JPH0760078A - Production of plasma treated membrane for carbon dioxide separation - Google Patents

Abstract

PURPOSE:To produce a carbon dioxide separation membrane excellent in the separation factor of carbon dioxide and the holdability of a carbon dioxide carrier liquid and not lowered in its membrane capacity even by the contact with water. CONSTITUTION:After a porous polymeric membrane is subjected to plasma treatment, hydrophilic vinyl monomer vapor is brought into contact with the plasma treated porous polymeric membrane to be subjected to graft polymerization and, subsequently, a carbon dioxide carrier liquid is impregnated into the porous polymeric membrane having the hydrophilic polymer surface layer thus obtained to be held thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon dioxide separation membrane.

[0002]

2. Description of the Related Art In order to separate and concentrate carbon dioxide (CO ₂ ) from a mixed gas, the mixed gas is brought into contact with one side (CO ₂ adsorption side) of the separation membrane and the other side (CO ₂ adsorption side) of the separation membrane. A method of separating and concentrating carbon dioxide on the CO ₂ release side) is known. In this carbon dioxide separation / concentration technology, the carbon dioxide separation efficiency is greatly affected by the performance of the separation membrane, and there is a demand for the development of a separation membrane having a high carbon dioxide separation coefficient.

As a gas separation membrane, one in which a plasma polymer thin film of a specific fluorine compound is formed on a porous membrane is known (JP-A-62-204825 and JP-A-62-20).
4826, 62-204827). However, these separation membranes have a CO ₂ / N ₂ separation coefficient of 3.9 to 8.0.
Therefore, it cannot be applied as a practical carbon dioxide separation membrane.

Further, a gas separation membrane using an aromatic polyimide which is a reaction product of an aromatic tetracarboxylic acid and an aromatic diamine is also known (JP-A-60-15).
0806, 61-133106, JP-A-63-1.
23420). The CO ₂ / N ₂ separation coefficient of these aromatic polyimide-based separation membranes is usually as high as 20 to 30, but it cannot be said to be an efficient carbon dioxide separation membrane. .

As a separation membrane having a high CO ₂ / N ₂ separation coefficient,
A porous membrane impregnated with polyethylene glycol is known (Journal of the Chemical Society of Japan, No. 6 (198).
3), p. 847-853). Although this separation membrane has a high CO ₂ / N ₂ separation coefficient of 110, it has a poor polyethylene glycol retention property on the porous membrane, and when it comes into contact with water, the polyethylene glycol is eluted and the membrane performance deteriorates. is there. Further, it is also known to use an immobilization liquid membrane obtained by impregnating and holding an aqueous alkali metal carbonate solution in a porous membrane as a carbon dioxide separation membrane [Sc
ience, 156 , 1481-1484 (196
7)]. However, this separation membrane also has poor retention of the aqueous solution,
When it comes into contact with water, there is a problem that the aqueous solution is easily eluted and the membrane performance is deteriorated.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems found in conventional carbon dioxide separation membranes, has an excellent carbon dioxide separation coefficient, excellent carbon dioxide carrier liquid retention, and water It is an object of the present invention to provide a method for producing a carbon dioxide separation membrane, the membrane performance of which does not easily deteriorate even when contacted.

[0007]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, after the porous polymer membrane is plasma-treated, the hydrophilic vinyl monomer vapor is brought into contact with the plasma-treated porous polymer membrane to be graft-polymerized, and then obtained in this manner. Also provided is a method for producing a plasma-treated carbon dioxide separation membrane, which comprises impregnating and holding a carbon dioxide carrier liquid in a porous polymer membrane having a hydrophilic polymer surface layer.

The carbon dioxide separation membrane of the present invention (hereinafter, also simply referred to as a separation membrane) is characterized by using a porous polymer membrane having a hydrophilic polymer layer on its surface as a support. The support for impregnating and holding the carbon dioxide carrier liquid used in the present invention is produced by a step of plasma-treating a porous polymer membrane and a step of graft-polymerizing a hydrophilic vinyl monomer on the plasma-treated porous polymer membrane. It As the porous polymer film, various conventionally known polymer films are used, and the type thereof is not particularly limited. Examples of such a porous polymer film include polyolefin resins such as polyethylene, polypropylene, polybutene, and ethylene / propylene copolymers, polyvinylidene fluoride, polyester, polyamide, polysulfone,
Examples of the porous membrane include various resins such as polyether sulfone, polyimide, polyurethane, cellulose acetate, and cellulose nitrate. In the porous polymer membrane, the average pore diameter is 0.5 μm or less, preferably 0.3 to 0.001 μm or less, and the porosity is 20.
~ 90%, preferably 25-80%. The thickness is 200 to 1 μm, preferably 100 to 1 μm. The shape of the porous polymer membrane can be various shapes such as a hollow fiber shape and a tubular body other than the film shape.

The plasma treatment for the porous polymer film is
It can be carried out by a conventionally known method. In this case, as the plasma generating gas, ammonia, methane, ethane, propane, hydrogen, nitrogen, argon or the like can be used. The plasma treatment temperature in this case is 0 to 200 ° C, preferably 10 to 100 ° C,
The pressure is 0.01 to 2 torr, preferably 0.05 to 1 torr, and the processing power is 10 to 200 W, preferably about 30 to 100 W. Processing time is 0.5-10
Minutes, preferably about 1 to 3 minutes. This plasma treatment causes a reaction between the polymer forming the surface part of the porous polymer film and the plasmaizing gas, and the polymer on the surface part of the porous polymer film has a large number of radical polymerization initiation points. Radical points are formed.

Hydrophilic vinyl monomer vapor is brought into contact with the plasma-treated porous polymer membrane obtained as described above, and the radical vinyl point formed on the surface of the membrane is used as a polymerization initiation point to convert the hydrophilic vinyl monomer. Graft-polymerize. As the hydrophilic vinyl monomer in this case, various ones having a hydroxyl group and a hydrophilic group such as a carboxyl group, an amino group, an amide group, a sulfone group and an ether group can be used. Examples thereof include acrylic acid, methacrylic acid, N, N-dimethylacryl acrylamide, N, N-dimethyl methacrylamide, hydroxyethyl acrylate, methoxy polyethylene glycol acrylate, methoxy polyethylene glycol methacrylate, acrylamide, vinylpyrrolidone,
Examples thereof include vinyl pyridine, styrene sulfonate, allyl alcohol, maleic acid, maleic anhydride, crotonic acid, itaconic acid, maleimide and the like. The proportion of hydrophilic vinyl monomer used is the concentration in the gas phase in the reaction vessel,
It is 10 ⁻⁷ to 10 ⁻² mol / 1, preferably 10 ⁻⁶ to 10 ⁻³ mol / 1. The reaction temperature for graft-polymerizing the hydrophilic vinyl monomer onto the porous polymer is 0 to 200 ° C, preferably 10 to 100 ° C, and the reaction pressure is 0.1 to 1 ° C.
It is 0 torr, preferably 0.5-5 torr. The reaction time is 1 to 180 minutes, preferably 10 to 60 minutes. The thickness of the hydrophilic vinyl monomer polymer layer formed on the surface of the porous polymer film can be adjusted by the reaction time, but is usually 0.01 to 100 μm, preferably 0.1 to 10 μm. . The degree of polymerization of the hydrophilic vinyl monomer polymer graft-polymerized on the porous polymer membrane is 10 or more, usually 100 to 1,000,000.

By the graft polymerization treatment of the hydrophilic vinyl monomer, a hydrophilic polymer layer is formed on the surface portion of the porous polymer membrane plasma-treated by the polymerization of the hydrophilic vinyl monomer by the graft polymerization of the vinyl monomer. It This polymer layer is mainly formed on the surface of the porous polymer membrane. That is, the polymer layer of the hydrophilic vinyl monomer is formed on the surface of the polymer film and on the inner surfaces of the pores in the film slightly inside the polymer film. The porous polymer membrane having such a hydrophilic polymer layer on the surface is suitable as a support for impregnating and holding a carbon dioxide carrier liquid. That is, since the hydrophilic polymer layer is formed on the surface of the porous polymer membrane, the carbon dioxide carrier liquid impregnated in the porous membrane is stable in the hydrophilic polymer layer. Held in. Further, the carbon dioxide carrier liquid once impregnated and held in the pores inside the porous membrane is not easily eluted even if the membrane surface is wet with water.

In the present invention, the carbon dioxide carrier solution to be impregnated and retained in the porous polymer membrane is a conventionally known one, for example, polyethylene glycol, an organic amine solution, an alkali metal carbonate solution, an alkali metal hydrogen carbonate solution. Etc. In the case of an organic amine solution, any organic amine can be used as long as it exhibits solvent solubility. Examples of such organic amines include ethylamine, propylamine,
Butylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tolpropylamine, dolibutylamine, monoethanolamine, diethanolamine, triethanolamine, ethylmonoethanolamine, n-
Butyl monoethanol amine, dimethyl ethanol amine, ethyl diethanol amine, n-butyl ethanol amine, di-n-butyl ethanol amine, triisopropanol amine, ethylene diamine, propylene diamine, etc. are mentioned. Particularly, the use of alkanolamine is preferable. As a solvent for dissolving the organic amine,
Examples thereof include water, an organic solvent, and a mixed solution of water and an organic solvent. In this case, any organic solvent can be used as long as it can dissolve an organic amine, but those having a high boiling point (for example, ethylene glycol, polyethylene glycol, imidazole, N-alkylimidazole, dimethyl, etc. (Sulfoxide, dimethylformamide, etc.) are preferable, and those having a boiling point of usually 100 ° C. or higher, preferably 150 ° C. or higher are advantageous. The organic amine concentration in the solution is 0.1 to 6
It is mol / l, preferably 0.5 to 5 mol / l. In the alkali metal carbonate solution, examples of the alkali metal carbonate include sodium carbonate, potassium carbonate and lithium carbonate. As the solvent for dissolving the alkali metal carbonate, water, an organic solvent, or a mixed liquid of water and an organic solvent is usually used. The concentration of the alkali metal carbonate in the solution is 0.1 to 4 mol / l, preferably 0.5 to
3 mol / l. In the alkali metal bicarbonate solution, examples of the alkali metal hydrogen carbonate include sodium hydrogen carbonate, potassium hydrogen carbonate, and lithium hydrogen carbonate. As the solvent for dissolving the alkali metal hydrogen carbonate, water, an organic solvent, or a mixed liquid of water and an organic solvent is usually used. The concentration of the alkali metal hydrogen carbonate in the solution is 0.1 to 6 mol / l, preferably 0.5 to
It is 5 mol / l.

In the present invention, in order to obtain a carbon dioxide separation membrane by impregnating and holding a carbon dioxide carrier liquid in a porous polymer membrane having a hydrophilic polymer layer as a support on the surface, The membrane may be dipped in a carbon dioxide carrier solution and the solution may be impregnated into the pores of the porous polymer membrane.

In order to separate and collect carbon dioxide from a mixed gas containing it using the separation membrane of the present invention, the separation membrane is attached to a permeation cell, and the mixed gas containing carbon dioxide is attached to one side of the membrane. Contact is made and the pressure on the mixed gas side is kept higher than the pressure on the opposite side. The side opposite to the mixed gas side is kept under reduced pressure, preferably vacuum. When the mixed gas is brought into contact with one side of the separation membrane in this way,
Each of the components in the mixed gas diffuses and permeates through the separation membrane due to the partial pressure difference between both sides of the membrane, but the components other than carbon dioxide are not subjected to the carrier action, whereas carbon dioxide is subjected to the carrier action. . Therefore, the membrane permeation amount of carbon dioxide is the permeation amount due to the partial pressure difference between the both sides of the membrane plus the permeation amount due to the carrier transportation. That is, the carrier liquid in the separation membrane selectively adsorbs carbon dioxide, diffuses in the membrane, and releases the carbon dioxide on the side (permeation side) opposite to the side in contact with the mixed gas, which is repeated. As a result, only the amount of permeation of carbon dioxide can be increased. The carbon dioxide permeation amount due to the carrier action is significantly larger than the permeation amount of the gas component due to only the partial pressure difference without depending on the carrier action. Therefore, in the separation membrane of the present invention, carbon dioxide permeation characteristics,
That is, the permeation rate of carbon dioxide and the separation coefficient are dramatically increased.

[0015]

EXAMPLES Next, the present invention will be described in more detail by way of examples. The gas permeation performance of the membrane in the following experiments was evaluated as follows. (Measurement of gas permeation performance) The measurement of gas permeation performance was performed by stacking the membrane and a silicone rubber having a thickness of 70 μm on a stainless steel membrane holder so that the silicone rubber is on the lower surface, and applying pressure of 1 kg / cm on the upper surface of the membrane. A mixed gas of CO ₂ and N ₂ humidified with saturated steam of about 25 ° C. at ² G is supplied, and the amount of gas passing through the membrane is analyzed and quantified by a gas chromatograph to obtain a permeation rate and a separation coefficient. I went by. The measurement was performed at 25 ° C.

Reference Example 1 97 mmol of 3,3,4,4-biphenyltetracarboxylic dianhydride, 4,4-diaminodiphenyl ether 6
0 mmol, 3,5-diaminobenzoic acid 30 mmol,
10 mmol of 4,4-diaminodiphenylmethane was placed in a separable flask equipped with a stirrer and a nitrogen gas introducing tube together with 24.7 g of parachlorophenol, and nitrogen gas was caused to flow to stir the reaction solution. 180
Polymerization was carried out at a polymerization temperature of ° C for 2 hours to prepare an aromatic polyimide film-forming solution having an aromatic polyimide concentration of 15%. This aromatic polyimide has a rotational viscosity of 7 at 100 ° C.
It was 4 poise. 400 this aromatic polyimide solution
A dope solution for film formation was prepared by filtering with a stainless steel wire mesh. This dope solution for film formation was cast on a glass plate having a smooth surface at 60 ° C, and the thickness was adjusted to 2 with a doctor knife.
It is cast to 00 μm, left for 3 minutes as it is, then immersed in 80 wt% ethanol aqueous solution (0 ° C.) for 5 minutes together with the glass plate, and further immersed in 60 wt% ethanol aqueous solution (25 ° C.) for 1 hour to complete the solidification. A polyimide asymmetric film was obtained. Finally, the asymmetric membrane was removed from the glass plate, and the solvent was thoroughly washed and replaced with ethanol and isooctane, dried at 100 ° C for 1 hour, and then heat-treated at 200 ° C for 1 hour to obtain a dried and heat-treated polyimide asymmetric membrane. Got The CO ₂ permeation rate of this membrane is 1.9 ×
10 ^-2 cm ³ (STP) / cm ² · sec · cmHg,
The separation coefficient from N ₂ was almost 1.

Example 1 Polypropylene porous membrane (manufactured by Daicel Chemical Industries, Ltd.,
Celguard 2500: Pore size 0.25 μm, Porosity 45
%) Is set on the ground side of the electrode of a plasma processing apparatus having a bell jar type reaction vessel, a parallel plate type electrode inside, and a plasma generating power source of 13.56 MHz, and introducing ammonia into the system at 22 cc / min. Meanwhile, glow discharge was performed for 3 minutes at an output of 100W. The pressure at this time was 0.5 Torr. After exhausting ammonia from the reactor after the treatment, acrylic acid vapor was immediately introduced into the system and brought into contact with the plasma-treated porous membrane for 30 minutes to give a polyacrylic acid graft polymer layer (on the membrane surface). Thickness: 5 μm) was formed on the film surface. The above graft-polymerized membrane was immersed in a 50 wt% triethanolamine (TEA) aqueous solution for about one night and then taken out to measure the gas permeability. The results are shown in Table 1.

Example 2 A polyacrylic acid graft polymerized film was obtained in the same manner as in Example 1 except that the aromatic polyimide asymmetric film formed in Reference Example 1 was used. This graft-polymerized membrane was immersed in a 50% by weight triethanolamine (TEA) aqueous solution for about one night as in Example 1, and then taken out to measure the gas permeability. The results are shown in Table 1.

Example 3 A polyvinylidene fluoride porous membrane (manufactured by Japan Millipore Limited, Durapore VVLP: pore size 0.1 μm, porosity 70%) was used, and contact time with acrylic acid vapor was 15 minutes. A graft polymerized film of polyacrylic acid was obtained in the same manner as in Example 1 except for the above. This graft-polymerized membrane was treated in the same manner as in Example 1 with 50% by weight of triethanolamine (T
EA) After soaking in the aqueous solution for about one night, the gas permeation performance of the taken out gas was measured. The results are shown in Table 1.

Example 4 A cellulose mixed ester porous membrane (MF Millipore VS manufactured by Japan Millipore Limited, pore size 0.025 μm, porosity 70%) was used, and a contact time with acrylic acid vapor was 15 minutes. A graft polymerization film of polyacrylic acid was obtained in the same manner as in Example 1 except that This graft-polymerized membrane was immersed in a 50% by weight triethanolamine (TEA) aqueous solution for about one night as in Example 1, and then taken out and the gas permeation performance was measured. The results are shown in Table 1.

Comparative Example 1 As in Example 1, the polypropylene porous membrane shown in Example 1 was immersed in a 50% by weight aqueous solution of triethanolamine (TEA) for about one night and then taken out to measure the gas permeation performance. The results are shown in Table 1.

[0022]

[Table 1]

[0023]

EFFECTS OF THE INVENTION According to the present invention, the separation coefficient of carbon dioxide is excellent, and the carbon dioxide carrier liquid is also highly retained, and the carbon dioxide carrier liquid is not easily eluted even when it comes into contact with water. A carbon dioxide separation membrane can be efficiently obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Sumiyama 2-8-11 Nishi-Shimbashi, Minato-ku, Tokyo 8th floor of 7th Toyo Kaijuku Building Research Institute for Global Environment and Industrial Technology CO2 Immobilization Project Room ( 72) Inventor Yusei Hirayama 2-8-11 Nishi-Shimbashi, Minato-ku, Tokyo 8th floor of 7th Toyo Kaiji Building CO2 immobilization project room, Japan Institute for Global Environmental Technology (72) Inventor Hiroshi Yanagishita Ibaraki Prefecture 1-1, Higashi, Tsukuba-shi

Claims (3)

[Claims] 1. After plasma-treating a porous polymer film,
The hydrophilic vinyl monomer vapor is brought into contact with the plasma-treated porous polymer membrane for graft polymerization, and then a carbon dioxide carrier liquid is added to the porous polymer membrane having the hydrophilic polymer surface layer thus obtained. A method for producing a plasma-treated carbon dioxide separation membrane, characterized in that the carbon dioxide separation membrane is impregnated and held. 2. The method of claim 1, wherein the hydrophilic vinyl monomer is acrylic acid. 3. The method according to claim 1, wherein the carbon dioxide carrier liquid is an aqueous alkanolamine solution.