A method for preparing a reverse osmosis membrane capable of withstanding high temperature water environment

Abstract

The invention provides a method for preparing a reverse osmosis membrane that can withstand a high-temperature water environment, comprising the following steps: first, synthesizing an α-cyclodextrin@polyethylene glycol supramolecular inclusion complex by a saturated aqueous solution coprecipitation method; second, preparing an aqueous phase solution containing m-phenylenediamine, D(+) camphorsulfonic acid, and triethylamine; then, preparing an oil phase solution containing trimesoyl chloride; then, preparing a secondary aqueous phase solution containing α-cyclodextrin@polyethylene glycol powder and triethylamine; then, forming an ultrathin polyamide separation layer on a base film by interfacial polymerization; finally, performing secondary interfacial polymerization to form an α-CD@PEG polyester protective layer, and storing the prepared reverse osmosis membrane in ultrapure water.

Description

Technical Field

[0001] The invention relates to the field of reverse osmosis membrane preparation, and in particular to a method for preparing a reverse osmosis membrane capable of withstanding a high-temperature water environment. Background Art

[0002] Reverse osmosis membrane technology, with its high efficiency, easy operation, small footprint, low energy consumption, wide applicability and low cost, has been widely used in the fields of seawater desalination, sewage and wastewater treatment, food and pharmaceutical purification, drinking water purification, etc. Currently, commercial reverse osmosis membranes are mainly aromatic polyamide composite membranes, which are composed of three parts: non-woven fabric, porous support layer and ultra-thin separation layer on the top.

[0003] The main disadvantage of commercial reverse osmosis membranes is their poor tolerance to high temperatures, with the maximum operating temperature generally below 45°C. At high temperatures, the polymer network structure expands, causing the membrane pore size to increase and the internal free volume to increase. At the same time, the structural changes in the support layer will pull the separation layer, ultimately resulting in reduced desalination performance of the reverse osmosis membrane, which limits the application of reverse osmosis membranes in high-temperature water treatment. A large amount of high-temperature wastewater is generated in many industries such as food, textiles, papermaking, and petrochemicals. When treating this part of the wastewater, it is necessary to reduce the temperature of the process water before the membrane separation process and then heat it back to its original temperature. This will not only increase operating costs and energy consumption, but also lead to more greenhouse gas emissions. Summary of the invention

[0004] The present invention hopes to provide a method for preparing a reverse osmosis membrane that can withstand a high-temperature water environment, so as to achieve the purpose of effectively treating high-temperature wastewater with a reverse osmosis membrane. The specific scheme is as follows:

[0005] A method for preparing a reverse osmosis membrane that can withstand a high-temperature water environment comprises the following steps:

[0006] (1) First, α-cyclodextrin@polyethylene glycol supramolecular inclusion complex (α-CD@PEG) was synthesized by saturated aqueous solution co-precipitation method: a certain amount of polyethylene glycol was first dissolved in ultrapure water to obtain a saturated polyethylene glycol aqueous solution, and then α-cyclodextrin powder was added, stirred at a constant temperature and allowed to stand. After cooling to ambient temperature, the precipitate was filtered and dried to obtain α-cyclodextrin@polyethylene glycol powder;

[0007] (2) preparing an aqueous phase solution: dissolving a certain amount of m-phenylenediamine, D(+) camphorsulfonic acid and triethylamine in a certain amount of ultrapure water to prepare an aqueous phase solution;

[0008] (3) Preparation of oil phase solution: dissolve a certain amount of trimesoyl chloride in a certain amount of n-hexane to prepare an oil phase solution;

[0009] (4) Preparing a secondary aqueous phase solution: dissolving a certain amount of α-cyclodextrin@polyethylene glycol powder and triethylamine in a certain amount of ultrapure water to prepare a secondary aqueous phase solution;

[0010] (5) Interfacial polymerization: Take the base film soaked in water, blow dry the surface water with nitrogen, pour the water phase solution on the surface of the base film and let it stay for 30 s to 180 s, remove the excess water phase solution and blow dry the surface of the base film with nitrogen, then pour the oil phase solution on the surface of the base film and remove the excess oil phase solution after reaction, and place the obtained film in an oven for thermal curing to form an ultra-thin polyamide separation layer;

[0011] (6) Secondary interfacial polymerization: The secondary aqueous phase solution is poured onto the membrane surface for reaction and then the excess liquid is removed to form an α-CD@PEG polyester protective layer. The surface of the prepared reverse osmosis membrane is rinsed with ultrapure water and then stored in ultrapure water.

[0012] In the step (1), the molar ratio of α-cyclodextrin to polyethylene glycol is one of 4:1, 5:1, 6:1, 7:1 and 8:1.

[0013] In the step (1), the constant temperature stirring temperature is 65° C., the constant temperature stirring time is 1 hour, and then the solution is left to stand for 12 hours.

[0014] The drying temperature in step (1) is 70° C. and the drying time is 12 hours.

[0015] In the step (2), the concentration of the intermediate phenylenediamine is 2-2.5 wt%, the concentration of D(+) camphorsulfonic acid is 1.2-2.4 wt%, and the concentration of triethylamine is 1.3 wt%. In the step (3), the concentration of trimesoyl chloride is 0.1 wt%.

[0016] In the step (5), the aqueous solution is poured onto the surface of the base film and allowed to remain there for 120-180 seconds.

[0017] In the step (5), the prepared film is placed in an oven at 80° C. for thermal curing for 5 minutes.

[0018] In step (6), the mixture is stored in ultrapure water at 4°C.

[0019] The α-cyclodextrin used in the present invention is a cyclic oligosaccharide with hydrophilic outer side and hydrophobic inner cavity, containing 6 glucose units. Its special structure makes it a natural complexing agent, which can wrap other molecules through its hydrophobic cavity, thereby improving the solubility and stability of these molecules. The driving force for forming the inclusion complex includes the release of high-energy water molecules from the α-cyclodextrin cavity, electrostatic interaction, van der Waals interaction, hydrophobic interaction, hydrogen bonding, etc. The thermal stability of both is improved by including polyethylene glycol in α-cyclodextrin. At the same time, α-cyclodextrin contains abundant hydroxyl groups, and polyethylene glycol itself is also an alcohol containing hydroxyl groups. The two react together with the residual acyl chloride on the surface of the polyamide membrane to form a polyester protective layer on the membrane surface. DETAILED DESCRIPTION

[0020] 1. A method for preparing a reverse osmosis membrane that can withstand high temperature water environment

[0021] The specific steps include:

[0022] (1) First, α-cyclodextrin@polyethylene glycol supramolecular inclusion complex (α-CD@PEG) was synthesized by saturated aqueous solution co-precipitation method: a certain amount of polyethylene glycol (PEG) was first dissolved in ultrapure water to prepare a PEG saturated aqueous solution (50 g / L). Subsequently, α-CD powder was added, and the molar ratio of α-CD to PEG could be 4:1, 5:1, 6:1, 7:1, or 8:1. The mixture was stirred at 65°C for 1 hour, and the resulting solution was allowed to stand for 12 hours. After cooling to ambient temperature, the precipitate was filtered and dried at 70°C for 12 hours to obtain α-CD@PEG powder.

[0023] (2) preparing an aqueous phase solution: dissolving a certain amount of m-phenylenediamine, D(+) camphorsulfonic acid and triethylamine in a certain amount of ultrapure water to prepare an aqueous phase solution;

[0024] (3) Preparation of oil phase solution: dissolve a certain amount of trimesoyl chloride in a certain amount of n-hexane to prepare an oil phase solution;

[0025] (4) Preparation of secondary aqueous phase solution: a certain amount of α-CD@PEG powder and triethylamine are dissolved in a certain amount of ultrapure water to prepare a secondary aqueous phase solution;

[0026] (5) Interfacial polymerization: Take the base film soaked in water, blow dry the surface water with nitrogen, pour the water phase solution on the surface of the base film and let it stay for 30 s to 180 s, remove the excess water phase solution and blow dry the membrane surface with nitrogen, then pour the oil phase solution on the membrane surface and let it react for 60 s, then remove the excess oil phase solution, and place the obtained membrane in an oven at 80 °C for thermal curing for 5 min to form an ultra-thin polyamide (PA) separation layer;

[0027] (6) Secondary interfacial polymerization: The secondary aqueous phase solution was poured onto the membrane surface and reacted for 3 min before removing the excess liquid to form an α-CD@PEG polyester protective layer. The prepared reverse osmosis membrane was rinsed with ultrapure water for 2 to 3 times and then stored in ultrapure water at 4 °C.

[0028] The α-cyclodextrin used in step (1) is a cyclic oligosaccharide with a hydrophilic outer surface and a hydrophobic inner cavity. It contains 6 glucose units. Its special structure makes it a natural complexing agent, which can encapsulate other molecules through its hydrophobic cavity, thereby improving the solubility and stability of these molecules. The driving forces for the formation of inclusion complexes include the release of high-energy water molecules from the cyclodextrin cavity, electrostatic interactions, van der Waals interactions, hydrophobic interactions, hydrogen bonds, etc. By encapsulating polyethylene glycol with α-cyclodextrin, the thermal stability of both is improved. At the same time, α-cyclodextrin contains abundant hydroxyl groups, and polyethylene glycol itself is also an alcohol containing hydroxyl groups. The two react together with the residual acyl chloride on the surface of the polyamide membrane to form a polyester protective layer on the membrane surface.

[0029] 2. Optimization of reverse osmosis membrane synthesis conditions

[0030] The orthogonal method was used to study the relationship between flux and desalination rate and five factors (water phase residence time, metaphenylenediamine (MPD) concentration, triethylamine (TEA) concentration, D(+) camphorsulfonic acid (CSA) concentration, and trimesoyl chloride concentration). The optimal flux and desalination rate combination of each level of the five factors was found, and finally the range analysis was performed to compare the advantages between the factors and the advantages and disadvantages of the specific levels of the factors, and the optimal factors and combinations were selected to determine the optimal synthesis conditions. The remaining reaction conditions remained unchanged: oil phase residence time 60 s, humidity 60% RH, and thermal curing temperature 80 ℃. The flux and desalination rate were based on the following standard tests: 2000 ppm NaCl, 225 psi (15.5 bar), 77℉ (25 ℃). The specific experimental design is shown in Table 1.

[0031] Table 1 Experimental factors and levels

[0032]

[0033] Table 2 Test results

[0034]

[0035] The results of the range analysis of the average flux are shown in Table 3. For the average flux, from the perspective of the five factors, combined with the comparison of the size of the R value, it can be seen that factor 1, namely TMC concentration, is the best factor, and factor 5, namely water phase residence time, is the worst factor. The five factors are ranked as follows: factor 1 (TMC concentration) > factor 3 (TEA concentration) > factor 2 (MPD concentration) > factor 4 (CSA concentration) > factor 5 (water phase residence time). Specifically combined with the optimal level of each factor, it can be seen that factor 1 (TMC concentration) is optimal at the first level, namely 0.10 wt%, factor 2 (MPD concentration) is optimal at the third level, namely 2.00 wt%, factor 3 (TEA concentration) is optimal at the fourth level, namely 1.30 wt%, factor 4 (CSA concentration) is optimal at the third level, namely 2.40 wt%, and factor 5 (water phase residence time) is optimal at the third level, namely 120 s.

[0036] According to the above analysis, the optimal factor for average flux is TMC concentration. The optimal combination for average flux is "TMC concentration 0.10 wt%, MPD concentration 2.00 wt%, TEA concentration 1.30 wt%, CSA concentration 2.40 wt%, water phase residence time 120 s".

[0037] Table 3 Average flux range analysis table

[0038]

[0039] The results of the range analysis of the average desalination rate are shown in Table 4. For the average flux, from the perspective of the five factors, combined with the comparison of the R value, it can be seen that factor 1, namely TMC concentration, is the best factor, and factor 2, namely MPD concentration, is the worst factor. The five factors are ranked as follows: factor 1 (TMC concentration) > factor 4 (CSA concentration) > factor 5 (water phase residence time) > factor 3 (TEA concentration) > factor 2 (MPD concentration). Specifically combined with the optimal level of each factor, it can be seen that factor 1 (TMC concentration) is optimal at the first level, namely 0.10wt%, factor 2 (MPD concentration) is optimal at the fourth level, namely 2.50 wt%, factor 3 (TEA concentration) is optimal at the third level, namely 1.30 wt%, factor 4 (CSA concentration) is optimal at the first level, namely 1.20 wt%, and factor 5 (water phase residence time) is optimal at the fourth level, namely 180 s.

[0040] According to the above analysis, the optimal factor for average desalination rate is TMC concentration. The optimal combination for average desalination rate is "TMC concentration 0.10 wt%, MPD concentration 2.50 wt%, TEA concentration 1.30 wt%, CSA concentration 1.20 wt%, water phase residence time 180s".

[0041] Table 4 Average desalination rate range analysis table

[0042]

[0043] Based on the above analysis, it can be seen that: according to the average flux and average rejection rate test results, the optimal factor for reverse osmosis membrane synthesis is TMC concentration, and the optimal combination range is "TMC concentration 0.10 wt%, MPD concentration 2.00~2.50 wt%, TEA concentration 1.30wt%, CSA concentration 1.20~2.40 wt%, and water phase residence time 120~180 s".

[0044] 3. Basement membrane screening

[0045] Four base membranes were selected for reverse osmosis membrane preparation. The synthesis conditions adopted the above-mentioned optimal combination of average flux: "TMC concentration 0.10 wt%, MPD concentration 2.00 wt%, TEA concentration 1.30 wt%, CSA concentration 2.40 wt%, water phase residence time 120 s". The other reaction conditions are still: oil phase residence time 60 s, humidity 60% RH, thermal curing temperature 80 ℃. Standard test conditions: 2000 ppm NaCl, 225 psi (15.5 bar), 77℉ (25 ℃). The test results at room temperature (25 ℃) are shown in Table 5.

[0046] Table 5 Performance of reverse osmosis membranes prepared with different base membranes at room temperature

[0047]

[0048] According to the performance of reverse osmosis membranes prepared from different base membranes under normal temperature test, the reverse osmosis membranes prepared from base membranes 2 and 3 have low desalination rates, and the reverse osmosis membrane prepared from base membrane 4 has low flux. Therefore, base membrane 1 was selected to prepare a reverse osmosis membrane using the above-mentioned "a method for preparing a reverse osmosis membrane that can withstand high temperature water environment", and a commercial reverse osmosis membrane was selected for comparison. During the test, the operating temperature was gradually increased from 25 ℃ to 80 ℃, and the test results are shown in Table 6.

[0049] Table 6 High temperature resistance of different reverse osmosis membranes

[0050]

[0051] After testing, the flux of the three reverse osmosis membranes gradually increased with the increase of temperature. The reverse osmosis membrane prepared by secondary interfacial polymerization had a desalination rate greater than 99.15% when operated at 25 ℃-80 ℃. The desalination rate of the reverse osmosis membrane prepared by primary interfacial polymerization was stable at more than 99.1% when operated below 50 ℃. After the operating temperature was greater than 50 ℃, the desalination rate began to gradually decrease, and the final desalination rate at 80 ℃ was 97.42%. The desalination rate of commercial reverse osmosis membranes gradually decreased with the increase of operating temperature, and the desalination rate was 98.22% at an operating temperature of 80 ℃.

[0052] It can be seen that the reverse osmosis membrane prepared by this method has good high temperature resistance. Next, it is subjected to a high temperature resistance cycle test. After the first high temperature resistance test, the membrane is placed in the test device to cool overnight before the second round of high temperature resistance test.

[0053] Table 7 Reverse osmosis membrane high temperature resistance performance cycle test

[0054]

[0055] After the high temperature cycle test, the flux of the second round of high temperature test was reduced. This was due to the compaction of the membrane after the initial high temperature test. The desalination rates at the operating temperatures of 25 ℃-80 ℃ in two rounds were both greater than 99.15%. This shows that the reverse osmosis membrane prepared by this method has good high temperature resistance, can withstand high temperature water environment, and achieve effective treatment of high temperature wastewater.

[0056] The above content describes the technical principles, beneficial effects and features of the present invention. It should be pointed out that the above is only a preferred implementation mode of the present invention, but is not limited to the above embodiments. For technicians in the technical field to which the present invention belongs, some improvements and optimizations can be made without departing from the content of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing a reverse osmosis membrane that can withstand high temperature water environment, characterized in that: The steps include: (1) First, the α-cyclodextrin@polyethylene glycol supramolecular inclusion complex was synthesized by a saturated aqueous solution co-precipitation method: a certain amount of polyethylene glycol was first dissolved in ultrapure water to obtain a saturated polyethylene glycol aqueous solution, and then α-cyclodextrin powder was added, stirred at a constant temperature and allowed to stand. After cooling to ambient temperature, the precipitate was filtered and dried to obtain α-cyclodextrin@polyethylene glycol powder; (2) preparing an aqueous phase solution: dissolving a certain amount of m-phenylenediamine, D(+) camphorsulfonic acid, and triethylamine in a certain amount of ultrapure water to prepare an aqueous phase solution; (3) Preparation of oil phase solution: dissolve a certain amount of trimesoyl chloride in a certain amount of n-hexane to prepare an oil phase solution; (4) Preparing a secondary aqueous phase solution: dissolving a certain amount of α-cyclodextrin@polyethylene glycol powder and triethylamine in a certain amount of ultrapure water to prepare a secondary aqueous phase solution; (5) Interfacial polymerization: Take the base film soaked in water, blow dry the surface water with nitrogen, pour the water phase solution on the surface of the base film and let it stay for 30 s to 180 s, remove the excess water phase solution and blow dry the surface of the base film with nitrogen, then pour the oil phase solution on the surface of the base film and remove the excess oil phase solution after reaction, and place the obtained film in an oven for thermal curing to form an ultra-thin polyamide separation layer; (6) Secondary interfacial polymerization: The secondary aqueous phase solution is poured onto the membrane surface and the excess liquid is removed after reaction to form an α-CD@PEG polyester protective layer. The surface of the prepared reverse osmosis membrane is rinsed with ultrapure water and stored in ultrapure water.

2. A method for preparing a reverse osmosis membrane capable of withstanding a high temperature water environment as claimed in claim 1, characterized in that: In the step (1), the molar ratio of α-cyclodextrin to polyethylene glycol is one of 4:1, 5:1, 6:1, 7:1 and 8:

1.

3. The method for preparing a reverse osmosis membrane capable of withstanding a high temperature water environment according to claim 1, characterized in that: In the step (1), the constant temperature stirring temperature is 65° C., the constant temperature stirring time is 1 hour, and then the solution is left to stand for 12 hours.

4. The method for preparing a reverse osmosis membrane capable of withstanding a high temperature water environment according to claim 1, characterized in that: The drying temperature in step (1) is 70° C. and the drying time is 12 hours.

5. The method for preparing a reverse osmosis membrane capable of withstanding a high temperature water environment according to claim 1, characterized in that: In the step (2), the concentration of the intermediate phenylenediamine is 2-2.5 wt%, the concentration of D(+) camphorsulfonic acid is 1.2-2.4 wt%, and the concentration of triethylamine is 1.3 wt%. In the step (3), the concentration of trimesoyl chloride is 0.1 wt%.

6. The method for preparing a reverse osmosis membrane capable of withstanding a high temperature water environment according to claim 1, characterized in that: In the step (5), the aqueous solution is poured onto the surface of the base film and allowed to remain there for 120-180 seconds.

7. The method for preparing a reverse osmosis membrane capable of withstanding a high temperature water environment according to claim 1, characterized in that: In the step (5), the prepared film is placed in an oven at 80° C. for thermal curing for 5 minutes.

8. The method for preparing a reverse osmosis membrane capable of withstanding a high temperature water environment according to claim 1, characterized in that: In step (6), the mixture is stored in ultrapure water at 4°C.

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