Preparation method of anti-pollution nanofiltration membrane

Abstract

The application provides a preparation method of an anti-pollution nanofiltration membrane, which comprises the following steps: coating glycine-N-carboxy-cyclamic acid on the surface of a nascent membrane generated after an interface, and reacting with part of acyl chloride groups in benzene tricarbonyl chloride, and then grafting on the surface of the membrane; the glycine-N-carboxy-cyclamic acid grafted on the surface of the membrane not only contains hydrophilic molecules, can adsorb a layer of water molecules, and effectively avoids the pollution of the membrane surface by organic matters, but also gradually hydrolyzes into hydrophilic molecules during use, and the hydrophilicity does not become weak with the use time, so that the anti-pollution nanofiltration membrane prepared by the method has wide application prospects in the fields of industrial water treatment, milk product concentration and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of nanofiltration membranes, and particularly relates to a preparation method of an anti-fouling nanofiltration membrane. BACKGROUND

[0002] Nanofiltration membrane separation technology has good selectivity and can realize selective removal of ions and high-molecular organic matters, and is widely used in fruit juice concentration, dairy product desalination and other food fields. However, in the food field, the organic matter content in the treated feed liquid is high, and the membrane fouling is usually much more serious than in other fields. Therefore, the nanofiltration membrane needs stronger anti-fouling performance.

[0003] Patent CN115069090A discloses a preparation method of an anti-fouling nanofiltration membrane, which introduces molecular chains with different charge properties on the surface of a conductive membrane, forms a double-layer structure by using the different responsiveness of the molecular chains to electric field stimulation, and uses the enhanced electrostatic repulsion to improve the anti-fouling performance of the separation membrane.

[0004] Patent CN114768561A discloses a preparation method of an anti-fouling composite membrane, which uses the dehydration condensation reaction between the amine groups on the surface after the interfacial polymerization and the carboxyl groups of a polyacid, and the carboxyl groups or sulfonic acid groups on the surface make the outermost surface of the membrane negatively charged, so that a protective layer with high charge and double pH cleaning responsiveness is formed on the surface of the skin layer of the composite membrane, and the cleaning and removal effect of stubborn organic and inorganic pollutants on the membrane surface is strengthened.

[0005] Patent CN114984785A discloses a composite nanofiltration membrane and a preparation method and application thereof, the composite nanofiltration membrane introduces silane coupling agent and tetraethyl orthosilicate into the active separation layer, and the water phase reactant and the oil phase reactant 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 good anti-fouling performance.

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

[0007] Patent CN114259884A discloses a positively charged composite nanofiltration membrane based on in-situ zwitterionization and a preparation method thereof, which is subjected to in-situ zwitterionization, has greatly improved anti-fouling performance and can be used for wastewater treatment.

[0008] Although these methods can improve the anti-fouling performance of the nanofiltration membrane, they all have the problem of not lasting, that is, the anti-fouling performance is easily weakened, especially after acid and alkali cleaning in the actual use process, the anti-fouling performance is obviously weakened. SUMMARY

[0009] The present application aims at providing a preparation method of anti-pollution nanofiltration membrane, which does not reduce the anti-pollution performance after acid and alkali washing.

[0010] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows.

[0011] The preparation method of the anti-pollution nanofiltration membrane comprises the following steps.

[0012] (1) Pour the prepared piperazine solution on the base membrane, soak for a certain time, then pour off the piperazine solution and remove the residual solution on the surface of the base membrane;

[0013] (2) Then, coat the prepared trimesoyl chloride solution on the base membrane treated in step (1), and after a certain time of static reaction, heat the membrane piece to complete the curing;

[0014] (3) After the curing is completed, coat the prepared glycine-N-carboxylic acid solution on the surface of the membrane treated in step (2), react for a certain time, take out the membrane piece and wash it with water to obtain the anti-pollution nanofiltration membrane.

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

[0016] Further, the base membrane in step (1) is a polysulfone ultrafiltration base membrane, and the soaking time of the base membrane in the piperazine solution is 0.5-2 minutes.

[0017] Further, the residual solution on the surface of the base membrane is removed by using an air knife in step (1).

[0018] Further, the solvent in the trimesoyl chloride solution in step (2) is an organic solvent, and preferably one or a mixture of several solvents selected from hexane, heptane, decane, cyclohexane and ethyl cyclohexane, and the mass concentration of the trimesoyl chloride is 0.1-1.0 wt%.

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

[0020] Further, in step (2), the membrane piece is heat-cured in an oven, the temperature of the oven is 50-80℃, and the curing time is 3-6 minutes.

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

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

[0023] Glycine-N-carboxy-cyclamic acid is a N-heterocyclic cyclamic acid, after step (2), the present application continues to react with the —NH in the glycine-N-carboxy-cyclamic acid molecule through the acyl chloride group remaining on the surface, and grafts the glycine-N-carboxy-cyclamic acid to the surface of the membrane through a chemical bond. The glycine-N-carboxy-cyclamic acid grafted to the surface of the membrane, due to its hydrophilicity, adsorbs a layer of water molecules on the surface of the membrane, preventing direct contact of organic pollutants with the surface of the membrane, and improving the anti-pollution property of the membrane. At the same time, with the long-period operation of the membrane, after acid-base cleaning, the cyclamic acid in the glycine-N-carboxy-cyclamic acid will hydrolyze to generate more hydrophilic groups, and the hydrophilicity will not weaken with the use time, and the anti-pollution property will not decay.

[0024] Compared with the prior art, the present application has the beneficial effects that:

[0025] The present application introduces glycine-N-carboxy-cyclamic acid into the surface of the membrane through a secondary interfacial reaction on the surface of the membrane, improves the anti-pollution property of the nanofiltration membrane, and the anti-pollution property does not decay after acid-base cleaning, has strong stability, and has wide application prospects in the fields of industrial water treatment, dairy product concentration, etc. DETAILED DESCRIPTION

[0026] The present application will be further described below through specific examples, and the examples described in the present application are only used to illustrate the present application and do not limit the scope of the present application.

[0027] The test methods used in the examples or comparative examples of the present application are described as follows:

[0028] The test method for anti-pollution in the present application is as follows:

[0029] ①The prepared membrane piece is rolled into an 8040 membrane element with an effective membrane area of 400ft 2 ;

[0030] ②The above membrane element is loaded into a pressure vessel for testing reverse osmosis membrane elements, and the anti-pollution performance test is carried out.

[0031] The evaluation method adds milk powder in the feed liquid to configure a 1000ppm milk powder simulation pollutant, and the flux decay drop size of the membrane element is calculated to reflect the anti-biological pollution ability of different flow channel nets, that is, the ratio of the flux (F1) of the membrane after pollution to the initial flux (F0), as shown in formula (1):

[0032] Flux decay rate = (F0-F1) / F0x100% formula (1)

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

[0034] Glycine-N-carboxylic cyclic inosine acid is purchased from Shanghai Aladdin Biochem Technology Co., Ltd.

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

[0036] Example 1

[0037] (1) Pour 0.5wt% piperazine aqueous solution on the base membrane, the soaking time is 1 min, after pouring off the aqueous solution, use the air knife to remove the residual solution on the surface of the membrane;

[0038] (2) Then, pour the prepared 0.5wt% trimesoyl chloride hexane solution on the base membrane treated in step (1), after 1 min of static reaction, put the above-mentioned membrane into the oven for heat curing at 60℃ for 5 min;

[0039] (3) After the curing is completed, pour the prepared 0.2wt% glycine-N-carboxylic cyclic inosine acid solution on the surface of the membrane treated in step (2), react for 10 min, take out the membrane and wash it with water to obtain the anti-fouling nanofiltration membrane.

[0040] Examples 2-10

[0041] Prepare the membrane element water inlet channel net according to the method in Example 1, and 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 without adding glycine-N-carboxylic cyclic inosine acid.

[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] Roll the membrane element of 8040 type specification using the membrane element water inlet channel nets prepared in different examples and comparative examples to perform the anti-fouling performance test, and the test results are shown in Table 1:

[0047] Table 1

[0048]

[0049]

[0050] From the test results of the examples and comparative examples, it can be seen that the flux decay of the nanofiltration membrane prepared by using glycine-N-carboxylic-cyclanic acid with different concentrations is better than that of the comparative examples, and after acid-base washing, not only the flux decay is better than that before acid-base washing, but also it is far better than that of the comparative examples, which shows that the nanofiltration membranes prepared by using glycine-N-carboxylic-cyclanic acid with different concentrations have good anti-pollution performance and the anti-pollution performance has no change after cleaning.

[0051] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the method of the present application, several improvements and supplements can also be made, and these improvements and supplements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing an antifouling nanofiltration membrane, characterized in that, Includes the following steps: (1) Pour the pre-prepared piperazine aqueous solution onto the bottom film, soak it, then pour off the piperazine aqueous solution to remove the residual solution on the bottom film surface; (2) Then the prepared pyromellitic chloride solution is coated on the substrate film treated in step (1), and the reaction is allowed to stand still. Then the film is heat-cured. (3) After the aging process is completed, the pre-prepared glycine-N-carboxyl-cyclic acid solution is coated on the membrane surface treated in step (2). After reacting for a certain period of time, 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 aqueous solution in step (1) is as follows: piperazine solid is dissolved in water, and the mass concentration of the piperazine aqueous solution is 0.1-1%.

3. The preparation method according to claim 1, characterized in that, The substrate membrane mentioned in step (1) is a polysulfone ultrafiltration substrate membrane, and the substrate membrane is soaked in piperazine aqueous solution for 0.5 to 2 minutes.

4. The preparation method according to claim 1, characterized in that, In step (1), an air knife is used to remove the residual solution on the bottom film surface.

5. The preparation method according to claim 1, characterized in that, In step (2), the solvent in the pyromellitic chloride solution is an organic solvent.

6. The preparation method according to claim 5, characterized in that, In step (2), the solvent is one or a mixture of several of the following: hexane, heptane, decane, cyclohexane, and ethylcyclohexane.

7. The preparation method according to claim 1, characterized in that, The mass concentration of pyromellitic acid chloride is 0.1–1.0 wt%.

8. The preparation method according to claim 1, characterized in that, The static reaction time of pyromellitic chloroformyl chloride in step (2) is 0.5 to 2 minutes.

9. The preparation method according to claim 1, characterized in that, In step (2), the film is heat-cured in an oven at a temperature of 50-80°C for 3-6 minutes.

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

11. The preparation method according to claim 1, characterized in that, In step (3), the reaction time is 5 to 15 minutes.

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