Preparation method of hollow fiber composite membrane containing hole structure

Abstract

The invention relates to a preparation method of a membrane material, in particular to a preparation method of a hollow fiber composite membrane containing a hole structure. Aiming at the characteristics of a hollow fiber carrier, interfacial polymerization is carried out by adopting a mode that an organic phase solution passes through the inside of the carrier, chlorine salt such as lithium chloride or sodium chloride is selectively added into the organic phase solution according to the problem of chloride ion deficiency in the later period of polymerization, and on one hand, the chlorine salt can supplement chloride ions missing in the silver chloride synthesis process; on the other hand, the polyamide can be used as a phase transfer agent to promote two-phase interfacial polymerization reaction and ensure the compactness of polyamide.

Description

Technical Field

[0001] The invention relates to a method for preparing a membrane material, in particular to a method for preparing a hollow fiber composite membrane containing a hole structure. Background Art

[0002] Polyamide composite membrane is a common water treatment membrane material, which can be well applied in many sub-fields such as nanofiltration, reverse osmosis, forward osmosis, etc. Water flux is an important indicator of polyamide composite membrane, and polyamide composite membrane with high flux has always been a research hotspot in this field.

[0003] In order to improve the water flux of polyamide composite membrane, researchers have tried to add hydrophilic additives to the casting solution or apply hydrophilic substances on the membrane surface, but the above methods all need to add non-membrane substances to the membrane, so there are problems with the compatibility of additives and membrane materials and problems of falling off during later applications. Another way to improve water flux is to change the membrane structure, by building a hole structure in the separation layer to achieve the demand for high flux. For example, CN112316753A attempts to generate silver chloride particles using interfacial polymerization byproduct HCl, and removes the hole structure by subsequent dissolution, achieving good flux effects. However, for interfacial polymerization, the early reaction is more intense, the byproduct HCl content is high, and large silver chloride particles are easily formed, while the later reaction decays, and the silver chloride particles formed are smaller, resulting in uneven distribution of silver chloride particles in the separation layer, so that the size of the hole structure in the separation layer after the silver chloride particles are removed in the later stage is seriously uneven, thus becoming a bottleneck for the increase of membrane flux. Therefore, how to optimize the above problems can significantly increase the water flux and needs to be solved. Summary of the invention

[0004] In response to the above problems, the present application designs a new method for preparing a hollow fiber composite membrane containing a hole structure, by continuously adding chloride ions to the aqueous phase to increase the particle size of silver chloride in the later stage, thereby ensuring that the hole structure in the separation layer is relatively uniform, thereby improving the overall flux performance of the membrane.

[0005] The present invention provides a method for preparing a hollow fiber composite membrane containing a hole structure, which is characterized by comprising the following steps: (1) preparing an aqueous monomer solution: adding a metal silver salt and a diamine monomer to pure water in sequence, and stirring for 0.5-2 hours to form a uniform aqueous monomer solution, wherein the concentration of the diamine in the aqueous monomer solution is 0.5-5wt%; (2) preparing an oil phase monomer solution; mixing and stirring a polyacid chloride and an organic solvent in a first tank to form an oil phase monomer solution; (3) Preparing an additive solution: Mixing the chloride salt and the organic solvent in a second tank to form an additive solution. (4) Preparation: Connecting both ends of the hollow fiber carrier to the first tank through pipelines, and connecting the second tank to the first tank so that the additive solution can be added to the first tank in a controlled manner; (5) Membrane formation: After the hollow fiber carrier is immersed in the aqueous monomer solution, the oil phase monomer solution in the first tank is continuously introduced into and out of the hollow fiber carrier and returned to the first tank. After a specific period of time, the additive solution is continuously added to the oil phase monomer solution and continued for a period of time to achieve interfacial polymerization to form an initial membrane, which is then dried.

[0006] (6) The preliminary membrane is immersed in a dissolving solution and then washed with pure water to obtain a hollow fiber composite membrane.

[0007] Preferably, in step (1), the molar ratio of silver to polyamine monomer in the aqueous monomer solution is 1:10-1:30, and the stirring time is 0.5-2h.

[0008] Preferably, the concentration of the diamine in the aqueous monomer solution in step (1) is 0.5-5 wt %, and the diamine is one of ethylenediamine, piperazine, m-phenylenediamine and p-phenylenediamine.

[0009] Preferably, the concentration of the polyacyl chloride in the oil phase monomer solution in step (2) is 1-3 wt %, and the polyacyl chloride is selected from one of trimesoyl chloride, phthaloyl chloride and terephthaloyl chloride.

[0010] Preferably, the chloride salt in step (3) is one of sodium chloride and lithium chloride, and the mass concentration of the additive solution is 10-20wt%.

[0011] Preferably, in step (5), the oil phase monomer solution enters and exits the hollow fiber carrier at a rate of 0.3-3 ml / min.

[0012] Preferably, the specific time in step (5) is 2-20 seconds.

[0013] Preferably, in step (5), the additive solution enters the aqueous monomer solution at a rate of 0.01-0.5 ml / min.

[0014] Preferably, the period of time in step (5) is 50-170 seconds, and the drying temperature is 40-80°C.

[0015] Preferably, the dissolving solution in step (6) is one of ammonium carbonate or sodium thiosulfate solution, with a concentration of 1-10wt%, and the immersion time is 30-180s.

[0016] Compared with the prior art, the present invention has the following advantages: The present invention adopts the method of passing the organic phase solution through the inside of the carrier to perform interfacial polymerization according to the characteristics of the hollow fiber carrier, and adds a chloride salt such as lithium chloride or sodium chloride to the organic phase solution according to the problem of lack of chloride ions in the late stage of polymerization. The chloride salt can supplement the chloride ions missing in the synthesis process of silver chloride on the one hand, and can also serve as a phase transfer agent to promote the interfacial polymerization reaction of the two phases and ensure the compactness of the polyamide on the other hand. At the same time, in order to ensure the best performance of the membrane, the present invention optimizes various parameters. DETAILED DESCRIPTION

[0017] Example 1 The hollow fiber composite membrane of this embodiment is prepared according to the following steps: (1) Preparation of an aqueous monomer solution: silver nitrate and ethylenediamine were sequentially added to 100 g of pure water and stirred for 1 h to form a uniform aqueous monomer solution, wherein the concentration of the diamine in the aqueous monomer solution was 0.5 wt %, and the molar ratio of silver nitrate to ethylenediamine was 1:15; (2) preparing an oil phase monomer solution; in a first tank, trimesoyl chloride and n-hexane are mixed and stirred to form an oil phase monomer solution, wherein the concentration of trimesoyl chloride is 1 wt %; (3) preparing an additive solution: mixing lithium chloride and n-hexane in a second tank to form an additive solution, wherein the concentration of lithium chloride is 20 wt %; (4) Preparation: Using a polyacrylonitrile hollow fiber ultrafiltration membrane as a hollow fiber carrier, the two ends of which are connected to the first tank body through pipelines, and the second tank body is connected to the first tank body so that the additive solution can be added to the first tank body in a controlled manner; (5) Membrane formation: After the carrier is immersed in the aqueous monomer solution for 5 minutes, the oil phase monomer solution in the first tank is continuously introduced into and out of the hollow fiber carrier at a rate of 2 ml / min and returned to the first tank. After 10 seconds, the additive solution is continuously added to the oil phase monomer solution at a rate of 0.2 ml / min and continued for 110 seconds to achieve interfacial polymerization to form an initial membrane, and then dried at 60°C; (6) The primary membrane was immersed in a 5 wt % sodium carbonate solution for 1 min and then washed with pure water to obtain a hollow fiber composite membrane.

[0018] Comparative Example 1 The hollow fiber composite membrane of this comparative example was prepared according to the following steps: (1) Preparation of an aqueous monomer solution: silver nitrate and ethylenediamine were sequentially added to 100 g of pure water and stirred for 1 h to form a uniform aqueous monomer solution, wherein the concentration of the diamine in the aqueous monomer solution was 0.5 wt %, and the molar ratio of silver nitrate to ethylenediamine was 1:15; (2) preparing an oil phase monomer solution; in a first tank, trimesoyl chloride and n-hexane are mixed and stirred to form an oil phase monomer solution, wherein the concentration of trimesoyl chloride is 1 wt %; (3) Preparation: Using a polyacrylonitrile hollow fiber ultrafiltration membrane as a hollow fiber carrier, the two ends of which are connected to the first tank through pipelines; (4) Membrane formation: After the carrier is immersed in the aqueous monomer solution for 5 min, the oily monomer solution in the first tank is continuously introduced into and out of the hollow fiber carrier at a rate of 2 ml / min and returned to the first tank for 120 s to achieve interfacial polymerization to form an initial membrane, which is then dried at 60 °C; (5) The primary membrane was immersed in a 5 wt % sodium carbonate solution for 1 min and then washed with pure water to obtain a hollow fiber composite membrane.

[0019] Comparative Example 2 The hollow fiber composite membrane of this embodiment is prepared according to the following steps: (1) Preparation of an aqueous monomer solution: silver nitrate and ethylenediamine were sequentially added to 100 g of pure water and stirred for 1 h to form a uniform aqueous monomer solution, wherein the concentration of the diamine in the aqueous monomer solution was 0.5 wt %, and the molar ratio of silver nitrate to ethylenediamine was 1:15; (2) preparing an oil phase monomer solution; in a first tank, trimesoyl chloride and n-hexane are mixed and stirred to form an oil phase monomer solution, wherein the concentration of trimesoyl chloride is 1 wt %; (3) preparing an additive solution: mixing lithium chloride and n-hexane in a second tank to form an additive solution, wherein the concentration of lithium chloride is 20 wt %; (4) Preparation: Connect both ends of the hollow fiber carrier to the first tank through pipes, and add 0.4 ml of the additive solution in the second tank to the first tank; (5) Membrane formation: After the polyacrylonitrile hollow fiber ultrafiltration membrane is used as a carrier and immersed in the aqueous monomer solution for 5 minutes, the oil phase monomer solution in the first tank body is continuously introduced into and out of the hollow fiber carrier at a rate of 2 ml / min and returned to the first tank body for 120 minutes to achieve interfacial polymerization to form an initial membrane, and then dried at 60°C; (6) The primary membrane was immersed in a 5 wt % sodium carbonate solution for 1 min and then washed with pure water to obtain a hollow fiber composite membrane.

[0020] The separation performance and pure water flux performance of the samples of Example 1 and Comparative Examples 1-2 were tested for a sodium sulfate solution with a concentration of 0.2% at an operating pressure of 0.5 MPa and a temperature of 25° C. after running for 1 hour. The results are shown in the following table: Table 1 Membrane properties of different embodiments and comparative examples The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a hollow fiber composite membrane containing a hole structure, characterized in that The following steps are involved: (1) preparing an aqueous monomer solution: adding a metal silver salt and a diamine monomer to pure water in sequence, and stirring for 0.5-2 hours to form a uniform aqueous monomer solution, wherein the concentration of the diamine in the aqueous monomer solution is 0.5-5wt%; (2) preparing an oil phase monomer solution; mixing and stirring a polyacid chloride and an organic solvent in a first tank to form an oil phase monomer solution; (3) preparing an additive solution: mixing a chloride salt and an organic solvent in a second tank to form an additive solution; (4) Preparation: Connecting both ends of the hollow fiber carrier to the first tank through pipelines, and connecting the second tank to the first tank so that the additive solution can be added to the first tank in a controlled manner; (5) Membrane formation: After the hollow fiber carrier is immersed in the aqueous monomer solution, the oil phase monomer solution in the first tank is continuously introduced into and out of the hollow fiber carrier and returned to the first tank. After a specific period of time, the additive solution is continuously added to the oil phase monomer solution for a period of time to achieve interfacial polymerization to form an initial membrane, which is then dried. (6) The preliminary membrane is immersed in a dissolving solution and then washed with pure water to obtain a hollow fiber composite membrane.

2. The preparation method according to claim 1, characterized in that In step (1), the molar ratio of silver to polyamine monomer in the aqueous monomer solution is 1:10-1:30, and the stirring time is 0.5-2h.

3. The preparation method according to claim 1, characterized in that In step (1), the concentration of the diamine in the aqueous monomer solution is 0.5-5wt%, and the diamine is one of ethylenediamine, piperazine, m-phenylenediamine and p-phenylenediamine.

4. The preparation method according to claim 1, characterized in that In step (2), the concentration of the polyacyl chloride in the oil phase monomer solution is 1-3 wt %, and the polyacyl chloride is selected from one of trimesoyl chloride, phthaloyl chloride and terephthaloyl chloride.

5. The preparation method according to claim 1, characterized in that In step (3), the chloride salt is one of sodium chloride and lithium chloride, and the concentration of the additive solution is 10-20wt%.

6. The preparation method according to claim 1, characterized in that In step (5), the oil phase monomer solution enters and exits the hollow fiber carrier at a rate of 0.3-3 ml / min.

7. The preparation method according to claim 1, characterized in that The specific time in step (5) is 2-20 seconds.

8. The preparation method according to claim 1, characterized in that In step (5), the additive solution enters the aqueous monomer solution at a rate of 0.01-0.5 ml / min.

9. The preparation method according to claim 1, characterized in that The period of time in step (5) is 50-170 seconds, and the drying temperature is 40-80°C.

10. The preparation method according to claim 1, characterized in that The dissolving solution in step (6) is one of ammonium carbonate or sodium thiosulfate solution, with a concentration of 1-10wt% and a soaking time of 30-180s.

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