CN116020263A - Nanofiltration membrane chlorine resistance and pollution resistance strengthening modification method based on ring-opening reaction - Google Patents
Nanofiltration membrane chlorine resistance and pollution resistance strengthening modification method based on ring-opening reaction Download PDFInfo
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Abstract
The invention discloses a nanofiltration membrane with high flux, low pressure and high selectivity, in particular to a method for strengthening and modifying chlorine resistance and pollution resistance of the nanofiltration membrane based on ring-opening reaction. The preparation method comprises the steps of dissolving a multi-element epoxy compound into an alcohol-water mixed solvent to serve as a modified solution A, preparing a dehydration catalyst and an aqueous solution of a carboxyl phosphate compound to serve as a modified solution B, immersing a nanofiltration membrane into the modified solution A and the modified solution B in sequence, and finally drying. The invention has the advantages that the surface of the polyamide nanofiltration membrane is modified by adopting a two-step method of a multi-element epoxy compound and a carboxyl phosphate compound, so that the defect of poor chlorine resistance of the polyamide nanofiltration membrane can be effectively improved, the hydrophilicity of the membrane is obviously improved, the precise control of the chemical properties of the membrane performance is realized, and the method is stable, reliable and easy to realize.
Description
Technical Field
The invention relates to a nanofiltration membrane with high flux, low pressure and high selectivity, in particular to a method for strengthening and modifying chlorine resistance and pollution resistance of the nanofiltration membrane based on ring-opening reaction.
Background
Can be widely applied in the fields of sea water desalination, brackish water desalination, pharmacy, biology and the like. However, the mainstream nanofiltration membrane at present adopts polyamide materials, and the problems of chemical oxidative degradation and membrane pollution generally exist, namely, active chlorine oxidant residues added into feed liquid in a real treatment process have a destructive effect on the polyamide membrane materials, and pollutants gradually accumulate on the surface of the membrane, so that the service life of the polyamide membrane is seriously influenced. The prior researches mainly strengthen the chlorine resistance and the pollution resistance of the polyamide membrane by adjusting the molecular chain chemical structure of the polyamide and chemically grafting or coating a protective layer on the surface of the membrane, and the method has two main problems: firstly, the surface modification increases the membrane resistance to a certain extent, and reduces the membrane separation performance; and most of the membrane chlorine resistance is not reversible, namely, the modified membrane cannot be regenerated after the chlorine resistance is saturated.
Aiming at the existing problems, researchers propose to remove active chlorallergic amino groups on the surface of the membrane by adopting a chemical modification method so that the chlorallergic amino groups cannot react with active chlorine of a water body, and then carry out chemical bridging with a physical coating layer to realize the surface modification of the hydrophilized membrane. The method can improve the oxidation resistance of the membrane material, can reduce the coating amount requirement of the protective layer, relieve the adverse effect of the additional resistance of the coating layer on the membrane permeability, can improve the interaction force between the protective layer material and the membrane surface, and relieve the loss problem of the protective layer in the long-term operation process, and the modified nanofiltration membrane material has good pollution resistance and chlorine oxidation resistance.
Aiming at the problems that the polyamide nanofiltration membrane material is easy to lose effectiveness by active chlorine oxidation and the membrane surface is easy to pollute in the using process, the invention provides a novel process for modifying and modifying the surface of the polyamide nanofiltration membrane, and adopts a two-step method of a multi-element epoxy compound and a carboxyl phosphoric acid compound to integrate the antioxidation and hydrophilization modification process into a set of process, thereby not only removing chlorine-sensitive secondary amine groups on the membrane surface, but also introducing anti-pollution functional groups, and the modified nanofiltration membrane has good pollution resistance and chlorine (oxygen) resistance. The method has simple operation and stable process, has good compatibility with the existing nanofiltration membrane manufacturing process, and is easy to produce and amplify.
Disclosure of Invention
Aiming at the problems that the polyamide nanofiltration membrane material is easy to lose effectiveness by active chlorine oxidation and the membrane surface is easy to pollute in the using process, the invention provides a two-step modification process, which not only removes chlorine-sensitive secondary amine groups on the membrane surface, but also introduces anti-pollution functional groups, and the modified nanofiltration membrane has good pollution resistance and chlorine (oxygen) resistance. In order to achieve the above purpose, the technical scheme of the invention is as follows:
the method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction is characterized by comprising the following steps:
(1) Dissolving a multi-element epoxy compound into an alcohol-water mixed solvent to be used as a modified solution A, wherein the mass percentage of the alcohol in the alcohol-water mixed solvent is 50-80%, and the mass percentage of the multi-element epoxy compound in the modified solution A is 0.5-2%; wherein the alcohol solvent is one of methanol, ethanol, ethylene glycol, isopropanol or propylene glycol; the multi-element epoxy compound is one of glycerol tri (1, 2-epoxy) propyl ether, di (2-epoxy propyl) ether, ethylene glycol diglycidyl ether, pentaerythritol diglycidyl ether, resorcinol diglycidyl ether, polyethylene glycol diglycidyl ether or trimethylolpropane triglycidyl ether;
preparing a dehydration catalyst with the mass percentage of 1-5% and an aqueous solution of a carboxyl phosphoric acid compound with the mass percentage of 0.5-2% as a modified solution B; wherein the dehydration catalyst is one of sodium acetate, sodium benzoate, ammonium benzoate or sulfuric acid, and the carboxyl phosphoric acid compound is one of 2-carboxyethyl phosphoric acid, 2-carboxyphenyl phosphoric acid, 3-carboxyphenyl phosphoric acid or 4-carboxyphenyl phosphoric acid;
preferably, the mass percentage of the alcohol in the alcohol-water mixed solvent is 60-75%; the mass percentage of the multi-element epoxy compound is 0.8-1.5%. Wherein the mass percentage of the dehydration catalyst is 2-4%; the mass percentage of the carboxyl phosphate compound is 0.8-1.5%.
(2) Immersing the nanofiltration membrane in the modified solution A at 40-60 ℃ for 5-30 minutes, and removing redundant solution; immersing the mixture into the modified solution B for 3 minutes, taking out the mixture to remove redundant solution, and then sending the mixture into a baking oven at 100-130 ℃ for heat treatment for 5-10 minutes. Preferably, wherein the temperature of the modifying solution A is controlled to be 45-55 ℃; the soaking time is 10-20 minutes. The heat treatment temperature of the film in the oven is 110-120 ℃; the heat treatment time in the oven is 6-8 minutes.
Preferably, the nanofiltration membrane in the ring-opening reaction-based nanofiltration membrane chlorine resistance and pollution resistance strengthening modification method is prepared by the following steps:
(1) Soaking an ultrafiltration base membrane in NaOH solution with pH value of 9-10 for 12 hours, cleaning in 30% isopropanol water solution for 12 hours, and then placing clean water for washing for later use, wherein the ultrafiltration membrane material is one of polyethylene, polypropylene, polysulfone, polyethersulfone, polyacrylonitrile or polyvinylidene fluoride; preferably, the ultrafiltration base membrane has a molecular weight cut-off of 40000-60000;
(2) Preparing a polyamine aqueous phase solution with the mass percentage of 0.2% -2%, wherein a polyamine monomer is one of piperazine, 2-piperazinone, piperazine-2-formic acid, ethylenediamine or 1, 4-cyclohexanediamine; preferably, the mass percentage of the polyamine monomer is 0.5% -1.5%; the mass percentage of the polybasic acyl chloride monomer is 0.2-0.4%;
preparing 0.01-0.5% of polybasic acyl chloride organic phase solution by mass percent, wherein the polybasic acyl chloride is one of isophthaloyl dichloride, 1, 4-cyclohexanediyl chloride, succinyl chloride, biphenyl diacetyl chloride, 4' -oxydi (benzoyl chloride) or trimesic acid chloride, and the organic phase solvent is one of pentane, hexane, cyclohexane or heptane;
(3) Placing the ultrafiltration base membrane into the aqueous phase solution for 1-5 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 1-5 minutes, taking out, and then sending the membrane into an oven at 80-120 ℃ for heat treatment for 5-20 minutes. Preferably, the heat treatment temperature is 90-100 ℃ and the heat treatment time is 10-15 minutes.
Compared with the prior nanofiltration membrane modification technology, the invention has the beneficial effects that:
the invention provides a new process for modifying and modifying the surface of a polyamide nanofiltration membrane, which integrates the antioxidation and hydrophilization modification processes into a set of process by adopting a two-step method of a multi-element epoxy compound and a carboxyl phosphoric acid compound. The principle of the invention is based on the fact that secondary amine (-NH-) and carboxyl (-COOH) simultaneously exist on the surface of the existing polyamide nanofiltration membrane, and the principle that epoxy groups can react with the secondary amine and the carboxyl simultaneously is utilized. Firstly, utilizing ring-opening reaction of epoxy groups in a multi-epoxy compound and residual secondary amine on the surface of a nanofiltration membrane to convert secondary amine groups which are easy to be attacked by active chlorine oxidation into stable tertiary amine groups, and strengthening the chlorine resistance of the polyamide nanofiltration membrane; simultaneously, the epoxy groups and residual carboxyl groups on the surface of the nanofiltration membrane are subjected to dehydration esterification reaction, so that a large number of active epoxy groups are introduced on the surface of the nanofiltration membrane; finally, the carboxyl phosphate compound is adopted to further carry out esterification reaction with epoxy groups on the surface of the membrane, a large number of phosphate groups with strong hydrophilicity are introduced on the surface of the nanofiltration membrane, and the hydrophilicity and pollution resistance of the surface of the membrane are obviously enhanced. In particular, in order to improve the reaction rate of the epoxy group and the secondary amine, an alcohol solvent and high temperature method is adopted, and in order to improve the esterification reaction rate of the epoxy group and the carboxyl, a dehydration catalyst is added, so that the method ensures that the modification reaction speed is high and the efficiency is high.
Compared with the prior patent (CN 202111457227.5, CN 202111457011.9) that the epoxy resin is adopted to chemically modify the polyolefin ultrafiltration base membrane, the patent adopts the epoxy compound to modify the polyamide nanofiltration separation layer, and the direct reaction area and the related reaction type of the polyamide nanofiltration separation layer are different. Compared with the prior art (CN 202111531135.7), the method has the advantages that the reverse osmosis membrane is firstly treated by adopting polyethylenimine, then epoxy propanol is used for reacting with amino in polyethylenimine, the pollution resistance of the membrane is improved by introducing hydroxyl, the surface of the polyamide membrane is firstly modified by adopting a multi-element epoxy compound, the secondary amine which is easy to oxidize in the membrane material structure is effectively eliminated to improve the chlorine resistance of the membrane, and then the carboxyl phosphate compound is used for modifying, the pollution resistance is improved by introducing a phosphate group with stronger hydrophilicity, and the reaction area and the related hydrophilic group are different. Compared with the prior patent (CN201811096789. X), the method adopts 2, 3-epoxypropane sodium sulfonate to modify the surface of the membrane in one step, and the patent adopts a two-step modification method (namely, firstly grafting a multi-epoxy compound and then grafting a carboxyl phosphoric acid compound), so that the controllable adjustment of the grafting density of the hydrophilic groups on the surface can be realized, and the adopted modification implementation method is different from the grafted hydrophilic groups. Compared with the prior patent (CN 201711155528.6) that the hydroxyl in the polybasic epoxy compound and the polyvinyl alcohol macromolecule are subjected to etherification reaction, the carboxyl in the polybasic epoxy compound and the carboxyl phosphate compound are subjected to esterification reaction, the reaction type and reaction condition are different, and in addition, the modified compound is small molecules, so that the problem of excessive reduction of membrane flux caused by modification of the membrane by adopting high molecular polymers (such as polyethyleneimine and polyvinyl alcohol) is avoided.
In a word, this patent adopts "polybasic epoxy compound + carboxyl phosphoric acid compound" two-step method modified polyamide nanofiltration membrane surface, both can effectively improve polyamide nanofiltration membrane chlorine resistance poor defect, show the hydrophilicity of improvement membrane simultaneously, realized the accurate control of the chemical nature of membrane performance, reliable and stable and easy realization.
The specific embodiment is as follows:
the present invention will be described in more detail below with reference to specific embodiments, however, the present invention is not limited to the following embodiments, but may be other embodiments in which some elements are replaced with equivalents.
The method for testing the flux and the desalination rate of the nanofiltration membrane is as follows:
the prepared nanofiltration membrane was pre-pressed with an electrolyte aqueous solution of 0.2% (mass percent) magnesium sulfate for half an hour under 0.48MPa, and the desalination performance and water flux of the nanofiltration membrane were tested.
In the membrane separation test process, 1) humic acid (common pollutants in water) is adopted as a typical pollutant, 0.2 percent (mass percent) of humic acid is added into a magnesium sulfate standard test solution and continuously runs for 12 hours, the change of membrane flux is inspected, the blocking degree of the pollutants on the surface of the membrane is verified, and the pollution resistance of the membrane is evaluated; 2) Sodium hypochlorite (common oxidant in water) is adopted as a typical oxidant, 0.05 percent (mass percent) of sodium hypochlorite is added into a magnesium sulfate standard test solution and the operation is continued for 12 hours, the change of the desalination rate of the membrane is inspected, and the compact integrity of the nanofiltration separation layer is verified, so that the chloridizing resistance of the membrane is evaluated. As a control, parallel tests were performed with unmodified nanofiltration membranes.
The water flux was calculated as follows:
wherein A is the effective membrane area, and the unit is m 2 The method comprises the steps of carrying out a first treatment on the surface of the t-time required by collecting Q volume of liquid, wherein the unit is h; q-the volume of product fluid collected over time t, in L.
The method for calculating the desalination of the membrane is as follows (2):
wherein, the desalination rate of the R-film, C f -conductivity of the stock solution in μs/cm; c (C) p The conductivity of the produced water in μS/cm.
Example 1
1) Adopting a polyethylene ultrafiltration base membrane (with the molecular weight cut-off of approximately 30000), soaking for 12 hours by using NaOH solution with the pH value of 9-10, cleaning for 12 hours by using 30% isopropanol water solution, and then placing into clear water for washing for standby;
2) Preparing a piperazine aqueous phase solution with the mass percentage of 0.2 percent and an isophthaloyl dichloride organic phase pentane solution with the mass percentage of 0.1 percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 1 minute, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 1 minute, taking out, sending the membrane into an 80 ℃ oven for heat treatment for 5 minutes, and placing the prepared nanofiltration membrane into pure water for later use.
4) The modified solution A was prepared by dissolving 0.5% by mass of tri (1, 2-epoxypropyl) glycerol in a methanol-water mixed solvent (50% by mass of an alcohol solvent). Preparing sodium acetate with the mass percentage of 1% and 2-carboxyethyl phosphoric acid with the mass percentage of 0.5% as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 5 minutes (the solution is preheated to 40 ℃), and extruding the nanofiltration membrane by using a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 100 ℃ oven for heat treatment for 5 minutes, taking out, and then putting into pure water for measurement.
Example 2
1) Adopting a polypropylene ultrafiltration base membrane (the molecular weight cut-off is approximately equal to 80000), soaking the membrane in NaOH solution with pH value of 9-10 for 12 hours, cleaning the membrane in 30% isopropanol water solution for 12 hours, and then placing the membrane in clear water for washing for standby;
2) Preparing 2% of 2-piperazinone aqueous phase solution by mass percent and 0.5% of 1, 4-cyclohexanedicarboxylic acid chloride organic phase hexane solution by mass percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 5 minutes, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 5 minutes, taking out, sending the membrane into a 120 ℃ oven for heat treatment for 20 minutes, and placing the prepared nanofiltration membrane into pure water for standby.
4) 2% by mass of bis (2-epoxypropyl) ether was dissolved in an ethanol-water mixed solvent (80% by mass of an alcohol solvent) as a modified solution A. Preparing sodium benzoate with the mass percentage of 1 percent and 2.0 percent of 2-carboxyphenyl phosphoric acid as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 30 minutes (the solution is preheated to 60 ℃), and extruding the nanofiltration membrane by using a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 130 ℃ oven for heat treatment for 10 minutes, taking out, and then putting into pure water for measurement.
Example 3
1) Soaking polysulfone ultrafiltration base membrane (with molecular weight cut-off of about 40000) in NaOH solution with pH=9-10 for 12 hr, washing with 30% isopropanol water solution for 12 hr, and washing with clear water;
2) Preparing a piperazine-2-formic acid aqueous phase solution with the mass percentage of 0.5 percent and preparing a succinyl chloride organic phase cyclohexane solution with the mass percentage of 0.2 percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 2 minutes, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 2 minutes, taking out, sending the membrane into a 90 ℃ oven for heat treatment for 10 minutes, and placing the prepared nanofiltration membrane into pure water for later use.
4) The ethylene glycol diglycidyl ether of 0.8 mass% was dissolved in an ethylene glycol-water mixed solvent (alcohol solvent of 60 mass%) as a modified solution a. Preparing ammonium benzoate with the mass percentage of 1 percent and 3-carboxyphenyl phosphoric acid with the mass percentage of 0.8 percent as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 10 minutes (the solution is preheated to 45 ℃) and extruding the solution by a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 110 ℃ oven for heat treatment for 6 minutes, taking out, and then putting into pure water for measurement.
Example 4
1) Adopting a polyethersulfone ultrafiltration membrane (with the molecular weight cut-off of about 60000), soaking for 12 hours by using NaOH solution with the pH value of about 9-10, cleaning for 12 hours by using 30% isopropanol water solution, and then placing into clear water for washing for standby;
2) Preparing an ethylenediamine aqueous phase solution with the mass percentage of 1.5 percent and a biphenyl diacetyl chloride organic phase heptane solution with the mass percentage of 0.4 percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 3 minutes, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 3 minutes, taking out, sending the membrane into a 100 ℃ oven for heat treatment for 15 minutes, and placing the prepared nanofiltration membrane into pure water for later use.
4) Pentaerythritol glycidyl ether with a mass percentage of 1.5% was dissolved in an isopropyl alcohol-water mixed solvent (alcohol solvent mass percentage of 75%) as a modifying solution a. Preparing sulfuric acid with the mass percentage of 1 percent and 4-carboxyphenyl phosphoric acid with the mass percentage of 1.5 percent as a modified solution B
5) Immersing the nanofiltration membrane into the modified solution A for 20 minutes (the solution is preheated to 55 ℃), and extruding the solution by using a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 120 ℃ oven for heat treatment for 8 minutes, taking out, and then putting into pure water for measurement.
Example 5
1) Adopting a polyacrylonitrile ultrafiltration base membrane (the molecular weight cut-off is approximately equal to 50000), soaking the membrane in NaOH solution with pH value of 9-10 for 12 hours, cleaning the membrane in 30% isopropanol water solution for 12 hours, and then placing the membrane in clear water for washing for standby;
2) Preparing 1.0% of 1, 4-cyclohexanediamine aqueous phase solution by mass percent and preparing 0.3% of 4,4' -oxybis (benzoyl chloride) organic phase pentane solution by mass percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 4 minutes, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 4 minutes, taking out, sending the membrane into a 90 ℃ oven for heat treatment for 10 minutes, and placing the prepared nanofiltration membrane into pure water for later use.
4) Resorcinol diglycidyl ether of 0.5 mass% was dissolved in a propylene glycol-water mixed solvent (alcohol solvent of 60 mass%) as a modifying solution a. Preparing sodium acetate with the mass percentage of 1% and 2-carboxyethyl phosphoric acid with the mass percentage of 0.8% as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 10 minutes (the solution is preheated to 45 ℃) and extruding the solution by a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 110 ℃ oven for heat treatment for 6 minutes, taking out, and then putting into pure water for measurement.
Example 6
1) Adopting a polyethylene ultrafiltration base membrane (with the molecular weight cut-off of about 70000), soaking the membrane in a NaOH solution with the pH value of about 9-10 for 12 hours, cleaning the membrane in a 30% isopropanol water solution for 12 hours, and then placing the membrane in clear water for washing for later use;
2) Preparing a piperazine aqueous phase solution with the mass percent of 0.5 percent and a trimesoyl chloride organic phase hexane solution with the mass percent of 0.01 percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 1 minute, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 1 minute, taking out, sending the membrane into a 95 ℃ oven for heat treatment for 15 minutes, and placing the prepared nanofiltration membrane into pure water for later use.
4) The polyethylene glycol diglycidyl ether with the mass percentage of 0.8% is dissolved into the mixed solvent of methanol and water (the mass percentage of the alcohol solvent is 65%) to be used as the modifying solution A. Preparing sodium benzoate with the mass percentage of 1 percent and 2-carboxyphenyl phosphoric acid with the mass percentage of 1.0 percent as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 15 minutes (the solution is preheated to 50 ℃), and extruding the nanofiltration membrane by using a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 115 ℃ oven for heat treatment for 7 minutes, taking out, and then putting into pure water for measurement.
Example 7
1) Adopting a polypropylene ultrafiltration base membrane (the molecular weight cut-off is approximately equal to 40000), soaking the membrane in NaOH solution with pH value of 9-10 for 12 hours, cleaning the membrane in 30% isopropanol water solution for 12 hours, and then placing the membrane in clear water for washing for standby;
2) Preparing 1.0% of 2-piperazinone aqueous phase solution by mass percent and preparing 0.5% of isophthaloyl dichloride organic phase cyclohexane solution by mass percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 2 minutes, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 2 minutes, taking out, sending the membrane into a 100 ℃ oven for heat treatment for 10 minutes, and placing the prepared nanofiltration membrane into pure water for later use.
4) Trimethylolpropane triglycidyl ether of 1.0% by mass was dissolved in an ethanol-water mixed solvent (70% by mass of an alcohol solvent) as a modified solution a. Preparing ammonium benzoate with the mass percentage of 1 percent and 3-carboxyphenyl phosphoric acid with the mass percentage of 1.2 percent as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 20 minutes (the solution is preheated to 55 ℃), and extruding the solution by using a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 120 ℃ oven for heat treatment for 8 minutes, taking out, and then putting into pure water for measurement.
Example 8
1) Soaking polysulfone ultrafiltration base membrane (with molecular weight cutoff of about 50000) in NaOH solution with pH=9-10 for 12 hr, washing with 30% isopropanol water solution for 12 hr, and washing with clear water;
2) Preparing a 1.2% piperazine-2-carboxylic acid aqueous phase solution by mass percent and a 0.2%1, 4-cyclohexanedicarboxylic acid chloride organic phase heptane solution by mass percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 3 minutes, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 3 minutes, taking out, sending the membrane into a 90 ℃ oven for heat treatment for 15 minutes, and placing the prepared nanofiltration membrane into pure water for later use.
4) The modified solution A was prepared by dissolving 0.5% by mass of tri (1, 2-epoxypropyl) glycerol in a glycol-water mixed solvent (75% by mass of an alcohol solvent). Preparing sulfuric acid with the mass percentage of 1% and 4-carboxyphenyl phosphoric acid with the mass percentage of 0.5% as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 10 minutes (the solution is preheated to 45 ℃) and extruding the solution by a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 110 ℃ oven for heat treatment for 6 minutes, taking out, and then putting into pure water for measurement.
Example 9
1) Adopting a polyethersulfone ultrafiltration membrane (with the molecular weight cut-off of approximately 50000), soaking for 12 hours by using a NaOH solution with the pH value of 9-10, cleaning for 12 hours by using a 30% isopropanol water solution, and then placing into clear water for washing for standby;
2) Preparing an ethylenediamine aqueous phase solution with the mass percentage of 2 percent and a succinyl chloride organic phase pentane solution with the mass percentage of 0.4 percent;
3) And (3) placing the ultrafiltration base membrane into the aqueous phase solution for 4 minutes, taking out, extruding by using a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 4 minutes, taking out, sending the membrane into a 100 ℃ oven for heat treatment for 20 minutes, and placing the prepared nanofiltration membrane into pure water for standby.
4) 1.5% by mass of bis (2-epoxypropyl) ether was dissolved in an isopropyl alcohol-water mixed solvent (60% by mass of an alcohol solvent) as a modified solution A. Preparing sodium acetate with the mass percentage of 1% and 2-carboxyethyl phosphoric acid with the mass percentage of 0.8% as a modified solution B;
5) Immersing the nanofiltration membrane into the modified solution A for 20 minutes (the solution is preheated to 55 ℃), and extruding the solution by using a stainless steel roller to remove redundant solution; immersing in the modified solution B for 3 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, sending into a 120 ℃ oven for heat treatment for 8 minutes, taking out, and then putting into pure water for measurement.
Film contamination test results
Reactive chlorine antioxidant test results
Claims (9)
1. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction is characterized by comprising the following steps:
(1) Dissolving a multi-element epoxy compound into an alcohol-water mixed solvent to be used as a modified solution A, wherein the mass percentage of the alcohol in the alcohol-water mixed solvent is 50-80%, and the mass percentage of the multi-element epoxy compound in the modified solution A is 0.5-2%; wherein the alcohol solvent is one of methanol, ethanol, ethylene glycol, isopropanol or propylene glycol; the multi-element epoxy compound is one of glycerol tri (1, 2-epoxy) propyl ether, di (2-epoxy propyl) ether, ethylene glycol diglycidyl ether, pentaerythritol diglycidyl ether, resorcinol diglycidyl ether, polyethylene glycol diglycidyl ether or trimethylolpropane triglycidyl ether;
preparing a dehydration catalyst with the mass percentage of 1-5% and an aqueous solution of a carboxyl phosphoric acid compound with the mass percentage of 0.5-2% as a modified solution B; wherein the dehydration catalyst is one of sodium acetate, sodium benzoate, ammonium benzoate or sulfuric acid, and the carboxyl phosphoric acid compound is one of 2-carboxyethyl phosphoric acid, 2-carboxyphenyl phosphoric acid, 3-carboxyphenyl phosphoric acid or 4-carboxyphenyl phosphoric acid;
(2) Immersing the nanofiltration membrane in the modified solution A at 40-60 ℃ for 5-30 minutes, and removing redundant solution; immersing the mixture into the modified solution B for 3 minutes, taking out the mixture to remove redundant solution, and then sending the mixture into a baking oven at 100-130 ℃ for heat treatment for 5-10 minutes.
2. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction according to claim 1, wherein the nanofiltration membrane is prepared by the following steps:
(1) Soaking an ultrafiltration base membrane in NaOH solution with pH value of 9-10 for 12 hours, cleaning in 30% isopropanol water solution for 12 hours, and then placing clean water for washing for later use, wherein the ultrafiltration membrane material is one of polyethylene, polypropylene, polysulfone, polyethersulfone, polyacrylonitrile or polyvinylidene fluoride;
(2) Preparing a polyamine aqueous phase solution with the mass percentage of 0.2% -2%, wherein a polyamine monomer is one of piperazine, 2-piperazinone, piperazine-2-formic acid, ethylenediamine or 1, 4-cyclohexanediamine;
preparing 0.01-0.5% of polybasic acyl chloride organic phase solution by mass percent, wherein the polybasic acyl chloride is one of isophthaloyl dichloride, 1, 4-cyclohexanediyl chloride, succinyl chloride, biphenyl diacetyl chloride, 4' -oxydi (benzoyl chloride) or trimesic acid chloride, and the organic phase solvent is one of pentane, hexane, cyclohexane or heptane;
(3) Placing the ultrafiltration base membrane into the aqueous phase solution for 1-5 minutes, taking out, extruding by a stainless steel roller to remove redundant solution, immersing into the organic phase solution for 1-5 minutes, taking out, and then sending the membrane into an oven at 80-120 ℃ for heat treatment for 5-20 minutes.
3. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction according to claim 2, wherein the ultrafiltration membrane in the step (1) has a molecular weight cut-off of 40000-60000.
4. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction according to claim 2, wherein the mass percentage of polyamine monomer in the step (2) is 0.5% -1.5%; the mass percentage of the polybasic acyl chloride monomer is 0.2-0.4%.
5. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction according to claim 2, wherein the heat treatment temperature in the step (3) is 90-100 ℃ and the heat treatment time is 10-15 minutes.
6. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring opening reaction according to claim 1, wherein the mass percentage of alcohol in the alcohol-water mixed solvent in the step (1) is 60-75%; the mass percentage of the multi-element epoxy compound is 0.8-1.5%.
7. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction according to claim 1, wherein the mass percentage of the dehydration catalyst in the step (1) is 2-4%; the mass percentage of the carboxyl phosphate compound is 0.8-1.5%.
8. The method for reinforcing and modifying chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction according to claim 1, wherein the temperature of the modifying solution A in the step (2) is controlled to be 45-55 ℃; the soaking time is 10-20 minutes.
9. The enhanced modification method of chlorine resistance and pollution resistance of nanofiltration membrane based on ring-opening reaction according to claim 1, wherein the heat treatment temperature of the membrane in the oven in the step (2) is 110-120 ℃; the heat treatment time in the oven is 6-8 minutes.
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