JPH0426889B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a composite membrane, and in detail,
In particular, the present invention relates to a method for manufacturing a composite membrane that can be suitably used for membrane separation treatment of organic solutions containing relatively small solutes with molecular weights of several tens to several thousand, and for concentrating and separating gases. Generally speaking, separation methods using semipermeable membranes have attracted attention in recent years when selectively removing specific components from liquid mixtures such as solutions, emulsions, and suspensions, and have already been put into practical use in some cases. However, conventionally, separation treatments using such semipermeable membranes have been limited to the separation of primarily aqueous liquid mixtures. As is well known, semipermeable membranes made of materials such as cellophane and cellulose acetate have almost no resistance to organic solvents, and semipermeable membranes made of synthetic resins such as polyvinyl chloride, polyacrylonitrile, and polysulfone also have little resistance to organic solvents. This is because they dissolve or swell in many common organic solvents and cannot be used to separate organic liquid mixtures. However, membrane separation can be applied not only to aqueous liquid mixtures.
There is also a strong need for organic liquid mixtures, typically organic solutions, and for this reason, there has been a demand for the development of semipermeable membranes that are resistant to organic solvents. In order to meet these demands, we have already developed semipermeable membranes made of aromatic polyimide resins, 1, 2, 3, 4
- Semipermeable membranes made of polyimide resin obtained by condensing butanetetracarboxylic acid or its derivatives with aromatic diamine have been proposed, and some have been put into practical use, but these polyimide resin semipermeable membranes separate Traditionally, the molecular weight of solutes that can be separated is limited to several thousand or more, and reverse osmosis, which can separate relatively low-molecular-weight solutes with molecular weights of several tens to several thousand, or an intermediate between reverse osmosis and ultrafiltration is used. It cannot be applied to regional membrane separation. In addition, in order to practically perform membrane separation in the reverse osmosis region, the semipermeable membrane used must have a sufficiently high rejection rate for low molecular weight solutes and a sufficiently high permeation flux for solvents. However, in general, the permeation flux of the solvent is mainly regulated by the thickness of the dense layer of the membrane. From this point of view, in place of the so-called anisotropic membrane or asymmetric membrane, which has an anisotropic structure in which a dense surface layer with solute removal performance is integrally supported by a continuous porous layer, Recently, a composite semipermeable membrane has been proposed in which a denser thin film having translucency is newly formed on a porous substrate containing such an anisotropic membrane having ultrafiltration performance. However, such composite semipermeable membranes still cannot be used for separation treatment of organic solutions because they use ultrafiltration membranes made of polysulfone, polyacrylonitrile, etc. as porous base materials. When forming a dense layer on an ultrafiltration membrane, since the ultrafiltration membrane as a base material has poor organic solvent resistance, it is necessary to use a solution of a polymer or its precursor substance to form a dense layer. An aqueous solution must be used, which limits the types of polymers or precursors thereof, and as a result, it is not possible to select the material for forming the dense layer depending on the required membrane performance. . On the other hand, semipermeable membranes, which have an effective exclusion ability for low molecular weight solutes with a molecular weight of several dozen or less, are known to be effective in separating gases and concentrating gases. In the case of membrane separation treatment, it is more advantageous to perform the gas membrane separation treatment at a higher temperature because the higher the temperature, the greater the gas permeation flux. In particular, in recent years, with the development of so-called C1 chemistry, separation membranes for synthesis gas have come to be required.
It is desirable that it can be used at high temperatures of 300°C or higher, and extremely high heat resistance is required. Furthermore, organic solvent resistance is naturally required for the separation of organic mixed gases. The present invention has been made to solve the various problems described above, and is particularly applicable to membrane separation of organic solutions containing low-molecular-weight solutes with a molecular weight of several tens to several thousand, and a wide temperature range including high temperatures. It is an object of the present invention to provide a method for manufacturing a composite membrane that can be suitably used for gas separation in a wide range of areas. The method for producing a composite membrane according to the present invention is to apply this membrane to the surface of a dense layer of a membrane made of polyimide resin and having an anisotropic structure in which a dense layer on the surface is integrally supported by a continuous porous layer. An organic solution of a crosslinkable resin having an average molecular weight equivalent to or larger than the molecular weight cut-off is brought into contact with the organic solution, and then the resin is crosslinked to form an organic solvent-insoluble resin on the dense layer of the anisotropic membrane. A method for producing a composite film forming a thin film made of resin, the method comprising: a crosslinkable resin containing 2
In a method for producing a composite membrane, which is a resin having two or more reactive groups, the reactive groups are crosslinked with each other to form a resin insoluble in organic solvents, in which the crosslinkable resin is hydroxyalkyl acrylate and/or A copolymer resin containing hydroxyalkyl methacrylate as a monomer component, which is crosslinked using a crosslinking agent with a polyfunctional compound having two or more functional groups in the molecule that can react with hydroxyl groups. shall be. That is, according to the present invention, before crosslinking, a crosslinkable resin that is soluble in an organic solvent is dissolved in an organic solvent to form a relatively dilute organic solution, and this is brought into contact with the surface of the dense layer of the polyamide resin. After forming a thin film of a resin solution, this organic solvent is evaporated and the crosslinkable resin is further crosslinked to form a thin film made of a resin insoluble in the organic solvent. It is possible to form a resin thin film using an organic resin solution, which has been difficult to use, and as a result, together with the excellent organic solvent resistance and heat resistance of the base polyimide resin ultrafiltration membrane, This makes it possible to produce a composite membrane that can be suitably used for the separation and concentration of solutions and organic gases, particularly for these operations at high temperatures. The anisotropic film made of polyimide resin used in the present invention preferably consists of repeating units represented by the following general formula. (However, R represents a divalent organic group.) As is already known, this anisotropic film made of polyimide resin has a dense layer on the surface that is integrally formed by a continuous porous layer. An anisotropic membrane having a supported anisotropic structure and having ultrafiltration properties, for example, according to the method described in JP-A-55-152507 and JP-A-56-139104. can do. Furthermore, an anisotropic ultrafiltration membrane made of a polyimide resin having repeating units represented by the following general formula can also be suitably used. (However, each R represents a divalent organic group.) Ultrafiltration membranes having an anisotropic structure made of these polyimide resins are already known, for example,
It can be produced according to the method described in H. Strathmann, Desalination, 26, 85 (1978), US Pat. No. 3,925,211, and the like. In addition, in the present invention, R in the above general formula contains an aromatic group so that the ultrafiltration membrane having an anisotropic structure made of polyimide resin as described above has excellent organic solvent resistance. is desirable. Preferred specific examples of the organic group containing such an aromatic group include, for example,

【Formula】Ya

[Formula] etc., where X is a divalent organic group, and preferred specific examples thereof include, for example,
_-CH2 , -C( _CH3 ) _2- , O-, _-SO2- , -S-,
-CO-, -Si( _CH3 ) _2- , etc. can be mentioned. In the present invention, the polyimide resin semipermeable membrane as described above preferably has a molecular weight cut-off of 2,000 to 100,000. In the case of an anisotropic membrane with a molecular weight cut-off of less than 2000, the permeation flux of the resulting composite membrane is not large enough;
If it is larger than 100,000, the crosslinking resin may penetrate into the membrane during the formation of a dense layer (described later), forming a dense layer with a three-dimensional network structure within the membrane, which may reduce the permeation flux of the membrane. This is because there is. Here, the molecular weight fraction can be determined by measuring the exclusion rate of an anisotropic membrane for a solute with a known molecular weight. Temperature of toluene solution containing at concentration
The molecular weight of polyethylene glycol that is supplied to the membrane surface at 25° C. and a pressure of 2 Kg/cm ² and has an exclusion rate of at least 90% is defined as the molecular weight cutoff of the membrane. Since an anisotropic membrane having such a molecular weight cut-off is generally called an ultrafiltration membrane in liquid separation, it may also be referred to as an ultrafiltration membrane instead of an anisotropic membrane in the present invention. Typically, the method of the present invention involves bringing an organic solution of a crosslinkable resin into contact with the surface of a dense layer of an anisotropic film made of such a polyimide resin, thereby depositing a uniform organic solution of a crosslinkable resin on the surface of the dense layer. The crosslinkable resin is then crosslinked by forming a thin layer of the resin solution, then evaporating the solvent from this thin layer of resin solution and further heating to a high temperature if necessary, thus forming a dense layer surface of the polyimide ultrafiltration membrane. A thin film made of a three-dimensionally cured resin insoluble in an organic solvent is formed thereon. Here, in the present invention, the crosslinkable resin refers to a resin that is soluble in organic solvents before crosslinking, but becomes insoluble in organic solvents after crosslinking, and in the present invention, acrylic esters having hydroxyl groups A copolymer resin containing ester or methacrylic acid ester as a monomer component is used. Such a copolymer resin reacts with the polyfunctional crosslinking agent that reacts with the hydroxyl group to give a three-dimensionally crosslinked resin. For example, the copolymer resin described above forms a crosslinked resin by reacting with polyisocyanate as a crosslinking agent. Examples of the polyisocyanate include tolylene diisocyanate, m-xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate, polytetramethylene glycol diisocyanate, polypropylene glycol diisocyanate, and triisocyanate "coronate".
(Nippon Polyurethane Industry Co., Ltd.) etc. can be used. In the present invention, an organic solution of the crosslinkable resin as described above is brought into contact with the surface of the dense layer of the anisotropic film made of the polyamide resin described above to form a thin layer of the resin solution, and then heated to form an organic solvent. By evaporating and heating to a higher temperature if necessary,
The crosslinkable resin is crosslinked to form a thin resin film that is insoluble in organic solvents, and it is desirable that this thin resin film be as thin as possible. That is, as described above, the liquid or gas permeation flux of the resulting composite membrane is substantially controlled by the thickness of this resin thin film, and the thinner the thin film, the larger the liquid or gas permeation flux. It is from. Therefore, in the present invention, it is desirable that the organic solution of the crosslinkable resin is relatively dilute, and usually the resin concentration is 0.01 to 10% by weight, preferably,
The content is adjusted to 0.1 to 5% by weight. but,
When the resin concentration is less than 0.01% by weight, it is undesirable because film defects such as pinholes are likely to occur in the thin film formed, whereas when it is higher than 10% by weight, the thickness of the thin film formed is too large. However, for practical purposes, the permeation flux is too small, which is not preferable. Furthermore, an important point is that when an organic solution of a crosslinkable resin is brought into contact with the surface of a dense layer of an anisotropic membrane made of polyimide resin, when the resin permeates inside the anisotropic membrane, when crosslinked, A dense resin layer is also formed inside the membrane, and as a result, the thickness of the dense layer becomes substantially large. Therefore, in the present invention, it is necessary that the average molecular weight of the crosslinkable resin is equal to or larger than the molecular weight cutoff of the polyimide resin anisotropic membrane used, and the above-mentioned crosslinkable resin It is selected so as to satisfy the above conditions in consideration of the molecular weight cutoff of the anisotropic resin membrane. Furthermore, in the present invention, since all of the polyimide resins described above have excellent organic solvent resistance, the organic solvent for forming the organic solution of the crosslinkable resin is not particularly limited, and may be used as appropriate depending on the resin. selected, such as resinous and aromatic hydrocarbon solvents,
Alcohol solvents, carboxylic acid solvents, ester solvents, ketone solvents, ether solvents, halogenated hydrocarbon solvents, etc. are used. More specifically, for example, hexane, heptane, benzene,
Toluene, xylene, methanol, ethanol,
propanol, butanol, acetic acid, acrylic acid,
Ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, methylene chloride, chloroform, carbon tetrachloride, 1,1,1-trichloroethane, chlorobenzene or a mixture of two or more thereof may be used, however, It is not limited to these. A relatively dilute solution of the crosslinkable resin dissolved in such an organic solvent is brought into contact with the surface of the dense layer of the polyimide resin anisotropic film.Practically speaking, the resin solution is applied to the surface of the dense layer, or Alternatively, the surface of the dense layer may be immersed in a resin solution. After this, the solvent is removed by heating to an appropriate temperature depending on the solvent, usually about 40 to 80°C, and as described above, the crosslinkable resin is crosslinked by heating to a higher temperature if necessary. ,
It is cross-linked and cured to form a three-dimensional network structure that is insoluble in organic solvents. The temperature required for this crosslinking varies depending on the type of crosslinking resin and crosslinking agent, but is usually 50 to 50℃.
Heat treatment is carried out at a temperature of 250°C, preferably from 100 to 200°C, for 1 to 60 minutes, preferably 3 to 30 minutes. The thin film made of crosslinked resin formed on the surface of the dense layer of the polyimide resin anisotropic film in this way is
Depending on the concentration of the crosslinking resin solution and the thickness of the thin layer of solution formed on the dense layer, it is usually 10 to 5000 Å,
Preferably, the thickness ranges from 100 to 2000 Å.
If this thin film is too thin, defects are likely to occur in the film, whereas if it is too large, the permeation flux of liquid or gas is too small for practical use. According to the method of the present invention, as described above, since a polyimide resin anisotropic membrane is used as a base material of a composite membrane, an organic solution of a crosslinkable resin can be used as a thin film forming material, and The selection range is wide, and thin films formed by crosslinking such crosslinkable resins do not dissolve or swell in organic solvents, and therefore can be suitably used for separation treatments of various organic solvents and organic gases. In addition, the composite membrane obtained by the method of the present invention has an effective ability to exclude low molecular weight solutes with a molecular weight of several tens to several thousand, and has the ability to effectively eliminate organic solutes, which have conventionally been difficult to separate through membranes. Widely used in reverse osmosis in the fields of industrial wastewater treatment, food, pharmaceuticals, fermentation, acid production, and chemical industries, or membrane separation in organic liquid concentration and separation operations in the intermediate area between reverse osmosis and ultrafiltration. Can be used. Furthermore, the composite membrane according to the present invention has excellent heat resistance and organic solvent resistance due to its base polyimide ultrafiltration membrane, so it can be used not only for oxygen enrichment in the air but also for gas separation at high temperatures, such as separation and concentration of synthesis gas. It can also be suitably used. For example, the composite membrane according to the present invention can combine benzene, toluene, xylene, nitrobenzene, etc. with aromatic hydrocarbons, ethers such as ethyl ether, tetrahydrofuran, dioxane, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexyl ketone, methanol, ethanol, etc. , propanol, butanol,
Alcohols such as cyclohexanol, glycols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, butanediol, polyhydric alcohol ethers such as methyl cellosolve, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethyl acetate, butyl acetate, ethyl propionate, Esters such as ethylene glycol mono- and diacetate, dichloromethane, 1,2-
It can be suitably used for separating and concentrating organic solutions and organic gases containing halogenated hydrocarbons such as dichloroethane, trichlene, chloroform, bromoform, and chlorobenzene. Also, methane, ethane, propane, ethylene,
propylene, butene, butadiene, isoprene,
It can also be suitably used to separate and concentrate gas mixtures such as hydrogen, helium, oxygen, nitrogen, neon, argon, carbon monoxide, carbon dioxide, hydrogen sulfide, and ammonia. However, the composite membrane of the present invention is not limited in its use, and it goes without saying that it can be used for separation treatment of aqueous liquid mixtures. The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In addition, in the following examples, the rejection rate and the permeation flux are values defined by the following equations. Rejection rate (%) = [1 - (solute concentration in membrane permeate / solute concentration in stock solution)] × 100 Rejection rate (%) = [1 - (solute concentration in membrane permeate / solute concentration in stock solution) )]×100 Permeation flux (/m ²・hour) = Membrane permeation amount of solvent () / (effective membrane area (m ² )・permeation time (hour)) Example 1 If the repeating unit is in the above general formula () R is Polyimide (N-methyl-2 at 30℃
- Intrinsic viscosity measured as a pyrrolidone solution [η]
A film was formed from an N-methyl-2-pyrrolidone solution containing 22% by weight of 0.91) and 22% by weight of diethylene glycol according to the conventional phase transformation method described in JP-A-55-152507. Then, an ultrafiltration membrane having a thickness of 200 μm and having an anisotropic structure as described above was prepared. The permeation flux of pure toluene through this ultrafiltration membrane was 155/m ² ·hr at a temperature of 20° C. and a pressure of 2 Kg/cm ² . In addition, the rejection rate of polyethylene glycol evaluated using a toluene solution containing 5000 ppm of polyethylene glycol with an average molecular weight of 20000 was 95.7%.
It was hot. Separately, 0.8 parts by weight of an acrylic resin, which is a copolymer consisting of 80% by weight of butyl methacrylate and 20% by weight of hydroxyethyl methacrylate and has an average molecular weight of 45,000, was added to trifunctional isocyanate "Coronate L" (Japan Polyurethane Industries Co., Ltd.). A dilute solution of acrylic resin was prepared by dissolving 0.5 parts by weight of acrylic resin in 100 parts by weight of toluene.The surface of the dense layer of the polyimide ultrafiltration membrane was immersed in this solution for about 30 seconds at room temperature, and then The toluene was completely evaporated by heating to 60°C.The membrane was then heated at a temperature of 120°C for 10 minutes to crosslink the acrylic resin with isocyanate, thus forming a dense layer on the surface of the polyimide ultrafiltration membrane. A composite membrane according to the present invention was obtained by forming a thin resin film insoluble in an organic solvent.This composite membrane was attached to a pressurized batch type cell, and 5000 ppm of polyethylene glycol with an average molecular weight of 400 was added.
Using an acetone solution as a stock solution, the temperature is 25℃ and the pressure is 42℃.
When the membrane performance was evaluated under the condition of Kg/ ^cm2 , the rejection rate was
The solvent permeation flux was 98.8%, and the solvent permeation flux was 4.8/m ² ·hr.

Claims (1)

[Claims] 1. A membrane is made of polyimide resin and has an anisotropic structure in which a dense layer on the surface is integrally supported by a continuous porous layer. An organic solution of a crosslinkable resin having an average molecular weight equal to or larger than the molecular weight is brought into contact with the resin, and then the resin is crosslinked to form a resin insoluble in organic solvents on the dense layer of the anisotropic film. A method for producing a composite material that forms a thin film, in which the crosslinkable resin has two or more reactive groups in the molecule, and these reactive groups are crosslinked with each other to form a resin that is insoluble in organic solvents. In the method for producing a composite membrane, the crosslinkable resin is a copolymer resin containing hydroxyalkyl acrylate and/or hydroxyalkyl methacrylate as a monomer component,
A method for producing a composite membrane, characterized in that the resin is crosslinked using a polyfunctional compound having two or more functional groups in its molecule that can react with hydroxyl groups as a crosslinking agent. 2. The method for producing a composite membrane according to claim 1, wherein the crosslinking agent is a polyisocyanate.