Hydrophilically modified polyamide pervaporation composite membranes and methods of making the same

Abstract

The application is based on the adsorption and desorption mechanism of water molecules in the pervaporation membrane, and a new type of pervaporation dehydration composite membrane with hydrophilic membrane surface and hydrophobic membrane interior is prepared. First, a relatively hydrophobic polyamide membrane layer is prepared by interfacial polymerization, and then a hydrophilic layer is coated on the surface of the polyamide membrane. By changing the preparation conditions of polyamide, the type and concentration of the hydrophilic layer, a high hydrophilic pervaporation membrane with less defects and conducive to the passage of water molecules is obtained. The method uses inexpensive and environmentally friendly materials as the hydrophilic layer, changes the complexity of the traditional polyamide post-processing method, and is easy to popularize. While improving the membrane separation performance, it can reduce bacterial growth, and is used for pervaporation dehydration membrane, pervaporation organic separation membrane, anti-fouling nanofiltration membrane, and anti-fouling reverse osmosis membrane, which opens up new ideas and methods for preparing high-performance membranes under harsh conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydrophilic modified polyamide pervaporation composite membrane and a preparation method thereof, which is suitable for the process of industrial production of anhydrous ethanol. BACKGROUND

[0002] To solve the problem of energy shortage and relieve the pressure of environmental pollution, fuel ethanol, generally refers to anhydrous ethanol with a volume concentration of 99.5% or more. The traditional methods for producing anhydrous ethanol mainly include distillation and extraction, which have problems such as serious environmental pollution, high energy consumption, poor separation effect, etc. Pervaporation, as an environmentally friendly mixed azeotrope separation technology, has the advantages of energy saving, simple operation, no secondary pollution, easy coupling with other processes, etc. compared with traditional separation technologies such as distillation, extraction and absorption. Pervaporation technology has developed rapidly in recent years and is expected to realize industrial application of solvent dehydration, desalination and organic separation. However, the research on pervaporation membrane is still in the laboratory stage, and its application in industry is less. Therefore, it has become a hot research field to develop a pervaporation membrane with simple preparation process, high stability, low cost and high separation performance.

[0003] At present, the methods for preparing pervaporation membranes include solution casting and coating. The composite membranes prepared by these methods often have a thick separation layer, which limits the further improvement of the permeation flux. Although the hollow fiber spinning method has a high flux, it requires high equipment and has a complex preparation process, which is difficult to be industrialized. Interfacial polymerization can have a high permeation flux without sacrificing the selectivity of the membrane, and is expected to break the trade-off effect between the conventional permeation flux and the separation selectivity. Due to its repeatability and scalability, interfacial polymerization has broad application potential in the field of pervaporation. Pervaporation membranes mainly separate based on the mechanism of dissolution and diffusion, i.e. the permeant is adsorbed to the membrane surface from the feed liquid, the permeant diffuses and desorbs in the membrane, and the permeant permeates from the membrane to the gas phase on the permeation side. However, after the common water-phase amine monomer reacts with the oil-phase monomer to form polyamide, the hydrophilicity of the membrane surface decreases and the membrane is not resistant to pollution. At the same time, the thickness of the polyamide is limited, and a small amount of defects will gradually expand during the pervaporation process, thereby affecting the performance of the membrane. Therefore, a hydrophilic material is coated on the surface of the polyamide to increase the hydrophilicity of the membrane surface and reduce the defects of the polyamide. Due to the hydrophilic material, the hydrophilicity of the membrane surface is increased, which is beneficial to the adsorption of water molecules on the surface of the pervaporation membrane; the hydrophobicity of the polyamide inside the membrane helps the rapid desorption and diffusion of water molecules in the membrane, thereby achieving the purpose of simultaneously improving the permeability and selectivity. SUMMARY

[0004] The purpose of the present application is to modify the surface of the common polyamide, to obtain a pervaporation membrane with a hydrophilic surface and a hydrophobic interior by using a low-cost, easily available and green and pollution-free modified material, so as to promote the rapid transmission of water molecules and improve the separation selectivity of the membrane.

[0005] The technical solution of the present application is summarized as follows:

[0006] The hydrophilic modified polyamide pervaporation composite membrane and its preparation method, including using different amine monomers to react with oil phase monomers to prepare polyamide membrane layer, and then coating a layer of hydrophilic modification material, which reduces the membrane defects and increases the hydrophilicity of the membrane, the preparation method mainly includes steps (1) treating the base membrane, step (2) combining amine / water solution on the base membrane, step (3) reacting the oil phase monomers with the amine monomers to generate polyamide, step (4) heat treating the polyamide membrane layer, and step (5) coating the hydrophilic material on the polyamide membrane layer to form a composite membrane.

[0007] The specific process of steps (1)-(5) is as follows:

[0008] Step (1) cut the base membrane into appropriate size, soak in deionized water for 5-24 h, wet the pore, remove the surface impurities, and then remove the surface deionized water; step (2) fix the base membrane on the film applicator or self-made plate frame, make the mass fraction of 0.5-2.5 wt% amine / water solution evenly distributed on the surface of the base membrane, stand for 5-15 min, pour away the excess solution, and remove the uncombined amine monomers on the surface of the membrane; step (3) evenly distribute the oil phase monomer solution with a volume fraction of 0.1-0.5 w / v% on the surface of the membrane in step (2), react for 200-600 s, pour away the excess oil phase / n-hexane solution, wash the unreacted monomers on the surface of the membrane with n-hexane, and then remove the liquid drops on the surface of the membrane; step (4) place the polyamide membrane layer obtained in step (3) in an oven at 40-100℃ for 5-20 min, so that the amine monomers and the oil phase monomers fully react; step (5) evenly coat the hydrophilic material with a mass fraction of 0.5-2.5 wt% on the surface of the membrane in step (4), soak for 10-50 min, pour away the excess solution, remove the excess solution on the surface of the membrane, so that there are no liquid drops on the surface of the membrane, and then soak in the crosslinking agent solution with a mass fraction of 0.1-1.5 wt%, soak for 30-90 min, then remove the excess solution on the surface of the membrane, and soak in deionized water for standby.

[0009] 2. The method according to claim 1, wherein the base membrane in step (1) is a poly sulfone, poly ether sulfone, polyacrylonitrile, polytetrafluoroethylene, hydrolyzed polyacrylonitrile, or the like.

[0010] 3. The method according to claim 1, wherein the method for removing the residual solution on the surface is to spin dry by using the rotating centrifugal force or to blow dry by using the air knife.

[0011] 4. The method according to claim 1, wherein the amine in step (2) is polyethyleneimine, diethylene triamine, m-phenylenediamine, triethylene tetramine, or ethylenediamine.

[0012] 5. The method of claim 1, wherein the oil phase monomer of step (3) is trimesoyl chloride, terephthaloyl chloride, 1,3,5-hexane tricarboxylic chloride, or cyclohexane tetracarboxylic chloride.

[0013] 6. The method of claim 1, wherein the hydrophilic material of step (5) is sodium alginate, polyvinyl alcohol, or dextran solution, and the corresponding crosslinking agent is calcium chloride, glutaraldehyde, or polyethyleneimine solution, respectively.

[0014] 7. The polyamide pervaporation composite membrane with a hydrophilic layer prepared according to claim 1, which can solve the problems of poor hydrophilicity, poor pollution resistance, and many defects of the polyamide membrane layer, and prepare a pervaporation dehydration membrane with a hydrophilic surface and a hydrophobic interior, so as to promote the rapid adsorption and desorption of water molecules on the membrane and improve the separation performance of the membrane.

[0015] Advantages of the present application:

[0016] 1. The present application solves the problems of poor hydrophilicity, poor pollution resistance, and defects of the common polyamide membrane, and is suitable for various substrate membrane materials such as polyacrylonitrile, polyether sulfone, and polysulfone, and various hydrophilic materials such as sodium alginate, polyvinyl alcohol, and dextran, and is simple to operate and easy to popularize.

[0017] 2. Based on the adsorption and desorption mechanism of water molecules on the pervaporation membrane, the pervaporation composite membrane prepared by the present application has the properties of a hydrophilic surface and a hydrophobic interior, which significantly improves the separation performance of the membrane. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the infrared spectrum of the modified polyamide pervaporation membrane with or without hydrophilic modification in the implementation of the present application.

[0019] Figure 2 is the water contact angle of the surface of the modified polyamide pervaporation membrane with or without hydrophilic modification in the implementation of the present application.

[0020] Figure 3 is the scanning electron microscope image of the modified polyamide pervaporation membrane with or without hydrophilic modification in the implementation of the present application. DETAILED DESCRIPTION

[0021] The substrate membrane material used is a commercial membrane.

[0022] The present application will be further described below in conjunction with specific examples.

[0023] Comparative Example

[0024] (1) Cut the polyacrylonitrile substrate membrane into appropriate size and immerse it in 55 oC 1.5 mol / L sodium hydroxide solution for 2 h to increase the hydrophilicity of the membrane surface, and then immersed in deionized water for 24 h to remove the water on the membrane surface by using the rotational centrifugal force;

[0025] (2) The surface of the substrate membrane obtained in step (1) was evenly infiltrated with a polyethyleneimine / water solution with a mass fraction of 1.5 wt%, and then left to stand for 5 min, the excess solution was poured out, and the unbound water-phase monomers on the membrane surface were removed by using the rotational centrifugal force;

[0026] (3) The surface of the material obtained in step (2) was evenly distributed with a mellophanic chloride / n-hexane solution with a mass fraction of 0.2 wt%, and then reacted for 120 s, the excess solution was poured out, and the unreacted oil-phase monomers on the membrane surface were removed by using the rotational centrifugal force after n-hexane washing;

[0027] (4) The material obtained in step (3) was placed in 60 o C for 7 min to obtain a uniform and dense polyamide separation layer.

[0028] The unmodified polyamide pervaporation composite membrane was tested, and the separation factor of the ethanol / water solution with a mass fraction of 85 wt% was 125.1 at 70 °C, and the permeation flux was 2574.1 g·m -2 ·h -1 .

[0029] Example 1

[0030] (1) The polyacrylonitrile substrate membrane cut to an appropriate size was immersed in deionized water for 5 h to remove surface impurities and wet the pores, and then fixed on a film applicator to remove the water on the membrane surface by using the rotational centrifugal force;

[0031] (2) The surface of the substrate membrane obtained in step (1) was evenly infiltrated with a m-phenylenediamine / water solution with a mass fraction of 1.5 wt%, and then left to stand for 5 min, the excess solution was poured out, and the unbound water-phase monomers on the membrane surface were removed by using the rotational centrifugal force;

[0032] (3) The surface of the material obtained in step (2) was evenly distributed with a terephthaloyl chloride / n-hexane solution with a mass fraction of 0.3 wt%, and then left to stand for 120 s, the excess solution was poured out, and the unreacted oil-phase monomers on the membrane surface were removed by using the rotational centrifugal force after n-hexane washing;

[0033] (4) The material obtained in step (3) was placed in 60 o C for 5 min to obtain a uniform and dense polyamide separation layer.

[0034] (5) The membrane obtained in step (4) was fixed with a self-made plate frame and clamped with a clamp around its four edges to prevent the leakage of the reaction solution. A 1.5 wt% sodium alginate solution was uniformly coated on the surface of the membrane, and the membrane was placed for 30 min. The excess solution was poured off, the membrane surface was washed with deionized water to remove the excess solution, and the membrane was dried with a wind knife. Then the membrane material was immersed in a 1.25 wt% calcium chloride solution for 30 min, taken out, and the excess calcium ions on the membrane surface were washed off, and the membrane was immersed in deionized water for standby.

[0035] In comparison with the comparative example, the polyamide Pervaporation composite membrane modified by sodium alginate and calcium chloride was tested on the unhydrolyzed polyacrylonitrile base membrane. The separation factor of the 85 wt% ethanol / water solution was 363.8, and the permeation flux was 1986.2 g·m -2 ·h -1 Compared with the unmodified polyamide pervaporation membrane, the increase in the hydrophilicity of the membrane surface significantly improved the separation selectivity of the membrane, and the increase in the thickness of the membrane slightly reduced the permeation flux.

[0036] Example 2

[0037] (1) The polyacrylonitrile base membrane was cut into an appropriate size and immersed in a 1.5 mol / L sodium hydroxide solution at 55 o C for 2 h to increase the hydrophilicity of the membrane surface, and then immersed in deionized water for 24 h. The membrane was fixed on a film applicator to remove the water on the surface of the membrane by rotary centrifugal force;

[0038] (2) A 1.5 wt% polyethyleneimine / water solution was uniformly infiltrated into the surface of the base membrane obtained in step (1), and the excess solution was poured off. The unbound water-phase monomer on the surface of the membrane was removed by rotary centrifugal force;

[0039] (3) A 0.2 wt% trimesoyl chloride / n-hexane solution was uniformly distributed on the surface of the base membrane obtained in step (2), and the reaction was carried out for 120 s. The excess solution was poured off, the membrane was washed with n-hexane, and the unreacted oil-phase monomer on the surface of the membrane was removed by rotary centrifugal force;

[0040] (4) The material obtained in step (3) was placed at 60 o C for 7 min to obtain a uniform and dense polyamide separation layer.

[0041] (5) The membrane obtained in step (4) was fixed with a self-made frame and clamped with a clamp around its four edges to prevent the leakage of the reaction solution. A 1.5 wt% sodium alginate solution was uniformly coated on the surface of the membrane, and the membrane was placed for 30 min. The excess solution was poured off, the membrane surface was washed with deionized water to remove the excess solution, and the membrane was dried with a wind knife. Then the membrane material was immersed in a 1.25 wt% calcium chloride solution for 30 min, taken out, and the excess calcium ions on the membrane surface were washed off, and the membrane was immersed in deionized water for standby.

[0042] The polyamide Pervaporation composite membrane modified by sodium alginate and calcium chloride on the polypropylene substrate membrane was tested. The separation factor of the 85 wt% ethanol / water solution was 525.1, and the permeation flux was 2087.9 g·m-2·h-1 at 70°C. -2 ·h -1 Compared with the unmodified polyamide pervaporation membrane, the separation selectivity of the membrane was increased by 4 times, and the increase in membrane thickness led to a decrease in permeation flux.

[0043] Example 3

[0044] (1) After the polysulfone substrate membrane was cut to the appropriate size, it was immersed in deionized water for 5 h to wet the pores and remove surface impurities. Then the membrane was fixed with a self-made frame, and the water on the surface of the membrane was blown off with a wind knife;

[0045] (2) A 1.5 wt% diethylene triamine / water solution was uniformly infiltrated into the surface of the substrate membrane obtained in step (1), and the membrane was placed for 5 min. The excess solution was poured off, and the unbound aqueous monomer on the surface of the membrane was blown off with a wind knife;

[0046] (3) A 0.2 wt% 1,3,5-cyclohexane trichloride / n-hexane solution was uniformly distributed on the surface of the material obtained in step (2), and the material was placed for 120 s. The excess solution was poured off, and the excess solution on the surface of the membrane was blown off with a wind knife;

[0047] (4) The material obtained in step (3) was placed at 50 o C for 7 min to obtain a uniform and dense polyamide separation layer.

[0048] (5) The membrane obtained in step (4) was fixed with the above-mentioned frame, and a 1.0 wt% dextran solution was uniformly coated on the surface of the membrane obtained in step (4). The membrane was placed for 10 min, and the excess solution was poured off. The membrane surface was washed with deionized water to remove the excess solution, and the membrane was dried with a wind knife. Then the membrane material was immersed in a 1.5 wt% polyethyleneimine solution for 1 h, and the unreacted solution on the surface of the membrane was washed off with a large amount of deionized water. The membrane was immersed in deionized water for standby.

[0049] The polyamide pervaporation composite membrane modified by dextran and polyethyleneimine on the polysulfone base membrane was tested. The separation factor of the membrane was 249.5 and the permeation flux was 2413.8 g·m -2 ·h -1 at 70 °C for the ethanol / water solution with a mass fraction of 85 wt%. Compared with the comparative example, the separation selectivity of the membrane was increased by 1 time and the permeation flux was slightly reduced.

[0050] Example 4

[0051] (1) The polyether sulfone base membrane was cut into a suitable size and then soaked in deionized water for 5 h to wet the pores and remove surface impurities. Then, the membrane was fixed by a self-made plate frame and the water on the surface of the membrane was blown off by a wind knife;

[0052] (2) The surface of the material obtained in step (1) was uniformly infiltrated with an ethylenediamine / water solution with a mass fraction of 1.5 wt%, and then placed for 5 min. The excess solution was poured out and the excess solution on the surface of the membrane was blown off by a wind knife so that there were no liquid drops on the surface of the membrane;

[0053] (3) The surface of the material obtained in step (2) was uniformly distributed with a terephthaloyl chloride / n-hexane solution with a mass fraction of 0.3 wt%, and then placed for 150 s. The excess solution was poured out and the excess solution on the surface of the membrane was blown off by a wind knife;

[0054] (4) The material obtained in step (3) was placed at 60 o C for 5 min to obtain a uniform and dense polyamide separation layer.

[0055] (5) The membrane of step (4) was fixed with a polymethyl methacrylate frame and a rubber sealing ring, and the four surrounding frames were clamped with a clamp to prevent the reaction solution from leaking out. A polyvinyl alcohol solution with a mass fraction of 1.0 wt% was uniformly coated on the surface of the membrane of step (4), and then placed for 30 min. The excess solution was poured out, the surface of the membrane was washed with deionized water to remove the excess solution, and then dried by a wind knife. Subsequently, the membrane was soaked in a glutaraldehyde solution with a mass fraction of 1.5 wt% at 70 o C for 1 h, and then taken out and washed with a large amount of deionized water to remove the unreacted solution on the surface. The membrane was soaked in deionized water for standby use.

[0056] The polyamide pervaporation composite membrane modified by polyvinyl alcohol and glutaraldehyde on the polyether sulfone base membrane was tested. The separation factor of the membrane was 396.3 and the permeation flux was 1956.8 g·m -2 ·h -1 at 70 °C for the ethanol / water solution with a mass fraction of 85 wt%.

[0057] Table 1 lists the main differences of the membrane preparation conditions between the comparative example and the examples 1-4, and Table 2 lists the pervaporation ethanol dehydration performances of the membrane materials prepared by the comparative example and the examples 1-4.

[0058] Table 1

[0059] Preparation device Substrate film material Aqueous phase monomer Oil phase monomer Hydrophilic modifying material / crosslinker Comparative example Rubber calender Post hydrolyzed polyacrylonitrile Polyethyleneimine Trimesoyl chloride No Example 1 Rubber calender - flat plate Polyacrylonitrile M-phenylenediamine Terephthaloyl chloride Sodium alginate / calcium chloride Example 2 Rubber calender - flat plate Post hydrolyzed polyacrylonitrile Polyethyleneimine Trimesoyl chloride Sodium alginate / calcium chloride Example 3 Flat plate - flat plate Polysulfone Diethylenetriamine 1,3,5-cyclohexanetricarbonyl chloride Dextran / polyethyleneimine Example 4 Flat plate - flat plate Polyethersulfone Ethylenediamine Terephthaloyl chloride Polyvinyl alcohol / glutaraldehyde

[0060] Table 2

[0061] Separation factor Flux (g.m -2 ·h -1 )]]> PSI (= J. (a - 1), x 10 5 , g. m -2 ·h -1 )]]> Comparative example 125.1 2574.1 3.2 Example 1 363.8 1986.2 7.2 Example 2 525.1 2087.9 10.9 Example 3 249.5 2413.8 6.0 Example 4 396.3 1956.8 7.7

[0062] As can be seen from the table, the separation factor of the hydrophilic modified polyamide pervaporation membrane is significantly improved due to the increase of the hydrophilicity of the active layer, at the same time, the increase of the thickness of the membrane layer increases the mass transfer resistance of water molecules, and the flux is reduced.

Claims

1. A method for preparing a hydrophilic modified polyamide pervaporation composite membrane, comprising the steps of: (1) treating a base membrane; (2) applying an aqueous solution of an amine monomer to the base membrane; (3) reacting an oil phase monomer with the amine monomer to form a polyamide layer; (4) heat treating the polyamide layer; and (5) applying a hydrophilic material to the polyamide layer to form a composite membrane. The steps (1)-(5) are carried out as follows: Step (1): cut the substrate membrane into appropriate size, soak in deionized water for 5-24 h, wet the pores, remove the surface impurities, then remove the surface deionized water; Step (2): fix the substrate membrane on a film applicator or a self-made frame, evenly distribute the aqueous solution of amine monomer with a mass fraction of 0.5-2.5 wt% on the surface of the substrate membrane, stand for 5-15 min, pour away the excess solution, and remove the unbound amine monomer on the membrane surface; Step (3): evenly distribute the oil phase monomer solution with a volume fraction of 0.1-0.5 w / v% on the surface of the membrane obtained in step (2), react for 200-600 s, pour away the excess solution, clean the unreacted monomer on the membrane surface with n-hexane, then remove the droplets on the membrane surface; Step (4): place the polyamide membrane layer obtained in step (3) in an oven at 40-100°C for 5-20 min to make the amine monomer and the oil phase monomer fully react; Step (5): evenly coat the hydrophilic material with a mass fraction of 0.5-2.5 wt% on the surface of the membrane obtained in step (4), soak for 10-50 min, pour away the excess solution, remove the excess solution on the membrane surface, so that there are no droplets on the membrane surface, then soak in the crosslinking agent solution with a mass fraction of 0.1-1.5 wt%, soak for 30-90 min, then take out and clean the excess solution on the membrane surface, and soak in deionized water for standby use; characterized in that The hydrophilic material in step (5) is a solution of sodium alginate or dextran, and the corresponding cross-linking agent is a solution of calcium chloride or polyethyleneimine, respectively.

2. The method of claim 1, wherein The base membrane in step (1) is a polysulfone, polyethersulfone, or polyacrylonitrile.

3. The method of claim 1, wherein The method for removing residual solution from the surface is spin-drying using centrifugal force or air knife drying.

4. The method of claim 1, wherein The amine monomer in step (2) is polyethyleneimine, diethylenetriamine, m-phenylenediamine, triethylenetetramine, or ethylenediamine.

5. The method of claim 1 wherein The oil phase monomer in step (3) is trimesoyl chloride, terephthaloyl chloride, 1,3,5-hexane tricarboxylic acid chloride, or cyclohexane tetracarboxylic acid chloride.

6. The polyamide pervaporation composite membrane with a hydrophilic layer prepared by the method of claim 1 can effectively solve the problems of poor hydrophilicity, poor resistance to pollution, and many defects of the polyamide membrane layer, and can prepare a pervaporation dehydration membrane with a hydrophilic surface and a hydrophobic interior, which promotes the rapid adsorption and desorption of water molecules on the membrane and improves the separation performance of the membrane.

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