阅读说明：本技术 一种耐碱性纳滤复合膜的制备方法 (Preparation method of alkali-resistant nanofiltration composite membrane ) 是由 周勇 顾凯锋 高从堦 于 2020-06-30 设计创作，主要内容包括：本发明公开了一种耐碱性纳滤复合膜的制备方法,聚乙烯亚胺作为复合层材料,多元环氧作为交联剂,在梯度交联工艺下得到纳滤复合膜。在膜过滤过程中,聚乙烯亚胺分子链上质子化氨基使膜表面带正电,对多价阳离子具有高选择性。由于氨基与环氧基反应开环形成碳碳饱和键和羟基,所以复合层在碱性环境下具有良好的稳定性和渗透性。本发明制备工艺简单,复合膜渗透性良好,可广泛用于碱性废水中小分子有机物的分级脱除。(The invention discloses a preparation method of an alkali-resistant nanofiltration composite membrane. In the process of membrane filtration, the protonated amino groups on the molecular chain of the polyethyleneimine enable the surface of the membrane to be positively charged, and the polyethyleneimine cation exchange membrane has high selectivity on multivalent cations. The amino and the epoxy react to open a ring to form a carbon-carbon saturated bond and a hydroxyl, so that the composite layer has good stability and permeability in an alkaline environment. The preparation process is simple, the composite membrane has good permeability, and the composite membrane can be widely used for removing small-molecular organic matters in alkaline wastewater in a grading manner.)

1. A preparation method of an alkali-resistant nanofiltration composite membrane is characterized by comprising the following steps: the method comprises the following steps:

(1) fixing an ultrafiltration membrane with non-woven fabric on an epoxy polyester frame, and drying the surface of the membrane at room temperature;

(2) uniformly coating the crosslinking agent solution on the surface of the ultrafiltration membrane, standing for a period of time, removing the excessive solution, and drying the membrane in a forced air drying oven;

(3) uniformly coating a polyethyleneimine water solution on the surface of an ultrafiltration membrane with a cross-linking agent on the surface, standing for a period of time, removing excessive solution, and placing the membrane in a forced air drying oven for heat treatment;

(4) the heat treated film was taken out and tested after soaking in deionized water for 24 hours.

2. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: the ultrafiltration membrane in the step (1) is one of polysulfone, polyethersulfone, polyvinylidene fluoride and polyvinyl chloride.

3. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: the cut-off molecular weight of the ultrafiltration membrane in the step (1) is 20000-50000 daltons.

4. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: in the step (2), the cross-linking agent is one of 1, 4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, bisphenol A diglycidyl ether, triglycidyl isocyanurate, trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, 1, 6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polypropylene glycol diglycidyl ether and resorcinol diglycidyl ether.

5. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: in the step (2), the mass volume concentration of the cross-linking agent is between 0.05 and 0.3 percent.

6. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: the solvent of the cross-linking agent solution in the step (2) is an equal-volume mixture of ethanol and water.

7. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: the cross-linking agent solution in the step (2) contains a surfactant with the mass volume concentration of 0.05-0.2%, and the surfactant is one of sodium dodecyl sulfate, cetyl trimethyl ammonium bromide, benzethonium chloride, thiobetaine and polyoxyethylene lauryl ether.

8. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: the standing time in the step (2) is 2-6 minutes; and (3) drying the film for 8-15 minutes at the temperature of 20-40 ℃ in an air drying oven, and taking out the film.

9. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: the molecular weight of the polyethyleneimine in the step (3) is 10000-70000 daltons; the mass volume concentration of the polyethyleneimine water solution is between 0.2 and 2 percent.

10. The method for preparing an alkali-resistant nanofiltration composite membrane according to claim 1, wherein the method comprises the following steps: the standing time in the step (3) is 3-5 minutes; the temperature of the air-blast drying box is between 60 and 90 ℃, and the heat treatment time is between 5 and 15 minutes.

Technical Field

The invention relates to a preparation method of a nanofiltration composite membrane, in particular to a preparation method of an alkali-resistant nanofiltration composite membrane, belonging to the technical field of membrane separation.

Background

Nanofiltration is one of the most researched membrane separation technologies in the present day, and the unique selective permeability of the nanofiltration is suitable for some special separation systems. Generally, nanofiltration may prevent divalent salts while allowing a portion of the monovalent salts to permeate the membrane. For example, the rejection rate of commercial piperazine polyamide nanofiltration membranes to sodium sulfate exceeds 98 percent, and the rejection rate of sodium chloride is only about 60 percent. In this case, the membrane surface is generally negatively charged, and this effect is produced by the combined effects of pore size sieving and southeast balance. The positively charged nanofiltration membrane shows special separation performance due to the south-road balance effect and the opposite effect of the negatively charged nanofiltration membrane. Electropositive membranes are generally highly selective for multivalent cations and highly permeable for multivalent anions. Such as high selectivity to magnesium chloride and high permeability to sodium sulfate.

Compared with the traditional treatment means, the membrane technology has unique advantages in energy consumption, environmental protection and efficiency. Aiming at some water bodies in extreme environments, a special nanofiltration membrane can be developed in the membrane preparation process. Alkaline wastewater is generated in many fields such as paper making, chemical industry, food, petrochemical industry and the like. For example, in the processes of printing and dyeing and spinning, a large amount of alkali liquor is used for removing grease on cotton yarns; for producing viscose fiber, about 20% of caustic soda or soda solution is needed to dip cellulose; caustic soda solution is needed to wash excessive acid in refined petroleum; in the paper industry, soda or soda ash is used as a cooking liquor to remove carbohydrates and thereby separate cellulose.

The cationic polymer used as the nanofiltration separation layer material can play a role in southeast to a great extent, and has extremely high efficiency in removing multivalent inorganic cations. Polyethyleneimine has been widely studied and used as the cationic polymer having the highest known charge density. In order to solve the problem that polyethyleneimine is easy to dissolve in water and strong in intermolecular force, a polyethyleneimine nanofiltration membrane with stable performance can be obtained by chemical crosslinking. The common crosslinking method is to perform amidation and ionization reactions on primary amine on a polyethyleneimine molecular chain, and under a strong alkaline condition, the crosslinked structure is difficult to exist stably. Therefore, some new attempts have been made to construct a crosslinked structure. The primary amine in the polyethyleneimine is highly chemically active, and the epoxy group can be subjected to ring-opening reaction without generating byproducts. The crosslinked structure has no unsaturated bonds and contains hydrophilic hydroxyl groups. From the structural analysis, the nanofiltration membrane composite layer has good stability and permeability.

Disclosure of Invention

The invention aims to prepare an alkali-resistant nanofiltration composite membrane, which is prepared on a porous supporting layer through cross-linking reaction of polyepoxy and polyethyleneimine.

The technical scheme of the invention is as follows: a preparation method of an alkali-resistant nanofiltration composite membrane is characterized by comprising the following steps: the method comprises the following steps:

(1) fixing an ultrafiltration membrane with non-woven fabric on an epoxy polyester frame, and drying the surface of the membrane at room temperature;

(2) uniformly coating the crosslinking agent solution on the surface of the ultrafiltration membrane, standing for a period of time, removing the excessive solution, and drying the membrane in a forced air drying oven;

(3) uniformly coating a polyethyleneimine water solution on the surface of an ultrafiltration membrane with a cross-linking agent on the surface, standing for a period of time, removing excessive solution, and placing the membrane in a forced air drying oven for heat treatment;

(4) the heat treated film was taken out and tested after soaking in deionized water for 24 hours.

Preferably, the ultrafiltration membrane in the step (1) is one of polysulfone, polyethersulfone, polyvinylidene fluoride and polyvinyl chloride.

Preferably, the cut-off molecular weight of the ultrafiltration membrane in the step (1) is 20000-50000 daltons.

Preferably, in the step (2), the crosslinking agent is one of 1, 4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, bisphenol a diglycidyl ether, triglycidyl isocyanurate, trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, 1, 6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and resorcinol diglycidyl ether.

The crosslinking reaction with polyethyleneimine forms saturated bonds without side products, such as:

preferably, the mass volume concentration (g/100 ml) of the cross-linking agent in the step (2) is between 0.05% and 0.3%.

Preferably, the solvent of the crosslinking agent solution in the above step (2) is an equal volume mixture of ethanol and water.

Preferably, in the step (2), the cross-linking agent solution contains 0.05-0.2% by mass/volume (g/100 ml) of surfactant, and the surfactant is one of sodium dodecyl sulfate, cetyltrimethylammonium bromide, benzethonium chloride, thiobetaine and polyoxyethylene lauryl ether.

Preferably, the standing time in the step (2) is 2-6 minutes; and (3) drying the film for 8-15 minutes at the temperature of 20-40 ℃ in an air drying oven, and taking out the film.

Preferably, the molecular weight of the polyethyleneimine in the step (3) is 10000-70000 daltons; the mass volume concentration (g/100 ml) of the polyethyleneimine water solution is between 0.2 and 2 percent.

Preferably, the standing time in the step (3) is 3-5 minutes; the temperature of the air-blast drying box is between 60 and 90 ℃, and the heat treatment time is between 5 and 15 minutes.

The invention takes polyethyleneimine as a composite layer material and takes polyepoxy as a cross-linking agent, and the nanofiltration composite membrane is obtained under the gradient cross-linking process. In the process of membrane filtration, the protonated amino groups on the molecular chain of the polyethyleneimine enable the surface of the membrane to be positively charged, and the polyethyleneimine cation exchange membrane has high selectivity on multivalent cations. Because the amino and the epoxy react to open a ring to form a carbon-carbon saturated bond and a hydroxyl, the composite layer has good stability and permeability in an alkaline environment, and can be widely used for fractional removal of small molecular organic matters in alkaline wastewater. The alkali-resistant nanofiltration membrane has simple preparation process and strong charge effect, can keep good desalting rate and permeability when running under low pressure, and can stably remove micromolecular organic matters under the alkaline condition.

Detailed Description

The following examples give the separation and permeation performance of the alkali resistant nanofiltration composite membrane under some conditions. However, these examples are provided only for partial illustration and are not intended to limit the invention.