JPS58180206A - Production of selective permeable membrane - Google Patents

Abstract

PURPOSE:To provide a membrane having excellent resistance to pressure and preventing generation of pinholes in a method for producing a selective gas- permeable membrane by coating a polymer soln. on a porous substrate covered by a thin film of a non-solvent for said polymer on the surface or filled with the non-solvent in the pores on the surface and drying the same. CONSTITUTION:In a method for producing a selective sepn. membrane for a gaseous mixture, more particularly, a composite membrane for enriching oxygen, a soln. prepd. by dissolving a polymer (more preferably a silicon-contg. polymer) in an org. solvent is coated on a porous substrate covered by a thin film of a non-solvent for said polymer or filled with the non-solvent in the pores near the surface and is dried, whereby the selective permeable membrane having excellent resistance to pressure and preventing generation of pinholes is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a selectively permeable membrane.
The present invention relates to a method for producing an oxygen-enriching composite membrane that is effective for selectively separating gaseous mixtures and obtaining oxygen-enriched air from air.

As a method for manufacturing such a composite membrane, the following methods have been proposed in the past.

(a) A dilute solution of a polymeric material for a gas separation membrane is cast onto the water surface, the solvent is evaporated, and the solidified ultrathin polymeric membrane is scooped up with a porous support membrane.

(b) A dilute solution of a polymer material for gas separation membranes is continuously supplied onto the water surface, and the solidified ultra-thin polymer membrane is moved along a roll partially immersed in water on a porous support membrane. Laminated and integrated.

However, in the above-mentioned conventional method, the thin film suspended on the water surface is thin and has poor strength, so the film may break during the removal stage, and when it is laminated on a porous support film, the film may break due to minute irregularities on the surface of the support film. The drawback is that pinholes occur in the thin film. Furthermore, due to the poor adhesion between the porous support membrane and the thin membrane, pinholes may occur in the thin membrane layer when gas separation operations are performed continuously for a long period of time, or the thin membrane layer may form pores in the porous support membrane. Phenomena such as falling inward occur, resulting in adverse effects such as deterioration of gas separation performance and reduction in gas permeation amount.

The purpose of the present invention is to eliminate the drawbacks of such prior art,
A gas separation active layer with a thickness of 1μ or less is uniformly laminated on a porous support membrane, and is pressure resistant.

The present invention aims to provide a method for manufacturing a selectively permeable membrane with excellent pinhole resistance.

The present invention has a primary configuration to achieve the above object.

That is, a solution of a polymer dissolved in an organic solvent is used to form a thin layer of a non-solvent of the polymer on the surface of the polymer, or at least the pores near the surface layer are filled with the non-solvent of the polymer. The present invention is characterized by a method for producing a gas selectively permeable composite membrane, which is coated on a porous support membrane and dried.

The polymer used in the present invention may have a degree of polymerization that is soluble in an organic solvent and exhibits film-forming ability (usually a polymer having a molecular weight of 10 or more is desirable). Examples of polymers include the following. .

Polystyrene, (poly-α-methylstyrene, polyvinyl acetate, polyethylene, polypropylene.

Vinyl polymers such as polybutene, poly-4-methylpentene, poly-1-hexene, poly-1-octene, polymethyl methacrylate, polybutadiene, polyacrylonitrile, polyvinyltrimethylsilane, polyallyltrimethylsilane, polyvinyldimethylphenylsilane, and copolymers synthesized from the monomers that make up these polymers.

polycarbonate, polysulfone, -polyethersulfone', poly(2,6-)methylphenylene oxide)
, cellucose acetate, cellulose nitrate, cellulose diacetate, -4=#0-striacetate, polyethylene terephthalate.

Condensation polymers such as polybutylene terephthalate.

Room temperature cross-linking silicone rubber containing the following structural units.

5i-0- (herein, R and Ff are alkyl groups having 1 to 10 carbon atoms,
phenyl group, substituted alkyl group, or nuclear-substituted phenyl group) poly(silua-1)lene siloxane containing the following structural units)
.

A polysilphenylene-siloxane block copolymer containing the following structural units.

(R and R' each represent an alkyl group having 1 to 10 carbon atoms, a phenyl group, a substituted alkyl group, or a nuclear-substituted phenyl group) Polysilanes R and R containing the following structural units.

(R,', R,, R,, R, is H or has 1 to 1 carbon atoms
10 alkyl groups, phenyl groups, substituted alkyl groups, or nuclear substituted phenyl groups).

Polysylmethylene containing the following structural units R,R.

number).

Polysilphenylene R, R4 containing the following structural unit (R*e R*a”** R4 is 7 with 1 to 1 carbon atoms
/l/kyl group, phenyl group, etc.).

Polysilazane+5t-NH-)- (R, R' are each an alkyl group having 1 to 1 o carbon atoms, a phenyl group, a substituted alkyl group, or a nuclear-substituted enyl group) containing the following structural unit.

Polyalkyleneoxysiloxane containing the following structural units 1 Alkyl group or nuclear substituted phenyl group 9° (R and R' are each an alkyl group having 1 to 1 carbon atoms, a phenyl group, a substituted alkyl group, or a nuclear substituted phenyl group) .

A polysiloxane-polysulfone block copolymer containing the following structural units.

(R and R' are each an alkyl group having 1 to 1 o carbon atoms, a phenyl group, a substituted alkyl group, or a nuclear-substituted formal group) A polysiloxane-polypinyltrimethelsilane block copolymer containing the following structural units.

(R and R/ are each an alkyl group having 1 to 1 carbon atoms, a phenyl group, a substituted alkyl group, or a nuclear-substituted phenyl group) A polymetallosiloxane containing the following structural units]! (M is a polyvalent metal, R and Pi are each an alkyl group having 1 to 10 carbon atoms, a phenyl group, or a substituted alkyl group.

or a nuclear-substituted phenyl group J ~ a polysilmethylene siloxa R' containing the following structural unit (R, R' are each a polysiloxane-polycarbonate block copolymer containing the following alkyl structural unit having 1 to 1 o carbon atoms);

Polysiloxane-polystyrene block copolymer (or polysiloxane-poly-α-methylstyrene block copolymer) containing the following structural units (R and R'\ are each an alkyl group having 1 to 10 carbon atoms,
phenyl group, substituted alkyl group, or nuclear-substituted difunctional, nyl group) Among the above polymers, preferred are polymers containing silicon atoms in repeating structural units.

Among the polymers used in the present invention, particularly preferred are:
Lelphenylene structure single OH in the repeating unit.

and a polymer containing a diorganosiloxane structural unit (there is one.The content of the silphenylene structural unit and the diorganosiloxane structural unit in the repeating unit is 20% by weight or more based on the total weight of one polymer, -f It is desirable that the weight is 10 or more.
R diorganosiloxane structural unit -8i÷
The substituents R and R' may be any alkyl group having 1 to 1 carbon atoms, a phenyl group, a substituted alkyl group, or a nuclear-substituted phenyl group.

Among them, particularly preferable structural units are exemplified below.

(3H, OX (OH,), 01.

J, H, OH, OH, ON OH, OH, OH, 0
NcH 1000 Raco H, HCHCHOF Silphenylene structural unit To structural unit Other than the Fujiorganosiloxane structural unit, the gas permeability of the ultra-thin film layer 1 Mechanical properties (pressure resistance, pinhole resistance, etc.) and porous support membrane Any structural units may be copolymerized or blended as long as the adhesion is not impaired, but those exemplified below are preferred.

C! H,0 CH.

OH, OO OH, I:! H.

OH,0 -G)(,C!)1.0-, -OH,-0H-0-0
H.

Oh.

? H'' OH,,0 Among the polymers used in the present invention, particularly preferred is a silphenylene-siloxane block copolymer.

Oh, C! H, CH.

C! H, CH, C6H.

Mataha polyfluorphenylene siloxane OH, CH.

and the lengths m and n of each sequence in the preferred copolymer are 5≦m≦1.01]0.0≦n≦
2000. ．． 0≦n/m≦50, and particularly preferable values of m and n are as follows.

10≦m≦500・ 0≦n≦5001. 0≦n　/’　m≦20 It is.

If n/m exceeds 50, the strength of the block copolymer film decreases, resulting in poor pressure resistance and pin-pole resistance in an ultra-thin film state, which is not preferable.

Note that l is a natural number.

The organic solvent applied to the present invention may be any solvent that dissolves the above polymer, but specifically, it is desirable to use the following.

Methylene chloride, trichlorethylene, 1,2-dichloroethane, tetrachloroethane, chloroform, trichlorethylene, tetrachlorethylene.

1.2.3-) Halogenated hydrocarbons such as lychloropropane, 1,1,2-monotrichloroethane, and carbon tetrachloride.

Ether compounds of tetrahydrofuran, dioxane, diisoglopylether, and di-n-butyl ether.

Cyclohexane, isopentane, n-hexane.

Hydrocarbon compounds such as n-hebutane, benzene, toluene, and xylene.

Ketone compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone.

Furthermore, in addition to the above solvents, the following solvents having particularly good compatibility with water may be added.

Hydroxyl group-containing compounds such as methyl alcohol, ethyl alcohol, inglobil alcohol, n-propyl alcohol, cyclohexanol, cyclohexenol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether.

Aldehyde compounds such as butyraldehyde and benzaldehyde.

Amine compounds such as n-butylamine, diimpropylamine, di-n-butylamine, cyclohexylamine, aniline, dimethylaniline, etc.

In addition, among the above solvents, especially cyclohexane, toluene,
Chloroform is preferred, and furthermore, when these preferred solvents are used in combination with a solvent that is miscible with water, the desirable effect of promoting ease of spreading on the water surface during thin film formation and making it easier to form a thin film with a uniform thickness is achieved. It will be done.

The concentration of the polymer of the present invention in the solvent is 0.01 to 10
% by weight, more preferably in the range of 0.1 to 2% by weight. When the thickness is lower than this range, pinholes occur, and when it is higher than this range, thickness unevenness tends to occur. It is desirable to use the polymer solution at a temperature within a range of 0° C. or higher and [the boiling point of the solvent −60° C.] or lower.

The porous support membrane in the present invention may be any porous molded product, and preferably the pore size of the micropores on one side of the support is o, ooi to 50μ, preferably 0.00μ.
A supporting membrane having a thickness of 5 to 0.1 μm and an air permeable structure is desirable. Among these, preferred examples are polypropylene, polysulfone, and cellulose acetate.

Examples include microporous membranes made of polyvinyl chloride and polytetrafluoroether.

If the micropore diameter on the surface of the porous support membrane is less than 0001 μm, the rate of gas permeation into the composite membrane will be low, which is undesirable.

On the other hand, if the micropore diameter on the surface of 1 exceeds 1μ, the ultra-thin membrane layer for gas separation will fall into the pores on the surface of the support membrane during the gas separation operation, causing pinholes and making it difficult to continue the gas separation operation. When this is done, an undesirable phenomenon occurs in which the amount of gas permeation deteriorates over time.

Furthermore, the micropore diameter on the surface of the porous support is preferably smaller than the thickness d of the ultra-thin membrane laminated thereon, and more preferably exceeds a/2, when the membrane is formed during gas separation. The membrane is easily deformed due to the pressure difference that acts through the membrane, and when gas separation operations are continued for a long period of time, the gas permeation rate often decreases over time and pinholes occur, so this is not recommended. do not have.

The non-solvent used in the present invention may be any solvent as long as it does not dissolve the polymer of the present invention. Among them, preferred are those exemplified below, and particularly preferred is water.

(1) Water (2) An aqueous solution of an anionic, cationic or nonionic surfactant (an example of a particularly preferred surfactant is sodium lauryl sulfate).

(3) Alcohol compounds such as methyl alcohol, isopropyl alcohol, and ethyl alcohol.

(4) Single or mixture of polyhydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol, and polypropylene glycol.

(5) Ether compounds such as cellosolve, butyl cellosolve, diethyl ether, diisopropyl ether, and di-n-butyl ether.

(6) Water and alcohol (or polyhydric alcohol).

ether compounds).

The thin layer made of a non-solvent in the present invention preferably covers the support uniformly along the unevenness of the surface of the porous support membrane, and the average thickness of the thin film is preferably thin. It is desirable that the layer be a thin layer with a monomolecular layer or more and 100μ or less, more preferably 01μ or more and 50μ or less.

In order to form a thin layer of the polymer of the present invention in a non-solvent on the surface of a porous support membrane or to fill the pores in the vicinity of the surface layer of the porous support membrane, the following method can be employed. That is, the simplest method is to immerse the porous support membrane in a cypress filled with a non-solvent for a certain period of time, then pull it out of the tank and scatter the non-solvent adhering to the surface with an air knife or the like as necessary. As another method, a coating machine illustrated below can also be used. Gravure roll coater, lipa, throttle, coater, car +7°: x-tar,
7 Aunten Courter, kiss. Coater, slit die coater, etc.

In order to apply a solution of the polymer of the present invention dissolved in an organic solvent onto the porous support film, it is preferable to use a conventional coating machine, such as a gravure roll coater, slit die coater, etc. , a kiss coater, a fountain coater, a curtain coater, and a dip coater are preferably used.

The impregnating and coating operations described above are preferably performed at around room temperature, but may be performed at slightly lower or higher temperatures if there are no particular problems.

To dry the solution prepared by dissolving the polymer of the present invention in an organic solvent after applying it, use an ordinary hot air circulation dryer for 50 minutes.
It is preferable to dry at ~200° C. for 10 seconds to 10 minutes, and before drying, it may be air-dried or pre-dried at a temperature slightly lower than the set temperature of the dryer.

The thickness of the ultra-thin film obtained by the wooden film method is determined almost exclusively by the concentration of the applied polymer solution and the amount of the polymer solution supplied per unit area of the support film. It is desirable to set the coating conditions so that the film thickness after drying is usually in the range of 0.05 to 2 μm, more preferably 0.1 to 1 μm.

As described above, the present invention is characterized in that a solution of a specific polymer is preliminarily applied to the surface to form a thin layer of water or a non-solvent for the polymer, or at least in the pores near the surface layer. A gas selectively permeable membrane was manufactured by applying the polymer solution onto a porous support membrane filled with a non-solvent and drying it.

The resulting composite membrane for gas separation had the following high properties.

fil Even if the gas separation operation is performed continuously for a long period of time, the pressure difference acting through the membrane may generate pimples/holes in the ultra-thin membrane layer, deteriorating the gas separation performance, or the ultra-thin membrane layer may form on the support membrane surface. There is no problem such as a decrease in gas permeation rate due to depression in the pores.

(2) During long-term gas separation operations, the ultra-thin film layer will not be ruptured by dust in the air and the gas separation performance will not deteriorate.

Embodiments of the present invention will be described below with reference to Examples.

Example 1 Mi-me pore filter vswpl average pore diameter 250A, 90
III[[lφ] was immersed in methanol for 30 ml and then in water for 10 ml. The surface of the filter that underwent this treatment was coated with a uniform layer of water.

To 100 parts by weight of cyclohexane, 10 parts by weight of silphenylene-siloxane protoxypolymer, l' copolymer (n = 58
0. n/m=5. (η)=24]) in Tolxone was added to uniformly dissolve it, and impentane was added to this solution to adjust the polymer solution to 0.5% (wt/wt).

This polymer solution was cast onto the Millipore filter described above (the membrane was held horizontally, and the block polymer solution was cast), then the membrane was turned vertically to allow unnecessary polymer solution to flow down, and after air drying, the film was heated at 70°C. dried in a hot air circulation dryer. The thickness of the silphenylene/siloxane block copolymer layer in the resulting composite film was 0.064 μm. The gas permeability of this composite membrane was evaluated at 25°0 using a gas permeability measuring device (GTR-10 model Y manufactured by Yanagimoto Seisakusho) using a gas chromatograph detector.

The permeation rate of oxygen gas is 4.69X10 ♂, //
! nloθθC・■Hge separation coefficient (po, /pN,
) was 23.

(Here, PO, and PN are the permeation rates for oxygen and nitrogen alone, respectively).

This composite membrane was attached to a cell with a diameter of 5 cm for gas separation,
Supply air at 1 atm to one side of the membrane.

The other side of the membrane was evacuated to 0.1 atm using a diaphragm vacuum pump. At the outlet of the pump, oxygen-enriched air with an oxygen concentration of 67 g was obtained at a flow rate of 180 g/min.

After continuing this gas separation operation for one month,
The oxygen concentration of the oxygen-enriched air was 36%, the flow rate of the oxygen-enriched air was 181 s+l/min, and it was confirmed that the initial performance was maintained.

Example 2 A dimethylformamide solution (solid content: 20 wt) of polysulfone resin (product of UCiC) was applied from a slit die onto a polyester nonwoven fabric running continuously along the drum surface.
%) was prepared by extrusion lamination followed by coagulation in a water bath. When the pore diameter of the micropores on the surface of this porous membrane was examined using a scanning electron microscope, it was found to be 120A on average. The solvent is removed by washing with water,
The polysulfone porous support membrane, which still contains water in its pores, is continuously rolled out, and the surface of the dense layer is coated with
A cyclohexane solution (1.5 wt%) of the silphenylene-siloxane block copolymer of Example 1 was continuously applied, dried, and then wound up.

The thickness of the silphenylene-siloxane block copolymer layer in the composite membrane thus obtained was 0.12μ.

When the gas permeation performance of this composite membrane was evaluated by the method of Example 1, the oxygen gas permeation rate was 2.11 xlo
an"/an" o se CeanHg, and the separation coefficient (""*/PNs) was 215.

Cut a small piece of sample from this long composite membrane.

An oxygen enrichment experiment was conducted in the same manner as in Example 1.

The initial performance is that oxygen-enriched air with an oxygen concentration of 65
Oxygen-enriched air with an oxygen concentration of 65 g was obtained at a flow rate of 148 g//min even after one month of long-term continuous operation.

Comparative Example 0.31 drops of the same solution of silphenylene-siloxane block copolymer as described in Example 1 were dropped onto a stationary water surface (temperature 20°C) using a micropipette. The polymer solution spread to a size of about 100 anφ. When the dry and solidified ultra-thin membrane was evaluated for gas permeation performance of this composite membrane using the method of Example 1, the oxygen gas permeation rate was 321 x 10 an"/an" @ El e
csanHg, the separation factor was 1.70.

Example 1: This composite membrane was attached to a cell for gas separation test.
Oxygen enrichment performance was evaluated using the same method.

The initial performance is oxygen-enriched air with an oxygen concentration of 28%.
However, after 5 days of continuous operation, the flow rate of oxygen-enriched air was 245 g.
//min, which was close to the initial performance.

The oxygen concentration dropped to 225 degrees.

As is clear from the above, it is possible to continuously produce a composite membrane that exhibits stable gas separation performance over a long period of time by the method of the present invention while maintaining a high level and stable quality.

Patent applicant: Toshi Co., Ltd.

Claims (1)

[Claims] (11) A solution in which a polymer is dissolved in an organic solvent. A thin layer made of a non-solvent of the polymer is formed on the surface, or at least the polymer is present in the pores near the surface layer. 1. A method for producing a selectively permeable membrane, which comprises coating a porous support membrane filled with a combined non-solvent and drying the membrane.