A method for preparing a hollow fiber composite membrane containing a cavity structure

Abstract

This invention relates to a method for preparing membrane materials, specifically a method for preparing hollow fiber composite membranes containing void structures. Addressing the characteristics of hollow fiber carriers, this invention employs an organic phase solution flowing into the carrier for interfacial polymerization. To address the issue of chloride ion loss in the later stages of polymerization, chloride salts such as lithium chloride or sodium chloride are added to the organic phase solution. These chloride salts replenish the chloride ions lost during silver chloride synthesis and act as phase transfer agents to promote the interfacial polymerization reaction between the two phases, ensuring the compactness of the polyamide.

Description

Technical Field

[0001] This invention relates to a method for preparing a membrane material, specifically a method for preparing a hollow fiber composite membrane containing a vacancy structure. Background Technology

[0002] Polyamide composite membranes are a common type of water treatment membrane material, finding wide application in various sub-fields such as nanofiltration, reverse osmosis, and forward osmosis. Water flux is a crucial indicator of polyamide composite membrane performance, and high-flux polyamide composite membranes have consistently been a research hotspot in this field.

[0003] To improve the water flux of polyamide composite membranes, researchers have attempted to add hydrophilic additives to the casting solution or coat the membrane surface with hydrophilic substances. However, both methods require the addition of non-membrane substances, leading to compatibility issues between the additives and the membrane material, as well as issues of detachment during later applications. Another approach to improving water flux involves altering the membrane structure by constructing void structures in the separation layer to achieve high flux. For example, CN112316753A attempted to utilize the interfacial polymerization byproduct HCl to generate silver chloride particles, which were then dissolved and removed to form void structures, achieving good flux results. However, for interfacial polymerization reactions, the initial reaction is more vigorous, resulting in a high content of the byproduct HCl and the formation of large silver chloride particles. Later, the reaction weakens, resulting in smaller silver chloride particles. This leads to uneven distribution of silver chloride particles in the separation layer, resulting in severely uneven void structure sizes after the removal of silver chloride particles, thus becoming a bottleneck for increasing membrane flux. Therefore, optimizing these issues to significantly increase water flux is a pressing problem. Summary of the Invention

[0004] To address the aforementioned issues, this application presents a novel method for preparing hollow fiber composite membranes with vacuoles. By continuously supplementing chloride ions into the aqueous phase to increase the particle size of silver chloride particles in the later stage, the vacuoles in the separation layer are made more uniform, thereby improving the overall flux performance of the membrane.

[0005] This invention provides a method for preparing a hollow fiber composite membrane containing a vacancy structure, characterized by comprising the following steps:

[0006] (1) Preparation of aqueous monomer solution: Add silver salt and diamine monomer sequentially to pure water and stir for 0.5-2 h to form a homogeneous aqueous monomer solution. The concentration of diamine in the aqueous monomer solution is 0.5-5 wt%.

[0007] (2) Preparation of oil phase monomer solution; In the first tank, polyacryl chloride and organic solvent are mixed and stirred to form oil phase monomer solution;

[0008] (3) Preparation of additive solution: In the second tank, chloride salt and organic solvent are mixed to form an additive solution.

[0009] (4) Preparation: Connect the two ends of the hollow fiber carrier to the first tank through pipelines, and connect the second tank to the first tank so that the additive solution can be added to the first tank in a controlled manner;

[0010] (5) Film formation: After the hollow fiber carrier is immersed in the aqueous monomer solution, the oil phase monomer solution in the first tank is continuously fed into and out of the hollow fiber carrier and returned to the first tank. After a certain 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 film, and then dried.

[0011] (6) The above-mentioned primary membrane is soaked in the dissolving solution and then washed with pure water to obtain a hollow fiber composite membrane.

[0012] 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.

[0013] 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.

[0014] Preferably, the concentration of polyacryl chloride in the oil phase monomer solution in step (2) is 1-3 wt%, and the polyacryl chloride is selected from one of pyromellitic chloroformyl chloride, phthaloyl chloride, and terephthaloyl chloride.

[0015] Preferably, in step (3), the chloride salt is one of sodium chloride and lithium chloride, and the mass concentration of the additive solution is 10-20 wt%.

[0016] 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.

[0017] Preferably, the specific time in step (5) is 2-20 seconds.

[0018] Preferably, in step (5), the additive solution is introduced into the aqueous monomer solution at a rate of 0.01-0.5 ml / min.

[0019] Preferably, the time period in step (5) is 50-170s, and the drying temperature is 40-80℃.

[0020] Preferably, the dissolving solution in step (6) is either ammonium carbonate or sodium thiosulfate solution, with a concentration of 1-10 wt% and a soaking time of 30-180 s.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention addresses the characteristics of hollow fiber carriers by employing an organic phase solution flowing into the carrier for interfacial polymerization. To address the issue of chloride ion loss in the later stages of polymerization, chloride salts such as lithium chloride or sodium chloride are added to the organic phase solution. These chloride salts replenish the chloride ions lost during silver chloride synthesis and act as phase transfer agents to promote the interfacial polymerization reaction between the two phases, ensuring the compactness of the polyamide. Furthermore, to guarantee optimal membrane performance, this invention optimizes various parameters. Detailed Implementation

[0023] Example 1

[0024] The hollow fiber composite membrane in this embodiment is prepared according to the following steps:

[0025] (1) Preparation of aqueous monomer solution: Silver nitrate and ethylenediamine are added sequentially to 100g of pure water and stirred for 1h to form a homogeneous aqueous monomer solution. The concentration of the diamine in the aqueous monomer solution is 0.5wt%, and the molar ratio of silver nitrate to ethylenediamine is 1:15.

[0026] (2) Preparation of oil phase monomer solution; in the first tank, pyromellitic chlorohydrin chloride and n-hexane are mixed and stirred to form oil phase monomer solution, the concentration of pyromellitic chlorohydrin chloride is 1 wt%;

[0027] (3) Preparation of additive solution: Lithium chloride and n-hexane are mixed in the second tank to form an additive solution, wherein the concentration of lithium chloride is 20 wt%;

[0028] (4) Preparation: The polyacrylonitrile hollow fiber ultrafiltration membrane is used as a hollow fiber carrier. Both ends are connected to the first tank through pipelines, and the second tank is connected to the first tank so that the additive solution can be added to the first tank in a controlled manner.

[0029] (5) Film formation: After immersing the carrier in the aqueous monomer solution for 5 min, the oil phase monomer solution in the first tank is continuously fed into and out of the hollow fiber carrier at a rate of 2 ml / min and returned to the first tank. After 10 s, the additive solution is continuously added to the oil phase monomer solution at a rate of 0.2 ml / min and continued for 110 s to achieve interfacial polymerization to form the initial film, and then dried at 60 ℃.

[0030] (6) The above-mentioned primary membrane is soaked in a 5 wt% sodium carbonate solution for 1 min and then washed with pure water to obtain a hollow fiber composite membrane.

[0031] Comparative Example 1

[0032] The hollow fiber composite membrane of this comparative example was prepared according to the following steps:

[0033] (1) Preparation of aqueous monomer solution: Silver nitrate and ethylenediamine are added sequentially to 100g of pure water and stirred for 1h to form a homogeneous aqueous monomer solution. The concentration of the diamine in the aqueous monomer solution is 0.5wt%, and the molar ratio of silver nitrate to ethylenediamine is 1:15.

[0034] (2) Preparation of oil phase monomer solution; in the first tank, pyromellitic chlorohydrin chloride and n-hexane are mixed and stirred to form oil phase monomer solution, the concentration of pyromellitic chlorohydrin chloride is 1 wt%;

[0035] (3) Preparation: The polyacrylonitrile hollow fiber ultrafiltration membrane is used as a hollow fiber carrier and connected to the first tank above through pipelines at both ends;

[0036] (4) Film formation: After immersing the carrier in the aqueous monomer solution for 5 minutes, the oil phase monomer solution in the first tank is continuously fed into and out of the hollow fiber carrier at a rate of 2 ml / min and returned to the first tank for 120 seconds to achieve interfacial polymerization to form a primary film, and then dried at 60°C.

[0037] (5) The above-mentioned primary membrane is soaked in a 5 wt% sodium carbonate solution for 1 min and then washed with pure water to obtain a hollow fiber composite membrane.

[0038] Comparative Example 2

[0039] The hollow fiber composite membrane in this embodiment is prepared according to the following steps:

[0040] (1) Preparation of aqueous monomer solution: Silver nitrate and ethylenediamine are added sequentially to 100g of pure water and stirred for 1h to form a homogeneous aqueous monomer solution. The concentration of the diamine in the aqueous monomer solution is 0.5wt%, and the molar ratio of silver nitrate to ethylenediamine is 1:15.

[0041] (2) Preparation of oil phase monomer solution; in the first tank, pyromellitic chlorohydrin chloride and n-hexane are mixed and stirred to form oil phase monomer solution, the concentration of pyromellitic chlorohydrin chloride is 1 wt%;

[0042] (3) Preparation of additive solution: Lithium chloride and n-hexane are mixed in the second tank to form an additive solution, wherein the concentration of lithium chloride is 20 wt%;

[0043] (4) Preparation: Connect the two 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;

[0044] (5) Film formation: After immersing the polyacrylonitrile hollow fiber ultrafiltration membrane as a carrier in the aqueous monomer solution for 5 min, the oil phase monomer solution in the first tank is continuously fed into and out of the hollow fiber carrier at a rate of 2 ml / min and returned to the first tank. This process is continued for 120 minutes to achieve interfacial polymerization to form the initial film, and then dried at 60°C.

[0045] (6) The above-mentioned primary membrane is soaked in a 5 wt% sodium carbonate solution for 1 min and then washed with pure water to obtain a hollow fiber composite membrane.

[0046] The separation performance and pure water flux of the samples from Example 1 and Comparative Examples 1-2 were tested after running in a 0.2% sodium sulfate solution at an operating pressure of 0.5 MPa and a temperature of 25°C for 1 hour. The results are shown in the table below:

[0047] Table 1. Membrane performance of different embodiments and comparative examples

[0048]

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a hollow fiber composite membrane containing a vacancy structure, characterized in that... Includes the following steps: (1) Preparation of aqueous monomer solution: Add silver salt and diamine monomer sequentially to pure water and stir for 0.5-2h to form a uniform aqueous monomer solution. The concentration of diamine in the aqueous monomer solution is 0.5-5wt%. (2) Preparation of oil-phase monomer solution: Mix polyacrylamide chloride and organic solvent in the first tank and stir to form an oil-phase monomer solution. (3) Preparation of additive solution: In the second tank, chloride salt and organic solvent are mixed to form an additive solution; (4) Preparation: Connect the two ends of the hollow fiber carrier to the first tank through pipelines, and connect the second tank to the first tank so that the additive solution can be added to the first tank in a controlled manner; (5) Film formation: After the hollow fiber carrier is immersed in the aqueous monomer solution, the oil phase monomer solution in the first tank is continuously fed into and out of the hollow fiber carrier and returned to the first tank. After a certain 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 film, and then dried. (6) The above-mentioned primary membrane is soaked in the 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 diamine 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 0.5-5 wt%, 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 polyacryl chloride in the oil phase monomer solution is 1-3 wt%, and the polyacryl chloride is selected from one of pyromellitic chloride, phthaloyl chloride, and terephthaloyl chloride.

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

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 mentioned in step (5) is 2-20 seconds.

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

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

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

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