Preparation method of ultra-low-pressure seawater desalination reverse osmosis composite membrane

Abstract

The invention discloses a preparation method of an ultra-low pressure sea water desalination reverse osmosis composite membrane, which comprises the following steps: (1) preparing a water phase solution containing a water phase monomer, and preparing an organic phase solution containing an acyl chloride substituted triptycene compound and an oil phase solvent; (2) immersing a porous support layer base membrane into the aqueous phase solution, removing the redundant aqueous phase solution on the surface of the base membrane by using a rubber roller, and then coating the surface of the membrane with an organic phase solution containing an acyl chloride substituted triptycene compound to obtain a reverse osmosis composite membrane; and (3) carrying out heat treatment on the composite film. The reverse osmosis composite membrane prepared by the method has high pure water flux, keeps high interception performance and is easy to industrialize.

Description

Technical Field

[0001] The invention relates to the technical field of composite membrane preparation, and in particular to an ultra-low pressure seawater desalination reverse osmosis composite membrane and a preparation method thereof. Background Art

[0002] Water resources are vital to ecosystems, human survival, and national security. With the rapid economic development and population growth, the shortage of fresh water resources has become one of the social challenges that need to be solved urgently. In the past two decades, the great progress of energy recovery technology and membrane technology has reduced the energy required for seawater desalination by two times. Membrane technology is currently the most commonly used seawater desalination technology. Among them, reverse osmosis thin film composite membrane has become the main solution to the shortage of fresh water in recent decades due to its advantages such as high filtration accuracy, small footprint, easy scale expansion, and low energy consumption.

[0003] Interfacial polymerization is an effective method for preparing reverse osmosis thin film composite membranes because of its simple operation and easy scale-up. The interfacial polymerization method mainly synthesizes polyamide membranes, and its separation performance is mainly determined by the selectivity layer, which is generally formed by the polymerization reaction of aqueous phase monomers and organic phase monomers at the interface of the two immiscible phases. The operating pressure requirement of traditional seawater desalination is as high as 70 bar. The high-pressure operation requirement is still the main disadvantage of reverse osmosis membranes. High pressure causes membrane compaction, deformation of the selective layer, shrinkage of membrane pores, and thus reduction of membrane permeability, making it difficult to break the balance between selectivity and permeability. The advantage of thin film composite reverse osmosis membranes is that their support layer and selective layer can be optimized to improve performance. Researchers have conducted a lot of research to improve the performance of reverse osmosis membranes. At present, many methods such as surface grafting, layer-by-layer polymerization and post-treatment have been proposed to increase surface charge and adjust pore size to achieve a balance between retention rate and permeability, but the effect is not ideal. Surface grafting and layer-by-layer polymerization increase the retention rate by increasing the thickness of the selective layer, but at the same time also increase the mass transfer resistance of water, resulting in loss of water flux. In recent years, some studies have proposed methods of introducing nanomaterials into the active layer. When nanomaterials are introduced into the active layer, ideally, they can increase the free volume of the selective layer. However, there is often a problem of poor compatibility between nanoparticles and the membrane, which easily forms non-selective holes at the interface, resulting in a sharp increase in flux but a decrease in selectivity. In order to address these issues, researchers have focused on molecular-level design to adjust membrane performance. Studies have shown that the use of rigid monomers with large and twisted structures can adjust the structure of the selective layer to increase flux.

[0004] Tripterygium is composed of three benzene rings, forming a unique three-dimensional paddle-wheel-shaped rigid symmetrical structure. Due to its high rigidity, triptychene will destroy the segment stacking when incorporated into polymer films, so that the membrane has a large internal free volume (IFV), which can effectively reduce the mass transfer resistance of water and improve the permeability of thin film composite membranes. At the same time, the benzene "blade" configuration adjusts the cavity structure and pore uniformity. At present, studies have used triptychene as a reaction monomer to prepare polyamide membranes. Compared with traditional polyamide membranes, the permeation flux has been improved. However, due to the poor solubility and low reactivity of triptychyl derivatives, the prepared polyamide membrane has a low degree of crosslinking, which in turn affects the desalination rate and cannot meet the standards for seawater desalination.

[0005] Therefore, how to prepare a polyamide reverse osmosis membrane that can improve the permeate flux while maintaining a high salt rejection rate and can desalinate seawater under low pressure conditions is still a key difficulty in current technology. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a reverse osmosis composite membrane, which is simple to operate and easy to scale up. The reverse osmosis membrane has excellent permeability and desalination rate and can operate at low pressure, greatly reducing energy consumption.

[0007] To achieve the above object, the present invention provides a method for preparing a reverse osmosis composite membrane, comprising the following steps:

[0008] (1) preparing an aqueous phase solution containing an aqueous phase monomer and an organic phase solution containing an acyl chloride-substituted triptycene compound;

[0009] (2) immersing the porous support layer base membrane in an aqueous solution, removing excess aqueous solution on the surface of the base membrane, and then coating the membrane surface with an organic phase solution containing an acyl chloride-substituted triptycene compound to obtain a reverse osmosis composite membrane;

[0010] (3) heat treating the reverse osmosis composite membrane;

[0011] (4) Post-treating the reverse osmosis composite membrane obtained by heat treatment.

[0012] Preferably, in the aqueous phase solution, the aqueous phase monomer is a water-soluble monomer that can undergo polymerization reaction with an acyl chloride compound, preferably an amine compound, one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, N,N-dimethyl-m-phenylenediamine, s-phenyltriamine, piperazine, 3-aminopiperazine, cyclohexanediamine, ethylenediamine, triethanolamine, polyethyleneimine, polyetheramine, aniline, m-toluidine, o-toluidine, p-nitroaniline, m-fluoroaniline, etc.; the mass fraction concentration of the aqueous phase monomer is 0.1wt%-5wt%;

[0013] Preferably, the porous supporting layer base membrane is immersed in the aqueous solution at room temperature for 30 seconds to 10 minutes.

[0014] Preferably, in the organic phase solution, the acyl chloride substituted triptycene compound is any one of monoacyl chloride substituted triptycene, diacyl chloride substituted triptycene, triacyl chloride substituted triptycene, tetraacyl chloride substituted triptycene, pentaacyl chloride substituted triptycene, and hexaacyl chloride substituted triptycene; the concentration of the triptycene compound in the organic phase solution is 0.005wt%-5wt%; the organic phase solvent is one or more of acetone, n-hexane, acetonitrile, ethyl acetate, methyl acetate, toluene, dichloromethane, 1,2-dichloroethane, cyclohexane, n-heptane, chloroform, mesitylene, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M, etc.;

[0015] Preferably, the coating time of the organic phase solution containing the acyl chloride-substituted triptycene compound is 30 s-10 min, and the temperature is 20-50°C.

[0016] Preferably, the porous supporting layer base membrane is any one of polysulfone, polyethersulfone, polyimide, polyetherimide, polybenzimidazole and polyacrylonitrile.

[0017] Another aspect of the present invention provides a reverse osmosis composite membrane prepared by the above preparation method.

[0018] Through the above technical scheme, the present invention introduces a rigid three-dimensionally twisted triptycene monomer into the organic phase solution, utilizes the highly rigid and bulky characteristics of the triptycene structure, increases the internal free volume of the polymer membrane, and regulates the desalination performance of the selective layer, so as to achieve the purpose of increasing the pure water flux and maintaining the salt retention performance; at the same time, the blade configuration of the triptycene structure can adjust the cavity structure to form interconnected network pores, which is beneficial to reducing the mass transfer resistance of water molecules in the membrane channel and improving the permeability of the reverse osmosis membrane, thereby solving the problem of low flux of the reverse osmosis membrane prepared by the prior art for ultra-low pressure seawater desalination.

[0019] The preparation method of the invention is simple and easy to implement, easy to scale up, excellent in performance and has good industrial applicability. DETAILED DESCRIPTION

[0020] In one aspect, the present invention provides a method for preparing a reverse osmosis composite membrane, comprising the following steps:

[0021] (1) preparing an aqueous phase solution containing an aqueous phase monomer and an organic phase solution containing an acyl chloride-substituted triptycene compound;

[0022] (2) immersing the porous support layer base membrane in an aqueous solution, removing excess aqueous solution on the surface of the base membrane, and then coating the membrane surface with an organic solution containing an acyl chloride-substituted triptycene compound to obtain a reverse osmosis composite membrane;

[0023] (3) heat treating the reverse osmosis composite membrane;

[0024] (4) Post-treating the reverse osmosis composite membrane obtained by heat treatment.

[0025] According to the present invention, a rigid three-dimensionally distorted triptycene monomer is introduced into an organic phase solution. When the interfacial polymerization reaction is carried out with an aqueous phase monomer, the highly rigid and bulky characteristics of the triptycene structure are utilized to adjust the stacking of polymer chain segments and increase the internal free volume of the polymer membrane. The generated polyamide network has a rigid and stable pore structure, and the desalination performance of the selective layer is regulated to achieve the purpose of improving the pure water flux and maintaining the salt retention performance. At the same time, the blade configuration of the triptycene structure can adjust the cavity structure to form interconnected network pores, which is beneficial to reducing the mass transfer resistance of water molecules in the membrane channel and improving the permeability of the reverse osmosis membrane, thereby solving the problem of low flux of the reverse osmosis membrane prepared by the prior art for ultra-low pressure seawater desalination from a molecular level.

[0026] According to the present invention, the aqueous phase monomer is a water-soluble monomer that can undergo polymerization reaction with an acyl chloride compound, preferably an amine compound, one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, N,N-dimethyl-m-phenylenediamine, s-phenyltriamine, piperazine, 3-aminopiperazine, cyclohexanediamine, ethylenediamine, triethanolamine, polyethyleneimine, polyetheramine, aniline, m-toluidine, o-toluidine, p-nitroaniline, m-fluoroaniline, etc.

[0027] According to some preferred embodiments of the present invention, the mass fraction concentration of the aqueous phase monomer is 0.1wt%-5wt%, for example, it can be 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1wt%, 2wt%, 3wt% and other specific but non-limiting concentrations or any range between the two.

[0028] According to the present invention, the acyl chloride substituted triptycene compound may contain one or more acyl chloride substituents, for example, the acyl chloride substituted triptycene compound may be selected from any one of monoacyl chloride substituted triptycene, diacyl chloride substituted triptycene, triacyl chloride substituted triptycene, tetraacyl chloride substituted triptycene, pentaacyl chloride substituted triptycene, and hexaacyl chloride substituted triptycene, preferably 2,6-di(benzoyl chloride)triptycene, 2,7-di(benzoyl chloride)triptycene, 9,10-di(benzoyl chloride)triptycene, 5,10-di(benzoyl chloride)triptycene, The invention relates to any one of tris(benzoyl chloride)tris(ene), 1,7,13-tris(benzoyl chloride)tris(ene), 2,7,13-tris(benzoyl chloride)tris(ene), 2,6,14-tris(benzoyl chloride)tris(ene), 2,7,14-tris(benzoyl chloride)tris(ene), 2,3,6,7-tetra(benzoyl chloride)tris(ene), and 2,3,6,7,14,15-hexa(benzoyl chloride)tris(ene); the invention has no particular limitation on the source of the tris(ene) compounds substituted with acyl chloride, and the tris(ene) compounds can be commercially available or prepared by any method known in the art.

[0029] According to the present invention, the organic phase can use a non-polar organic solvent commonly used in the art; preferably, the organic solvent is selected from one or more of acetone, n-hexane, acetonitrile, ethyl acetate, methyl acetate, toluene, dichloromethane, 1,2-dichloroethane, cyclohexane, n-heptane, chloroform, mesitylene, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M, etc.

[0030] The present invention does not particularly limit the method for preparing the solution in step (1), as long as the above-mentioned components can be fully dissolved and evenly mixed to form a uniform solution; according to some preferred embodiments of the present invention, the method for preparing the aqueous phase and organic phase solutions includes: mixing the aqueous phase monomer with water, mixing the acyl chloride-substituted pterygium compound with the organic phase solvent, and then performing ultrasonic treatment, and the ultrasonic treatment can be performed in an ultrasonic cleaning machine; treatment conditions: ultrasonic frequency is 40kHz-60kHz, and ultrasonic time is 5min-60min.

[0031] According to some preferred embodiments of the present invention, the immersion time of the aqueous solution is 30s-10min.

[0032] Preferably, the temperature of the organic phase is 20° C.-50° C., and the coating time of the organic phase is 30 s-10 min.

[0033] According to the present invention, an interfacial polymerization reaction is carried out on the porous support layer base membrane through step (2) to generate a primary selective layer, and then a thermal cross-linking treatment is further carried out through step (3) to further cross-link the polymer of the primary selective layer, which is beneficial to make the polymer network more complete, reduce defects, and improve the desalination rate.

[0034] Preferably, in step (3), the heat treatment temperature is 40°C-70°C and the time is 6min-20min.

[0035] In order to further improve the permeability of the prepared polyamide reverse osmosis thin film composite membrane, the preparation method further comprises: washing the thin film composite membrane obtained by the heat treatment, and the washing method is preferably immersion.

[0036] Preferably, the washing solution is any one of methanol, ethanol, water, etc.; and the washing time is 5 min-60 min.

[0037] The present invention has no particular limitation on the type of the porous support layer base membrane, and any polymer porous support carrier known in the art that can play a supporting role can be used in the present invention.

[0038] Preferably, the base film is made of at least one of polysulfone, polyethersulfone, polyimide, polyetherimide, polybenzimidazole and polyacrylonitrile.

[0039] The present invention has no particular limitation on the source of the base film, and the base film can be prepared by any conventional method disclosed in the art, or can be purchased commercially.

[0040] Another aspect of the present invention provides a polyamide reverse osmosis thin film composite membrane prepared by the above preparation method.

[0041] Another aspect of the present invention provides application of the polyamide reverse osmosis thin film composite membrane in ultra-low pressure seawater desalination treatment.

[0042] The present invention will be described in detail below by way of examples.

[0043] In the following examples, unless otherwise specified, the raw materials used were commercially available.

[0044] In the following examples, the room temperature is 25°C ± 5°C.

[0045] Example 1

[0046] 1) dissolving 4'4-diaminobiphenyl in water, wherein the concentration of 4'4-diaminobiphenyl is 0.5wt%, dissolving 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene in a mixed solution of n-hexane and ethyl acetate, wherein the concentration of 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene is 0.02wt%; and ultrasonically treating the two solutions for 30 minutes to obtain an aqueous phase solution and an organic phase solution, respectively.

[0047] 2) The aqueous solution was coated on the upper surface of a commercially available polysulfone base membrane for 2 minutes. After removing the surface droplets, the organic solvent was coated on the membrane surface for 5 minutes at a temperature of 30°C.

[0048] 3) After the interfacial polymerization reaction is completed, the composite film is placed in a 60° C. oven for further thermal crosslinking. The thermal crosslinking time is 10 minutes.

[0049] 4) The composite membrane after thermal cross-linking was immersed in methanol for post-treatment for 60 min, and then stored in deionized water for later use. The obtained reverse osmosis composite membrane was recorded as M1.

[0050] Example 2

[0051] 1) dissolving 2,4,6-tris(4-aminophenyl)-1,3,5-triazine in water, wherein the concentration of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is 0.5wt%; dissolving 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene in a mixed solution of n-hexane and ethyl acetate, wherein the concentration of 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene is 0.04wt%; and subjecting the two solutions to ultrasonic treatment for 30 minutes to obtain an aqueous phase solution and an organic phase solution, respectively.

[0052] 2) The aqueous solution was coated on the upper surface of a commercially available polysulfone base membrane for 5 minutes. After removing the surface droplets, the organic solvent was coated on the membrane surface for 5 minutes at a temperature of 30°C.

[0053] 3) After the interfacial polymerization reaction is completed, the composite film is placed in a 60° C. oven for further thermal crosslinking. The thermal crosslinking time is 10 minutes.

[0054] 4) The composite membrane after thermal cross-linking was immersed in methanol for post-treatment for 60 min, and then stored in deionized water for later use. The obtained reverse osmosis composite membrane was recorded as M2.

[0055] Example 3

[0056] 1) dissolving polyethyleneimine in water, wherein the concentration of polyethyleneimine is 0.5wt%, dissolving 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene in a mixed solution of n-hexane and ethyl acetate, wherein the concentration of 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene is 0.02wt%; and ultrasonically treating the two solutions for 30 minutes to obtain an aqueous phase solution and an organic phase solution, respectively.

[0057] 2) The aqueous solution was coated on the upper surface of a commercially available polysulfone base membrane for 3 minutes. After removing the surface droplets, the organic solvent was coated on the membrane surface for 5 minutes at a temperature of 40°C.

[0058] 3) After the interfacial polymerization reaction is completed, the composite film is placed in a 60° C. oven for further thermal crosslinking for 15 minutes.

[0059] 4) The composite membrane after thermal cross-linking was immersed in methanol for post-treatment for 60 min, and then stored in deionized water for later use. The obtained reverse osmosis composite membrane was recorded as M3.

[0060] Example 4

[0061] 1) dissolving a polyetheramine in water, wherein the concentration of the polyetheramine is 0.5 wt %, dissolving 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene in a mixed solution of n-hexane and ethyl acetate, wherein the concentration of 2,3,6,7,14,15-hexa(benzoyl chloride)triptycene is 0.02 wt %; and subjecting the two solutions to ultrasonic treatment for 30 min to obtain an aqueous phase solution and an organic phase solution, respectively.

[0062] 2) The aqueous solution was coated on the upper surface of a commercially available polysulfone base membrane for 3 minutes. After removing the surface droplets, the organic solvent was coated on the membrane surface for 5 minutes at a temperature of 40°C.

[0063] 3) After the interfacial polymerization reaction is completed, the composite film is placed in a 60° C. oven for further thermal crosslinking for 15 minutes.

[0064] 4) The composite membrane after thermal cross-linking was immersed in methanol for post-treatment for 60 min, and then stored in deionized water for later use. The obtained reverse osmosis composite membrane was recorded as M4.

[0065] Seawater desalination performance test:

[0066] Permeation flux and rejection rate are two important indicators to measure reverse osmosis performance. A reverse osmosis cross-flow device was used to test the polyamide reverse osmosis thin film composite membrane.

[0067] Permeate flux is the amount of water that passes through a unit membrane area (A, m2) per unit time (t, h) at a unit pressure (P, bar) under certain operating conditions. 2 ) of water (V, L); the prepared reverse osmosis thin film composite membrane was operated at a pressure of 4 bar for two hours to stabilize the membrane permeability, and the pure water flux was tested three times repeatedly, and the average data was taken as the final result.

[0068] The retention rate refers to the ability of the membrane to retain a certain component in the feed solution. Under certain operating conditions, the difference between the feed solution salt concentration (C1) and the permeate salt concentration (C2) is divided by the feed solution salt concentration (C1). The present invention uses a 2000ppm sodium chloride aqueous solution with a solution pH of 7.5±0.5 and an operating temperature of 25±0.5°C. After running for 1 hour at an operating pressure of 4bar, the permeate is collected, and the concentrations of the feed solution and the permeate are measured by a conductivity meter. Three parallel tests are performed to ensure the accuracy of the final result.

[0069] The flux and sodium chloride rejection rate of the reverse osmosis membranes prepared in the above examples and comparative examples during long-term operation are shown in Table 1.

[0070] Table 1

[0071]

[0072] It can be seen from the results in Table 1 that the polyamide reverse osmosis thin film composite membrane prepared in the embodiment of the present invention has excellent salt rejection and permeability, and is superior to the polyamide reverse osmosis of the comparative example. Therefore, it can be seen that the introduction of a rigid three-dimensional triptycene structure with large steric hindrance into the polymer network and the special blade configuration of triptycene can also effectively adjust the cavity structure and improve the salt rejection rate of sodium chloride.

[0073] The preferred embodiments of the present invention are described in detail above, but are not limited thereto. A person skilled in the art in the field of the present invention may make simple changes and optimizations to the technical solution of the present invention, including making appropriate combinations of the various technical features therein, and these simple changes and combinations shall be regarded as the contents disclosed by the present invention and shall all belong to the protection scope of the present invention.

Claims

1. A method for preparing a reverse osmosis composite membrane, characterized in that: The preparation method specifically comprises: (1) preparing an aqueous phase solution containing an aqueous phase monomer and an organic phase solution containing an acyl chloride-substituted triptycene compound; (2) immersing the porous support layer base membrane in an aqueous solution, removing excess aqueous solution on the surface of the base membrane, and then coating the membrane surface with an organic phase solution containing an acyl chloride-substituted triptycene compound to obtain a reverse osmosis composite membrane; (3) heat treating the reverse osmosis composite membrane; (4) Post-treating the reverse osmosis composite membrane obtained by heat treatment.

2. The preparation method according to claim 1, characterized in that: In step (1), the aqueous phase monomer is a water-soluble monomer that can undergo polymerization reaction with an acyl chloride compound, preferably an amine compound, one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, N,N-dimethyl-m-phenylenediamine, s-phenyltriamine, piperazine, 3-aminopiperazine, cyclohexanediamine, ethylenediamine, triethanolamine, polyethyleneimine, polyetheramine, aniline, m-toluidine, o-toluidine, p-nitroaniline, m-fluoroaniline, etc.; The mass fraction concentration of the aqueous phase monomer in the aqueous phase solution is 0.1 wt % to 5 wt %.

3. The preparation method according to claim 1, characterized in that: The acyl chloride substituted triptycene compound in step (1) is any one of monoacyl chloride substituted triptycene, diacyl chloride substituted triptycene, triacyl chloride substituted triptycene, tetraacyl chloride substituted triptycene, pentaacyl chloride substituted triptycene, and hexaacyl chloride substituted triptycene; the mass fraction concentration of the triptycene compound in the organic phase solution is 0.005wt%-5wt%; The organic phase solvent is one or more of acetone, n-hexane, acetonitrile, ethyl acetate, methyl acetate, toluene, dichloromethane, 1,2-dichloroethane, cyclohexane, n-heptane, chloroform, mesitylene, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M, etc.

4. The preparation method according to claim 1, characterized in that: In step (2), the immersion time of the aqueous solution is 30s-10min; The coating time of the organic phase solution is 30s-10min, and the temperature is 20-50°C; In step (3), the heat treatment time is 2-20 minutes, and the heat treatment temperature is 40-70°C.

5. The preparation method according to claim 1, characterized in that: In step (4), the reverse osmosis composite membrane obtained by the heat treatment is immersed in a post-treatment solution; Wherein, the post-treatment solution is any one of methanol, ethanol and water.

6. The preparation method according to claim 1, characterized in that: In step (2), the porous support layer base membrane is any one of polysulfone, polyethersulfone, polyimide, polyetherimide, polybenzimidazole and polyacrylonitrile.

7. A reverse osmosis composite membrane prepared by the preparation method according to any one of claims 1 to 6.

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