Preparation method of anti-pollution nanofiltration membrane

Abstract

According to the preparation method of the anti-pollution nanofiltration membrane, the surface of a nascent state membrane generated after an interface is coated with glycine-N-carboxyl-cycloendoic acid, the glycine-N-carboxyl-cycloendoic acid reacts with part of acyl chloride groups in trimesoyl chloride, then the glycine-N-carboxyl-cycloendoic acid is grafted to the surface of the membrane, and the glycine-N-carboxyl-cycloendoic acid grafted to the surface of the membrane contains hydrophilic molecules and also contains hydrophilic groups; the glycine-N-carboxyl-cyclic acid can adsorb a layer of water molecules and effectively prevent organic matters from polluting the surface of the membrane, and in the use process, the glycine-N-carboxyl-cyclic acid is gradually hydrolyzed into hydrophilic molecules, the hydrophilicity cannot be weakened along with the change of the use time, and the anti-pollution nanofiltration membrane prepared by the method can be applied to industrial water treatment and industrial wastewater treatment. Wide application prospects are realized in the fields of dairy product concentration and the like.

Description

Technical Field

[0001] The invention belongs to the field of nanofiltration membranes, and in particular relates to a method for preparing an anti-pollution nanofiltration membrane. Background Art

[0002] Nanofiltration membrane separation technology has good selectivity and can achieve the selective removal of ions and high molecular weight organic matter. It is widely used in juice concentration, dairy product desalination, and other food fields. However, in the food field, due to the high content of organic matter in the treated liquid, membrane pollution is usually much more serious than in other fields. Therefore, nanofiltration membranes need stronger anti-pollution performance.

[0003] Patent CN115069090A discloses a method for preparing an anti-pollution nanofiltration membrane, which introduces molecular chains with different charges on the surface of a conductive membrane, utilizes their different responsiveness to electric field stimulation to form a double-layer structure, and utilizes enhanced electrostatic repulsion to improve the anti-pollution performance of the separation membrane.

[0004] Patent CN114768561A discloses a method for preparing an anti-pollution composite membrane, which utilizes the dehydration condensation reaction of some of the amino groups on the surface with the carboxyl groups of the polyacid after the interfacial polymerization reaction. The carboxyl groups or sulfonic acid groups on the surface make the outermost surface of the membrane negatively charged, and form a highly charged protective layer with dual pH cleaning responsiveness on the cortical surface of the composite membrane, thereby enhancing the cleaning and removal effect of stubborn organic and inorganic pollutants on the membrane surface.

[0005] Patent CN114984785A discloses a composite nanofiltration membrane and its preparation method and application. The composite nanofiltration membrane introduces silane coupling agent and tetraethyl orthosilicate into the active separation layer, and the water phase reactants and the oil phase reactants form an interpenetrating network structure polymer, so that the composite nanofiltration membrane has a narrow pore size distribution, high hydrophilicity and a dense and slightly thick active separation layer, and has good anti-pollution performance.

[0006] Patent CN114713044A discloses a method for improving the anti-pollution performance of a composite nanofiltration membrane, which has good anti-pollution performance and provides an important reference for the widespread application of nanofiltration membranes.

[0007] Patent CN114259884A discloses a positively charged composite nanofiltration membrane based on in-situ zwitterionization and a preparation method thereof. By performing in-situ zwitterionization, the anti-pollution performance is greatly improved and the membrane can be used for sewage treatment.

[0008] Although these methods can improve the anti-pollution property of nanofiltration membranes, they all have the problem of short-term anti-pollution performance, that is, the anti-pollution performance is easily weakened, especially in the actual use process, after acid and alkali washing, the anti-pollution performance is significantly weakened. Summary of the invention

[0009] The object of the present invention is to provide a method for preparing an anti-pollution nanofiltration membrane in view of the above-mentioned deficiencies in the prior art, and the anti-pollution performance will not be attenuated after acid and alkali washing.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing an anti-pollution nanofiltration membrane, characterized in that it comprises the following steps:

[0012] (1) pouring a pre-prepared piperazine solution onto the base film, and after soaking for a certain period of time, pouring out the piperazine solution to remove the residual solution on the surface of the base film;

[0013] (2) coating the prepared trimesoyl chloride solution on the base film treated in step (1), allowing the film to react for a period of time, and then thermally aging the film;

[0014] (3) After the aging is completed, the pre-prepared glycine-N-carboxyl-cyclic acid solution is coated on the membrane surface treated in step (2), reacted for a certain period of time, and the membrane is taken out and washed with water to obtain an anti-fouling nanofiltration membrane.

[0015] Furthermore, the preparation process of the piperazine solution in step (1) is: dissolving a certain amount of piperazine solid in water, and the mass concentration of the piperazine aqueous solution is 0.1-1%.

[0016] Furthermore, the bottom membrane described in step (1) is a polysulfone ultrafiltration bottom membrane, and the bottom membrane is immersed in the piperazine solution for 0.5 to 2 minutes.

[0017] Furthermore, in step (1), an air knife is used to remove the residual solution on the surface of the base film.

[0018] Furthermore, in the trimesoyl chloride solution in step (2), the solvent is an organic solvent, preferably one or a mixed solvent of hexane, heptane, decane, cyclohexane and ethylcyclohexane, and the mass concentration of trimesoyl chloride is 0.1-1.0 wt%.

[0019] Furthermore, the static reaction time of trimesoyl chloride in step (2) is 0.5 to 2 minutes.

[0020] Furthermore, in the step (2), the film is heat-cured in an oven at a temperature of 50 to 80° C. for a curing time of 3 to 6 minutes.

[0021] Furthermore, in the step (3), the mass concentration of the glycine-N-carboxyl-cyclic acid solution is 0.1-0.5%, and the solvent is water.

[0022] Furthermore, in the step (3), the reaction time is 5 to 15 minutes.

[0023] Glycine-N-carboxyl-cyclic acid is an N-heterocyclic cyclic acid. After step (2), the present invention uses the residual acyl chloride group on the surface to continue to react with the -NH in the glycine-N-carboxyl-cyclic acid molecule, and grafts the glycine-N-carboxyl-cyclic acid to the surface of the membrane through chemical bonds. The glycine-N-carboxyl-cyclic acid grafted to the surface of the membrane, due to its hydrophilicity, adsorbs a layer of water molecules on the surface of the membrane, prevents direct contact between organic pollutants and the membrane surface, and improves the pollution resistance of the membrane. At the same time, as the membrane runs for a long period of time, after acid and alkali cleaning, the cyclic acid in the glycine-N-carboxyl-cyclic acid will hydrolyze to produce more hydrophilic groups, and the hydrophilicity will not weaken with the use time, and the pollution resistance will not decay.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The invention introduces glycine-N-carboxyl-cyclic acid into the surface of the membrane through a secondary interface reaction method, thereby improving the anti-pollution property of the nanofiltration membrane. The anti-pollution property will not be attenuated after acid and alkali cleaning, and the stability is strong. The invention has broad application prospects in the fields of industrial water treatment, dairy product concentration, etc. DETAILED DESCRIPTION

[0026] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0027] The following describes the test methods used in the embodiments or comparative examples of the present invention:

[0028] The anti-pollution test method in the present invention is:

[0029] ① Roll the prepared membrane into a roll with an effective membrane area of ​​400 ft 2 8040 membrane element;

[0030] ② Place the above membrane elements into a pressure vessel for testing reverse osmosis membrane elements and conduct an anti-pollution performance test.

[0031] In this evaluation method, milk powder is added to the feed liquid to simulate the pollutant of 1000ppm. The anti-biological fouling ability of different flow channel networks is reflected by calculating the attenuation amplitude of the membrane element flux, that is, the ratio of the membrane flux (F1) after fouling to the initial flux (F0), as shown in formula (1):

[0032] Flux attenuation rate = (F0-F1) / F0×100% Formula (1)

[0033] The degree of anti-fouling of the membrane element can be quantitatively calculated, and then the chemical cleaning operation is performed in the form of "alkaline washing + acid washing" to evaluate the change of the membrane's anti-fouling property with the number of cleaning times. The alkaline washing solution uses NaOH, and the pH of the alkaline washing solution is adjusted to 13. The acid washing solution uses HCl, and the pH of the acid washing solution is adjusted to 1. The number of "alkaline washing + acid washing" is 30 times.

[0034] Glycine-N-carboxyl-cyclic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0035] NaCl, NaOH, HCl, piperazine, trimesoyl chloride, hexane, heptane, decane, cyclohexane, and ethylcyclohexane were purchased from Komiou Chemical.

[0036] Example 1

[0037] (1) pouring a 0.5 wt% piperazine aqueous solution onto the base film for 1 min, and then removing the residual solution on the film surface with an air knife after pouring out the aqueous solution;

[0038] (2) coating the prepared 0.5 wt % hexane solution of trimesoyl chloride on the base film treated in step (1), allowing the film to react for 1 minute, and then placing the film in an oven for heat aging at 60° C. for 5 minutes;

[0039] (3) After the aging is completed, the pre-prepared 0.2 wt% glycine-N-carboxyl-cyclic acid solution is coated on the membrane surface treated in step (2), reacted for 10 minutes, and the membrane piece is taken out and washed with water to obtain an anti-fouling nanofiltration membrane.

[0040] Embodiments 2 to 10

[0041] The membrane element inlet flow channel network was prepared according to the method in Example 1. The reaction conditions are shown in Table 1.

[0042] Comparative Example 1

[0043] The main difference between this comparative example and Example 1 is that in step (3), the coating solution is pure water, and no glycine-N-carboxyl-cyclic acid is added.

[0044] Comparative Example 2

[0045] The main difference between this comparative example and Example 1 is that in step (3), the coating solution is glycine.

[0046] The membrane elements of 8040 specifications were rolled using the membrane element inlet flow channel nets prepared in different embodiments and comparative examples, and the anti-fouling performance test was carried out. The test results are shown in Table 1:

[0047] Table 1

[0048]

[0049]

[0050] From the test results of the embodiments and the comparative examples, it can be seen that the nanofiltration membrane prepared with different concentrations of glycine-N-carboxyl-cyclic acid has a better flux attenuation than the comparative example, and after acid and alkali washing, not only the flux attenuation is better than before acid and alkali washing, but also much better than the comparative example, indicating that the nanofiltration membrane prepared with different glycine-N-carboxyl-cyclic acid has good anti-pollution performance and the anti-pollution performance is basically unchanged after cleaning.

[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing an anti-pollution nanofiltration membrane, characterized in that: The steps include: (1) pouring the pre-prepared piperazine solution onto the base film, and after soaking, pouring out the piperazine solution to remove the residual solution on the surface of the base film; (2) coating the prepared trimesoyl chloride solution on the base film treated in step (1), allowing the reaction to stand, and then thermally aging the film; (3) After the aging is completed, the pre-prepared glycine-N-carboxyl-cyclic acid solution is coated on the membrane surface treated in step (2), reacted for a certain period of time, and the membrane is taken out and washed with water to obtain an anti-fouling nanofiltration membrane.

2. The preparation method according to claim 1, characterized in that: The preparation process of the piperazine solution in step (1) is as follows: dissolving piperazine solid in water, wherein the mass concentration of the piperazine aqueous solution is 0.1-1%.

3. The preparation method according to claim 1, characterized in that: The bottom membrane described in step (1) is a polysulfone ultrafiltration bottom membrane, and the bottom membrane is immersed in the piperazine solution for 0.5 to 2 minutes; Furthermore, in step (1), an air knife is used to remove the residual solution on the surface of the base film.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the trimesoyl chloride solution in step (2), the solvent is an organic solvent, preferably one or a mixed solvent of hexane, heptane, decane, cyclohexane and ethylcyclohexane, and the mass concentration of trimesoyl chloride is 0.1 to 1.0 wt %; Furthermore, the static reaction time of trimesoyl chloride in step (2) is 0.5 to 2 minutes; Furthermore, in the step (2), the film is heat-cured in an oven at a temperature of 50 to 80° C. for a curing time of 3 to 6 minutes.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In the step (3), the mass concentration of the glycine-N-carboxyl-cyclic acid solution is 0.1-0.5%, and the solvent is water.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the step (3), the reaction time is 5 to 15 minutes.

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