, P is C in the adjusted gas. NO2 and p H2O P indicates a position that satisfies formula (A) or formula (B) described below. As indicated by P, in the gas separation method of this disclosure, it is preferable that the NO2 concentration and water vapor partial pressure in the adjusted gas satisfy formula (A) or formula (B) after the adjustment step and before the concentration step.

[0015] Methods for reducing NO2 concentration in the nitrogen oxide reduction process include, for example, (a) to (c), with (b) being preferred due to its good processing efficiency. These can be used individually or in combination of two or more. These methods can effectively reduce NO2 concentration. (a) Method by reduction of NO2 (b) Method by NO2 adsorption (c) Method by absorption of NO2 Examples of (a) include selective catalytic reduction (SCR; for example, reducing NO2 in the presence of a catalyst using a reducing agent such as ammonia or urea) and selective non-catalytic reduction (SNCR; for example, reducing NO2 with a reducing agent under high temperature conditions without using a catalyst). (b) For example, a method of adsorbing and removing NO2 using adsorbents such as zeolite and activated carbon is an example. (c) For example, a method of absorbing and removing NO2 using an absorbent solution such as an alkaline aqueous solution is one example.

[0016] Methods for reducing the water vapor partial pressure in the water vapor partial pressure reduction process include, for example, (h) to (j), and (h) is preferred because it can remove water vapor simply and efficiently. These can be used individually or in combination of two or more. These methods can effectively reduce the water vapor partial pressure. (h) Methods for removing water vapor by condensation (e.g., by cooling or compression) (i) Method of adsorbing and removing water vapor using an adsorbent (j) Method of absorbing and removing water vapor using an absorbent solution (h) is, for example, a method of condensing water vapor by cooling or compression and separating the resulting condensed water. Examples of adsorbents in (i) include silica gel, zeolite, activated alumina, etc. Examples of the absorbent liquid in (j) include aqueous glycol solution.

[0017] When both a nitrogen oxide reduction process and a water vapor partial pressure reduction process are included, the order in which these processes are performed does not matter. For example, the processes may be performed in the order of nitrogen oxide reduction, water vapor partial pressure reduction, and concentration, and other processes may be included between these processes. Alternatively, the processes may be performed in the order of water vapor partial pressure reduction, nitrogen oxide reduction, and concentration, and other processes may be included between these processes. Such a sequence of execution makes it easier to adjust the NO2 concentration and water vapor partial pressure to the desired range.

[0018] It is also preferable that the NO2 concentration and water vapor partial pressure in the conditioned gas satisfy equation (B) in addition to equation (A). Satisfying equation (B) can further improve the membrane life of the CO2 separation membrane.

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[0019] C in equations (A) and (B) NO2 The concentration is preferably 6.0 ppm or less, more preferably 1.5 ppm or less, even more preferably 0.5 ppm or less, and even more preferably 0.2 ppm or less. NO2 The concentration is preferably 0.001 ppm or higher, more preferably 0.005 ppm or higher, even more preferably 0.01 ppm or higher, and even more preferably 0.05 ppm or higher. Within this range, stable separation operations can be performed under practical exhaust gas conditions while suppressing deterioration of the CO2 separation membrane, and the increase in equipment size and energy consumption can be suppressed.

[0020] p in equations (A) and (B) H2O The pressure is preferably 5.0 kPa or less, more preferably 3.0 kPa or less, even more preferably 2.0 kPa or less, and even more preferably 1.0 kPa or less. H2O The pressure is preferably 0.01 kPa or higher, more preferably 0.05 kPa or higher, even more preferably 0.1 kPa or higher, and even more preferably 0.5 kPa or higher. Within this range, the deterioration of the CO2 separation membrane due to the effects of water vapor is suppressed, the CO2 separation performance by the CO2 separation membrane is stabilized, and the size of the equipment and the increase in energy consumption can be suppressed.

[0021] When calculating equations (A) and (B), C NO2 and p H2O The value shall be calculated using a value to one decimal place (rounding to the second decimal place and beyond).

[0022] CO2-containing gases include combustion exhaust gas, cement exhaust gas, exhaust gas from natural gas reforming equipment, and exhaust gas from hydrogen production equipment, with combustion exhaust gas and cement exhaust gas being preferred. Furthermore, CO2-containing gases may also include processed gas in natural gas refining (natural gas sweetening) processes, off-gas derived from oil or gas fields, processed gas in biogas refining or upgrading processes, gas derived from livestock or biomass (including resource recycling (CCU) applications), CO2-containing gas supplied or recovered for agricultural applications (smart agriculture, plant factories, etc.), gases targeted for recovery in CO2 capture and utilization (CCUS) or CCS, and CO2-containing gases obtained by direct atmospheric capture (DAC).

[0023] Combustion exhaust gas is preferably exhaust gas produced by the combustion of fuel or combustible materials, and examples include exhaust gas from incinerators that burn waste in waste treatment facilities (e.g., waste incineration facilities), exhaust gas from thermal power generation facilities (e.g., coal-fired power generation facilities, natural gas (LNG) thermal power generation facilities, oil-fired power generation facilities, etc.), exhaust gas from boiler facilities, exhaust gas from various industrial furnaces, exhaust gas from gas turbine facilities, exhaust gas from biomass combustion facilities, exhaust gas from sintering furnaces or heating furnaces in steelmaking facilities, exhaust gas from heating furnaces in petroleum refining facilities, exhaust gas from heating furnaces in chemical plants, and exhaust gas from internal combustion engines such as marine engines and automobile engines. These combustion exhaust gases contain CO2 produced in conjunction with the combustion of fuel or combustible materials, and often contain NO2 and water vapor depending on the combustion conditions, making them suitable targets for application of the gas separation method of this disclosure.

[0024] Cement exhaust gas refers to exhaust gas generated in cement manufacturing facilities, such as exhaust gas discharged from firing furnaces, preheaters, precalcina, clinker cooling equipment, etc., in the cement manufacturing process. In the cement manufacturing process, a large amount of CO2 is generated due to the firing and decomposition of raw materials such as limestone, and exhaust gas containing NO2 and water vapor is often discharged depending on the combustion conditions. Therefore, the gas separation method of this disclosure is suitable for application.

[0025] CO2-containing gases may also contain gases derived from their respective applications, such as N2, H2, CO, O2, nitrogen oxides other than NO2 (NOx), sulfur oxides (SOx), hydrogen chloride (HCl), mercury (Hg), etc. The gas separation method of this disclosure can also be applied to CO2-containing gases that contain these gas components.

[0026] The CO2 concentration in the CO2-containing gas is preferably 3 to 30 vol%, more preferably 5 to 25 vol%, even more preferably 6 to 20 vol%, and even more preferably 8 to 12 vol%. Within this range, CO2 recovery can be performed under practical exhaust gas conditions.

[0027] The NO2 concentration in the CO2-containing gas is preferably 0.1 to 300 ppm, more preferably 1 to 100 ppm, and even more preferably 2 to 50 ppm. Within this range, CO2 recovery can be performed under practical exhaust gas conditions.

[0028] The H2O concentration in the CO2-containing gas is preferably 1 to 25 vol%, more preferably 5 to 20 vol%, and even more preferably 8 to 15 vol%. Within this range, CO2 recovery can be performed under practical exhaust gas conditions.

[0029] [Concentration process] The concentration step in the gas separation method is a step in which the CO2 in the adjusted gas obtained in the adjustment step is concentrated using a CO2 separation membrane. The concentration step generates a permeate gas in which CO2 is concentrated. By using a concentration step with a CO2 separation membrane, it is possible to reduce energy consumption and miniaturize equipment compared to other CO2 recovery methods such as absorption methods.

[0030] The concentration process, which includes a CO2 separation membrane, is a method using an apparatus with the configuration shown in Figure 2. Figure 2 is a schematic diagram showing the configuration of a concentration apparatus with a CO2 separation membrane. In Figure 2, 21 is the CO2 separation membrane, 22 is the inlet for the conditioned gas in the concentration process, and 23 is the permeate section for the conditioned gas. Also, in the figure, a represents the conditioned gas, b represents the permeate gas, and c represents the non-permeate gas.

[0031] Of the components contained in the adjusted gas a shown in Figure 2, CO2 selectively passes through the CO2 separation membrane and moves to the permeate section 23 shown in Figure 2. As a result, the concentration of CO2 increases in the permeate section 23, and the permeate gas b shown in Figure 2 is prepared. The non-permeate gas c shown in Figure 2 has a lower CO2 concentration than adjusted gas a. Thus, permeate gas b and non-permeate gas c are discharged from the concentration process.

[0032] The CO2 separation membrane is preferably a CO2 permeable membrane because it facilitates the recovery of CO2 on the permeate side. The CO2 separation membrane is not particularly limited, and for example, organic membranes, inorganic membranes, and ionic liquid membranes can be used, but organic membranes are preferred from the viewpoint of processability and separation performance.

[0033] As for the organic membrane, an organic membrane having amide bonds, ester bonds, ether bonds, carbonate bonds, etc., which has good CO2 separation performance is preferred, and an organic membrane containing one or more selected from the group consisting of amide bonds, ester bonds, and ether bonds is particularly preferred, and an organic membrane having amide bonds and / or ether bonds is more preferred. Organic membranes having these bonds tend to degrade in the presence of NO2 and water vapor, but by controlling them within the range of formula (A), the degradation of the CO2 separation membrane can be suppressed even with membranes having these bonds.

[0034] Examples of organic films include polyamide films, polyether films, polyether block amide films, polycarbonate films, and silicone films.

[0035] The separation membrane element is not particularly limited, and can be of the hollow fiber type, spiral type, plate and frame type, etc., with the plate and frame type being preferred from the viewpoint of processability and pressure loss.

[0036] The temperature of the regulating gas is preferably 80°C or lower, more preferably 0 to 65°C, even more preferably 10 to 50°C, and even more preferably 20 to 40°C. Within this range, the concentration process using the CO2 separation membrane can be operated stably. In Embodiment 1, the temperature of the conditioned gas refers to the temperature of the conditioned gas introduced into the concentration process, while in Embodiment 2, it refers to the temperature of the conditioned gas introduced into the concentration apparatus.

[0037] The gas separation method may include, in addition to the step of concentrating the CO2 in the adjusted gas obtained in the adjustment step described above using a CO2 separation membrane (hereinafter also referred to as the "first concentration step"), a subsequent step of further concentrating the CO2 in the exhaust gas of the first concentration step obtained in the first concentration step (hereinafter also referred to as the "second concentration step").

[0038] Figure 3 is a conceptual diagram showing another example of the gas separation equipment of this disclosure. In Figure 3, the gas separation equipment 5 introduces a CO2-containing gas g and uses an adjustment device 4, which includes a water vapor partial pressure reducer 1 and a nitrogen oxide reducer 2, to remove C from the CO2-containing gas g. NO2 and / or p H2O The system has a configuration that, after adjustment, supplies the adjusted gas to the first concentrator 3a and the second concentrator 3b. In the first concentrator 3a and the second concentrator 3b, CO2 is concentrated by adjusting the pressure on the supply side and the permeate side using a pressurizing pump 6a and vacuum pumps 6b and 6c. The adjustment device 4 may be equipped with either a water vapor partial pressure reduction device 1 or a nitrogen oxide reduction device 2, and if both are provided, the arrangement order of these devices is not limited to that shown in the figure. In the figure, P represents C in the adjusted gas. NO2 and p H2OP indicates a position that satisfies formula (A) or formula (B). As indicated by P, in a gas separation method where the concentration process is carried out in multiple stages, it is preferable that the NO2 concentration and water vapor partial pressure in the adjusted gas satisfy formula (A) or formula (B) after the adjustment process and before the first concentration process.

[0039] When a second concentration step is included, the number of steps in the second concentration step is not particularly limited, but one or more is preferred, three or fewer is preferred, and two or fewer is more preferred. By having one or more second concentration steps, the CO2 contained in the conditioned gas is further concentrated each time it passes through multiple concentration steps, making it possible to produce a permeate gas with a higher CO2 concentration. Furthermore, by limiting the number of second concentration steps to three or fewer, the gas separation method does not become excessively large, and the excessive complexity of the apparatus configuration can be suppressed.

[0040] The second concentration step is not particularly limited as long as it can concentrate the CO2 in the exhaust gas from the first concentration step, but examples include a step of concentration using a CO2 separation membrane, and a step of concentration using a substance (hereinafter also referred to as "substance X") that is capable of adsorbing and / or absorbing CO2 and also capable of desorption.

[0041] If the second concentration step is a step of concentration using a CO2 separation membrane, the CO2 separation membrane used in the first concentration step can be the same type as the CO2 separation membrane used in the first concentration step. The CO2 separation membranes in the first concentration step and the second concentration step may be the same type of CO2 separation membrane, or they may be different types of CO2 separation membranes.

[0042] Substance X is not particularly limited, and for example, amines, zeolites, and activated carbon can be used. If the second concentration step comprises multiple second concentration steps containing substance X, the substance X in each concentration step may be the same type of substance or may be different types of substances.

[0043] The CO2 concentration of the permeate gas is preferably at least twice, and more preferably at least three times, the CO2 concentration of the regulating gas. Within this range, CO2 can be efficiently concentrated, and stable operation of the concentration process is possible. Here, the CO2 concentration of the permeate gas refers to the CO2 concentration of the permeate gas obtained in the downstream concentration step of the gas separation method in Embodiment 1, and to the CO2 concentration of the permeate gas obtained in the downstream concentration device of the gas separation equipment in Embodiment 2.

[0044] It is preferable that the CO2 concentration of the non-permeable gas be half or less of the CO2 concentration of the regulating gas, and more preferably one-quarter or less. Within this range, the CO2 concentration on the non-permeable side can be sufficiently reduced. Here, the CO2 concentration of the impermeable gas refers to the CO2 concentration of the impermeable gas obtained in the downstream concentration step of the gas separation method in Embodiment 1, and to the CO2 concentration of the impermeable gas obtained in the downstream concentration device of the gas separation equipment in Embodiment 2.

[0045] The CO2 concentrations of the permeate and non-permeate gases relative to the CO2 concentration of the regulated gas can be controlled by appropriately adjusting the selectivity during enrichment and the conditions for enriching CO2.

[0046] Selectivity in concentration can be expressed, for example, as the ratio (permeance ratio) of the rates at which two of the compounds contained in the conditioned gas permeate the CO2 separation membrane. Alternatively, selectivity in concentration can be expressed, for example, as the ratio of the rates at which two of the compounds contained in the conditioned gas are adsorbed and / or absorbed by substance X. Specific examples of the ratio of two compounds include CO2 / N2, CO2 / O2, and CO2 / H2O. Selectivity in concentration can vary depending on the type of CO2 separation membrane and substance X.

[0047] Conditions for concentrating CO2 include, for example, the pressure at which the conditioning gas is supplied (hereinafter also referred to as "supply pressure") and the pressure of the permeate gas (hereinafter also referred to as "permeation pressure"). Another condition for concentrating CO2 is the ratio of the supply pressure to the permeation pressure. Methods for controlling the supply pressure and permeation pressure include installing, for example, pressure valves, back pressure valves, vacuum pumps, etc., at the supply point of the regulating gas and / or the discharge point of the permeation gas to control the pressure of the regulating gas and / or the permeation gas. The supply pressure is preferably set higher than the permeation pressure, and is preferably 0 to 200 kPaG, more preferably 10 to 100 kPaG. Within this range, stable membrane separation can be performed without placing an excessive load on the CO2 separation membrane. The permeation pressure is preferably 1 to 50 kPaA, more preferably 5 to 30 kPaA. Within this range, the pressure on the permeation side can be kept low, and the permeation of CO2 can be efficiently promoted. Furthermore, the ratio of permeation pressure to supply pressure (permeation pressure / supply pressure) is preferably 0.01 to 0.5, more preferably 0.05 to 0.2, and even more preferably 0.05 to 0.1.

[0048] The permeate gas discharged from the concentration process may be recovered directly into a recovery device, or a portion of it may be reused within the gas separation method. The non-permeate gas discharged from the concentration process may be discharged directly outside the facility, or a portion of it may be reused within the gas separation method.

[0049] [Embodiment 2: Gas Separation Equipment] The gas separation equipment provided in this disclosure includes a regulating device that adjusts at least one of the NO2 concentration and water vapor partial pressure in a CO2-containing gas containing NO2 and water vapor, and a concentrating device equipped with a CO2 separation membrane that concentrates the CO2 in the regulating gas discharged from the regulating device, characterized in that the NO2 concentration and water vapor partial pressure in the regulating gas satisfy formula (A). NO2 concentration in regulating gas C NO2 and water vapor partial pressure p H2OBy satisfying equation (A), the degradation of the CO2 separation membrane is effectively suppressed. The following describes in detail each device included in the gas separation equipment. For parts of the gas separation equipment that are common with the gas separation method, refer to the explanation in Embodiment 1 described above.

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[0050] [Adjustment device] The adjustment device in the gas separation equipment is a device that adjusts at least one of the NO2 concentration and water vapor partial pressure in a CO2-containing gas that includes NO2 and water vapor. The adjustment device can produce and discharge an adjusted gas in which at least one of the NO2 concentration and water vapor partial pressure has been adjusted. NO2 and water vapor partial pressure p H2O It is configured to adjust so that it satisfies equation (A).

[0051] The adjustment device should be installed upstream of the concentration device. By pre-adjusting the gas properties before introducing it into the concentration device, membrane degradation of the CO2 separation membrane can be effectively suppressed. The adjustment device and the concentration device may be directly connected, or other devices may be installed between them.

[0052] The adjustment device is not particularly limited as long as it can control each component to satisfy formula (A). The adjustment device is a device that adjusts at least one of the NO2 concentration and water vapor partial pressure in a CO2-containing gas containing NO2 and water vapor, preferably a device that adjusts both the NO2 concentration and water vapor partial pressure. The adjustment device may include, for example, at least one or both of a nitrogen oxide reduction device that reduces the NO2 concentration in the CO2-containing gas and a water vapor partial pressure reduction device that reduces the water vapor partial pressure in the CO2-containing gas. This can suppress film degradation caused by NO2 and water vapor.

[0053] In the gas separation equipment 5, as shown by P in Figure 1, the NO2 concentration C in the adjusted gas is measured along the path from the adjustment device 4 to the concentration device 3. NO2 and water vapor partial pressure p H2O It is preferable that the formula satisfies formula (A) or formula (B).

[0054] The nitrogen oxide reduction device is not particularly limited, but examples include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), adsorption devices (e.g., adsorption towers), and absorption devices (absorption towers). Adsorption devices are preferred because they offer good processing efficiency. These devices may be installed individually or in combination. With these devices, nitrogen oxides can be effectively removed, thereby reducing the NO2 concentration and making it easier to adjust the NO2 concentration in the conditioned gas.

[0055] While there are no particular limitations on the water vapor partial pressure reduction device, examples include a condenser that removes water vapor by condensation (e.g., by cooling or compression), an adsorption device that removes water vapor by adsorption of an adsorbent, and an absorption device that removes water vapor by absorption of an absorbent liquid. A condenser is preferred because it can remove water vapor simply and efficiently. These devices may be installed individually or in combination. With these devices, the partial pressure of water vapor in the CO2-containing gas can be reduced by effectively removing water vapor, making it easier to adjust the partial pressure of water vapor in the regulated gas. The adsorbent and absorbent liquid exemplified above are preferably used.

[0056] When both a nitrogen oxide reduction device and a water vapor partial pressure reduction device are provided, either the nitrogen oxide reduction device or the water vapor partial pressure reduction device may be placed upstream. For example, they may be arranged in the order of nitrogen oxide reduction device, water vapor partial pressure reduction device and concentration device, with other devices placed between them. Alternatively, they may be arranged in the order of water vapor partial pressure reduction device, nitrogen oxide reduction device and concentration device, with other devices placed between them. Such arrangements make it easier to adjust the NO2 concentration and water vapor partial pressure to the desired range.

[0057] It is also preferable that the NO2 concentration and water vapor partial pressure in the conditioned gas satisfy equation (B) in addition to equation (A). Satisfying equation (B) can further improve the membrane life of the CO2 separation membrane.

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[0058] The adjustment device may further include at least one of a NO2 sensor for detecting the NO2 concentration in the adjustment gas and a humidity sensor for detecting the partial pressure of water vapor in the adjustment gas, as well as a control unit that controls the adjustment device based on the detection results of the sensors. This allows for real-time monitoring of fluctuations in each component and automatic adjustment of the operating intensity of the adjustment device to satisfy the conditions of equation (A).

[0059] [Concentrator] The concentration unit in a gas separation facility is equipped with a CO2 separation membrane and concentrates CO2 in the adjusted gas discharged from the adjustment unit. The concentration unit can produce and discharge a permeate gas in which CO2 has been concentrated. By using a concentration unit equipped with a CO2 separation membrane, it is possible to reduce energy consumption and miniaturize the equipment compared to other CO2 recovery methods such as absorption methods. An example of a concentration unit equipped with a CO2 separation membrane is a device with the configuration shown in Figure 2.

[0060] The gas separation equipment may include, in addition to a device (hereinafter also referred to as the "first concentration device") equipped with the aforementioned CO2 separation membrane that concentrates CO2 in the adjusted gas discharged from the adjustment device, one or more devices (hereinafter also referred to as the "second concentration device") downstream that further concentrate CO2 in the exhaust gas from the first concentration device discharged from the first concentration device. Note that the first concentration process and the second concentration process are not limited to a single series, but may consist of multiple series (for example, a device equipped with multiple CO2 separation membranes arranged in parallel).

[0061] In the gas separation facility 5, which is equipped with multiple concentration devices, as shown by P in Figure 3, the NO2 concentration C in the adjusted gas is measured along the path from the adjustment device 4 to the first concentration device 3a. NO2 and water vapor partial pressure p H2O It is preferable that the formula satisfies formula (A) or formula (B).

[0062] When a second concentrator is provided, the number of second concentrators is not particularly limited, but one or more is preferred, three or fewer is preferred, and two or fewer is more preferred. By providing one or more second concentrators, the CO2 contained in the conditioned gas is further concentrated each time it passes through multiple concentrators, and a permeate gas with a higher CO2 concentration can be produced. Furthermore, by limiting the number of second concentrators to three or fewer, the gas separation equipment does not become excessively large, and the complexity of the equipment configuration can be suppressed.

[0063] The provision of one or more second enrichment devices means that the method of this disclosure using gas separation equipment is carried out through two or more enrichment steps.

[0064] The second concentration device is not particularly limited as long as it can concentrate CO2 in the exhaust gas of the first concentration device, but examples include a device equipped with a CO2 separation membrane, a device equipped with substance X, etc.

[0065] If the second concentration device is equipped with a CO2 separation membrane, the CO2 separation membranes in the first concentration device and the second concentration device may be of the same type or different types.

[0066] An apparatus equipped with substance X can, for example, use substance X instead of a CO2 separation membrane in a concentration apparatus having the configuration shown in Figure 2. In this case, of the components contained in the adjusted gas a shown in Figure 2, CO2 is selectively adsorbed and / or absorbed by substance X. Subsequently, the adsorbed and / or absorbed CO2 is released into the permeate section 23 in Figure 2. As a result, the CO2 concentration in the permeate section 23 increases, and the permeate gas b shown in Figure 2 is prepared. Note that the non-permeate gas c shown in Figure 2 has a lower CO2 concentration than the adjusted gas a.

[0067] The permeate gas discharged from the concentration unit may be recovered directly into the recovery unit, or a portion of it may be reused within the gas separation equipment. The non-permeate gas discharged from the concentration unit may be discharged directly outside the equipment, or a portion of it may be reused within the gas separation equipment. [Examples]

[0068] The contents of this disclosure will be explained in more detail below with reference to examples, but the contents of this disclosure are not limited by the examples below, and it is certainly possible to implement the disclosure with appropriate modifications to the extent that it is in line with the spirit of the preceding and following statements, and all such modifications are included within the technical scope of this disclosure.

[0069] [Fabrication of CO2 separation membranes] A CO2 separation membrane was fabricated by laminating a nonwoven fabric and porous substrate (polyacrylonitrile) as a reinforcing support layer, a gutter layer (polydimethylsiloxane), a separation function layer (Pebax® polyether block amide copolymer), and a protective layer (polydimethylsiloxane) in this order.

[0070] [Concentrator] Using the aforementioned CO2 separation membrane, a CO2 concentration apparatus having the configuration shown in Figure 4 was fabricated. Figure 4 is a schematic diagram showing the configuration of the CO2 concentration apparatus used in the examples and comparative examples. Specifically, the CO2 separation membrane was punched out into a circle with a diameter of 35 mm to obtain a circular CO2 separation membrane 11. The CO2 separation membrane 11 was sandwiched between two cells, a supply-side cell and a permeate-side cell, to create a separation device consisting of the CO2 separation membrane 11 and an evaluation cell 12 that holds the CO2 separation membrane 11. The evaluation cell 12 was equipped with a supply port 13 and a supply outlet 14 on the supply side cell, and a permeation outlet 15 on the permeation side cell. The evaluation cell 12 was placed inside a constant temperature bath. The supply sources (supply tanks) for CO2, N2, N2+NO2, and H2O (water vapor) were connected to the supply port 13 by conduits. These conduits merged before reaching the supply port 13 and connected to the supply port 13 as a single conduit. Furthermore, mass flow controllers (MFCs) were installed in the CO2, N2, and N2+NO2 supply lines, and a pump 16 was installed in the H2O supply line. A back pressure valve 19 is provided at the supply outlet 14, and a conduit connecting to tank 20a is connected to it. A conduit connecting to tank 20b is connected at the permeate outlet 15, and a control valve 18 and a vacuum pump 17 are provided in this conduit, and it is connected to a GC (gas chromatography) system. The vacuum pump 17 is located closer to the GC system than the control valve 18. A CO2 concentration device was constructed using the above configuration.

[0071] [Concentration method] Using the aforementioned concentration apparatus, CO2, N2, N2+NO2, and H2O (water vapor) gases were supplied to concentrate carbon dioxide. These gases were mixed at the confluence point to prepare a gas mixture. The total flow rate of the gas mixture was 500 NmL / min (dry state). The composition of CO2, N2, and NO2 in the gas mixture was set by adjusting the flow rates of CO2, N2, and N2+NO2 using a mass flow controller. The partial pressure of water vapor was set by adjusting the flow rate of H2O using pump 16. The pressure in the supply cell (supply pressure) was adjusted to 20 kPaG by the back pressure valve 19, and the pressure in the permeate cell (permeate pressure) was adjusted to 10 kPaA by the control valve 18 and the vacuum pump 17. Furthermore, the temperature inside the constant temperature bath was set to 40°C.

[0072] [Evaluation Method] In the examples and comparative examples, the permeation rates [GPU] of CO2 and N2 were measured, and the CO2 / N2 selectivity was calculated from these values. The CO2 / N2 selectivity at the start of evaluation was set as the baseline value (100%), and the time until the CO2 / N2 selectivity decreased to 70% was evaluated as the maintenance time of the separation performance of the CO2 separation membrane. The maintenance time of the separation performance was evaluated according to the following criteria A to C. Measurement was started after the gas permeation reached a steady state. A: Maintenance time of 200 hours or more B: Maintenance time 100 hours or more but less than 200 hours C: Maintenance time less than 100 hours

[0073] [Examples 1-7, Comparative Examples 1-5] In Examples 1-7 and Comparative Examples 1-5, the NO2 concentration and water vapor partial pressure in the supply gas were adjusted to achieve the conditions shown in Table 1.

[0074] [Table 1]

[0075] As shown in Examples 1 to 7, when formula (A) was satisfied, the maintenance time of separation performance was 100 hours or more. In other words, it was confirmed that by adjusting the NO2 concentration and water vapor partial pressure to satisfy formula (A), the deterioration of the CO2 separation membrane was suppressed and the membrane life was improved.

[0076] Furthermore, as shown in Examples 1 to 4, when formula (B) was satisfied, the maintenance time for separation performance was 200 hours or more. In other words, it was confirmed that by adjusting the NO2 concentration and water vapor partial pressure to satisfy formula (B), the deterioration of the CO2 separation membrane was further suppressed and the membrane life was further improved.

[0077] On the other hand, as shown in the comparative example, when formula (A) was not satisfied, the maintenance time was less than 100 hours, and the film lifetime was not sufficient. [Explanation of Symbols]

[0078] 1. Water vapor partial pressure reduction device 2. Nitrogen oxide reduction device 3 Concentrator 3a 1st concentrator 3b Second concentrator 4 Adjustment device 5. Gas separation equipment 6a Pressure pump 6b, 6c Vacuum pump 11 CO2 separation membrane 12 evaluation cells 13 Supply port 14 Supply outlet 15 Transmission outlet 16 pumps 17 Vacuum pump 18 Control valve 19 Back pressure valve 20a, 20b tanks 21 CO2 separation membrane 22 Inlet of regulating gas 23 Permeable section for regulating gas g CO2-containing gas a. Regulating gas b Permeable gas c. Impermeable gas P C in regulated gas NO2 and p H2O The position that satisfies equation (A) or equation (B)

Claims

1. NO ２ and CO2 containing water vapor ２ NO in the contained gas ２ A preparation step to adjust at least one of the concentration and the partial pressure of water vapor, CO in the adjusted gas obtained in the adjustment step ２ CO ２ This includes a concentration step in which concentration is performed using a separation membrane. NO in the regulating gas ２ A gas separation method characterized in that the concentration and water vapor partial pressure satisfy equation (A). [Math 1] [In formula (A), C ＮＯ２ represents NO ２ concentration (ppm), and p Ｈ２Ｏ represents the partial pressure of water vapor (kPa).]

2. NO in the regulating gas ２ The gas separation method according to claim 1, wherein the concentration and the partial pressure of water vapor satisfy formula (B). [Math 2] [In formula (B), C ＮＯ２ and p Ｈ２Ｏ This is the same as above.

3. C in formulas (A) and (B) ＮＯ２ The gas separation method according to claim 1 or 2, wherein the concentration is 6.0 ppm or less.

4. In formulas (A) and (B), p Ｈ２Ｏ The gas separation method according to claim 1 or 2, wherein the pressure is 5.0 kPa or less.

5. The adjustment step is the CO ２ NO in the contained gas ２ A nitrogen oxide reduction process to reduce the concentration and / or the CO ２ The gas separation method according to claim 1, comprising a water vapor partial pressure reduction step for reducing the water vapor partial pressure in the contained gas.

6. NO in the nitrogen oxide reduction process ２ The gas separation method according to claim 5, wherein the method for reducing the concentration includes one or more methods selected from the group consisting of (a), (b), and (c). (a) NO ２ Method by reduction (b) NO ２ Method by adsorption (c) NO ２ Method by absorption

7. The gas separation method according to claim 5, wherein the method for reducing the water vapor partial pressure in the water vapor partial pressure reduction step includes one or more methods selected from the group consisting of (h), (i), and (j). (h) Method of removing water vapor by condensation (i) Method of adsorbing and removing water vapor using an adsorbent (j) Method of absorbing and removing water vapor using an absorbent solution

8. The gas separation method according to claim 1, wherein the temperature of the adjustment gas is 80°C or lower.

9. The aforementioned CO ２ The gas separation method according to claim 1, wherein the contained gas is combustion exhaust gas, cement exhaust gas, exhaust gas from a natural gas reforming plant, or exhaust gas from a hydrogen production plant.

10. The aforementioned CO ２ The gas separation method according to claim 1, wherein the separation membrane comprises one or more selected from the group consisting of organic membranes, inorganic membranes, and ionic liquid membranes.

11. The aforementioned CO ２ The gas separation method according to claim 10, wherein the separation membrane is an organic membrane having one or more bonds selected from the group consisting of amide bonds, ester bonds, ether bonds, and carbonate bonds.

12. NO ２ and CO2 containing water vapor ２ NO in the contained gas ２ A control device that adjusts at least one of the concentration and the partial pressure of water vapor, CO ２ A separation membrane is provided, and the CO2 in the adjusted gas discharged from the adjustment device ２ Includes a concentration device for concentrating, NO in the regulating gas ２ A gas separation apparatus characterized in that the concentration and water vapor partial pressure satisfy formula (A). [Math 3] [In formula (A), C ＮＯ２ The answer is NO. ２ The concentration (ppm) is expressed as p Ｈ２Ｏ This represents the partial pressure of water vapor (kPa).

13. NO in the regulating gas ２ The gas separation apparatus according to claim 12, wherein the concentration and the partial pressure of water vapor satisfy formula (B). [Math 4] [In formula (B), C ＮＯ２ and p Ｈ２Ｏ This is the same as above.

14. C in formulas (A) and (B) ＮＯ２ However, the gas separation equipment according to claim 12 or 13, wherein the concentration is 6.0 ppm or less.

15. In formulas (A) and (B), p Ｈ２Ｏ The gas separation equipment according to claim 12 or 13, wherein the pressure is 5.0 kPa or less.

16. The adjustment device, ２ NO in the contained gas ２ A nitrogen oxide reduction device for reducing the concentration, and the CO ２ The gas separation apparatus according to claim 12, comprising at least one or both of the water vapor partial pressure reducing devices for reducing the water vapor partial pressure in the contained gas.

17. The gas separation apparatus according to claim 16, wherein the nitrogen oxide reduction apparatus includes one or more apparatus selected from the group consisting of a selective catalytic reduction apparatus (SCR), a selective non-catalytic reduction apparatus (SNCR), an adsorption apparatus, and an absorption apparatus.

18. The gas separation apparatus according to claim 16, wherein the water vapor partial pressure reduction device includes one or more devices selected from the group consisting of a condenser, an adsorption device, and an absorption device.

19. The gas separation apparatus according to claim 12, wherein the temperature of the regulating gas is 80°C or lower.

20. The aforementioned CO ２ The gas separation apparatus according to claim 12, wherein the contained gas is combustion exhaust gas, cement exhaust gas, exhaust gas from a natural gas reforming plant, or exhaust gas from a hydrogen production plant.

21. The aforementioned CO ２ The gas separation apparatus according to claim 12, wherein the separation membrane is an organic membrane, an inorganic membrane, or an ionic liquid membrane.

22. The aforementioned CO ２ The gas separation apparatus according to claim 21, wherein the separation membrane is an organic membrane having one or more bonds selected from the group consisting of amide bonds, ester bonds, ether bonds, and carbonate bonds.

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