阅读说明：本技术 一种可用于水质软化的纳滤复合膜制备方法 (Preparation method of nanofiltration composite membrane for softening water ) 是由 周勇 顾凯锋 高从堦 于 2020-06-30 设计创作，主要内容包括：本发明公开了一种可用于水质软化的纳滤复合膜制备方法,在超滤膜表面通过均苯三甲酸交联剂与聚乙烯亚胺交联得到复合层,并通过季铵化作用提高膜表面荷电效应,从而提高选择性。本发明充分发挥出聚乙烯亚胺亲水性好、荷电性强、成膜性稳定等优势,对脱盐率和水通量都有极大的提升；制膜过程简单,工艺参数易于优化,原料廉价易得,有利于纳滤复合膜的扩大生产；氨基季铵化后电荷效应增强,膜选择性进一步提高。(The invention discloses a preparation method of a nanofiltration composite membrane for softening water, which comprises the steps of crosslinking a trimesic acid crosslinking agent and polyethyleneimine on the surface of an ultrafiltration membrane to obtain a composite layer, and improving the surface charge effect of the membrane through quaternization, so as to improve the selectivity. The invention fully exerts the advantages of good hydrophilicity, strong charge property, stable film forming property and the like of polyethyleneimine, and greatly improves the desalination rate and water flux; the membrane preparation process is simple, the technological parameters are easy to optimize, the raw materials are cheap and easy to obtain, and the expanded production of the nanofiltration composite membrane is facilitated; the charge effect is enhanced after the amino quaternization, and the membrane selectivity is further improved.)

1. A preparation method of a nanofiltration composite membrane for softening water quality is characterized by comprising the following steps: the method comprises the following steps:

1) dissolving methyl iodide and polyethyleneimine in water at a certain temperature and for a certain time to obtain a quaternized polyethyleneimine aqueous solution;

2) coating a trimesic acid crosslinking agent solution on the surface of the ultrafiltration membrane, standing for a period of time, removing the excessive solution, and drying in a blast drying oven;

3) soaking the surface of the dried ultrafiltration membrane with the cross-linking agent in a quaternized polyethyleneimine aqueous solution, standing for a period of time, and performing heat treatment in a forced air drying oven to obtain a nanofiltration membrane;

4) and soaking the nanofiltration membrane in deionized water for 24 hours, taking out and testing the performance.

2. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: the molecular weight of the polyethyleneimine in the step 1) is 50000-100000 daltons.

3. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: the mass volume concentration of the polyethyleneimine water solution in the step 1) is 0.2-3%; the mass volume concentration of the methyl iodide is between 0.01 and 0.16 percent.

4. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: in the step 1), the co-dissolution temperature of the methyl iodide and the polyethyleneimine is 20-100 ℃, and the co-dissolution time of the methyl iodide and the polyethyleneimine is 1-24 hours.

5. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: the ultrafiltration membrane in the step 2) is one of polysulfone and polyethersulfone; the cutoff molecular weight of the ultrafiltration membrane is 30000-50000 daltons.

6. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: in the step 2), the mass volume concentration of the trimesic acid is between 0.05 and 5 percent.

7. A method for preparing a nanofiltration composite membrane for water softening 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 miscible solvent of ethanol and water.

8. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: the cross-linking agent solution in the step 2) comprises a surfactant sodium dodecyl sulfate with the mass volume concentration of 0.1-0.5%.

9. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: standing for 3-6 minutes in the step 2); the temperature of the air-blast drying box is 20-40 ℃, and the drying time is 8-12 minutes.

10. A method for preparing a nanofiltration composite membrane for water softening according to claim 1, wherein the method comprises the following steps: the standing time in the step 3) is 1-5 minutes; the temperature of the air-blast drying oven is between 40 and 100 ℃, and the heat treatment time is between 5 and 20 minutes.

Technical Field

The invention relates to a preparation method of a nanofiltration composite membrane, in particular to a preparation method of a nanofiltration composite membrane for softening water, belonging to the technical field of membrane separation.

Background

The high-hardness water has great influence on drinking water and domestic water of people, and polyvalent metal salts such as calcium salt, magnesium salt and the like mainly cause the hardness of the water to be increased. There is a correlation between the content of calcium and magnesium plasma in drinking water and colorectal cancer, gastric cancer, breast cancer, confusion and renal function deterioration. In addition, for laundry and kitchen cleaning waters, these multivalent ions can react with the saponification anions, resulting in a reduction in cleaning efficiency. The long-term use of hard water can cause the problems of scaling, corrosion and the like of equipment such as boiler pipelines and the like.

At present, different methods such as chemical precipitation, ion exchange, adsorption, nanofiltration, reverse osmosis, electrodialysis and the like are used for treating the problem of high water hardness. Nanofiltration technology offers significant advantages over other methods in terms of throughput, efficiency, energy consumption, economic evaluation, etc., due to its unique permselectivity. The membrane material itself determines the nanofiltration membrane performance. Polyethyleneimine is a cationic polymer with high charge density and hydrophilicity, and can form a nanofiltration membrane separation layer with positive charge by a chemical crosslinking method, wherein the positive charge can retain most polyvalent cations and allow some monovalent cations to permeate the membrane.

At present, a common polyethyleneimine positively charged nanofiltration membrane has a relatively high rejection rate on divalent cations, but the rejection rate on monovalent ions is also relatively high, and the ideal separation efficiency cannot be achieved in the deep treatment of water quality. This is mainly due to the dense pore size of the selective layer and the large membrane thickness, which also weakens the membrane permeability. During the crosslinking process, nanofiltration membranes with such performance can be formed after the reaction is too fast, so that a crosslinking agent which has a moderate reaction with polyethyleneimine is selected as a method for optimizing the performance of the nanofiltration membrane. In addition, the molecular chain of polyethyleneimine contains a large number of protonated amino groups, and after quaternization treatment, the particle degree is deepened, the positive charge is enhanced, and the inorganic ion discrimination is enlarged.

Disclosure of Invention

The invention aims to prepare a nanofiltration composite membrane for softening water, and the nanofiltration composite membrane for softening water is prepared on the surface of an ultrafiltration membrane through the cross-linking reaction of trimesic acid and quaternized polyethyleneimine.

The technical scheme of the invention is as follows: a preparation method of a nanofiltration composite membrane for softening water quality is characterized by comprising the following steps: the method comprises the following steps:

1) dissolving methyl iodide and polyethyleneimine in water at a certain temperature and for a certain time to obtain a quaternized polyethyleneimine aqueous solution;

2) coating a trimesic acid crosslinking agent solution on the surface of the ultrafiltration membrane, standing for a period of time, removing the excessive solution, and drying in a blast drying oven;

3) soaking the surface of the dried ultrafiltration membrane with the cross-linking agent in a quaternized polyethyleneimine aqueous solution, standing for a period of time, and performing heat treatment in a forced air drying oven to obtain a nanofiltration membrane;

4) and soaking the nanofiltration membrane in deionized water for 24 hours, taking out and testing the performance.

Preferably, the molecular weight of the polyethyleneimine in the step 1) is 50000-100000 daltons.

Preferably, the mass volume concentration (g/100 ml) of the polyethyleneimine aqueous solution in the step 1) is between 0.2% and 3%; the mass volume concentration (g/100 ml) of the methyl iodide is between 0.01 and 0.16 percent.

Preferably, in the step 1), the co-dissolution temperature of the methyl iodide and the polyethyleneimine is 20-100 ℃, and the co-dissolution time of the methyl iodide and the polyethyleneimine is 1-24 hours.

Preferably, the ultrafiltration membrane in the step 2) is one of polysulfone and polyethersulfone; the cutoff molecular weight of the ultrafiltration membrane is 30000-50000 daltons.

Preferably, the mass volume concentration (g/100 ml) of the trimesic acid in the step 2) is between 0.05% and 5%.

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

Preferably, the crosslinking agent solution in the step 2) contains 0.1 to 0.5 mass volume percent (g/100 ml) of sodium dodecyl sulfate serving as a surfactant.

Preferably, the standing time in the step 2) is 3-6 minutes; the temperature of the air-blast drying box is 20-40 ℃, and the drying time is 8-12 minutes.

Preferably, the standing time in the step 3) is between 1 and 5 minutes; the temperature of the air-blast drying oven is between 40 and 100 ℃, and the heat treatment time is between 5 and 20 minutes.

Has the advantages that: the nanofiltration composite membrane for softening water quality has simple preparation process, easy operation, good membrane permeability under low pressure, further improved membrane selectivity caused by quaternized polyethyleneimine, strong discrimination on mixed ions, and further improved permeability in the process of separating salt solution while maintaining desalting performance.

The separation layer of the nanofiltration composite membrane is formed by quaternized polyethyleneimine crosslinked trimesic acid, so that the advantages of good hydrophilicity, strong charge property, stable membrane forming property and the like of polyethyleneimine are fully exerted, and the desalination rate and the water flux are greatly improved. The method has the advantages of simple membrane preparation process, easy optimization of process parameters, cheap and easily-obtained raw materials and contribution to the expanded production of the nanofiltration composite membrane. The charge effect is enhanced after the amino quaternization, and the membrane selectivity is further improved. In a water softening application system, the nanofiltration composite membrane prepared by the invention has sensitive selective separation performance and good permeability.

Detailed Description

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