A method for preparing a fiber polyamide forward osmosis membrane

Abstract

This invention relates to a method for preparing a forward osmosis membrane, specifically a method for preparing a fiber polyamide forward osmosis membrane. Firstly, this invention improves the flatness of the fiber membrane by loading a fine fiber membrane onto a coarse fiber membrane and using in-situ hydrolysis of silane to generate silica to fill the surface voids of the fine fiber membrane, thus facilitating interfacial polymerization to form a high-flux polyamide forward osmosis membrane.

Description

Technical Field

[0001] This invention relates to a method for preparing a forward osmosis membrane, specifically a method for preparing a fiber polyamide forward osmosis membrane. Background Technology

[0002] Forward osmosis is a novel membrane separation technology characterized by the spontaneous movement of water molecules from the feed side to the draw side of the membrane due to the osmotic pressure difference across the membrane, without external pressure. Compared to other membrane separation technologies, forward osmosis offers significant advantages such as low membrane fouling, low energy consumption, and high water production rate, thus gaining widespread attention and application in fields such as pure water production, seawater desalination, power generation, and food concentration. However, concentration polarization has always been a major bottleneck hindering the development of forward osmosis membranes.

[0003] Fiber membranes prepared by electrospinning technology, due to their unique pore structure and high porosity, are an effective solution to reduce concentration polarization. Existing technologies have already used fiber membranes as substrates for polyamide forward osmosis membranes with good results. However, the surface unevenness of the fiber membrane limits the density of the polyamide layer, thus affecting the membrane's permeation performance. To overcome this problem, existing technologies often introduce a transition layer on the fiber membrane surface. However, the transition layer is made of different materials from both the fiber layer and the polyamide layer, resulting in different interfacial stresses between the membrane layers and increasing the likelihood of membrane delamination. Therefore, how to reduce membrane delamination while maintaining the flatness of the fiber membrane warrants further in-depth exploration. Summary of the Invention

[0004] This invention proposes a method for preparing a fiber polyamide forward osmosis membrane. By loading a fine fiber membrane onto a coarse fiber membrane and using in-situ hydrolysis of silane to generate silica to fill the voids on the surface of the fine fiber membrane, the flatness of the fiber membrane is improved. Furthermore, the fiber membrane is made of the same material as the polyamide layer, which reduces the difference in interfacial stress between different membrane layers and lowers the possibility of membrane layer detachment.

[0005] This invention provides a method for preparing a fiber polyamide forward osmosis membrane, which includes the following steps;

[0006] Polyamide is dissolved in a first organic solvent, and silica particles are added and stirred evenly to obtain a coarse fiber spinning solution. The coarse fiber spinning solution contains 15-20 wt% polyamide and 2-8 wt% silica.

[0007] Polyamide of the same specification is dissolved in a second organic solvent, and an appropriate amount of silane coupling agent is added. The mixture is stirred evenly to obtain a fine fiber spinning solution. The polyamide content in the fine fiber spinning solution is 10-15 wt%, and the silane coupling agent content is 1-5 wt%.

[0008] 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.

[0009] The surface of the fiber membrane is immersed in an alkaline solution to hydrolyze silane into silicon dioxide in situ, and the treated fiber membrane is then subjected to hot compaction.

[0010] Aqueous monomer solution and organic monomer solution are sequentially contacted on the surface of the hot-pressed fiber membrane to polymerize and form a polyamide forward osmosis membrane.

[0011] Preferably, the coarse fiber membrane has a coarse fiber diameter of 80-120 nm, and the fine fiber membrane has a fine fiber diameter of 30-70 nm.

[0012] Preferably, the polyamide has a molecular weight of 10,000-100,000.

[0013] Preferably, the silica particles in step (1) have a particle size of 50-200 nm.

[0014] Preferably, the first organic solvent and the second organic solvent are independently selected from one of dimethylformamide, dimethylacetamide, formic acid, and acetic acid.

[0015] Preferably, the silane coupling agent in step (2) is one of a monoamino silane coupling agent, a diamino silane coupling agent, and a polyamino silane coupling agent.

[0016] As a preferred option, in step (3), when the coarse fiber membrane and the fine fiber membrane are electrospun, the spinning voltage is 40-80KV, the receiving distance is 10-30cm, and the humidity is 40-50%.

[0017] Preferably, the alkaline solution in step (4) is sodium hydroxide or potassium hydroxide, with a pH of 8-10.

[0018] Preferably, the aqueous monomer solution in step (5) is one of ethylenediamine, m-phenylenediamine, or piperazine, with a concentration of 0.5-5 wt%.

[0019] Preferably, the organic phase monomer solution in step (5) is one of pyromellitic phthaloyl chloride, terephthaloyl chloride, isophthaloyl chloride and phthaloyl chloride, with a concentration of 0.1-2 wt%.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] First, the present invention improves the flatness of the fiber membrane by loading a fine fiber membrane onto a coarse fiber membrane and using in-situ hydrolysis of silane to generate silica to fill the voids on the surface of the fine fiber membrane, which is more conducive to interfacial polymerization to form a high-flux polyamide forward osmosis membrane.

[0022] 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 interfacial stress between different membrane layers and reduces the possibility of membrane layer detachment.

[0023] In addition, the present invention utilizes the addition of silica particles to the coarse fiber membrane. The difference in silica content in the coarse and fine fiber membranes creates enhanced hydrophilicity along the water flow direction, reducing water resistance and making it easier for water molecules to pass through the membrane layer. Attached Figure Description

[0024] Figure 1 These are SEM images of the surface of the fiber membrane prepared in Example 1;

[0025] Figure 2 This is a SEM image of the surface of the polyamide forward osmosis membrane prepared in Example 1. Detailed Implementation Example 1

[0026] This embodiment prepares a fiber polyamide forward osmosis membrane, and the preparation method is as follows:

[0027] Polyamide with an average molecular weight of 80,000 was dissolved in formic acid, and silica particles with a particle size of 50 nm were added. The mixture was stirred evenly to obtain a coarse fiber spinning solution. The coarse fiber spinning solution contained 16 wt% polyamide and 5 wt% silica.

[0028] Separately, polyamide of the same specification was dissolved in formic acid, and γ-aminopropyltriethoxysilane was added and stirred evenly to obtain a fine fiber spinning solution. The polyamide content in the fine fiber spinning solution was 10 wt%, and the silane coupling agent content was 2 wt%.

[0029] Coarse fiber spinning solution is electrospun into a coarse fiber membrane using a specific spinning head. Then, fine fiber spinning solution is electrospun onto the coarse fiber membrane using a specific spinning head to form a fine fiber membrane for use as a fiber membrane carrier. When electrospinning both the coarse and fine fiber membranes, the spinning voltage is 50KV, the receiving distance is 20cm, and the humidity is 50%. The diameter of the coarse fiber in the coarse fiber membrane is 102nm, and the diameter of the fine fiber in the fine fiber membrane is 44nm.

[0030] The surface of the fiber membrane was immersed in a NaOH solution with a pH of 9 to hydrolyze silanes in situ into silica, and the treated fiber membrane was then subjected to hot compaction (SEM image shown). Figure 1 (as shown)

[0031] A polyamide forward osmosis membrane was polymerized by sequentially contacting a 2 wt% m-phenylenediamine solution and a 1 wt% trimesoyl chloride solution on the surface of a hot-pressed fiber membrane (SEM image shown). Figure 2 (As shown).

[0032] Comparative Example 1

[0033] This embodiment prepares a fiber-polyamide forward osmosis membrane, which is made only of coarse fibers and silica particles. The preparation method is as follows:

[0034] Polyamide with an average molecular weight of 80,000 was dissolved in formic acid, and silica particles with a particle size of 50 nm were added. The mixture was stirred evenly to obtain a coarse fiber spinning solution. The coarse fiber spinning solution contained 16 wt% polyamide and 5 wt% silica.

[0035] The coarse fiber spinning solution is electrospun to form a coarse fiber membrane. When the coarse fiber membrane is electrospun, the spinning voltage is 50KV, the receiving distance is 20cm, and the humidity is 50%.

[0036] The fiber membrane is hot-pressed.

[0037] A polyamide forward osmosis membrane is formed by sequentially contacting a 2 wt% m-phenylenediamine solution and a 1 wt% pyromellitic acid chloride solution on the surface of a hot-pressed fiber membrane to polymerize it.

[0038] Comparative Example 2

[0039] This comparative example prepares a fiber polyamide forward osmosis membrane, which includes a coarse fiber membrane and a fine fiber membrane, but the fine fiber membrane is made of silica particles. The preparation method is as follows:

[0040] Polyamide with an average molecular weight of 80,000 was dissolved in formic acid, and silica particles with a particle size of 50 nm were added. The mixture was stirred evenly to obtain a coarse fiber spinning solution. The coarse fiber spinning solution contained 16 wt% polyamide and 5 wt% silica.

[0041] Separately, polyamide of the same specification was dissolved in formic acid, and silica particles with a particle size of 50 nm were added. The mixture was stirred evenly to obtain a fine fiber spinning solution. The polyamide content in the fine fiber spinning solution was 10 wt%, and the silica content was 2 wt%.

[0042] 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 electrospinning the coarse fiber membrane and the fine fiber membrane, the spinning voltage is 50KV, the receiving distance is 20cm, and the humidity is 50%.

[0043] The fiber membrane is hot-pressed.

[0044] A polyamide forward osmosis membrane is formed by sequentially contacting a 2 wt% m-phenylenediamine solution and a 1 wt% pyromellitic acid chloride solution on the surface of a hot-pressed fiber membrane to polymerize it.

[0045] Comparative Example 3

[0046] This comparative example prepares a fiber-polyamide forward osmosis membrane, which comprises two layers of coarse fiber membranes. The bottom coarse fiber membrane is made of silica particles, and the upper coarse fiber membrane is prepared by in-situ hydrolysis of silica. The preparation method is as follows:

[0047] Polyamide with an average molecular weight of 80,000 was dissolved in formic acid, and silica particles with a particle size of 50 nm were added. The mixture was stirred evenly to obtain the first coarse fiber spinning solution. The first coarse fiber spinning solution contained 16 wt% polyamide and 5 wt% silica.

[0048] Separately, polyamide of the same specification was dissolved in formic acid, and γ-aminopropyltriethoxysilane was added and stirred evenly to obtain a second coarse fiber spinning solution. The polyamide content in the second coarse fiber spinning solution was 16 wt%, and the silane coupling agent content was 2 wt%.

[0049] The first and second coarse fiber spinning solutions were sequentially used to form coarse fiber membranes. During electrospinning, the spinning voltage of both layers was 50KV, the receiving distance was 20cm, and the humidity was 50%.

[0050] The surface of the fiber membrane was immersed in a NaOH solution with a pH of 9 to hydrolyze silane in situ into silicon dioxide, and the treated fiber membrane was then subjected to hot compaction.

[0051] A polyamide forward osmosis membrane is formed by sequentially contacting a 2 wt% m-phenylenediamine solution and a 1 wt% pyromellitic acid chloride solution on the surface of a hot-pressed fiber membrane to polymerize it.

[0052] The forward osmosis membranes of the above examples and comparative examples were tested in FO mode with the polyamide side facing the feed solution. The test temperature was room temperature. 1 mol / L NaCl was used as the draw solution, and deionized water was used as the feed solution. The flow rate of both the draw solution and the feed solution was controlled at 150 mL / min. The test results are shown in Table 1.

[0053] Table 1. Forward osmosis performance of different samples

[0054]

[0055] As can be seen from the table above, the fiber polyamide forward osmosis membrane prepared by this invention has high flux and retention rate, which meets the requirements of practical industrial applications.

[0056] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a fiber polyamide forward osmosis membrane, characterized in that... Includes the following steps; Polyamide is dissolved in a first organic solvent, and silica particles are added and stirred evenly to obtain a coarse fiber spinning solution. The coarse fiber spinning solution contains 15-20 wt% polyamide and 2-8 wt% silica. Polyamide of the same specification is dissolved in a second organic solvent, and an appropriate amount of silane coupling agent is added. The mixture is stirred evenly to obtain a fine fiber spinning solution. The polyamide content in the fine fiber spinning solution is 10-15 wt%, and the silane coupling agent content is 1-5 wt%. 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. The surface of the fiber membrane is immersed in an alkaline solution to hydrolyze silane into silicon dioxide in situ, and the treated fiber membrane is then subjected to hot compaction. Aqueous monomer solution and organic monomer solution are sequentially contacted on the surface of the hot-pressed fiber membrane to polymerize and form a polyamide forward osmosis membrane.

2. The preparation method according to claim 1, characterized in that... The coarse fiber membrane has a diameter of 80-120 nm, while the fine fiber membrane has a diameter of 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 silica 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 monoamino silane coupling agent and a polyamino silane coupling agent.

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

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

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

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

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