JPH07112122A - Carbon dioxide separation gel membrane and method for producing the same - Google Patents

Abstract

(57) [Abstract] [Purpose] Separation membrane (liquid membrane) containing carbon dioxide carrier
The present invention provides a carbon dioxide-enhanced transport membrane that can be put to practical use and a method for producing the same, which solves the problem of lacking long-term stability, which is the greatest drawback of the above, and the difficulty of maintaining this membrane in a thin film form. A carbon dioxide separation gel membrane, comprising a hydrogel membrane formed by absorbing an aqueous solution containing a carbon dioxide carrier into a vinyl alcohol-acrylate copolymer having a crosslinked structure. An uncrosslinked vinyl alcohol-acrylic acid salt copolymer aqueous solution is applied in a film form on a carbon dioxide permeable support, and then heated and crosslinked to make it insoluble in water. A method for producing a carbon dioxide separation gel membrane, which comprises absorbing and gelling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide separation gel membrane for separating and concentrating carbon dioxide in a mixed gas and a method for producing the same.

[0002]

2. Description of the Related Art As a separation membrane (carbon dioxide facilitated transport membrane) containing a substance having an affinity for carbon dioxide (carbon dioxide carrier), a liquid membrane using an alkali metal carbonate aqueous solution, an alkanolamine or the like is known. There is. Although these membranes have excellent carbon dioxide separation and permeation performance,
Since it is in a liquid state, it is difficult to maintain its characteristics stably for a long period of time due to leakage of the solution, drying, etc. On the other hand, as a gel film for gas separation, as shown in Japanese Patent Publication No. 3-63413, a plasma polymerized layer mainly composed of hydroxyethyl methacrylate formed on a water-repellent asymmetric film is formed with an aqueous silver nitrate solution. Wet films and gelatin gel films containing silver nitrate solution are known. These membranes are used as separation membranes for saturated hydrocarbons and unsaturated hydrocarbons.

[0003]

The object of the present invention is to lack the long-term stability, which is the biggest drawback of the separation membrane (liquid membrane) containing the carbon dioxide carrier, and to keep this membrane in a thin film form. It is intended to solve the problem that is difficult, and to provide a carbon dioxide facilitated transport membrane that can be put to practical use and a method for producing the same.

[0004]

DISCLOSURE OF THE INVENTION As a result of repeated studies to solve the above problems, the present inventors have found that a vinyl alcohol-acrylate copolymer having a crosslinked structure has a sufficient water absorption capacity and at the time of high water absorption. It has been found that the hydrogel membrane having the strength of, and having a copolymer membrane absorbing an aqueous solution containing a carbon dioxide carrier has very excellent properties as a gel membrane for carbon dioxide separation. It came to completion. That is, according to the present invention, a carbon dioxide separation gel membrane comprising a hydrogel membrane formed by absorbing an aqueous solution containing a carbon dioxide carrier into a vinyl alcohol-acrylate copolymer having a crosslinked structure. Provided. Further, according to the present invention, an uncrosslinked vinyl alcohol-acrylic acid salt copolymer aqueous solution is applied in a film form on a carbon dioxide permeable support, then heated and crosslinked to make it water-insoluble. There is provided a method for producing a carbon dioxide separation gel membrane, which comprises causing an insoluble matter to absorb an aqueous solution of a carbon dioxide carrier for gelation.

In the present invention, a vinyl alcohol acrylate copolymer having a crosslinked structure is used as a polymer material which absorbs an aqueous solution containing a carbon dioxide gas carrier and hydrogels. Conventionally, as polymeric materials for forming hydrogels, polysaccharides such as starch and cellulose and modified products thereof, as well as polyacrylic acid, polyethylene oxide and the like are known. However, hydrogels formed from polysaccharides and modified products thereof have drawbacks such as lack of long-term water retention and reduced strength at high water absorption capacity. On the other hand, although an electrolyte polymer such as polyacrylic acid has a high water absorption capacity, it is weak in strength and difficult to be formed into a film. Non-electrolyte polymers such as polyethylene oxide have the drawback of poor water absorption capacity.

The above-mentioned copolymer used in the present invention does not have the above-mentioned defects found in other hydrogel-forming polymers, and has a high water-absorbing ability and a high hydrogel strength even at the time of high water-absorption. It has the feature. In the copolymer used in the present invention, the content of the polyacrylic acid salt is 5 to 95 mol%, preferably 30 to 70 mol%, and the polyacrylic acid salt is an alkali such as sodium salt or potassium salt. In addition to metal salts, ammonium salts and organic ammonium salts can be used.

The crosslinked vinyl alcohol-acrylate copolymer used in the present invention can be obtained by crosslinking an uncrosslinked vinyl alcohol-acrylate copolymer. As the vinyl alcohol acrylate copolymer having an uncrosslinked structure, various types are conventionally known, for example, Sumikagel L-5H (Sumitomo Chemical Co., Ltd.) is commercially available. The vinyl alcohol-acrylic acid salt copolymer having a crosslinked structure in the present invention can be produced by using such a commercially available product and crosslinking it.

The cross-linking of the vinyl alcohol-acrylic acid salt copolymer is carried out on the pre-formed uncrosslinked vinyl alcohol-acrylic acid salt copolymer film. The vinyl alcohol-acrylate copolymer film can be formed by a conventionally known method such as a casting method, a coating method and an extrusion molding method. The cross-linking can be performed by heating the uncross-linked vinyl alcohol-acrylate copolymer film to about 100 to 150 ° C.

The copolymer film used in the present invention is preferably used while being supported by a support. As the support in this case, any support can be used as long as it exhibits CO ₂ permeability. The support used in the present invention is a porous material having a pore size of 10 μm or less, preferably 1.0 μm or less, or a CO ₂ permeation rate of 10 ⁻⁵ cm ³ (STP) / cm.
A non-porous body having a length of ² sec or more can be used. The thickness of the support is not particularly limited, but is 500 to 1 μm, preferably 100 to 1 μm. The material of the support is not particularly limited, and may be plastic, ceramics, metal, glass or the like. The shape of the support is a flat film,
It may have various shapes such as a hollow fiber shape and a cylindrical shape.

In order to preferably produce the carbon dioxide separation gel membrane supported on the support according to the present invention, first, an aqueous solution of vinyl alcohol-acrylate copolymer having an uncrosslinked structure is prepared. The concentration of the copolymer in this aqueous solution is 10% by weight or less, preferably 0.5 to 5% by weight. Next, this aqueous solution is applied onto a CO ₂ permeable support by a conventionally known method, and then at a temperature of 100 to 150 ° C. for 30 minutes.
Heat treatment is carried out for a minute to 2 hours, whereby the copolymer film is cross-linked and made water-insoluble. Then, it is brought into contact with a carbon dioxide carrier aqueous solution by a dipping method or the like, and the crosslinked copolymer membrane is made to absorb the carbon dioxide carrier aqueous solution to form a hydrogel membrane. The thickness of the hydrogel film thus obtained depends on the thickness of the water-insoluble copolymer film, but is generally about 200 to 1 μm.

As the carbon dioxide carrier aqueous solution used in the present invention, various conventionally known ones can be used. In this case, the carbon dioxide carrier is a substance having an affinity for carbon dioxide, and various water-soluble inorganic and organic substances showing basicity are used. The carbon dioxide carrier aqueous solution preferably used in the present invention is an aqueous solution containing an alkali metal carbonate and / or an alkali metal bicarbonate,
Examples thereof include an aqueous solution in which a polydentate ligand that forms a complex with an alkali metal ion is added to an aqueous solution containing an alkali metal carbonate and / or an alkali metal bicarbonate, and an alkanolamine aqueous solution. These aqueous solutions give carbon dioxide separation gel membranes with a high carbon dioxide separation coefficient.

Examples of the alkali metal carbonate used as a carbon dioxide carrier include lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate and cesium carbonate. Examples of the alkali metal bicarbonate include lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, rubidium hydrogen carbonate, and cesium hydrogen carbonate. Examples of the alkanolamine include various water-soluble ones such as monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine and tripropanolamine. The carbon dioxide carrier is not limited to those described above, and may be any one that has an affinity for carbon dioxide and exhibits water solubility,
Various substances such as alkali metal salts of organic acids can be used.

As a polydentate ligand which forms a complex with an alkali metal ion, conventionally known ones, for example, 12-crown-4, 15-crown-5, 18-crown-6,
Benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, dibenzo-12-
Crown-4, dibenzo-15-crown-5, dibenzo-18-crown-6, dicyclohexyl-12-crown-4, dicyclohexyl-15-crown-5,
Cyclic polyethers such as dicyclohexyl-18-crown-6, n-octyl-12-crown-4, n-octyl-15-crown-5, n-octyl-18-crown-6; cryptands [2.1], Cyclic polyether amines such as cryptand [2.2]; Bicyclic polyether amines such as cryptand [2.2.1] and cryptand [2.2.2], as well as porphyrin, phthalocyanine, polyethylene glycol and ethylenediamine. Tetraacetic acid or the like can be used.

The concentration of the alkali metal carbonate and / or the alkali metal bicarbonate in the aqueous solution is 0.1 to 5.0 mol.
/ L is preferably 1.0 to 4.0 mol / l. The concentration of the polydentate ligand that forms a complex with an alkali metal ion in the aqueous solution is 0.001 to 1.0 mol / l, preferably 0.01 to 0.1 mol / l. Further, it is preferable that the concentration of the alkanolamine, which is another example of the substance having an affinity for carbon dioxide, in the aqueous solution is specified to be 10% by weight or more.

The vinyl alcohol-acrylate copolymer constituting the carbon dioxide separation gel membrane of the present invention has a composite structure composed of two phases of a polyvinyl alcohol-rich portion and a polyacrylate-rich portion. Presumed to have. The polyacrylate-rich portion in this copolymer absorbs and swells the carbon dioxide carrier aqueous solution to form a gel phase. The polyvinyl alcohol phase shows a slight water swelling property, but is stretched and oriented when the polyacrylate salt phase swells, and has an action of supporting the polyacrylate gel phase in a highly water absorbing state. Due to such a peculiar structure found in vinyl alcohol-acrylate copolymer, a hydrogel phase in a highly water-absorbed state, which was conventionally formed into a thin film and was difficult to maintain its shape under pressure, The thickness can be kept effective as a separation membrane. In addition, this hydrogel phase is excellent in water retention, salt solution absorbability, and weather resistance, which are necessary for maintaining the performance of the gel film for a long period of time. The carbon dioxide separation gel membrane of the present invention selectively dissolves carbon dioxide in a carbon dioxide carrier aqueous solution (hydrogel) retained in a polyacrylate phase, and exhibits extremely high carbon dioxide selective permeability.

[0014]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 Sumika Gel L-5H (sodium salt) manufactured by Sumitomo Chemical Co., Ltd. (sodium salt solution) was subjected to a hydrophilic treatment to obtain a polyvinylidene fluoride porous membrane (GVWP manufactured by Millipore, pore size 0.2).
2 μm, film thickness 110 μm) spin coating method (150
(0 rpm, 12 sec) or by a dipping method, and then heat-treated at 120 ° C. for 1 hour to form a bridge. This membrane was immersed in an aqueous potassium carbonate solution having a concentration of 2 mol / l for 30 minutes to prepare a carbon dioxide separation gel membrane. A mixed gas of CO ₂ / N ₂ : 10/90 (volume ratio) was supplied as a test gas to the membrane (effective area 9.62 cm ² ) obtained above under a saturated steam pressure at a flow rate of 60 ml / min and a total pressure of 1 atm. The permeate side was depressurized. The permeated gas was analyzed by a gas chromatograph, and the CO ₂ permeation rate and the separation coefficient were calculated.
The results are shown in Table 1.

Example 2 Similar to Example 1, Sumikagel L-5H was used as a polytetrafluoroethylene porous membrane (FP01 manufactured by Sumitomo Electric Industries, Ltd.).
After coating with 0, a pore diameter of 0.1 μm, and a thickness of 55 μm by the casting method, a gel film was formed by heat treatment in the same manner as in Example 1, and its CO ₂ permeation characteristics were measured. The results are shown in Table 1.

Example 3 A gel film prepared by the same method as in Example 1 was used at 2 mol / mol.
A carbon dioxide separation gel membrane was prepared by immersing in an aqueous solution containing 1 liter of potassium carbonate and 0.07 mol / l of cryptand [2.1] for 30 minutes. The transmission characteristics of this membrane were measured by the same method as in Example 1. The results are shown in Table 1. The cryptand [2.1] is represented by the following structural formula.

[Chemical 1]

[0018]

[Table 1]

Example 4 The long-term characteristics of the carbon dioxide separation gel membrane produced in Example 1 were measured under the same conditions as in Example 1. The results are shown in Table 2.
Shown in.

[0020]

[Table 2]

[0021]

As described above, by using the carbon dioxide separation gel membrane of the present invention, carbon dioxide can be selectively separated and concentrated from the mixed gas. In particular, the carbon dioxide separation gel membrane of the present invention is effective for recovering and reusing carbon dioxide in a gas containing almost all water vapor such as flue gas in a saturation range in the field of technology for coping with the problem of global warming. It can be a means.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Makoto Nakabayashi Makoto Nakabayashi 2-8-11 Nishi-Shimbashi, Minato-ku, Tokyo 7th Toyo Kaijuku Building 8F CO2 fixation etc. 72) Inventor Takayuki Mishima 2-8-11 Nishi-Shimbashi, Minato-ku, Tokyo 7th Toyo Kaijuku Building 8th floor, Research Institute for Global Environmental Technology, CO2 fixation etc. Project room (72) Inventor Hiroshi Mano Tokyo Port 2-8-11 Nishi-Shimbashi, 7th Toyo Kaijuku Building, 8th floor, Research Institute for Global Environmental Technology CO2 fixation, etc. (72) Inventor Kenji Haratani 1-1-1, Higashi, Tsukuba-shi, Ibaraki Material Institute of Engineering and Technology

Claims (4)

[Claims] 1. A carbon dioxide separation gel membrane comprising a hydrogel membrane formed by absorbing an aqueous solution containing a carbon dioxide carrier into a vinyl alcohol-acrylate copolymer having a crosslinked structure. 2. The carbon dioxide separating gel membrane according to claim 1, wherein the hydrogel layer is supported on a carbon dioxide permeable support. 3. The carbon dioxide carrier aqueous solution comprises (i)
A polydentate ligand that forms a complex with an alkali metal ion is added to an aqueous solution containing an alkali metal carbonate and / or an alkali metal bicarbonate, and (ii) an aqueous solution containing an alkali metal carbonate and / or an alkali metal bicarbonate. Aqueous solution or (iii)
The carbon dioxide separation gel membrane according to claim 1 or 2, which is an alkanolamine aqueous solution. 4. An uncrosslinked vinyl alcohol-acrylic acid salt copolymer aqueous solution is applied in a film form on a carbon dioxide permeable support, and then heated and crosslinked to make it insoluble in water. A method for producing a carbon dioxide separation gel membrane, which comprises gelling by absorbing an aqueous solution of carbon dioxide carrier.