Anti-scaling composite membrane as well as preparation method and application thereof

Abstract

The invention discloses an anti-scaling composite membrane as well as a preparation method and application thereof. The preparation method of the anti-scaling composite membrane comprises the step of modifying a polyamide membrane to obtain the anti-scaling composite membrane. The modification mode of the polyamide membrane is that in-situ filtration is sequentially carried out on a polyphenol compound solution and a sulfamic acid compound solution through the polyamide membrane, and then modification is completed. According to the preparation method, surface modification is carried out on an existing polyamide membrane, the hydrophilicity of the surface of the polyamide membrane is improved, the chemical property of the surface of the membrane is changed, and therefore the anti-pollution performance of the polyamide membrane can be improved. After modification, the hydrophilicity of the surface of the polyamide membrane is increased, and the surface of the polyamide membrane has a polyphenol-sulfamic acid grafting layer. As the affinity of Ca < 2 + > ions, hydroxyl, sulfo groups and phosphate groups is relatively low, the acting force between the membrane surface and Ca scale is relatively weak, and the anti-scaling capability is relatively good.

Description

Technical Field

[0001] The invention belongs to the technical field of reverse osmosis membranes, and in particular relates to an anti-scaling composite membrane and a preparation method and application thereof. Background Art

[0002] Commercial reverse osmosis membranes and nanofiltration membranes are mainly polyamide thin-layer composite membranes prepared by interfacial polymerization. The pollution of polyamide membranes has almost always been a problem encountered in the application of reverse osmosis and nanofiltration membranes. Ion scaling in the water treatment process is also the main factor restricting the improvement of the recovery rate of polyamide composite membranes. The influent water usually contains a large amount of alkaline earth metal cations (such as Ca 2 + Mg 2+ ), anionic groups (CO3 2- 、SO4 2- ) and soluble silicates. With the increase of ion concentration caused by concentration and concentration polarization, inorganic ions are enriched on the membrane surface. When the concentration product of ions exceeds their solubility product, cations and anions combine to form calcium carbonate scale, calcium sulfate scale, metal oxide scale and silica scale.

[0003] After the polyamide membrane is contaminated or scaled on the surface, the flux decreases, and chemical cleaning is necessary to restore its performance. Frequent chemical cleaning will reduce the service life of the membrane and increase operating costs. For scaling caused by inorganic substances, adding scale inhibitors to the feed liquid is a common method to prevent scaling, but this will increase costs. Summary of the invention

[0004] In order to solve the above technical problems, the object of the present invention is to provide a method for preparing an anti-scaling composite membrane, which has good surface hydrophilicity and excellent anti-scaling performance.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present invention is as follows: a method for preparing an anti-scaling composite membrane, wherein the anti-scaling composite membrane can be obtained by modifying a polyamide membrane; the modification method of the polyamide membrane is to successively filter a polyphenol compound solution and an aminosulfonic acid compound solution in situ through the polyamide membrane to complete the modification.

[0006] The in-situ filtration in the above technical solution is carried out at room temperature and under a pressure of 4-20 kg, and the pH of the polyphenol compound solution and the aminosulfonic acid compound solution are both 7-9.

[0007] In the above technical solution, each in-situ filtration lasts for 10-60 minutes.

[0008] The polyphenol compound in the above technical solution is at least one of tannic acid, pyrogallol, catechol and gallic acid.

[0009] The aminosulfonic acid compound in the above technical solution is at least one of taurine, homotaurine, phenylenediaminesulfonic acid and aminobenzenesulfonic acid.

[0010] The concentration of the polyphenol compound solution in the above technical solution is 0.01-0.2wt%.

[0011] The concentration of the aminosulfonic acid compound solution in the above technical solution is 0.01-0.1wt%.

[0012] The polyphenol compound solution and aminosulfonic acid compound solution in the above technical solution are both aqueous solutions.

[0013] A second object of the present invention is to provide an anti-scaling composite membrane prepared by the preparation method as described above.

[0014] A third object of the present invention is to provide an application of the anti-scaling composite membrane as described above in water purification.

[0015] The beneficial effect of the present invention is that: the present invention improves the hydrophilicity of the surface of the polyamide membrane by modifying the surface of the existing polyamide membrane, and introduces hydroxyl and sulfonic acid groups into the membrane surface. 2+ Ion complexation, CaSO4 and silica scale further heterogeneously nucleate to form membrane pollutants, and the surface of the modified membrane is rich in hydroxyl and sulfonic acid groups. 2+ The affinity between ions and hydroxyl groups and sulfonic acid groups is low, so the modified membrane surface has a weaker interaction with Ca scale and has better anti-scaling ability. At present, the surface modification of polyamide membranes is mainly surface grafting, such as oxygen reduction free radical-initiated grafting, light-initiated grafting, carboxyl-activated grafting, etc., which have high requirements for reaction conditions. The method of the present invention has easy-to-obtain materials, simple process and no organic solvent involved, and is a green modification method. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a result diagram of the pollution-cleaning cycle test before and after the modification of the polyamide membrane described in Example 1 of the present invention;

[0017] Figure 2 This is a result diagram of the pollution-cleaning cycle test of the polyamide membrane before and after modification in Example 2 of the present invention;

[0018] Figure 3 This is a graph showing the results of the pollution-cleaning cycle test before and after the modification of the polyamide membrane described in Example 3 of the present invention. DETAILED DESCRIPTION

[0019] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention. The advantages and features of the present invention will be more clearly described according to the following description and claims.

[0020] The invention provides a method for preparing an anti-scaling composite membrane. The anti-scaling composite membrane can be obtained by modifying a polyamide membrane. The polyamide membrane is modified by successively filtering a polyphenol compound solution and an aminosulfonic acid compound solution in situ through the polyamide membrane to complete the modification.

[0021] The in-situ filtration described in the above technical scheme is carried out at room temperature under a pressure of 4-20 kg (can be 4 kg, 5 kg, 6 kg, 7 kg, 8 kg, 9 kg, 10 kg, 11 kg, 12 kg, 13 kg, 14 kg, 15 kg, 16 kg, 17 kg, 18 kg, 19 kg and any value of 19 kg or a range corresponding to any two values), wherein if the pressure is lower than 4 kg, the flux is small, so that the modification effect of the polyamide membrane is not good, on the contrary, if the pressure is higher than 20 kg, the microstructure of the polyamide membrane may be deformed, resulting in the compaction of the membrane, and the pH of the polyphenol compound solution and the aminosulfonic acid compound solution are both 7-9 (polyphenol is prone to oxidative self-polymerization under weak alkaline conditions, and polyphenol can also react with residual amino groups in the polyamide membrane, so polyphenol can be grafted / deposited on the surface of the polyamide membrane and the membrane pores, and subsequent further filtration of the aminosulfonic acid compound can introduce sulfonic acid groups into the membrane surface).

[0022] In the above technical scheme, the duration of each in-situ filtration is 10-60min (any value among 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 55min and 60min, or the corresponding range between any two values), wherein, if the in-situ filtration time is less than 10min, the flux is small, which will also lead to poor modification effect of the polyamide membrane. Conversely, if the in-situ filtration time is higher than 60min, the microscopic pores of the polyamide membrane will be deformed.

[0023] The polyphenol compound in the above technical scheme is at least one of tannic acid, pyrogallol, catechol and gallic acid; the aminosulfonic acid compound is at least one of taurine, homotaurine, phenylenediaminesulfonic acid and aminobenzenesulfonic acid; the polyphenol compound solution and the aminosulfonic acid compound solution are both aqueous solutions.

[0024] The concentration of the polyphenol compound solution in the above technical solution is 0.01-0.2wt% (0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt% and 0.2wt%). any value or a range corresponding to any two values); the concentration of the aminosulfonic acid compound solution is 0.01-0.1wt% (0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt% and 0.1wt% any value or a range corresponding to any two values), wherein, if the concentrations of the aminosulfonic acid compound solution and the polyphenol compound solution are too low, the modification time will be prolonged, while if the concentrations are too high, the flux of the membrane will be reduced.

[0025] Example 1

[0026] A polyphenol aqueous solution with a concentration of 0.05wt% and a taurine aqueous solution with a concentration of 0.02wt% are prepared, and an existing commercial low-pressure polyamide reverse osmosis membrane is installed in a cross-flow device. At room temperature and under a pressure of 5 kg, the polyphenol aqueous solution is introduced into the cross-flow device to filter the low-pressure polyamide reverse osmosis membrane for in-situ modification for 30 minutes; then at room temperature and under a pressure of 5 kg, the taurine aqueous solution is continued to be introduced into the cross-flow device to continue filtering the low-pressure polyamide reverse osmosis membrane for in-situ modification for 30 minutes, and then pure water is introduced into the cross-flow device to flush the low-pressure polyamide reverse osmosis membrane in-situ, so as to obtain an anti-scaling polyamide reverse osmosis membrane (that is, an anti-scaling composite membrane).

[0027] The retention performance of the low-pressure polyamide reverse osmosis membrane before and after modification was tested at 25°C and 5 kg pressure using a 0.2 g / L NaCl solution. The membrane flux before modification was 6.63 L / (m 2 h bar), the rejection rate of NaCl was 94.83%. After modification, the membrane flux was 4.65 L / (m 2 h bar), the retention rate of NaCl was about 97.06%.

[0028] Na2SiO3, CaCl2, MgCl2 and NaCl were mixed with water to prepare an inorganic scale simulation liquid, wherein the concentrations of the components in the inorganic scale simulation liquid were: 0.3g / L Na2SiO3, 0.7g / L CaCl2, 0.48g / L MgCl2 and 2g / L NaCl; at 25°C, the low-pressure polyamide reverse osmosis membrane before and after modification was subjected to a pollution-cleaning cycle test at a pressure of 5 kg using the inorganic scale simulation liquid and pure water. The results are as follows: Figure 1 It can be seen that the flux is high and the flux decay is slow during the pollution test. After two pollution tests lasting 20 hours, the recovery rate of pure water flux is 61%, which is higher than the recovery rate of pure water flux of the unmodified membrane (the recovery rate of pure water flux of the unmodified membrane is 50%).

[0029] Example 2

[0030] Same as Example 1, except that the concentration of the polyphenol aqueous solution is 0.03 wt % and the concentration of the taurine aqueous solution is 0.03 wt %.

[0031] The retention performance of the low-pressure polyamide reverse osmosis membrane before and after modification was tested at 25°C and 5 kg pressure using a 0.2 g / L NaCl solution. The membrane flux before modification was 7.3 L / (m 2 h bar), the rejection rate of NaCl was 91.4%, and after modification, the membrane flux was 4.6L / (m 2 h bar), the retention rate of NaCl was about 98.4%.

[0032] The low-pressure polyamide reverse osmosis membrane before and after modification was subjected to a pollution-cleaning cycle test at a pressure of 5 kg using an inorganic scale simulation liquid and pure water. The results are as follows: Figure 2 It can be seen that the flux is high and the flux decay is slow during the pollution test. After two pollution tests lasting 20 hours, the recovery rate of pure water flux is 69%, which is higher than the recovery rate of pure water flux of the unmodified membrane (the recovery rate of pure water flux of the unmodified membrane is 45%).

[0033] Example 3

[0034] Same as Example 1, except that the concentration of the polyphenol aqueous solution is 0.03 wt % and the concentration of the taurine aqueous solution is 0.02 wt %.

[0035] The retention performance of the low-pressure polyamide reverse osmosis membrane before and after modification was tested at 25°C and 5 kg pressure using a 0.2 g / L NaCl solution. The membrane flux before modification was 6.8 L / (m 2 h bar), the rejection rate of NaCl was 94.5%, and after modification, the membrane flux was 4.5L / (m 2h bar), the retention rate of NaCl was about 98.8%.

[0036] The low-pressure polyamide reverse osmosis membrane before and after modification was subjected to a pollution-cleaning cycle test at a pressure of 5 kg using an inorganic scale simulation liquid and pure water. The results are as follows: Figure 3 It can be seen that the flux is high and the flux decay is slow during the pollution test. After two pollution tests lasting 20 hours, the recovery rate of pure water flux is 72%, which is higher than the recovery rate of pure water flux of the unmodified membrane (the recovery rate of pure water flux of the unmodified membrane is 45%).

[0037] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an anti-scaling composite membrane, characterized in that: The anti-scaling composite membrane can be obtained by modifying the polyamide membrane; the modification method of the polyamide membrane is to filter the polyphenol compound solution and the aminosulfonic acid compound solution in situ in sequence through the polyamide membrane to complete the modification.

2. The method for preparing the anti-scaling composite membrane according to claim 1, characterized in that: The in-situ filtration is carried out at room temperature and under a pressure of 4-20 kg, and the pH of the polyphenol compound solution and the aminosulfonic acid compound solution are both 7-9.

3. The method for preparing the anti-scaling composite membrane according to claim 1, characterized in that: Each in-situ filtration lasts for 10-60 minutes.

4. The method for preparing the anti-scaling composite membrane according to claim 1, characterized in that: The polyphenol compound is at least one of tannic acid, pyrogallol, catechol and gallic acid.

5. The method for preparing the anti-scaling composite membrane according to claim 1, characterized in that: The aminosulfonic acid compound is at least one of taurine, homotaurine, phenylenediaminesulfonic acid and aminobenzenesulfonic acid.

6. The method for preparing the anti-scaling composite membrane according to claim 1, characterized in that: The concentration of the polyphenol compound solution is 0.01-0.2 wt %.

7. The method for preparing the anti-scaling composite membrane according to claim 1, characterized in that: The concentration of the aminosulfonic acid compound solution is 0.01-0.1 wt %.

8. The method for preparing the anti-scaling composite membrane according to claim 1, characterized in that: The polyphenol compound solution and the aminosulfonic acid compound solution are both aqueous solutions.

9. An anti-scaling composite membrane, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. An application of the anti-scaling composite membrane according to claim 9, characterized in that: Used in water purification.

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