CN1218774C - Manufacturing method of polymer fluid separation composite membrane - Google Patents

Abstract

The present invention relates to a method for making composite polymer membranes for fluid separation, which comprises the following steps: firstly, making a polymer microporous membrane used as a supporting layer; submerging the microporous membrane in a solvent to saturate the pores of the microporous membrane by the solvent, taking the microporous membrane out of the solvent, and removing the solvent attached to the surface of the membrane; then, dissolving another polymer, corresponding crosslinking agents, additive, compounding agents, etc. in another solvent to prepare membrane making liquid for an active cortical layer; finally, polymerizing the membrane making liquid and the microporous membrane into a composite membrane. The composite membrane made by the method has the advantages of uniform thickness of the separated active cortical layer without defects, and stable separation selectivity. Meanwhile, the active cortical layer easily becomes ultrathin, and the intrinsic permeation rate is high. Because the pores of the microporous membrane are expedite, the membrane has very high permeation flux. The compaction cortical layer of the composite membrane made by the method can be a reverse permeation membrane, a permeation vaporization membrane, or a permeation extraction membrane, etc. The composite membrane made by the method is an ideal composite membrane used for fluid separation.

Description

Manufacturing method of polymer fluid separation composite membrane

1. Technical field

The invention relates to a manufacturing method of a polymer composite membrane, in particular to a manufacturing method of a polymer composite membrane with a dense non-porous separation active skin layer for reverse osmosis and pervaporation of fluid separation.

2. Background technology

Most of the dense non-porous multilayer composite membranes used in reverse osmosis and pervaporation for fluid separation are made of high molecular polymers. In order to obtain high membrane permeation flux and ensure the separation selectivity of the membrane, it must be made into a very thin and defect-free membrane. There are two general approaches to fabricate membranes with thin or ultrathin separation active skins. One is the so-called L-S immersion gel method for manufacturing asymmetric membranes, which have an ultra-thin dense top layer and a porous support bottom layer for separation. An asymmetric membrane has an asymmetric geometry across the membrane thickness, but the membrane material is homogeneous. The most typical example is that Loeb and Sourirajan used this method to make the original "asymmetric cellulose acetate reverse osmosis membrane" [S.Loeb, S.Sourirajan, Adv.Chem.Ser., 38(1963), 117-] . Another approach is to fabricate multilayer composite films composed of different materials. It is to first use a material to make a microporous support membrane with good chemical, physical and mechanical properties, and then compound a dense skin layer of another material with excellent separation characteristics on the support membrane. The microporous support layer usually has a symmetrical structure, and its manufacturing methods include solvent evaporation, water vapor inhalation and thermal gelation. The dense cortex is also a symmetrical structure, and the methods for its film formation and compounding with the support layer are as follows: 1. The mechanical composite method of directly covering the film-formed cortex on the support layer; 2. Coating the surface of the support layer Membrane solution, physical composite method of film formation after solvent volatilization; 3. Chemical composite method of interfacial polymerization or in-situ polymerization or plasma polymerization or surface grafting film formation on the surface of the support layer.

When making dense non-porous multilayer composite membranes, the main goals pursued by people are: (1) the dense separation active skin layer has a very thin or ultra-thin thickness to ensure its high permeation flux; (2) the dense skin layer has no or There are almost no defects to ensure its good separation selectivity; (3) the microporous support layer has a uniform pore size distribution and extremely high porosity to ensure that its resistance to penetration is completely negligible; (4) the dense cortex and support layer The bonding is good so that the swelling behavior of the membrane does not have a destructive effect on the membrane. In order to achieve the above goals, various film-making methods have been studied. Such as U.S. Patent 4857080 [R.W.Baker etc., MTR Membrane Technology Company, August, 1989] discloses a kind of three-layer composite membrane of silicon rubber-palladium alloy-polymer microporous support layer, and the silicon rubber layer thickness is less than 5 microns, uses Separate and purify hydrogen at higher temperature. The separation active skin layer of the composite membrane is metal palladium, which has a high separation selectivity for hydrogen, but it inevitably has significant defects when it is ultra-thin. Therefore, a layer of ultra-thin silicone rubber is compounded on the metal palladium active skin layer, which is specially used to block defects, but reduces the intrinsic permeability of the membrane. Another example is U.S. Patent 4,243,701 [R.L.Riley et al., VOP Company, 1st, 1981] invented a silicone rubber-microporous support layer two-layer gas separation composite membrane for hydrogen-carbon dioxide separation. In this invention, the prefabricated microporous support membrane is immersed in a very low concentration polydimethylsiloxane (PDMS) film-making solution, and after taking it out, it is cross-linked and solidified to form a polydimethylsiloxane active skin layer . In order to prevent the polydimethylsiloxane membrane-making fluid from penetrating into the pores of the support layer, the molecular weight of the polydimethylsiloxane prepolymer for preparing the membrane fluid must be precisely controlled. However, it is difficult to determine the molecular weight of the prepolymer in actual operation, and it cannot be guaranteed that the membrane-forming solution will not penetrate into the micropores of the support layer. In addition, Chinese patent (Application No. 98114022.X) discloses "Preparation and Application of a Composite Gas Separation Membrane". This invention can be used for the separation of organic vapor. The microporous support layer is then coated with polydimethylsiloxane (PDMS) casting solution on the microporous support layer, and cured by heating to form a polydimethylsiloxane (PDMS) active skin layer. The disadvantage of this method is that it is difficult to ensure that the polydimethylsiloxane (PDMS) casting solution does not penetrate into the pores of the microporous support layer. Though above prior art all has its characteristic, also there is defective separately.

3. Contents of the invention

The present invention is aimed at the defects in the above-mentioned prior art, and proposes a method for manufacturing polymer composite membranes for reverse osmosis and pervaporation of fluid separation. The non-porous composite membrane can not only form a uniform ultra-thin separation active skin layer, but also has high permeation flux and stable high separation selectivity. The composite membrane made by the invention can be used for reverse osmosis, pervaporation, permeation extraction and the like.

The technical solution of the present invention is realized by the following measures. The method for manufacturing a polymer fluid separation composite membrane is as follows: firstly, a polymer microporous membrane as a support layer is made; the support layer microporous membrane is immersed in a solvent, so that the pores of the microporous membrane are covered by the solvent saturated; then take out the microporous membrane from the solvent, and carefully remove the solvent on the surface of the microporous membrane, even if the solvent attached to the surface of the microporous membrane is basically volatilized; another polymer and the corresponding crosslinking agent, additive and The compounding agent and the like are dissolved in another solvent to make a polymer film-making solution for the active skin layer; then the active skin layer film-making solution is coated on the surface of the polymer microporous membrane of the supporting layer whose micropores are saturated by the solvent; then Carry out heat treatment to cross-link and solidify the polymer film-making solution to form an ultra-thin active skin layer; after the active skin layer is solidified and stabilized, the formed film is finally treated under high temperature and vacuum to make the micropores of the support layer The solvent is evaporated and finally a dry polymer composite film is obtained.

The polymer material used in the microporous membrane of the supporting layer of the present invention can be polysulfone (PS), polyacrylonitrile (PAN) or other polymer materials. The polymer material used in the polymer film-forming solution of the active skin layer can be polyvinyl alcohol, polydimethylsiloxane (PDMS), or other polymer materials. The saturated solvent of the microporous membrane of the support layer can be glycerin, water or other solvents, and the solvent for dissolving another polymer and corresponding crosslinking agent, additive and compounding agent can be water, benzene or other solvents.

The manufacturing method of the polymer fluid separation composite membrane of the present invention has the following characteristics: its pores of the supporting layer microporous membrane of the present invention are saturated by the solvent glycerin, and due to the protective effect of the solvent glycerin, the membrane-making solution of the active cortex will not enter the support layer. In the micropores, the used solvent glycerin has good affinity with the microporous membrane of the support layer, but it is immiscible with another solvent, water. The solvent glycerin cannot dissolve the polymer of the active skin layer and its additives, compounding agents, etc., while the other solvent water and the polymer of the active skin layer and its additives, compounding agents, etc. can form a good film-forming solution. Therefore, the composite membrane can form a uniform ultra-thin separation active skin layer, that is, the active skin layer is easy to be ultra-thin. The polymer composite membrane prepared by the invention not only has high intrinsic permeability, but also has stable separation selectivity, and the pore channels of the microporous membrane of the supporting layer are completely unblocked, so that the composite membrane has high permeation flux.

4. Description of drawings

Fig. 1 is a schematic cross-sectional structure diagram of the support layer microporous membrane of the present invention. This is just a modeling of the membrane pore structure, and the actual structure under the scanning electron microscope is much more complicated. It is reasonable to use this model to illustrate the membrane pore structure.

Fig. 2 is a schematic diagram showing that the pores of the microporous membrane of the support layer of the present invention are saturated by the solvent glycerin.

Fig. 3 is a schematic diagram of the film forming process of the active skin layer on the support layer of the present invention. That is, it is a schematic diagram of the process of coating the skin layer film-forming solution including solvent, active skin layer polymer, crosslinking agent, additives, etc. on the surface of the support layer for in-situ polymerization to form the skin layer. During the gradual evaporation of the solvent and the solidification of the active skin layer to form a film, the solvent in the micropores of the support layer should basically remain non-volatile.

Fig. 4 is a schematic diagram of the cross-sectional structure of the polymer composite membrane of the present invention after forming and evaporating the solvent in the microporous membrane of the support layer.

In the accompanying drawings, 1 is the polymer microporous membrane of the support layer, 2 is the micropore, 3 is the saturated solvent of the microporous membrane of the support layer, 4 is the dissolving solvent for making the film-making solution, 5 is the active cortex film-making solution, and 6 is the active cortex.

5. Specific implementation

The polymer fluid separation composite membrane manufactured by the present invention will be further described below in conjunction with the accompanying drawings and examples.

First, the manufacturing method of the supporting layer microporous membrane 1 of the present invention adopts the solvent volatilization method, and the thickness of the prepared supporting layer microporous membrane 1 is between 50 and 1000 microns, and the optimum thickness is between 100 and 500 microns. 2 The size is between 0.05 and 1 micron, and the optimal size is between 0.1 and 1 micron. The two solvents 3 and 4 selected should have the following characteristics: the solvent 3 has a good affinity with the microporous membrane of the support layer, and the solvent 3 and the dissolving solvent 4 in the membrane-forming solution are not miscible. The vacuum degree of solvent 3 volatilization is higher than 90 kPa, and the volatilization temperature is between 30 and 200 ° C. Solvent 3 cannot dissolve the polymer of the active skin layer and its additives, compounding agents, etc.; while solvent 4 and the polymer of the active skin layer and its additives , compounding agent, etc. can form a good film-forming solution; solvent 4 is more volatile than solvent 3.

The method for the microporous membrane pores of the support layer to be saturated with solvent 3 can be determined according to the microporous membrane material used. If the solvent 3 has a good affinity with the microporous membrane material, the impregnation method can be used, that is, the microporous membrane can be directly The membrane is immersed in the solvent, causing the pores to be filled with the solvent. If the affinity between the solvent 3 and the microporous membrane material is not good enough, mechanical or physical coercive methods, such as pressure or vacuum, can be used to press the solvent into the pores.

Since the active cortex film-forming solution 5 of the present invention is a dilute solution of the polymer used, its concentration is between 0.1% and 10% based on the mass ratio of the polymer to the solvent, and the optimum concentration is between 1% and 5%. The cross-linking and curing method of the active skin layer can use in-situ polymerization.

In order to make the active skin layer 6 form a good film, on the premise of ensuring that the micropores of the microporous membrane 1 of the support layer are saturated with solvent, the solvent on the composite interface should be removed as much as possible. The solidification of the active skin layer on the interface with the support layer to form a film is a volatilization process of the solvent 4. During this process, the solvent 3 should be kept as non-volatile in the pores as possible to ensure the uniformity and defect-free thickness of the active skin layer 6. After the active skin layer 6 is solidified into a film and stabilized, the film is placed in a vacuum higher than 90kPa and the temperature is between 30 and 200°C, so that the solvent 3 in the micropores of the support layer is evaporated, and finally a dry polymer flow is formed. Body separation composite membrane. The optimum temperature for volatilization of the solvent 3 used in the present invention is between 60°C and 100°C.

The polymer composite membrane produced by the present invention can be of tube type or flat type, and the corresponding membrane module can be of hollow fiber, plate basket or winding type. The dense skin layer of the composite membrane can be a reverse osmosis membrane, a pervaporation membrane or a permeation extraction membrane, etc.

Embodiment one

A circular support layer microporous membrane with a diameter of 200 mm was produced by solvent evaporation method. The polymer material used was polysulfone (PS), the micropore size was 0.6 micron, the porosity was 60%, and the microporous film thickness was 150 micron. Use the solvent glycerin to filter through this microporous membrane to make the pores saturated with glycerin, and carefully remove the glycerin on the surface of the membrane. Polyvinyl alcohol (PVA) and corresponding cross-linking agents, additives and compounding agents are dissolved in solvent water to prepare a film-forming solution for the active skin layer of polyvinyl alcohol. The concentration of polyvinyl alcohol is 5% (W/W). Coat the polyvinyl alcohol membrane-making solution on the polysulfone support membrane whose pores are saturated with glycerin, and then place it at a temperature of 60°C to solidify the polyvinyl alcohol to form an active skin layer, and then place the membrane at a temperature of 100°C and The dry composite film was obtained by treating under the vacuum of 10k Pa for 2 hours. The SEM photograph of the composite film shows that the thickness of the skin layer is about 4 microns. The reverse osmosis evaluation experiment was carried out with 0.2% sodium chloride aqueous solution, and the permeation flux exceeded 5kg/m ² ·h, and the desalination rate exceeded 96%.

Embodiment two

Adopt the solvent volatilization method to make a circular support layer microporous membrane with a diameter of 200 mm. The material used is polyacrylonitrile (PAN). is 150 microns. Use solvent glycerin to filter through this microporous membrane to make the pores saturated with glycerin, and carefully remove the glycerin on the surface of the membrane. Polyvinyl alcohol (PVA) and corresponding cross-linking agents, additives and compounding agents are dissolved in solvent water, and the concentration of polyvinyl alcohol is 2% (W/W) to prepare a film-forming solution for the active skin layer of polyvinyl alcohol. Coat the film-making solution on the microporous polyvinyl nitrile support membrane saturated with glycerol, place it at a temperature of 60°C to solidify the polyvinyl alcohol to form an active skin layer, and then place the film at a temperature of 100°C and 10kPa Treat under vacuum for 2 hours to obtain a dry composite film. The SEM photograph of the composite film shows that the thickness of the skin layer is about 1.5 microns. Ethanol-water solution with ethanol concentration of 95% was used for water pervaporation evaluation experiment at 70°C, the permeation flux was over 0.6kg/m ² ·h, and the selectivity coefficient (separation factor) was over 900.

Embodiment three

The polysulfone (PS) microporous hollow fiber membrane is made by the LS phase inversion method, the outer diameter of the fiber tube is 500 microns, the inner diameter is 250 microns, and the pore diameter is 0.1 microns. Immerse the fiber tube in solvent water to saturate the pores with water. Polydimethylsiloxane (PDMS) and corresponding crosslinking agents, catalysts and additives were dissolved in solvent benzene, and the concentration of polydimethylsiloxane (PDMS) was 10% (W/W). Seal both ends of the fiber tube, then immerse it in polydimethylsiloxane film-making solution for 1-2 mm, take it out to let the benzene volatilize naturally, and then place it at a temperature of 100 ° C and treat it under a vacuum of 10 kPa for 3 hours to form a dry hollow fiber composite membrane. The SEM photograph of the composite film shows that the thickness of the polydimethylsiloxane (PDMS) composite layer is 2 microns. When used for air separation, the O ₂ /N ₂ separation factor is 2.4, and the permeability is 4.53×10 ^-8 ml·cm/cm ² ·s·cmHg.

Claims (11)

1, a kind of manufacturing method of the polymer composite membrane that is used for fluid separation, it is characterized in that the step of this manufacturing method is: at first make a kind of polymer microporous membrane (1) as supporting layer; The membrane (1) is submerged in a solvent (3), so that the pores of the microporous membrane are saturated by the solvent (3); then the microporous membrane is taken out from the solvent (3), and the solvent on the surface of the microporous membrane is removed, even The solvent attached to the surface of the membrane is volatilized; another polymer and the corresponding crosslinking agent, additives and compounding agents are dissolved in another solvent (4) to make a membrane-forming solution (5) for the active skin layer (6) ; The active cortex film-making solution (5) is coated on the surface of the support layer polymer microporous membrane (1) saturated by the solvent (3) in the micropore (2); then heat treatment is carried out to make the polymer film The solution is cross-linked and solidified to form an ultra-thin active skin layer (6); after the active skin layer (6) is cured to form a film and stabilized, the formed film is finally placed under high temperature and vacuum to make the support layer microporous film (1) The solvent (3) in the micropores (2) is evaporated, and finally a dry polymer composite film is formed. 2. The manufacturing method of polymer composite membrane according to claim 1, characterized in that the polymer used to make the support layer microporous membrane (1) is polysulfone (PS) or polyacrylonitrile (PAN). 3, according to the manufacture method of the described polymer composite membrane of claim 1, it is characterized in that the polymer used in the polymer membrane solution (5) of said active skin layer (6) is polyvinyl alcohol (PVA), polyvinyl alcohol Dimethylsiloxane (PDMS). 4, according to the manufacture method of the described polymer composite membrane of claim 1, it is characterized in that as the solvent (3) that submerges saturated polymer microporous membrane (1) is glycerin, water solvent, as dissolving another kind of polymer and The solvent (4) of the corresponding crosslinking agent, additive and compounding agent is water and benzene solvent. 5. The method for producing a polymer composite membrane according to claim 4, characterized in that the solvent (3) and the solvent (4) are immiscible, and the solvent (4) is more volatile than the solvent (3). 6. The method for producing a polymer composite membrane according to claim 1, characterized in that the thickness of the microporous membrane (1) of the support layer is between 50 and 1000 microns, and the size of the micropores (2) is between 0.05 and 1 micron between. 7. The method for producing a polymer composite membrane according to claim 6, characterized in that the thickness of the microporous membrane (1) of the supporting layer is between 100 and 500 microns, and the size of the micropores (2) is between 0.1 and 1 micron between. 8. The method for producing a polymer composite membrane according to claim 1, characterized in that the active skin layer membrane-making solution (5) is a dilute solution of the polymer used, with a concentration of 0.1 in terms of its mass ratio to the solvent. ~10%. 9. The method for producing a polymer composite membrane according to claim 8, wherein the concentration is between 1% and 5%. 10. The manufacturing method of polymer composite membrane according to claim 4, characterized in that the solvent (3) submerged in the saturated microporous membrane has a vacuum degree higher than 90kPa and a volatilization temperature between 30-200°C. 11. According to the method for producing a polymer composite membrane according to claim 10, the microporous membrane is immersed in a solvent, which is characterized in that the volatilization temperature of the solvent (3) immersed in the saturated microporous membrane is between 60 and 100°C, which can make the The solvent in the micropore (2) evaporates cleanly.

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