JP6431481B2 - Method for separating CO2 permselective membrane and CO2 from mixed gas - Google Patents

Description

The present invention relates to a CO ₂ permselective membrane and a method for separating CO ₂ from a mixed gas.

Selectively transmits CO _2, as CO ₂ selective permeation membrane which can be used to separate CO ₂ from a gas mixture, various polymer membranes have been developed (e.g., Non-Patent Document 1). However, polymeric membranes, in order to generally based on the solution-diffusion mechanism physically transmit CO _2, a limit to the improvement of the CO ₂ permeation rate, and selectivity to _{N 2} in the CO _{2 (CO} 2 / _{N 2} selectivity) was there.

Therefore, studies have been made on a permeable membrane called a facilitated transport membrane that uses a substance called “carrier” that selectively reacts with CO ₂ and selectively permeates gas by a facilitated transport mechanism in addition to a dissolution and diffusion mechanism. (For example, Non-Patent Documents 2 and 3). In the facilitated transport mechanism, a specific gas is selectively permeated based on a reversible chemical reaction between a specific gas and a carrier in a film.

Furthermore, in recent years, permeable membranes using ionic liquids have been proposed as membranes oriented to the facilitated transport mechanism (Non-patent Documents 4 and 5). In particular, Patent Document 1 discloses an ionic liquid comprising an amino acid anion and a specific cation. A carbon dioxide gas separation membrane containing benzene is disclosed, and the membrane is said to be excellent in CO ₂ permeability coefficient and CO ₂ / H ₂ permeability coefficient ratio.

JP 2010-214324 A

J. et al. Membr. Sci. , 2008, vol. 320, p. 390-400 Ind. Eng. Chem. Res. , 2000, vol. 39, p. 247 J. et al. Membr. Sci. , 2007, vol. 291, p. 157 J. et al. Membr. Sci. , 2008, vol. 314, p. 1 J. et al. Menbr. Sci. , 2008, vol. 322, p. 28

However, the conventional facilitated transport membrane has room for improvement because the CO ₂ permeation rate and CO ₂ / N ₂ selectivity are not always sufficient depending on temperature and humidity conditions.

Therefore, the present invention achieves a sufficiently high CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity even in a wider range of temperature conditions and relative humidity conditions than the conventional facilitated transport membrane. An object is to provide a CO ₂ permselective membrane capable of satisfying the requirements.

Another object of the present invention is to provide a method for stably and effectively separating CO ₂ from a mixed gas using the above-mentioned CO ₂ permselective membrane.

As a result of intensive studies, the present inventors have surprisingly found that a cation having a specific structure is used in the ionic liquid, and in a wider range of temperature conditions and relative humidity conditions than in the prior art. In addition, the inventors have found that a CO ₂ permselective membrane having a sufficiently high CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity can be obtained, and the present invention has been completed.

That is, the present invention is a CO ₂ permselective membrane having an ionic liquid containing a cation and an anion and a porous membrane impregnated with the ionic liquid, wherein the cation is represented by the following formula (1). And a CO ₂ permselective membrane comprising at least one selected from the group consisting of ammonium and phosphonium represented by the following formula (2).

［式（１）及び（２）において、各Ｒは、それぞれ独立に、アミノ基、フッ素原子で置換されていてもよいＣ_１−Ｃ_３アルキル基、フッ素原子で置換されていてもよいＣ_２−Ｃ_３アルケニル基、又はフッ素原子で置換されていてもよいＣ_２−Ｃ_３アルキニル基を表し、前記アミノ基は、１個又は２個のＣ_１−Ｃ_３アルキル基、Ｃ_２−Ｃ_３アルケニル基、又はＣ_２−Ｃ_３アルキニル基で置換されていてもよい。］

[In the formulas (1) and (2), each R is independently an amino group, a C ₁ -C ₃ alkyl group optionally substituted with a fluorine atom, or a C ₂ optionally substituted with a fluorine atom. -C ₃ alkenyl group or optionally substituted with fluorine atom _C 2 -C ₃ alkynyl group, the amino group, one or two _C 1 -C ₃ alkyl _group, C 2 -C ₃ alkenyl, or C ₂ -C ₃ alkynyl groups may be substituted. ]

The above-mentioned CO ₂ permselective membrane has a sufficiently high CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity even in a wider range of temperature conditions and relative humidity conditions than the conventional facilitated transport membrane. Can be achieved.

The anion may include a carboxylate anion. By adopting an anion containing a carboxylate anion as an anion, a CO ₂ permselective membrane having a more excellent CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity can be provided.

In formulas (1) and (2), at least one of each R may be the amino group. By adopting a cation having an amino group in the molecule, the saturated absorption of CO ₂ can be increased, and as a result, CO having a better CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity. _{A two} permselective membrane can be provided.

The present invention also relates to a CO ₂ selective permeation membrane as described above, by passing the CO ₂ in the mixed gas containing CO _2, the CO ₂ comprising the step of separating from the mixed gas, a mixed gas of CO ₂ Provide a method of separating from Since this method employs a CO ₂ permselective membrane as described above, CO ₂ can be mixed stably and effectively over a wider range of temperature and relative humidity conditions than in the prior art. It can be separated from the gas.

According to the present invention, a sufficiently high CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity can be achieved even in a wider range of temperature conditions and relative humidity conditions than in the prior art. A CO ₂ permselective membrane can be provided.

The present invention can also provide a method for stably and effectively separating CO ₂ from a mixed gas by using the above-mentioned CO ₂ permselective membrane.

It is a schematic diagram which shows one Embodiment of a membrane separator. It is a graph showing the relationship between the CO ₂ permeability and temperature CO ₂ selectively permeable membrane. Is a graph showing the relationship between the N ₂ permeability and temperature CO ₂ selectively permeable membrane. CO ₂ is a graph showing the relationship between the _CO 2 / _{N 2} selectivity and the temperature of the permselective membrane. It is a graph showing the relationship between the CO ₂ permeability and temperature CO ₂ selectively permeable membrane. Is a graph showing the relationship between the N ₂ permeability and temperature CO ₂ selectively permeable membrane. CO ₂ is a graph showing the relationship between the _CO 2 / _{N 2} selectivity and the temperature of the permselective membrane. It is a graph showing the relationship between the CO ₂ permeability and relative humidity of the CO ₂ selective permeation membrane. Is a graph showing the relationship between the N ₂ permeability and relative humidity of the CO ₂ selective permeation membrane. CO ₂ is a graph showing the relationship between the _CO 2 / _{N 2} selectivity and relative humidity of the permselective membrane.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

FIG. 1 is a schematic view showing an embodiment of a membrane separation apparatus having a CO ₂ permselective membrane. Membrane separation apparatus 10 shown in FIG. 1 is mainly composed of a CO ₂ selective permeation membrane 1, and the permeation cell 3 that accommodates the CO ₂ selective permeation membrane 1, the heating unit 5 for heating the CO ₂ selective permeation membrane 1 .

A space in which the CO ₂ selective permeable membrane 1 is mounted is provided inside the permeation cell 3, and this space is divided by the CO ₂ selective permeable membrane 1 into a feed side portion and a sweep side portion. A feed gas (mixed gas) F1 containing CO ₂ is supplied to the feed side portion and discharged as a feed gas F2. The sweep gas S1 is normally supplied to the sweep side portion. The sweep gas S1 is generally an inert gas such as helium gas. CO ₂ selectively permeable membrane 1 selectively permeable to CO ₂ which has moved to the sweep side portion gas is discharged together with the sweep gas as a discharge gas S2. As a result, CO ₂ is separated from the feed gas F1.

The CO ₂ permselective membrane according to this embodiment includes an ionic liquid containing a cation and an anion, and a porous membrane impregnated with the ionic liquid.

  The cation includes at least one selected from the group consisting of ammonium represented by the following formula (1) and phosphonium represented by the following formula (2).

In the formulas (1) and (2), each R is independently an amino group, a C ₁ -C ₃ alkyl group optionally substituted with a fluorine atom, or a C _2- optionally substituted with a fluorine atom. Represents a C ₃ alkenyl group or a C ₂ -C ₃ alkynyl group optionally substituted by a fluorine atom, wherein the amino group is one or two C ₁ -C ₃ alkyl groups, C ₂ -C ₃ alkenyl Group or a C ₂ -C ₃ alkynyl group.

  The combination of the anion and cation is arbitrarily selected as a combination that forms an ionic liquid. The ionic liquid may contain a small amount of moisture. The water concentration of the ionic liquid may be, for example, 0 to 50% by mass or 5 to 10% by mass.

An anion in particular is not restrict | limited, The arbitrary thing which can form an ionic liquid with a counter cation can be selected suitably. Such anions may include, for example, carboxylate anions. In addition, from the viewpoint of CO ₂ permeation rate and CO ₂ / N ₂ selectivity according to the present embodiment, the anion includes a primary amino group (—NH ₂ ), a secondary amino group (—NH—), and You may have 1 type, or 2 or more types of amino groups chosen from tertiary amino group (-N =). Especially, the said anion may contain the carboxylate anion which has said amino group.

  Such anions include, for example, arginine, histidine, lysine, aspartic acid, glutamic acid, serine, threonine, asparagine, glutamine, cysteine, glycine, proline, alanine, isoleucine, leucine, methionine, phenylalanine, tryptophan, tyrosine, and valine. An anion formed from at least one amino acid selected from the group consisting of: Some or all of the hydrogen atoms of the amino group of these amino acids may be substituted with an alkyl group or an aryl group. For example, the anion can include N-alkyl amino acids and N-aryl amino acids having secondary amino groups, N, N-dialkyl amino acids and N-alkyl-N-aryl amino acids having tertiary amino groups. In particular, it may be an anion formed from at least one amino acid selected from glycine and proline.

  The cation is at least one selected from the group consisting of ammonium represented by the above formula (1) and phosphonium represented by the above formula (2).

In formula (1), each R independently represents an amino group, a C ₁ -C ₃ alkyl group optionally substituted with a fluorine atom, a C ₂ -C ₃ alkenyl group optionally substituted with a fluorine atom, or be substituted by a fluorine atom represent also good _C 2 -C ₃ alkynyl group, the amino group, one or two _C 1 -C ₃ alkyl _group, C 2 -C ₃ alkenyl group or _{C 2} it may be substituted by -C ₃ alkynyl group. Among them, R represents may be a C ₁ -C ₃ alkyl group may be a methyl group or an ethyl group. By reducing the molecular size and reducing the free volume, the N ₂ permeation rate is suppressed, and as a result, the CO ₂ selective permeation performance can be improved. Specific examples of ammonium include tetramethylammonium.

In formula (2), each R independently represents an amino group, a C ₁ -C ₃ alkyl group optionally substituted with a fluorine atom, a C ₂ -C ₃ alkenyl group optionally substituted with a fluorine atom, or be substituted by a fluorine atom represent also good _C 2 -C ₃ alkynyl group, the amino group, one or two _C 1 -C ₃ alkyl _group, C 2 -C ₃ alkenyl group or _{C 2} it may be substituted by -C ₃ alkynyl group. Among them, R represents may be a C ₁ -C ₃ alkyl group may be a methyl group or an ethyl group. By reducing the molecular size and reducing the free volume, the N ₂ permeation rate is suppressed, and as a result, the CO ₂ selective permeation performance can be improved. Specific examples of phosphonium include tetramethylphosphonium.

In the formulas (1) and (2), at least one of each R may be the amino group. The cation is, by having an amino group, for amino group and CO ₂ in the molecule is reacted with CO ₂ is absorbed, resulting in CO ₂ permeation rate, and CO 2 _/ N ₂ to more increase the selectivity Can do. Specific examples of such ammonium or phosphonium include 1,1,1-trimethylhydrazinium, aminotrimethylphosphonium, and the like.

  The porous membrane can be appropriately selected from those usually used as a support membrane for the selectively permeable membrane. The porous membrane may be hydrophilic or hydrophobic, but may be hydrophilic when the ionic liquid is hydrophilic. The porous membrane includes, for example, polytetrafluoroethylene. The thickness of the porous film is not particularly limited, but is, for example, 10 to 100 μm. The voids in the porous membrane may be sufficiently filled with the ionic liquid, or may be partially unfilled. The porous membrane may be impregnated with a material other than the ionic liquid, if necessary, in addition to the ionic liquid. The type and amount of this additional material can be arbitrarily selected without departing from the spirit of the present invention.

The CO ₂ permselective membrane can be produced by a method including a step of impregnating a porous membrane with an ionic liquid. Impregnation can be performed by a method usually used in the art.

When CO ₂ is separated from the feed gas F1 using the CO ₂ permselective membrane and the membrane separator 10 according to the present embodiment, the feed gas (mixed gas) F1 that passes through the membrane separator 10 and the CO ₂ permselective membrane This temperature can be appropriately set experimentally by those skilled in the art, and a sufficiently high CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity can be achieved even in a wide range of temperature conditions. As an upper limit of temperature conditions, 150 degrees C or less may be sufficient, and 110 degrees C or less may be sufficient. On the other hand, as a minimum of temperature conditions, 10 degreeC or more may be sufficient and 80 degreeC or more may be sufficient. Specific temperature is 10-150 degreeC, for example, and 80-110 degreeC may be sufficient as it. The CO ₂ permselective membrane 1 is heated by the heating unit 5 as necessary. As the heating unit 5, for example, an oven capable of accommodating the transmission cell 3 is used.

The feed gas F1 often contains N ₂ in addition to CO ₂ . The CO ₂ permselective membrane according to the present embodiment maintains a high CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity even when the CO ₂ partial pressure is low. Thus, if the partial pressure of CO ₂ separates the CO ₂ from the gas mixture is not so high, CO ₂ selectively permeable film according to the present embodiment is particularly useful. In general, as the feed gas flows downstream, the CO ₂ partial pressure in the feed gas tends to decrease. Therefore, practically even, in many cases, may include the step of separating CO ₂ from a gas mixture of low partial pressure of CO ₂ is assumed. Specifically, the CO ₂ partial pressure of the feed gas (mixed gas) F1 may be 15 kPa or less.

Furthermore, the CO ₂ permselective membrane according to the present embodiment has a sufficiently high CO ₂ permeation rate and / or CO ₂ / N even under a wider range of humidity conditions than the conventional facilitated transport membrane. _Two selectivity can be achieved. In general, in the facilitated transport membrane, when separating CO ₂ gas from a low-humidity mixed gas, it is often necessary to add water vapor to the mixed gas, but according to this embodiment, it is not necessary to add water vapor. , CO ₂ can be separated efficiently. Since enormous energy is required to supply water vapor, the necessity of water vapor is very significant in terms of environment and economy. Specifically, the relative humidity of the feed gas (mixed gas) F1 may be less than 50%, 30% or less, and 5% or less. The lower limit of the relative humidity is not particularly limited, but may be 0% or more, for example. Further, the water vapor concentration of the feed gas (mixed gas) F1 may be less than 30 mol% and 5 mol% or less. The lower limit of the water vapor concentration is not particularly limited, but may be, for example, 0 mol% or more.

The flow rate of the feed gas F1 is not particularly limited, but is, for example, _{2 to} 1000 mL / min per 10 cm ² area of the CO ₂ permselective membrane. The pressure of the feed gas is not particularly limited, but may be atmospheric pressure, and may be adjusted within a range of 100 to 10000 kPa or 100 to 1000 kPa, for example.

The flow rate of the sweep gas S1 is not particularly limited, but is, for example, 1 to 500 mL / min per 10 cm ² area of the CO ₂ permselective membrane. The pressure of the sweep gas is not particularly limited, but may be atmospheric pressure or less than atmospheric pressure, and may be adjusted to a range of 30 to 5000 kPa or 30 to 1000 kPa, for example. When the partial pressure of CO ₂ in the feed gas is sufficiently high, the sweep gas may not necessarily flow.

The present invention is not limited to the embodiment described above, and can be appropriately modified without departing from the spirit of the present invention. For example, an arbitrary layer may be laminated on one side or both sides of the CO ₂ permselective membrane.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
Tetramethylammonium glycine (hereinafter referred to as [N1111] [Gly]) was prepared as an ionic liquid.

  The ionic liquid was synthesized by a neutralization method. That is, while cooling an aqueous solution containing 40% by mass of tetramethylammonium hydroxide (hereinafter referred to as [N1111] [OH]) to 8 ° C. in a nitrogen atmosphere, an amount of 5% excess of the number of moles thereof is achieved. The solution was added dropwise to an aqueous glycine solution containing glycine and 100 mL of pure water. Then, the neutralization reaction of the hydroxide ion and the hydrogen ion derived from glycine was performed by stirring for 24 hours or more. After the neutralization reaction, water was removed at 40 ° C. by an evaporator. Water was removed until the prepared ionic liquid became a 90 mass% aqueous solution (water concentration 10 mass%). A porous polytetrafluoroethylene (PTFE) porous membrane (thickness 35.7 μm, average pore diameter 0.2 μm) is immersed in the ionic liquid thus prepared, and the pressure is reduced in that state for 1800 seconds to obtain porous. The membrane was impregnated with ionic liquid. The porous membrane impregnated with the ionic liquid was taken out, and the excess ionic liquid adhering to the surface was removed to obtain a permeable membrane for evaluation.

(Comparative Example 1)
By using the same method as in Example 1, tetrabutylammonium glycine (hereinafter referred to as [N4444] [Gly]) was prepared as an ionic liquid, and this was impregnated into a PTFE porous membrane to prepare a comparative permeable membrane. Obtained.

(Comparative Example 2)
By using the same method as in Example 1, tetrabutylphosphonium glycine (hereinafter referred to as [P4444] [Gly]) was prepared as an ionic liquid, and this was impregnated into a PTFE porous membrane to prepare a comparative permeable membrane. Obtained.

(Comparative Example 3)
In the same manner as in Example 1, tetrabutylphosphonium proline (hereinafter referred to as [P4444] [Pro]) was prepared as an ionic liquid, and this was impregnated into a PTFE porous membrane, and a comparative permeable membrane was prepared. Obtained.

(Test Example 1)
Each prepared permeable membrane was attached to a stainless steel permeation cell. This permeation cell was accommodated in an oven equipped with a thermostat to prepare an evaluation apparatus having the same configuration as the apparatus shown in FIG. The oven was adjusted to a predetermined temperature with a thermostat.

As the feed gas F1, a dry mixed gas (CO ₂ partial pressure: 1.0 kPa) containing CO ₂ gas and N ₂ gas and substantially free of moisture was used. The feed gas F1 was adjusted to a flow rate of 200 mL / min and a temperature of 25 ° C. The pressure on the feed side was maintained at atmospheric pressure. Helium gas was used as the sweep gas S1. The sweep gas S1 was adjusted to a flow rate of 40 mL / min and a temperature of 25 ° C. The pressure on the sweep side was maintained at atmospheric pressure. The outlet side sweep gas (exhaust gas) S2 was analyzed by gas chromatography (GC). From the GC analysis results, CO ₂ and N ₂ permeation rates and CO ₂ / N ₂ selectivity were calculated.

For the permeable membranes obtained in Example 1 and Comparative Examples 1 to 3, the humidity of the oven was set to 50 RH%, and the CO ₂ permeation rate and N ₂ permeation rate when the set temperature was changed from 30 to 100 ° C., respectively. 2 and 3 show the CO ₂ / N ₂ selectivity in FIG. 4, respectively.

2 and 3, the permeation speed is shown as “permeability”. Permeability is expressed as the amount of gas that has passed through a membrane having a unit surface area and unit thickness when a unit pressure drop is applied at a predetermined temperature. The unit of permeability is expressed as “barrer”, and 1 barr is 10 ⁻¹⁰ [cm ³ · cm ² / cm ² · cmHg · s]. In calculating the permeation speed, the thickness of the porous film (35.7 μm) was used as the film thickness. The same applies to FIGS.

As shown in FIG. 3, the result was that the permeable membrane of Example 1 was smaller than the permeable membranes of Comparative Examples 1 to 3 with respect to the N ₂ permeation rate. This is thought to be because the free volume of the ionic liquid itself was reduced by selecting a cation having a molecular size as small as possible as the constituent molecule of the ionic liquid, thereby reducing the amount of N ₂ dissolved in the ionic liquid. . This tendency was particularly noticeable in the high temperature region.

As a result, as shown in FIG. 4, it was found that the permeable membrane of Example 1 had excellent CO ₂ / N ₂ selectivity as compared with the permeable membranes of Comparative Examples 1 to 3.

(Example 2)
As an ionic liquid, 1-aminotrimethylammonium glycine (hereinafter referred to as [aN111] [Gly]) was prepared.

The ionic liquid was synthesized by a neutralization method. That is, 16.1630 g of commercially available 1,1,1-trimethylhydrazinium iodide (hereinafter referred to as [aN111] [I]) is dissolved in 200 mL of pure water, and 12 times the weight of [I] OH ^- type ion exchange resin was added so that the anion exchange reaction proceeded by stirring for 10 minutes. The [I] concentration in the solution after the reaction was 50 mg / L. Thereafter, the ion exchange resin was removed from the reaction solution by filtration, and the reaction solution was added dropwise to an aqueous glycine solution containing 5% excess glycine and 100 mL of pure water than the [aN111] [I] concentration in the solution. After allowing the neutralization reaction to proceed for 24 hours under cooling (7 ° C.), water was removed at 60 ° C. using an evaporator. Thereafter, 50 mL of ethanol was added to precipitate unreacted glycine, the glycine was removed by filtration, and the solvent was removed at 60 ° C. by an evaporator.

  The PTFE porous membrane was impregnated with [aN111] [Gly] thus obtained in the same manner as in Example 1 to obtain a permeable membrane for evaluation.

(Test Example 2)
About the permeable membrane obtained in Example 2, the result of having done the test similar to Test Example 1 is shown to FIGS. 5 to 7 also show the results of Comparative Example 1.

As shown in FIGS. 5 and 6, the permeable membrane of Example 2 has a higher CO ₂ permeation rate in addition to the lower N ₂ permeation rate than the permeable membrane of Comparative Example 1. became. This is presumably because the CO ₂ saturation absorption increased by selecting a cation having an amino group as a constituent molecule of the ionic liquid.

As a result, as shown in FIG. 7, it was found that the permeable membrane of Example 2 had extremely excellent CO ₂ / N ₂ selectivity as compared with the permeable membrane of Comparative Example 1.

(Test Example 3)
An evaluation apparatus was prepared in the same manner as in Test Example 1.

For the permeable membranes obtained in Examples 1 and 2 and Comparative Example 1, the CO ₂ permeation rate, the N ₂ permeation rate when the oven temperature was set to 100 ° C. and the set humidity was changed from 0 to 90 RH%, and CO ₂ / N ₂ selectivity is shown in FIGS.

As shown in FIG. 9, the results similar to Test Examples 1 and 2 were obtained in which the permeable membranes of Examples 1 and 2 were smaller in N ₂ permeation rate than the permeable membrane of Comparative Example 1. This tendency was particularly noticeable in the low humidity region.

As a result, as shown in FIG. 10, it was found that the permeable membranes of Examples 1 and ₂ had excellent CO ₂ / N ₂ selectivity as compared with the permeable membrane of Comparative Example 1, particularly in the low humidity region. It was.

On the other hand, as shown in FIG. 8, the CO ₂ permeation rate of the permeable membrane of Example 2 was larger than the permeable membrane of Comparative Example 1, which was the same result as Test Example 2. This tendency was particularly noticeable in a high humidity region of 50% or more.

As a result, as shown in FIG. 10, especially in a high humidity region of 50% or more, the permeable membrane of Example 2 has extremely excellent CO ₂ / N ₂ selectivity as compared with the permeable membrane of Comparative Example 1. It turns out to have.

As described above, from the results of Test Examples 1 to 3, by selecting a cation having a molecular size as small as possible as a constituent molecule of the ionic liquid, the N ₂ permeation rate of the permeable membrane is reduced, and as a result, excellent CO ₂ A CO ₂ permselective membrane having / N ₂ selectivity can be provided. Further, it can be seen that the permeation membrane has the effect even under a wide range of temperature conditions and relative humidity conditions.

Furthermore, by selecting a cation having an amino group as a constituent molecule of the ionic liquid, the CO ₂ permeation rate of the permeable membrane is remarkably improved, and as a result, CO ₂ having extremely excellent CO ₂ / N ₂ selectivity. A selectively permeable membrane can be provided. In addition, it can be seen that the permeation membrane has sufficient effects even under a wide range of temperature conditions and relative humidity conditions (particularly under low humidity conditions).

According to the present invention, a sufficiently high CO ₂ permeation rate and / or CO ₂ / N ₂ selectivity can be achieved even in a wider range of temperature conditions and relative humidity conditions than in the prior art. A CO ₂ permselective membrane can be provided.

The present invention can also provide a method for stably and effectively separating CO ₂ from a mixed gas by using the above-mentioned CO ₂ permselective membrane.

1 ... CO ₂ selectively permeable membrane, 3 ... permeation cell, 5 ... heating section, 10 ... membrane separator, F1, F2 ... feed gas (mixed gas), S1, S2 ... sweep gas (exhaust gas).

Claims (2)

A CO ₂ permselective membrane having an ionic liquid containing a cation and an anion, and a porous membrane impregnated with the ionic liquid,
The cation is seen containing at least one selected from the group consisting of phosphonium represented by ammonium and the following formula represented by the following formula (1) (2),
Said anion, carboxylate anion including, CO ₂ selectively permeable membrane.

[In the formulas (1) and (2), each R is independently an amino group, a C ₁ -C ₃ alkyl group optionally substituted with a fluorine atom, or a C ₂ optionally substituted with a fluorine atom. -C ₃ alkenyl group or optionally substituted with fluorine atom _C 2 -C ₃ alkynyl group, the amino group, one or two _C 1 -C ₃ alkyl _group, C 2 -C ₃ alkenyl, or C ₂ -C ₃ rather it may also be substituted with an alkynyl group, in which at least one of the amino groups of each R in formula (1) and (2). ] The CO ₂ selective permeation membrane according to claim 1, by passing the CO ₂ in the mixed gas containing CO _2, comprising the step of separating CO ₂ from the gas mixture to separate the CO ₂ from the gas mixture Method.

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