High-stability ultra-low pressure reverse osmosis membrane and preparation method thereof

Abstract

The invention provides a high-stability ultra-low pressure reverse osmosis membrane and a preparation method thereof. The reverse osmosis membrane comprises a non-woven fabric, a polysulfone support layer and a polyamide separation function layer containing a metal organic framework with the chemical formula of [Zn (L) (DMF) 2] n, and L is from bicycloalkane dicarboxylic acid H2L. According to the invention, uniform growth of the metal organic framework on the surface of polyamide is realized, and the prepared reverse osmosis membrane has excellent storage stability on the basis of high permeation flux and salt rejection rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a high-stability ultra-low pressure reverse osmosis membrane and a preparation method thereof. Background Art

[0002] Currently, the mainstream reverse osmosis membrane is a crosslinked aromatic polyamide composite reverse osmosis membrane. An interfacial polymerization reaction is carried out between m-phenylenediamine and trimesoyl chloride on the surface of a polysulfone substrate membrane to form a polyamide separation functional layer. This type of reverse osmosis membrane is widely used in the fields of industrial pure water production, industrial wastewater treatment, and seawater desalination. The ultra-low pressure reverse osmosis membrane can achieve the same permeation flux as that of the low-pressure reverse osmosis membrane under 2 / 3 of the operating pressure. However, the improvement of the permeation flux generally comes at the cost of sacrificing the crosslinking degree of the polyamide separation functional layer, which is bound to cause a loss of salt rejection rate and a decrease in storage stability. Therefore, it is of great significance to improve the permeation flux and storage stability of the reverse osmosis membrane on the basis of ensuring the salt rejection rate.

[0003] In the prior art, the main way to improve the permeation flux of the reverse osmosis membrane is to construct an intermediate layer between the polysulfone substrate membrane and the polyamide separation functional layer. For example, in CN 113289500 A, a nano-calcium carbonate layer is deposited on the polysulfone substrate membrane as a blocking layer, which limits the growth of polyamide during the interfacial polymerization reaction, reduces the depth of polyamide in the pore structure of the polysulfone substrate membrane, reduces the water conduction resistance, and improves the permeation flux of the reverse osmosis membrane; in CN 109847586 B, dopamine / ZIF-8 is grown on the surface of the polysulfone substrate membrane to obtain a polysulfone substrate membrane with a dopamine / ZIF-8 intermediate nano-layer. Its hydrophilicity and roughness are further enhanced, which is beneficial to preparing a more uniformly distributed and thinner polyamide separation functional layer. The as-prepared reverse osmosis membrane after interfacial polymerization is soaked in pure water to dissolve the intermediate nano-layer, and a reverse osmosis membrane with high permeation flux is obtained. In the prior art, the main way to improve the storage stability of the reverse osmosis membrane is to coat a surface protection layer on the reverse osmosis membrane. For example, in CN 114247298 B, an aqueous solution containing PVA, a surfactant, and a specific additive is uniformly coated on the surface of the nascent reverse osmosis membrane, and a reverse osmosis membrane with high storage stability is obtained after drying.

[0004] Although some technical solutions for improving the permeation flux and storage stability of the reverse osmosis membrane have been formed in the prior art, the method of improving the permeation flux by constructing an intermediate layer is relatively complex, and the method of improving the storage stability by coating a surface protection layer does not change the stability of the polyamide separation functional layer. Therefore, the technical solutions for improving the permeation flux and storage stability need to be further improved.

[0005] In summary, when improving the permeation flux of the reverse osmosis membrane while maintaining its salt rejection rate, there is still a problem that the storage stability is difficult to improve and needs to be solved urgently. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a high-stability ultra-low pressure reverse osmosis membrane. The prepared reverse osmosis membrane has excellent storage stability while maintaining high permeation flux and salt rejection rate.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions:

[0008] A high-stability ultra-low pressure reverse osmosis membrane, wherein the reverse osmosis membrane comprises a non-woven fabric, a polysulfone support layer, and a polyamide separation functional layer containing a metal-organic framework with the chemical formula [Zn(L)(DMF)2] n ; wherein, L is derived from bicycloalkane dicarboxylic acid H2L, and preferably the bicycloalkane dicarboxylic acid comprises one or more of bicyclo[1.1.1]pentane-1,3-dicarboxylic acid, bicyclo[2.2.1]heptane-1,4-dicarboxylic acid, and bicyclo[2.2.2]octane-1,4-dicarboxylic acid.

[0009] Another objective of the present invention is to provide a preparation method for the reverse osmosis membrane.

[0010] A method for preparing the above reverse osmosis membrane, the method comprising the following steps:

[0011] S1: Immerse the polysulfone support layer in an aqueous solution containing a polyfunctional amine and a zinc salt, remove the excess aqueous solution after taking it out, and obtain a support layer A;

[0012] S2: Coat an organic solution containing a polyfunctional acyl chloride on the surface of the support layer A, remove the excess oil solution, and obtain a primary reverse osmosis membrane B;

[0013] S3: Immerse the primary reverse osmosis membrane B in a solution containing a bicycloalkane dicarboxylic acid and a surfactant, heat it, and grow the metal-organic framework on the surface of the polyamide to obtain a wet membrane C;

[0014] S4: Immerse the wet membrane C in an aqueous solution of a humectant, take it out and dry it to obtain a reverse osmosis membrane.

[0015] In one embodiment of the present invention, the polyfunctional amine in S1 is an aromatic amine containing at least two primary amino groups and / or an aliphatic amine containing at least two primary amino groups. Preferably, the aromatic amine is one or more of phenylenediamine, xylylenediamine, and 1,3,5-triaminobenzene, and the aliphatic amine is one or more of ethylenediamine, propylenediamine, and piperazine. More preferably, the polyfunctional amine is m-phenylenediamine; preferably, in the aqueous solution containing the polyfunctional amine and the zinc salt, the mass percentage of the polyfunctional amine is 1.0-5.0 wt%.

[0016] In one embodiment of the present invention, the zinc salt in S1 is a divalent soluble zinc salt, preferably zinc nitrate; preferably, in the aqueous solution containing polyfunctional amine and zinc salt, the mass percentage of the zinc salt is 0.001 - 0.01 wt%.

[0017] In one embodiment of the present invention, the polyvalent acyl chloride in S2 is aromatic polyvalent acyl chloride and / or aliphatic polyvalent acyl chloride. Preferably, the aromatic polyvalent acyl chloride is trimesoyl chloride and / or terephthaloyl chloride, and the aliphatic polyvalent acyl chloride is adipoyl chloride and / or cyclopropanetricarboxylic acid chloride. More preferably, the polyvalent acyl chloride is trimesoyl chloride.

[0018] In one embodiment of the present invention, the organic solvent in S2 is an alkane with a boiling point higher than 160°C, preferably n-decane; preferably, in the organic solution containing polyvalent acyl chloride, the mass percentage of the polyvalent acyl chloride is 0.1 - 0.2 wt%.

[0019] In one embodiment of the present invention, in S2, air is purged to remove the excess oil solution.

[0020] In one embodiment of the present invention, in the solution containing dicycloalkane dicarboxylic acid and surfactant in S3, the mass percentage of the dicycloalkane dicarboxylic acid is 0.001 - 0.01 wt%.

[0021] In one embodiment of the present invention, the surfactant in S3 is one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone, preferably polyvinylpyrrolidone; preferably, the mass percentage of the surfactant in the solution of S3 is 0.01 - 0.05 wt%.

[0022] In one embodiment of the present invention, the solvent in the solution of S3 is N,N-dimethylformamide and water; preferably, the mass ratio of N,N-dimethylformamide to water is (0.25 - 1):1.

[0023] In one embodiment of the present invention, the heating method in S3 is water bath heating or microwave heating, preferably microwave heating; preferably, the heating temperature is 70 - 90°C and the time is 5 - 20 min.

[0024] In one embodiment of the present invention, the humectant in S4 is glycerol and / or citric acid, preferably glycerol.

[0025] In one embodiment of the present invention, in S4, the mass percentage of the humectant is 1 - 10 wt%.

[0026] In one embodiment of the present invention, the soaking temperature in S4 is 70 - 90°C and the time is 1 - 5 min.

[0027] In an embodiment of the present invention, the drying temperature in S4 is 70 - 90 °C, and the time is 3 - 6 min.

[0028] Another object of the present invention is to provide a use of a reverse osmosis membrane.

[0029] A use of a reverse osmosis membrane, wherein the reverse osmosis membrane is the above-mentioned reverse osmosis membrane or the reverse osmosis membrane prepared by the above method, and the reverse osmosis membrane is used in the fields of industrial pure water production, industrial wastewater treatment and seawater desalination, preferably in the fields of industrial pure water production, industrial wastewater treatment and seawater desalination that require high-stability ultra-low-pressure reverse osmosis membranes.

[0030] In the present invention, first, due to the similar solubility of the bicyclic structure with aliphatic organic solvents, the content and diffusion rate of the bicyclic alkane dicarboxylic acid in the organic solvent are increased, enabling it to fully contact with the zinc ions at the water-oil interface, and realizing the uniform growth of the metal-organic framework on the polyamide surface; second, the metal-organic framework contains a large number of pores, providing channels for water molecules and increasing the flux of the reverse osmosis membrane. At the same time, during the reaction process, N,N-dimethylformamide in the solution forms hydrogen bonds with the polyamide, making the polyamide more porous and further increasing the flux of the reverse osmosis membrane; furthermore, due to the steric hindrance of the bicyclic structure, the diffusion resistance of glycerol molecules into the polyamide network is increased, and at the same time, the low-polarity bicyclic structure further reduces the diffusion rate of highly polar glycerol molecules into the polyamide network. Therefore, the prepared reverse osmosis membrane is not easily swollen by glycerol even in high-temperature and high-humidity environments, greatly improving its storage stability.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The uniform growth of the metal-organic framework with the chemical formula [Zn(L)(DMF)2] n (L comes from the bicyclic alkane dicarboxylic acid H2L) on the polyamide surface is realized. Compared with the reverse osmosis membrane without the metal-organic framework, on the basis of ensuring the salt rejection rate, the flux is increased by 15 - 25%, and after the membrane is placed in a high-temperature and high-humidity environment for 5 days, the performance remains stable, and the salt rejection rate is maintained above 99.50%. Therefore, the reverse osmosis membrane with the grown metal-organic framework has high flux and excellent storage stability. Detailed Embodiments

[0033] 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, but the content of the present invention is not limited to the following embodiments only.

[0034] Unless otherwise specified, the reagents used in the following examples or comparative examples are all commercially available conventional reagents. The main reagent information is shown in Table 1.

[0035] Table 1 Information of Main Reagents

[0036] Reagent Name Manufacturer Polysulfone Resin / P-3500 LCD MB7 Solvay S.A. N,N-Dimethylformamide Shanghai Aladdin Biochemical Technology Co., Ltd. Polyester Nonwoven Fabric Mitsubishi Paper Mills Limited m-Phenylenediamine Shanghai Anon Aromatic Chemicals Co., Ltd. Zinc Nitrate Hexahydrate Shanghai Aladdin Biochemical Technology Co., Ltd. Zinc Chloride Shanghai Aladdin Biochemical Technology Co., Ltd. Trimesoyl Chloride Qingdao Sanlibenno New Materials Co., Ltd. n-Decane Shanghai Aladdin Biochemical Technology Co., Ltd. Isopar G Shanghai Aladdin Biochemical Technology Co., Ltd. Bicyclo[1.1.1]pentane-1,3-dicarboxylic Acid Shanghai Aladdin Biochemical Technology Co., Ltd. Bicyclo[2.2.1]heptane-1,4-dicarboxylic Acid Shanghai Aladdin Biochemical Technology Co., Ltd. Bicyclo[2.2.2]octane-1,4-dicarboxylic Acid Shanghai Aladdin Biochemical Technology Co., Ltd. Polyvinylpyrrolidone / K30 BASF SE Glycerol Tianjin Kermel Chemical Reagent Co., Ltd. Citric Acid Tianjin Kermel Chemical Reagent Co., Ltd.

[0037] The performance evaluation method of the reverse osmosis membrane in the following examples or comparative examples:

[0038] 1. Evaluation of Permeation Flux and Salt Rejection

[0039] Permeation flux and salt rejection are two important parameters for evaluating the separation performance of reverse osmosis membranes. In this invention, the separation performance of reverse osmosis membranes is evaluated according to GB / T 32373-2015 "Test Methods for Reverse Osmosis Membranes".

[0040] The permeation flux is defined as: under certain operating conditions, the volume of water passing through a unit membrane area per unit time, and its unit is L·m -2 ·h -1 .

[0041] The salt rejection (R) is defined as: under certain operating conditions, the difference between the salt concentration (C f ) of the feed solution and the salt concentration (C p ) in the permeate, and then divided by the salt concentration (C f ) of the feed solution, that is:

[0042]

[0043] The operating conditions adopted for the determination of the performance of the reverse osmosis membrane in this invention are: the feed solution is an aqueous sodium chloride solution with a concentration of 1500 ppm, the solution pH is 7.0 ± 0.5, the operating pressure is 150 psi (1.03 MPa), and the operating temperature is 25 ± 1 °C.

[0044] Example 1

[0045] Prepare an N,N-dimethylformamide solution containing 16.5 wt% polysulfone. After filtration and degassing, it is evenly coated on a polyester non-woven fabric with a coating thickness of 140 μm. After staying in the air for 1.5 s, it is immersed in a pure water coagulation bath to obtain a polysulfone support membrane A. The polysulfone support membrane A is immersed in an aqueous solution containing 3.0 wt% m-phenylenediamine and 0.005 wt% zinc nitrate hexahydrate, and left standing for 30 s. After taking it out, a rubber extrusion roller is used to remove the excess aqueous solution; a n-decane solution containing 0.1 wt% trimesoyl chloride is coated on its surface, and left standing for 30 s. The excess oil solution is removed by air blowing; the membrane is immersed in an N,N-dimethylformamide and aqueous solution containing 0.005 wt% bicyclo[1.1.1]pentane-1,3-dicarboxylic acid and 0.02 wt% polyvinylpyrrolidone. The mass ratio of N,N-dimethylformamide to water is 0.5:1. It is placed in a microwave reactor and microwave-heated (microwave hydrothermal parallel synthesizer, model: XH-800-S, power: 1500 W) to 80 °C and reacted for 10 min; the membrane is taken out and immersed in a 4 wt% glycerol aqueous solution at 80 °C for 2 min. After taking it out, it is dried at 80 °C for 5 min to obtain a reverse osmosis membrane.

[0046] The polyamide and polysulfone layers on the polyester non-woven fabric layer of the reverse osmosis membrane obtained in Example 1 are manually peeled off; the polyamide and polysulfone layers are immersed in N,N-dimethylformamide for 12 h to dissolve the polysulfone layer; the polyamide layer containing the metal-organic framework is washed with pure water and immersed in 30 wt% hydrogen peroxide for 48 h to oxidize and remove the polyamide layer; the remaining metal-organic framework solid is washed with pure water and immersed in an N,N-dimethylformamide and aqueous solution containing 0.005 wt% zinc nitrate hexahydrate, 0.005 wt% bicyclo[1.1.1]pentane-1,3-dicarboxylic acid and 0.02 wt% polyvinylpyrrolidone. The mass ratio of N,N-dimethylformamide to water is 0.5:1. It is placed in a high-pressure reaction kettle and reacted at 80 °C for 72 h to obtain a single crystal of the metal-organic framework; an X-ray single crystal diffractometer is used to measure the crystal data of the obtained single crystal, with the model being Bruker Smart Apex CCD and the test parameters being: radiation source Mo / Kα, λ = 0.071073 nm, and the test temperature being 20 °C. The crystal data is shown in Table 2.

[0047] Example 2

[0048] A reverse osmosis membrane is obtained in the same manner as in Example 1, except that the concentrations of zinc nitrate hexahydrate and bicyclo[1.1.1]pentane-1,3-dicarboxylic acid are both 0.001 wt%.

[0049] Example 3

[0050] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the concentrations of zinc nitrate hexahydrate and bicyclo[1.1.1]pentane-1,3-dicarboxylic acid were both 0.01 wt%.

[0051] Example 4

[0052] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the organic ligand was bicyclo[2.2.1]heptane-1,4-dicarboxylic acid.

[0053] Example 5

[0054] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the organic ligand was bicyclo[2.2.2]octane-1,4-dicarboxylic acid.

[0055] Example 6

[0056] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the concentration of polyvinylpyrrolidone was 0.01 wt%, the mass ratio of N,N-dimethylformamide to water was 0.25:1, the microwave heating temperature was 70 °C, and the heating time was 5 min.

[0057] Example 7

[0058] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the concentration of polyvinylpyrrolidone was 0.05 wt%, the mass ratio of N,N-dimethylformamide to water was 1:1, the microwave heating temperature was 90 °C, and the heating time was 20 min.

[0059] Example 8

[0060] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the surfactant was sodium dodecyl sulfate, the humectant was citric acid, and the heating method was water bath heating.

[0061] Example 9

[0062] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the concentration of m-phenylenediamine was 1 wt%.

[0063] Example 10

[0064] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the concentration of m-phenylenediamine was 5 wt% and the concentration of trimellitic trichloride was 0.2 wt%.

[0065] Example 11

[0066] The reverse osmosis membrane was obtained in the same manner as in Example 1, except that the polyfunctional amine was p-phenylenediamine and the polyvalent acid chloride was terephthaloyl chloride.

[0067] Example 12

[0068] An RO membrane was obtained in the same manner as in Example 1, except that the polyfunctional amine was piperazine and the polyvalent acyl chloride was adipoyl chloride.

[0069] Example 13

[0070] An RO membrane was obtained in the same manner as in Example 1, except that the concentration of glycerol was 1 wt%, the immersion temperature of glycerol was 70 °C, the immersion time was 1 min, the drying temperature was 70 °C, and the drying time was 3 min.

[0071] Example 14

[0072] An RO membrane was obtained in the same manner as in Example 1, except that the concentration of glycerol was 10 wt%, the immersion temperature of glycerol was 90 °C, the immersion time was 5 min, the drying temperature was 90 °C, and the drying time was 6 min.

[0073] Example 15

[0074] An RO membrane was obtained in the same manner as in Example 1, except that the divalent soluble zinc salt was zinc chloride and the organic solvent was Isopar G.

[0075] Table 2 Crystal data of polyamide surface metal-organic frameworks

[0076]

[0077] Comparative Example 1

[0078] An RO membrane was obtained in the same manner as in Example 1, except that zinc nitrate hexahydrate and dicycloalkane dicarboxylic acid were not included in the preparation process.

[0079] Comparative Example 2

[0080] An RO membrane was obtained in the same manner as in Example 1, except that the organic ligand was 2-methylimidazole.

[0081] Table 3 Performance of RO membranes obtained in Examples and Comparative Examples

[0082]

[0083] It can be seen from the experimental results in Table 3 that the RO membrane grown with the metal-organic framework of the chemical formula [Zn(L)(DMF)2] n (L is from dicycloalkane dicarboxylic acid H2L) has a relatively high permeation flux, and the performance remains stable after the membrane is placed in a high-temperature and high-humidity environment for 5 days, and the salt rejection rate is maintained above 99.50%.

Claims

1. A highly stable ultra-low pressure reverse osmosis membrane, characterized in that, The reverse osmosis membrane comprises a non-woven fabric, a polysulfone support layer, and a polyamide separation functional layer containing a metal-organic framework with the chemical formula [Zn(L)(DMF)2] n ; Among them, L is derived from bicycloalkane dicarboxylic acid H2L. Preferably, the bicycloalkane dicarboxylic acid includes one or more of bicyclo[1.1.1]pentane-1,3-dicarboxylic acid, bicyclo[2.2.1]heptane-1,4-dicarboxylic acid, and bicyclo[2.2.2]octane-1,4-dicarboxylic acid.

2. A method for preparing the reverse osmosis membrane according to claim 1, characterized in that, The method includes the following steps: S1: Immerse the polysulfone support layer in an aqueous solution containing polyfunctional amine and zinc salt, remove the excess aqueous solution after taking it out, and obtain support layer A; S2: Coat an organic solution containing polyvalent acyl chloride on the surface of support layer A, remove the excess oil solution, and obtain the primary reverse osmosis membrane B; S3: Immerse the primary reverse osmosis membrane B in a solution containing bicycloalkane dicarboxylic acid and surfactant, heat it, and grow metal-organic framework on the polyamide surface to obtain wet membrane C; S4: Immerse wet membrane C in an aqueous solution of humectant, take it out and dry it to obtain a reverse osmosis membrane.

3. The method according to claim 2, characterized in that, The polyfunctional amine in S1 is an aromatic amine containing at least two primary amino groups and / or an aliphatic amine containing at least two primary amino groups. Preferably, the aromatic amine is one or more of phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, and the aliphatic amine is one or more of ethylenediamine, propylenediamine, and piperazine. More preferably, the polyfunctional amine is m-phenylenediamine; Preferably, in the aqueous solution containing polyfunctional amine and zinc salt, the mass percentage of polyfunctional amine is 1.0 - 5.0 wt%; And / or, the zinc salt in S1 is a divalent soluble zinc salt, preferably zinc nitrate; Preferably, in the aqueous solution containing polyfunctional amine and zinc salt, the mass percentage of zinc salt is 0.001 - 0.01 wt%.

4. The preparation method according to claim 2 or 3, characterized in that, The polyvalent acyl chloride in S2 is an aromatic polyvalent acyl chloride and / or an aliphatic polyvalent acyl chloride. Preferably, the aromatic polyvalent acyl chloride is trimesoyl chloride and / or terephthaloyl chloride, and the aliphatic polyvalent acyl chloride is adipoyl chloride and / or cyclopropanetricarboxylic acid chloride. More preferably, the polyvalent acyl chloride is trimesoyl chloride; And / or, the organic solvent in S2 is an alkane with a boiling point higher than 160°C, preferably n-decane; Preferably, in the organic solution containing polyvalent acyl chloride, the mass percentage of polyvalent acyl chloride is 0.1 - 0.2 wt%; And / or, in S2, air is blown to remove the excess oil solution.

5. The preparation method according to any one of claims 2-4, characterized in that, In the solution containing bicycloalkane dicarboxylic acid and surfactant in S3, the mass percentage of bicycloalkane dicarboxylic acid is 0.001 - 0.01 wt%; And / or, the surfactant in S3 is one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone, preferably polyvinylpyrrolidone; Preferably, the mass percentage of surfactant in the solution in S3 is 0.01 - 0.05 wt%; And / or, the solvent in the solution in S3 is N,N-dimethylformamide and water; Preferably, the mass ratio of N,N-dimethylformamide to water is (0.25 - 1):1; And / or, the heating method in S3 is water bath heating or microwave heating, preferably microwave heating; Preferably, the heating temperature is 70 - 90°C and the time is 5 - 20 min.

6. The preparation method according to any one of claims 2-5, characterized in that, The humectant in S4 is glycerol and / or citric acid, preferably glycerol; And / or, the mass percentage of the moisturizer described in S4 is 1-10 wt%; And / or, the soaking temperature described in S4 is 70-90 °C, and the time is 1-5 min; And / or, the drying temperature described in S4 is 70-90 °C, and the time is 3-6 min.

7. Use of a reverse osmosis membrane, the reverse osmosis membrane being the reverse osmosis membrane according to claim 1, or the reverse osmosis membrane prepared by the method according to any one of claims 2-6, the reverse osmosis membrane being used in the fields of industrial pure water production, industrial wastewater treatment and seawater desalination, preferably in the fields of industrial pure water production, industrial wastewater treatment and seawater desalination that require a highly stable ultra-low pressure reverse osmosis membrane.

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