Carbon dioxide separation membrane, manufacturing method of carbon dioxide separation membrane, carbon dioxide separation method, and carbon dioxide separation membrane module

Abstract

To provide a carbon dioxide separation membrane that has a large permeation flow flux of carbon dioxide, and a high carbon dioxide selectivity.SOLUTION: A carbon dioxide separation membrane includes: a porous membrane in which a permeation flow flux of air is 10,000 GPU or higher; and a separation function layer formed on a surface of the porous membrane. The separation function layer is made of a composition containing: a water-soluble polymer not having a bridge structure; and an amine compound with a molecular mass of 500 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a carbon dioxide separation membrane that selectively separates carbon dioxide from a carbon dioxide-containing mixed gas, a method for producing the carbon dioxide separation membrane, a carbon dioxide separation method using the carbon dioxide separation membrane, and a carbon dioxide separation membrane module using the carbon dioxide separation membrane. [Background technology]

[0002] It has been known that polymeric materials have gas permeability specific to the material, and therefore gas components can be separated by membranes made of polymeric materials (see, for example, Non-Patent Document 1). Gas separation membranes that utilize this property are an energy-saving and space-saving separation technology and are used in a variety of fields.

[0003] Meanwhile, in recent years, technology to separate and capture carbon dioxide, which causes global warming, before it is emitted into the atmosphere from large-scale sources such as thermal power plants and steelworks blast furnaces has been attracting attention. One such technology that has been put to practical use is a process in which carbon dioxide is absorbed by amines and desorbed by heating. However, the need for heating to desorb carbon dioxide has led to an issue of high capture costs.

[0004] In order to overcome the above problems, a carbon dioxide separation and capture process using membrane separation has been proposed. In particular, processes using polymer membranes have attracted attention because polymer membranes are easy to chemically modify and modularize, and mass production is possible, enabling low costs. However, at present, there are no examples of practical application, and studies are limited to the pilot level (for example, see Non-Patent Document 2). The reason why practical application has not been achieved is that the carbon dioxide permeation rate and carbon dioxide selectivity are low, falling short of the required characteristics.

[0005] In order to improve carbon dioxide selectivity, research and development on facilitated transport membranes has been conducted. A facilitated transport membrane is a membrane that introduces a substance (carrier) that reacts reversibly and selectively only with a specific permeant. Since the permeant can permeate by forming a reaction product with the carrier in addition to the dissolution and diffusion mechanism through the membrane matrix, it is possible to obtain high selectivity compared with coexisting components other than the permeant that permeates only by the dissolution and diffusion mechanism. As such facilitated transport membranes, a polymer membrane in which a gel layer consisting of a polyvinyl alcohol-polyacrylic acid copolymer gel membrane and 2,3-diaminopropionic acid is supported on a hydrophilic ultrafiltration membrane (see, for example, Patent Document 1), a polymer membrane containing a water-soluble polymer and a specific amine compound (see, for example, Patent Document 2), and a polymer membrane consisting of a polyamidoamine dendrimer, a substance having affinity for carbon dioxide, and a polyethylene glycol crosslinked body obtained by photocrosslinking polymerization of polyethylene glycol dimethacrylate (see, for example, Patent Document 3) have been disclosed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2008-36463 A [Patent Document 2] JP 2018-144022 A [Patent Document 3] JP 2009-185118 A [Non-patent literature]

[0007] [Non-Patent Document 1] Toray Research Center, Research and Development Division, "New Developments in Gas Separation Technology", Toray Research Center, Inc., 1990, pp.345-362 [Non-Patent Document 2] Journal of Membrane Science,2010,Vol.359,Issue1-2,p.126-139 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in order to reduce the cost of carbon dioxide capture, even higher carbon dioxide selectivity is required, and there is a demand for higher performance polymer membranes.

[0009] An object of the present disclosure is to provide a carbon dioxide separation membrane having a large carbon dioxide permeation flux and high carbon dioxide selectivity. Another object of the present disclosure is to provide a method for producing the carbon dioxide separation membrane, a carbon dioxide separation method using the carbon dioxide separation membrane, and a carbon dioxide separation membrane module using the carbon dioxide separation membrane. [Means for solving the problem]

[0010] As a result of intensive research, the inventors have discovered that in a carbon dioxide separation membrane having a porous membrane and a separation functional layer formed on its surface, the above-mentioned problem can be solved by using a porous membrane having an air permeation flux of a specific value or more and a separation functional layer of a specific composition. In other words, the present disclosure is summarized as follows.

[0011] [1] A carbon dioxide separation membrane having a porous membrane with an air permeation flux of 10,000 GPU or more and a separation functional layer formed on the surface of the porous membrane, the separation functional layer being made of a composition containing a water-soluble polymer not having a cross-linked structure and an amine compound having a molecular weight of 500 or less. [2] The carbon dioxide separation membrane according to [1], wherein the water-soluble polymer not having a crosslinked structure is at least one selected from the group consisting of polyvinyl alcohol, poly(meth)acrylic acid, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, polyallylamine, polysaccharides, salts thereof, and copolymers thereof. [3] The carbon dioxide separation membrane according to [1] or [2], wherein the amine compound having a molecular weight of 500 or less is at least one selected from the group consisting of a compound represented by the following formula (1) and a compound represented by the following formula (2): [ka] (In formula (1), R 1 , R 2 and R 3 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a hydroxyethyl group. [ka] (In formula (2), R 4 , R 5 and R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. [4] The carbon dioxide separation membrane according to any one of [1] to [3], wherein the porous membrane is a hollow fiber membrane, and the separation functional layer is formed on either or both of the outer surface and the inner surface of the hollow fiber membrane. [5] A method for producing a carbon dioxide separation membrane according to any one of [1] to [4], A method for producing a carbon dioxide separation membrane, comprising: a retaining step of contacting the porous membrane with a solution containing the water-soluble polymer not having a crosslinked structure, the amine compound having a molecular weight of 500 or less, and a solvent, and retaining the solution on the surface of the porous membrane; and a drying step of removing the solvent from the solution retained in the porous membrane. [6] A method for separating carbon dioxide, comprising a separation step of contacting a mixed gas containing carbon dioxide with one end of the carbon dioxide separation membrane described in any one of [1] to [4] and allowing the carbon dioxide in the mixed gas to permeate to the other end of the carbon dioxide separation membrane. [7] A carbon dioxide separation membrane module comprising the carbon dioxide separation membrane according to any one of [1] to [4]. Effect of the Invention

[0012] According to the present disclosure, it is possible to provide a carbon dioxide separation membrane having a large carbon dioxide permeation flux and high carbon dioxide selectivity. Also, according to the present disclosure, it is possible to provide a method for producing the carbon dioxide separation membrane, a carbon dioxide separation method using the carbon dioxide separation membrane, and a carbon dioxide separation membrane module using the carbon dioxide separation membrane. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram of a gas separation apparatus used in the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present disclosure will be described in detail below. The carbon dioxide separation membrane according to the first embodiment of the present disclosure comprises a porous membrane having an air permeation flux of 10,000 GPU or more, and a separation functional layer formed on the surface of the porous membrane, and is characterized in that the separation functional layer is made of a composition containing a water-soluble polymer not having a cross-linked structure and an amine compound having a molecular weight of 500 or less.

[0015] In general, in gas separation membranes made of polymeric materials, there is a trade-off between gas permeation flux and selectivity, with membranes with high permeation flux having low selectivity. In contrast, the carbon dioxide separation membrane of this embodiment has both high carbon dioxide permeation flux and selectivity, and is highly practical. In addition, the carbon dioxide separation membrane of this embodiment has very excellent stability because the amine compound having carbon dioxide separation ability is not supported but is incorporated within the membrane.

[0016] The porous membrane used in this embodiment is preferably an ultrafiltration membrane, and in the case of an ultrafiltration membrane, the molecular weight cutoff is preferably 500,000 or less, more preferably 500 to 200,000, and may be a composite membrane consisting of multiple layers. When the molecular weight cutoff is in the above range, the interface between the separation functional layer formed on the surface of the porous membrane and the porous membrane becomes clear, and the diffusion of water-soluble polymers without a crosslinked structure into the inside of the porous membrane is suppressed, so that the gas permeation resistance is reduced and the permeation flux of carbon dioxide is improved. When the porous membrane is an ultrafiltration membrane, the fractionation characteristics are defined by the molecular weight cutoff, and the average pore size is not particularly defined, but is preferably about 1 to 50 nm. In this embodiment, several types of marker molecules with different molecular weights are introduced into the porous membrane to measure the rejection rate, and the molecular weight at which the rejection rate is 90% is defined as the molecular weight cutoff of the membrane. Proteins such as insulin, cytochrome C, and pepsin are used as marker molecules.

[0017] The air permeation flux of the porous membrane used in this embodiment is 10,000 GPU or more, preferably 10,000 to 500,000 GPU, more preferably 20,000 to 200,000 GPU, and even more preferably 20,000 to 100,000 GPU. The permeation flux is the permeation rate of a fluid divided by the membrane area and the transmembrane pressure difference. In this embodiment, The air permeation flux is calculated by measuring the amount of air passing through with a mass flow meter and dividing it by the membrane area. It is believed that a porous membrane with a permeation flux in this range has a high surface openness, which reduces the gas permeation resistance and improves the carbon dioxide permeation flux. The GPU used here is the unit of permeation flux, and 1 GPU = 7.5 x 10 -12 m 3 (STP) / (m 2 It is expressed as a pressure (MPa) per unit area (s·Pa). It is unclear why the carbon dioxide selectivity is affected by the porous membrane substrate, but the use of a porous membrane with an air permeation flux of 10,000 GPU or more improves the carbon dioxide permeation selectivity of the carbon dioxide separation membrane.

[0018] The shape of the porous membrane includes a sheet-like flat membrane and a hollow fiber membrane, among which a hollow fiber membrane is preferred. When the porous membrane is a flat membrane, its thickness is preferably 10 to 3,000 μm, more preferably 50 to 500 μm. A flat membrane having the above thickness is preferred because it is possible to ensure low permeation resistance and mechanical strength. On the other hand, when the porous membrane is a hollow fiber membrane, the inner diameter of the hollow fiber (hereinafter sometimes referred to as "membrane inner diameter") is preferably 100 to 3,000 μm, and the membrane thickness is preferably 25 to 300 μm. The thicknesses of the porous membrane and the separation functional layer are measured by observation with a scanning electron microscope (SEM).

[0019] The structure of the porous membrane is not particularly limited, but an asymmetric structure in which the surface layer is a dense layer with a small pore size and the lower layer is a support layer with a large pore size is preferable because it can reduce the permeation resistance and increase the permeation flux. The porosity of the cross section of the porous membrane is preferably 60 to 90%, more preferably 70 to 85%. The porosity of the porous membrane is calculated by mercury intrusion porosimetry or image analysis of the membrane cross section using a scanning electron microscope.

[0020] There are no particular limitations on the material of the porous membrane, and examples of the material include polyolefins such as polyethylene and polypropylene; fluorine-containing polymers such as polytetrafluoroethylene, polyvinyl fluoride and polyvinylidene fluoride; chlorine-containing polymers such as polyvinyl chloride and polyvinylidene chloride; vinyl polymers such as polystyrene, polyacrylonitrile and polymethyl methacrylate; condensation polymers such as polysulfone, polyethersulfone, polyetherimide, polyamide, polyurethane and polyimide; and polysaccharides such as cellulose acetate and chitosan.

[0021] The separation functional layer used in this embodiment is made of a composition containing a water-soluble polymer having no crosslinked structure and an amine compound having a molecular weight of 500 or less, and is formed on the surface of the porous membrane. This composition is preferably a homogeneous composition. This is because a carbon dioxide separation membrane in which a separation functional layer is formed from a homogeneous composition has more amine compounds having a molecular weight of 500 or less incorporated into the membrane, and the stability is further improved. In addition, the composition constituting the separation functional layer is preferably made of only a water-soluble polymer having no crosslinked structure and an amine compound having a molecular weight of 500 or less, but may contain other components other than the water-soluble polymer having no crosslinked structure and the amine compound having a molecular weight of 500 or less within a range that does not inhibit the above-mentioned effect. When the composition contains other components, the content of the other components in the composition is preferably 30% by weight or less.

[0022] When the porous membrane is a flat membrane having an asymmetric structure, the separation functional layer is formed on the surface of a dense layer having a small pore size. When the porous membrane is a hollow fiber membrane, the separation functional layer is preferably formed on either or both of the outer and inner surfaces of the hollow fiber membrane, and it is more preferable that the separation functional layer is formed on the inner surface, since the separation functional layer can be uniformly formed and the separation functional layer is less likely to be damaged even when the membranes contact each other. There is no particular limit to the thickness of the separation functional layer, but it is preferably in the range of 0.1 to 10.0 μm. When the thickness of the separation functional layer is in this range, the amine compound having a molecular weight of 500 or less contained in the membrane can be stably retained, so durability can be ensured. In addition, a membrane thickness of 10.0 μm or less is preferable because it can increase the permeation flux of carbon dioxide.

[0023] The water-soluble polymer having no cross-linked structure constituting the separation functional layer is a polymer that can be dissolved in water and dried. There are no particular limitations as long as the polymer can form a film when used, but a water-soluble polymer without a crosslinked structure that has excellent affinity with an amine compound with a molecular weight of 500 or less that coexists in the separation functional layer is preferred. The term "water-soluble polymer without a crosslinked structure" used here refers to a linear or branched water-soluble polymer in which the polymers are not bonded to each other via a covalent bond or an ionic bond. Since a polymer without a crosslinked structure has high molecular mobility, it is preferable that the diffusion coefficient of carbon dioxide in the separation functional layer increases when used in the separation functional layer, thereby increasing the permeation flux of the separation membrane. Examples of such water-soluble polymers without a crosslinked structure include polyvinyl alcohol, poly(meth)acrylic acid, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, polyallylamine, polysaccharides, salts thereof, copolymers thereof, and blends thereof. Among these water-soluble polymers without a crosslinked structure, polyvinyl alcohol has high film strength and is also highly compatible with an amine compound with a molecular weight of 500 or less, and is therefore preferably used. In this disclosure, "(meth)acrylic acid" refers to either or both of acrylic acid and methacrylic acid.

[0024] The molecular weight of the water-soluble polymer having no crosslinked structure varies greatly depending on the type of water-soluble polymer having no crosslinked structure used, but the weight average molecular weight is preferably in the range of 10,000 to 1,000,000. If the weight average molecular weight is in this range, the mechanical strength of the separation functional layer can be ensured, the solution viscosity during coating is within an appropriate range, and the thickness of the separation functional layer is also uniform, which is preferable. The weight average molecular weight of the water-soluble polymer having no crosslinked structure is measured by size exclusion chromatography.

[0025] Another component constituting the separation functional layer, an amine compound having a molecular weight of 500 or less, is a carrier component that plays a role in adsorbing, transporting, and desorbing carbon dioxide in the carbon dioxide separation membrane according to this embodiment. When the molecular weight of the amine compound is 500 or less, the molecular mobility is large, and the diffusion of carbamic acid produced by the reaction of the amine compound with carbon dioxide in the separation functional layer is also fast, so that the permeation flux of carbon dioxide is increased and high performance of the separation membrane can be achieved. In this embodiment, examples of amine compounds having a molecular weight of 500 or less that are preferably used include amine compounds represented by the following formula (1) and amine compounds represented by the following formula (2).

[0026] [ka] (In formula (1), R 1 , R 2 and R 3 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a hydroxyethyl group.

[0027] [ka] (In formula (2), R 4 , R 5 and R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0028] R of the amine compound represented by formula (1) 1 ~R 3 and R of the amine compound represented by formula (2) 4 ~R 6 Examples of the alkyl group having 1 to 4 carbon atoms in the formula (I) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group and a tert-butyl group.

[0029] Examples of the amine compound having a molecular weight of 500 or less used in this embodiment include N-(2-aminoethyl)ethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine, N-[2-(diethylamino)ethyl]ethanolamine, N-(1,2-dihydroxy-n-propyl)piperazine, N-[(1-hydroxymethyl-2-hydroxy)-n-propyl]piperazine, N-[(1-hydroxy-2-hydroxymethyl)-n-propyl]piperazine, N-(1,2-dihydroxy-n-propyl)piperazine, N-(1-hydroxy-2-hydroxymethyl) ... N-[1,2-bis(hydroxymethyl)-n-propyl]piperazine, N-[1,2-bis(hydroxymethyl)-n-propyl]-N'-methyl-piperazine, diethylenetriamine (DETA); 1,4,7,10-tetraazadecane, N,N-bis(2-aminoethyl)-1,2-ethanediamine, 1-[2-[(2-aminoethyl)amino]ethyl]-piperazine, 1,4-bis(2-aminoethyl)-piperazine, etc. triethylenetetramine (TETA); 1,4 ,7,10,13-pentaazatridecane, N,N,N'-tris(2-aminoethyl)-1,2-ethanediamine, 1-[2-[2-[2-[(2-aminoethyl)amino]ethyl]amino]ethyl]-piperazine, 1-[2-[bis(2-aminoethyl)amino]ethyl]-piperazine, bis[2-(1-piperazinyl)ethyl]amine, etc. tetraethylenepentamine (TEPA); and 1,4,7,10,13,16-hexaazahexadecane, N,N,N',N'-tetrakis(2-aminoethyl)-1,2 pentaethylenehexamine (PEHA) such as N,N-bis(2-aminoethyl)-N'-[2-[(2-aminoethyl)amino]ethyl]-1,2-ethanediamine, 1-[2-[2-[2-[2-[2-[(2-aminoethyl)amino]ethyl]amino]ethyl]amino]ethyl]-piperazine, 1-[2-[2-[2-[bis(2-aminoethyl)amino]ethyl]amino]ethyl]piperazine, and N,N'-bis[2-(1-piperazinyl)ethyl]-1,2-ethanediamine.Among these, as the amine compound having a molecular weight of 500 or less, N-(2-aminoethyl)ethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine, N-[2-(diethylamino)ethyl]ethanolamine, N-(1,2-dihydroxy-n-propyl)piperazine, N-[(1-hydroxymethyl-2-hydroxy)-n-propyl]piperazine, N-[(1-hydroxy-2-hydroxymethyl)-n-propyl]piperazine, N-(1,2-dihydroxy-n-propyl)-N'-methyl-piperazine, N-[1,2-bis(hydroxymethyl)-n-propyl]piperazine, and N-[1,2-bis(hydroxymethyl)-n-propyl]-N'-methyl-piperazine are preferred, and N-(2-aminoethyl)ethanolamine and N-(1,2-dihydroxy-n-propyl)piperazine are particularly preferred.

[0030] The separating functional layer in this embodiment is made of a composition containing a water-soluble polymer having no crosslinked structure and an amine compound having a molecular weight of not more than 500. The content ratio of these components is not particularly limited, but the content of the amine compound having a molecular weight of not more than 500 is preferably 2 to 95% by weight, more preferably 30 to 90% by weight, of the total content of the water-soluble polymer having no crosslinked structure and the amine compound having a molecular weight of not more than 500.

[0031] Next, a method for producing a carbon dioxide separation membrane according to a second embodiment of the present disclosure will be described. The method for producing a carbon dioxide separation membrane according to the present embodiment is a method for producing a carbon dioxide separation membrane according to the first embodiment of the present disclosure, comprising contacting a porous membrane with a solution obtained by dissolving a water-soluble polymer having no crosslinked structure and an amine compound having a molecular weight of 500 or less in a solvent, and and a drying step of removing the solvent from the solution retained in the porous membrane.

[0032] The solvent used in this embodiment is not particularly limited as long as it dissolves both the amine compound having a molecular weight of 500 or less and the water-soluble polymer not having a crosslinked structure and does not react with each other, but from the viewpoint of solubility, at least one solvent selected from the group consisting of water, methanol, ethanol, propanol, ethylene glycol, acetone, dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, and dioxane is used. Among these, water, methanol, ethanol, propanol, and ethylene glycol are preferred solvents, and water is particularly preferred solvent.

[0033] The mixing method for preparing the solution is not particularly limited, and known methods can be used. For example, stirring with a stirring blade, stirring with a stirrer and stirring bar, stirring with a shaker, stirring with a roller mixer, and stirring with ultrasonic waves (homogenizer) can be mentioned. As for the stirring conditions, for example, when stirring with a stirring blade, the rotation speed of the stirring blade is usually in the range of 1 to 1000 rpm, preferably in the range of 10 to 400 rpm.

[0034] There is no particular restriction on the order of mixing, but for example, it is preferable to add and mix an amine compound having a molecular weight of 500 or less after fully dissolving a water-soluble polymer having no crosslinked structure in a solvent. By mixing a water-soluble polymer having no crosslinked structure in a fully dissolved state with an amine compound having a molecular weight of 500 or less, it is possible to suppress the formation of coarse particles, which takes time to dissolve, and the loss of uniformity during film formation. In addition, when preparing the solution, the water-soluble polymer having no crosslinked structure and the amine compound having a molecular weight of 500 or less may be mixed while heating. The heating temperature is not particularly limited as long as it is equal to or higher than the temperature at which each of the above-mentioned components solidifies and equal to or lower than the temperature at which each component decomposes, boils, or reacts. It is usually in the range of 30 to 100°C, preferably in the range of 30 to 80°C.

[0035] The concentration of the solution is not particularly limited as long as the solution has an appropriate fluidity, and the total concentration of the water-soluble polymer not having a crosslinked structure and the amine compound having a molecular weight of 500 or less can be selected in the range of 0.05 to 10% by weight. The content ratio of the water-soluble polymer not having a crosslinked structure and the amine compound having a molecular weight of 500 or less is also not particularly limited, but the content of the amine compound having a molecular weight of 500 or less is preferably 2 to 95% by weight, more preferably 30 to 90% by weight, of the total content of the water-soluble polymer not having a crosslinked structure and the amine compound having a molecular weight of 500 or less.

[0036] In the method for producing a carbon dioxide separation membrane according to this embodiment, as a method for contacting a solution of a water-soluble polymer having no crosslinking structure and an amine compound having a molecular weight of 500 or less with a porous membrane, if the porous membrane is a flat membrane, a spin coating method, a bar coating method, a die coating method, a blade coating method, a knife coating method, a gravure coating method, a roll coating method, a spray coating method, a dip coating method, a cast method, a comma roll method, a kiss coating method, a screen printing method, an inkjet printing method, and a spin coating method can be adopted. In addition, if the porous membrane is a hollow fiber membrane, a dip coating method and a circulation coating method can be adopted. The circulation coating method referred to here refers to a method in which a solution containing a water-soluble polymer having no crosslinking structure, an amine compound having a molecular weight of 500 or less, and a solvent is passed through the hollow fiber membrane and circulated to form a separation functional layer as a dynamic layer on the inside (inner surface) or outside (outer surface) of the hollow fiber membrane.

[0037] In the retention step, the amount of solution retained on the surface of the porous membrane may be adjusted appropriately depending on the desired thickness of the carbon dioxide separation membrane separation functional layer, but it is usually sufficient to retain the solution so that the thickness of the separation functional layer after drying is in the range of 0.01 to 50 μm, preferably 0.05 to 10 μm.

[0038] In the drying step, the drying conditions when removing the solution held in the porous membrane to form a separation functional layer are not particularly limited, but include a method of drying under reduced pressure, in the air, or in a non-oxidizing atmosphere such as helium, argon, and nitrogen. There are also no particular limitations on the drying temperature and drying time, and they can be appropriately selected as long as the solvent volatilizes at an appropriate speed and the amine compound with a molecular weight of 500 or less is not dissipated. Specifically, the drying temperature is 20 to 150°C, and the drying time is about 5 minutes to 48 hours.

[0039] Next, a carbon dioxide separation method according to a third embodiment of the present disclosure will be described. The carbon dioxide separation method according to this embodiment is characterized by including a separation step of contacting a mixed gas containing carbon dioxide with one end of a separation functional layer of a carbon dioxide separation membrane according to the first embodiment of the present disclosure, and permeating the carbon dioxide in the mixed gas to the other end of the carbon dioxide separation membrane. When a hollow fiber membrane module having a separation functional layer formed on the inside of a hollow fiber membrane is used for carbon dioxide separation, a mixed gas containing carbon dioxide is introduced into a primary side that communicates with the inside of the hollow fiber membrane of the hollow fiber membrane module, and the carbon dioxide in the mixed gas is permeated to a secondary side that communicates with the outer peripheral space of the hollow fiber membrane.

[0040] In the separation method according to the present embodiment, it is preferable to provide a pressure difference between the gas supply side and the gas permeation side of the separation membrane. This pressure difference is provided by pressurizing the gas supply side of the separation membrane or by reducing the pressure on the gas permeation side. In addition, it is desirable to carry out the separation method according to the present embodiment under temperature conditions of usually 5 to 140°C, preferably 20 to 100°C.

[0041] The mixed gas that can be applied to the separation method according to this embodiment is not particularly limited as long as it is a mixed gas containing carbon dioxide, but in order to improve the separation performance between carbon dioxide and other gases, it is desirable to adjust the relative humidity of the mixed gas to 30% or more, preferably 60 to 100%.

[0042] In this embodiment, the value of the carbon dioxide and nitrogen separation selectivity at 40°C calculated by the following formula (3) is preferably 100 or more. There is no particular limit to the upper limit of the carbon dioxide and nitrogen separation selectivity at 40°C, since the higher the value, the better the separation performance of the membrane, but it is preferable to exhibit an appropriate separation selectivity in consideration of the permeation flux. Specific examples of the upper limit include values ​​of 1,000 or less, but the upper limit is not limited to these. CO2 / N2 separation selectivity = (CO2 gas permeability) / (N2 gas permeability) (3) The carbon dioxide and nitrogen separation selectivity shown in formula (3) may be expressed as a carbon dioxide selectivity coefficient α. The carbon dioxide selectivity coefficient α is calculated by the formula described in the examples below, and is the same value as the carbon dioxide and nitrogen separation selectivity shown in formula (3).

[0043] In the separation method according to the present embodiment, there is no problem if a process other than the separation process is added. For example, a cooling process, a heating process, a washing process, an extraction process, an ultrasonic treatment process, a distillation process, and other processes of treatment with chemicals can be appropriately performed.

[0044] The separation method according to the present embodiment can be applied to, for example, separating carbon dioxide from combustion exhaust gas generated in thermal power plants, steel plants, cement factories, etc. The method can also be applied to refining light hydrocarbons in natural gas fields and refining methane in biogas.

[0045] Next, a carbon dioxide separation membrane module according to a fourth embodiment of the present disclosure will be described. The carbon dioxide separation membrane module according to this embodiment is a carbon dioxide separation membrane according to the first embodiment of the present disclosure housed in a housing. When the carbon dioxide separation membrane is a flat membrane, specific examples of the carbon dioxide separation membrane module include a laminated module in which the membranes are laminated as they are, or membrane elements are prepared from the membranes and laminated; a pleated module in which the flat membrane is folded and housed in a cylindrical container; and a spiral module in which the flat membrane is bonded in an envelope shape with a permeation side spacer (net) sandwiched therebetween, and this is wound around an axis that is a permeation flow path via a supply side spacer; etc. On the other hand, when the carbon dioxide separation membrane is a tube-shaped, pipe-shaped, or hollow fiber membrane, examples of the carbon dioxide separation membrane module include a tubular module and a hollow fiber membrane module in which these are converged. In addition, when the carbon dioxide separation membrane is a monolith type, examples of the carbon dioxide separation membrane module include a tubular module in which monolith type elements are converged. EXAMPLES

[0046] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

[0047] <Manufacturing of carbon dioxide separation membrane modules> Example 1 3 g of polyvinyl alcohol (molecular weight approximately 60,000, manufactured by Aldrich) as a water-soluble polymer was dissolved in 582 g of pure water, and then 15 g of N-(2-aminoethyl)ethanolamine (manufactured by Tokyo Chemical Industry Co., Ltd.) as an amine compound with a molecular weight of 500 or less was added to prepare a mixed solution.

[0048] The resulting mixed solution was then introduced into the primary side of a hollow fiber membrane module (Kitz Microfilter Corporation, membrane inner diameter 0.36 mm, molecular weight cutoff 10,000, air permeation flux 29,000 GPU, hereinafter referred to as "ultrafiltration membrane module 1") and allowed to pass for 10 minutes. The hollow fiber membrane module that had been subjected to the liquid passing treatment was then dried at 20°C under atmospheric conditions for 24 hours to obtain a hollow fiber membrane module in which a separation functional layer was formed on the inside of the hollow fiber membrane. The thickness of the separation functional layer measured using SEM was 0.7 μm. The resulting carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 1".

[0049] Example 2 A carbon dioxide separation membrane module was produced in the same manner as in Example 1, except that a hollow fiber membrane module with an air permeation flux of 61,000 GPU (manufactured by Kitz Microfilter Corporation, membrane inner diameter 0.64 mm, molecular weight cutoff 10,000, hereinafter referred to as "ultrafiltration membrane module 2") was used as the hollow fiber membrane module. The thickness of the separation functional layer formed on the inside of the hollow fiber membrane was 0.8 μm. The obtained carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 2".

[0050] Comparative Example 1 A carbon dioxide separation membrane module was produced in the same manner as in Example 1, except that a hollow fiber membrane module with an air permeation flux of 6,700 GPU (manufactured by Kitz Microfilter Corporation, membrane inner diameter 0.64 mm, molecular weight cutoff 10,000, hereinafter referred to as "ultrafiltration membrane module 3") was used instead of ultrafiltration membrane module 1. The thickness of the separation functional layer formed on the inside of the hollow fiber membrane was 0.3 μm. The obtained carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 3".

[0051] Comparative Example 2 Instead of the ultrafiltration membrane module 1, a hollow fiber membrane module with an air permeation flux of 7,200 GPU (Kitz Microfilter Co., Ltd., membrane inner diameter 0.70 mm, molecular weight cutoff 1 A carbon dioxide separation membrane module was produced in the same manner as in Example 1, except that a carbon dioxide separation membrane module having a thickness of 0.0001 mm was used (hereinafter referred to as "ultrafiltration membrane module 4"). The separation functional layer formed on the inner side of the hollow fiber membrane had a thickness of 0.3 μm. The obtained carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 4".

[0052] <Separation test of carbon dioxide and coexisting gases> Carbon dioxide separation ability was measured using the carbon dioxide separation membrane modules (separation membrane modules 1 to 4) produced in Examples 1 and 2 and Comparative Examples 1 and 2. In the following explanation and formulas, carbon dioxide is abbreviated as CO2 and nitrogen is abbreviated as N2.

[0053] The outline of the gas separation apparatus used for measuring the carbon dioxide separation ability is shown in FIG. 1. In the gas separation apparatus shown in FIG. 1, CO2 and N2 are supplied from a CO2 gas cylinder 1 and an N2 gas cylinder 2, respectively, to prepare a mixed gas (CO2 10%, N2 90%). This mixed gas is controlled to a predetermined gas flow rate by a flow control meter 4, and the relative humidity is adjusted to 90% by a humidifier 5, and then supplied to a carbon dioxide separation membrane module 8 at a predetermined pressure. In addition, helium supplied from a helium gas cylinder 3 is humidified by a humidifier 5, and the obtained sweep gas is supplied to the permeation side of the carbon dioxide separation membrane module 8 at a predetermined pressure. The relative humidity of the mixed gas and the sweep gas are measured by a dew point meter 7, and the pressure of the mixed gas and the sweep gas supplied to the carbon dioxide separation membrane module 8 is measured by a pressure meter 6. The gas discharged from the carbon dioxide separation membrane module 8 is dried by a dehumidification trap 9 and then introduced into a gas chromatograph 10. The permeation fluxes Q(CO2) and Q(N2) (unit: 1 GPU = 7.5 × 10) of the gases permeating the carbon dioxide separation membrane module 8 were measured by a gas chromatograph 10 and a flow meter (not shown). -12 m 3 (STP) / (s m 2 ·Pa) is measured. The measurement conditions are as follows, and the permeation flux is calculated according to the following formula (4).

[0054] Table 1 shows the permeability coefficient of the carbon dioxide separation membrane module measured using the gas separation apparatus shown in Figure 1 and the carbon dioxide selectivity coefficient α(CO2 / N2)=(Q(CO2) / Q(N2)) of the carbon dioxide separation membrane module calculated from the permeation flux.

[0055]

number

[0056] [Gas permeability measurement conditions] Gas supply: 450mL / min Measurement temperature: 40℃ Supply gas composition: CO2 / N2=10 / 90(vol / vol) Permeate side sweep gas: Helium Sweep gas volume: 300mL / min Relative humidity: 90% Pressure: Supply side = 155kPa, Permeation side = 105kPa

[0057] From Table 1, it can be seen that the CO2 separation membrane module according to the present disclosure not only has a large CO2 permeation flux, but also has high CO2 selectivity, making it an excellent CO2 separation membrane module.

[0058] [Table 1] [Industrial Applicability]

[0059] As described above, according to the present disclosure, it is possible to provide a carbon dioxide separation membrane having a large carbon dioxide permeation flux and high carbon dioxide selectivity, a method for producing the carbon dioxide separation membrane, a carbon dioxide separation method using the carbon dioxide separation membrane, and a carbon dioxide separation membrane module using the carbon dioxide separation membrane. The carbon dioxide separation membrane and carbon dioxide separation membrane module of the present disclosure have excellent carbon dioxide separation characteristics, and are expected to enable separation and capture of carbon dioxide at low cost from exhaust gases from large-scale sources such as thermal power plants, steelworks blast furnaces, and cement plants. Furthermore, since the separation membrane system is compact, it is expected to enable efficient separation and capture of carbon dioxide from relatively small-scale carbon dioxide sources. Thus, the carbon dioxide separation membrane of the present disclosure is considered to greatly contribute to suppressing carbon dioxide emissions. [Explanation of symbols]

[0060] 1 CO2 gas cylinder 2 N2 gas cylinders 3. Helium gas cylinder 4 Flow control meter 5 Humidifier 6. Pressure gauge 7 Dew point meter 8 Carbon dioxide separation membrane module 9. Dehumidification Trap 10 Gas chromatograph

Claims

1. A carbon dioxide separation membrane comprising a porous membrane having an air permeation flux of 10,000 GPU or more and a separation functional layer formed on the surface of the porous membrane, the separation functional layer being made of a composition containing a water-soluble polymer not having a cross-linked structure and an amine compound having a molecular weight of 500 or less.

2. 2. The carbon dioxide separation membrane according to claim 1, wherein the water-soluble polymer not having a crosslinked structure is at least one selected from the group consisting of polyvinyl alcohol, poly(meth)acrylic acid, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, polyallylamine, polysaccharides, salts thereof, and copolymers thereof.

3. The carbon dioxide separation membrane according to claim 1, wherein the amine compound having a molecular weight of 500 or less is at least one selected from the group consisting of compounds represented by the following formula (1) and compounds represented by the following formula (2): 【Chemistry 1】 (In formula (1), R １ , R ２ and R ３ each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a hydroxyethyl group. 【Chemistry 2】 (In formula (2), R ４ , R ５ and R ６ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

4. 2. The carbon dioxide separation membrane according to claim 1, wherein the porous membrane is a hollow fiber membrane, and the separation functional layer is formed on either or both of an outer surface and an inner surface of the hollow fiber membrane.

5. A method for producing the carbon dioxide separation membrane according to any one of claims 1 to 4, A method for producing a carbon dioxide separation membrane, comprising: a retaining step of contacting the porous membrane with a solution containing the water-soluble polymer not having a crosslinked structure, the amine compound having a molecular weight of 500 or less, and a solvent, and retaining the solution on a surface of the porous membrane; and a drying step of removing the solvent from the solution retained in the porous membrane.

6. A method for separating carbon dioxide, comprising a separation step of contacting a mixed gas containing carbon dioxide with one end of the carbon dioxide separation membrane according to any one of claims 1 to 4 and allowing carbon dioxide in the mixed gas to permeate to the other end of the carbon dioxide separation membrane.

7. A carbon dioxide separation membrane module comprising the carbon dioxide separation membrane according to any one of claims 1 to 4.

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