Antifouling nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses an antifouling nanofiltration membrane and a preparation method and application thereof.The preparation method comprises the following steps that 1, a cross-linking agent and a catalyst are added into a poly (vinyl methyl ether-alt-maleic anhydride) solution, pre-crosslinking is conducted under the room temperature condition, and a pre-crosslinking solution is obtained; and 2, coating the surface of an ultrafiltration support membrane with the pre-crosslinking liquid, standing, removing the residual liquid on the surface of the membrane, and carrying out heat treatment on the membrane to obtain the poly (vinyl methyl ether-alt-maleic anhydride) composite nanofiltration membrane (namely the antifouling nanofiltration membrane) after the heat treatment is completed. Acid anhydride in poly (vinyl methyl ether-alt-maleic anhydride) and amine in the cross-linking agent are subjected to a nucleophilic substitution reaction to generate amide and carboxylic acid, the amide and the carboxylic acid form a cross-linked structure under the catalytic condition, ionic groups of methoxyl and carboxylic acid can enhance the hydrophilicity of the membrane, and therefore the prepared nanofiltration membrane has good antifouling performance.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration membranes, and in particular relates to an anti-fouling nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] Nanofiltration membrane has a microporous structure less than 2nm, and its molecular weight cutoff is in the range of 200-1000Da. It has good interception capacity for multivalent ions, sugars, and peptide molecules. It has been widely used in wastewater treatment, separation and concentration of organic matter, drug purification, pretreatment of seawater desalination, etc. It is an efficient, energy-saving, environmentally friendly and simple water treatment method. At present, the main preparation methods of nanofiltration membranes include interfacial polymerization, layer-by-layer self-assembly, coating-crosslinking, etc. Each method has its own characteristics in preparation and material selection. The interfacial polymerization method uses two monomers with high reaction activity (usually diamine and polyacyl chloride) to undergo polymerization reaction at two immiscible interfaces to form a dense polyester or polyamide layer, but this method requires the use of volatile organic solvents, and the membrane has poor chlorine resistance; layer-by-layer self-assembly is a method reported in recent years to prepare polyelectrolyte nanofiltration membranes, but due to the swelling of anionic and cationic polyelectrolytes bound by electrostatic forces in water, the membrane retention rate is low, and the preparation method has many steps and is time-consuming; the coating-crosslinking method is a simple process for preparing nanofiltration membranes. The structure and pore size of the membrane can be adjusted by adjusting the coating thickness and crosslinking degree. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing an anti-fouling nanofiltration membrane which has a simple preparation method and does not use an organic solvent in the preparation process of a composite separation layer.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows: A method for preparing an anti-fouling nanofiltration membrane comprises the following steps:

[0005] Step 1: adding a crosslinking agent and a catalyst to a poly(vinyl methyl ether-alt-maleic anhydride) solution, performing pre-crosslinking at room temperature, and obtaining a pre-crosslinking solution;

[0006] Step 2: Coat the surface of the ultrafiltration support membrane with the pre-crosslinking liquid, remove the residual liquid on the membrane surface after standing, and heat treat it. After the heat treatment is completed, a poly (vinyl methyl ether-alt-maleic anhydride) composite nanofiltration membrane is obtained. The prepared poly (vinyl methyl ether-alt-maleic anhydride) composite nanofiltration membrane is an anti-fouling nanofiltration membrane.

[0007] Step 1 in the above technical solution meets at least one of the following conditions a1-e1:

[0008] a1: the crosslinking agent is one of an aminosilane coupling agent, a phenylenediamine crosslinking agent and a branched polyethyleneimine crosslinking agent;

[0009] b1: the catalyst is one of concentrated sulfuric acid, p-toluenesulfonic acid and triethylamine;

[0010] c1: the mass fraction ratio of the poly(vinyl methyl ether-alt-maleic anhydride) to the crosslinking agent is 1:1-20;

[0011] d1: the content of the catalyst in the pre-crosslinking liquid is 0.1-1.2wt%;

[0012] e1: The duration of the pre-crosslinking is 10 min-120 min.

[0013] The model of the aminosilane coupling agent in the above technical solution is KH540, KH550, KH902, KH170, KH602, KH792, NQ62 or KH892.

[0014] The phenylenediamine cross-linking agent in the above technical solution is m-phenylenediamine, p-phenylenediamine or phenylenediamine sulfonic acid.

[0015] The model of the branched polyethyleneimine cross-linking agent in the above technical solution is PEI300, PEI600, PEI1800, PEI10000 or PEI70000.

[0016] In the step 1 of the above technical solution, the poly(vinyl methyl ether-alt-maleic anhydride) solution is an aqueous solution of poly(vinyl methyl ether-alt-maleic anhydride), and the concentration of the poly(vinyl methyl ether-alt-maleic anhydride) solution is 0.01-0.2 wt %.

[0017] Step 1 in the above technical solution meets at least one of the following conditions a2-d2:

[0018] a2: The ultrafiltration support membrane is one of a polysulfone membrane, a polyethersulfone membrane or a polyacrylonitrile membrane;

[0019] b2: The molecular weight cut-off of the ultrafiltration support membrane is within 70KDa;

[0020] c2: After the pre-crosslinking liquid is coated, the standing time on the surface of the ultrafiltration support membrane is 10-90 minutes;

[0021] d2: The heat treatment temperature is 40-120°C, and the heat treatment time is 10-40min.

[0022] The anti-fouling nanofiltration membrane in the above technical solution has a molecular weight cutoff of 200-2000Da.

[0023] The second object of the present invention is to provide an antifouling nanofiltration membrane which is prepared by the preparation method as described above and has good hydrophilicity and good antifouling performance.

[0024] A third object of the present invention is to provide an antifouling nanofiltration membrane as described above for use in wastewater treatment, separation and concentration of organic matter, drug purification or seawater desalination.

[0025] The beneficial effects of the present invention are as follows: (1) The present invention uses the anhydride in poly(vinyl methyl ether-alt-maleic anhydride) and the amine in the cross-linking agent to undergo a nucleophilic substitution reaction to generate amide and carboxylic acid, which form a cross-linked structure under catalytic conditions, wherein the methoxyl group and the ionic group of the carboxylic acid can enhance the hydrophilicity of the membrane, thereby making the prepared nanofiltration membrane have better antifouling performance;

[0026] (2) The anti-fouling nanofiltration membrane provided by the present invention does not use organic solvents during preparation, and the pollution during preparation is small;

[0027] (3) The performance of the antifouling nanofiltration membrane provided by the present invention can be adjusted by adjusting parameters such as reaction time, concentrations of two reaction monomers, and acid concentration. DETAILED DESCRIPTION

[0028] The principles and features of the present invention are described below in conjunction with the embodiments, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. The present invention is described more specifically by way of example with reference to the embodiments in the following paragraphs. According to the following description and the claims, the advantages and features of the present invention will be more clearly described.

[0029] This embodiment provides a method for preparing an anti-fouling nanofiltration membrane, comprising the following steps:

[0030] Step 1: adding a crosslinking agent and a catalyst to a poly(vinyl methyl ether-alt-maleic anhydride) solution, performing pre-crosslinking at room temperature, and obtaining a pre-crosslinking solution;

[0031] Step 2: Coat the surface of the ultrafiltration support membrane with the pre-crosslinking liquid, remove the residual liquid on the membrane surface after standing, and heat treat it. After the heat treatment is completed, a poly (vinyl methyl ether-alt-maleic anhydride) composite nanofiltration membrane is obtained. The prepared poly (vinyl methyl ether-alt-maleic anhydride) composite nanofiltration membrane is an anti-fouling nanofiltration membrane.

[0032] Step 1 in the above technical solution meets at least one of the following conditions a1-e1:

[0033] a1: the crosslinking agent is one of an aminosilane coupling agent, a phenylenediamine crosslinking agent and a branched polyethyleneimine crosslinking agent (specifically, the aminosilane crosslinking agent is of type KH540, KH550, KH902, KH170, KH602, KH792, NQ62 or KH892; the phenylenediamine crosslinking agent is m-phenylenediamine, p-phenylenediamine or diaminobenzenesulfonic acid; the branched polyethyleneimine crosslinking agent is of type PEI300, PEI600, PEI1800, PEI10000 or PEI70000);

[0034] b1: the catalyst is one of concentrated sulfuric acid, p-toluenesulfonic acid and triethylamine;

[0035] c1: the mass fraction ratio of the poly(vinyl methyl ether-alt-maleic anhydride) to the crosslinking agent is 1:1-20;

[0036] d1: the content of the catalyst in the pre-crosslinking liquid is 0.1-1.2wt% (can be any value among 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt% and 1.2wt% or the range corresponding to any two values);

[0037] e1: The duration of the pre-crosslinking is 10 min-120 min (it can be any value among 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min and 120 min, or a range corresponding to any two values).

[0038] In the step 1 of the technical scheme, the poly(vinyl methyl ether-alt-maleic anhydride) solution is an aqueous solution of poly(vinyl methyl ether-alt-maleic anhydride); the concentration of the poly(vinyl methyl ether-alt-maleic anhydride) solution is 0.01-0.2wt% (it can be any value among 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.18wt% and 0.2wt% or the corresponding range between any two values).

[0039] Step 1 in the above technical solution meets at least one of the following conditions a2-d2:

[0040] a2: The ultrafiltration support membrane is one of a polysulfone membrane, a polyethersulfone membrane or a polyacrylonitrile membrane;

[0041] b2: The molecular weight cutoff of the ultrafiltration support membrane is within 70 KDa (specifically, it may be within 1 KDa, within 10 KDa, within 20 KDa, within 30 KDa, within 40 KDa, within 50 KDa, within 60 KDa or within 70 KDa);

[0042] c2: the standing time of the pre-crosslinking liquid on the surface of the ultrafiltration support membrane after coating is 10-90 min (any value among 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min and 90 min or the corresponding range between any two values);

[0043] d2: The heat treatment temperature is 40-120°C (any value among 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C and 120°C, or a range corresponding to any two values), and the heat treatment time is 10-40min (any value among 10min, 15min, 20min, 25min, 30min, 35min and 40min, or a range corresponding to any two values).

[0044] The molecular weight cutoff of the anti-fouling nanofiltration membrane described in the above technical scheme is 200-2000Da (any value among 200Da, 300Da, 400Da, 500Da, 600Da, 700Da, 800Da, 900Da, 1000Da, 1100Da, 1200Da, 1300Da, 1400Da, 1500Da, 1600Da, 1700Da, 1800Da, 1900Da and 2000Da, or the corresponding range between any two values).

[0045] Example 1

[0046] The present embodiment provides a method for preparing an antifouling nanofiltration membrane, the steps of which are as follows: adding a crosslinking agent (KH550 aminosilane coupling agent) to an aqueous solution of poly(vinyl methyl ether-alt-maleic anhydride) with a concentration of 0.01wt% to obtain a mixed solution 1, wherein the concentration of the crosslinking agent in the mixed solution 1 is 0.1wt%, adding a catalyst (sulfuric acid) to the mixed solution 1 to obtain a mixed solution 2, wherein the concentration of sulfuric acid in the mixed solution 2 is 0.8wt%, and reacting the mixed solution 2 at room temperature for 50min to obtain a pre-crosslinked solution;

[0047] The ultrafiltration support membrane [prepared by phase inversion method of 16 wt% polyethersulfone DMAc (dimethylacetamide) solution] was soaked in the pre-crosslinking liquid for 40 minutes, then taken out and the residual liquid on the surface of the membrane was drained, and the membrane was placed in an oven at 80°C and heated for 15 minutes. The obtained membrane was the antifouling nanofiltration membrane.

[0048] The antifouling nanofiltration membrane was taken out and stored in deionized water for later use. Its retention performance was tested in a homemade cross-flow device using a 0.2 g / L PEG200 solution. At 25 °C, the membrane flux was 13 L / (m 2 hbar), the retention rate of PEG200 is about 70%. According to the contact angle test results, the contact angle of the prepared membrane is 50°, and the membrane antifouling performance is tested using 0.5g / L BSA (bovine serum albumin) solution. After 24h of pollution test, the pure water normalized flux of the membrane is about 0.8.

[0049] Example 2

[0050] Same as Example 1, except that the concentration of the poly(vinyl methyl ether-alt-maleic anhydride) aqueous solution is 0.05 wt %, the concentration of the crosslinking agent in the mixed solution 1 is 0.5 wt %, and the mixed solution 2 is reacted at room temperature for 50 min to obtain a pre-crosslinked solution;

[0051] After the membrane was drained, it was placed in an oven at 100°C for 25 min;

[0052] The membrane flux was measured to be 8 L / (m 2 hbar), and the rejection rate of PEG200 was about 90%. The membrane was tested for antifouling performance using 0.5 g / L BSA (bovine serum albumin) solution. After 24 hours of fouling test, the normalized flux of the membrane was about 0.95.

[0053] Example 3

[0054] Same as Example 2, except that the concentration of the poly(vinyl methyl ether-alt-maleic anhydride) aqueous solution is 0.1wt%, the concentration of the crosslinking agent (m-phenylenediamine) in the first mixed solution is 0.1wt%, the catalyst is triethylamine, and the concentration of the catalyst in the second mixed solution is 0.25wt%, and the second mixed solution is reacted at room temperature for 20min to obtain a pre-crosslinked solution;

[0055] The membrane flux was measured to be 9 L / (m 2 hbar), the rejection rate of PEG200 is about 45%. The membrane antifouling performance is tested using 0.5g / L BSA (bovine serum albumin) solution. After 24h of fouling test, the normalized flux of pure water of the membrane is about 0.96.

[0056] Example 4

[0057] Same as Example 2, except that the concentration of the poly(vinyl methyl ether-alt-maleic anhydride) aqueous solution is 0.2wt%, the concentration of the crosslinking agent (polyethyleneimine with a model number of PEI600) in the first mixed solution is 0.25wt%, and the concentration of sulfuric acid in the second mixed solution is 0.25wt%;

[0058] The membrane flux was measured to be 8 L / (m 2 hbar), and the rejection rate of PEG200 was about 90%. The membrane was tested for antifouling performance using 0.5 g / L BSA (bovine serum albumin) solution. After 24 hours of fouling test, the pure water normalized flux of the membrane was about 0.90.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an antifouling nanofiltration membrane, characterized in that: The steps include: Step 1: adding a crosslinking agent and a catalyst to a poly(vinyl methyl ether-alt-maleic anhydride) solution, performing pre-crosslinking at room temperature, and obtaining a pre-crosslinking solution; Step 2: Coat the surface of the ultrafiltration support membrane with the pre-crosslinking liquid, remove the residual liquid on the membrane surface after standing, and heat treat it. After the heat treatment is completed, a poly (vinyl methyl ether-alt-maleic anhydride) composite nanofiltration membrane is obtained. The prepared poly (vinyl methyl ether-alt-maleic anhydride) composite nanofiltration membrane is an anti-fouling nanofiltration membrane.

2. The method for preparing the antifouling nanofiltration membrane according to claim 1, characterized in that: In step 1, at least one of the following conditions a1-e1 is met: a1: the crosslinking agent is one of an aminosilane coupling agent, a phenylenediamine crosslinking agent and a branched polyethyleneimine; b1: the catalyst is one of concentrated sulfuric acid, p-toluenesulfonic acid and triethylamine; c1: the mass fraction ratio of the poly(vinyl methyl ether-alt-maleic anhydride) to the crosslinking agent is 1:1-20; d1: the content of the catalyst in the pre-crosslinking liquid is 0.1-1.2wt%; e1: The duration of the pre-crosslinking is 10 min-120 min.

3. The method for preparing the antifouling nanofiltration membrane according to claim 2, characterized in that: The model of the aminosilane coupling agent is KH540, KH550, KH902, KH170, KH602, KH792, NQ62 or KH892.

4. The method for preparing the antifouling nanofiltration membrane according to claim 2, characterized in that: The phenylenediamine cross-linking agent is m-phenylenediamine, p-phenylenediamine or phenylenediamine sulfonic acid.

5. The method for preparing the antifouling nanofiltration membrane according to claim 2, characterized in that: The model of the branched polyethyleneimine is PEI 300, PEI 600, PEI 1800, PEI 10000 or PEI 70000.

6. The method for preparing the antifouling nanofiltration membrane according to claim 1, characterized in that: The poly(vinyl methyl ether-alt-maleic anhydride) solution in step 1 is an aqueous solution of poly(vinyl methyl ether-alt-maleic anhydride), and the concentration of the poly(vinyl methyl ether-alt-maleic anhydride) solution is 0.01-0.2 wt %.

7. The method for preparing the antifouling nanofiltration membrane according to claim 1, characterized in that: In step 1, at least one of the following conditions a2-d2 is met: a2: The ultrafiltration support membrane is one of a polysulfone membrane, a polyethersulfone membrane or a polyacrylonitrile membrane; b2: The molecular weight cut-off of the ultrafiltration support membrane is within 70KDa; c2: After the pre-crosslinking liquid is coated, the standing time on the surface of the ultrafiltration support membrane is 10-90 minutes; d2: The heat treatment temperature is 40-120°C, and the heat treatment time is 10-40min.

8. The method for preparing the antifouling nanofiltration membrane according to claim 1, characterized in that: The antifouling nanofiltration membrane has a molecular weight cutoff of 200-2000Da.

9. An antifouling nanofiltration membrane, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. An application of the antifouling nanofiltration membrane according to claim 9, characterized in that: Used in wastewater treatment, separation and concentration of organic matter, drug purification or seawater desalination.