Composite reverse osmosis membrane as well as preparation method and application thereof
By introducing PVA on the surface of the reverse osmosis membrane to form a polyamide layer and increasing the negative hydroxyl functional groups on the membrane surface, the problem of low chloride ion removal efficiency of the existing reverse osmosis membrane is solved, and higher removal efficiency and water flux are achieved.
Patent Information
- Application Number
- CN202410151275.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-02-02
- Publication Date
- 2025-08-05
AI Technical Summary
The existing reverse osmosis membranes have low efficiency in removing chloride ions.
Co-deposition method is used to introduce polyvinyl alcohol (PVA) on the surface of the reverse osmosis membrane, and form a polyamide layer through interfacial polymerization, increasing the proportion of negative hydroxyl functional groups on the membrane surface, and improving the removal efficiency of chloride ions.
It effectively improves the removal efficiency of the reverse osmosis membrane on chloride ions, and enhances the hydrophilicity and water flux of the membrane.
Smart Images
Figure CN120420847A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of reverse osmosis membranes, and particularly to a composite reverse osmosis membrane, a preparation method thereof, and an application thereof. Background Art
[0002] RO is an abbreviation of the English Reverse Osmosis, and its Chinese meaning is reverse osmosis. Generally, the flow mode of water is from low concentration to high concentration. Once water is pressurized, it will flow from high concentration to low concentration, that is, the principle of reverse osmosis. Since the pore size of the RO membrane is one millionth of a hair (0.0001 micrometers), which is generally invisible to the naked eye, and bacteria and viruses are 5000 times its size. Therefore, only water molecules and some mineral ions can pass through (the passing ions have no beneficial or harmful orientation), and other impurities and heavy metals are discharged through the waste water pipe. Top-grade RO membranes are used for polymer filtration both at home and abroad. The pore size of the RO reverse osmosis membrane is as small as the nanometer level (1 nanometer = 10 -9 meters). Under a certain pressure, water molecules can pass through the RO membrane, while inorganic salts, heavy metal ions, organic matters, colloids, bacteria, viruses and other impurities in the source water cannot pass through the RO membrane, so that the permeable pure water and the non-permeable concentrated water can be strictly separated.
[0003] However, the water permeation amount and desalination rate of the existing RO membranes are both relatively low. Therefore, the existing technology still needs to be improved and developed. Summary of the Invention
[0004] In view of the above deficiencies of the existing technology, the purpose of the present invention is to provide a composite reverse osmosis membrane, a preparation method thereof, and an application thereof, aiming to solve the problem that the existing reverse osmosis membrane has a low removal efficiency for chloride ions.
[0005] The technical solution of the present invention is as follows:
[0006] A preparation method of a composite reverse osmosis membrane, which includes the steps of:
[0007] Using a polyethersulfone ultrafiltration membrane as the base membrane and fixing it;
[0008] Dripping a PVA aqueous solution on the surface of the base membrane, and performing suction filtration on the base membrane after staying for a first predetermined time;
[0009] After suction filtration until there are no water droplets on the surface of the base membrane, then dripping an oil-phase solution on the surface of the base membrane, and performing cleaning treatment on the base membrane after reacting for a second predetermined time;
[0010] Placing the cleaned base membrane in an oven for heat treatment to obtain a composite reverse osmosis membrane.
[0011] In the preparation method of the composite reverse osmosis membrane, the PVA concentration of the PVA aqueous solution is 8wt% - 20wt%.
[0012] The preparation method of the composite reverse osmosis membrane, wherein the first predetermined time is 2 - 5 min.
[0013] The preparation method of the composite reverse osmosis membrane, wherein the oil phase solution is a n - hexane solution in which trimesoyl chloride is dissolved.
[0014] The preparation method of the composite reverse osmosis membrane, wherein the second predetermined time is 30 s - 3 min.
[0015] The preparation method of the composite reverse osmosis membrane, wherein the temperature of the heat treatment is 50 - 70 °C.
[0016] The present invention also discloses a composite reverse osmosis membrane prepared by using the preparation method of the composite reverse osmosis membrane of the present invention.
[0017] On the other hand, the present invention also discloses a composite reverse osmosis membrane, including a base membrane and a polyamide layer intercalated with PVA stacked in sequence, and the base membrane is a polyethersulfone ultrafiltration membrane.
[0018] Further, the polyamide layer is formed by cross - linking piperazine intercalated with PVA and trimesoyl chloride.
[0019] On the other hand, the present invention also discloses an application of the composite reverse osmosis membrane, wherein the composite reverse osmosis membrane of the present invention is used for chloride ion removal.
[0020] Beneficial effects: The present invention uses a co - deposition method to introduce PVA to increase the proportion of negatively charged functional groups of hydroxyl groups on the membrane surface of the polyethersulfone ultrafiltration membrane, effectively improving the chloride ion removal efficiency of the RO membrane; the modification method of the present invention is simple and easy to implement and is suitable for experimental scale - up. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 It is a flowchart of a preparation method of a composite reverse osmosis membrane provided by the present invention.
[0022] Figure 2 It is a test result diagram of the contact angles of PW1, PW2, PW3, and PW4 membranes.
[0023] Figure 3 It is the XPS total spectrum of PW1, PW2, PW3, and PW4 membranes.
[0024] Figure 4 In it, A is the XPS diagram of C1s of PW1 membrane, B is the XPS diagram of C1s of PW2 membrane, C is the XPS diagram of C1s of PW3 membrane, and D is the XPS diagram of C1s of PW4 membrane.
[0025] Figure 5In Figure A is the XPS spectrum of O1s of the PW1 membrane, Figure B is the XPS spectrum of O1s of the PW2 membrane, Figure C is the XPS spectrum of O1s of the PW3 membrane, and Figure D is the XPS spectrum of O1s of the PW4 membrane.
[0026] Figure 6 is the SEM-mapping full scan spectrum of the PW1 membrane.
[0027] Figure 7 is the SEM-mapping full scan spectrum of the PW2 membrane.
[0028] Figure 8 is the SEM-mapping full scan spectrum of the PW3 membrane.
[0029] Figure 9 is the SEM-mapping full scan spectrum of the PW4 membrane.
[0030] Figure 10 is the FTIR spectrum of the PW1, PW2, PW3, and PW4 membranes. Detailed implementation manners
[0031] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several adjustments and improvements can still be made. These all fall within the protection scope of the present invention.
[0032] Please refer to Figure 1 , Figure 1 which is a flowchart of a preparation method of a composite reverse osmosis membrane provided by the present invention. As shown in the figure, it includes the steps:
[0033] S10. Use a polyethersulfone ultrafiltration membrane as the base membrane and fix it;
[0034] S20. Drop a PVA aqueous solution on the surface of the base membrane, and after staying for the first predetermined time, perform suction filtration on the base membrane;
[0035] S30. After suction filtration until there are no water droplets on the surface of the base membrane, then drop an oil phase solution on the surface of the base membrane. After reacting for the second predetermined time, perform cleaning on the base membrane;
[0036] S40. Place the cleaned base membrane in an oven for heat treatment to obtain a composite reverse osmosis membrane.
[0037] The present invention aims to enhance the rejection of chloride ions by introducing negatively charged functional groups on the membrane surface, and uses the co-deposition method to introduce polyvinyl alcohol (PVA) during the interfacial polymerization (IP) process to increase the proportion of negatively charged hydroxyl functional groups on the membrane surface of the polyethersulfone ultrafiltration membrane, and improve the removal efficiency of chloride ions by the RO membrane.
[0038] In some embodiments, the PVA aqueous solution is an aqueous piperazine solution dissolved with PVA.
[0039] In some embodiments, the PVA concentration of the PVA aqueous solution is 8wt%-20wt%, but not limited thereto. By way of example, the PVA concentration of the PVA aqueous solution can be 8wt%, 10wt%, 15wt%, 18wt%, 20wt%, etc.
[0040] In some embodiments, the first predetermined time is 2-5 min, but not limited thereto. By way of example, the first predetermined time can be 2 min, 3 min, 4 min, 5 min, etc.
[0041] In some embodiments, the oil phase solution is a n-hexane solution dissolved with trimesoyl chloride (TMC).
[0042] In some embodiments, the second predetermined time is 30 s-3 min. By way of example, the second predetermined time can be 30 s, 1 min, 2 min, 3 min, etc.
[0043] In some embodiments, the temperature of the heat treatment is 50-70 °C. By way of example, the temperature of the heat treatment can be 50 °C, 60 °C, 70 °C, etc.
[0044] In some embodiments, a composite reverse osmosis membrane is further provided, wherein the composite reverse osmosis membrane is prepared by using the preparation method of the composite reverse osmosis membrane of the present invention.
[0045] In some embodiments, an application of a composite reverse osmosis membrane is further provided, wherein the composite reverse osmosis membrane of the present invention is used for chloride ion removal.
[0046] The following further explains and illustrates the present invention through specific examples:
[0047] Example 1
[0048] Taking the polyethersulfone ultrafiltration membrane as the base membrane and fixing it, dropping an 8wt% PVA aqueous solution on the surface of the base membrane, and performing suction filtration on the base membrane after staying for 3 min;
[0049] After suction filtration until there are no water droplets on the surface of the base membrane, dropping the oil phase solution on the surface of the base membrane again, reacting for 2 min, and then performing cleaning treatment on the base membrane;
[0050] The cleaned base membrane was placed in an oven for heat treatment at 60° C. for 5 min, and then naturally cooled to obtain a composite reverse osmosis membrane, which was designated as PW2.
[0051] The oil phase solution is a n-hexane solution containing 0.1 wt % of trimesoyl chloride.
[0052] The aqueous phase solution is a piperazine (PIP) aqueous solution in which 8 wt % PVA is dissolved.
[0053] Example 2
[0054] A polyethersulfone ultrafiltration membrane was used as a base membrane and fixed, and a 15 wt% PVA aqueous solution was dripped onto the surface of the base membrane. After the solution was left for 2 minutes, the base membrane was filtered.
[0055] After the basement membrane is filtered until there are no water droplets on the surface, the oil phase solution is dripped onto the surface of the basement membrane, and after reacting for 30 seconds, the basement membrane is cleaned;
[0056] The cleaned base membrane was placed in an oven for heat treatment at 50° C. for 5 min, and then naturally cooled to obtain a composite reverse osmosis membrane, which was designated as PW3.
[0057] The oil phase solution is a n-hexane solution containing 0.1 wt % of trimesoyl chloride.
[0058] The aqueous phase solution is a piperazine aqueous solution in which 15 wt% PVA is dissolved.
[0059] Example 3
[0060] A polyethersulfone ultrafiltration membrane was used as a base membrane and fixed, and a 20 wt% PVA aqueous solution was dripped onto the surface of the base membrane. After the solution was left for 5 minutes, the base membrane was filtered.
[0061] After filtering until there are no water droplets on the surface of the basement membrane, the oil phase solution is dripped onto the surface of the basement membrane, and after reacting for 3 minutes, the basement membrane is cleaned;
[0062] The cleaned base membrane was placed in an oven for heat treatment at 70° C. for 5 min, and then naturally cooled to obtain a composite reverse osmosis membrane, which was designated as PW4.
[0063] The oil phase solution is a n-hexane solution containing 0.1 wt % of trimesoyl chloride.
[0064] The aqueous phase solution is a piperazine aqueous solution in which 20 wt% PVA is dissolved.
[0065] Comparative Example 1
[0066] The preparation method of Comparative Example 1 was similar to that of Example 1. Similarly, a polyethersulfone ultrafiltration membrane was used as the base membrane. The difference was that the aqueous solution in this comparative example did not contain PVA. The prepared reverse osmosis membrane was denoted as PW1.
[0067] The water flux, rejection rate, and Zeta potential of the composite reverse osmosis membranes prepared in Examples 1-3 and the PW1 reverse osmosis membrane in Comparative Example 1 were tested. The results are shown in Table 1. The concentration of piperazine in the aqueous solutions of Examples 1 to 3 and Comparative Example 1 was the same.
[0068] Table 1 Performance test results
[0069]
[0070] Among them, the operating pressure for water flux was 5 bar; the feed water for rejection rate 1 was 1000 mg / L MgCl2 solution, and the feed water for rejection rate 2 was 1000 mg / L NaCl solution; the test conditions for Zeta potential were 10 mM KCl and pH = 7.
[0071] It can be seen from the data in Table 1 that as the PVA content increased, the water fluxes of the composite reverse osmosis membranes PW2, PW3, and PW4 gradually increased, indicating that the water permeability of the membrane was enhanced due to the introduction of PVA. This was mainly because when the PVA content increased, more PVA molecules participated in the interfacial polymerization reaction, resulting in more hydroxyl groups in the separation layer and improving the hydrophilicity of the membrane.
[0072] The rejection effects of the composite reverse osmosis membranes on two chloride salts, MgCl2 and NaCl, were investigated. When the PVA content increased, the rejection rate of MgCl2 showed a trend of first increasing and then decreasing, which was attributed to the decrease in the Zeta potential on the membrane surface, indicating that an appropriate amount of PVA could reduce the membrane surface potential to enhance the rejection of divalent salts containing chloride ions; while during the process of increasing the content, the rejection rate of the composite reverse osmosis membrane for NaCl remained basically unchanged, always maintaining at about 30%. This might be because the addition of a small amount of PVA did not significantly affect the cross-linked structure of the separation layer, resulting in no obvious change in the rejection of NaCl by the membrane.
[0073] The membrane contact angle test results of PW1-PW4 are as Figure 2 shown. It can be seen from Figure 2 that the contact angle of the PW1 membrane decreased significantly after adding PVA, indicating an increase in hydrophilicity. It was speculated that the introduction of hydroxyl groups contained in PVA improved the hydrophilicity of the membrane. As the concentration of added PVA increased, the contact angle of the membrane gradually decreased, indicating that the hydrophilicity of the membrane gradually increased with the increase in PVA content; however, there was little difference between PW3 and PW4, indicating that when the PVA concentration was greater than 15%, further increasing the PVA concentration did not significantly improve the hydrophilicity.
[0074] XPS analysis was carried out on the PW1 - PW4 membranes, and the results are as Figure 3 shown. It can be seen from Figure 3 that the four elements C, N, O, and S exist on the surfaces of all four membranes. The C1s of the PW1 - PW4 membranes was peak - split to obtain Figure 4 . The peak of C that appears at 288 eV in all four membranes exists in the form of C=O (as shown by A - D in Figure 4 ). In PW1, -C=O- is formed by PIP and TMC, while in PW2, PW3, and PW4, -C=O- is formed by the reaction of TMC and PVA. Figure 4 The peak of C that appears at 285.7 eV in C and D of Figure 5 exists in the form of C - N, which is analyzed as the C - N carried by PIP. All of the above indicate that PVA has been successfully compounded on the polyamide layer. Figure 5 Figure
[0075] is the O1s peak - split diagram of the PW1 - PW4 membranes. It can be seen from A - D in Figures 6 - 9 that the O element exists on the membrane surface. The OH- peak (at 531 eV) appears in all PVA - modified membranes. OH- is a characteristic functional group of PVA, indicating the successful compounding of PVA.
[0076] Table 2 Element ratio distribution on the membrane surface
[0077]
[0078]
[0079] Element ratio distribution analysis was carried out on the surfaces of the PW1 - PW4 membranes, and the results are as Figure 10 shown. 3330 - 3500 cm -1 is the vibration peak of O - H, and the spectral band at 1695 - 1630 cm -1 belongs to the special vibration peaks of C=O and C=C bonds. Both of them appear on the membrane surface, indicating that the PW2, PW3, and PW4 membrane surfaces contain PVA. The spectral band at 1350 - 1020 cm -1 belongs to the special vibration peak of the C - N bond, which appears on the membrane surface, indicating that the membrane surface contains PIP.
[0080] In summary, the present invention improves the rejection efficiency of chloride ions by introducing PVA during the IP process; experiments have found that the rejection rate of the composite reverse osmosis membrane for MgCl2 has been improved to a certain extent (the rejection rate of divalent salts has been increased by 23%), and the rejection effect of NaCl has not been significantly improved; the hydrophilicity and flux of the membrane (the contact angle has been reduced by about 30°, and the flux has been increased by about 20%) have both been improved. The relevant characterizations of the element distribution on the membrane surface and the functional groups on the membrane surface of the present invention show that PVA has been successfully introduced into the polyamide layer, and the introduction of PVA is the key to the improvement of membrane performance.
[0081] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, modifications or variations can be made according to the above description, and all such modifications and variations should fall within the protection scope of the appended claims of the present invention.
Claims
1. A method for preparing a composite reverse osmosis membrane, characterized in that: Including steps: Polyethersulfone ultrafiltration membrane is used as base membrane and fixed; Adding the PVA aqueous solution dropwise to the surface of the basement membrane, leaving it for a first predetermined time, and then filtering the basement membrane; After filtering until there are no water droplets on the surface of the basement membrane, dripping the oil phase solution on the surface of the basement membrane, reacting for a second predetermined time, and then cleaning the basement membrane; The cleaned base membrane is placed in an oven for heat treatment to obtain a composite reverse osmosis membrane.
2. The method for preparing a composite reverse osmosis membrane according to claim 1, wherein The PVA concentration of the PVA aqueous solution is 8 wt % to 20 wt %.
3. The method for preparing a composite reverse osmosis membrane according to claim 1, wherein: The first predetermined time is 2-5 minutes.
4. The method for preparing a composite reverse osmosis membrane according to claim 1, wherein The oil phase solution is a n-hexane solution in which trimesoyl chloride is dissolved.
5. The method for preparing a composite reverse osmosis membrane according to claim 1, wherein: The second predetermined time is 30 seconds to 3 minutes.
6. The method for preparing a composite reverse osmosis membrane according to claim 1, wherein: The temperature of the heat treatment is 50-70°C.
7. A composite reverse osmosis membrane, characterized in that: The composite reverse osmosis membrane is prepared by the preparation method of any one of claims 1 to 6.
8. A composite reverse osmosis membrane, characterized in that: The invention comprises a base film and a polyamide layer mixed with PVA which are stacked in sequence, wherein the base film is a polyethersulfone ultrafiltration membrane.
9. The composite reverse osmosis membrane according to claim 8, characterized in that The polyamide layer is formed by cross-linking reaction of piperazine mixed with PVA and trimesoyl chloride.
10. An application of a composite reverse osmosis membrane, characterized in that: The composite reverse osmosis membrane according to claim 7, 8 or 9 is used for removing chloride ions.