A reverse osmosis membrane for seawater desalination with both high throughput and high desalination rate and its preparation method

Abstract

The present invention discloses a reverse osmosis membrane for seawater desalination with both high throughput and high desalination rate, and a preparation method thereof. The preparation method includes the following steps: Step 1, prepare an aqueous solution; Step 2, prepare an oil-phase solution containing polyacrylate and its derivatives; Step 3, immerse one side of the ultrafiltration membrane in the aqueous solution, then perform surface drying treatment, and then contact and react with the oil-phase solution to obtain a nascent reverse osmosis membrane; Step 4, heat-treat the nascent reverse osmosis membrane obtained in Step 3, then soak and wash it in an aqueous solution with a pH value of 2-12, and finally rinse it thoroughly with deionized water to obtain a reverse osmosis membrane for seawater desalination. The present invention creatively uses polyacrylate as an additive to prepare a reverse osmosis membrane and achieves outstanding effects. The water flux and desalination rate of the reverse osmosis membrane can reach 45 LMH and over 99.8% simultaneously.

Description

Technical Field

[0001] The present invention relates to the technical field of reverse osmosis membranes for seawater desalination, and particularly to a reverse osmosis membrane for seawater desalination with both high flux and high salt rejection rate and a preparation method thereof. Background Art

[0002] Seawater desalination has become a strategic choice for countries around the world to cope with the water resource crisis. Due to advantages such as low energy consumption, wide application range, easy modularization, and simple operation, reverse osmosis technology has become the preferred technology for seawater desalination. Reverse osmosis membranes with both high flux and high salt rejection performance have always been the common goal of the academic and industrial circles. However, due to the trade-off effect between water flux and salt rejection rate, so far, how to simultaneously improve water flux and salt rejection rate remains a difficult problem.

[0003] Currently, methods for improving the performance of reverse osmosis membranes include introducing nanoparticles, small molecule additives, and co-solvents, etc. These methods often increase the flux while accompanied by a decrease in salt rejection rate. The fundamental reason is that the linear part of polyamide increases and the cross-linked part decreases, thus increasing the free volume. Therefore, there is an urgent need in this field for a method to simultaneously improve flux and salt rejection rate. Summary of the Invention

[0004] The object of the present invention is to solve the problem that reverse osmosis membranes for seawater desalination in the prior art cannot have both high flux and salt rejection rate, and to provide a preparation method for a reverse osmosis membrane for seawater desalination with both high flux and high salt rejection rate.

[0005] Another object of the present invention is to provide a reverse osmosis membrane for seawater desalination prepared by the above preparation method.

[0006] The technical solution adopted to achieve the object of the present invention is as follows:

[0007] A preparation method for a reverse osmosis membrane for seawater desalination with both high flux and high salt rejection rate, comprising the following steps:

[0008] Step 1, prepare an aqueous solution: Add m-phenylenediamine, camphorsulfonic acid, and triethylamine to deionized water in sequence to obtain a homogeneous and transparent aqueous solution;

[0009] Step 2, prepare an oil phase solution: Add a polyacrylate co-solvent with a mass fraction of 0.5 - 5 wt% to an isoparaffin solvent to form a mixed solvent, and then add trimellitic acid chloride and polyacrylate or its derivative to the mixed solvent in sequence to obtain a homogeneous and transparent oil phase solution, wherein the mass fraction of the trimellitic acid chloride is 0.15 - 5 wt%, and the mass fraction of the polyacrylate or its derivative is 0.01 - 1 wt%;

[0010] Step 3: Immerse one side of the ultrafiltration membrane in the aqueous solution, then perform surface drying treatment, and then contact and react with the oil-phase solution to obtain a nascent reverse osmosis membrane. The polyacrylate molecular chains are interspersed in the polyamide network to form a mixed matrix structure;

[0011] Step 4: Heat-treat the nascent reverse osmosis membrane obtained in Step 3, then soak and wash it in an aqueous solution with a pH value of 2 - 12, and finally rinse it thoroughly with deionized water to obtain a seawater desalination reverse osmosis membrane.

[0012] In the above technical solution, the polyacrylate is one or more of methyl polyacrylate, ethyl polyacrylate, n-propyl polyacrylate, isopropyl polyacrylate, n-butyl polyacrylate, isobutyl polyacrylate, or tert-butyl polyacrylate. Alternatively, the polyacrylate is a copolymer containing at least two monomers among methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, or tert-butyl acrylate; the derivative of polyacrylate is polymethacrylate.

[0013] In the above technical solution, the molecular weight of the polyacrylate and its derivative is between 1 kDa and 150 kDa. Preferably, the molecular weight is between 2 kDa and 15 kDa.

[0014] In the above technical solution, the polyacrylate co-solvent is at least one of acetone, ethyl acetate, benzene, and dichloroethane, and preferably ethyl acetate.

[0015] In the above technical solution, in Step 1, the mass fraction of m-phenylenediamine is 2 - 5 wt%, the mass fraction of camphorsulfonic acid is 2 - 5 wt%, and the mass fraction of triethylamine is 1 - 2 wt%.

[0016] In the above technical solution, in Step 3, the impregnation time is 60 - 120 s, and the contact reaction time is 60 - 120 s.

[0017] In the above technical solution, in Step 4, the heat treatment temperature is 90 - 120 °C, and the heat treatment time is 4 - 6 min.

[0018] In the above technical solution, in Step 4, the cleaning time is 1 - 10 min.

[0019] On the other hand, the present invention provides a seawater desalination reverse osmosis membrane prepared by the above preparation method.

[0020] In the above technical solution, the water flux of the seawater desalination reverse osmosis membrane is greater than 45 LMH, and the salt rejection rate is greater than 99.8%.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. The present invention creatively uses polyacrylate as an additive to prepare a reverse osmosis membrane, achieving outstanding results. The water flux and salt rejection rate of the reverse osmosis membrane can simultaneously reach 45 LMH and over 99.8% (test conditions: sodium chloride concentration 32000 mg / L, test temperature 25 °C, test pressure 5.5 MPa). Polyacrylate does not participate in the interfacial polymerization reaction and does not affect the reaction between polyamine and polyacyl chloride. Instead, it interpenetrates the polyamide network to form a mixed matrix structure, especially tending to embed in the linear chain part of polyamide, effectively reducing the free volume of the polyamide linear structure and facilitating the improvement of salt rejection rate. After polyacrylate is hydrolyzed into polyacrylic acid, it still interpenetrates the polyamide network to maintain the mixed matrix structure. The hydrophilicity of polyacrylic acid is conducive to increasing the water flux of the reverse osmosis membrane, and the charge property of acrylic acid is conducive to increasing the salt rejection rate.

[0023] 2. The preparation method of the present invention is simple, inexpensive, does not change the existing membrane-making process, and is easy to produce on existing production lines. Detailed Embodiment

[0024] The following further elaborates on the present invention in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0025] In this detailed embodiment, the purity of m-phenylenediamine ≥ 99.5%, the purity of camphorsulfonic acid ≥ 99.5%, the purity of triethylamine ≥ 99%, the concentration of trimesoyl chloride > 98%, the water content of polyacrylate ≤ 0.001%, and the water content of the polyacrylate cosolvent ≤ 0.001%. Embodiment

[0026] A seawater desalination reverse osmosis membrane is prepared by the following method:

[0027] Step 1, prepare an aqueous solution. Add m-phenylenediamine (mass fraction 2.5%), camphorsulfonic acid (mass fraction 2.5%), and triethylamine (mass fraction 1.2%) to deionized water in sequence to obtain a homogeneous and transparent aqueous solution.

[0028] Step 2, prepare an oil phase solution: Add trimesoyl chloride (mass fraction 0.15%) and polymethyl acrylate (molecular weight 15000, mass fraction 0.01%) to a mixed solvent (where the contents of IsoparG and ethyl acetate are 97% and 3% respectively) to obtain a homogeneous and transparent oil phase solution.

[0029] Step 3, dip one side of the ultrafiltration membrane in the aqueous solution for 60 seconds, air-dry it, and then contact it with the oil phase solution for reaction for 60 seconds to obtain a nascent reverse osmosis membrane.

[0030] Step 4: Heat-treat the nascent reverse osmosis membrane obtained in Step 3 in an oven at 85°C for 5 minutes, then soak and clean the membrane in an aqueous solution with a pH value of 2 for 5 minutes, and finally rinse it thoroughly with deionized water to obtain a reverse osmosis membrane dedicated for seawater desalination. Example

[0031] The difference between this example and Example 1 is that the mass fraction of polymethyl methacrylate is 0.1%. Example

[0032] The difference between this example and Example 1 is that the mass fraction of polymethyl methacrylate is 0.3%. Example

[0033] The difference between this example and Example 1 is that the mass fraction of polymethyl methacrylate is 0.5%. Example

[0034] The difference between this example and Example 1 is that the mass fraction of polymethyl methacrylate is 0.7%. Example

[0035] The difference between this example and Example 1 is that the mass fraction of polymethyl methacrylate is 0.9%. Example

[0036] The difference between this example and Example 1 is that the mass fraction of polymethyl methacrylate is 1.0%. Example

[0037] The difference between this example and Example 1 is that polymethyl acrylate is replaced by polymethyl methacrylate, and the mass fraction is 0.5%. Example

[0038] The difference between this example and Example 1 is that polymethyl acrylate is replaced by polyethyl methacrylate, and the mass fraction is 0.5%. Example

[0039] The difference between this example and Example 1 is that polymethyl acrylate is replaced by polyethyl acrylate, and the mass fraction is 0.5%. Example

[0040] The difference between this example and Example 1 is that polymethyl acrylate is replaced by isopropyl acrylate, and the mass fraction is 0.5%.

[0041] The difference between this comparative example and Example 1 is that the mass fraction of polymethyl methacrylate in the oil-phase solution is 0%. Example

[0042] The performance test conditions of the reverse osmosis membrane are as follows: sodium chloride concentration is 32000 mg / L, test temperature is 25 °C, and test pressure is 5.5 MPa. The membrane performances of the comparative examples and the examples are shown in Table 1.

[0043] Table 1 Membrane performances of the comparative examples and the examples.

[0044] Membrane Number Water Flux / LMH Salt Rejection / % Contact Angle Isoelectric Point pH Example 1 46.2 99.81 50.1 3.60 Example 2 48.7 99.82 48.8 3.52 Example 3 51.2 99.86 46.9 3.44 Example 4 54.8 99.90 45.5 3.36 Example 5 56.5 99.91 41.1 3.28 Example 6 58.6 99.87 38.1 3.15 Example 7 60.3 99.83 36.7 3.06 Example 8 57.8 99.91 44.7 3.31 Example 9 58.4 99.92 46.1 3.35 Example 10 55.8 99.91 45.3 3.30 Example 11 56.8 99.90 47.2 3.41 Comparative Example 1 42.1 99.53 62.4 3.78

[0045] It can be seen from the experimental results in Table 1 that, compared with the comparative examples without using the polyacrylate compound of the present invention, adding the polyacrylate compound in the oil-phase solution in the examples significantly improves both the water flux and the salt rejection rate of the prepared reverse osmosis membrane, showing excellent permeability and selectivity; the surface contact angle of the reverse osmosis membrane decreases significantly, which is one of the reasons for the increase in water flux; the isoelectric point of the membrane surface decreases and the surface charge of the membrane increases, which is one of the reasons for the increase in salt rejection rate.

[0046] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a seawater desalination reverse osmosis membrane with both high flux and high desalination rate, characterized in that: The following steps are involved: Step 1, preparing an aqueous phase solution: adding m-phenylenediamine, camphorsulfonic acid and triethylamine to deionized water in sequence to prepare a uniform and transparent aqueous phase solution; Step 2, preparing an oil phase solution, adding 0.5-5wt% of polyacrylate cosolvent to an isoparaffin solvent to form a mixed solvent, and then sequentially adding trimesoyl chloride and polyacrylate or its derivative to the mixed solvent to prepare a uniform and transparent oil phase solution, wherein the mass fraction of trimesoyl chloride is 0.15-5wt%, and the mass fraction of polyacrylate or its derivative is 0.01-1wt%; Step 3, immersing one side of the ultrafiltration membrane in an aqueous solution, then drying the surface, and then contacting and reacting with an oil solution to obtain a nascent reverse osmosis membrane, in which polyacrylate molecular chains are interspersed in a polyamide network to form a mixed matrix structure; Step 4, heat-treating the primary reverse osmosis membrane obtained in step 3, then immersing and cleaning it in an aqueous solution with a pH value of 2-12, and finally rinsing it with deionized water to obtain a seawater desalination reverse osmosis membrane.

2. The preparation method according to claim 1, characterized in that The polyacrylate is one or more of polymethyl acrylate, polyethyl acrylate, polyn-propyl acrylate, polyisopropyl acrylate, polyn-butyl acrylate, polyisobutyl acrylate or polytert-butyl acrylate; or, the polyacrylate is a copolymer comprising at least two monomers of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate or tert-butyl acrylate; the derivative of the polyacrylate is polymethacrylate.

3. The preparation method according to claim 1, characterized in that: The molecular weight of the polyacrylate and its derivatives is between 1 kDa and 150 kDa.

4. The preparation method according to claim 1, characterized in that: The polyacrylate cosolvent is at least one of acetone, ethyl acetate, benzene and ethylene dichloride.

5. The preparation method according to claim 1, characterized in that: The mass fraction of the intermediate phenylenediamine in step 1 is 2-5wt%, the mass fraction of camphorsulfonic acid is 2-5wt%, and the mass fraction of triethylamine is 1-2wt%.

6. The preparation method according to claim 1, characterized in that: In step 3, the immersion time is 60-120 seconds, and the contact reaction time is 60-120 seconds.

7. The preparation method according to claim 1, characterized in that: The heat treatment temperature in step 4 is 90-120° C., and the heat treatment time is 4-6 minutes.

8. The preparation method according to claim 1, characterized in that: The cleaning time in step 4 is 1-10 min.

9. A seawater desalination reverse osmosis membrane, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

10. The seawater desalination reverse osmosis membrane according to claim 9, characterized in that: The water flux of the seawater desalination reverse osmosis membrane is greater than 45LMH, and the desalination rate is greater than 99.8%.