A high-efficiency nanofiltration membrane for intercepting multivalent anions and cations, and a preparation method and application thereof

Abstract

The application discloses a kind of high-efficiency interception polyvalent anion and cation nanofiltration membrane and its preparation method and application.The method includes the following preparation process:1) preparation concentration is 0.1-2wt% of apigenin class of substance aqueous solution, and concentration is 0.1-0.5wt% of multi-acid chloride organic phase solution;2) make polymer support membrane in aqueous solution 1-5min, remove the surface excess solution, then immerse into oil phase solution, react 1-15min;3) after reaction, remove the surface excess solution, solidify 5-20min under 60-80 DEG C, obtain the nanofiltration membrane.The application is with apigenin, apigenin-7-o-glucuronide and / or isofraxidin as aqueous monomer, and multi-acid chloride is prepared by interfacial polymerization reaction to obtain negative NF membrane, not only maintain the high interception rate to polyvalent anion, and also have very high interception rate to polyvalent cation, can efficiently permeate monovalent ion, and water flux is larger.

Description

Technical Field

[0001] This invention relates to a nanofiltration membrane and its preparation, and more particularly to a nanofiltration membrane for high-efficiency retention of multivalent anions and cations, its preparation method, and its application. Background Technology

[0002] Global freshwater resources are finite, and population growth and more intensive industrial activity are driving a continuous increase in demand for freshwater. A key solution to address this growing demand and prevent further deterioration of freshwater supply is the development of brackish water resources. In water-scarce regions, brackish water is abundant and has low salinity. Existing desalination processes can be broadly categorized into thermal and membrane methods. Thermal processes are mainly used for seawater desalination and in regions where fossil fuel prices are low. Therefore, in energy-scarce regions, membrane processes are the preferred method for treating low-salinity brackish water.

[0003] Currently, nanofiltration (NF) and reverse osmosis (RO) are the most advanced technologies for brackish water desalination. However, during the RO process, the calcium content in the brackish water... 2+ Mg 2+ and SO4 2-Scaling ions can form precipitates, causing RO membrane fouling and reducing treatment efficiency. Nanofiltration (NF) is favored for its selective removal of multivalent ions and offers advantages such as low operating pressure, low energy consumption, and high flux, leading researchers to focus on its application in brackish water desalination. Traditional commercial nanofiltration membranes are prepared using piperazine (PIP) and trimesoyl chloride (TMC) as reactants (PIP-TMC membranes). Due to the negatively charged membrane surface and the Donnan effect, they exhibit high rejection rates for multivalent anions but cannot effectively retain multivalent cations (only 20-40%). To address this issue, recent work has focused on using various techniques to prepare positively charged nanofiltration membranes using polyethyleneimine (PEI), which contains abundant active amine groups and leverages its protonation properties. Gu et al. (Journal of Membrane Science, 2019, 581: 214-223) prepared a novel positively charged nanofiltration membrane by gradient crosslinking of PEI and trimethoxy acid (TMA) on the surface of a PES ultrafiltration membrane to increase the rejection rate of polyvalent cations (MgCl2 rejection rate of 93.0%). Li et al. (Separation and Purification Technology, 2022, 280) achieved a MgCl2 rejection rate of 97.5% by interfacial polymerization of PEI and 1,2,3,4-cyclobutanetetracarboxylic acid chloride (BTC). However, due to the Donnan effect, these membranes could not effectively retain Na2SO4, with a rejection rate as low as 8.8%. Simultaneously, the water flux of these membranes was generally low. Furthermore, since many contaminants in aqueous solutions are negatively charged, such as silica, humic acid, polysaccharides, and bacteria, the electrostatic attraction between the positively charged membrane and the negatively charged contaminants accelerates membrane fouling.

[0004] Therefore, preparing a novel, highly efficient negatively charged NF membrane that can retain multivalent anions and cations is an important challenge. Summary of the Invention

[0005] To address the above technical problems, this invention proposes a highly efficient nanofiltration membrane for retaining multivalent anions and cations, its preparation method, and its application. This invention uses apigenin, apigenin-7-O-glucuronide, and / or isovitexin as aqueous monomers, and performs interfacial polymerization with polyacryl chlorides to prepare a negatively charged NF membrane, which not only maintains the retention of multivalent anions (such as SO42-) but also... 2- High rejection rate for ) and for polyvalent cations (such as Mg) 2+ It also has an extremely high rejection rate, allowing monovalent ions to pass through efficiently, and has a large water flux. In addition, the negatively charged NF membrane avoids electrostatic attraction to negatively charged pollutants, which helps to extend its service life.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a nanofiltration membrane with high efficiency for retaining multivalent anions and cations includes the following preparation process:

[0008] 1) Prepare an aqueous solution of apigenin-like substances with a concentration of 0.1-2 wt%, and an organic solution of polyacrylamide chloride with a concentration of 0.1-0.5 wt%;

[0009] 2) Immerse the polymer support membrane in an aqueous solution for 1-5 minutes, remove excess solution from the surface, and then immerse it in an oil solution for 1-15 minutes.

[0010] 3) After the reaction, remove the excess solution from the surface and cure at 60-80℃ for 5-20 min to obtain the nanofiltration membrane.

[0011] In some specific implementations, the apigenin-like substances are selected from one or more of apigenin, apigenin-7-O-glucuronide, and isovitexin.

[0012] In some specific embodiments, the aqueous solution also contains 1-5 wt% DMF as a co-solvent for apigenin-like substances.

[0013] As a preferred process condition, apigenin-like substances can be dissolved in an aqueous solution by ultrasonic oscillation.

[0014] In some specific embodiments, the polyacryl chloride is selected from one or more of pyromellitic chloroformyl chloride, terephthaloyl chloride, orthophthaloyl chloride, and isophthaloyl chloride;

[0015] The solvent in the organic phase solution is one or more of n-hexane, n-heptane, cyclohexane, and ethylcyclohexane.

[0016] In some specific embodiments, the polymer support membrane is selected from one or more of polysulfone-based membranes, polyacrylonitrile, and polyethersulfone.

[0017] In some specific embodiments, the polymer support membrane is preferably first soaked in deionized water (DI) for 12-24 hours, and then immersed in an aqueous solution.

[0018] Preferably, the polymer support film can be fixed in a polytetrafluoroethylene mold, and then an aqueous phase solution and an organic phase solution can be poured in for wetting treatment; before pouring in the organic phase solution, the aqueous phase solution needs to be poured out and excess solution on the surface needs to be removed.

[0019] The present invention also provides a highly efficient nanofiltration membrane for retaining multivalent anions and cations prepared by the method described above.

[0020] The present invention also provides an application of the highly efficient nanofiltration membrane for retaining multivalent anions and cations prepared by the method described above in the field of water treatment, especially in the field of brackish water treatment.

[0021] The nanofiltration membrane preparation method of this invention is simple and mild, and has the classification characteristics of simultaneously and efficiently retaining multivalent anions and cations, which has broad prospects in practical brackish water treatment. Detailed Implementation

[0022] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0023] Unless otherwise specified, the raw materials and reagents used in the following embodiments of the present invention can be obtained through commercial channels.

[0024] The present invention evaluates the separation performance of the prepared nanofiltration membrane, mainly through two characteristic parameters: water flux and salt rejection rate.

[0025] Water flux (LMH) is defined as the volume of water passing through the effective membrane area per unit time under a certain operating pressure.

[0026] The formula for calculating the salt rejection rate is: R = (1 – Cp / Cf) × 100%, where R (%) is the inorganic salt rejection rate, and Cf (mg·L) is the rejection rate. -1 ) and Cp(mg·L -1 The concentrations of the solutes in the permeate solution and feed solution are the concentrations of the salt, which are measured by a conductivity meter.

[0027] The test conditions for the membrane separation performance of the present invention are as follows: the feed solution is an aqueous solution of sodium sulfate, magnesium chloride and sodium chloride at 2000 ppm, the feed solution temperature is 25°C, and the operating pressure is 6 bar.

[0028]

Example 1

[0029] A method for preparing a nanofiltration membrane includes the following preparation process:

[0030] 1) Prepare an aqueous solution of apigenin-7-O-glucuronide with a concentration of 0.1 wt% and a hexane solution of pyromellitic trimethylol chloride with a concentration of 0.1 wt%; the aqueous solution also contains 1 wt% DMF as a co-solvent for apigenin-like substances, and dissolves them uniformly by ultrasonic vibration.

[0031] 2) Soak the polysulfone-based membrane in deionized water (DI) for 24 hours, fix it in a polytetrafluoroethylene mold, and let the surface moisture dry; then pour the aqueous solution into the mold, let the polysulfone-based membrane wet for 2 minutes, pour off the aqueous solution and remove the excess solution on the surface of the polysulfone-based membrane, then pour in the hexane solution of trimesoyl chloride, and perform interfacial polymerization reaction for 2 minutes.

[0032] 3) After the reaction, remove the excess solution from the surface and cure at 60°C for 10 min to obtain the nanofiltration membrane.

[0033]

Examples 2-6

[0034] Nanofiltration membranes were prepared using a method essentially the same as in Example 1, except that the process parameters and raw materials in each example were adjusted according to the variables in Table 1.

[0035] Table 1. Process parameters and raw material information for Examples 1-6

[0036]

[0037]

[0038] Comparative Example 1

[0039] Nanofiltration membranes were prepared using essentially the same method as in Example 1, except that apigenin-7-O-glucuronide was replaced with piperazine (PIP).

[0040] Comparative Example 2

[0041] Nanofiltration membranes were prepared using essentially the same method as in Example 1, except that apigenin-7-O-glucuronide was replaced with catechin (CA).

[0042] The nanofiltration membranes prepared in the above embodiments and comparative examples were subjected to the performance tests shown in Table 2, and the results are as follows.

[0043] Table 2. Test Results of Nanofiltration Membrane Performance

[0044]

[0045] As can be seen from the test results in Table 2, the negatively charged NF membrane provided by this invention is effective against multivalent anions (SO42-). 2- It has a high rejection rate and is effective against polyvalent cations (Mg). 2+ It also has an extremely high rejection rate, allowing for efficient permeation of monovalent ions, and has a large water flux. Based on the principle of charge conservation in aqueous solutions, that is, the number of positive and negative charges are equal to achieve an electroneutrally neutral state. SO4 2- Retention rate refers to the retention rate of Na2SO4 and Mg. 2+ The rejection rate refers to the MgCl2 rejection rate.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a nanofiltration membrane with high efficiency for retaining multivalent anions and cations, characterized in that, The preparation process includes the following: 1) Prepare an aqueous solution of apigenin-like substances with a concentration of 0.1-2 wt%, and an organic solution of polyacrylamide chloride with a concentration of 0.1-0.5 wt%; 2) Immerse the polymer support membrane in an aqueous solution for 1-5 minutes, remove excess solution from the surface, and then immerse it in an oil solution for 1-15 minutes. 3) After the reaction, remove the excess solution from the surface and cure at 60-80℃ for 5-20 min to obtain the nanofiltration membrane.

2. The method for preparing a high-efficiency nanofiltration membrane for retaining multivalent anions and cations according to claim 1, characterized in that, The apigenin-like substances are selected from one or more of apigenin, apigenin-7-O-glucuronide, and isovitexin.

3. The method for preparing a high-efficiency nanofiltration membrane for retaining multivalent anions and cations according to claim 1, characterized in that, The aqueous solution also contains 1-5 wt% DMF as a co-solvent for apigenin-like substances.

4. The method for preparing a high-efficiency nanofiltration membrane for retaining multivalent anions and cations according to any one of claims 1-3, characterized in that, The polyacryl chloride is selected from one or more of pyromellitic chloromethyl chloride, terephthaloyl chloride, phthaloyl chloride, and isophthaloyl chloride; The solvent in the organic phase solution is one or more of n-hexane, n-heptane, cyclohexane, and ethylcyclohexane.

5. The method for preparing a high-efficiency nanofiltration membrane for retaining multivalent anions and cations according to any one of claims 1-4, characterized in that, The polymer support membrane is selected from one or more of polysulfone-based membranes, polyacrylonitrile, and polyethersulfone.

6. A highly efficient nanofiltration membrane for retaining multivalent anions and cations, prepared by the method according to any one of claims 1-5.

7. The application of a high-efficiency nanofiltration membrane for retaining multivalent anions and cations prepared by the method according to any one of claims 1-5 in the field of water treatment, especially in the field of brackish water treatment.

Images