JPH0153631B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a novel method for producing a composite membrane having excellent performance as a separation membrane for pervaporation. [Technical Background] A pervaporation method is known as an effective separation method for separating liquid components from an organic liquid mixture or a solution of an organic compound (hereinafter collectively referred to as a liquid mixture). In the pervaporation method, a liquid mixture is supplied to one chamber (processed liquid chamber) divided by a separation membrane, and the other chamber (permeated vapor chamber) is evacuated or depressurized to extract a specific liquid from the liquid mixture. This method takes out the components in a vaporized state into a permeation vapor chamber. Separation membranes used in the above pervaporation method include cellulose polymer membranes, polyethylene, polypropylene, polyacrylonitrile, polyvinyl alcohol, polyvinyl acetal, polystyrene, polyester, polyamide, polytetrafluoroethylene, or copolymers of these. Membranes, membranes whose surfaces are further treated with ultraviolet rays, etc., and membranes whose polymer chains have ion exchange groups such as sulfonic acid groups and carboxylic acid groups are known. Although these separation membranes exhibit a certain degree of permeability coefficient (Q) representing the permeation rate of liquid components in the pervaporation method, it is insufficient for practical use, and improvement in permeation performance has been desired. [Prior Art] Conventionally, as a method for improving the permeation performance of a separation membrane used in the pervaporation method, there has been a method in which a thin membrane with separation performance is supported on a porous support and used as a separation membrane. Proposed.
That is, a method of fusing a thin film having separation performance to a support, a method of adhering the thin film to a support,
There is a method in which a liquid monomer forming the thin film is deposited in a layer on a support and then polymerized. [Problems to be Solved by the Invention] However, in the above method, the pores tend to be clogged due to melting of the support due to heat during fusion, and the separation performance of the resulting composite membrane tends to deteriorate. Also,
Even in the above method, the separation performance of the resulting composite membrane tends to deteriorate due to the presence of an adhesive layer.
Methods for these methods are effective as methods for improving separation performance, but sufficient research has not been conducted on their production, and composite membranes obtained by conventional methods have poor adhesion between the thin membrane and the support. However, there is a problem in that the thin film cracks and wrinkles occur due to temperature changes during use or handling. [Means for Solving the Problems] The present inventors have conducted repeated research to improve the adhesion between the thin membrane and the support in the above method without reducing the separation performance of the resulting composite membrane. . As a result, by using a porous sheet with a specific pore size as a support, supporting a liquid monomer with a specific viscosity, and polymerizing it, the thin film is supported with good adhesion to the support. The present invention has been completed based on the discovery that a composite membrane can be obtained that does not wrinkle or crack at all during use or handling and has excellent separation performance in pervaporation methods. In the present invention, a monomer liquid having a viscosity of 100 to 900 centipoise (hereinafter abbreviated as CP) at 20°C is prepared by forming pores with a pore diameter of 0.1 to 10μ at 70°C.
The method for producing a composite membrane is characterized in that the monomer is polymerized after being supported in a layered manner on the surface of a porous sheet having the above ratio and not being swollen by the liquid substance of the monomer. In the present invention, viscosity refers to a value measured using a single cylinder rotational viscometer, and pore diameter and percentage of pores having a specific pore size refer to values measured using a mercury porosimeter. In the present invention, the porous sheet used as a support has 70% of all pores with a pore diameter of 0.1 to 10μ.
It is necessary to have the above, preferably 80% or more. In other words, pores smaller than the above pore diameter range are
When a liquid monomer described below is supported on the sheet surface by means such as coating or casting, it is difficult for the liquid to penetrate into the pores even if the viscosity of the liquid is lowered.
The effect of improving the adhesion of the thin film due to the anchor effect caused by the infiltration of the liquid monomer into the pores is not exhibited. In addition, if the pores are larger than the above-mentioned pore diameter range, even if the viscosity of the monomer liquid is increased, the liquid will penetrate deeply into the pores, substantially increasing the thickness of the formed thin film. This causes a decrease in speed. Therefore, in the present invention, the relationship between the viscosity of the monomer liquid and the viscosity of the monomer liquid described later can be improved by controlling the proportion of pores having a pore diameter within the above range in the porous sheet used as the support within the above range. Accordingly, the thin film can be supported on the surface of the porous sheet with excellent adhesion without substantially increasing the film thickness. Incidentally, in the present invention, the term "sheet" does not have a particularly strict meaning in terms of thickness, and also includes "film." The porous sheet may be any material as long as it has pores with the above-mentioned pore diameter and is not swollen by the liquid monomer, and any known porous sheet that satisfies the above conditions may be used without particular restriction. be done. For example, any porous sheet made of synthetic resin, ceramic, metal, etc. that satisfies the above conditions may be used, regardless of whether it is organic or inorganic. Among these, a porous sheet made of synthetic resin is suitable. Examples of such synthetic resins include polyolefin resins, polysulfone resins, fluorine resins, polystyrene resins, vinyl resins, and cellulose. Further, as for the method of manufacturing the porous sheet, known general manufacturing methods such as a stretching method, a sintering method, a phase separation method, a mixed extraction method, etc. can be applied. Particularly desirable synthetic resin porous sheets are prepared by mixing and melting pellets or powder of olefinic resin such as polyethylene or polypropylene with inorganic powder such as calcium carbonate or silica, or different polymer powder, and then extruding or calendering. After forming the sheet into a sheet, it is stretched uniaxially or biaxially to create voids between different solids,
Examples include porous sheets that meet the above conditions. It should be noted that the above-mentioned porous sheet also includes a porous sheet obtained by stretching the porous sheet and then extracting an inorganic powder or a different type of polymer using an acid, an organic solvent, or the like. In addition, the ceramic porous sheet includes silicon oxide, aluminum oxide, titanium oxide,
In general, inorganic powders such as calcium oxide and magnesium oxide are used singly or as a mixture of several types, and a binder is added to form a sheet for sintering molding, press molding, etc. Furthermore, as the metal porous sheet, those obtained by pressure sintering or thermal decomposition of powders of nickel, iron oxide, stainless steel, etc. or powders of these metal salts are generally used. The above-mentioned porous sheet has a 40 dyne/cm
As mentioned above, those having a surface wettability index of preferably 45 to 55 dynes/cm are preferred. For example, in the case of the porous sheet made of polyolefin resin,
The surface may be treated by means such as corona discharge treatment to adjust the surface wettability index to the above range. Also,
In order to form a homogeneous thin film, it is preferable that the surface of the porous sheet be as smooth as possible. Furthermore, the porous sheet preferably has a porosity that does not impede permeation of liquid components through the thin film supported on its surface as much as possible. Generally more than 50%, preferably 70%
Porous sheets with porosity of ~90% are preferred. The monomer liquid used in the present invention is generally one in which a membrane formed by polymerizing the monomer can separate liquid components in a pervaporation method. In particular, it is preferable to use a liquid monomer having an ion exchange group or a functional group into which an ion exchange group can be introduced, since the effect of improving the permeability coefficient by forming a thin film is remarkable.
For example, styrene, styrene-divinylbenzene, styrene-divinylbenzene to which polyethylene, polypropylene, polyvinyl chloride, polybutadiene, polytetrafluoroethylene, etc. are added as a binder, styrene-divinylbenzene-vinylpyridine, styrene-divinylbenzene- Polyethylene as a binder to vinylpyridine,
Polypropylene, polyvinyl chloride, polybutadiene, polytetrafluoroethylene, etc. added, styrene-chloromethylstyrene-divinylbenzene, styrene-chloromethylstyrene-divinylbenzene as a binder, polyethylene, polypropylene, polyvinyl chloride, polybutadiene,
A monomer liquid containing polytetrafluoroethylene or the like can be used. A suitable plasticizer and a polymerization melting medium may be added to these monomer liquids, and these liquid monomers are coated on a porous sheet to a predetermined thickness so as to form a separation membrane, and then subjected to known methods such as heating polymerization. A separation membrane is formed by polymerization using the method described in the following. Furthermore, if the separation membrane is provided with an exchange group such as a cation exchange group or an anion exchange group through post-treatment, further improvement in separation properties can be expected. For example, styrene-divinylbenzene, polyvinyl chloride powder, plasticizer,
After applying a monomer liquid consisting of a polymerization catalyst onto a porous polypropylene sheet and polymerizing it,
Method of imparting cation exchange groups by sulfonation with concentrated sulfuric acid, applying a monomer liquid consisting of styrene-divinylbenzene, polyvinyl chloride powder, plasticizer, 2-methyl-5-vinyl pyridine, and polymerization medium onto a porous polypropylene sheet. There are methods such as polymerization, quaternization with a methyl iodide solution, and imparting an anion exchange group. Among the liquid monomers mentioned above, those containing a crosslinking agent as one component are extremely suitable for use because the thin film formed on the porous sheet has excellent heat resistance, dimensional stability, and long-term strength. It is. The ratio of such crosslinking agent used is 2% to the total monomer.
~40% by weight, preferably 5-30% by weight is typical. In the present invention, the liquid monomer supported on the surface of the porous sheet has a viscosity of 100 to 900 CP, preferably 200 to 800 CP at 20°C. If the viscosity of the monomer liquid is lower than the above range, the monomer liquid supported on the surface of the porous sheet will penetrate deeply into the pores, resulting in a thin film formed by polymerizing the monomer liquid. Since this results in a substantial increase in thickness, the effect of improving the permeation rate of liquid components by thinning the film is hardly exhibited. In addition, if the viscosity of the monomer liquid is higher than the above range, it will not only be difficult to uniformly support the monomer liquid on the surface of the porous sheet, but also when using a porous sheet with a distribution of pore sizes, It becomes difficult for the liquid monomer to penetrate into the pores having a pore size of 0.1 μm or less, and the anchoring effect due to the polymerization of the monomer is not sufficiently exerted. The method for adjusting the viscosity of the monomer liquid within the above range is not particularly limited. For example, if the monomer liquid is a paste-like material in which a thermoplastic resin is mixed with the liquid monomer, the viscosity can be changed by increasing or decreasing the amount of the thermoplastic resin added or by adjusting the amount of the plasticizer added. can be adjusted. Furthermore, when a liquid monomer is used alone, its viscosity can be adjusted by partially polymerizing the liquid monomer. In the present invention, there are no particular limitations on the method of supporting the liquid monomer in a layered manner on the surface of the porous sheet. Generally, the monomer liquid is rolled,
A method of applying with a brush or the like, a method of placing a porous sheet on a horizontal surface, providing a frame around it as necessary, and casting a liquid monomer, etc. are employed.
The thickness of the layer of the liquid monomer is desirably 5 μm or more, preferably 10 μm or more, because if it is made too thin, the separation performance will deteriorate. On the other hand, if the thickness is increased, the effect of improving the permeation rate decreases due to the thin film, so the upper limit of the thickness is preferably 100μ, preferably 80μ. The liquid monomer is polymerized by a known polymerization method to form a thin film on the porous sheet, thereby obtaining the composite membrane of the present invention. [Effects of the Invention] As understood from the above explanation, the composite membrane obtained by the method of the present invention has excellent adhesion between the porous sheet and the thin film, and prevents the occurrence of wrinkles, cracks, etc. in the thin film. This can be effectively prevented, and because the hollow parts of the pores of the porous sheet are filled with the polymer constituting the thin film at a shallow depth, the effect of improving the separation properties of the membrane achieved by making the film thinner is extremely effective. expensive. For example, when the composite membrane of the present invention is used as a separation membrane in a pervaporation method, it exhibits excellent permeation characteristics. In this case, the composite membrane is generally provided with a thin membrane facing toward the processing liquid chamber. Further, although the operating conditions in this case are not particularly limited, the pressure on the mixed liquid chamber side for supplying the liquid mixture is preferably in the range of 1 to 10 atmospheres, preferably at or near atmospheric pressure. On the other hand, the pressure on the side of the permeation gas chamber is preferably at most atmospheric pressure, preferably a vacuum of 100 mmHg or less. In other words, in the pervaporation method, at the membrane surface on the permeate gas chamber side,
Since it is necessary to evaporate the liquid component that has permeated the membrane and take it out in vapor form, it is preferable to maintain the pressure on the permeate gas chamber side as low as possible than the vapor pressure of the substance that permeates the membrane. The temperature of the liquid mixture in the processing liquid chamber is not particularly limited, but a high temperature is preferable in terms of the permeability coefficient.
However, if the temperature is too high, the film may crack or its durability may deteriorate, so the temperature is generally 10 to 100°C, preferably 30 to 80°C. The pervaporation method using the composite membrane of the present invention is preferably applied to a liquid mixture in which at least one component is a polar solvent and does not have an adverse effect on the membrane. Examples of liquid mixtures consisting of two components include methanol/water, ethanol/
Water, i- or n-propanol/water, methyl ethyl ketone/water, dioxane/water, methanol/
Examples include liquid mixtures such as azeotropic mixtures such as acetone and benzene/n-hexane, and mixtures with close boiling points. [Examples] Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In addition, in the Examples and Comparative Examples, the peel test was conducted by the following method. Peeling test: 1 cm ² of the thin film located on the surface of the test piece
A checkerboard pattern was cut at 2 mm intervals within each corner, a cellophane adhesive tape manufactured by Nichiban Co., Ltd. was applied to the surface of the cut, and when this was removed, the remaining percentage of the thin film was expressed as an area ratio x/100. Example 1 Fine polyvinyl chloride powder was added to 70 parts of 4-vinylpyridine, 20 parts of styrene, and 10 parts of divinylbenzene (purity 50%) in the proportions shown in Table 1, and 2 parts of benzoyl peroxide was further added. A pasty liquid having a viscosity shown in Table 1 was prepared. Next, a porous sheet was prepared in which a polypropylene sheet highly filled with calcium carbonate was made porous by biaxial stretching and the surface was subjected to corona discharge treatment. This sheet has a thickness of 120μ, a porosity of 70%, a pore size distribution of 0.3-3μ, an average pore diameter of 0.8μ, and a surface wetting index.
It is 47dyne/cm. Next, the above-mentioned paste-like liquid material was applied uniformly onto the porous sheet using a roll, wrapped in Tetron film to prevent the monomer from volatilizing, tightened between two iron plates, and placed in an autoclave at 80°C. Polymerization was carried out for 4 hours. After the polymerization is complete, the obtained polymer sheet is mixed with methyl iodide:methanol=
Anion exchange groups were added by immersing the sample in a 1:1 quaternization solution at room temperature for 20 hours. Subsequently, the composite membrane was obtained by immersion treatment in a mixed solution of water/acetone=1/2 (vol%) for 20 hours, followed by washing with water. When the composite membrane was observed using an electron microscope or the like, a polymer separation membrane was formed on the polypropylene porous sheet with the thickness shown in Table 1. The anion exchange capacity of the thin film part of this composite membrane is
The dry weight was 1.7 to 2.2 meq/g. Next, using the composite membrane, water and an i-propanol mixed solution (water/i-propanol = 10/90 weight ratio) were separated by a pervaporation method. The mixed liquid side has a liquid temperature of 55°C and atmospheric pressure, and a vapor permeation side pressure of 5.
The separation performance obtained at mmHg was as shown in Table 1. The results of the peel test are also shown in Table 1.

[Table] *Nos. 1, 5 and 6 show comparative examples.
Example 2 Thickness made porous by stretching as a porous sheet
70μ, porosity 85%, pore size distribution 0.2~8μ, average pore size 2μ
A composite membrane with a polymer separation membrane part thickness of 50 μm was produced in the same manner as in Example 1, using a polyethylene sheet of No. 2 and using the same paste-like liquid material as No. 2 of Example 1. The composite membrane was used to separate a water and i-propanol mixture in the same manner as in Example 1. The separation performance was as follows: permeate amount: 830 g/m ² ·hr, separation coefficient: 94. In addition, the results of the peel test are
It was 100/100. Example 3 A porous sheet was made by mixing diatomaceous earth and a binder, compression molding and sintering. Thickness 3mm, porosity 65
%, a pore size distribution of 0.4 to 10 μm, and an average pore size of 1.5 μm, a composite membrane with a polymer separation membrane portion of 35 μm was fabricated using the same pasty liquid film forming method as No. 2 of Example 1. Using the composite membrane, water and i-propanol mixture were separated in the same manner as in Example 1. The separation performance was as follows: permeate amount: 740 g/m ² ·hr, separation coefficient: 80. In addition, the peel test results were 92/
It was 100. Example 4 100 parts of 2-methyl-5-vinylpyridine, 40 parts of styrene
A paste-like liquid having a viscosity of 600 centipoise was prepared, which consisted of 10 parts of divinylbenzene, 20 parts of dioctyl phthalate, 90 parts of polyvinyl chloride fine powder, and 4 parts of benzoyl peroxide. Using the polypropylene porous sheet used in Example 1 as the porous sheet, a membrane was formed in the same manner as in Example 1 to produce a composite membrane with a thickness of 70 μm in the polymer separation membrane portion. The exchange capacity of the composite membrane was 1.02 meq/g dry weight.
Using this membrane, a mixture of water and methanol (water/methanol = 20/80, weight ratio) was separated using the pervaporation method at a temperature of 50°C, atmospheric pressure, and a pressure of 5 mmHg on the vapor permeation side. Ivy. The separation performance is
The amount of permeate was 1320 g/m ² ·hr, and the separation coefficient was 35. The peel test result was 100/100. Comparative Example A porous sheet obtained by biaxially stretching a polypropylene sheet highly filled with calcium carbonate at a high magnification, and then subjecting it to acid treatment to extract calcium carbonate was used. This porous sheet has a thickness of
120μ, porosity 79%, pore size distribution 3-17μ (45% of pores larger than 10μ), average pore size 12μ, surface wettability index
It was 36dyne/cm. A composite membrane was obtained using the above porous sheet in the same manner as No. 2 of Example 1. Using the obtained composite membrane, water and i-propanol mixed liquid were separated in the same manner as in Example 1. Separation performance is permeated liquid volume 297g/m ²・hour, separation coefficient
It was 111. The peel test result was 80/100.

Claims (1)

[Scope of Claims] 1. A liquid product of a monomer having a viscosity of 100 to 900 centipoise at 20°C, which has pores with a pore diameter of 0.1 to 10 μ at a ratio of 70% or more of the total pores, and a liquid product of the monomer. 1. A method for producing a composite membrane, which comprises supporting the monomer in a layered manner on the surface of a porous sheet that does not swell with water, and then polymerizing the monomer. 2. The method according to claim 1, wherein the porous sheet has a porosity of 50% or more. 3. The method according to claim 1, wherein the porous sheet has a surface wettability index of 40 dynes/cm or more. 4. The method according to claim 1, wherein the layer formed by the liquid monomer has a thickness of 5 to 100 microns. 5. The method according to claim 1, wherein the liquid monomer is a paste mixture of a liquid monomer and a thermoplastic resin. 6. The method according to claim 1, wherein the liquid monomer has an ion exchange group or is a liquid monomer into which an ion exchange group can be introduced.