JPS6230522A - Method for preparing composite membrane for separating gas - Google Patents

Abstract

PURPOSE:To make it possible to continuously prepare a membrane in a laterally widened state and to thinly and uniformly form the membrane, by dissolving the membrane material of a membrane layer in a good solvent and diluting the resulting solution with a solvent having low surface tension to form a uniform solution which is, in turn, applied to a membrane. CONSTITUTION:A polymer having high gas permeability or a material having high gas separability is dissolved in a good solvent. The good solvent must has a characteristic not damaging a membrane to be applied. The obtained solution is diluted with a solvent having low surface tension. As the solvent having low surface tension, one not precipitating a polymer material is selected so as to prepare a uniform solution. The amount of the diluting solvent is set to 50% or more by wt. of the good solvent and the concn of the polymer material is finally set to 0.03wt% or more. This solution is applied to a membrane and dried.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a composite membrane for gas separation.

More specifically, the present invention relates to a method for producing a composite membrane for gas separation that is effective for obtaining oxygen-enriched air from air by membrane separation.

[Conventional technology]

In recent years, gas separation by demethods, particularly the method of obtaining oxygen-enriched air by membrane separation, has attracted attention from the viewpoint that the energy required for separation is small. A membrane that can be practically used for this oxygen enrichment is required to have high oxygen permeability and high oxygen/nitrogen separation performance in terms of separation cost. In order to meet such performance, it is necessary to use a membrane material with high oxygen/nitrogen separation performance as a thin film with few pinholes, and to combine this non-self-supporting thin film with a porous support membrane. . As such a method, Japanese Unexamined Patent Publication No. 5
Conventionally, methods proposed in Japanese Patent Laid-Open No. 4-40868 and Japanese Patent Laid-Open No. 55-41808 have been known.

[Problem that the invention seeks to solve]

However, in these methods, a solution of a highly separable material such as poly(4-methylpentene-1) is cast onto the water surface, and the thin film formed on the water surface is supported on a porous support membrane. The so-called water surface casting method is used to obtain composite membranes, and it has drawbacks such as breakage when supporting a thin film on a porous support membrane, and the inability to obtain a large-area thin film because the solution is cast on the water surface. Therefore, it is not suitable as a membrane manufacturing method on an industrial scale.

On the other hand, the so-called solution coating method, in which a solution of a high-resolution material is applied to a porous support membrane and dried to form a composite membrane of 1q, is an extremely superior method in terms of widening the membrane and continuous production. However, if a composite membrane is created using a coating solution prepared with a good solvent of a conventionally known high-separation material, only a composite membrane with low oxygen permeability and oxygen/nitrogen separation performance can be obtained. There was a drawback.

The present invention provides a method for manufacturing a composite membrane for gas separation that takes advantage of the wide membrane width and continuous production of these solution coating methods and has high oxygen permeability and oxygen/nitrogen separation performance. This is what I am trying to do.

[Means for solving problems]

In order to achieve the above object, the present invention consists of the following configuration.

"Composite IFJ (B) in which a thin film layer of a highly gas permeable polymer is provided on a porous support membrane (A) or on the porous support membrane
When producing a composite membrane for gas separation by forming a thin film layer (C) of a highly gas-separating material on top of the thin film layer (B),
Or, after dissolving at least one membrane material in (C) in advance in a good solvent, the obtained solution is diluted with a low surface tension solvent to make a homogeneous solution, and then the obtained diluted solution is dissolved in a porous support membrane ( A method for producing a composite membrane for gas separation, characterized by coating on the composite membrane (B). "The porous support III (A) in the present invention may be any support with a porous structure capable of supporting a thin film, and includes Japanese paper, nonwoven fabric, synthetic paper, filter paper, cloth, wire mesh; filtration membrane, ultraviolet. Ultrafiltration with a small pore size is recommended in order to suppress the impregnation of the solution of the high gas separation material applied into the pores as much as possible and to prevent the function of the supporting membrane from being impaired. Preferably, membranes are used. Ultra: For the filtration membrane, a film such as a polypropylene porous support membrane (“Celguard” manufactured by Celanese Co., Ltd.) or a polytetrafluoroethylene porous support membrane (“Millipore Filter” manufactured by Millibore Co., Ltd.) is used. There are types in which pores are formed by stretching, and those manufactured by a wet film forming method using water as a coagulation bath, such as polysulfone porous support membranes, ethyl cellulose porous support membranes, polyether or sulfone porous support membranes, etc. However, the latter type is preferable because the pore size is small and the amount of gas permeation is relatively large.

In the present invention, the composite membrane (B) is one in which a thin film layer of a highly gas permeable polymer is formed on the porous support membrane (A) as described above.

Here, the high gas permeability polymer refers to oxygen permeability PO2 (c
c(STP) 4 cm/cd ・Sec * cml
lg > 1 x 10-8 or more, such as polydimethylsiloxane, copolymers of polydimethylsiloxane and other polymers, such as polydimethylsiloxane/polysilphenylene copolymers, polydimethylsiloxane/ polycarbonate copolymer, polydimethylsiloxane/polystyrene copolymer, etc.), polytrimethylsilylpropyne, and the like. By applying a solution of the polymer to the porous support membrane and drying it, a composite membrane (B) provided with a thin film layer can be obtained.

The composite membrane (B) with a thin film layer of a highly gas permeable polymer has the pores of the porous support membrane blocked by the thin film layer, so when a solution of a highly gas permeable material is applied, the pores are Since there is no impregnation of solution into the membrane, it is easy to form a pinhole-free thin film.According to the method of the present invention, the porous support membrane (△)
Although a thin film of a material with high gas separation property can be formed satisfactorily on the top, in order to form a thinner pinhole-free thin film, it is preferable to use a composite film (B) that is not impregnated with a solution.

The high gas separation material (C) of the present invention refers to a polymer having an oxygen and nitrogen separation coefficient of 2.5 or more. Specific examples include the following polymers. For example, vinyl polymers such as poly(4-methylpentene-1), poly(1,2-butadiene), polyvinyltrimethylsilane, and styrene-butadiene copolymers, cellulose derivatives such as ethylcellulose, and polyarylene oxides having organosilyl groups. , polyarylene oxide-organosiloxane copolymer, polyarylene oxide-organosyl alkylene copolymer, and substituted acetylene polymers such as polytertiary-butylacetylene. Among these polymers, poly(4-methylpentene-1), polyvinyltrimethylsilane, and polyarylene oxide having an organosilyl group are preferred because they have a high oxygen permeability PO2 and a high oxygen/nitrogen separation coefficient. Among these, poly(4-methylpentene-1) has excellent thin film forming properties.
is most preferred.

A good solvent for the high gas separation material refers to a solvent that can dissolve the above-mentioned high gas separation material, but since it is applied to a porous support membrane, it is necessary to It is necessary to use a non-solvent of the material. Therefore, the selection of solvent is
It is necessary to consider the combination of high gas separation material and porous support membrane material.

For example, when using a polysulfone porous support membrane as a porous support membrane, poly(4 methylpentene-1), poly(
1,2-butadiene), polyvinyl 1-lymethylsilane, styrene-butadiene copolymer, poly-tert-butylacetylene, etc., cyclohexane or cyclohexene is preferable. Ethanol is preferred for ethylcellulose. Cyclohexane may be used as the polyarylene oxide having an organosilyl group, but this polymer
Trichlorotrifluoroethane is a low surface tension solvent and is preferred because it can be directly dissolved in this solvent.

In the present invention, the low surface tension solvent is a solvent whose surface tension is lower than that of the porous support membrane or the high gas permeability polymer, and may include the following solvents. For example, halogenated lower alkyl compounds such as trichlorotrifluoroethane and trichlorofluoromethane, impentane, dimethyl ether, diethyl ether, perfluorohexane,
Perfluoropentane, etc.

When diluting the solution of the above-mentioned high gas separation material with these low surface tension solvents, the low surface tension solvents have poor solubility and may cause the high gas separation material to precipitate.
It is necessary to select one that does not precipitate. That is, it is important to form a homogeneous solution. For example, trichlorotrifluoroethane has a low surface tension in poly(4-methylpentene-1)/cyclohexane solution, poly(1,2-butadiene)/cyclohexane solution, polyvinyltrimethylsilane/cyclohexane solution, polytertiary-butylacetylene/cyclohexane solution, etc. preferred as a solvent. For styrene-butadiene copolymer/cyclohexane solutions, trichlorofluoromethane or diethyl ether is preferred. Isopentane is the preferred low surface tension solvent for ethylcellulose/ethanol solutions. Since polyarylene oxide having an organosilyl group can be dissolved in trichlorotrifluoroethane, it can be prepared using this solvent alone.

The preparation method of these solutions was
) is exemplified by poly(4-methylpentene-1)
is first dissolved in cyclohexane, cyclohexene, or a mixed solvent of both.

The concentration of poly(4 methylpentene-1) in the solution is 0°0
5 weight% or more and 5.0% by weight or less, more preferably 0.1
It is preferable that the amount is 2.0% by weight or more and 2.0% by weight or less. concentration is 0
．． If it is less than 0.05%, it is not preferable because it is difficult to form a pinhole-free thin film even if a solution diluted with trifluorotrichloroethane is used. On the other hand, if the concentration exceeds 5.0% by weight, poly(4-methylpentene-1) will readily precipitate in the diluted solution when diluted with trifluorotrichloroethane, which is not preferable.

Poly(4 methylpentene-1) dissolved in a given solvent
The solution is then diluted with trifluorotrichloroethane. Poly(4-methylpentene-1) itself does not dissolve in trifluorotrichloroethane, and is also difficult to dissolve in a mixed solvent of trifluorotrichloroethane and cyclohexane or cyclohexene.

Therefore, in the present invention, it is important to previously dissolve poly(4-methylpentene-1) in cyclohexane, cyclohexene, or a mixed solvent of both, and then dilute the resulting solution with trichlorotrifluoroethane.

The amount of trichlorotrifluoroethane added to the primary solvent such as cyclohexane is preferably 50% by weight or more. If the blending amount of trichlorotrifluoroethane is less than 50% by weight and the blending amount of a primary solvent such as cyclohexane is large, it is not preferable because it becomes difficult to form a pinhole-free thin film.

The concentration of poly(4-methylpentene-1) in the coating solution diluted with trichlorotrifluoroethane is 0°03%
It is preferable to do the above. poly(4 methylpentene-1
) is less than 0.03% by weight, which is not preferable because a thin film will not be formed.

In order to apply the solution prepared in this way onto the porous support membrane (△) or the composite membrane (B), a commonly known reverse coater, slit die coater, kiss coater, gravure coater, etc. It is preferable to use a coater because the coating thickness can be controlled and coating unevenness in the width direction is reduced. Among these, slit die coaters and kiss coaters, which are suitable for coating with low viscosity coating liquids, are more preferable in terms of preventing uneven coating.

The wet thickness of coating is preferably as thin as possible as long as there is no uneven coating, but with coaters currently available on the market, it is
is the limit.

〔Example〕

Next, an actual IM aspect of the present invention will be explained based on an example.

Note that the evaluation criteria for characteristics in the present invention are as follows.

(1) Gas permeability and gas separation properties The pressure on the downstream side is 2 atm, and the pressure on the secondary side is 1
ATM, and the permeation rate of the gas that permeated through the composite membrane (V element or nitrogen) was measured using a precision membrane flowmeter SF-101 (manufactured by Standard Technology).

Oxygen permeation rate (displayed as Q10.Unit is Ura!/Tr1
2.hr -atm) is the gas permeation performance, and the separation coefficient (expressed as α) is the ratio of the oxygen permeation rate to the nitrogen permeation rate (expressed as QN2, the unit is 1/Tr12.hr -atm). ) was used as the evaluation standard for gas separation performance.

Example 1 Poly(4methylpen-1>(TPX t4X
OO1 (manufactured by Mitsui Petrochemical Co., Ltd.) was dissolved in cyclohexane to adjust the concentration to 2.0% by weight. The solution is diluted 4 times with trichlorotrifluoroethane (Freon R-113, manufactured by Mitsui Fluorochemical Co., Ltd.) to prepare a 0.5% by weight coating solution.Polysulfone porous support membrane (Ultrafilter, UK) -50, manufactured by Toyo Roshi Co., Ltd.).
Coat with a thickness of approximately 100 μm and dry promptly at a drying temperature of 100°C. Table 1 shows the gas permeation performance and gas separation performance of the obtained composite membrane for gas separation.

Comparative Example 1 Poly(4-methylpentene-1) is dissolved in cyclohexane to prepare a 0.5% by weight coating liquid. The coating liquid was applied to the same polysulfone porous support membrane as in Example 1 in a wet thickness of about 100 μm.
, and dry quickly at a drying temperature of 100°C. Table 1 shows the gas permeability and gas separation performance of the composite membrane obtained.
Shown below.

The separation coefficient of the composite membrane obtained in Example 1 is clearly higher than that of Comparative Example 1, indicating that the composite membrane obtained by the method of the present invention has excellent gas permeation performance.

Example 2 Silphenylene/dimethylsiloxane copolymer (PSO
95, Chisuko Co., Ltd. M, W, = 300,000) was dissolved in cyclohexane to adjust the concentration to 0.5% by weight. The solution was applied to the same polysulfone porous support membrane as in Example 1 to a wet thickness of 100 μm, and dried at a drying temperature of 100° C. to prepare a base material. 2.0 tl of poly(4 methylpentene-1)
If 1% cyclohexane solution is diluted 8 times with trichlorotrifluoroethane to prepare a 0.25% by weight coating solution. The coating liquid was applied to a composite film of silphenylene/dimethylsiloxane copolymer prepared in advance to a wet thickness of 20 mm.
Coat with μ and dry at 100°C. Table 1 shows the gas permeability and gas separation performance of the composite membrane obtained.

Comparative Example 2 Poly(4-methylpentene-1) is dissolved in cyclohexene to prepare a 0.25% by weight coating liquid. The coating solution was applied to a composite film of silphenylene/dimethylsiloxane copolymer prepared under the same conditions as in Example 2 to a wet thickness of 20 μm, and dried at a drying temperature of 100° C. for 10 minutes. Table 1 shows the gas permeability and gas separation performance of the composite membrane thus obtained.

It can be seen that the composite membrane obtained in Example 2 clearly has a higher separation coefficient than Comparative Example 2, and has excellent gas permeability and gas separation performance.

Example 3 Polydimethylsiloxane with silanol groups at both ends (
9.5 parts by weight (number average molecular weight approximately 50,000), 0.4 parts by weight of ethyl orthosilicate, and 0.1 parts by weight of Stanas 2-ethylhexoate were dissolved in cyclohexane to obtain a solid content of 0.
．． Adjust to 5% by weight. The solution was coated on the same polysulfone porous support membrane as in Example 1 to a wet thickness of 50 μm.
Dry at 0°C to obtain a polydimethylsiloxane composite membrane.

A 0.25% by weight coating solution of poly(4-methylpentene-1)/cyclohexane/trifluorotrichloroethane similar to that in Example 2 was applied to the composite film at a wet thickness of 20μ, and dried at a temperature of 100°C to form a composite film. It was created. Table 1 shows the gas permeability and gas separation performance of the composite membrane obtained.

Comparative Example 3 Poly(4 methylpentene-1) was dissolved in carbon tetrachloride and 0
．． A 25% by weight solution was prepared. The coating liquid was applied to a polydimethylsiloxane composite film prepared under the same conditions as in Example 3.
It was coated to a thickness of 20 μm and dried at a drying temperature of 100° C. for 10 minutes to obtain a composite film. Table 1 shows the gas permeability and gas separation performance of this composite membrane.

Example 4 Polyvinyltrimethylsilane (M, W, = 30,000) was dissolved in cyclohexane to prepare a 1.0% by weight solution. The solution was diluted 4 times with trichlorotrifluoroethane to prepare a 0.25% by weight coating solution. The coating solution was applied to a polydimethylsiloxane composite film prepared under the same conditions as in Example 3 to a wet thickness of 20 μm, and dried at a temperature of 100°C.

Table 1 shows the gas permeability and gas separation performance of the composite membrane obtained.

Comparative Example 4 Polyvinyl 1-limethylsilane (M, W, = 30,000) is dissolved in cyclohexane to prepare a 0.25'lff1% solution. The solution was applied to the same polydimethylsiloxane composite membrane as in Example 3 and dried at 100°C to obtain a composite membrane. Table 1 shows the gas permeability and gas separation performance of the obtained composite membrane.
Shown below.

Example 5 Styrene-butadiene copolymer (styrene/butadiene=
(25/75 molar ratio, M, W, = 40,000) is dissolved in cyclohexane to prepare a 0.5 wt ω% solution. The solution is diluted twice with trichlorofluoromethane (Freon-11, manufactured by Mitsui Fluorochemical Co., Ltd.) to prepare a 0.25% by weight coating solution. This coating liquid was applied to the same polydimethylsiloxane composite film as in Example 3 at a wet thickness of 30 μm.
Dry with hot air at 0°C to obtain a composite membrane. Table 1 shows the gas permeability and gas separation performance of the composite membrane obtained.

Comparative Example 5 The same styrene-butadiene copolymer as in Example 5 was dissolved in cyclohexane to prepare a 0.25% coating solution. This coating liquid was applied to the same polydimethylsiloxane composite film as in Example 3 to a wet thickness of 30 μm.

Dry with hot air at 150°C to obtain a composite membrane. Table 1 shows the gas permeability and gas separation performance of the composite membrane obtained.

As is clear from the above, the composite membrane for gas separation of the present invention is
It can be seen that both gas permeability and gas separation properties are excellent.

Table 1 *1 Oxygen permeation rate (m'/112-hr-atm
)*2 Nitrogen permeation rate (m'/m2・hr -atm
)*3 Separation coefficient [Effect of the invention] The method for producing a composite membrane for gas separation of the present invention takes advantage of the wide membrane width and continuous production of the solution coating method to form a thin and uniform membrane. As a result, a composite membrane for gas separation with high oxygen permeability and oxygen/nitrogen separation performance could be obtained. Of course, there were no defects such as pinholes, and the method was industrially efficient and excellent.

Claims (8)

[Claims] (1) On a porous support membrane (A) or on a composite membrane (B) in which a thin layer of a highly gas permeable polymer is provided on the porous support membrane, ) to form a composite membrane for gas separation, at least one membrane material of the thin film layer (B) or (C) is dissolved in a good solvent in advance, and then the resulting solution is dissolved in a material with a low surface tension. A method for producing a composite membrane for gas separation, which comprises diluting with a solvent to obtain a homogeneous solution, and then applying the resulting diluted solution onto a porous support membrane (A) or a composite membrane (B). (2) The good solvent for the membrane material of the thin film layer (B) or (C) is one or more solvents selected from cyclohexane, cyclohexene, ethanol, and trichlorotrifluoroethane ( 1) A method for producing a composite membrane for gas separation as described in section 1). (3) The dilution solvent with low surface tension is trichlorotrifluoroethane, trichlorofluoromethane, isopentane,
The method for producing a composite membrane for gas separation according to claim (1), characterized in that the solvent is one or more types selected from dimethyl ether, diethyl ether, perfluorohexane, perfluoropentane, and halogenated lower alkyl compounds. . (4) The porous support membrane (A) is selected from a polysulfone porous support membrane, an ethylcellulose porous support membrane, a polyether or a sulfone porous support membrane. A method for manufacturing a composite membrane for gas separation. (5) Composite membrane with a thin layer of highly gas permeable polymer (B
) is the oxygen permeability PO_2 (cc (STP) cm/c
Claim (1) characterized in that it is a polymer with a m^2・sec・cmHg) of 1×10^-^8 or more.
A method for producing a composite membrane for gas separation as described in Section 1. (6) Composite membrane with a thin layer of highly gas permeable polymer (B
) is selected from polydimethylsiloxane, polydimethylsiloxane/polysilphenylene copolymer, polydimethylsiloxane/polycarbonate copolymer, polydimethylsiloxane/polystyrene copolymer), and polytrimethylsilylpropyne. A method for producing a composite membrane for gas separation according to claim (5). (7) Gas separation according to claim (1), wherein the thin film layer (C) of the highly gas-separating material is a polymer having a separation coefficient of oxygen and nitrogen of 2.5 or more. Method for manufacturing composite membrane for use. (8) The thin film layer (C) of the highly gas-separating material is made of poly(4-methylpentene-1), polyvinyltrimethylsilane, polyarylene oxide having an organosilyl group, and poly(arylene oxide-organosiloxane) copolymer. A method for producing a composite membrane for gas separation according to claim (8), characterized in that the membrane is selected from the following.