JPS5814908A - Preparation of composite semi-permeable membrane - Google Patents

Abstract

PURPOSE:To make it possible to prepare a composite semi-permeable membrane suitable for membrane separation of an org. solution, by a method wherein a solution containing a specific reactive substrate is applied on a polyimide ultrafiltration membrane and contacted with a polyfunctional crosslinking agent. CONSTITUTION:The surface of a polyimide ultrafiltration membrane, which comprises a repeating unit shown by the general formulaI(wherein R is a divalent org. group) and has exclusion ratios of 50-90% and 20% or less, respectively, against polyethylene glycols with average MW of 20,000 and 60,000 and a pure water permeation rate of 10<-1>-10<-4>g/cm<2>.sec.atm., is coated or impregnated with a reactive substrate solution comprising an aqueous solution or a water/1-4C aliphatic alcohol solution of a compound having at least two functional groups selected from among a primary amino group, a secondary amino group and a hydroxyl group in a molecule. In the next stage, the thus treated membrane is contacted with a polyfunctional crosslinking agent having at least two functional groups such as an acid halide group in a molecule to crosslink and polymerize said substrate to form a dense semi-permeable layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composite semipermeable membrane, and in particular, a composite semipermeable membrane that can be suitably used for membrane separation of organic solutions containing solutes with molecular weights ranging from several hundred to 1000 or less. Relating to a manufacturing method.

In general, membrane separation processing using semipermeable membranes has been attracting attention when selectively removing specific components in liquid mixtures such as solutions, emulsions, and suspensions. This has only been done for aqueous liquid mixtures.

As is well known, cellophane, cellulose acetate,
Semipermeable membranes made from cellulose such as cellulose are generally not resistant to organic solvents, and semipermeable membranes made from synthetic resins such as polyvinyl chloride, polypropylene, and polysulfone are resistant to organic solvents. This is because it dissolves or swells even if it does not dissolve, making it unsuitable for use as a semipermeable membrane.

However, membrane separation treatment is highly necessary not only for aqueous liquid mixtures but also for organic liquid mixtures, typically organic solutions, and there has been a conventional demand for the development of semipermeable membranes for this purpose.

In order to meet these demands, we have already developed semipermeable membranes made of aromatic polyamides and polyimides obtained by polycondensation of 1,2,3,4-butanetetracarbonate vinegar or its derivatives with aromatic diamines. Semipermeable membranes have been proposed, but these semipermeable membranes can separate solutes with molecular weights of several thousand or more.

Since k is limited, it is difficult to apply it to reverse osmosis, which separates low-molecular-weight solutes with molecular weights of about several hundred to 1,000, or to membrane separations in the intermediate range between reverse osmosis and ultrapolar filtration.

On the other hand, for practical membrane separation in the reverse osmosis region, the semipermeable membrane used must have a sufficiently high rejection rate for low-molecular-weight solutes and at the same time a sufficiently high water permeation rate. Ru. Therefore, in the field of water treatment,
In place of so-called asymmetric membranes or anisotropic membranes, in which a dense layer on the surface that has solute removal performance is integrally supported by a porous layer, which is made of cellulose acetate or polyamide, etc., this membrane has recently been developed on a porous substrate. A composite semipermeable membrane has been proposed in which a semipermeable dense ultrathin membrane is formed from a polymer different from the base material. All of these composite semipermeable membranes use a polysulfone ultrap-permeable membrane as a porous base material, so they have WIW1
It is not suitable for body treatment, and membrane separation of solutes with a molecular weight of several hundred to 1,000 as described above is not considered.

The present invention has been made to solve the various problems described above, and can be suitably used for membrane separation of organic liquids containing low molecular weight solutes of several hundred to 1000 molecules. An object of the present invention is to provide a method for manufacturing an I-composite semipermeable membrane.

The first method for producing a sacrificial semipermeable membrane according to the present invention mainly consists of repeating units represented by the general formula (wherein R represents a divalent organic group), and has an average molecular weight of 2000.
0 50-95% for polyethylene glycol
has an exclusion rate of 20% or less for polyethylene glycol with an average molecular weight of 6000,
A polyimide ultrafiltration membrane having a pure water permeation rate of 10-1 to 10-' jF /cj-sec.atmospheric pressure is provided with a functional group selected from 11" of primary amino groups, secondary amino groups, and hydroxyl groups. After applying or impregnating a solution of a reactive substrate having a small number (both of which are two) in one molecule, contacting with a polyfunctional crosslinking agent having at least two functional groups in one molecule that can react with the above functional group, It is characterized by crosslinking and polymerizing a reactive substrate to form a semipermeable dense layer.

The polyimide ultrafiltration membrane used in the present invention is, for example, as described in JP-A No. 55-152507, in which polyimide represented by the above general formula is mixed with a suitable additive such as diethylene glycol and a mixture such as N-methylpyrrolidone. The film-forming solution is applied onto a suitable substrate and contacted with a coagulating solvent such as water, either immediately or after partially evaporating the solvent if necessary. It will be done. The polyimide ultrafiltration membrane obtained in this way is an asymmetric membrane or an anisotropic membrane in which a dense surface layer is integrally supported by a relatively coarse porous structure below; As described below, by further providing a semi-permeable dense layer on top of the above-mentioned dense layer according to the present invention, it is possible to achieve excellent performance even in membrane separation where the liquid to be treated is treated at high pressure such as in a reverse osmosis region. A composite semipermeable membrane having compaction resistance can be obtained.

In addition to the above points, from the viewpoints of film formability, organic solvent resistance, etc.
In the present invention, especially in the general formula, R is % cut.
A polyimide ultrapure membrane having an aromatic ring such as 000 or 000 is preferably used. Furthermore, the polyimide ultrafiltration membrane used in the present invention has a pure water permeation rate (hereinafter referred to as membrane constant).

) is 10-1 to 10-4 f/Cd・sec・atmosphere, and 0 of polyethylene glycol with an average molecular weight of 20,000.
．． It has a rejection rate of 50 to 95% when a 5-stroke aqueous solution is treated under a pressure of 2KfIC-, and has a rejection rate of 20% or less when treated with a 0.5% aqueous solution of polyethylene glycol with an average molecular weight of 16000. . If the membrane constant is too large or the rejection rate for polyethylene glycol with an average molecular weight of 20,000 is too small, use this as a support layer and apply the composite semi-i! of the present invention. ! When a film is formed, the reproducibility of the film performance is poor, the film constant is too small, and polyethylene glycol with an average molecular weight of 6000 is used.
If the rejection rate for 1 is too large, the amount of solvent permeation will be too small when a composite semipermeable membrane is formed using this as a support layer, which is not preferable. In particular, in the present invention, evaluation was made using a 0.5% aqueous solution of polyethylene glycol with a membrane constant of 5 x 10-1 to 10-" f/C-sec/atmospheric pressure and an average molecular !t of 20,000 at a pressure of 2 KII/cj. Particularly preferred are polyimide ultrafiltration membranes that have an exclusion rate of 60 to 90% when tested and an exclusion rate of 10% or less when evaluated with a 0.5% aqueous solution of polyethylene glycol having an average molecular weight ω. In the polyimide, the repeating units represented by the above general formula preferably account for 70% by weight or more of the total repeating units, and up to 30% by weight may contain a polyamic acid structure as exemplified below.

1 0 0 1 However, preferably 90% by weight or more, particularly preferably 90% by weight or more
A polyimide in which 8% by weight or more consists of repeating units represented by the above two general formulas is used.

In the method of the present invention, the composite semipermeable membrane is a solute removal film formed by crosslinking and polymerizing a reactive substrate with a polyfunctional crosslinking agent on a dense layer of the polyimide ultrafiltration membrane as described above. A semi-permeable membrane with performance is formed as a dense layer of ultra-thin film.

Reactive substrates refer to heptads, oligomers, and polymers that have at least two functional groups selected from primary amino groups, secondary amino groups, and hydroxyl groups in one molecule, and are conventionally crosslinked using polyfunctional crosslinking agents. , any known that can be polymerized to form semipermeable ultrathin films.

Specific examples of reactive substrates having an amino group include monomers such as ethylenediamine, piperazine, aminopiperidine, and phenylenediamine, oligomers such as piperazine-trimesic acid chloride oligomer, polyethyleneimine, amine-modified polyepichlorohydrin, and amine-modified (shrimp) Examples include polymers such as chlorohydrin-ethylene oxide copolymer, and one or more kinds thereof may be used. especially,
In the present invention, since the porous support is a nitrogen-containing hydrophilic polyimide ultrafiltration membrane, such polyamino compounds have excellent wettability, and as described later, an aqueous solution of these polyamino compounds is applied to the polyimide ultrafiltration membrane. Can be applied evenly. Moreover, polyvinyl alcohol is suitable as the reactive substrate having a hydroxyl group.

In the composite semipermeable membrane of the present invention, an ultra-thin membrane is formed by crosslinking the above-mentioned reactive substrate with a polyfunctional crosslinking agent on a dense layer of a polyimide ultrafiltration membrane. Such a dense layer of an ultra-thin film is produced by coating or impregnating a polyimide film with a solution of a reactive substrate, and then contacting the polyimide film with a polyfunctional crosslinking agent to cause crosslinking and polymerization.

The solvent for preparing a solution of a reactive substrate (hereinafter referred to as a stock solution) is preferably water, but a combination of water, methanol, ethanol, propatool, butanol, etc. having 1 to 4 carbon atoms is preferable.
A mixed solvent of aliphatic alcohols may also be used. The concentration of the reactive substrate in the stock solution is adjusted to 0.05-15% by weight, preferably 0.1-10% by weight. This stock solution may contain a surfactant to reduce the surface tension when coating or impregnating the polyimide ultrafiltration membrane (also, if hydrochloric acid, etc. is produced as a by-product during crosslinking with a crosslinking agent, , such by-product scavengers such as sodium hydroxide, aqueous ammonia, etc. may be included.

The amount of the stock solution applied to the polyimide ultrafiltration membrane is 0.05 to 25 f/bi, preferably 0.1 to 5 f/bi, in terms of reactive substrate.
If necessary, after coating the undiluted solution on the polyimide film, the coating amount is adjusted to be within the above range by air drying, draining, pressing with a rubber roll, etc.

The polyfunctional crosslinking agent used in the present invention is a functional group that can react with a primary amino group, a secondary amino group, and/or a hydroxyl group, such as an acid halide group, an isocyanate group, a halogen sulfonyl group, an N- Refers to a compound having two or more of one or more of haloformyl groups, haloformate groups, epoxy groups, aldehyde groups, acid anhydride groups, etc. in one molecule, and its molecular weight is usually 100 to 400, preferably 150 to 3.
It is about 00. Preferred specific examples include inphthaloyl chloride, terephthaloyl chloride, trimesic acid trichloride, trimellitic acid trichloride, trimellitic acid chloride acid anhydride, 1,3-benzenedisulfonyl dichloride, dipicolinic acid dichloride, 5-chlorosulfonyl inphthaloyl chloride,゛Piperazine-N, N'
-dicarboxylic acid dichloride, tolylene diisocyanate, m-xylylene diisocyanate), 4,4'-diphenyl ether diincyanate, 4,4'-diphenylmethane diisocyanate, cyclohexane diisocyanate, dimethyl diisocyanate adamantane, and the like.

A method for bringing the polyfunctional crosslinking agent as described above into contact with a coating layer of a stock solution containing a reactive substrate is to dissolve the crosslinking agent in an organic solvent that is immiscible with the solvent forming the stock solution, and then add a solution of the crosslinking agent to the solution. It is preferable that the coating layer is brought into contact with the
As a result, the reactive substrate is crosslinked and polymerized through an interfacial reaction with the polyfunctional crosslinking agent. In the present invention, as the solvent for forming the crosslinking agent solution, organic solvents used in ordinary interfacial polymerization reactions are appropriately used because the polyimide ultrafiltration membrane that is the support has excellent resistance to organic solvents. However,
Preferred specific examples include pentane, hexane, heptane,
Aliphatic and alicyclic hydrocarbons such as octane, cyclopentane, cyclohexane, and petroleum ether; halogenated hydrocarbons such as chloroform, methylene chloride, carbon tetrachloride, and trichlorotrifluoroethane; and aromatic carbons such as benzene, xylene, and toluene. Examples include hydrogen and ketones such as cyclohexanone. In the case of hydrocarbons, the number of carbon atoms is 5 or more
12 is appropriate. The concentration of the crosslinking agent solution is usually 0.05
-10% by weight, preferably 0.1-5% by weight. The contact temperature and time with the undiluted solution coating layer depend on the type and concentration of the crosslinking agent,
Although it varies depending on the concentration of the stock solution and the type of polyfunctional crosslinking agent, it is usually about lθ seconds to lO minutes, preferably about 30 seconds to 5 minutes, at 10 to 60°C, for example, room temperature.

After being coated or impregnated with the stock solution as described above and then brought into contact with the crosslinking agent, the polyimide ultrafiltration membrane is usually subjected to a heat treatment in order to effect further crosslinking. Heating temperature is 50-180″c1 preferably 100~
The temperature is 150°C, and the heating time is 1 to 60 minutes, preferably 5 minutes.
~30 minutes.

Next, the second method for producing a composite semipermeable membrane according to the present invention mainly consists of repeating units represented by the general formula (however, the general formula represents a divalent organic group), and has an average molecular weight of 2000.
0 50-95% for polyethylene glycol
A polyimide having a rejection rate of 20% or less for polyethylene glycol having an average molecular weight of 6000, and a pure water permeation rate of 10-1-10 f/crl-sec/atm'. A solution containing a polymerizable monomer that polymerizes in the presence of a catalyst and the catalyst is applied or impregnated onto the ultrafiltration membrane, and the polymerizable monomer is crosslinked and polymerized to make it semipermeable. It is characterized by forming a dense layer with

That is, in the second method for producing a composite semipermeable membrane according to the present invention, in the first method for producing a composite semipermeable membrane, a reactive substrate is mixed with a polyfunctional crosslinking agent on the dense layer of the polyimide ultrafiltration membrane. Instead of interfacial polymerization, polymerizable monomers are crosslinked and polymerized in the presence of a catalyst to form a semi-permeable ultra-thin dense layer.

Therefore, a description of the polyimide ultrafiltration membrane will be omitted. Examples of polymerizable monomers include polymerizable alcohols such as furfuryl alcohol and tri(hydroxyethyl)in cyanurate, and water-soluble water such as polymerizable methylols such as monomethylol urea, dimethylol urea, hexamethylolmelamine, and methylolphenol. ! Group-containing monomers are preferred, and examples of the catalysts include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and organic acids such as methanesulfonic acid and 1)-)luenesulfonic acid, with sulfuric acid being particularly preferred. However, if necessary, a water bath solution or an organic solution containing other monomers and an alkali catalyst or other catalyst can also be used.

In addition, when using an aqueous solution of the above-mentioned hydroxyl group-containing polymerizable monomer, if the reactivity of the monomer is extremely high, the aqueous solution may be mixed with alcohol or other alcohol such as propatool to increase the stability of the monomer. An organic solvent may be appropriately contained.

In the case of the above-mentioned water-soluble hydroxyl group-containing monomer, the monomer concentration in the solution containing the polymerizable monomer and catalyst (hereinafter referred to as stock solution) is usually 0.05 to 15% by weight, preferably is 0.1~lO weight! %, and the amount of acid catalyst is usually
The amount is 20 to soom* parts, preferably 50 to 200 parts by weight, per 100 parts by weight of the monomer, but is not necessarily limited to this range depending on the monomer and the catalyst. The stock solution may contain a surfactant to reduce its surface tension. The amount of the stock solution applied to the polyimide ultrafiltration membrane is the same as above (0.0 in terms of monomer).
5 to 2597M1', preferably 0.1 to 597*', and if necessary, after applying the stock solution to the polyimide film, air drying,
The coating amount is adjusted to be within the above range by operations such as draining and pressing with a rubber roll. After this, it is preferably heat-treated to complete crosslinking and polymerization of the monomers. The heating temperature is 50 to 200°C, preferably 1
The heating time is 1 to 60 minutes, preferably 5 to 30 minutes.

The thickness of the dense layer formed on the polyimide ultrafiltration membrane according to the present invention is determined by the degree of reactive group τf or polymerizable monomer in the stock solution, the concentration of the crosslinking agent solution, the concentration of the reactive substrate and the crosslinking agent, and the concentration of the crosslinking agent solution. Depending on the contact time etc., it is usually 50 to 5000λ, preferably 200 to 2000X.

If the ultra-thin film is too thin, local defects are likely to occur on the film surface (on the other hand, if it is too thick, the solvent marketability will decrease, which is undesirable).

According to the present invention, since the reactive substrate or polymerizable monomer in the dense layer is highly crosslinked and polymerized as described above, it hardly dissolves or swells in ordinary organic solvents, and supports It exhibits excellent resistance to organic KI agents similar to that of the polyimide ultrafiltration membrane, which is a polyimide ultrafiltration membrane. Therefore, the selective composite permeable membrane according to the method of the present invention is suitable for ultrapolar filtration of organic liquid mixtures, and is suitable for use in organic factories. In addition to wastewater treatment, it can be advantageously used in concentration and purification processes in fields such as food, medicine, fermentation, and brewing.

For example, the permeable membrane obtained by the method of the present invention is suitable for separating organic liquid mixtures containing organic solvents as exemplified below. Namely, aromatic solvents such as benzene, toluene, xylene, and nitrobenzene, ether solvents such as ethyl ether, tetrahydrofuran, and dioxane, ketone solvents such as acetone and methyl ethyl ketone, and monohydric alcohols such as methanol, ethanol, propatool, and butanol. Polyvalent fluors such as mM, ethylene glycol, diethylene glycol, 1,3-butylene glycol:
L-based/a agents, methyl cellosolve, ethyl cellosolve, diethylene glycol monomethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl, polyhydric alcohol ether solvents such as ether, ethyl vinegar, n5-butyl vinegar, ethyl propionate, ethylene glycol Ester-based/iI agents such as mono- and diacetate esters, mono- and diacetate esters of diethylene glycol, dichloromethane, l,2-dichloroethane,
Halogenated hydrocarbon solvents such as tricrene, chloroform, bromoform, and ylorbenzene.

Of course, it will be clear that the selective filter obtained by the method of the present invention can also be suitably used for membrane separation treatment of aqueous liquid mixtures.

Preferred examples of the method of the present invention are listed below, but the present invention is not limited thereto. In addition, in the examples, the rejection rate and the re-overspeed are values defined by the following equations.

A polyimide ultrafiltration membrane was prepared by a conventional method from an N-methylpyrrolidone solution containing polyimide having an imidization rate of 99% or more (intrinsic viscosity [η) at 30°C = 0.76320 parts by weight] and 20 parts by weight of diethylene glycol. was prepared. This ultrap-permeable membrane has a membrane constant of 4 x 1O-8f/crl・sec・
Under the pressure of 2 K9/cj, the rejection rate is 90% for a 0.5% aqueous solution of polyethylene glycol with an average molecular weight of 20,000, and 90% for a 0.5% aqueous solution of polyethylene glycol with an average molecular weight of 6,000. 5% against
Met.

Polyethyleneimine (Evomin P-1000 manufactured by Nippon Shokubai Chemical Co., Ltd.) is placed on the dense layer of the polyimide ultrafiltration membrane.
After uniformly applying a 1% aqueous solution, the ultrapolar membrane was coated with 2.
4-) It was immersed in a 10wt% n-hexane solution of lylene diincyanate at a temperature of 25°C for 1 minute. After pulling this up and volatilizing the n-hexane attached to the membrane surface,
Heat treatment was performed at a temperature of 110° C. for 10 minutes.

The composite permeable membrane prepared in this manner was attached to a pressurized batch type cell, and a 0.0-.
Temperature: 25°C, pressure: 42°C using 5% toluene solution as feed liquid
To? /Cd, the rejection rate was 9.
9%, and the solvent permeation rate was 6017 n''·day.

Examples 2 to 5 In Example 1, the reactive substrates and polyfunctional crosslinking agents shown in the following table were used instead of polyethyleneimine as the reactive substrate and 2.4-) lylene diisocyanate as the polyfunctional crosslinking agent. A composite semipermeable membrane was obtained in exactly the same manner as in Example 1. The membrane performance of these composite semi-aluminum membranes was measured under the same conditions as in Example 1, and is shown in the table below.

Example 6 On the dense layer of the polyimide ultrafiltration obtained in Example 1, double it% furfuryl alcohol, 2if 1% sulfuric acid and 0.
After applying a water-isopropyl alcohol (volume ratio 70:30) solution containing 2% by weight of sodium dodecyl sulfate, it was heated at 150° C. for 101 minutes.

The membrane performance of the obtained composite semipermeable membrane was that under the same conditions as in Example 1, the rejection rate was 99.5% and the solvent permeation rate was 45 e/m''·day.

Comparative example polyimide ultrap instead of hypersmeation membrane constant 1.02X10
An offshore semi-permeable membrane was obtained in exactly the same manner as in Example 1, except that a polysulfone ultrap-permeable membrane of -1/Crl·sec·Ki was used. It dissolved immediately.

Patent applicant: Nitto Electric Industry Co., Ltd. Patent attorney Itsube Makino 41

Claims (1)

Scope of Claims: (1) Consists mainly of repeating units represented by the general formula (wherein R represents a divalent organic group), and has an average molecular weight of 2,000
0 50-95% for polyethylene glyfur
(has an exclusion rate of 20% or less for polyethylene glycol with an average molecular weight of 6000,
10-1 to 10-4 On an ultrafiltration membrane having a pure water permeation rate of fl/cd/sec/atm, 1 functional group selected from 7 primary amino groups, 7 secondary amino groups, and m water groups is added. After applying or impregnating a solution of a reactive substrate having at least two in its molecule, it is brought into contact with a polyfunctional crosslinking agent having at least two Cζ functional groups in one molecule that can react with the above-mentioned functional group, and the reactive substrate is A method for producing a composite semipermeable membrane, which comprises crosslinking and polymerizing to form a semi-fugitive dense layer. (2) The method for producing a composite semipermeable membrane according to claim 1, wherein the solution containing the reactive substrate is an aqueous solution or a water/aliphatic alcohol solution having 1 to 4 carbon atoms. (3) The polyfunctional crosslinking agent is a compound having two or more functional groups selected from acid halide groups, acid hydrate groups, isocyanate groups, halogensulfonyl groups, haloformate groups, and N-haloformate groups. A method for manufacturing a composite semipermeable membrane according to claim 1. (4) A patent claim characterized in that after coating or impregnating a polyimide ultrafiltration membrane with a solution of a reactive substrate, the multifunctional crosslinking agent is brought into contact with a crosslinking agent bath liquid dissolved in an organic solvent that is immiscible with water. Any one of fJS items 1 to 3
A method for producing a composite semipermeable membrane as described in section. (5) The composite semipermeable membrane according to claim 4, wherein the solvent of the crosslinking agent solution is an aliphatic or aromatic hydrocarbon having 5 to 12 carbon atoms and optionally containing a halogen. manufacturing method. (6) Mainly consists of repeating units represented by the general formula (wherein R represents a divalent organic group), and has an average molecular weight of 2000
It has a rejection rate of 50 to 95 arc for polyethylene glycol with an average molecular ffi of 6000 and a rejection rate of less than 20% for polyethylene glycol with an average molecular ffi of 6000 and a A solution containing a polymerizable monomer that polymerizes in the presence of a catalyst and the catalyst is applied or impregnated onto an ultrapolar membrane having a pure water permeation amount of , and the polymerizable monomer is crosslinked. Let it polymerize,
A composite semipermeable membrane characterized by forming a dense layer with semipermeability. The method for producing a composite semipermeable membrane according to claim 6, characterized in that the catalyst is methylolphenol and the catalyst is an acid catalyst. (8) The solution of the polymerizable monomer is an aqueous solution. A method for producing a composite semipermeable membrane according to claim 7.