Liquid composition, method for producing carbon dioxide separation membrane, carbon dioxide separation membrane, and separation membrane module

Abstract

Provided are: a liquid composition from which it is possible to form a carbon dioxide separation membrane exhibiting both permeability and selective separability; a method for producing a carbon dioxide separation membrane in which the liquid composition is used; a carbon dioxide separation membrane; and a separation membrane module.　A liquid composition according to the present invention is for forming a carbon dioxide separation membrane. The liquid composition contains a solvent and a resin. As the solvent, a poor solvent having a boiling point of at most 170°C and a good solvent having a boiling point of at most 100°C are contained. As the resin, a cellulose resin that has, as a substituent, an acyl group having at least three carbon atoms is mainly contained. The ratio of the poor solvent to the entire solvent is within the range of 30-60 mass%. The ratio of the resin to the entire liquid composition is at most 14 mass%.

Description

Liquid composition, method for producing a carbon dioxide separation membrane, carbon dioxide separation membrane, and separation membrane module

[0001] The present invention relates to a liquid composition, a method for producing a carbon dioxide separation membrane, a carbon dioxide separation membrane, and a separation membrane module.

[0002] Carbon dioxide (CO2) is a greenhouse gas. ２ The development of technologies for efficiently separating and recovering carbon dioxide (CO2) is a critical industrial and environmental challenge. One known CO2 separation and recovery technology is membrane separation using resin. In CO2 separation using resin membranes, carbon dioxide is first adsorbed onto the surface of the resin. The adsorbed carbon dioxide is thought to dissolve inside the resin and then pass through the gaps in the resin's molecular chains. Because the ease of adsorption and dissolution on the resin surface differs depending on the type of gas, there is a difference in permeability between carbon dioxide and other gases, allowing them to be separated.

[0003] It is generally known that there is a trade-off between the selective separation and permeability of carbon dioxide in a separation membrane. A pressure difference is required to permeate carbon dioxide, and energy is needed for pressurization. Higher permeability means less energy is needed for pressurization. Therefore, from the perspective of reducing the total cost of carbon dioxide separation and recovery, permeability is more important than selective separation in order to reduce the energy required for pressurization.

[0004] The thinner the separation membrane, the higher its permeability. However, if the separation membrane is too thin, it becomes difficult to handle. Therefore, a method has been devised in which a thin gas separation functional layer is coated onto a porous support layer to form a composite membrane. By making the separation membrane a laminate of a porous support layer and a thin gas separation functional layer, it is possible to improve permeability while maintaining mechanical strength.

[0005] One method for forming a laminate consisting of a porous support layer and a thin gas separation functional layer is to create an asymmetric porous membrane from a resin solution using a phase separation method. This asymmetric porous membrane has a dense layer that contributes to separation and a porous layer that functions as a support layer responsible for mechanical strength.

[0006] The Rob-Thrilleryan method is a well-known method for forming asymmetric porous membranes (see, for example, Patent Document 1). In the Rob-Thrilleryan method, for example, a resin is dissolved in a good solvent, applied to a glass plate, and then immersed in water, which is a non-solvent. When the film is dried after immersion, voids are formed where the resin is less likely to exist in the areas immersed in the non-solvent, thus forming an asymmetric porous membrane. However, the Rob-Thrilleryan method is not economical because of the costs involved in introducing and maintaining the non-solvent bath equipment.

[0007] As a method for producing asymmetric porous membranes that differs from the Rob-Thrilleryan method, a technique has also been developed in which a poor solvent is added to a resin solution and phase separation is performed during the solvent evaporation process (see, for example, Patent Document 2).

[0008] Japanese Patent Publication No. 2023-156932 Japanese Patent Publication No. 2009-237160

[0009] In the film formation method described in Patent Document 2, it is technically important to control the solvent evaporation process and evaporation rate, making it difficult to form a thin, defect-free dense layer. If the dense layer has defects, selective separation performance decreases. Simply increasing the thickness of the dense layer to eliminate defects reduces permeability. The present invention has been made in view of the above situation. The problem that the present invention aims to solve is to provide a liquid composition that can form a carbon dioxide separation membrane that achieves both permeability and selective separation performance, as well as a method for producing a carbon dioxide separation membrane using the liquid composition, a carbon dioxide separation membrane, and a separation membrane module.

[0010] The above-mentioned problems according to the present invention are solved by the following means.

[0011] 1. A liquid composition for forming a carbon dioxide separation membrane, comprising a solvent and a resin, wherein the solvent comprises a poor solvent having a boiling point of 170°C or less and a good solvent having a boiling point of 100°C or less, and the resin mainly comprises a cellulose resin having an acyl group with 3 or more carbon atoms as a substituent, the ratio of the poor solvent to the total solvent is in the range of 30 to 60% by mass, and the ratio of the resin to the total liquid composition is 14% by mass or less.

[0012] 2. The liquid composition according to claim 1, wherein the liquid composition contains an organosilicon compound in an amount of 0.01 to 0.4% by mass relative to the entire liquid composition.

[0013] 3. The liquid composition according to paragraph 1, wherein the boiling point of the poor solvent is 10°C or more greater than the boiling point of the good solvent.

[0014] 4. A method for producing a carbon dioxide separation membrane, comprising exposing the liquid composition described in paragraph 1 to a temperature above the boiling point of the good solvent and volatilizing the good solvent to produce a carbon dioxide separation membrane in which a portion is porous.

[0015] 5. A method for producing a carbon dioxide separation membrane according to paragraph 4, comprising applying the liquid composition onto a nonwoven fabric which is a base material, and exposing the liquid composition applied onto the nonwoven fabric to a temperature above the boiling point of the good solvent.

[0016] 6. A carbon dioxide separation membrane comprising a cellulose resin having an acyl group with three or more carbon atoms as a substituent, and a residual solvent, wherein the residual solvent contains a good solvent and a poor solvent, the residual amount of the good solvent is greater than the residual amount of the poor solvent, the ratio of the residual solvent to the entire carbon dioxide separation membrane is 1000 ppm or less, and the boiling point of the poor solvent is 10°C or more greater than the boiling point of the good solvent.

[0017] 7. A separation membrane module comprising the carbon dioxide separation membrane described in paragraph 6.

[0018] According to the present invention, a liquid composition capable of forming a carbon dioxide separation membrane that achieves both permeability and selective separation properties, a method for producing a carbon dioxide separation membrane using the liquid composition, a carbon dioxide separation membrane, and a separation membrane module can be provided.

[0019] SEM image of a cross-section of a carbon dioxide separation membrane; schematic diagram showing an example of a carbon dioxide separation membrane manufacturing apparatus; schematic diagram with a partial cutout showing an example of a separation membrane module; a cylindrical winding with a laminate wound around a permeable gas manifold; a cross-sectional perspective view showing a part of the winding; schematic diagram showing the state before the laminate is wound around the permeable gas manifold.

[0020] The following description illustrates one or more embodiments of the present invention with reference to the drawings. The effects and features of the embodiments of the present invention will be understood from the following detailed description and drawings. The following detailed description and drawings are provided for illustrative purposes only and do not limit the scope of the present invention.

[0021] In this application, "~" is used to mean that the numerical values ​​written before and after it are included as the lower limit and upper limit.

[0022] [Liquid Composition] The liquid composition of the present invention is for forming a carbon dioxide separation membrane and contains a solvent and a resin. The liquid composition can become dope 2 in the formation of a carbon dioxide separation membrane 4 by evaporation-induced phase separation (EIPS). Evaporation-induced phase separation is a method for producing a porous membrane by evaporating a good solvent and a poor solvent from dope 2.

[0023] The liquid composition of the present invention contains a poor solvent and a good solvent as solvents. This enables the formation of a carbon dioxide separation membrane by evaporation-induced phase separation. The liquid composition may also contain other components such as plasticizers.

[0024] A good solvent is one that has a strong interaction with the resin used and can dissolve the resin on its own. The good solvent according to the present invention can untangle the hydrogen bonds within the cellulose resin molecular chains. In a good solvent, the resin molecules swell and stretch, forming an elongated state, and then dissolve. When the resin is mixed with the solvent, if the cohesive force between the resin molecules is weaker than the affinity between the resin molecules and the solvent, the resin molecules will dissolve through a swelling process. Specifically, a good solvent is one in which, when a dissolution test is performed by mixing the resin used with the solvent to a concentration of 1% by mass and stirring for 24 hours, it can be visually confirmed that there are no solid particles remaining from the undissolved resin. If two or more types of resin are used, the ratio of each resin mixed into the solvent in the dissolution test should be adjusted so that the total ratio is within 1% by mass and is the same as the ratio of each resin in the liquid composition.

[0025] A poor solvent is one that has weak interaction with the resin being used, causing the resins to clump together and repel the solvent when mixed (partial separation). Specifically, a solvent is considered a poor solvent if, after mixing the resin to a concentration of 1% by mass and stirring for 24 hours, undissolved solid particles can be visually confirmed. If two or more resins are used, the ratio of the resins should be adjusted within 1% by mass to match the ratio of the resins being used.

[0026] In the present invention, the boiling point of the poor solvent is 170°C or lower. This allows the poor solvent to be evaporated without shrinking the cellulose resin during the production of the carbon dioxide separation membrane 4, even when the glass transition temperature of the cellulose resin is around 180°C. From this viewpoint, the boiling point of the poor solvent is preferably 140°C or lower, and more preferably 120°C or lower.

[0027] On the other hand, from the viewpoint of facilitating the evaporation of the good solvent first, the boiling point of the poor solvent is preferably 70°C or higher, more preferably 90°C or higher, and even more preferably 110°C or higher. When the good solvent evaporates first during the production of the carbon dioxide separation membrane 4, the resin precipitates more easily, and porosity is more easily achieved. As a result, the dense layer becomes appropriately thin, and permeability is improved. From the same viewpoint, the boiling point of the poor solvent is preferably 10°C or higher than the boiling point of the good solvent, more preferably 30°C or higher, and even more preferably 60°C or higher.

[0028] In the present invention, the boiling point of the good solvent is 100°C or lower. This makes it easier for the difference in boiling points between the poor solvent and the good solvent to become large, and the good solvent is more likely to evaporate first during the production of the carbon dioxide separation membrane 4. From this viewpoint, the boiling point of the good solvent is preferably 80°C or lower, and more preferably 60°C or lower.

[0029] In this invention, the ratio of the poor solvent to the total solvent is within the range of 30 to 60% by mass. If there is too little poor solvent, the dense layer becomes too thick, reducing permeability. When the ratio of the poor solvent to the total solvent is 30% by mass or more, the dense layer does not become too thick, and permeability is good. If there is too much poor solvent, the dense layer becomes too thin, causing defects, which reduces selective separation. When the ratio of the poor solvent to the total solvent is 60% by mass or less, the dense layer does not become too thin, and selective separation is good.

[0030] Whether a solvent is good or poor depends on the substituents and degree of substitution of the cellulose resin used. For example, if the resin is diacetylcellulose (acetyl group substitution degree 2.4) or cellulose acetate propionate, acetone is a good solvent. For example, if the resin is triacetylcellulose (acetyl group substitution degree 2.8), acetone is a poor solvent.

[0031] Diacetylcellulose has a low degree of acetyl group substitution and strong hydrogen bonding within its molecular chains. Therefore, when dichloromethane is mixed with diacetylcellulose at a concentration of 1% by mass and stirred for 24 hours, it does not dissolve. Thus, when the resin is diacetylcellulose, dichloromethane is a poor solvent. However, if about 10% of a water-soluble alcohol-based solvent is mixed with dichloromethane to prevent hydrogen bonding between the hydroxyl groups of diacetylcellulose, the diacetylcellulose will dissolve in the mixed solvent. Triacetylcellulose and cellulose acetate propionate can be dissolved in dichloromethane alone, but to achieve a similar effect to the above, a small amount of water-soluble alcohol-based solvent may be mixed with dichloromethane when using triacetylcellulose or cellulose acetate propionate to prevent the molecular chains from curling and to reduce viscosity.

[0032] Examples of solvents that may be contained in the mixed solvent according to the present invention include organic halogen compounds such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, propyl acetate, methyl ethyl ketone (2-butanone), methyl isobutyl ketone, acetone, N-methylpyrrolidone, dimethylformamide, dioxane, dioxolane, dioxolane derivatives, dichloromethane, chloroform, tetrachloroethane, dimethyl sulfoxide, methylene chloride, tetrahydrofuran, cyclohexanone, and 2,2,2-trifluoride. Examples include ethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, alcohols having 1 to 8 carbon atoms, monochlorobenzene, benzene, toluene, cyclohexane, methyl cellulose, ethylene glycol monomethyl ether, water, etc. Examples of alcohols having 1 to 8 carbon atoms include methanol, ethanol, n-propanol (1-propanol), iso-propanol (2-propanol), n-butanol (1-butanol), sec-butanol (2-butanol), tert-butanol (2-methyl-2-propanol), 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and the like.

[0033] The liquid composition may contain a good solvent with a boiling point above 100°C and / or a poor solvent with a boiling point above 170°C, but it is preferable that it does not contain such solvents.

[0034] The liquid composition of the present invention mainly contains a cellulose resin having an acyl group with three or more carbon atoms as a substituent. This means that the proportion of the cellulose resin having an acyl group with three or more carbon atoms as a substituent is 60% by mass or more of the total resin.

[0035] Since the resin is a cellulose resin, it is easy to form an asymmetric porous membrane. When this cellulose resin has an acyl group with 3 or more carbon atoms in the substituent, the diffusivity of carbon dioxide in the carbon dioxide separation membrane 4 is improved, and the permeability is improved. The cellulose resin preferably has a structure represented by the following general formula (1).

[0036]

[0037] 〔In the general formula (1), R １ , R ２ and R ３ are each independently a hydrogen atom or an acyl group. At least one of R １ , R ２ and R ３ is an acyl group having 3 or more carbon atoms. n represents the degree of polymerization.〕

[0038] The degree of polymerization n is the number of each repeating structure, and is, for example, about 20 to 500, preferably 81 to 500, more preferably 85 to 400, and particularly preferably 90 to 250. R １ , R ２ and R ３ in each repeating structure may be the same or different.

[0039] Examples of the acyl group having 3 or more carbon atoms include a propionyl group, a butyryl group, a pentanoyl (valeryl) group, a hexanoyl group, a heptanoyl group, an octanoyl group, a nonanoyl group, a decanoyl group, an undecanoyl group, a dodecanoyl group, and the like. The acyl group having 3 or more carbon atoms is preferably a propionyl group or a butyryl group.

[0040] In the present invention, the ratio of resin to the total liquid composition is 14% by mass or less. A ratio of 14% by mass or less of resin to the total liquid composition facilitates proper porosity formation, preventing the dense layer from becoming too thick and resulting in good permeability. Furthermore, because the resin is easily dissolved in the solvent, defects are less likely to occur in the dense layer, and selective separation is also likely to be good. A ratio of 10% by mass or less of resin to the total liquid composition is preferable because it tends to result in even better permeability. From the viewpoint of reducing the drying load of the solvent, a ratio of 1% by mass or more of resin to the total liquid composition is preferable, and more preferably 3% by mass or more.

[0041] The liquid composition of the present invention preferably contains an organosilicon compound. When the liquid composition containing the organosilicon compound is applied to a support or the like, the organosilicon compound rises to the surface of the resin, which is the gas-liquid interface, reducing the surface tension and preventing the generation of bubbles. As a result, the dense layer becomes smoother, making it less prone to defects, and even a thin dense layer exhibits good selective separation properties.

[0042] The ratio of organosilicon compounds to the total liquid composition is preferably in the range of 0.01 to 0.4% by mass. A ratio of 0.01% by mass or more of organosilicon compounds makes it easier to prevent the generation of bubbles. A ratio of 0.4% by mass or less of organosilicon compounds reduces the possibility that the organosilicon compounds will be present inside the dense layer and hinder selective separation. Furthermore, if the ratio of organosilicon compounds is too high, there is a higher possibility that the liquid composition will peel off from the support during the drying process when manufacturing the carbon dioxide separation membrane 4. From this viewpoint as well, a ratio of 0.4% by mass or less of organosilicon compounds is preferable.

[0043] The organosilicon compound preferably has a structure represented by the following general formula (2).

[0044] In general formula (2), R ４ and R ５Each of these is independently a polyol, a polyether, a hydroxyl group, an acyl group, or an alkoxy group having 1 to 12 carbon atoms. n represents the degree of polymerization. n is, for example, in the range of 5,000 to 100,000.

[0045] As an organosilicon compound, for example, KP-341 (polyether-type surface modifier, medium molecular weight) manufactured by Shin-Etsu Chemical Co., Ltd. can be used. The organosilicon compound may also be an organosilicon compound that is a component of the defoaming agent composition described in Japanese Patent Publication No. 2017-506154 or Japanese Patent Application Publication No. 2018-171619.

[0046] [Carbon Dioxide Separation Membrane] The above-mentioned liquid composition is used in the production of a carbon dioxide separation membrane 4. For example, by exposing the liquid composition to a temperature above the boiling point of a good solvent and volatilizing the good solvent, a partially porous carbon dioxide separation membrane 4 is produced. "Exposing the liquid composition to a temperature above the boiling point of a good solvent" is not limited to exposing the liquid composition to a temperature above the boiling point of a good solvent when it is doped, but also includes exposing the liquid composition to a temperature above the boiling point of a good solvent after it has become a web. In other words, even if the liquid composition is not exposed to a temperature above the boiling point of a good solvent when it is doped, and is only exposed to a temperature above the boiling point of a good solvent after it has become a web, this is also included in "exposing the liquid composition to a temperature above the boiling point of a good solvent".

[0047] The carbon dioxide separation membrane 4 contains a cellulose resin with an acyl group having three or more carbon atoms as a substituent. The carbon dioxide separation membrane 4 also contains residual solvent, but the ratio of residual solvent to the total carbon dioxide separation membrane 4 is preferably 1000 ppm or less. By keeping the ratio of residual solvent to 1000 ppm or less, the solvent vapor is less likely to hinder gas permeability. It is preferable that the amount of good solvent remaining is greater than the amount of poor solvent remaining. As the organic solvent used as the poor solvent, solvents with high affinity for water, such as alcohols, are often used. Therefore, if a large amount of poor solvent remains in the carbon dioxide separation membrane, it becomes easier to dissolve water in the carbon dioxide separation membrane, and carbon dioxide and water will be adsorbed competitively. In order to maintain high carbon dioxide permeability and separation performance, it is necessary to avoid competitive adsorption with water, so it is preferable to reduce the amount of poor solvent.

[0048] The residual solvent contained in the carbon dioxide separation membrane 4 may be the poor solvent and good solvent contained in the liquid composition. If the boiling point of the poor solvent contained in the liquid composition is 10°C or more higher than the boiling point of the good solvent, then the boiling point of the poor solvent in the residual solvent contained in the carbon dioxide separation membrane 4 will also be 10°C or more higher than the boiling point of the good solvent. A carbon dioxide separation membrane 4 formed using a poor solvent and a good solvent with such a relationship in boiling points has a dense layer that is appropriately thin and has good permeability.

[0049] Figure 1 is an SEM image of a cross-section of the carbon dioxide separation membrane 4. Preferably, the carbon dioxide separation membrane 4 is an asymmetric porous membrane having a dense layer 4A which contributes to separation and a porous layer 4B which functions as a support layer responsible for mechanical strength, as shown in Figure 1.

[0050] From the viewpoint of handling, the thickness of the carbon dioxide separation membrane 4 is preferably 10 to 200 μm, and more preferably 20 to 100 μm.

[0051] Figure 2 is a schematic diagram showing an example of a manufacturing apparatus 1 used in the production of a carbon dioxide separation membrane 4 by evaporation-induced phase separation. The manufacturing apparatus 1 shown in Figure 2 comprises a casting apparatus 101, a first drying apparatus 102, a stretching apparatus 103, a second drying apparatus 104, and a winding apparatus 105.

[0052] The casting apparatus 101 performs the casting process. The casting apparatus 101 comprises a support 101a which is an endless belt, a casting die 101b, a heating device 101c, and a peeling roll 101g.

[0053] The support 101a is held rotatably (in the direction of the arrows in the figure) by roll 101a1 and roll 101a2. The support 101a is preferably made of a material with a mirror-finished surface, for example, a metal belt made of cast iron with a plated surface. The width of the support 101a is preferably 1700 to 2700 mm.

[0054] The casting die 101b casts the dope 2 onto the support 101a. Here, the dope 2 is the liquid composition described above. The cast dope 2 is cast while being transported together with the support 101a. The width of the cast dope 2 is preferably 80 to 99% of the width of the support 101a. The thickness of the cast dope 2 can be adjusted by the amount of dope 2, the transport speed, etc., so that the thickness of the carbon dioxide separation membrane 4 that becomes the product is a predetermined thickness.

[0055] The heating device 101c removes the solvent from the dope 2 on the support 101a in order to form a web 3 that can be peeled off from the support 101a. The heating device 101c comprises a drying box 101c1, a first heated air supply device 101d, a second heated air supply device 101e, and an exhaust pipe 101f, all of which are disposed in the drying box 101c1. The first heated air supply device 101d comprises a heated air supply pipe 101d1 and a header 101d2. The second heated air supply device 101e comprises a heated air supply pipe 101e1 and a header 101e2.

[0056] The temperature of the heated air supplied by the first heated air supply device 101d may be a constant temperature, or it may be several different temperatures depending on the direction of movement of the support 101a. The same applies to the temperature of the heated air supplied by the second heated air supply device 101e.

[0057] The air pressure of the heated air supplied from the first heated air supply device 101d and the second heated air supply device 101e is preferably 50 to 5000 Pa, taking into consideration the uniformity of solvent evaporation, the degree of dispersion of fine particles, etc.

[0058] In the casting process, the temperature of dope 2 is preferably -5 to 70°C, and more preferably 0 to 45°C, taking into consideration the transport rate due to the evaporation time of the solvent, the degree of dispersion of fine particles, productivity, etc. Furthermore, in the casting process, it is preferable that the temperatures of the upper and lower surfaces of dope 2 are different. This makes it easier for the ratio of poor solvent to good solvent to change in the thickness direction of dope 2, and facilitates the formation of an asymmetric porous film. The upper surface of dope 2 is the surface opposite to the support 101a. The temperature of the upper surface of dope 2 can be adjusted, for example, by the heating temperature of the first heated air supply device 101d and the second heated air supply device 101e. The lower surface of dope 2 is the surface on the side of the support 101a. The temperature of the lower surface of dope 2 can be adjusted, for example, by the temperature of the support 101a.

[0059] The heating device 101c shown in Figure 2 is an example where heated air is used, but there are no particular limitations on the heating means, and it can be appropriately selected as needed. The heating means may be, for example, a method of heating the dope 2 on the support 101a with an infrared heater, or a method of blowing hot air onto the back surface of the support 101a and heating it from the back side.

[0060] The peeling roll 101g peels the web 3, which has been formed by removing some of the solvent from the dope 2, from the support 101a.

[0061] The casting time can be adjusted depending on the thickness of the carbon dioxide separation membrane 4 to be manufactured, the solvent used, etc. Considering the ease of peeling from the support 101a, the casting time is preferably 0.5 to 5 minutes.

[0062] When the web 3 is peeled from the support 101a, the amount of residual solvent in the web 3 is preferably 30 to 200% by mass, taking into consideration peelability, transportability after peeling, and the physical properties of the carbon dioxide separation membrane 4.

[0063] When the web 3 is peeled from the support 101a, the web 3 is stretched in the direction of transport (Machine Direction: MD direction) by the peeling tension and the subsequent transport tension. Therefore, the peeling and transport tensions when peeling the web from the support 101a are preferably 50 to 400 N / m.

[0064] The amount of residual solvent in the web 3 from the time it is peeled from the support 101a until stretching begins in the stretching device 103 is preferably 5 to 50% by mass, taking into account curling, wrinkling, etc., of the carbon dioxide separation membrane 4.

[0065] The first drying apparatus 102 performs the first drying process. The first drying apparatus 102 comprises a drying box 102a, one or more upper conveying rolls 102d, and one or more lower conveying rolls 102e. The drying box 102a has a drying air intake 102b and an exhaust port 102c. The upper conveying rolls 102d and the lower conveying rolls 102e convey the web 3. The first drying apparatus 102 allows for adjustment of the amount of solvent contained in the web 3 before it enters the stretching apparatus 103.

[0066] The drying temperature in the first drying apparatus 102 varies depending on the amount of residual solvent in the web 3 when it enters the stretching apparatus 103. The drying temperature can be appropriately determined considering the amount of residual solvent, drying time, shrinkage uniformity, stability of expansion and contraction, etc., and is preferably between 50 and 200°C. A drying temperature of 50°C or higher makes it easier to remove the solvent sufficiently. A drying temperature of 200°C or lower reduces the energy required for drying and reduces carbon dioxide emissions. The drying temperature may be constant or may be divided into several stages, for example, two to four stages.

[0067] The stretch ratio in the MD direction of the web 3 from the time it is peeled from the support 101a until the start of stretching in the stretching device 103 is preferably 1 to 25%, taking into consideration the elastic modulus and optical properties of the carbon dioxide separation membrane 4. Furthermore, the stretch ratio in the direction perpendicular to the transport direction of the web 3 (Transverse Direction: TD direction) is preferably -1 to -25%, taking into consideration the elastic modulus and optical properties of the carbon dioxide separation membrane 4.

[0068] The stretching device 103 performs a stretching process. The stretching process can adjust the size of the pores in the porous layer of the carbon dioxide separation membrane 4. The stretching device 103 comprises an outer casing 103a and a tenter 103d placed inside the outer casing 103a. The outer casing 103a has a dry air intake 103b and an exhaust port 103c. The tenter 103d may be, for example, a clip tenter, a pin tenter, etc. The tenter may be selected as needed.

[0069] In the tenter 103d, the web 3 can be stretched in the MD and TD directions as needed. The stretching rate in the stretching process is preferably 10-50% to control the stretching rate in a way that connects the porous materials and further increases permeability. The stretching rate in the stretching process is calculated using the following formula. The width of the web 3 from the center to the end is measured using a C-type JIS Class 1 steel scale. Stretching rate (%) = (Width of web 3 from center to end after stretching / Width of web 3 from center to end before stretching) × 100

[0070] The amount of residual solvent in the web at the start of stretching in the stretching device 103 is preferably 10 to 30% by mass, taking into consideration scratches, shrinkage rate, deformation, etc. The positions of the drying air intake port 103b and the exhaust port 103c may be reversed. The solvent removal means in the stretching device 103 is shown as using heated air, but there are no particular limitations on the solvent removal means. In addition to using heated air, the solvent removal means in the stretching device 103 may also be, for example, heating with an infrared heater.

[0071] The second drying apparatus 104 performs a second drying process. The second drying process facilitates the formation of an asymmetric porous membrane. The second drying apparatus 104 comprises a drying box 104a, one or more upper conveying rolls 104d, and one or more lower conveying rolls 104e. The drying box 104a has a drying air intake 104b and an exhaust port 104c. The upper conveying rolls 104d and the lower conveying rolls 104e convey the web 3. The number of conveying rolls arranged in the second drying apparatus 104 can be appropriately set depending on the drying conditions, method, length of the carbon dioxide separation membrane 4 to be manufactured, etc. The upper conveying rolls 104d and the lower conveying rolls 104e are free-rotating rolls that are not rotated by a drive source. Furthermore, not all conveying rolls that rotate freely are used between the second drying device 104 and the winding device 105. Typically, one to several drive rolls for conveying (rolls that are driven to rotate by a drive source) are required. The purpose of these drive rolls is to convey the carbon dioxide separation membrane 4 by their drive. For this reason, the drive rolls are equipped with a mechanism, such as a nip or suction (air suction), to synchronize the conveying of the carbon dioxide separation membrane 4 with the rotation of the drive rolls.

[0072] In the second drying step of the second drying apparatus 104, heated air, infrared rays, etc. may be used individually, or heated air and infrared rays may be used in combination. For simplicity, it is preferable that the second drying apparatus 104 uses heated air. Figure 2 shows the case when the second drying apparatus 104 uses heated air. The drying temperature in the second drying step can be appropriately determined considering the amount of residual solvent, drying time, shrinkage uniformity, stability of expansion and contraction, etc., and is preferably 50 to 200°C. A drying temperature of 50°C or higher makes it easier to sufficiently remove the solvent. A drying temperature of 200°C or lower reduces the energy required for drying and reduces carbon dioxide emissions. The drying temperature may be constant, or it may be divided into several stages, for example, 2 to 4 stages.

[0073] The drying temperature in the second drying step is preferably different from the drying temperature in the first drying step, and preferably higher than the drying temperature in the first drying step. This facilitates the formation of an asymmetric porous film.

[0074] The winding device 105 performs the winding process. The winding device 105 winds the carbon dioxide separation membrane 4, which is the dried web 3, onto the winding core to the required length. When winding, it is preferable to cool the carbon dioxide separation membrane 4 to room temperature to prevent scratches and loosening due to shrinkage after winding. The winding machine used is not particularly limited and can be one that is commonly used. The winding method may be a constant tension method, a constant torque method, a tapered tension method, a programmed tension control method with constant internal stress, etc.

[0075] The expansion and contraction ratio of the wound carbon dioxide separation membrane 4 is preferably 0 to 20% in the MD direction and -3 to 20% in the TD direction, taking into consideration the physical properties of the carbon dioxide separation membrane 4.

[0076] Another embodiment of the method for producing a carbon dioxide separation membrane of the present invention involves coating a nonwoven fabric, which is a substrate, with the liquid composition of the present invention, and exposing the liquid composition coated on the nonwoven fabric to a temperature above the boiling point of a good solvent. As a result, the good solvent volatilizes from the liquid composition, and a carbon dioxide separation membrane is obtained in which part is porous. This results in a laminate comprising a nonwoven fabric and a carbon dioxide separation membrane laminated on the nonwoven fabric.

[0077] Examples of the above-mentioned base material (nonwoven fabric) include polyester polymers, polyamide polymers, polyolefin polymers, or mixtures and copolymers thereof. Among these, fabrics made of polyester polymers, which have high mechanical and thermal stability, are particularly preferred.

[0078] The base material has an air permeability of 0.5 cc / cm². ２ / sec or more, 5.0cc / cm ２ It is preferable that the air permeability of the substrate is less than or equal to / sec. When the air permeability of the substrate is within the above range, the polymer solution that forms the porous support layer is impregnated into the substrate, thereby improving adhesion to the substrate and enhancing the physical stability of the microporous support film.

[0079] The thickness of the substrate is preferably in the range of 10 to 200 μm, and more preferably in the range of 30 to 120 μm. In this specification, unless otherwise specified, thickness refers to the average value. Here, the average value represents the arithmetic mean. That is, the thickness of the substrate and the porous support layer is determined by calculating the average value of the thicknesses of 20 points measured at 20 μm intervals in a direction perpendicular to the thickness direction (the surface direction of the film) in a cross-sectional observation.

[0080] Commercially available nonwoven fabrics can be used as the base material for Awa Paper Co., Ltd. Examples include Awa Paper Co., Ltd.'s product number PY120-47 (thickness 60 μm) and Hirose Paper Co., Ltd.'s product number 05TH100S (thickness 100 μm).

[0081] [Separation Membrane Module] The separation membrane module 50 includes the carbon dioxide separation membrane 4 described above. Figure 3 is a partially cutaway schematic diagram showing an example of the separation membrane module 50. As shown in Figure 3, the separation membrane module 50 may have as its basic structure a permeate gas manifold 52, one or more laminates 54, a coating layer 56, and a telescope prevention plate 58. In the example shown in Figure 3, one or more laminates 54 are wrapped around the permeate gas manifold 52. The coating layer 56 covers the outermost periphery of the laminates 54. The telescope prevention plate 58 is attached to both ends of the unit having the permeate gas manifold 52, the laminates 54, and the coating layer 56.

[0082] The separation membrane module 50 separates the raw material gas 60 containing carbon dioxide supplied from one end 50A into carbon dioxide 62 and other gases 64, and discharges them separately from the other end 50B.

[0083] The permeable gas manifold 52 is a cylindrical tube with multiple through-holes 52A formed in its wall. One end of the permeable gas manifold 52 (end 50A) is closed. The other end of the permeable gas manifold 52 (end 50B) is open and serves as an outlet 66 through which carbon dioxide 62 collected through the through-holes 52A after permeating the laminate 54 is discharged.

[0084] The ratio of through-holes 52A to the surface area of ​​the permeate gas manifold 52 (opening ratio) is preferably 1.5 to 80%, more preferably 3 to 75%, and even more preferably 5 to 70%. Furthermore, from a practical standpoint, the opening ratio is preferably 5 to 25%. When the opening ratio is above each lower limit, carbon dioxide 62 can be collected efficiently. When the opening ratio is below each upper limit, the strength of the cylinder can be increased and sufficient workability can be ensured.

[0085] The shape of the through-hole 52A is not particularly limited, but it is preferable that it is a circular hole with a diameter of 1 to 20 mm. It is preferable that the through-hole 52A are uniformly arranged on the surface of the permeable gas manifold 52.

[0086] The coating layer 56 is formed of a barrier material capable of blocking the raw material gas 60 passing through the separation membrane module 50. The barrier material preferably has heat resistance and moisture resistance. "Heat resistance" means that even after being stored in an environment of 80°C or higher for 2 hours, the shape before storage is maintained and no visible curl occurs due to thermal shrinkage or thermal melting. "Moisture resistance" means that even after being stored in an environment of 40°C and 80% RH for 2 hours, the shape before storage is maintained and no visible curl occurs due to thermal shrinkage or thermal melting.

[0087] The telescopic prevention plate 58 has an outer annular portion 58A, an inner annular portion 58B, and radial spoke portions 58C. Preferably, the outer annular portion 58A, the inner annular portion 58B, and the radial spoke portions 58C are made of a material that has heat resistance and moisture resistance.

[0088] The laminate 54 is composed of a folded carbon dioxide separation membrane 4 and a supply gas flow channel member 70 sandwiched inside it. A sealing portion 74 is permeated into the carbon dioxide separation membrane 4 and the supply gas flow channel member 70. The carbon dioxide separation membrane 4 is adhesively sealed to the permeate gas flow channel member 76 via the sealing portion 74 on its radially inner side. As described above, the carbon dioxide separation membrane 4 is an asymmetric porous membrane having a dense layer 4A which contributes to separation and a porous layer 4B which functions as a support layer responsible for mechanical strength.

[0089] The number of laminates 54 wrapped around the permeable gas manifold 52 is not particularly limited and may be one or more. By increasing the number of laminates 54 wrapped around the permeable gas manifold 52 (number of layers), the membrane area of ​​the dense layer 4A can be increased. By increasing the membrane area of ​​the dense layer 4A, the amount of carbon dioxide 62 separated by a single separation membrane module 50 can be increased. The length of the laminate 54 may be increased to increase the membrane area of ​​the dense layer 4A.

[0090] The number of layers in the laminate 54 is not particularly limited, but is preferably 50 or less, more preferably 45 or less, and even more preferably 40 or less. This makes it easier to wrap the laminate 54 and improves its processability.

[0091] The width of the laminate 54 is not particularly limited, but is preferably 50 to 10,000 mm, more preferably 60 to 9,000 mm, and even more preferably 70 to 8,000 mm. Furthermore, from a practical standpoint, the width of the laminate 54 is preferably 200 to 2,000 mm. By having a width of the laminate 54 above each lower limit, an effective film area of ​​the dense layer 4A can be secured even with resin coating (sealing). By having a width of the laminate 54 below each upper limit, the horizontality of the winding core can be maintained and the occurrence of winding misalignment can be suppressed.

[0092] Figure 4 is a cross-sectional perspective view showing a portion of a cylindrical winding body in which a laminate 54 is wound around a permeable gas manifold 52. Figure 4 schematically shows the entire width of the cylindrical winding body, with the central portion shortened. As shown in Figure 4, the laminates 54 are bonded to each other via sealing portions 80 that have permeated the carbon dioxide separation membrane 4, and are stacked around the permeable gas manifold 52. Specifically, the laminate 54 is made up of a permeable gas flow path member 76, a carbon dioxide separation membrane 4, a supply gas flow path member 70, and a carbon dioxide separation membrane 4, stacked in that order from the permeable gas manifold 52 side. The raw material gas 60 is supplied from the end of the supply gas flow path member 70. Of the supplied raw material gas 60, carbon dioxide 62 is separated by permeating through the carbon dioxide separation membrane 4 partitioned by the coating layer 56. The separated carbon dioxide 62 is collected in the permeable gas manifold 52 via the permeable gas flow path member 76 and the through-hole 52A, and is recovered from the outlet 66 connected to this permeable gas manifold 52. The remaining gas 64, from which the carbon dioxide 62 has been separated, is discharged from the supply gas flow path member 70 on the side where the outlet 66 is provided, or from the end of the carbon dioxide separation membrane 4.

[0093] Figure 5 is a schematic diagram showing the state before the laminate 54 is wrapped around the permeate gas manifold 52. Figure 5 shows an example of the formation regions of the sealing portion 74 and the sealing portion 80. The sealing portion 80 seals the carbon dioxide separation membrane 4 and the permeate gas flow path member 76 while the laminate 54 is wrapped around the permeate gas manifold 52 in the direction of arrow R in the figure. On the other hand, the sealing portion 74 seals the carbon dioxide separation membrane 4 and the permeate gas flow path member 76 while they are still attached to the permeate gas manifold 52, even before the laminate 54 is wrapped around it.

[0094] The sealing portion 74 has a circumferential sealing portion 74A and an axial sealing portion 74B. The sealing portion 80 has a circumferential sealing portion 80A and an axial sealing portion 80B. The circumferential sealing portions 74A and 80A seal both ends of the carbon dioxide separation membrane 4 and the permeate gas flow path member 76 along the circumferential direction of the permeate gas manifold 52. The axial sealing portions 74B and 80B seal the circumferential ends of the carbon dioxide separation membrane 4 and the permeate gas flow path member 76.

[0095] The circumferential sealing portion 74A and the axial sealing portion 74B are connected, and the sealing portion 74 as a whole is envelope-shaped with an open circumferential end between the carbon dioxide separation membrane 4 at the beginning of the winding and the permeate gas flow path member 76. Between the circumferential sealing portion 74A and the axial sealing portion 74B, a flow path P1 is formed through which carbon dioxide 62 that has permeated the carbon dioxide separation membrane 4 flows to the through hole 52A. Similarly, the circumferential sealing portion 80A and the axial sealing portion 80B are connected, and the sealing portion 80 as a whole is envelope-shaped with an open circumferential end between the carbon dioxide separation membrane 4 at the beginning of the winding and the permeate gas flow path member 76. Between the circumferential sealing portion 80A and the axial sealing portion 80B, a flow path P2 is formed through which carbon dioxide 62 that has permeated the carbon dioxide separation membrane 4 flows to the through hole 52A.

[0096] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, the operations were carried out at room temperature (25°C). In the following examples, unless otherwise specified, "%" and "parts" mean "mass%" and "parts by mass," respectively.

[0097] The following resins were used: • Cellulose resin A (cellulose acetate propionate, acetyl group substitution degree 1.6, propionyl group substitution degree 0.9, total acyl group substitution degree 2.5, number average molecular weight (Mn) 64000) • Cellulose acetate propionate CAP-482-20 (manufactured by Eastman) • Cellulose acetate butyrate CAB-381-20 (manufactured by Eastman) • Cellulose acetate CA394-60LF (manufactured by Eastman) • Cellulose acetate L-70 (manufactured by Daicel)

[0098] [Preparation of Liquid Composition No. 1] A mixed solvent was prepared by mixing dichloromethane (good solvent) and ethanol (poor solvent). The ratio of ethanol (poor solvent) in the mixed solvent was 45% by mass. Cellulose resin A was added to the mixed solvent as a resin so that the resin content was 8% by mass. This was heated and stirred to completely dissolve the resin in the mixed solvent. This was filtered using Asaka filter paper No. 244 (manufactured by Asaka Filter Paper Co., Ltd.). Liquid composition No. 1 was obtained.

[0099] [Production of Liquid Compositions No. 2 to 23] Liquid compositions No. 2 to 23 were produced in the same manner as in the production of liquid composition No. 1, except that the following conditions were changed as shown in Tables I and II. In the production of liquid compositions No. 7 and No. 8, KP341 (manufactured by Shin-Etsu Chemical Co., Ltd.) was added as an organosilicon compound. • Type of resin (two types were used in a mass ratio of 1:1 for liquid composition No. 17) and ratio • Type and ratio of good solvent • Type and ratio of poor solvent • Ratio of organosilicon compound

[0100] In Tables I, II, and V, "Ratio A" represents the ratio to the entire liquid composition. In Tables I, II, and V, "Ratio B" represents the ratio to the entire solvent.

[0101] [Production of carbon dioxide separation membranes No. 1 to 23] Using the production apparatus 1 shown in Figure 1, carbon dioxide separation membranes No. 1 to 23 were produced from liquid compositions No. 1 to 23 according to the following procedure.

[0102] A liquid composition maintained at a temperature of 20°C was uniformly cast as a dope onto a support 101a with a set temperature of 25°C at a casting speed of 2 m / min. As the support 101a, an endless belt made of stainless steel with a mirror-finished surface was used. Using the manufacturing apparatus 1 shown in Figure 1, drying air at a set temperature of 30°C, a wind pressure of 500 Pa, and a wind speed of 5 m / s was supplied to the liquid composition during casting from the first heated air supply device 101d and the second heated air supply device 101e, causing phase separation on the support 101a. This formed a web.

[0103] Next, the web was peeled from the support 101a using a peeling roll 101g. Then, the web was exposed to temperatures above the boiling point of a good solvent using a first drying apparatus 102, a stretching apparatus 103, and a second drying apparatus 104, causing the good solvent to volatilize and partially making the web porous. The setting temperature for the first drying apparatus 102 was 60°C. The setting temperature for the stretching apparatus 103 was 180°C. The setting temperature for the second drying apparatus 104 was 120°C for the production of carbon dioxide separation membranes other than No. 11 to 13, 140°C for the production of carbon dioxide separation membrane No. 11, 160°C for the production of carbon dioxide separation membrane No. 12, and 180°C for the production of carbon dioxide separation membrane No. 13.

[0104] Next, the dried web of the carbon dioxide separation membrane was wound up using the winding device 105. Through the above procedure, carbon dioxide separation membranes No. 1 to 23, each with a width of 300 mm and a length of 5 m, were obtained.

[0105] [Preparation of Liquid Compositions 24-28] Liquid composition No. 24 and liquid composition No. 25 were the same as liquid composition No. 4. Liquid composition No. 26 was the same as liquid composition No. 4 except that the good solvent was acetone. Liquid composition No. 27 was the same as liquid composition No. 4 except that the good solvent was ethyl acetate. Liquid composition No. 28 was the same as liquid composition No. 4 except that the good solvent was methyl ethyl ketone.

[0106] [Manufacturing of Carbon Dioxide Separation Membranes No. 24-28] In the manufacturing of carbon dioxide separation membrane No. 24, a nonwoven fabric with a width of 320 mm and a length of 200 m was used as the base material. Liquid composition No. 24, kept at 20°C, was applied to the surface of the nonwoven fabric by vacuum extrusion using a die coater, and phase separation was performed by passing it through a drying zone. The amount of liquid composition No. 24 applied was 20% less than the amount used when manufacturing carbon dioxide separation membrane No. 4. The drying zone is a zone supplied with drying air at a set temperature of 30°C, a wind pressure of 500 Pa, and a wind speed of 5 m / s. The speed at which the material passed through the drying zone (line speed) was set to 1 m / min. Phase separation is the formation of a dense layer and a porous layer during the drying process of the liquid composition. After that, it was dried under the same drying conditions as carbon dioxide separation membrane No. 1, and then wound up using a winding device to obtain carbon dioxide separation membrane No. 24. The obtained carbon dioxide separation membrane was partially permeated into the nonwoven fabric, and the penetration depth into the nonwoven fabric observed in the cross-sectional SEM image was 11 μm. In the production of carbon dioxide separation membranes No. 24 to 28, the nonwoven fabric used was PY120-47 (thickness 60 μm), manufactured by Awa Paper Co., Ltd.

[0107] Carbon dioxide separation membrane No. 25 was manufactured in the same manner as carbon dioxide separation membrane No. 24, except that the amount of liquid composition No. 25 applied was 30% less than that used to manufacture carbon dioxide separation membrane No. 4. The penetration depth into the nonwoven fabric observed in cross-sectional SEM images was 9 μm.

[0108] Carbon dioxide separation membranes No. 26 to 28 were manufactured in the same manner as carbon dioxide separation membrane No. 25, except that the liquid compositions were designated as liquid compositions No. 26 to 28, respectively. The penetration depth into the nonwoven fabric of carbon dioxide separation membranes No. 26 to 28, as observed in cross-sectional SEM images, was 9 μm for all of them.

[0109] [Cross-sectional SEM image observation] Cross-sectional SEM images of carbon dioxide separation membranes No. 1 to 28 were observed, and all were found to be asymmetric porous membranes with a thickness of approximately 40 μm, consisting of a dense layer and a porous layer. The thicknesses of the dense layer and porous layer measured from the cross-sectional SEM images are shown in Tables III, IV, and VI.

[0110] [Residual Solvent] Residual solvent analysis using headspace GC-FID was performed to analyze the poor and good solvents present in carbon dioxide separation membranes No. 1 to 23. As a result, in all of carbon dioxide separation membranes No. 1 to 23, the amount of good solvent remaining was greater than the amount of poor solvent remaining, the ratio of the total residual solvent to the entire carbon dioxide separation membrane was 1000 ppm or less, and the types of poor and good solvents were the same as those used in the production of the liquid composition.

[0111] [Permeability] The gas permeability [GPU] through the carbon dioxide separation membrane was measured using a gas permeability measuring device (GTR-11A manufactured by GTR Tech) in accordance with JIS K 7126 Part 1 (differential pressure method, gas chromatography). A mixed gas consisting of nitrogen and carbon dioxide was used as the gas. "1 GPU" is equal to "1 × 10⁻¹⁶". －６ cm ３ (STP) / (sec・cm ２ ・cmHg) ３ "(STP)" is a unit of gas volume at 1 atmosphere and 0°C. A higher value for permeability [GPU] indicates higher permeability. The permeability [GPU] values ​​for carbon dioxide separation membranes No. 1 to 23 are shown in Tables III, IV, and VI. In the case of carbon dioxide separation membrane No. 13, the set temperature of the second drying apparatus 104 was close to the glass transition point of the resin, causing the resin to shrink, and as a result, it was not possible to evaluate the permeability.

[0112] [Selective Separation] In the permeability test described above, the ratio of the volume of carbon dioxide V1 to the volume of nitrogen V2 that permeated the carbon dioxide separation membrane, V1 / V2, was determined. A larger value of V1 / V2 indicates higher selective separation. The V1 / V2 values ​​for carbon dioxide separation membranes No. 1 to 23 are shown in Table III, Table IV, and Table VI. In the case of carbon dioxide separation membrane No. 13, the set temperature of the second drying apparatus 104 was close to the glass transition point of the resin, causing the resin to shrink, and as a result, the selective separation could not be evaluated.

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] From the above results, it was confirmed that the liquid composition of the present invention can form a carbon dioxide separation membrane that achieves both permeability and selective separation. Furthermore, it was found that laminating the carbon dioxide separation membrane onto a nonwoven fabric makes it possible to make the carbon dioxide separation membrane thinner. It was also found that lamination of the carbon dioxide separation membrane onto a nonwoven fabric does not impair its permeability and selectivity.

[0120] The above description and drawings are for illustrative purposes only and do not intend to limit the scope of the present invention. The scope of the present invention should be interpreted as stated in the claims.

[0121] According to the liquid composition of this disclosure, a carbon dioxide separation membrane that achieves both permeability and selective separation can be formed. According to the method for producing a carbon dioxide separation membrane of this disclosure, a carbon dioxide separation membrane that achieves both permeability and selective separation can be formed using the liquid composition of this disclosure. According to the carbon dioxide separation membrane and separation membrane module of this disclosure, both permeability and selective separation can be achieved.

[0122] 1. Manufacturing equipment 101. Casting apparatus 102. First drying apparatus 103. Stretching apparatus 104. Second drying apparatus 105. Winding apparatus 2. Dope (liquid composition) 3. Web 4. Carbon dioxide separation membrane 4A. Dense layer 4B. Porous layer 50. Separation membrane module

Claims

1. A liquid composition for forming a carbon dioxide separation membrane, comprising a solvent and a resin, wherein the solvent comprises a poor solvent having a boiling point of 170°C or less and a good solvent having a boiling point of 100°C or less, and the resin mainly comprises a cellulose resin having an acyl group with 3 or more carbon atoms as a substituent, the ratio of the poor solvent to the total solvent is in the range of 30 to 60% by mass, and the ratio of the resin to the total liquid composition is 14% by mass or less.

2. The liquid composition according to claim 1, wherein the liquid composition contains an organosilicon compound in an amount of 0.01 to 0.4% by mass relative to the entire liquid composition.

3. The liquid composition according to claim 1, wherein the boiling point of the poor solvent is 10°C or more greater than the boiling point of the good solvent.

4. A method for producing a carbon dioxide separation membrane, comprising exposing the liquid composition described in claim 1 to a temperature above the boiling point of the good solvent and volatilizing the good solvent to produce a carbon dioxide separation membrane in which a portion is porous.

5. A method for producing a carbon dioxide separation membrane according to claim 4, comprising applying the liquid composition onto a nonwoven fabric which is a base material, and exposing the liquid composition applied onto the nonwoven fabric to a temperature above the boiling point of the good solvent.

6. A carbon dioxide separation membrane comprising a cellulose resin having an acyl group with three or more carbon atoms as a substituent, and a residual solvent, wherein the residual solvent contains a good solvent and a poor solvent, the residual amount of the good solvent is greater than the residual amount of the poor solvent, the ratio of the residual solvent to the entire carbon dioxide separation membrane is 1000 ppm or less, and the boiling point of the poor solvent is 10°C or more greater than the boiling point of the good solvent.

7. A separation membrane module comprising the carbon dioxide separation membrane described in claim 6.

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