Preparation method of fiber polyamide forward osmosis membrane

Abstract

The invention relates to a preparation method of a forward osmosis membrane, in particular to a preparation method of a fiber polyamide forward osmosis membrane. Firstly, a fine fiber membrane is loaded on a crude fiber membrane, in-situ hydrolysis of silane is matched to generate silicon dioxide to fill gaps in the surface of the fine fiber membrane, so that the flatness of the fiber membrane is improved, and interfacial polymerization is more facilitated to form a high-flux polyamide forward osmosis membrane.

Description

Technical Field

[0001] The invention relates to a method for preparing a forward osmosis membrane, in particular to a method for preparing a fiber polyamide forward osmosis membrane. Background Art

[0002] Forward osmosis technology is a new type of membrane separation technology. Its characteristic is that under the condition of no external pressure, the osmotic pressure difference on both sides of the membrane is used to make the water molecules on one side of the raw liquid spontaneously pass through the membrane to the side of the draw liquid. Compared with other membrane separation technologies, forward osmosis technology has significant advantages such as low membrane pollution, low energy consumption and high water production rate. Therefore, it has received widespread attention and application in the fields of pure water preparation, seawater desalination, power generation and food concentration. For forward osmosis membranes, concentration polarization has always been a major bottleneck that has plagued the development of forward osmosis membranes.

[0003] The fiber membrane prepared by electrospinning technology has a special pore structure and high porosity, making it a good way to reduce the concentration polarization problem. The existing technology already uses fiber membrane as the substrate of polyamide forward osmosis membrane, and has achieved good results. However, the unevenness of the fiber membrane surface limits the density of the polyamide layer, thereby affecting the permeability of the membrane. In order to overcome the above problems, the existing technology often introduces a transition layer on the surface of the fiber membrane, but the material of the transition layer is different from that of the fiber layer and the polyamide layer, which leads to different interfacial stresses between the membrane layers, thereby increasing the possibility of membrane shedding. Therefore, how to reduce the shedding of the membrane layer while ensuring the flatness of the fiber membrane is worthy of further exploration. Summary of the invention

[0004] The present invention proposes a method for preparing a fiber polyamide forward osmosis membrane, which improves the flatness of the fiber membrane by loading a fine fiber membrane on a coarse fiber membrane and coordinating the in-situ hydrolysis of silane to generate silicon dioxide to fill the surface gaps of the fine fiber membrane. The fiber membrane uses the same material as the polyamide layer, which reduces the difference in interface stress between different membrane layers and reduces the possibility of membrane layer shedding.

[0005] The present invention provides a method for preparing a fiber polyamide forward osmosis membrane, which comprises the following steps: The polyamide is dissolved in a first organic solvent, and silica particles are added, and stirred to obtain a crude fiber spinning solution, wherein the polyamide content in the crude fiber spinning solution is 15-20wt%, and the silica content is 2-8wt%; The same specifications of polyamide dissolved in a second organic solvent, and add an appropriate amount of silane coupling agent, stirring to obtain a fine fiber spinning solution, the fine fiber spinning solution polyamide content of 10-15wt%, silane coupling agent content of 1-5wt%; Electrospinning the coarse fiber spinning solution to form a coarse fiber membrane, and then electrospinning the fine fiber spinning solution onto the coarse fiber membrane to form a fine fiber membrane for use as a fiber membrane carrier; The surface of the fiber membrane is immersed in an alkali solution to hydrolyze the silane into silicon dioxide in situ, and the treated fiber membrane is subjected to a hot compaction treatment; The surface of the heat-pressed fiber membrane is sequentially contacted with an aqueous monomer solution and an organic monomer solution to polymerize and form a polyamide forward osmosis membrane.

[0006] Preferably, the diameter of the coarse fibers in the coarse fiber membrane is 80-120 nm, and the diameter of the fine fibers in the fine fiber membrane is 30-70 nm.

[0007] Preferably, the molecular weight of the polyamide is 10,000-100,000.

[0008] Preferably, the particle size of the silicon dioxide particles in step (1) is 50-200 nm.

[0009] Preferably, the first organic solvent and the second organic solvent are independently selected from one of dimethylformamide, dimethylacetamide, formic acid and acetic acid.

[0010] Preferably, the silane coupling agent in step (2) is one of a monoaminosilane coupling agent, a bisaminosilane coupling agent and a polyaminosilane coupling agent.

[0011] Preferably, in step (3), when the coarse fiber membrane and the fine fiber membrane are electrospun, the spinning voltage is 40-80 KV, the receiving distance is 10-30 cm, and the humidity is 40-50%.

[0012] Preferably, the alkali solution in step (4) is sodium hydroxide or potassium hydroxide, and the pH value is 8-10.

[0013] Preferably, the aqueous monomer solution in step (5) is one of ethylenediamine, m-phenylenediamine and piperazine, with a concentration of 0.5-5wt%.

[0014] Preferably, the organic phase monomer solution in step (5) is one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and phthaloyl chloride, with a concentration of 0.1-2 wt%.

[0015] Compared with the prior art, the present invention has the following advantages: Firstly, the present invention improves the flatness of the fiber membrane by loading a fine fiber membrane on a coarse fiber membrane and coordinating the in-situ hydrolysis of silane to generate silicon dioxide to fill the surface gaps of the fine fiber membrane, which is more conducive to interfacial polymerization to form a high-flux polyamide forward osmosis membrane.

[0016] Secondly, the coarse and fine fiber membranes of the present invention are made of the same material as the polyamide layer, which reduces the difference in interface stress between different membrane layers and reduces the possibility of membrane layer shedding.

[0017] In addition, the present invention adds silica particles to the coarse fiber membrane, and forms enhanced hydrophilicity along the water flow direction through the different silica contents in the coarse and fine fiber membranes, thereby reducing water resistance and making it easier for water molecules to pass through the membrane layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Is a SEM image of the fiber membrane surface prepared in Example 1; Figure 2 This is a SEM picture of the surface of the polyamide forward osmosis membrane prepared in Example 1. DETAILED DESCRIPTION Example 1

[0019] This embodiment prepares a fiber polyamide forward osmosis membrane, and its preparation method is as follows: The average molecular weight of 80000 polyamide was dissolved in formic acid, and a particle size of 50nm silica particles were added, and stirred to obtain a crude fiber spinning solution, the polyamide content of the crude fiber spinning solution was 16wt%, the silica content was 5wt%; Another polyamide of the same specifications was dissolved in formic acid, and γ-aminopropyltriethoxysilane was added, and stirred to obtain a fine fiber spinning solution, the polyamide content in the fine fiber spinning solution was 10wt%, and the silane coupling agent content was 2wt%; The coarse fiber spinning solution is electrospun using a specific spinning head to form a coarse fiber membrane, and then the fine fiber spinning solution is electrospun using a specific spinning head to form a fine fiber membrane on the coarse fiber membrane to be used as a fiber membrane carrier. When the coarse fiber membrane and the fine fiber membrane are electrospun, the spinning voltage is 50KV, the receiving distance is 20cm, the humidity is 50%, the coarse fiber diameter in the coarse fiber membrane is 102nm, and the fine fiber diameter in the fine fiber membrane is 44nm.

[0020] The fiber membrane surface was immersed in a NaOH solution with a pH of 9 to hydrolyze silane into silicon dioxide in situ, and the treated fiber membrane was subjected to hot compaction treatment (the SEM image of which is shown in Figure 1 shown); The surface of the hot-pressed fiber membrane was sequentially contacted with a 2 wt % m-phenylenediamine solution and a 1 wt % trimesoyl chloride solution to form a polyamide forward osmosis membrane (the SEM image of which is shown in FIG. Figure 2 as shown).

[0021] Comparative Example 1 This embodiment prepares a fiber polyamide forward osmosis membrane, wherein the fiber membrane is made of only coarse fibers and silicon dioxide particles, and the preparation method is as follows: The average molecular weight of 80000 polyamide was dissolved in formic acid, and a particle size of 50nm silica particles were added, and stirred to obtain a crude fiber spinning solution, the polyamide content of the crude fiber spinning solution was 16wt%, the silica content was 5wt%; The coarse fiber spinning solution is electrospun to form a coarse fiber membrane. When the coarse fiber membrane is electrospun, the spinning voltage is 50 KV, the receiving distance is 20 cm, and the humidity is 50%.

[0022] The fiber membrane is subjected to a heat compaction treatment; The surface of the heat-pressed fiber membrane is sequentially contacted with a 2 wt % m-phenylenediamine solution and a 1 wt % trimesoyl chloride solution to polymerize and form a polyamide forward osmosis membrane.

[0023] Comparative Example 2 In this comparative example, a fiber polyamide forward osmosis membrane is prepared, wherein the fiber membrane includes a coarse fiber membrane and a fine fiber membrane, but the fine fiber membrane is made of silicon dioxide particles. The preparation method is as follows: The average molecular weight of 80000 polyamide was dissolved in formic acid, and a particle size of 50nm silica particles were added, and stirred to obtain a crude fiber spinning solution, the polyamide content of the crude fiber spinning solution was 16wt%, the silica content was 5wt%; Another polyamide of the same specifications was dissolved in formic acid, and silica particles having a particle size of 50 nm were added, and stirred to obtain a fine fiber spinning solution, in which the polyamide content in the fine fiber spinning solution was 10wt%, and the silica content was 2wt%; The coarse fiber spinning solution is electrospun to form a coarse fiber membrane, and then the fine fiber spinning solution is electrospun onto the coarse fiber membrane to form a fine fiber membrane for use as a fiber membrane carrier. When the coarse fiber membrane and the fine fiber membrane are electrospun, the spinning voltage is 50KV, the receiving distance is 20cm, and the humidity is 50%.

[0024] The fiber membrane is subjected to a heat compaction treatment; The surface of the heat-pressed fiber membrane is sequentially contacted with a 2 wt % m-phenylenediamine solution and a 1 wt % trimesoyl chloride solution to polymerize and form a polyamide forward osmosis membrane.

[0025] Comparative Example 3 In this comparative example, a fiber polyamide forward osmosis membrane is prepared, which comprises two layers of crude fiber membranes, the bottom layer of crude fiber membrane is made of silicon dioxide particles, and the upper layer of crude fiber membrane is made of silicon dioxide in situ hydrolysis. The preparation method is as follows: The average molecular weight of 80000 polyamide was dissolved in formic acid, and a particle size of 50nm silica particles were added, and stirred to obtain a first crude fiber spinning solution, the first crude fiber spinning solution polyamide content of 16wt%, silica content of 5wt%; Another polyamide of the same specifications was dissolved in formic acid, and γ-aminopropyl triethoxysilane was added, and stirred to obtain a second crude fiber spinning solution, the polyamide content of the second crude fiber spinning solution was 16wt%, and the silane coupling agent content was 2wt%; The first and second coarse fiber spinning solutions are sequentially formed into coarse fiber membranes. During the electrostatic spinning of the double layers, the spinning voltage is 50 KV, the receiving distance is 20 cm, and the humidity is 50%.

[0026] The fiber membrane surface is immersed in a NaOH solution with a pH of 9 to hydrolyze silane into silicon dioxide in situ, and the treated fiber membrane is subjected to a hot compaction treatment; The surface of the heat-pressed fiber membrane is sequentially contacted with a 2 wt % m-phenylenediamine solution and a 1 wt % trimesoyl chloride solution to polymerize and form a polyamide forward osmosis membrane.

[0027] The forward osmosis membranes of the above embodiments and comparative examples were placed in FO mode, with the polyamide surface facing the raw liquid. The test temperature was room temperature, 1 mol / L NaCl was used as the draw liquid, deionized water was used as the raw liquid, the draw liquid flow rate was controlled at 150 mL / min, and the raw liquid flow rate was controlled at 150 mL / min. The test results are shown in Table 1 Table 1 Forward osmosis performance of different samples

[0028] Based on the above table, it can be seen that the fiber polyamide forward osmosis membrane prepared by the present invention has high flux and retention rate, which meets the requirements of practical industrial applications.

[0029] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a fiber polyamide forward osmosis membrane, characterized in that The method comprises the following steps: The polyamide is dissolved in a first organic solvent, and silica particles are added, and stirred to obtain a crude fiber spinning solution, wherein the polyamide content in the crude fiber spinning solution is 15-20wt%, and the silica content is 2-8wt%; The same specifications of polyamide dissolved in a second organic solvent, and add an appropriate amount of silane coupling agent, stirring to obtain a fine fiber spinning solution, the fine fiber spinning solution polyamide content of 10-15wt%, silane coupling agent content of 1-5wt%; Electrospinning the coarse fiber spinning solution to form a coarse fiber membrane, and then electrospinning the fine fiber spinning solution onto the coarse fiber membrane to form a fine fiber membrane for use as a fiber membrane carrier; The surface of the fiber membrane is immersed in an alkali solution to hydrolyze the silane into silicon dioxide in situ, and the treated fiber membrane is subjected to a hot compaction treatment; The surface of the heat-pressed fiber membrane is sequentially contacted with an aqueous monomer solution and an organic monomer solution to polymerize and form a polyamide forward osmosis membrane.

2. The preparation method according to claim 1, characterized in that The diameter of coarse fibers in the coarse fiber membrane is 80-120 nm, and the diameter of fine fibers in the fine fiber membrane is 30-70 nm.

3. The preparation method according to claim 1, characterized in that The molecular weight of the polyamide is 10,000-100,000.

4. The preparation method according to claim 1, characterized in that The particle size of the silicon dioxide particles in step (1) is 40-100 nm.

5. The preparation method according to claim 1, characterized in that The first organic solvent and the second organic solvent are independently selected from one of dimethylformamide, dimethylacetamide, formic acid and acetic acid.

6. The preparation method according to claim 1, characterized in that The silane coupling agent in step (2) is one of a monoaminosilane coupling agent, a bisaminosilane coupling agent and a polyaminosilane coupling agent.

7. The preparation method according to claim 1, characterized in that When the coarse fiber membrane and the fine fiber membrane are electrospun in step (3), the spinning voltage is 40-80 KV, the receiving distance is 10-30 cm, and the humidity is 40-50%.

8. The preparation method according to claim 1, characterized in that In step (4), the alkali solution is sodium hydroxide or potassium hydroxide, and the pH value is 8-10.

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

10. The preparation method according to claim 1, characterized in that The organic phase monomer solution in step (5) is one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride and phthaloyl chloride, and the concentration is 0.1-2wt%.

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