In-situ anti-fouling and self-cleaning functional modification method of composite membrane module

Abstract

The application relates to an in-situ anti-pollution and self-cleaning functional modification method of a composite membrane assembly. First, a water-soluble functional material containing an amino functional group is used to perform pressurized circulation treatment on the composite membrane assembly, and then an aldehyde-based cellulose derivative is used to construct an isolation layer on the membrane material surface in-situ through Schiff base reaction between an aldehyde group and an amino group. The application has the advantages that the water-soluble functional material and the cellulose derivative are used to construct the isolation layer, the isolation layer has the functions of improving the hydrophilicity of the membrane surface, reducing the roughness of the membrane surface and adjusting the electric charge characteristics of the membrane material, and the membrane material is endowed with the anti-pollution function. After the modified membrane assembly is used and is polluted, the isolation layer constructed by the acid or the alkali can be dissolved, the isolation layer and the pollutants are removed from the membrane surface, and the self-cleaning function is realized. Finally, the method can be repeatedly used for modifying the composite membrane assembly, and can completely meet the industrial application, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of separation membrane preparation, in particular to a method for in-situ anti-pollution and self-cleaning functional modification of a composite membrane module. TECHNICAL BACKGROUND

[0002] Reverse osmosis and nanofiltration membrane separation technology is a high-efficiency, energy-saving and green new separation technology, which has the outstanding characteristics of simple equipment, mild operating conditions, large treatment capacity, high separation efficiency, etc., and has been widely used in seawater and brackish water desalination, wastewater treatment and resource utilization, biological product separation, environmental engineering, food, medicine and other fields. In recent years, with the increasing shortage of global water resources, the increasing pollution of water resources, and the increasing urgency of resource efficient recycling, reverse osmosis / nanofiltration membrane separation technology has been more widely applied and valued in the fields of seawater desalination, water reuse, clean production, drinking water purification, resource recycling, etc.

[0003] The core and basis of reverse osmosis / nanofiltration membrane separation technology is a high-performance separation membrane module. During the use of the separation membrane module, impurities and pollutants in the treated system will be retained on the surface of the membrane and form a pollution layer on the membrane surface as the separation process continues. Therefore, membrane pollution is inevitable in the application process of reverse osmosis / nanofiltration membrane separation technology. Membrane pollution is usually caused by the following processes: deposition of colloidal particles in raw water on the membrane --- colloidal pollution; deposition of insoluble inorganic salts on the membrane --- fouling; adhesion and growth of microorganisms on the membrane --- biological pollution; physical or chemical reaction between some components in the raw water and the components on the membrane surface --- chemical pollution; adhesion of organic matter in the raw water to the membrane surface --- organic pollution. Membrane pollution will directly lead to a significant decrease in the permeation flux of reverse osmosis membranes, a decrease in system production efficiency, an increase in operating cost and energy consumption; at the same time, membrane pollution will also lead to frequent cleaning of the system, failure of the device to operate normally, serious deterioration of the membrane's rejection characteristics, deterioration of the quality of the produced water, reduction of the membrane's service life and frequent replacement of the membrane.

[0004] Membrane pollution can be first alleviated by process pretreatment and cleaning. Pretreatment can remove as many substances as possible in the treated liquid that may cause membrane pollution, which can to some extent alleviate membrane pollution, but will increase the operating cost of the membrane separation process. Membrane cleaning can also to some extent alleviate membrane pollution and restore membrane performance, but due to the variety and structure of pollutants in the actual use process and the insufficient understanding of the mechanism of membrane pollution, the selection of membrane cleaning process is very complex and blind, and the cleaning efficiency of membrane pollution cannot be guaranteed, especially the cleaning efficiency of membrane pollution in complex systems is generally low, which leads to the decline and ultimate failure of the membrane separation performance.

[0005] By improving the production process of reverse osmosis and nanofiltration membranes, preparing reverse osmosis and nanofiltration membrane modules with anti-pollution function is another effective way to reduce membrane pollution in the application process of reverse osmosis and nanofiltration membrane modules. Physical coating and chemical grafting processes are used for secondary processing of the surface of reverse osmosis and nanofiltration membranes. By changing the surface roughness, hydrophilicity, charge characteristics and chemical structure of the membrane material, the adsorption and deposition of pollutants on the membrane surface are reduced, thereby reducing the pollution of pollutants to the membrane. However, due to the complex and variable types of pollutants, single mode of membrane surface modification cannot achieve the anti-pollution function of the membrane material when treating different materials. At the same time, the surface modification treatment during the manufacturing process of the membrane material will increase the production cost and the complexity of the manufacturing process, and cannot realize the large-scale in-situ modification of the membrane module.

[0006] Therefore, how to modify the membrane module in-situ by a simple and practical method according to the characteristics of the treated material, and endow the membrane module with anti-pollution and self-cleaning functions, is an urgent technical problem to be solved, which is necessary and of great practical significance for reducing membrane module pollution, prolonging the service life of the membrane module, and expanding the use range of reverse osmosis / nanofiltration membranes. SUMMARY

[0007] The present application proposes an in-situ anti-pollution and self-cleaning functional modification method for reverse osmosis / nanofiltration membrane modules to solve the problem of membrane pollution in the use of existing reverse osmosis / nanofiltration membrane modules, and the shortcomings of high cost and poor adaptability in existing pretreatment, membrane cleaning and membrane material modification technologies for solving membrane pollution.

[0008] The technical problems to be solved by the present application are how to construct an anti-pollution layer on the surface of the membrane material in the reverse osmosis / nanofiltration membrane module in-situ, and how to realize the self-cleaning of the pollutants on the polluted membrane surface. A simple solution modification method is used to deposit functional materials on the surface of the membrane material to construct an anti-pollution isolation layer and realize the in-situ anti-pollution functionalization of the membrane module. The constructed anti-pollution isolation layer can be dissolved and automatically removed from the surface of the membrane material together with the pollutants through simple acid or alkaline solution circulation immersion treatment after the membrane module is polluted, thereby realizing the self-cleaning of the pollutants on the surface of the membrane material.

[0009] The present application is realized by the following technical solutions:

[0010] An in-situ anti-pollution and self-cleaning functional modification method for a composite membrane module, characterized by comprising the following steps:

[0011] S1, a certain amount of water-soluble functional material containing amino functional group is dissolved in pure water to prepare a water solution with a certain concentration as a modified solution A; a certain amount of aldehyde-based cellulose derivative is dissolved in pure water to prepare a water solution with a certain concentration as a modified solution B;

[0012] S2, at room temperature, the reverse osmosis / nanofiltration membrane assembly cleaned is subjected to pressurized circulation immersion treatment with the modified solution A, and after a certain time, the modified solution is drained, and the membrane assembly is washed with pure water;

[0013] S3, at room temperature, the membrane assembly treated with the modified solution A and washed with pure water is subjected to immersion treatment with the modified solution B, and after a certain time, the modified solution is drained, and the membrane assembly is washed with pure water.

[0014] The in-situ anti-pollution and self-cleaning functional modification method of the composite membrane assembly provided by the application, the water-soluble functional material containing amino functional group in step S1 is one or more of polyethyleneimine, chitosan, and silk glue; the mass percentage concentration of the water-soluble functional material in the modified solution A is 0.005%-0.02%;

[0015] The in-situ anti-pollution and self-cleaning functional modification method of the reverse osmosis / nanofiltration membrane assembly provided by the application, the aldehyde-based cellulose derivative in step S1 is aldehyde-based carboxymethyl cellulose sodium or aldehyde-based polyquaternary ammonium salt; the mass percentage concentration of the aldehyde-based cellulose derivative in the modified solution B is 0.1%-2.0%;

[0016] The in-situ anti-pollution and self-cleaning functional modification method of the reverse osmosis / nanofiltration membrane assembly provided by the application, the circulation time of the modified solution A in step S2 is 10-30 minutes;

[0017] The in-situ anti-pollution and self-cleaning functional modification method of the reverse osmosis / nanofiltration membrane assembly provided by the application, the immersion time of the modified solution B in step S3 is 5-60 minutes.

[0018] Compared with existing technologies, the advantages of this invention are as follows: Firstly, this invention utilizes water-soluble functional materials containing amino functional groups to perform surface deposition treatment on cleaned reverse osmosis / nanofiltration membrane modules through pressurized circulation. Then, using aldehyde-modified cellulose derivatives, an isolation layer with antifouling and self-cleaning functions is constructed in situ on the membrane material surface through a Schiff base reaction between aldehyde and amino groups. On one hand, the isolation layer constructed using water-soluble functional materials and cellulose derivatives enhances the hydrophilicity of the membrane material surface, reduces surface roughness, and regulates the charge characteristics of the membrane material, thereby endowing the membrane material with antifouling capabilities. On the other hand, after the modified membrane module is used and becomes fouled, the isolation layer constructed based on the Schiff base reaction between amino and aldehyde groups can be dissolved using acidic or alkaline solutions, removing the isolation layer along with contaminants from the membrane surface, achieving self-cleaning functionality. Furthermore, this method allows for repeated modification treatment of reverse osmosis / nanofiltration membrane modules, fully meeting the requirements for industrial applications.

[0019] The innovations of this invention are mainly reflected in several aspects: First, it allows for in-situ treatment of the composite membrane module; second, both are aqueous solutions; third, an antifouling isolation layer is constructed on the membrane surface through the Schiff base reaction of amino and aldehyde groups; fourth, after the membrane module is used and becomes contaminated, the Schiff base bonds are broken by acid or alkali treatment, the isolation layer dissolves, and the contaminant layer on the surface is removed from the membrane surface, achieving a self-cleaning function; fifth, our modification allows for repeated operation of the membrane module. Detailed Implementation

[0020] The implementation of the present invention will be described in detail below:

[0021] The following examples illustrate the in-situ antifouling and self-cleaning functionalization modification of polyamide reverse osmosis / nanofiltration membrane modules, as well as their separation performance, antifouling performance, and self-cleaning function. It is clear that the described examples are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0022] Reverse osmosis / nanofiltration membrane module: Purchase commercial reverse osmosis / nanofiltration membranes from the market, soak them in pure water at 20-30℃ for 30 minutes, then rinse them clean with pure water and set aside.

[0023] Preparation of Modification Solution A: Dissolve a certain amount of water-soluble functional material containing amino functional groups in pure water to prepare a modification solution A with a mass percentage concentration of 0.005%-0.02%. The water-soluble functional material containing amino functional groups includes at least one of polyethyleneimine, chitosan, and sericin.

[0024] Preparation of modified solution B: Dissolve a certain amount of aldehyde-modified cellulose derivative in pure water to prepare a modified solution B with a mass percentage concentration of 0.1%-2.0%. The aldehyde-modified cellulose derivative is aldehyde-modified sodium carboxymethyl cellulose or aldehyde-modified polyquaternary ammonium salt.

[0025] Membrane module circulatory immersion in modified solution A: Use modified solution A to pressurize and circulate the cleaned reverse osmosis / nanofiltration membrane module for 10 to 30 minutes at 0.05 to 0.15 MPa, drain modified solution A, and wash the membrane module with pure water.

[0026] Immerse the membrane module in modified solution B: Immerse the membrane module that has been treated with modified solution A and washed with pure water in modified solution B for 5-60 minutes, drain modified solution B, and wash the membrane module with pure water.

[0027] This invention evaluates the separation performance (desalination rate (R) and water flux (F)), antifouling performance, and self-cleaning function of reverse osmosis / nanofiltration membrane modules.

[0028] Evaluation of desalination rate and water flux of reverse osmosis / nanofiltration membrane modules: Cross-flow experiment was conducted with 1000 mg / L NaCl aqueous solution as feed liquid, and the test was performed under the conditions of 1.0 MPa, 25℃, and pH 7.0 ± 0.2.

[0029] Evaluation of the antifouling and self-cleaning functions of reverse osmosis membrane modules: A cross-flow method was used, with bovine serum albumin as the contaminant. The specific steps are as follows:

[0030] (1) Using pure water as feed liquid, the pure water flux of the reverse osmosis / nanofiltration membrane module was measured at a pressure of 1.0 MPa and a temperature of 25 ± 1 °C, and used as the initial flux (J0);

[0031] (2) Maintaining constant operating pressure, add 100 mg / L bovine serum albumin to pure water. After running for 60 minutes, measure the steady-state water flux (J) of the reverse osmosis / nanofiltration membrane module. s );

[0032] (3) Use pure water to physically rinse the reverse osmosis membrane module for 30 minutes. After rinsing, test the pure water permeation flux (J2) of the membrane module under the same pressure.

[0033] (4) The membrane module was circulated and soaked for 30 minutes at 0.1 MPa using hydrochloric acid aqueous solution with pH 2.0 or sodium hydroxide aqueous solution with pH 11.0. After rinsing with pure water, the pure water permeation flux (J3) of the membrane module was tested under the same pressure.

[0034] result:

[0035] Table 1: Separation performance of reverse osmosis / nanofiltration membrane modules

[0036]

[0037]

[0038] The data in Table 1 show that after modifying the reverse osmosis / nanofiltration membrane module using the method of the present invention, the water flux of both the reverse osmosis and nanofiltration membrane modules did not change significantly, while the desalination rate of sodium chloride by the reverse osmosis membrane module was slightly improved.

[0039] Table 2: Antifouling performance of reverse osmosis / nanofiltration membrane modules

[0040]

[0041]

[0042] The data in Table 2 show that, under the same conditions, when treating bovine serum albumin aqueous solution, the method of this invention resulted in higher stable water flux, lower flux decay rate, higher water flux after washing, and higher flux recovery rate for the reverse osmosis / nanofiltration membrane module compared to the unmodified membrane module. This indicates that the modification method of this invention can effectively improve the antifouling performance of reverse osmosis / nanofiltration membrane modules.

[0043] Table 3 Self-cleaning function of reverse osmosis / nanofiltration membrane modules

[0044]

[0045] The data in Table 3 shows that, after the reverse osmosis / nanofiltration membrane module is fouled by bovine serum albumin aqueous solution using the method of the present invention, the antifouling barrier layer can be dissolved using an acidic or alkaline solution, removing the barrier layer along with the contaminants from the membrane surface, and the membrane module flux can be restored to its initial value. In contrast, the water flux of the unmodified membrane module can only be restored to about 70% of its initial value. This demonstrates that the modification method of the present invention can endow the reverse osmosis / nanofiltration membrane module with a self-cleaning function.

Claims

1. A method for in-situ antifouling and self-cleaning functional modification of a composite membrane module, characterized in that... Includes the following steps: S1. A certain amount of water-soluble functional material containing amino functional groups is dissolved in pure water to prepare an aqueous solution of a certain concentration, which is used as modification solution A; a certain amount of aldehyde-modified cellulose derivative is dissolved in pure water to prepare an aqueous solution of a certain concentration, which is used as modification solution B. S2. At room temperature, the cleaned reverse osmosis / nanofiltration membrane module is subjected to pressurized circulation immersion treatment with modified solution A. After a certain period of time, the modified solution A is drained, and the membrane module is washed with pure water. S3. At room temperature, immerse the membrane module that has been treated with modified solution A and washed with pure water in modified solution B. After a certain period of time, drain the modified solution and wash the membrane module with pure water.

2. The in-situ antifouling and self-cleaning functional modification method for a composite membrane module according to claim 1, characterized in that: The water-soluble functional material containing amino functional groups is one or more of polyethyleneimine, chitosan, or sericin; the mass percentage concentration of the water-soluble functional material containing amino functional groups is 0.005%-0.02%.

3. The in-situ antifouling and self-cleaning functional modification method for a composite membrane module according to claim 1, characterized in that: The aldehyde-modified cellulose derivative is sodium aldehyde methyl cellulose or aldehyde-modified polyquaternary ammonium salt; the mass percentage concentration of the aldehyde-modified cellulose derivative is 0.1%-2.0%.

4. The in-situ antifouling and self-cleaning functional modification method for a composite membrane module according to claim 1, characterized in that: The time for pressurized cyclic immersion treatment of the membrane module with modified solution A is 10-30 minutes.

5. The in-situ antifouling and self-cleaning functional modification method for a composite membrane module according to claim 1, characterized in that: The soaking time for the membrane module treated with modified solution A and washed with pure water using modified solution B is 5-60 minutes.

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