JPH06114245A - Semipermeable membrane for separating organic matter and its production - Google Patents

Abstract

PURPOSE:To obtain a high separation performance and to significantly increase the transmitting rate compared with a coating-type composite membrane by filling fine pore parts in the surface of the separation active layer of a semipermeable membrane with a high molecular material different from the material of the semipermeable membrane in a manner that no layer of this polymer material is present on the surface of the semipermeable membrane. CONSTITUTION:The semipermeable membrane for the separation of org. matter used for pervaporation or vapor transmitting method has such the structure that fine pore parts in the surface of the separation active layer of the simipermeable membrane is filled with a polymer material different from the material of the semipermeable membrane and that no layer of the polymer material is present on the surface of the membrane. Thereby, such a problem of conventional composite membrane is avoided that a polymer coating layer acts as a resistance for transmission and that the transmission rate is largely decreased. Further, since the fine pore parts of the porous membrane are filled with a polymer material, no defect void appears on the membrane surface which occurs in the conventional pervaporation membrane having an asymmetric structure. When a soln. having high concn. of transmitting material is to be pervaporized, the swelling of a coating layer with the transmitting material like a coating composite membrane can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pervaporative membrane or vapor permeable membrane having a novel structure, and a method for producing the same. More specifically, the present invention relates to a semipermeable membrane for organic substance separation for separating and concentrating an organic substance mixed liquid or an organic substance mixed vapor by a pervaporation method or a vapor permeation method, and a method for producing the same.

[0002]

2. Description of the Related Art Regarding the concentration and separation of an organic matter aqueous solution using a membrane, a reverse osmosis method has been put into practical use for concentrating a portion of a low-concentration organic matter aqueous solution. However, since the reverse osmosis method needs to apply a pressure higher than the osmotic pressure of the separation liquid to the liquid to be separated, it cannot be applied to a high-concentration aqueous solution having a high osmotic pressure, and the concentration of the solution that can be separated cannot be increased. There is a limit.

On the other hand, permeation vaporization method and vapor permeation method are being spotlighted as new separation methods which are not affected by osmotic pressure. The pervaporation method is a method in which a separation liquid is supplied to the primary side of a membrane and the secondary side (permeation side) of the membrane is depressurized or a carrier gas is aerated to permeate a separation substance in a gas state. The vapor permeation method is different from the pervaporation method in that the supply to the primary side of the membrane is mixed vapor. The membrane-permeable substance can be collected by cooling and condensing the permeated vapor. Many studies have been reported so far regarding the pervaporation method. For example, for the separation of aqueous ethanol solutions, U.S. Pat.
U.S. Pat. No. 30,350,60 has an example of polyvinyl alcohol.

For pervaporation membranes or vapor permeable membranes used industrially, it is required to thin a membrane material having high separation performance to increase the permeation rate, and a skin layer having separation activity and a skin layer having the separation activity. An asymmetric membrane structure having a sponge layer that retains mechanical strength or a composite membrane structure in which a polymer coating is applied on a porous support membrane to form a thin layer has been developed. An asymmetric membrane formed by a phase conversion method of a membrane-forming solution can have a thin separation active surface layer (skin layer), but often has a relatively large void which becomes a film defect in this separation active layer. Since the organic mixture permeates as it is through this void, high separation performance may not be obtained.

On the other hand, in the composite film formed by the polymer coating method, by increasing the number of coatings, this defective void can be prevented and the separation performance can be improved. As a method for producing a flat membrane type composite membrane, for example, JP-A-50-41958, JP-A-53-144884, and JP-A-54-5268.
Polymer coating methods are disclosed in Japanese Patent No. 3 and Japanese Patent No. 54-100984. Examples of the hollow fiber type composite membrane include JP-A Nos. 61-35803, 61-18402, and 63-207304. However, the dense coating layer formed on the surface of the porous membrane by this polymer coating method becomes a resistance when the permeative substance in the organic mixture permeates the separation membrane, and the permeation rate may be significantly reduced. In general, the polymer used for coating is selected so that it has a high affinity for the selectively permeable substance to the membrane, so that it contacts the mixed solution as the concentration of the permeable substance in the mixed solution to be separated increases. The coating polymer swells and the free volume of the polymer becomes remarkably large. Therefore, separation due to the difference in size of permeation molecules becomes difficult and the separation performance of the membrane is significantly reduced.

[0006]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to solve the above-mentioned problems, and as a result, as a result, without forming a new separation active layer of a polymer substance on the semipermeable membrane surface. By substantially filling only the micropores of the membrane with a polymeric substance, the permeation resistance of the permeation substance is small, and the separation performance is high even when the permeation substance of the organic mixed liquid has a wide range of concentrations. The inventors have invented a pervaporation membrane or a vapor permeable membrane having a different structure.

That is, according to the present invention, the micropores on the surface of the separation active layer of the semipermeable membrane are substantially filled with a polymer substance different from the material of the semipermeable membrane, and the polymer surface is filled with the polymer. The present invention relates to a semipermeable membrane for separating organic substances used in a pervaporation or vapor permeation method, which is characterized by having substantially no substance layer. In the present invention, a polymer solution different from the material of the semipermeable membrane is permeated into the semipermeable membrane to fill the micropores on the surface of the separation active layer of the membrane, The present invention relates to a method for producing a semipermeable membrane for separating organic substances, characterized in that the polymeric substance is washed and removed, and then the polymeric substance is crosslinked to be insolubilized to substantially close the micropores.

Here, the layer of the polymeric substance which does not substantially exist on the surface of the porous membrane in the present invention means that the surface of the membrane of the present invention is observed even when it is magnified 5000 times with an electron microscope. It is an extremely thin layer in which the existence of the polymer layer cannot be ascertained, and means that the thickness of the layer is 0.2 μm or less.

In the separation membrane according to the present invention, since the polymer substance is not substantially present on the surface of the membrane, there is no problem that the polymer coating layer has a permeation resistance unlike the conventional composite membrane and the permeation rate is significantly reduced. Since the macromolecules are filled in the micropores of the porous membrane, no defect void appears on the membrane surface like the conventional pervaporation membrane having an asymmetric structure,
High separation performance can be obtained. Further, since the membrane of the present invention is confined within a certain pore size having a high molecular substance filled in the membrane micropores, even when a solution having a high concentration of permeate is pervaporated, the conventional coat type composite is used. Unlike the membrane, the coating layer does not swell with the permeative substance, and therefore, high separation performance of the mixed solution can be obtained without increasing the free volume of the filled polymer.

When separating the organic mixed substance using the separation membrane of the present invention, the permeabilizing substance permeates between the free volumes of the polymer substance filled in the micropores of the membrane, and at the same time the free volume of the membrane material is It is also desired to obtain a high transmission rate. Therefore, the semipermeable membrane in the present invention is preferably a membrane having an affinity for the permeation substance, and a conventional reverse osmosis membrane, an ultrafiltration membrane or a microfiltration membrane made of an organic polymer material or an inorganic material can be used. . The pore size or molecular weight fraction of the semipermeable membrane is not particularly limited, and the polymer physical properties such as molecular weight, shape, and physicochemical properties of the polymer substance to be filled, and the polymer solution when the polymer solution is filled through the membrane Although it can be appropriately selected depending on the filling treatment conditions such as the concentration and the permeation pressure, the fraction of the membrane is preferably about 1 to 10 times the molecular weight of the polymer substance.

The polymer substance used in the present invention is different from the above-mentioned material of the semipermeable membrane in the present invention, and it is desirable that it has an affinity with the permeation substance in the organic substance mixed liquid or the organic substance mixed vapor. For example, in the case of selectively permeating water from an organic / water mixture using the membrane of the present invention,
The polymer substance is preferably a hydrophilic polymer, for example, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, chitosan, polyacrylic acid, carboxymethyl cellulose, etc., or an aqueous emulsion of an acrylic polymer containing a hydrophilic monomer component, etc. Can be applied.

In the present invention, in order to fill the micropores of the semipermeable membrane with the polymer substance, the polymer solution is filtered under pressure or under reduced pressure, or the semipermeable membrane is immersed in the polymer solution. Then, a method of diffusing and permeating the polymer into the inside of the micropores can be applied. When a polymer substance is permeated into the membrane by a press-fitting method, the polymer is adsorbed to the micropores, the pores are blocked by the polymer, and eventually a gel layer of the polymer is deposited on the membrane surface. Since the gel layer thus deposited forms a new coat layer on the film surface, it is desirable to stop the permeation of the polymer solution before the gel layer is sufficiently deposited. The concentration of the polymer solution to be permeated and the permeation pressure are not particularly limited, but can be set in consideration of the adsorptivity of the polymer to the semipermeable membrane and the blockage of the micropores in the membrane. It is possible to increase the filling amount of the polymer in the micropores in a shorter permeation time as the value is higher.

The gel layer deposited on the film surface by press-fitting the polymer must be removed by thoroughly washing the film surface. The washing method is not particularly limited, but usually, the gel layer can be peeled off by flushing the membrane surface with water.

In the present invention, the polymer filled in the micropores of the semipermeable membrane is preferably not dissolved in the solution to be separated or the vapor to be separated and is retained in the micropores. For this,
It is preferable to insolubilize the polymer retained in the micropores of the membrane. In order to insolubilize the polymer filled in the micropores, there are a thermal crosslinking method of the polymer, a chemical crosslinking method using a crosslinking agent and the like. In the heat-crosslinking method, for example, when using polyvinyl alcohol as a filled polymer and a polyacrylonitrile-based porous membrane is used, the membrane after permeation of the polymer solution is 50 to
It is desirable to heat-treat at 100 ° C. to insolubilize the polymer. The heat treatment time is not particularly limited, but it is usually preferable to perform the treatment for about several hours.

In the method according to the present invention described above, for example, a pervaporation membrane having a void which is a defect on the membrane surface and having a very small separation performance is filled with a polymer substance in the void portion to repair the membrane defect. However, it can be used for the purpose of obtaining a pervaporation membrane having a high separation coefficient.

[0016]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A polyacrylonitrile ultrafiltration flat membrane (fraction molecular weight 40,000) was used as a semipermeable membrane, and 0.2% by weight of polyvinyl alcohol (Kuraray Co., Ltd.) having an average molecular weight of 75,000 was pure. The solution dissolved in water is ultrafiltered under a pressure of 1.0 kg / cm ² ,
Filtration was terminated when the amount of filtrate per unit area became about 1.5 ml / cm ² . Next, the membrane was taken out from the filter, and about 250 ml of pure water was flushed onto the membrane surface using a washing bottle to wash and remove the polyvinyl alcohol attached to the membrane surface. Further, this film was heat-treated in a dryer at 95 ° C. for about 10 hours. Using the separation membrane obtained above,
A boiling mixture or boiling mixture of isopropyl alcohol (IPA) / water (weight ratio: 98/2) at a temperature of 83 ° C was subjected to pervaporation or vapor permeation experiments under a pressure on the permeation side of the membrane of 10 mmHg, Liquid nitrogen was condensed with a cold trap using a refrigerant and collected as a permeate.The permeation rate was calculated from the weight of this permeate, and the composition of the permeate was analyzed by gas chromatography. It was calculated.

[0018]

[Equation 1]

The results obtained are shown in Table 1.

Examples 2 and 3 Polyacrylonitrile-based ultrafiltration membrane (molecular weight cutoff of 5,000)
A 5.0% by weight aqueous solution of polyvinyl alcohol (Aldrich) having an average molecular weight of 50,000 was subjected to ultrafiltration under reduced pressure on the permeate side of 10 mmHg for 1 hour (Example 2) or the ultrafiltration membrane was placed in the aqueous solution. Soak for 1 hour under normal pressure (Example 3)
did. Next, the permeation side pressure is normal pressure and the membrane surface is about 300 m.
After washing with 1 l of pure water, this film was heat-treated at 80 ° C. for about 6 hours. The cross section of this film was observed by a scanning electron microscope and is shown in FIG. From FIG. 1, it is understood that the separation membrane of the present invention has substantially no polyvinyl alcohol layer on the membrane surface. The pervaporation and vapor permeation performance of this membrane was measured under the same experimental conditions as in Example 1, and the results shown in Table 1 were obtained.

Comparative Example 1 After the same ultrafiltration membrane as in Example 1 was immersed in pure water, this membrane was heat-treated at a temperature of 95 ° C. for about 10 hours. The cross section of this untreated film was observed by a scanning electron microscope and is shown in FIG. Table 1 shows the results of measuring the performance of this film under the same experimental conditions as in Example 1.

COMPARATIVE EXAMPLE 2 The same ultrafiltration membrane surface as in Examples 2 and 3 was cast with a 15% by weight aqueous solution of polyvinyl alcohol, and then this membrane was removed.
Heat treatment was performed at 80 ° C. for about 6 hours. FIG. 3 shows a scanning electron micrograph of the cross section of the film. From FIG. 3, it can be seen that the film surface has a coat layer of about 5 μm. In addition, Table 1 shows the membrane performance measured under the same experimental conditions as in Example 1.

[0023]

[Table 1]

Example 4 Using the same ultrafiltration membrane as in Example 1, an average molecular weight of 700,
000 of 0.2% by weight aqueous solution of polyacrylamide under pressure 1
After pressure ultrafiltration at kg / cm ² for 30 minutes, the membrane surface is about 300 ml.
After flushing and cleaning with pure water, the film was heat treated at 95 ° C. for about 6 hours. The membrane performance obtained under the same experimental conditions as in Example 1 was as follows: Pervaporation performance: Permeation rate = 0.26 kg / m ² hr, Separation coefficient = 51
10 Vapor permeation performance: Permeation rate = 0.25 kg / m ² hr, Separation coefficient = 21
Even when filled with polyacrylamide, a membrane having high separation performance can be obtained as in the case of filling with polyvinyl alcohol.

[0025]

EFFECTS OF THE INVENTION The organic separation membrane according to the present invention has the following effects by substantially filling the micropores of the semipermeable membrane with the polymer substance. 1) Since there is no thick permeation resistance layer on the membrane surface unlike the coat type composite membrane, the permeation rate is high. 2) Even when the concentration of the permeative substance in the feed liquid is high, the filled polymer does not swell and has high separation performance. 3) Void defects that often occur in the separation active layer on the membrane surface can be noticed and high separation performance is achieved. 4) Permeation membrane or vapor permeable membrane modules can be easily obtained by using various forms of semipermeable membrane modules to permeate the polymer solution into the membrane pores.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing a fiber shape and a particle structure in a cross section near the surface of the separation membrane of the present invention according to Example 2 (magnification: 5,000 times).

FIG. 2 is a scanning electron micrograph showing a fiber shape and a particle structure in a cross section near the surface of the untreated film according to Comparative Example 1 (magnification: 5,000 times).

FIG. 3 is a scanning electron micrograph showing a fiber shape and a particle structure in a cross section near the surface of a composite film obtained by a conventional coating method according to Comparative Example 2 (magnification: 3,000 times).

Claims (9)

[Claims] 1. A microporous material on the surface of a separation active layer of a semipermeable membrane is substantially filled with a polymer substance different from the material of the semipermeable membrane, and a layer of the polymer substance is formed on the membrane surface. A semipermeable membrane for separating organic substances used in pervaporation or vapor permeation, characterized by being substantially absent. 2. The semipermeable membrane for separating organic substances according to claim 1, wherein the semipermeable membrane is an ultrafiltration membrane, and the separation coefficient after filling the polymer substance is 10 times or more of the original. film. 3. The semipermeable membrane for separating organic substances according to claim 1 or 2, wherein the semipermeable membrane is a polyacrylonitrile-based separation membrane. 4. The semipermeable membrane for separating organic substances according to claim 1, wherein the polymer substance is a crosslinkable polymer. 5. The semipermeable membrane for separating organic substances according to claim 4, wherein the crosslinkable polymer is polyvinyl alcohol. 6. A polymer solution different from the material of the semipermeable membrane is allowed to permeate into the semipermeable membrane to fill the micropores on the surface of the separation active layer of the membrane, and to dispose the high pores attached to the surface of the membrane. A method for producing a semipermeable membrane for separating organic matter, which comprises washing and removing a molecular substance and then cross-linking the polymer substance to make it insoluble, thereby substantially closing the micropores. 7. The method for producing a semipermeable membrane for separating organic substances according to claim 6, wherein the semipermeable membrane is a polyacrylonitrile-based separation membrane. 8. The method for producing a semipermeable membrane for separating organic substances according to claim 6, wherein the polymer substance is polyvinyl alcohol. 9. The method for producing a semipermeable membrane for separating organic substances according to claim 8, wherein the insolubilization of polyvinyl alcohol is by thermal crosslinking.