Polyamide reverse osmosis membrane and preparation method thereof

Abstract

The invention discloses a polyamide reverse osmosis membrane and a preparation method thereof. The preparation method comprises the steps of hydrogel solution preparation, organic phase solution preparation, interfacial polymerization reaction and heat treatment. According to the preparation method, sodium polyacrylate is added into a water phase solution to prepare a hydrogel solution, the interface reaction process of MPD on a hydrophobic polyethylene substrate and an active monomer is optimized through the hydrogel solution, and the obtained composite membrane has excellent organic solvent resistance and chemical stability; meanwhile, the membrane has the advantages of low preparation cost, high desalination efficiency, long service life and the like, and can be widely applied to membrane separation processes in the fields of seawater desalination, industrial wastewater treatment, chemical separation and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of reverse osmosis membrane water treatment, and particularly relates to a polyamide reverse osmosis membrane and a preparation method thereof. Background Art

[0002] With the acceleration of the industrialization process and the rapid growth of the population, the shortage of fresh water resources has become a global challenge that urgently needs to be solved. Reverse osmosis (RO) technology, as a highly potential means for fresh water treatment, has received extensive attention. In the past few decades, polyamide (PA) thin film composite (TFC) membranes have become the main choice for commercial reverse osmosis (RO) membranes due to their excellent high permeability selectivity, and are widely used in fields such as seawater desalination and brackish water treatment.

[0003] Most traditional commercial RO membranes use polysulfone (PSF) or polyethersulfone (PES) as the support material. However, these materials have some limitations, such as relatively low mechanical strength and poor chemical stability (especially resistance to organic solvents), which limit their application in harsh environments. To overcome these limitations, researchers have explored various polymer materials as the support layer of TFC membranes, including polypropylene (PP), polyacrylonitrile, polyvinyl fluoride, polytetrafluoroethylene, polyimide, and sulfonated polyphenylsulfone, etc. Among them, polyolefin (PE) is considered an ideal support material for TFC membranes due to its high mechanical strength, excellent chemical durability, high porosity, and regular pore structure. In addition, the uniform pore structure and high surface porosity of PE contribute to the formation of a uniform and highly cross-linked PA selective layer through the interfacial polymerization (IP) process, and its highly interconnected and open pore structure can further improve the water flux of the membrane. Therefore, developing a suitable technical route to prepare RO membranes with high water flux and high NaCl rejection rate is of great significance for expanding the application of RO membranes under mechanical and chemical harsh conditions.

[0004] Although there have been some technical solutions in the prior art to improve the performance of hydrophobic polyamide reverse osmosis membranes. For example, patent CN202410805173.4 discloses a reverse osmosis membrane based on hydrophobic materials and a preparation method thereof. This method coats an oil-phase solution on the back of the hydrophobic substrate membrane to make it infiltrate towards the front of the substrate membrane, and at the same time coats an aqueous-phase solution on the front of the substrate membrane. The reaction monomers in the aqueous phase and the oil phase undergo a polymerization reaction at the interface, thereby forming a uniform desalination layer on the surface of the substrate membrane, and finally obtaining a double-sided coated reverse osmosis membrane. However, there is still a large room for exploration and improvement in the current technical solutions for further improving the performance of hydrophobic polyamide reverse osmosis membranes. Summary of the Invention

[0005] The object of the present invention is to overcome the defects of the above-mentioned prior art and provide a polyamide reverse osmosis membrane and a preparation method thereof to improve the stability of interfacial polymerization on its hydrophobic bottom membrane.

[0006] The technical solution adopted by the present invention is as follows: A preparation method of a polyamide reverse osmosis membrane, comprising the following steps:

[0007] 1) Preparation of hydrogel solution: Add m-phenylenediamine and camphorsulfonic acid to pure water, stir until completely dissolved and homogeneous, adjust the pH of the aqueous solution to 10 with triethylamine, then add isopropanol, and the miscible ratio with water is 1:2; finally, add 0.3 wt% sodium polyacrylate to the aqueous solution, dissolve and stir to form a hydrogel;

[0008] 2) Preparation of organic phase solution: Add trimesoyl chloride monomer to n-hexane solvent, stir evenly until completely dissolved, wherein the concentration of trimesoyl chloride is 0.06-1 wt%, and the preferred concentration is 0.1 wt%;

[0009] 3) Interfacial polymerization reaction: Place the polyethylene porous support layer in the hydrogel solution prepared in step 1). After sufficient contact, use a wet film former to scrape off the excess hydrogel solution on the surface of the bottom film, and then place it in the organic phase solution prepared in step 2). After 30 s of sufficient contact, a polyamide nascent membrane is obtained;

[0010] 4) Heat treatment: Dry the polyamide nascent membrane prepared in step 3) by hot air drying at 70 °C, and the heat treatment time is 10 min.

[0011] Another technical solution of the present invention is the polyamide reverse osmosis membrane obtained by the above method.

[0012] The base membrane adopted by the invention is a hydrophobic polyethylene membrane, and the aqueous solution cannot adhere to the membrane surface, so it is difficult to carry out conventional interfacial polymerization. Therefore, the present invention prepares it into a hydrogel solution by adding sodium polyacrylate to the aqueous solution, and optimizes the interfacial reaction process of MPD between the hydrophobic polyethylene substrate and the active monomer through the hydrogel solution. The hydrogel can also adhere to the surface of the hydrophobic polyethylene membrane, enabling the interfacial polymerization to be successfully carried out. The obtained composite membrane has excellent organic solvent resistance (can tolerate organic solvents such as alcohols and ketones) and chemical stability, and at the same time has the advantages of low preparation cost, high desalination efficiency (>96%), long operation life, etc., and can be widely used in membrane separation processes in fields such as seawater desalination, industrial wastewater treatment, and chemical separation. Brief Description of the Drawings

[0013] Figure 1 is the process flow chart of the present invention. Detailed Embodiments

[0014] To better understand the technical solution of the present invention, the content of the present invention will be further elaborated below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments. Unless otherwise specified, the raw materials used in the following examples or comparative examples are all commercially available conventional raw materials.

[0015] The following methods used or possibly used in the embodiments or comparative examples of the present invention are described:

[0016] Comparative Example 1:

[0017] Preparation of polyamide desalination layer: First, dissolve 2.0 wt% of m-phenylenediamine and 4 wt% of camphorsulfonic acid in pure water, then adjust the pH of the solution to 10 with triethylamine to obtain an aqueous solution. After that, contact the aqueous solution with a polyethylene porous support layer for 5 min. After draining the water droplets adsorbed on its surface, then contact it fully with an organic phase solution containing 0.1 wt% of trimesoyl chloride (the solvent is n-hexane of the company) and react for 30 s to obtain a polyamide nascent membrane. The obtained polyamide nascent membrane is dried with hot air at 70 °C for 10 min, and finally the composite membrane is rinsed with deionized water to obtain a composite reverse osmosis membrane containing a polyamide desalination layer.

[0018] The initial desalination rate of the obtained reverse osmosis membrane is 30%, and the permeation flux is 20 L / (m 2 ·h).

[0019] Examples 1-5:

[0020] Preparation of polyamide desalination layer: First, dissolve 2.0 wt% of m-phenylenediamine and 4 wt% of camphorsulfonic acid in pure water, then adjust the pH of the solution to 10 with triethylamine to obtain an aqueous solution. After that, add isopropyl alcohol to the aqueous solution, and the ratio of mutual solubility with water is 1:2. Finally, add 0.2 wt%, 0.4 wt%, 0.6%, 0.8%, 1.0% of polyacrylate with different molecular weights and dissolve and stir to obtain a hydrogel solution; then contact the hydrogel solution with a polyethylene porous support layer for 5 min. Use a wet film former to remove the excess hydrogel solution on the membrane surface, and then contact it fully with an organic phase solution containing 0.1 wt% of trimesoyl chloride (the solvent is n-hexane of the company) and react for 30 s to obtain a polyamide nascent membrane. The obtained polyamide nascent membrane is dried with hot air at 70 °C for 10 min, and finally the composite membrane is rinsed with deionized water to obtain a composite reverse osmosis membrane containing a polyamide desalination layer.

[0021] The initial desalination rate and permeation flux of the obtained reverse osmosis membrane are as follows in the table:

[0022]

[0023] It can be concluded from the comparison of Examples 1 - 5 that the film - forming performance is optimal when 0.4 wt% of sodium polyacrylate is added to the aqueous phase.

[0024] Examples 6 - 10:

[0025] Preparation of the polyamide desalination layer: First, dissolve 2.0 wt% of m - phenylenediamine and 4 wt% of camphorsulfonic acid in pure water, then adjust the pH of the solution to 10 with triethylamine to obtain an aqueous solution. After that, add isopropanol to the aqueous solution, with a ratio of 1:2 to water. Finally, add 0.4 wt% of sodium polyacrylate, dissolve and stir to obtain a hydrogel solution. Then, contact the hydrogel solution with a polyethylene porous support layer for 5 min. Use a wet - film former to remove the excess hydrogel solution on the membrane surface, and then contact it fully with an organic phase solution containing 0.1 wt% of trimesoyl chloride (the solvent is n - hexane from the company) for 30 s to obtain a nascent polyamide membrane. Dry the obtained nascent polyamide membrane under hot air at 70 °C for 10 min. Finally, rinse the composite membrane with deionized water to obtain a composite reverse osmosis membrane containing a polyamide desalination layer.

[0026] The initial desalination rate and permeation flux of the obtained reverse osmosis membrane are as follows in the table:

[0027]

[0028] It can be concluded from Examples 5 - 10 that the salt - rejection performance of this membrane can reach about 96.6%.

[0029] Examples 11 - 15:

[0030] Preparation of the polyamide desalination layer: First, dissolve 2.0 wt% of m - phenylenediamine and 4 wt% of camphorsulfonic acid in pure water, then adjust the pH of the solution to 10 with triethylamine to obtain an aqueous solution. After that, add isopropanol to the aqueous solution, with a ratio of 1:2 to water. Finally, add 0.4 wt% of sodium polyacrylate, dissolve and stir to obtain a hydrogel solution. Then, contact the hydrogel solution with a polyethylene porous support layer for 5 min. Use a wet - film former to remove the excess hydrogel solution on the membrane surface, and then contact it fully with an organic phase solution containing 0.1 wt% of trimesoyl chloride (the solvent is n - hexane from the company) for 30 s to obtain a nascent polyamide membrane. Dry the obtained nascent polyamide membrane under hot air at 70 °C for 10 min. Finally, rinse the composite membrane with deionized water to obtain a composite reverse osmosis membrane containing a polyamide desalination layer. Then, conduct a test on the resistance of the membrane to DMAC organic solvent, and the changes in salt - rejection rate and water flux are as follows in the table:

[0031]

[0032] It is not difficult to see from the table that the water flux of the membrane increases, and the salt rejection rate decreases slightly. The overall performance is relatively stable. The superior chemical stability of the FC-PE membrane is attributed to its chemically inert structure (-CH2-) and the inherent strong organic solvent resistance of the PE carrier endowed by its high crystallinity. This beneficial property of the TFC-PE membrane will enable us to expand the application scope of the membrane to the treatment of wastewater containing organic solvents and the purification of organic solution systems.

Claims

1. A method for preparing a polyamide reverse osmosis membrane, comprising the following steps: 1) Preparation of hydrogel solution: Add m-phenylenediamine and camphorsulfonic acid to pure water, stir until completely dissolved and homogeneous, adjust the pH of the aqueous solution to 10 with triethylamine, then add isopropanol, and finally add sodium polyacrylate to the aqueous solution, dissolve and stir to form a hydrogel; 2) Preparation of organic phase solution: Add trimesoyl chloride monomer to n-hexane solvent, stir evenly until completely dissolved; 3) Interfacial polymerization reaction: Place the polyethylene porous support layer in the hydrogel solution prepared in step 1). After sufficient contact, use a wet film former to scrape off the excess hydrogel solution on the surface of the bottom film, and then place it in the organic phase solution prepared in step 2). After 30 s of sufficient contact, a polyamide nascent membrane is obtained; 4) Heat treatment: Dry the polyamide nascent membrane prepared in step 3) by hot air drying.

2. The preparation method of the polyamide reverse osmosis membrane according to claim 1, wherein: In the said step 1), the ratio of isopropanol miscible with water is 1:2; 0.3 wt% of sodium polyacrylate is added to the aqueous solution.

3. The preparation method of the polyamide reverse osmosis membrane according to claim 1, characterized in that: The concentration of trimesoyl chloride is 0.06-1 wt%, and the preferred concentration is 0.1 wt%.

4. The preparation method of the polyamide reverse osmosis membrane according to claim 1, characterized in that: In the said step 4), the heat treatment temperature is 70 °C and the heat treatment time is 10 min.

5. A polyamide reverse osmosis membrane prepared by the method according to any one of claims 1-4.

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