Method and apparatus for separating carbon dioxide

Abstract

The present invention provides a carbon dioxide (CO2) separation-recovery technology having excellent separation processing capacity and processing stability. The present invention involves: supplying a raw material gas to a first gas flow passage facing a separation function layer of a CO2 separation membrane; and supplying a sweep gas to a second gas flow passage isolated from the first gas flow passage by the CO2 separation membrane to separate, into the second gas flow passage, CO2 in the raw material gas. As the separation function layer, a layer containing a hydrophilic polymer and an amine compound is used. Reduced-pressure steam is used as the sweep gas.

Description

Method and apparatus for separating carbon dioxide

[0001] This invention relates to a method and apparatus for separating carbon dioxide.

[0002] In recent years, technologies for separating and recovering carbon dioxide, a cause of global warming, have been investigated. One such carbon dioxide separation and recovery technology involves separating impurities other than carbon dioxide from a raw material gas in a first supply space, removing water vapor from the treated raw material gas in a second supply space, and using the treated gas as a regenerated gas for carbon dioxide recovery (see, for example, Patent Document 1).

[0003] Furthermore, a carbon dioxide separation and recovery technology is known in which carbon dioxide contained in a raw material gas is separated from the raw material gas using a carbon dioxide permeable membrane, and the processed gas containing the separated carbon dioxide is cooled by the heat of vaporization of a refrigerant and the carbon dioxide is recovered by suction on the downstream side (see, for example, Patent Document 2).

[0004] Japanese Patent Publication No. 2024-114783 Japanese Patent Publication No. 2023-33659

[0005] To reduce carbon dioxide capture costs, high separation and processing capacity, such as a large carbon dioxide permeation flux and high carbon dioxide selectivity, is required, as well as processing stability. Conventional technologies, as described above, still have room for improvement in terms of achieving both high separation and processing capacity and processing stability.

[0006] One aspect of the present invention aims to provide a carbon dioxide separation and recovery technology that is excellent in separation and processing capacity and processing stability.

[0007] As a means to solve the above problems, the present invention provides the following carbon dioxide separation method and carbon dioxide separation apparatus.

[0008] In other words, a carbon dioxide separation method according to one aspect of the present invention includes the steps of supplying a raw material gas containing carbon dioxide to a first gas channel, which is separated from a second gas channel by a carbon dioxide separation membrane having a separation functional layer formed on the surface of a separation membrane support layer that allows carbon dioxide to pass through and selectively permeates carbon dioxide, and the separation functional layer is positioned toward the first gas channel, and supplying a sweep gas to the second gas channel in synchronization with the step of supplying the raw material gas, wherein the separation functional layer is a layer containing a hydrophilic polymer and an amine compound, and reduced pressure steam is used as the sweep gas.

[0009] Furthermore, a carbon dioxide separation apparatus according to one aspect of the present invention is a carbon dioxide separation apparatus in which a raw material gas containing carbon dioxide is supplied to a first gas channel, which is separated from a second gas channel by a carbon dioxide separation membrane that has a separation functional layer formed on the surface of a separation membrane support layer through which carbon dioxide passes and selectively separates carbon dioxide, and the separation functional layer is positioned toward the first gas channel, and a sweep gas is supplied to the second gas channel in synchronization with the supply of the raw material gas, wherein the separation functional layer is a layer containing a hydrophilic polymer and an amine compound, and the sweep gas is reduced pressure steam.

[0010] According to one aspect of the present invention, a carbon dioxide separation and recovery technology with excellent separation and processing capacity and processing stability can be provided.

[0011] This figure schematically shows the configuration of one embodiment of the separation device according to the present invention.

[0012] One embodiment of the present invention will be described in detail below.

[0013] [Method for separating carbon dioxide] A method for separating carbon dioxide according to one embodiment of the present invention includes a raw material gas supply step of supplying a raw material gas containing carbon dioxide to a first gas flow path, and a sweep gas supply step of supplying a sweep gas to a second gas flow path in synchronization with the raw material gas supply step.

[0014] [Raw material gas supply process] The first gas channel is separated from the second gas channel by a carbon dioxide separation membrane. For example, if the chamber is divided into two spaces by a sheet-like carbon dioxide separation membrane, the first gas channel is the space on one surface side of the carbon dioxide separation membrane, and the second gas channel is the space on the other surface side of the carbon dioxide separation membrane. If the carbon dioxide separation membrane is tubular, the first gas channel is one of the spaces inside and outside the tube of the carbon dioxide separation membrane, and the second gas channel is the other space inside and outside the tube of the carbon dioxide separation membrane.

[0015] <Raw Material Gas> The raw material gas used is a gas containing carbon dioxide. Using such a raw material gas is preferable from the viewpoint of suppressing the emission of carbon dioxide into the atmosphere. Examples of such raw material gases include exhaust gas, biogas, and natural gas. Furthermore, it is preferable that the raw material gas contains carbon dioxide at a sufficiently high concentration and that the raw material gas is produced in large quantities, from the viewpoint of separating and recovering carbon dioxide at low cost. From this viewpoint, it is preferable that the raw material gas is exhaust gas, and more preferably that it is exhaust gas from facilities that generate such exhaust gas on a large scale, such as thermal power plants, blast furnaces of steel mills, and cement plants.

[0016] Thus, the separation method according to this embodiment can be applied, for example, to the separation of carbon dioxide from combustion exhaust gases generated in thermal power plants, steel plants, and cement factories. It can also be applied to the purification of light hydrocarbons in natural gas fields or to the purification of methane in biogas.

[0017] The raw material gas may be supplied directly from the source to the first gas flow path via a supply pipe (such as an exhaust pipe) at the source of the raw material gas connected to the first gas flow path, or the raw material gas may be filled into a container such as a cylinder and supplied to the first gas flow path by connecting the container to the first gas flow path.

[0018] <Carbon Dioxide Separation Membrane> The carbon dioxide separation membrane includes a separation membrane support layer and a separation function layer, comprising the separation membrane support layer and the separation function layer formed on at least one surface thereof, with the separation function layer positioned toward the first gas flow path. The separation function layer absorbs and separates carbon dioxide from the raw gas at a high rate. Therefore, a high separation processing capacity is achieved in the separation and recovery of carbon dioxide.

[0019] In a preferred embodiment of the present invention, a hollow fiber membrane having a separation functional layer on its inner surface is used as a carbon dioxide separation membrane. A raw material gas is supplied to the hollow portion of the hollow fiber membrane, and a sweep gas is supplied to the outside of the hollow fiber membrane. That is, the hollow portion of the hollow fiber membrane becomes the first gas flow path, and the space outside the hollow fiber membrane becomes the second gas flow path.

[0020] (Separation membrane support layer) The separation membrane support layer is preferably a porous membrane with an air permeation flux of 10,000 GPU or more, from the viewpoint of improving the carbon dioxide separation processing capacity.

[0021] The air permeation flux through the porous membrane 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. Permeation flux is the fluid permeation rate divided by the membrane area and the differential pressure between membranes. In this embodiment, the air permeation flux is determined by measuring the amount of air permeated with a mass flow meter and dividing it by the membrane area and the differential pressure between membranes.

[0022] Porous membranes with permeation fluxes within this range are thought to have a high surface opening ratio, which reduces gas permeation resistance and improves carbon dioxide permeation flux. GPU used here is a unit of permeation flux, where 1 GPU = 7.5 × 10⁻⁶ －１２ I understand ３ (STP) / (m) ２ It is expressed as (s・Pa). The reason why the selectivity of carbon dioxide is affected by the porous membrane is unknown, but using a porous membrane with an air permeation flux of 10,000 GPU or more as the separation membrane support layer is preferable from the viewpoint of improving the permeation selectivity of carbon dioxide in the carbon dioxide separation membrane.

[0023] Furthermore, it is preferable that the porous membrane is an ultrafiltration membrane from the viewpoint of improving the permeation flux of carbon dioxide. In the case of an ultrafiltration membrane, it is preferable from the above viewpoint that its fractional molecular weight is 500,000 or less, and more preferably 500 to 200,000, and it may be a composite membrane consisting of multiple layers. When the fractional molecular weight is within 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 that do not have a cross-linking structure into the interior of the porous membrane is suppressed, so the gas permeation resistance is reduced and the permeation flux of carbon dioxide is improved.

[0024] When the porous membrane is an ultrafiltration membrane, the fractionation characteristics of the ultrafiltration membrane are determined by the fractionation molecular weight, and the average pore size of the ultrafiltration membrane is not particularly specified, but it is preferable that it be around 1 to 50 nm from the above viewpoint (improvement of carbon dioxide permeation flux). In this embodiment, several types of marker molecules with different molecular weights are introduced into the porous membrane and the rejection rate is measured, and the molecular weight at which the rejection rate is 90% is taken as the fractionation molecular weight of the membrane. Proteins such as insulin, cytochrome C, and pepsin can be used as marker molecules.

[0025] Possible shapes of porous membranes include sheet-like flat membranes and hollow fiber membranes, with hollow fiber membranes being preferred. When the porous membrane is a flat membrane, its thickness is preferably 10 to 3,000 μm, and more preferably 50 to 500 μm. Flat membranes are preferred because having the above thickness allows for low permeation resistance and ensures mechanical strength. On the other hand, when the porous membrane is a hollow fiber membrane, the inner diameter of the hollow fibers is preferably 100 to 3,000 μm, and the film thickness is preferably 25 to 300 μm. The thickness of the porous membrane and the separation functional layer is measured by scanning electron microscopy (SEM).

[0026] The structure of the porous membrane is not particularly limited, but an asymmetrical structure containing a dense layer with small pore sizes in the surface layer and a support layer with large pore sizes in the lower layer is preferable from the viewpoint of reducing permeation resistance and increasing permeation flux. Furthermore, a porosity of 60 to 90% in the cross-section of the porous membrane is preferable from the viewpoint of the above-mentioned permeation resistance and permeation flux, and 70 to 85% is more preferable. The porosity of the porous membrane is calculated by mercury intrusion or by image analysis of the membrane cross-section using a scanning electron microscope.

[0027] There are no particular restrictions on the material of the porous membrane, and for example, polymer materials can be preferably employed. Examples of such polymer materials 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.

[0028] Usually, in a gas separation membrane composed of a polymer material, the gas permeation flux and selectivity are in a trade-off relationship, and a membrane with a high permeation flux has low selectivity. In contrast, the carbon dioxide separation membrane according to the present embodiment has both a high permeation flux and selectivity of carbon dioxide, and its practicality is extremely high.

[0029] (Separation functional layer) A layer containing a hydrophilic polymer and an amine compound is used for the separation functional layer. In the carbon dioxide separation membrane according to the present embodiment, the amine compound having carbon dioxide separation ability is not supported on the separation membrane support layer or the separation functional layer, but is incorporated into the separation functional layer. Therefore, its stability is extremely excellent.

[0030] (Hydrophilic polymer) The hydrophilic polymer is not particularly limited as long as it can dissolve in water and form a film when dried, but it is preferably a polymer having excellent affinity with the amine compound coexisting in the separation functional layer. Such a "polymer having excellent affinity" refers to a polymer in which polymers are not bonded via a covalent bond or an ionic bond, that is, a linear or branched water-soluble polymer, and preferably a polymer having no crosslinked structure. Since a polymer having no crosslinked structure has high molecular mobility, using such a polymer in the separation functional layer is preferable from the viewpoint of increasing the diffusion coefficient of carbon dioxide in the separation functional layer and increasing the permeation flux of the carbon dioxide separation membrane. Examples of such hydrophilic polymers include polyvinyl alcohol, poly(meth)acrylic acid, polyethylene glycol, polyvinyl pyrrolidone, polyethyleneimine, polyallylamine, polysaccharides, salts thereof, copolymers thereof, and blends thereof. Among these, polyvinyl alcohol is more preferable because it has high film strength and high affinity with the amine compound. In the present disclosure, "(meth)acrylic acid" means either or both of acrylic acid and methacrylic acid.

[0031] The hydrophilic polymer may be a polymer (hydroxymethylene-vinyl alcohol copolymer) having a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).

[0032]

[0033] The separation functional layer may be composed of a composition containing a hydroxymethylene-vinyl alcohol copolymer and an amine compound. In the present embodiment, the composition may be formed on the surface of the separation membrane support layer. It is preferable that this composition is a homogeneous composition from the viewpoint of incorporating more amine compounds in the layer and further enhancing the stability of the separation functional layer.

[0034] The hydroxymethylene-vinyl alcohol copolymer preferably has 1 to 2,000 constituent units represented by formula (1) (hereinafter referred to as "hydroxymethylene units") per molecule, from the viewpoint of enhancing the stability of the amine compound and increasing the mechanical strength of the separation functional layer, and more preferably has 50 to 1,000. Furthermore, the vinyl alcohol copolymer preferably has 1 to 2,000 constituent units represented by formula (2) (hereinafter referred to as "vinyl alcohol units") per molecule, from the viewpoint of imparting water solubility, and more preferably has 50 to 1,000.

[0035] From the viewpoint of water solubility, the content of hydroxymethylene units in the hydroxymethylene-vinyl alcohol copolymer is preferably 70 mol% or less. Therefore, from the viewpoint of achieving both the water solubility of the hydrophilic polymer and the mechanical strength of the separation functional layer, the molar ratio of hydroxymethylene units to vinyl alcohol units in the hydroxymethylene-vinyl alcohol copolymer is preferably hydroxymethylene units:vinyl alcohol units = 1:99 to 70:30, and particularly preferably hydroxymethylene units:vinyl alcohol units = 30:70 to 70:30.

[0036] The molecular weight of the hydroxymethylene-vinyl alcohol copolymer is preferably in the range of 10,000 to 1,000,000 by weight average molecular weight. This range is preferable because it ensures the mechanical strength of the separation functional layer, maintains an appropriate solution viscosity during coating, and results in a uniform thickness of the separation functional layer. In this disclosure, the weight average molecular weight of the polymer is measured by size exclusion chromatography.

[0037] The above hydrophilic polymer (hydroxymethylene-vinyl alcohol copolymer) may further have either or both of the constituent units represented by the following formula (3) and the constituent units represented by the following formula (4).

[0038]

[0039] It is preferable for the hydroxymethylene-vinyl alcohol copolymer to further contain constituent units represented by formula (3) (hereinafter referred to as "vinylene carbonate units") from the viewpoint of reducing the crystallinity of polyhydroxymethylene and improving water solubility. In this case, it is preferable from the above viewpoint for the copolymer to have 1 to 2,000 vinylene carbonate units per molecule, and more preferably 10 to 500. Furthermore, if the hydroxymethylene-vinyl alcohol copolymer contains constituent units represented by formula (4) (hereinafter referred to as "vinyl ester units"), it is preferable from the viewpoint of imparting flexibility to the copolymer for the copolymer to have 1 to 2,000 vinyl ester units per molecule, and more preferably 10 to 500.

[0040] In formula (4), R is an acyl group having 1 to 4 carbon atoms. Examples of acyl groups having 1 to 4 carbon atoms include the acetyl group, propionyl group, oleyl group, and benzoyl group.

[0041] When the hydroxymethylene-vinyl alcohol copolymer contains either vinylene carbonate units or vinyl ester units, or both, the molar ratio of hydroxymethylene units to vinylene carbonate units in the hydroxymethylene-vinyl alcohol copolymer is preferably hydroxymethylene units:vinylene carbonate units = 1:99 to 100:0, and particularly preferably hydroxymethylene units:vinylene carbonate units = 80:20 to 100:0, from the viewpoint of achieving both water solubility and stability maintenance of the amine compound. Furthermore, the molar ratio of vinyl alcohol units to vinyl ester units in the hydroxymethylene-vinyl alcohol copolymer is preferably vinyl alcohol units:vinyl ester units = 1:99 to 100:0, and particularly preferably vinyl alcohol units:vinyl ester units = 80:20 to 100:0, from the viewpoint of imparting flexibility to the copolymer.

[0042] The hydrophilic polymer (hydroxymethylene-vinyl alcohol copolymer) mentioned above is produced by copolymerizing vinylene carbonate and vinyl ester, followed by saponification.

[0043] There are no particular restrictions on the method for producing vinylene carbonate-vinyl ester copolymers, but a method using radical polymerization is simple and preferred. Polymerization of the copolymer can be carried out in various forms, such as bulk polymerization without solvent, solution polymerization using a solvent in which both monomers and polymers dissolve, precipitation polymerization using a solvent in which monomers dissolve but polymers do not, and dispersion polymerization or suspension polymerization using a solvent in which neither monomers nor polymers dissolve. When producing vinylene carbonate-vinyl ester copolymers by radical polymerization, the production conditions can be arbitrarily selected, with the polymerization temperature being selected in the range of 20°C to 120°C and the polymerization time being selected in the range of 10 minutes to 24 hours. Specific examples of vinyl esters include vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl pivalate, vinyl neononanoate, vinyl decanoate, vinyl neodecanoate, vinyl stearate, and vinyl benzoate, with vinyl acetate being preferred.

[0044] There are no particular restrictions on the saponification method for vinylene carbonate-vinyl ester copolymers. The vinylene carbonate-vinyl ester copolymer is dissolved or dispersed in water or an aqueous solvent, and a base is added to carry out the saponification reaction. The reaction conditions can be arbitrarily set within the range of reaction temperature 0 to 90°C and reaction time 30 minutes to 120 hours.

[0045] Alternatively, the hydrophilic polymer may be a polymer (polyhydroxyurethane) having a constituent unit represented by the following formula (5).

[0046]

[0047] In this embodiment, the separation functional layer may be composed of a composition containing a hydrophilic polymer having hydroxyurethane as a constituent unit and an amine compound. It is preferable that this composition is a homogeneous composition from the viewpoint of incorporating more amine compounds into the layer and further enhancing the stability of the separation functional layer.

[0048] A hydrophilic polymer having hydroxyurethane as a constituent unit preferably has 1 to 2,000 constituent units represented by formula (5) in one molecule, and more preferably 50 to 1,000.

[0049] From the viewpoint of water solubility, the content of the constituent unit represented by formula (5) in the hydrophilic polymer having hydroxyurethane as a constituent unit is preferably 60 mol% or more and 100 mol% or less.

[0050] In formula (5), R' represents a hydroxyl group or an organic group having 1 to 30 carbon atoms. The organic group referred to here may contain oxygen, nitrogen, sulfur, halogens, etc., in addition to carbon and hydrogen. Examples of organic groups having 1 to 30 carbon atoms include methyl group, ethyl group, propyl group, butyl group, hexyl group, octyl group, phenyl group, benzyl group, methylphenyl group, trichlorophenyl group, cyclohexyl group, hydroxymethyl group, hydroxyethyl group, hydroxypropyl group, methoxymethyl group, methoxyethyl group, methoxypropyl group, ethoxyethyl group, ethoxypropyl group, isopropoxypropyl group, phenoxymethyl group, tetrahydrofurfuryl group, N,N-dimethylaminoethyl group, N,N-dimethylaminopropyl group, methylthiophenyl group, and methylthiobenzimidazole group.

[0051] The molecular weight of the hydrophilic polymer having hydroxyurethane as a constituent unit is preferably in the range of 10,000 to 1,000,000 in weight-average molecular weight, from the viewpoint of the mechanical strength of the separation functional layer and the manufacturing stability of the separation functional layer. When the weight-average molecular weight of the polymer having the constituent unit is in this range, it is preferable from the viewpoint of ensuring the mechanical strength of the separation functional layer, and also from the viewpoint of ensuring a uniform thickness of the separation functional layer, as the solution viscosity during coating is within an appropriate range.

[0052] A hydrophilic polymer having a constituent unit represented by formula (5) may further have a constituent unit represented by the following formula (6). When a hydrophilic polymer having hydroxyurethane as a constituent unit has a constituent unit represented by formula (6), it is preferable from the viewpoint of improving mechanical strength that the hydrophilic polymer has 1 to 2,000 of the constituent units represented by formula (6) in one molecule, and more preferably 10 to 500.

[0053]

[0054] When a polymer having hydroxyurethane as a constituent unit has a constituent unit represented by formula (6), the molar ratio of the constituent unit represented by formula (5) and the constituent unit represented by formula (6) in the hydrophilic polymer is arbitrary, but from the viewpoint of water solubility of the hydrophilic polymer, it is preferably that the molar ratio of the constituent unit represented by formula (5) to the constituent unit represented by formula (6) is 60:40 to 100:0.

[0055] Polymers having hydroxyurethane as a constituent unit are produced by polymerizing vinylene carbonate and performing aminolysis with an amino group-containing compound. There are no particular restrictions on the method of polymerizing vinylene carbonate, and it can be produced in the same manner as described above.

[0056] There are no particular restrictions on the above aminolysis reaction; the reaction is carried out by dissolving or dispersing polyvinylene carbonate in a solvent and adding an amino group-containing compound. The reaction conditions can be arbitrarily set within the range of a reaction temperature of 30 to 120°C and a reaction time of 1 to 72 hours.

[0057] The amino group-containing compounds used in the aminolysis reaction are compounds having a primary or secondary amine, and examples include methylamine, ethylamine, propylamine, butylamine, hexylamine, dimethylamine, diethylamine, ethanolamine, propanolamine, butanolamine, aniline, benzylamine, toluidine, trichloroaniline, cyclohexylamine, methoxyethanolamine, methoxypropanolamine, tetrahydrofurfurylamine, and mixtures thereof.

[0058] Although the aminolysis reaction can be carried out without a solvent, it is preferable to use a solvent to ensure a uniform and quantitative reaction. Suitable solvents include water, alcohols such as methanol and ethanol, ethers such as diethyl ether, tetrahydrofuran and dioxane; esters such as ethyl acetate, isopropyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; amides such as formamide, dimethylformamide, dimethylacetamide and N-methyl-2-pyrrolidone; and dimethyl sulfoxide.

[0059] The molecular weight of hydrophilic polymers varies greatly depending on the type of polymer, but a weight-average molecular weight in the range of 10,000 to 1,000,000 is preferred. A weight-average molecular weight within this range ensures the mechanical strength of the separation functional layer, maintains an appropriate solution viscosity during coating, and is preferable from the viewpoint of achieving a uniform thickness of the separation functional layer. The weight-average molecular weight of water-soluble polymers without cross-linking structures is measured by size exclusion chromatography.

[0060] (Amine Compound) The amine compound, another component constituting the separation functional layer, is a carrier component in the carbon dioxide separation membrane according to this embodiment, playing a role in adsorbing, transporting, and desorbing carbon dioxide. In particular, it is preferable for the molecular weight of the amine compound to be 500 or less from the viewpoint of increasing the permeation flux of carbon dioxide in the carbon dioxide separation membrane and from the viewpoint of achieving high performance of the carbon dioxide separation membrane. This is because when the molecular weight of the amine compound is 500 or less, the molecular mobility is large, and the diffusion of carbamic acid, which is produced by the reaction of the amine compound with carbon dioxide, in the separation functional layer is also faster, so the permeation flux of carbon dioxide increases and high performance of the carbon dioxide separation membrane can be achieved.

[0061] The amine compound may be at least one compound selected from the group consisting of compounds represented by the following formula (7) and compounds represented by the following formula (8).

[0062]

[0063] In formula (7), 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, respectively. Further, in formula (8), R ４ , R ５ and R ６ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms in R １ to R ３ of the amine compound represented by formula (7) and R ４ to R ６ of the amine compound represented by formula (8) include, for example, 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.

[0064] Examples of the amine compound having a molecular weight of 500 or less, which is the amine compound used in the present embodiment, include triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PEHA).

[0065] Examples of triethylenetetramine 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)-N'-methyl-piperazine, 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, and 1,4-bis(2-aminoethyl)-piperazine.

[0066] Examples of tetraethylenepentamines include 1,4,7,10,13-pentazatridecane, 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, and bis[2-(1-piperazinyl)ethyl]amine.

[0067] Examples of pentaethylenehexamines include 1,4,7,10,13,16-hexaazahexadecane, N,N,N',N'-tetrakis(2-aminoethyl)-1,2-ethanediamine, N,N-bis(2-aminoethyl)-N'-[2-[(2-aminoethyl)amino]ethyl]-1,2-ethanediamine, 1-[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.

[0068] Among these, 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'-methylpiperazine, N-[1,2-bis(hydroxymethyl)-n-propyl]piperazine, and N-[1,2-bis(hydroxymethyl)-n-propyl]-N'-methylpiperazine are preferred as amine compounds with a molecular weight of 500 or less, with N-(2-aminoethyl)ethanolamine and N-(1,2-dihydroxy-n-propyl)piperazine being particularly preferred.

[0069] In this embodiment, the ratio of hydrophilic polymer to amine compound content in the separation functional layer is not particularly limited, but from the viewpoint of maintaining the mechanical strength of the separation functional layer, the amine compound content is preferably 2 to 95% by weight of the total content of the hydrophilic polymer and amine compound, and more preferably 30 to 90% by weight.

[0070] (Other Components) The separation functional layer may further contain other components besides the hydrophilic polymers and amine compounds described above, to the extent that the effects of the present invention are obtained. Examples of such other components include additives such as antioxidants or plasticizers. These other components may be included in the separation functional layer in an appropriate type and quantity that obtains both the effects of the present invention and the effects of the other components.

[0071] [Sweep Gas Supply Process] In this embodiment, the sweep gas supply process supplies the sweep gas to the second gas flow path in synchronization with the raw material gas supply process.

[0072] The sweep gas is a gas that facilitates the release of carbon dioxide gas, which has been taken into the carbon dioxide separation membrane from the first gas channel, into the second gas channel. "Synchronization" means that the sweep gas is supplied to the second gas channel at a time when its function is fully realized in relation to the raw material gas flowing through the first gas channel. The timing of the sweep gas supply in the second gas channel may be exactly the same as the timing of the raw material gas supply in the first gas channel, or it may be different. Furthermore, the supply of sweep gas in the second gas channel may be continuous or intermittent.

[0073] Reduced-pressure steam is used as the sweep gas. "Reduced-pressure steam" refers to a gas that contains water vapor as its main component and has a pressure lower than atmospheric pressure. For example, saturated water vapor produced under reduced pressure can be used as reduced-pressure steam. When reduced-pressure steam is supplied to the second gas channel, the carbon dioxide in the second gas channel is diluted. As a result, the partial pressure of carbon dioxide in the second gas channel becomes lower than the partial pressure of carbon dioxide in the first gas channel, and the amount of carbon dioxide permeated through the carbon dioxide separation membrane increases. In this way, the supply of reduced-pressure steam to the second gas channel promotes the separation of carbon dioxide in the carbon dioxide separation membrane.

[0074] Furthermore, since the sweep gas is reduced-pressure steam, its temperature is below 100°C. Therefore, thermal damage to the carbon dioxide separation membrane (especially the separation function layer) from the second gas flow path is suppressed. As a result, the high processing and separation function of the separation function layer is stably achieved. The physical properties of the reduced-pressure steam used as the sweep gas can be appropriately determined within the range where the above effects are obtained.

[0075] For example, the sweep gas temperature is preferably 100°C or lower, and more preferably 90°C or lower, from the viewpoint of suppressing thermal damage to the separation functional layer. On the other hand, if the sweep gas temperature is too low, the sweep gas pressure will be even lower, which may cause damage to the carbon dioxide separation membrane or the separation device module containing the membrane due to negative pressure. From the viewpoint of pressure resistance, the sweep gas temperature is preferably 40°C or higher, and more preferably 80°C or lower.

[0076] Furthermore, the sweep gas pressure is usually negative. From the viewpoint of suppressing thermal damage to the separation functional layer, the sweep gas pressure is preferably low, for example, preferably 60 kPa or less, and preferably 50 kPa or less. On the other hand, from the viewpoint of suppressing damage to the separation device module due to negative pressure, the sweep gas pressure is preferably somewhat high, for example, it may be 10 kPa or more.

[0077] Furthermore, if the relative humidity of the sweep gas is too low, the separation functional layer may dry out, which can reduce the carbon dioxide separation capacity of the separation functional layer. From the viewpoint of allowing the separation functional layer to fully exhibit carbon dioxide separation capacity, the relative humidity of the sweep gas is preferably 70% or higher, preferably 80% or higher, and preferably 90% or higher. There is no particular upper limit to the relative humidity of the sweep gas due to the above effects, and the relative humidity of the sweep gas may be, for example, 100% or less.

[0078] [Conditions for both processes] In the separation method according to this embodiment, it is preferable to have a pressure difference between the first gas channel, which is the gas supply side of the carbon dioxide separation membrane, and the second gas channel, which is the gas permeation side. This pressure difference can be achieved by pressurizing the first gas channel and depressurizing the second gas channel, or both.

[0079] Furthermore, from the viewpoint of improving the carbon dioxide separation performance of the carbon dioxide separation membrane, it is preferable that the relative humidity of the raw material gas supplied to the first gas flow path is sufficiently high. From this viewpoint, the relative humidity of the raw material gas supplied to the first gas flow path is preferably 30% or higher, preferably 60% or higher, preferably 70% or higher, and preferably 80% or higher. There is no particular upper limit to the relative humidity of the raw material gas from the above viewpoint, and the relative humidity of the raw material gas may be 100% or less.

[0080] [Other Steps] The separation method according to this embodiment may further include other components besides the raw material gas supply step and sweep gas supply step described above, to the extent that the effects of the present invention can be obtained. In this separation method, for example, a cooling step, a heating step, a washing step, an extraction step, an ultrasonic treatment step, a distillation step, and other chemical treatment steps can be appropriately carried out. Among these, it is preferable to include a cooling step in order to facilitate the separation of sweep gas from the gas (mainly a mixed gas of carbon dioxide and sweep gas) taken out into the second gas channel.

[0081] [Method for Manufacturing a Carbon Dioxide Separation Membrane] Furthermore, the carbon dioxide separation membrane used in the separation method of this embodiment can be manufactured by a process of forming (or regenerating) the separation functional layer by coating the material of the separation functional layer onto the separation membrane support layer. For example, if the separation membrane support layer is a hollow fiber membrane, the carbon dioxide separation membrane used in the separation method of this embodiment can be manufactured by a circulating coating process in which an aqueous solution of one or both of a hydrophilic polymer and an amine compound is supplied to the hollow portion of the hollow fiber membrane and the water in the aqueous solution is discharged to the outside of the hollow fiber membrane.

[0082] This circulating coating process can be achieved by circulating an aqueous solution of the separation functional layer material in the first gas channel of the separation device module where the hollow fiber membrane is located, and discharging the water from the aqueous solution into the second gas channel. Furthermore, the separation functional layer can be regenerated by applying this circulating coating process with an aqueous solution containing some or all of the separation functional layer material to a carbon dioxide separation membrane that is in use.

[0083] The aqueous solution of the material in the circulating coating process may further contain other solvents besides water. These other solvents may be components that are soluble in the material and substantially non-reactive, and examples include methanol, ethanol, propanol, ethylene glycol, acetone, dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, and dioxane. Among these, methanol, ethanol, propanol, and ethylene glycol are preferred from the viewpoint of solubility.

[0084] Aqueous solutions of the material for the separation layer can be prepared using known methods. These aqueous solutions can be prepared, for example, by mixing the material with a solvent by stirring with a stirring blade, stirring with a stirrer and stirring bar, stirring with a shaker, stirring with a roller mixer, or stirring with ultrasound (homogenizer). 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.

[0085] In preparing the aqueous material solution, it is preferable to thoroughly dissolve the hydrophilic polymer in the solvent, then add and mix the amine compound, from the viewpoint of quickly preparing a homogeneous aqueous solution. Furthermore, heating may be performed during the preparation of the aqueous material solution as needed. The heating temperature should be such that no solidification, decomposition, boiling, or reaction of each component substantially occurs, for example, in the range of 30 to 100°C, preferably in the range of 30 to 80°C.

[0086] The concentration of the aqueous material solution may be determined appropriately within a range in which the solution has adequate fluidity. For example, the total concentration of the hydrophilic polymer and amine compound in the aqueous material solution may be in the range of 0.05 to 10% by weight. The content of the amine compound relative to the total amount of the hydrophilic polymer and amine compound may be, for example, 2 to 95% by weight or 30 to 90% by weight.

[0087] The amount of the material aqueous solution circulated can be appropriately determined according to the thickness of the separation functional layer to be formed. For example, the material aqueous solution should typically be supplied in such a way that the thickness of the separation functional layer after drying is in the range of 0.01 to 50 μm, preferably in the range of 0.05 to 10 μm.

[0088] The circulating coating process may include a drying process to dry the hollow fiber film after the circulating supply of the aqueous material solution. This drying process may involve drying under reduced pressure in the atmosphere, or in a non-oxidizing atmosphere such as helium, argon, and nitrogen. The drying temperature and drying time may be appropriately determined within a range in which the solvent volatilizes at a suitable rate and the amine compound does not dissipate. The drying temperature may be, for example, 20 to 150°C, and the drying time may be about 5 minutes to 48 hours.

[0089] Furthermore, if the separation membrane support layer is a flat membrane such as a sheet membrane rather than a hollow fiber membrane, it is possible to form a separation functional layer on the surface of the separation membrane support layer by applying the aforementioned aqueous material solution to the separation membrane support layer using known techniques. Examples of such known techniques include spin coating, bar coating, die coating, blade coating, knife coating, gravure coating, roll coating, spray coating, dip coating, casting, comma-roll, kiss coating, screen printing, and inkjet printing.

[0090] (Raw material gas preparation step) The separation method of this embodiment may further include a raw material gas preparation step to prepare the raw material gas supplied to the first gas flow path. The raw material gas preparation step may be, for example, a step of removing nitrogen oxides and sulfur oxides that can react with amine compounds in the separation functional layer from the raw material gas using an anion exchanger. Such a raw material gas preparation step is preferable from the viewpoint of improving separation efficiency and reducing costs because it can be implemented with a simple configuration.

[0091] The raw material gas preparation process can be implemented by passing the raw material gas through an anion exchanger-packed column filled with anion exchangers. The shape of the packed column may be cylindrical or rectangular, and the height of the anion exchanger layer within the column may be, for example, 1 cm to 500 cm, depending on the cross-sectional area of ​​the packed column and the flow rate of the gas to be treated. The anion exchanger may be constructed by introducing anion exchange groups into a substrate. Any known anion exchanger can be appropriately used as the anion exchanger.

[0092] In the raw material gas preparation process, it is preferable to appropriately control the temperature of the anion exchanger, for example, between 20°C and 100°C, from the viewpoint of improving the stability of the anion exchanger and realizing a rapid ion exchange reaction by the anion exchanger. Such temperature control can be achieved, for example, by installing the anion exchanger packed column in a constant temperature bath.

[0093] Furthermore, the raw material gas used in the raw material gas preparation process is preferable to being in a humid state rather than a dry state, from the viewpoint of improving the efficiency of removing nitrogen oxides and sulfur oxides from the raw material gas. From this viewpoint, the relative humidity of the raw material gas is more preferably 50% to 95%, and even more preferably 70% to 90%. Similarly, the moisture content of the anion exchanger is also preferably 30% to 80%.

[0094] The flow rate of the raw material gas used in the raw material gas preparation process may be determined appropriately from the viewpoint of processing speed and contactability. For example, the flow rate of the raw material gas is preferably 0.01 m / sec to 1.00 m / sec in linear velocity, more preferably 0.10 m / sec to 0.50 m / sec, even more preferably 0.13 m / sec to 0.50 m / sec, and also 100 hr in space velocity. －１ ~10,000 hours －１ Preferably, 500hr －１ ~9,000hr －１ It is more preferable that this be the case, 1,000 hours －１ ~5,000 hours －１ It is even more preferable that the time be 2,400 hours. －１ ~3,600 hours －１ It is even more preferable that it be so.

[0095] The flow rate of the raw material gas in the raw material gas adjustment process can be controlled by control means such as a mass flow controller and a flow control valve. The temperature of the raw material gas in the raw material gas adjustment process can be controlled by control means such as a heater, cooler, and heat exchanger. Furthermore, the humidity of the raw material gas in the raw material gas adjustment process can be controlled by a bubbler and a precision humidity generator.

[0096] [Carbon Dioxide Separation Apparatus] The carbon dioxide separation apparatus according to an embodiment of the present invention is a carbon dioxide separation apparatus in which a raw material gas containing carbon dioxide is supplied to a first gas channel, which is separated from a second gas channel by a carbon dioxide separation membrane that has a separation functional layer formed on the surface of a separation membrane support layer through which carbon dioxide passes and selectively separates carbon dioxide, and the separation functional layer is positioned toward the first gas channel, and a sweep gas is supplied to the second gas channel in synchronization with the supply of the raw material gas. In this separation apparatus, the separation functional layer is a layer containing a hydrophilic polymer and an amine compound, and the sweep gas is reduced-pressure steam.

[0097] For example, the separation apparatus may consist of a chamber containing a hollow fiber membrane, a first pipeline connected to the hollow fiber membrane and communicating the inside and outside of the chamber, and a second pipeline located outside the hollow fiber membrane in the chamber and communicating the inside and outside of the chamber. A source of raw material gas is connected to the upstream side of the first pipeline. A steam generator is connected to the upstream side of the second pipeline, and a cooler and a vacuum pump are connected to the downstream side. A device for recovering the gas in the second pipeline (such as a tank) is connected to the downstream side of the second pipeline. The first pipeline corresponds to the first gas flow path, and the second pipeline corresponds to the second gas flow path. The above configuration can be constructed by appropriately adopting known technologies (for example, the aforementioned Patent Documents 1 and 2). Among these, it is preferable to include a cooler in order to facilitate the separation of sweep gas from the gas (mainly a mixed gas of carbon dioxide and sweep gas) taken out into the second gas flow path.

[0098] The separation apparatus may have any other configurations. For example, the separation apparatus may further have an anion exchange tower for passing the raw material gas in the first pipeline, a humidity control device for adjusting the humidity of the raw material gas, and a temperature control device for adjusting the temperature of the raw material gas connected to the upstream side of the first pipeline. Furthermore, a temperature control device for the sweep gas in the second pipeline may further be connected to the upstream side of the second pipeline, and a dehumidifier for dehumidifying the gas in the second pipeline may further be connected to the downstream side of the second pipeline.

[0099] [Summary] The present invention has been described above based on its embodiments. As mentioned above, the present invention includes the following embodiments 1 to 14.

[0100] [1] A method for separating carbon dioxide, comprising the steps of supplying a raw material gas containing carbon dioxide to a first gas channel, which is separated from a second gas channel by a carbon dioxide separation membrane having a separation functional layer formed on the surface of a separation membrane support layer that allows carbon dioxide to pass through and selectively permeates carbon dioxide, and the separation functional layer is positioned toward the first gas channel, and supplying a sweep gas to the second gas channel in synchronization with the step of supplying the raw material gas, wherein the separation functional layer is a layer containing a hydrophilic polymer and an amine compound, and reduced pressure steam is used as the sweep gas.

[0101] [2] The method for separating carbon dioxide as described in [1] above, wherein the hydrophilic polymer is at least one polymer selected from the group consisting of polyvinyl alcohol, poly(meth)acrylic acid, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, polyallylamine, polysaccharides, salts thereof, and copolymers thereof.

[0102] [3] The method for separating carbon dioxide according to [1] above, wherein the hydrophilic polymer is a polymer having a constituent unit represented by the following formula (1) and a constituent unit represented by the following formula (2).

[0103]

[0104] [4] The method for separating carbon dioxide according to [3] above, wherein the hydrophilic polymer is further a polymer having either or both of the constituent units represented by the following formula (3) and the constituent units represented by the following formula (4).

[0105] (In the formula, R represents an acyl group having 1 to 4 carbon atoms.)

[0106] [5] The method for separating carbon dioxide as described in [1] above, wherein the hydrophilic polymer is a polymer having a structural unit represented by the following formula (5).

[0107] (In the formula, R' represents a hydroxyl group or an organic group having 1 to 30 carbon atoms.)

[0108] [6] The method for separating carbon dioxide according to [5] above, wherein a polymer having a constituent unit represented by the following formula (6) is used in addition to the hydrophilic polymer.

[0109]

[0110] [7] The method for separating carbon dioxide according to any one of [1] to [6] above, wherein the amine compound used is an amine compound with a molecular weight of 500 or less.

[0111] [8] The method for separating carbon dioxide according to any one of [1] to [7] above, wherein the amine compound is at least one compound selected from the group consisting of the compound represented by the following formula (7) and the compound represented by the following formula (8).

[0112] (In formula (7), R １ , R ２ and R ３ Each of these independently represents a hydrogen atom, a C1-C4 alkyl group, or a hydroxyethyl group. Also, in formula (8), R ４ , R ５ and R ６ Each of these independently represents either a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0113] [9] The method for separating carbon dioxide according to any one of [1] to [8] above, wherein the separation membrane support layer is a porous membrane having an air permeation flux of 10,000 GPU or more.

[0114]

[10] A method for separating carbon dioxide according to any one of [1] to [9] above, wherein a hollow fiber membrane having a separation functional layer on its inner surface is used as a carbon dioxide separation membrane, a raw material gas is supplied to the hollow portion of the hollow fiber membrane, and a sweep gas is supplied to the outside of the hollow fiber membrane.

[0115]

[11] The method for separating carbon dioxide according to any one of [1] to

[10] above, wherein the pressure of the sweep gas is 50 kPa or less.

[0116]

[12] A method for separating carbon dioxide according to any one of [1] to

[11] above, wherein the relative humidity of the sweep gas is 70% or higher.

[0117]

[13] A method for separating carbon dioxide according to any one of [1] to

[12] above, wherein the raw material gas is one or more gases selected from the group consisting of exhaust gas, biogas, and natural gas.

[0118]

[14] A carbon dioxide separation apparatus comprising a carbon dioxide separation membrane having a separation functional layer formed on the surface of a separation membrane support layer that allows carbon dioxide to pass through and selectively separates carbon dioxide, and a carbon dioxide separation membrane that is positioned toward the first gas flow path, wherein a raw material gas containing carbon dioxide is supplied to the first gas flow path, and a sweep gas is supplied to the second gas flow path in synchronization with the supply of the raw material gas, wherein the separation functional layer is a layer containing a hydrophilic polymer and an amine compound, and the sweep gas is reduced pressure steam.

[0119] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0120] The carbon dioxide separation method and separation apparatus according to the embodiments of the present invention described above exhibit excellent carbon dioxide separation characteristics. Therefore, it is expected that it will be possible to separate and recover carbon dioxide at low cost from exhaust gases of large-scale sources such as thermal power plants, blast furnaces of steel mills, and cement factories. Furthermore, the separation apparatus has a compact configuration. Therefore, it is expected that it will be possible to efficiently separate and recover carbon dioxide from relatively small-scale carbon dioxide sources. In this way, the technology of the present invention is expected to make a significant contribution to reducing carbon dioxide emissions, and such the present invention is expected to contribute to achieving, for example, Goal 12 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Responsible Consumption and Production."

[0121] The calculation results of specific examples in embodiments of the present invention are described below.

[0122] The separation and recovery results are calculated when carbon dioxide is separated and recovered from a raw gas using a carbon dioxide separation device module, which has the aforementioned hollow fiber membrane, chamber, first conduit, and second conduit, and has a separation functional layer containing a hydrophilic polymer and an amine compound with a molecular weight of 500 or less on the inner surface of the hollow fiber membrane, under various conditions.

[0123] [Calculation Example 1] The raw material gas is a mixture of carbon dioxide and nitrogen, and the composition of the raw material gas is N ２ / CO ２ The ratio is 85 / 15, the flow rate is 10 L / min, the temperature is 60°C, and the relative humidity is 90%. Also, the area of ​​the separation functional layer (area of ​​the hollow fiber membrane) is 1 m². ２ Furthermore, the sweep gas will be steam, with a temperature of 60°C, a pressure of 20 kPa, and a flow rate of 10 L / min. The composition of the sweep gas will be 100% water vapor.

[0124] Under these conditions, the following items were calculated and evaluated for the gas extracted from the first gas channel to the second gas channel.

[0125] (1) Carbon dioxide purity (%) The carbon dioxide content in the gas extracted from the first gas channel (inside the hollow fiber membrane) to the second gas channel (outside the hollow fiber membrane) was calculated by dividing the carbon dioxide content by the nitrogen content.

[0126] (2) Recovery Rate (%) The recovery rate (%) of carbon dioxide recovered in the second gas channel was calculated. The carbon dioxide recovery rate is the ratio of the amount of carbon dioxide extracted into the second gas channel to the sum of the amount of carbon dioxide in the first gas channel and the amount of carbon dioxide extracted into the second gas channel.

[0127] (3) Separation from sweep gas The possibility of separating the sweep gas from the gas extracted into the second gas channel (mainly a mixed gas of carbon dioxide and sweep gas) was evaluated. Separation possibility was evaluated as "possible" if the concentration of carbon dioxide in the mixed gas exceeded 80% when the mixed gas was cooled to 2°C, and as "difficult" if it did not exceed 80%.

[0128] The calculation results from Calculation Example 1 are shown in Table 1.

[0129]

[0130] [Calculation Example 2] The separation and recovery results were calculated and evaluated in the same manner as in Calculation Example 1, except that the sweep gas flow rate was set to 5 L / min. The results are shown in Table 1.

[0131] [Calculation Comparison Example 1] The separation and recovery results were calculated and evaluated in the same manner as in Calculation Example 1, except that sweep gas was not supplied. The results are shown in Table 1.

[0132] [Calculation Comparison Example 2] The separation and recovery results were calculated and evaluated in the same manner as in Calculation Example 1, except that helium gas with a relative humidity of 90% and a pressure of 105 kPa was used instead of steam. The results are shown in Table 1.

[0133] [Calculation Example 3] The separation and recovery results were calculated and evaluated in the same manner as in Calculation Example 1, except that the temperature of the source gas was set to 80°C, the temperature of the sweep gas to 80°C, and the pressure to 50 kPa. The results are shown in Table 1.

[0134] [Calculation Example 4] The separation and recovery results were calculated and evaluated in the same manner as in Calculation Example 1, except that the temperature of the source gas was set to 80°C, the temperature of the sweep gas to 80°C, and the pressure to 20 kPa. The results are shown in Table 1.

[0135] [Calculation Comparison Example 3] The separation and recovery results were calculated and evaluated in the same manner as in Calculation Example 3, except that the temperature of the raw material gas was set to 80°C and no sweep gas was supplied. The results are shown in Table 1.

[0136] [Example 1] Carbon dioxide was separated and recovered using a separation apparatus under the same conditions as the calculation example described above. First, the separation apparatus used in the following examples and comparative examples will be explained.

[0137] <Configuration of the Separation Device> Figure 1 schematically shows the configuration of the separation device used in the following examples and comparative examples. The separation device has a separation membrane module 6. The separation membrane module 6 has a chamber and a hollow fiber membrane housed therein, and is substantially the same as that of Calculation Example 1 described above. The separation membrane module 6 is connected to a first conduit that is connected to the hollow fiber membrane and communicates the inside and outside of the chamber, and a second conduit that communicates the inside and outside of the chamber on the outside of the hollow fiber membrane in the chamber.

[0138] The first pipeline consists of an anion exchanger packed tower 1, a flow controller 2, a humidifier 3, a pressure gauge 4, a dew point meter 5, and a dehumidifying trap 7. The anion exchanger packed tower 1 is configured to receive exhaust gas as a raw material from a raw material gas supply source, such as a thermal power plant that generates exhaust gas after combustion mainly containing nitrogen and carbon dioxide. The anion exchanger packed tower 1, the flow controller 2, the humidifier 3, the pressure gauge 4, and the dew point meter 5 constitute the pipeline upstream of the separation membrane module 6 in the first pipeline, and the dehumidifying trap 7 constitutes the pipeline downstream of the separation membrane module 6 in the first pipeline.

[0139] The second pipeline consists of a steam generator 10, a flow controller 11, a pressure gauge 12, a dew point meter 13, a flow meter 14, a dehumidifying trap 15, and a vacuum pump 16. A device for recovering gas from the second pipeline (such as a tank) is connected to the downstream side of the second pipeline. The steam generator 10, flow controller 11, pressure gauge 12, and dew point meter 13 constitute the pipeline upstream of the separation membrane module 6 in the second pipeline, while the flow meter 14, dehumidifying trap 15, and vacuum pump 16 constitute the pipeline downstream of the separation membrane module 6 in the second pipeline.

[0140] Furthermore, the pressure gauge 4, dew point meter 5, separation membrane module 6, pressure gauge 12, dew point meter 13, and flow meter 14 are installed in the constant temperature bath 8, while the steam generator 10 and flow controller 11 are installed in the constant temperature bath 9.

[0141] <Conditions for implementation> The composition of the raw material gas is N ２ / CO ２ Except for setting the ratio to 87 / 13, the sweep gas pressure to 15 kPa, and the flow rate to 12 L / min, carbon dioxide was separated and recovered from the raw material gas using the above separation apparatus under the same conditions as in Calculation Example 1 described above. The results of the separation and recovery were determined and evaluated in the same manner as in Calculation Example 1. The results of Example 1 are shown in Table 2.

[0142]

[0143] [Example 2] Carbon dioxide separation and recovery were carried out and evaluated in the same manner as in Example 1, except that the sweep gas flow rate was set to 8 L / min. The results are shown in Table 2.

[0144] [Example 3] Carbon dioxide separation and recovery were carried out and evaluated in the same manner as in Example 1, except that the sweep gas flow rate was set to 6.5 L / min. The results are shown in Table 2.

[0145] [Comparative Example 1] Carbon dioxide separation and recovery were carried out and evaluated in the same manner as in Example 1, except that sweep gas was not supplied. The results are shown in Table 2.

[0146] [Comparative Example 2] Carbon dioxide separation and recovery were performed and evaluated in the same manner as in Example 1, except that helium gas at a temperature of 60°C and a pressure of 110 kPa was used instead of steam, and the sweep gas flow rate was set to 7.5 L / min. The results are shown in Table 2.

[0147] [Example 4] Carbon dioxide separation and recovery were carried out and evaluated in the same manner as in Example 1, except that the sweep gas temperature was 70°C, the sweep gas pressure was 25 kPa, and the sweep gas flow rate was 8 L / min. The results are shown in Table 2.

[0148] [Example 5] Carbon dioxide separation and recovery were carried out and evaluated in the same manner as in Example 4, except that the sweep gas flow rate was set to 6.5 L / min. The results are shown in Table 2.

[0149] [Discussion] According to Table 1, a comparison between calculation examples 1 and 2 and calculation comparison examples 1 and 2, and a comparison between calculation examples 3 and 4 and calculation comparison example 3, shows that calculation examples 1 to 4, which use reduced-pressure steam as the sweep gas, showed high values ​​for both carbon dioxide purity and recovery rate. Furthermore, by cooling the mixed gas in the second gas flow path, the reduced-pressure steam, which is the sweep gas, can be easily separated, making it possible to easily recover carbon dioxide from the mixed gas with high efficiency.

[0150] Furthermore, in calculation examples 1 to 4, the separation functional layer in the carbon dioxide separation membrane separating the first and second gas flow paths is subjected to heat from the steam gas, but the steam temperature is less than 100°C. Therefore, the amine compounds in the separation functional layer are less susceptible to heat damage. Thus, under the conditions of calculation examples 1 to 4, it is expected that highly efficient separation and recovery of carbon dioxide from the raw material gas can be stably carried out over a long period of time.

[0151] In comparative example 1 of the calculation, although the purity of the carbon dioxide gas extracted into the second gas channel was high, the amount of carbon dioxide permeate through the carbon dioxide separation membrane was low. This is thought to be because the effect of promoting carbon dioxide permeation by the sweep gas was not realized.

[0152] In the calculation example 2, although both the purity and recovery rate of carbon dioxide are as high as in the calculation example, it is difficult to separate carbon dioxide from the sweep gas.

[0153] In comparative example 3 of the calculation, although the purity of the carbon dioxide gas extracted into the second gas channel was high, the amount of carbon dioxide permeate through the carbon dioxide separation membrane was low. This is thought to be because the effect of promoting carbon dioxide permeation by the sweep gas was not realized.

[0154] Furthermore, in Examples 1 to 5 and Comparative Examples 1 and 2, the carbon dioxide recovery rate tends to be generally lower than that of the calculation example. However, as is clear from, for example, the comparison between Examples 1 to 3 and Comparative Example 1 or Comparative Example 2, the embodiments of the present invention that use reduced-pressure steam as the sweep gas tend to show a higher carbon dioxide recovery rate compared to cases where there is no sweep gas or when helium is used as the sweep gas, similar to the calculation example described above.

[0155] This invention can be used in technologies for efficiently recovering carbon dioxide from sources of carbon dioxide gas.

[0156] 1. Anion exchanger packed column 2, 11. Flow controller 3. Humidifier 4, 12. Pressure gauge 5, 13. Dew point meter 6. Separation membrane module 7, 15. Dehumidification trap 8, 9. Constant temperature bath 10. Steam generator 14. Flow meter 16. Vacuum pump

Claims

1. A method for separating carbon dioxide, comprising the steps of: supplying a raw material gas containing carbon dioxide to a first gas channel, which has a separation functional layer formed on the surface of a separation membrane support layer that allows carbon dioxide to pass through and selectively permeates carbon dioxide, and which is separated from a second gas channel by a carbon dioxide separation membrane that is positioned toward the first gas channel; and supplying a sweep gas to the second gas channel in synchronization with the step of supplying the raw material gas, wherein the separation functional layer is a layer containing a hydrophilic polymer and an amine compound, and the sweep gas is reduced-pressure steam.

2. The method for separating carbon dioxide according to claim 1, wherein the hydrophilic polymer is at least one polymer 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 method for separating carbon dioxide according to claim 1, wherein the hydrophilic polymer is a polymer having a constituent unit represented by the following formula (1) and a constituent unit represented by the following formula (2).

4. The method for separating carbon dioxide according to claim 3, wherein the hydrophilic polymer further comprises a polymer having either or both of the constituent units represented by the following formula (3) and the constituent units represented by the following formula (4). (In the formula, R represents an acyl group having 1 to 4 carbon atoms.) 5. The method for separating carbon dioxide according to claim 1, wherein the hydrophilic polymer is a polymer having a structural unit represented by the following formula (5). (In the formula, R' represents a hydroxyl group or an organic group having 1 to 30 carbon atoms.) 6. The method for separating carbon dioxide according to claim 5, wherein the hydrophilic polymer further uses a polymer having a structural unit represented by the following formula (6).

7. The method for separating carbon dioxide according to claim 1, wherein the amine compound used is an amine compound with a molecular weight of 500 or less.

8. The method for separating carbon dioxide according to claim 1, wherein the amine compound is at least one compound selected from the group consisting of the compound represented by the following formula (7) and the compound represented by the following formula (8). (In formula (7), R １ , R ２ and R ３ Each of these independently represents a hydrogen atom, a C1-C4 alkyl group, or a hydroxyethyl group. Also, in formula (8), R ４ , R ５ and R ６ Each of these independently represents either a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

9. The method for separating carbon dioxide according to claim 1, wherein the separation membrane support layer is a porous membrane having an air permeation flux of 10,000 GPU or more.

10. A method for separating carbon dioxide according to claim 1, wherein a hollow fiber membrane having the separation functional layer on its inner surface is used as the carbon dioxide separation membrane, the raw material gas is supplied to the hollow portion of the hollow fiber membrane, and the sweep gas is supplied to the outside of the hollow fiber membrane.

11. The method for separating carbon dioxide according to claim 1, wherein the pressure of the sweep gas is 50 kPa or less.

12. The method for separating carbon dioxide according to claim 1, wherein the relative humidity of the sweep gas is 70% or higher.

13. The method for separating carbon dioxide according to claim 1, wherein the raw material gas is one or more gases selected from the group consisting of exhaust gas, biogas, and natural gas.

14. A carbon dioxide separation apparatus comprising a carbon dioxide separation membrane having a separation functional layer formed on the surface of a separation membrane support layer that allows carbon dioxide to pass through and selectively separates carbon dioxide, and the separation functional layer being positioned toward the first gas flow path, wherein a raw material gas containing carbon dioxide is supplied to the first gas flow path, and a sweep gas is supplied to the second gas flow path in synchronization with the supply of the raw material gas, wherein the separation functional layer is a layer containing a hydrophilic polymer and an amine compound, and the sweep gas is reduced-pressure steam.

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