JPS60132605A - Preparation of asymmetric membrane - Google Patents

Abstract

PURPOSE:To prepare an asymmetric membrane imparting excellent permselectivity, by dissolving an 1-monoalkyldimethylsilylpropine polymer in tetrahydrofuran before forming a membrane. CONSTITUTION:It is necessary to use an 1-monoalkyldimethylsilylpropine polymer represented by the formula at least as a part and said polymer has an average MW of 10,000 or more and is pref. contained in an amount of 50wt% or more. This polymer is dissolved in a solvent containing 50wt% or more of tetrahydrofuran in a concn. of 0.1-30wt% to prepare a membrane forming solution. In this case, a membrane preparing conditioner may be adequately added. Said solution is cast on a support so as to adjust a thickness to 10-1,000mum and, after the solvent is partially evaporated, the formed membrane is gelled through the contact with a coagulation medium and, thereafter, subjected to heat treatment, if necessary.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing an asymmetric membrane.

More specifically, the present invention relates to a method for producing an asymmetric membrane having good permeability and selectivity.

In recent years, single-membrane separation technology has attracted attention as an energy-saving technology. For example, in addition to solution-based separation membranes such as RO membranes (reverse osmosis membranes) used for seawater desalination, 2 UF membranes (ultrafiltration membranes) useful for food processing, and oxygen enrichment membranes that enrich the oxygen in the air. Gas separation membranes such as membranes, and pervaporation membranes that are said to be useful for separating water-ethanol mixtures produced from biomass, which is being researched as an alternative fuel.
゛It covers a wide range of fields.

The present patent application ILL found that monoalkylsilylpropyne polymers are materials for highly permeable gas separation membranes and pervaporation membranes (Patent Application No. 58-2
No. 9786 and 58-286'884 April specifications)
When producing an asymmetric membrane from this polymer, the polymer must be dissolved in an organic solvent to create a dope, but the organic solvent for the polymer may be aromatic hydrocarbons, aliphatic hydrocarbons, or halogenated hydrocarbons. has been reported by Takushita et al.
-1178 pages). However, 1. When an asymmetric membrane is created using these solvents.

When used as a selectively permeable membrane even when pinholes are generated and there are no pinholes.

The disadvantage is that good selectivity cannot be obtained.

The present inventors have conducted intensive studies to overcome these drawbacks and obtain an asymmetric membrane exhibiting good permselectivity. As a result, we have developed a solvent that has not been previously reported for 1-monoalkyldimethylsilylpropyne polymers. The inventors have discovered that tetrahydrofuran is an excellent co-solvent for producing this asymmetric membrane, leading to the present invention. That is, the present invention introduces a dope consisting of a solution of a single polymer in an organic solvent into a coagulation bath,
When coagulating to produce an asymmetric membrane of a polymer, l-monoalkyldimethylsilyl having a repeating unit represented by the general formula (wherein R is a C8-4 alkyl group) as at least a part of the polymer. This is a method for producing an asymmetric membrane characterized by using a propyne polymer and using a solvent mainly consisting of tetrahydrofurans as an organic solvent.

In the general formula (υ), the C1-4 alkyl group of R1 is a straight-chain alkyl group such as methyl, ethyl, propyl,
Examples thereof include a butyl group and a branched alkyl group such as an isobutyl group and a tertiary-butyl group.

Examples of l-monoalkyldimethylsilylpropyne used to obtain a polymer having a repeating unit represented by the general formula (υ) include 1-trimethylsilylpropyne and 1-monoethyldimethylsilylpropyne.

1-Mono-1-propyldimethylsilylpropyne.

Examples include 1-mono-n-butyldimethylsilylpropyne. Among these, preferred is 1-trimethylsilylpropyne.

l-Trimethylsilylpropyne is a commercially available monomer (a product of Petrarch in the United States, a product of Chisso's SI' Development Department T87).
28) can be used.

This polymer is made of niobium (Nb), which is a group V transition metal.
, based on tantalum (Ta) (catalysts such as NbCg
s, TaCe5, NbBr5, TaBr5
) as well as solvents (aromatic hydrocarbons such as benzene, toluene, xylene, and alicyclic hydrocarbons such as cyclohexene.

1. It can be obtained by polymerizing in the presence of a chlorinated solvent such as 2-dichloroethane, carbon tetrachloride, etc., usually at 80° C. to 100° C. for 12 to 36 hours. Also.

It can also be obtained by the method described in Japanese Patent Application No. 58-84626.

The obtained polymer is a white fibrous or powdery polymer. Its number average molecular weight is usually 10,000 by light scattering method.
or more, preferably 100,000 or more.

The l-monoalkyldimethylsilylpropyne polymer can be used in combination with other polymers if necessary. Other polymers include 1-alkyne polymers (polymers such as tertiary-butylacetylene, neopentylacetylene, tertiary-butylacetylene, etc., preferably tertiary-butylacetylene polymers), vinylorganosilane polymers (vinyl trimethyl Silane, vinyltriethylsilane.

Polymers such as vinyltripropylsilane (preferably vinyltrimethyl, silane polymers), polyorganosiloxanes (dimethylsiloxane, polymethylphenylsiloxane, polydiphenylsiloxane, etc.), cellulose polymers (ethylcellulose, hydroxyethylcellulose, triacetylcellulose) cellulose, preferably ethylcellulose).

α-olefin polymers (such as polymers of 4-methylpentene-1), alkyl sulfone polymers (copolymers of α-olefin and 502, preferably long-chain alkyl sulfones in which the alkyl group has 10 to 2 carbon atoms) polymers, etc.)
, tertiary amine-containing polymer (vinyl pyridine polymer, N
, N-diethylaminoethyl acrylate polymer, N,
Examples include N-dimethylaminostyrene polymer, preferably vinylpyridine polymer.

When a monoalkyldimethylsilylpropyne polymer and a second component (another polymer) are used together, the content of the monoalkyldimethylsilylpropyne polymer is usually 50% by weight or more based on the weight of the total polymer, and preferably It is 70% by weight or more.

In organic solvents mainly composed of tetrahydrofurans used for dope preparation, tetrahydrofurans include tetrahydrofuran and alkyl-substituted compounds of tetrahydrofuran (2-methyltetrahydrofuran, 2,5
-dimethyltetrahydrofuran, etc.). Preferred among these is tetrahydrofuran.

Along with tetrahydrofurans, other cyclic ethers (pyran, pyran,
Dioxane, etc.) can also be used. E-recorded”
The content of tetrahydrofurans in the organic solvent is usually 50% by weight or more, preferably 70% by weight or more.

Promote phase separation when forming asymmetric membranes.

Films are often formed by adding other substances to adjust the solubility of the polymer.

As such a film forming regulator, a compound having a compatibility of 0.1% or more with l'-fine of the polymer can be used.

Conditioners include aliphatic hydrocarbons (petroleum ether, hexane, etc.) that are solvents for polymers, aromatic hydrocarbons (toluene, xylene, etc.), halogenated hydrocarbons (carbon tetrachloride, chloromethyl, etc.), and others. Additionally, inorganic salts that are soluble in the dope, such as alkali metal inorganic acid (hydrochloric acid, perchloric acid, etc.) salts (lithium chloride, lithium perchlorate, etc.), can also be used. In addition, water, lower alcohol (
(methanol, ethanol, etc.), polyethylene glycol, etc. can also be used.

The concentration (weight) of the polymer in the film-forming dope is usually 0.1 to
It is 30% by weight, preferably 1 to 20% by weight.

If the polymer concentration is less than 0.1% by weight, a strong asymmetric membrane cannot be obtained, and if it exceeds 30% by weight, the viscosity of the dope solution is too high and there is no requirement for casting.

The amount of film-forming regulator or additive in the dope solution varies depending on the solvent and polymer concentration of the film-forming solution, and if the additive acts as a swelling agent or solvent for the polymer, it is generally from 10% to the weight of the polymer. Several tens of times the amount is used. Also, inorganic salts account for 0.1% of the weight of the polymer.
It is about 200%.

The viscosity of the dope solution is generally 5 to 1000 poise, but it varies depending on the degree of polymerization of the polymer and the type of modifier. The membrane can be formed by casting onto a plate or tubular body, or it can be extruded into a hollow fiber from a die having an annular orifice to form a membrane into a plate, tube or hollow fiber. Alternatively, a composite asymmetric membrane may be formed by directly casting and coating a dope solution onto a woven or nonwoven fabric made of organic fibers such as polyester, nylon, or acrylic fibers or inorganic fibers such as glass as a base material.

The thickness of the coating film in the present invention is 10 to 1000 P, preferably 50 to 70 P! It is adjusted so that Even if the coating thickness is the same, the dope concentration and evaporation time will vary.

The thickness of the asymmetric membrane obtained varies depending on the temperature and other factors.

In some cases, the dope is gelled by being brought into contact with a coagulation medium immediately after it is cast, but generally it is gelled after some of the solvent is evaporated to form an extremely thin dense layer on the membrane surface.

The temperature and time for this solvent evaporation vary depending on the type of solvent and the desired membrane performance, but generally the temperature is between -50°C and 100°C.
It is carried out at a temperature in the range of 0 to several tens of minutes. As the gelling liquid (L stands for coagulation bath), water, methanol, ethanol, acetone, an aqueous solution of an inorganic salt, or a six-mer mixture thereof, which is a non-solvent for the polymer and compatible with tetrahydrofuran, is used. Among these, water is preferred.

Membrane gelling operations are typically carried out at temperatures below the boiling point of the gelling medium. For example, when the gelling medium is water, it is usually 0 to
The temperature is 80°C. The time required for this gelation varies depending on the gelation temperature, but is usually several minutes to several hours. After gelation, the membrane is soaked in running water for about a day and night in order to flush out the solvent and additives remaining in the membrane. In some cases, after soaking in an organic medium such as alcohol, wash with running water.

The permeable membrane obtained as described above is an asymmetric membrane, and is composed of a dense skin layer forming the membrane surface and a porous layer forming the lower layer. The prepared asymmetric and symmetric membranes are treated with water, water,
Heat treatment in a medium such as ethylene glycol or salt water can be used to adjust the performance of the membrane. Processing temperature is 50~
The treatment is preferably carried out at 150° C. for a treatment time of several minutes to several hours.

In this way, an asymmetric membrane with the desired performance is an RO membrane,
It can be used as a UF membrane, dialysis membrane, gas separation membrane, and pervaporation membrane.

When the asymmetric membrane obtained as described above is used as a gas separation membrane, it is necessary to use dry membrane binding-C.

Methods for obtaining such a dry film (when gelation is performed in water for ¥4J) include: - Freeze-drying the film, - Replace the solvent with a water-miscible organic bath agent, and if necessary, use a non-polar organic solvent. Methods such as substitution methods, (2) simple air drying or breeze drying, and reduced pressure drying methods are mentioned.

In method (2), the water-miscible organic solvent is preferably an alcohol, glycol, or ketone solvent having 1 to 4 carbon atoms, which easily replaces the water in the wet film and has a low melting point.

Ether etc. can be used as the non-polar organic solvent. Further, in the case of simply air drying, breeze drying, or reduced pressure drying in method (2), it may be carried out at room temperature or under heating.

The present invention is a method for producing an asymmetric membrane having excellent permselectivity from a 1-monoalkyldimethylsilylpropyne polymer.

The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 8 1-trimethylsilylpropyne polymer (hereinafter referred to as PMS P
) (The intrinsic viscosity of PMSP is 1 ruene.

69 at 30 DEG C.), PMSI) Li2 and other polymers were mixed and dissolved at a predetermined concentration in a solvent mainly consisting of -C tetrahydrofuran solution to prepare a dope solution.

The dope was cast onto a glass plate using a 600μ applicator, and a part of the solvent was evaporated at room temperature.
After that, adjust the water temperature to the specified temperature and put it into a gelling bath.
C gelled. Furthermore, in order to completely remove the solvent remaining in the membrane, the membrane was left immersed in running water all day and night. The asymmetric membrane thus obtained is flexible and has a milky white appearance.

Table 1 shows the conditions and results (ILJ thickness).

Table 1 1) Polyvinyltrimethylsilane 2) Tertiary-butylacetylene 11Σ Combination Example 9 The asymmetric membranes prepared in Examples 2 and 5 were immersed in methanol and then air-dried to prepare dry membranes. The gas permeability (oxygen, nitrogen) of the membrane was evaluated as shown in Table 2.

Example 10 Pervaporation experiment A pervaporation separation experiment was conducted using the membrane of Example 2. An ethanol 10% (by weight) water bath liquid was used as the pervaporation separation target (water-organic liquid mixture). Using. The device used was a flat membrane ultrafiltration device (with a magnetic cooler inside the cell) made by Toyo Kagaku Sangyo (Sakae) with an effective membrane diameter of 45 mm and a vacuum line connected to it. The permeation experiment was carried out at 25°C. The degree of vacuum was 1, OTo r r,
The permeate was collected in a trap cooled with liquid nitrogen.

Collect the permeate for a certain period of time and calculate the flow rate (kg/m2・h). On the other hand, the organic matter concentration of the permeate was determined by gas chromatography.

These experimental results are shown below.

Permeate flow N123kgZ port]2・l] Permeate ethanol 64%

Claims (1)

[Claims] 1. In producing an asymmetric polymer membrane by introducing a dope consisting of a solution of a polymer in an organic solvent into a coagulation bath and coagulating it,
A 1-monoalkyldimethylsilylpropyne polymer having a repeating unit represented by the general formula (wherein R is an alkyl group of 01 to 4) is used as at least a part of the polymer, and tetrahydrofuran is used as an organic solvent. A method for producing an asymmetric membrane characterized by using a similar main solvent. 2. The manufacturing method according to claim 1, wherein the concentration of the polymer in the dope is 1 to 20%.