Method for preparing high-performance composite reverse osmosis membrane based on polyamide layer catalyst modification

Abstract

The invention discloses a preparation method of a high-performance composite reverse osmosis membrane based on interfacial polymerization reaction in-situ modification. According to the method, after m-phenylenediamine (MPD) and 1, 3, 5-benzoyl chloride (TMC) are subjected to interfacial polymerization to form a polyamide (PA) selection layer, a nucleophilic catalyst is innovatively introduced to carry out in-situ modification on the selection layer, and a novel PA separation layer with a loose and uniform structure is obtained by regulating and controlling molecular crosslinking density and a chemical structure. Compared with the prior art, the modified reverse osmosis membrane shows remarkably improved hydrophilicity and optimized pore size distribution, the water flux is improved by more than 50% on the premise of not influencing the rejection rate, and meanwhile, excellent long-term operation stability is kept. The technology breaks through the bottleneck of mutual restriction of permeability and selectivity of the traditional reverse osmosis membrane, and has wide application prospects in the fields of seawater desalination, wastewater reuse and the like.

Description

Technical Field

[0001] This invention belongs to the field of reverse osmosis membrane technology, specifically involving in-situ modification of nucleophilic catalysts in polyamide selective layers to improve performance. Background Technology

[0002] With the increasing severity of global water scarcity, developing efficient and sustainable water treatment technologies has become a crucial international issue. Among numerous water treatment technologies, reverse osmosis technology based on membrane separation has become the mainstream solution in seawater desalination and wastewater reuse due to its high treatment efficiency and relatively low energy consumption. PA reverse osmosis membranes, in particular, dominate the reverse osmosis membrane market due to their excellent separation performance and good physicochemical stability. Currently, interfacial polymerization is the main process for preparing composite reverse osmosis membranes. This process forms a PA selective layer through the polymerization reaction of aqueous polyamine monomers and organic polyacrylamide chloride compounds at the interface, offering significant advantages such as simple operation and controllable cost.

[0003] However, reverse osmosis membranes prepared by traditional interfacial polymerization methods have always faced the technical bottleneck of balancing permeation and retention performance. Studies have shown that in-membrane residues (including unreacted MPD monomers and amino-containing oligomers) occupy membrane pores and increase water molecule diffusion resistance, while insufficient hydrophilicity of the membrane surface affects water molecule adsorption and transport. These factors collectively lead to low membrane flux, resulting in increased energy consumption in practical applications. Meanwhile, although unreacted TMC and its acyl chloride hydrolysis-generated carboxyl compounds on the membrane surface can enhance the hydrophilicity and electronegativity of the membrane surface, traditional processes struggle to precisely control this process. How to significantly improve membrane flux while maintaining excellent retention performance has become a research hotspot and cutting-edge direction in the field of reverse osmosis. Developing novel post-treatment technologies that can effectively remove in-membrane residues and optimize the physicochemical properties of the membrane surface has significant theoretical and practical value for promoting the innovation and development of reverse osmosis technology and reducing desalination energy costs.

[0004] In recent years, researchers have made significant progress in the field of reverse osmosis membrane modification, particularly in the optimization of the support layer base membrane and the PA selective layer. Among these, the regulation of the PA selective layer has attracted considerable attention due to its direct impact on membrane separation performance. Current main modification strategies include novel polymerization methods, surface modification, nanoparticle incorporation, and post-treatment. However, these methods generally suffer from problems such as complex processes, limited improvement in membrane performance, or insufficient long-term stability.

[0005] Therefore, this invention innovatively proposes a simple and efficient post-treatment modification method for composite reverse osmosis membranes. By introducing two highly efficient nucleophilic catalysts, DMAP and PPy, the PA selective layer is modified in situ after the interfacial polymerization reaction. On the one hand, the catalysts promote the reaction between residual amino and acyl chloride groups, increasing the content of hydrolyzable carboxyl groups within the membrane and enhancing the hydrophilicity of the membrane surface. On the other hand, by weakening the hydrogen bond network of the PA layer, the spatial confinement within the PA layer is reduced, promoting the release of unreacted substances and oligomers, effectively expanding the membrane pore structure. This dual-action mechanism synergistically optimizes the membrane microstructure, significantly improves water molecule transport efficiency, and exhibits long-term stability. Summary of the Invention

[0006] To address the aforementioned problems, this invention aims to provide a universal composite reverse osmosis membrane material modification technology method that significantly improves membrane permeation performance while maintaining excellent separation selectivity, thus breaking through the performance bottleneck of traditional reverse osmosis membranes.

[0007] In this invention, PSF UF serves as the support layer; an aqueous solution of MPD (2%), CSA (1%), TEA (0.5%), DMSO (1%), and SDS (0.2%) is used as the aqueous phase; and a hexane solution of TMC (0.15%) is used as the organic phase for interfacial polymerization. After the reaction is complete, two nucleophilic catalysts, DMAP and PPy, are used to modify the PA selective layer in situ, thereby significantly improving the membrane performance.

[0008] The technical solution of this invention is as follows:

[0009] A method for modifying a composite reverse osmosis membrane material, comprising the following modification steps:

[0010] (1) Rinse the support membrane in deionized water four times consecutively, and then immerse it completely in deionized water for at least 24 hours.

[0011] (2) Spread the ultrafiltration membrane obtained in step (1) on a glass substrate, pour in the above aqueous solution, and let stand for 5 minutes.

[0012] (3) Remove the residual aqueous phase in step (2) by roller pressing and air-dry at room temperature for 1 minute.

[0013] (4) The TMC solution is uniformly covered on the membrane surface after the treatment in step (3), and the reaction is carried out for 1 minute to form a PA selective layer.

[0014] (5) Rinse the membrane sample obtained in step (4) with n-hexane for 30 seconds.

[0015] (6) Pour a solution containing 0.1% w / v DMAP or PPy n-hexane onto the surface of the membrane obtained in step (5) and keep it in contact for 5 minutes.

[0016] (7) Place the membrane sample obtained in step (6) in an 80°C oven and heat for 5 minutes.

[0017] (8) Place the membrane sample obtained in step (7) in deionized water at 4°C to prepare the composite reverse osmosis membrane material.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. It effectively reduces the surface roughness of the final membrane and promotes the homogenization of the membrane surface microstructure; it forms a more porous membrane structure with higher hydrophilicity and larger pore size distribution, thereby enhancing the membrane permeability.

[0020] 2. While maintaining the NaCl rejection rate (>98%), the water permeation flux was significantly increased, and the stability of the membrane during long-term operation was ensured. Attached Figure Description

[0021] Figure 1 This is a flowchart of the in-situ modification of the nucleophilic catalyst to prepare a composite reverse osmosis membrane according to the present invention. Detailed Implementation

[0022] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto. Any variations without departing from the content and scope of the present invention should be included within the technical scope of the present invention.

[0023] This invention uses PSF UF as the support layer, MPD aqueous solution and TMC organic phase as the reaction monomer system, selects two nucleophilic catalysts, DMAP and PPy, for in-situ modification after post-treatment, and systematically evaluates and compares the permeation flux and retention performance of the prepared modified composite reverse osmosis membrane under standard test conditions using a cross-flow membrane filtration device.

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and examples:

[0025] Example 1.

[0026] After rinsing the supporting membrane four times consecutively in deionized water, it was then completely immersed in deionized water for at least 24 hours for thorough cleaning. The membrane was then laid flat on a glass substrate, the above aqueous solution was poured in, and it was allowed to stand for 5 minutes. Residual aqueous phase was removed using a roller pressing method, and the membrane was air-dried at room temperature for 1 minute. Next, TMC solution was uniformly applied to the membrane surface and reacted for 1 minute to form a PA selective layer. The membrane was then rinsed with n-hexane solution for 30 seconds, and DMAP n-hexane solution was poured onto the membrane surface and kept in contact for 5 minutes to complete interfacial polymerization. The membrane was then heated in an 80°C oven for 5 minutes. Finally, the resulting membrane sample was stored in deionized water at 4°C for later use. To evaluate membrane performance, the prepared composite reverse osmosis membrane was installed in a cross-flow filtration system and operated in circulation mode to maintain a constant feed concentration. The effective membrane area was measured to be 42 cm². 2 The operating pressure is 15.5 bar, the temperature is 25°C, the feed solution is 10 L of 2000 ppm NaCl solution, and the circulation flow rate is 60 L / h. -1 .

[0027] Results: The water permeability of the original membrane was 2.6 L·m³. -2 ·h -1 ·bar -1 The salt rejection rate is 98.8%, and the water permeability of the membrane after DMAP modification is 4.1 L·m³. -2 ·h -1 ·bar -1 The salt rejection rate is 98.3%, meaning that the water permeability of the modified membrane is increased by 57%, while the salt rejection rate is basically maintained.

[0028] Example 2.

[0029] After rinsing the supporting membrane four times consecutively in deionized water, it was then completely immersed in deionized water for at least 24 hours for thorough cleaning. The membrane was then laid flat on a glass substrate, the above aqueous solution was poured in, and it was allowed to stand for 5 minutes. Residual aqueous phase was removed using a roller pressing method, and the membrane was air-dried at room temperature for 1 minute. Next, TMC solution was uniformly applied to the membrane surface and reacted for 1 minute to form a PA selective layer. The membrane was then rinsed with n-hexane solution for 30 seconds, and then PPy n-hexane solution was poured onto the membrane surface and kept in contact for 5 minutes to complete interfacial polymerization. The membrane was then heated in an 80°C oven for 5 minutes. Finally, the resulting membrane sample was stored in deionized water at 4°C for later use. To evaluate membrane performance, the prepared composite reverse osmosis membrane was installed in a cross-flow filtration system and operated in circulation mode to maintain a constant feed concentration. The effective membrane area was measured to be 42 cm². 2 The operating pressure is 15.5 bar, the temperature is 25°C, the feed solution is 10 L of 2000 ppm NaCl solution, and the circulation flow rate is 60 L / h. -1 .

[0030] Results: The water permeability of the original membrane was 2.6 L·m³. -2 ·h -1 ·bar -1 The salt rejection rate is 98.8%, and the water permeability of the membrane after PPy modification is 3.9 L·m³. -2 ·h -1 ·bar -1 The salt rejection rate is 98.1%, meaning that the water permeability of the modified membrane is increased by 50%, while the salt rejection rate is basically maintained.

[0031] In summary, in-situ modification of the PA layer of a reverse osmosis membrane using two nucleophilic catalysts, DMAP and PPy, resulted in a 57% and 50% increase in water permeability, respectively, compared to the original membrane, while maintaining the salt rejection rate essentially. These results demonstrate that the invention can significantly improve the permeation performance of reverse osmosis membranes while maintaining excellent separation selectivity, exhibiting promising application prospects.

Claims

1. A reverse osmosis membrane, characterized in that, Using polysulfone ultrafiltration membrane (PSF UF) as the support layer, and MPD aqueous solution and TMC organic phase as the reactant monomer system, an interfacial polymerization reaction was carried out. Then, the membrane post-treatment was modified in situ using two nucleophilic catalysts, 4-dimethylaminopyridine (DMAP) and 4-pyrrolidinylpyridine (PPy).

2. The composite reverse osmosis membrane material according to claim 1, characterized in that, Compared to traditional reverse osmosis membranes, it can significantly improve membrane permeation performance while maintaining excellent separation selectivity.

3. The method for modifying a reverse osmosis membrane material according to claims 1 and 2, characterized in that, The modification steps include the following: (1) Rinse the support membrane in deionized water four times consecutively, and then immerse it completely in deionized water for at least 24 hours. (2) Spread the ultrafiltration membrane obtained in step (1) on a glass substrate, pour in the MPD aqueous solution, and let it stand for 5 minutes. (3) Remove the residual aqueous phase in step (2) by roller pressing and air-dry at room temperature for 1 minute. (4) The TMC solution is uniformly covered on the membrane surface after the treatment in step (3), and the reaction is carried out for 1 minute to form a PA selective layer. (5) Rinse the membrane sample obtained in step (4) with n-hexane for 30 seconds. (6) Pour a solution containing 0.1% w / v DMAP or PPy n-hexane onto the surface of the membrane obtained in step (5) and keep it in contact for 5 minutes. (7) Place the membrane sample obtained in step (6) in an 80°C oven and heat for 5 minutes. (8) Place the membrane sample obtained in step (7) in deionized water at 4°C to prepare the composite reverse osmosis membrane material.

4. The method for modifying a reverse osmosis membrane material according to claim 1, characterized in that, An aqueous solution of m-phenylenediamine (MPD, 2%), camphor sulfonic acid (CSA, 1%), triethylamine (TEA, 0.5%), dimethyl sulfoxide (DMSO, 1%) and sodium dodecyl sulfate (SDS, 0.2%) was used as the aqueous phase.

5. The method for modifying a reverse osmosis membrane material according to claim 1, characterized in that, The residual aqueous phase was removed by roller pressing.

6. The method for modifying a reverse osmosis membrane material according to claim 1, characterized in that, A hexane solution containing 0.15% TMC was used as the organic phase.

7. The method for modifying a reverse osmosis membrane material according to claim 1, characterized in that, Allow the membrane to come into full contact with a 0.1% w / v DMAP or PPy hexane solution for 5 minutes.

8. The method for modifying a reverse osmosis membrane material according to claim 1, characterized in that, Heat in an 80℃ oven for 5 minutes.

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