Composite pervaporation desalination membrane, preparation method and application thereof

Abstract

The application provides a composite pervaporation desalination membrane and a preparation method and application thereof. The composite pervaporation desalination membrane comprises a separation layer with a separation function and an organic porous base membrane layer serving as a support; the raw materials of the separation layer comprise a polyvinyl alcohol aqueous solution, a PFSA-g-GO nanocomposite and a crosslinking agent, the addition amount of the PFSA-g-GO nanocomposite is 0.2-4.5 mass%, the addition amount of the crosslinking agent is 1-10 mass%, and the mass% is the percentage of the mass of each component to the mass of the polyvinyl alcohol; and the organic porous base membrane layer is a polyacrylonitrile membrane or a polyethersulfone membrane. The preparation method is simple and easy to implement, and has low cost, and can simultaneously improve the water flux and desalination rate of the composite pervaporation desalination membrane.

Description

Technical Field

[0001] This invention specifically relates to a composite pervaporation desalination membrane, its preparation method, and its application. Background Technology

[0002] With the continuous increase in the global population, the demand for freshwater is growing, and water scarcity has become one of the major challenges facing society today. Since seawater accounts for more than 95% of the world's total water resources, desalination is a viable approach to producing freshwater.

[0003] Pervaporation (PV) is a process in which substances are separated based on their properties, driven by a pressure difference across a membrane, using the membrane as the separation medium. PV is commonly used in industrial production of ethanol and dehydration of organic solvents, and its potential desalination performance has also attracted considerable attention. First, PV has a high salt rejection rate, especially for monovalent salts, typically exceeding 99%. Second, water undergoes a phase change during PV, eliminating the need to overcome the osmotic pressure of the brine; therefore, PV can treat high-concentration brine. Finally, PV has low temperature requirements for the treated solution, generally requiring only 40℃-70℃. Therefore, PV can utilize low-grade heat sources such as solar energy, geothermal energy, or industrial waste heat to heat the brine, reducing costs and making PV-based seawater desalination more competitive.

[0004] Polyvinyl alcohol (PVA) is widely used in the preparation of separation membranes due to its excellent film-forming properties. Modified PVA membranes possess both high desalination rates and high water flux. Chinese patent application CN 1978036 mentions a method of coating PA reverse osmosis membranes with acid-treated PVA. However, the resulting PVA / PA composite pervaporation membrane has low flux and a desalination rate that cannot reach 99%. Chinese patent document CN 109012197A describes a polyimide composite pervaporation membrane prepared by vacuum filtration, filling, and interfacial polymerization. The hydrophilic modified multi-walled carbon nanotubes provide sufficient hydrophilicity to the composite membrane, and the modified polyimide layer provides chlorine resistance, improving the long-term stability of the composite membrane. However, the non-hydrophilic surface results in a low overall water flux, failing to meet the levels required for practical applications.

[0005] Therefore, there is an urgent need to develop a pervaporation seawater desalination separation membrane with high throughput and high separation performance. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of low water flux and low desalination rate of existing pervaporation desalination membranes, and to provide a composite pervaporation desalination membrane, its preparation method, and its application. The preparation method of this invention is simple, easy to implement, and low in cost, and can simultaneously improve the water flux and desalination rate of the composite pervaporation desalination membrane.

[0007] This invention constructs a hydrophilic membrane surface by mixing PFSA-g-GO nanocomposite with a film-forming substance and adding a crosslinking agent. Combined with the mechanical strength and hydrophilicity of the matrix membrane, water molecules can pass through quickly, while the dense active membrane layer can effectively retain salt in the salt solution. It also has good performance when facing high concentrations of brine, providing a way for the application of pervaporation membranes in seawater desalination.

[0008] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0009] This invention provides a composite pervaporation desalination membrane, which includes a separation layer with separation function and an organic porous base membrane layer that provides support.

[0010] The separation layer is made of polyvinyl alcohol (PVA) aqueous solution, PFSA-g-GO nanocomposite and crosslinking agent. The amount of PFSA-g-GO nanocomposite added is 0.2-4.5 mass%, and the amount of crosslinking agent added is 1-10 mass%. Mass% is the percentage of the mass of each component to the mass of the polyvinyl alcohol.

[0011] The organic porous base membrane is a polyacrylonitrile (PAN) membrane or a polyethersulfone (PES) membrane.

[0012] In this invention, the thickness of the separation layer is preferably 0.2-1 μm.

[0013] In this invention, the water flux of the composite pervaporation desalination membrane can be 4.46 kg / m³. 2 h-30.58kg / m 2 ·h, for example 4.66kg / m 2 ·h、5.06kg / m 2 ·h、5.61kg / m 2 h, 6.14 kg / m 2 ·h、6.43kg / m 2 ·h、7.55kg / m 2 ·h、7.86kg / m 2 ·h or 10kg / m 2 •h (salt solution concentration is 3.5wt%, temperature is 30℃).

[0014] In this invention, the desalination rate of the composite pervaporation desalination membrane can be 92.48%-99.99%, preferably 95%-99.99%, for example 97.46%, 99.83% or 99.99% (salt solution concentration is 3.5wt%, temperature is 30℃).

[0015] In this invention, the separation layer is obtained by cross-linking polymerization of polyvinyl alcohol (PVA) and PFSA-g-GO nanocomposite.

[0016] In this invention, the thickness of the separation layer can be adjusted by controlling the concentration of the separation layer raw material and the thickness of the coating blade.

[0017] In this invention, the amount of the PFSA-g-GO nanocomposite added is preferably 0.5-4 mass%, for example 1 mass% or 2 mass%.

[0018] In this invention, the crosslinking agent is preferably maleic acid, tartaric acid, or 4-sulfophthalic acid, and more preferably 4-sulfophthalic acid.

[0019] In this invention, the amount of crosslinking agent added is preferably 2-6 mass%, for example, 5 mass%.

[0020] In this invention, the mass concentration of the polyvinyl alcohol (PVA) aqueous solution is preferably 2-4%, for example 3%.

[0021] In this invention, the polyvinyl alcohol (PVA) aqueous solution can be obtained by dilution.

[0022] The polyvinyl alcohol (PVA) aqueous solution may have a mass concentration of 8-12% before dilution, for example, 10%.

[0023] In order to obtain the polyvinyl alcohol (PVA) aqueous solution before dilution, it is preferable to mix polyvinyl alcohol (PVA) powder with deionized water and then heat it.

[0024] The heating is preferably carried out under stirring conditions.

[0025] The heating temperature is preferably 70°C-90°C.

[0026] The heating time is preferably 4-8 hours.

[0027] After heating is completed, filtration is generally required, and the filtrate should be left to stand overnight to remove air bubbles.

[0028] In this invention, the PFSA-g-GO nanocomposite is preferably prepared by esterification reaction of PFSA resin and GO nanoparticles.

[0029] In this invention, under the action of an activator and a catalyst, the carboxyl groups (-COOH) on GO nanoparticles undergo an esterification reaction with the hydroxyl groups (-OH) in PFSA, thereby achieving the effect of modifying GO nanoparticles with PFSA.

[0030] In this invention, the preparation process of the PFSA-g-GO nanocomposite preferably includes: firstly, adding an activator, a catalyst, and a PFSA solution to a DMSO solution containing GO nanoparticles to obtain a mixture; then reacting the mixture at a temperature of 30-50℃ for 48-72 h; and finally, obtaining the PFSA-g-GO nanocomposite through post-treatment.

[0031] The concentration of the DMSO solution containing GO nanoparticles can be 0.01-0.2 g / mL, preferably 0.01-0.1 g / mL, for example 0.03 g / mL.

[0032] Preferably, the GO nanoparticles are dispersed in a DMSO solution by ultrasonication.

[0033] The duration of the ultrasound is preferably 1-3 hours.

[0034] The activator is preferably N,N'-dicyclohexylcarbodiimide (DCC).

[0035] The preferred mass ratio of the activator to the GO nanoparticles is (40-50):1, for example, 46:1.

[0036] The catalyst is preferably 4-dimethylaminopyridine (DMAP).

[0037] The mass ratio of the catalyst to the activator is preferably 1:(10-150), for example 1:135.

[0038] Preferably, the PFSA is dissolved in DMSO.

[0039] The concentration of the PFSA solution is preferably 0.02-0.2 g / mL, for example 0.05 g / mL.

[0040] The post-treatment preferably includes centrifugation, acetone washing, washing with an ethanol-water solution at 80–95°C, and drying.

[0041] The GO nanoparticles are preferably prepared from natural graphite powder using a modified Hummers process.

[0042] The preparation of the GO nanoparticles preferably includes the following steps:

[0043] (1) Add 4.0-5.0g of graphite and sodium nitrate in a mass ratio of 1:1-2:1 to 70mL of 98% concentrated sulfuric acid solution and stir at a temperature of 0-5℃. Then add 8-10g of potassium permanganate and keep the temperature below 20℃.

[0044] (2) Transfer the above reactants to a temperature of 30-40℃ and react for 0.5-1h to form a viscous substance;

[0045] (3) Add 600-700 mL of water and react for 15-20 min, then slowly add 20-25 mL of 30% hydrogen peroxide solution;

[0046] (4) The obtained solution was centrifuged and washed with 250-350 mL of hydrochloric acid aqueous solution with a volume ratio of 1:10-1:14. Then it was sonicated, centrifuged, dialyzed, and finally freeze-dried to obtain GO nanoparticles.

[0047] The present invention also provides a method for preparing the composite pervaporation desalination membrane as described above, which includes the following steps:

[0048] A coating solution containing the polyvinyl alcohol (PVA) aqueous solution, the PFSA-g-GO nanocomposite and the crosslinking agent is coated onto an organic porous base membrane layer, and then heat-treated to obtain a composite pervaporation desalination membrane.

[0049] In this invention, the temperature of the heat treatment can be 40-140°C, preferably 40-80°C, for example 60°C.

[0050] In this invention, the heat treatment time can be 6-36 hours, preferably 15-30 hours, for example 24 hours.

[0051] In this invention, the heat treatment equipment can be conventional in the art, such as a vacuum oven.

[0052] In this invention, drying is preferably performed before the heat treatment.

[0053] The drying process can be conventional in the art, such as natural air drying.

[0054] The drying time can be 3-5 hours.

[0055] In this invention, the preparation method of the coating solution preferably includes the following steps: first, mixing the PFSA-g-GO nanocomposite and the polyvinyl alcohol (PVA) aqueous solution for the first time to obtain solution A; then, mixing the crosslinking agent and solution A for the second time.

[0056] The mixing is preferably carried out under stirring conditions.

[0057] Preferably, the first mixing involves adding the PFSA-g-GO nanocomposite to the polyvinyl alcohol (PVA) aqueous solution.

[0058] The temperature of the first mixing can be 15-35℃, preferably 15-25℃.

[0059] The time for the first mixing can be 4-16 hours, for example, 6 hours.

[0060] Preferably, the crosslinking agent is added to solution A during the second mixing.

[0061] The temperature of the second mixing can be 15-35℃, preferably 15-25℃.

[0062] The second mixing time can be 2-8 hours, for example, 4 hours.

[0063] In this invention, the organic porous base film layer is preferably soaked in an alkaline solution before coating.

[0064] The alkaline solution can be a sodium hydroxide solution or a potassium hydroxide solution.

[0065] The concentration of the alkaline solution can be 0.5 mol / L to 4 mol / L, for example, 1.0 mol / L.

[0066] The soaking time can be 0.5-2 hours, for example, 1 hour.

[0067] After soaking, it is preferable to wash with water until neutral and then air dry.

[0068] The water can be conventional in this field, such as tap water or deionized water.

[0069] The present invention also provides an application of the composite pervaporation desalination membrane in the fields of chemical industry, pharmaceutical industry, seawater desalination and wastewater reuse treatment.

[0070] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0071] The reagents and raw materials used in this invention are all commercially available.

[0072] The positive and progressive effects of this invention are as follows:

[0073] (1) The method for preparing the composite pervaporation desalination membrane provided by the present invention is simple, easy to implement, and low in cost. It can simultaneously improve the water flux and desalination rate of the membrane and can be widely used in the fields of chemical industry, medicine, seawater desalination and wastewater regeneration treatment. It has good application prospects.

[0074] (2) After grafting GO with PFSA, the PFSA-g-GO nanocomposite can exist stably in the membrane and is not easy to fall off, thus improving the long-term performance of the membrane. Detailed Implementation

[0075] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0076] Example 1

[0077] The specific steps for preparing PFSA-g-GO nanocomposites are as follows:

[0078] (1) GO nanoparticles were prepared from natural graphite powder using a modified Hummers method. The mass of graphite and sodium nitrate was 5g each. After adding concentrated sulfuric acid, the entire system was stirred at about 2°C. Then, 10g of potassium permanganate was slowly added, and the temperature was maintained at about 4°C during the addition process. After the addition was completed, the temperature was raised and the temperature of the entire system was maintained at about 30°C for 1h. Then, 700mL of water was added and reacted for 20min. Then, 25mL of 30% hydrogen peroxide solution was slowly added. The resulting solution was centrifuged and washed with 350mL of hydrochloric acid aqueous solution with a volume ratio of 1:14. Then, the solution was sonicated, centrifuged, dialyzed, and finally freeze-dried to obtain GO nanoparticles.

[0079] (2) Preparation of PFSA-g-GO nanocomposite: First, GO nanoparticles were dissolved in DMSO to obtain a solution with a concentration of 0.03 g / mL. Then, N,N'-dicyclohexylcarbodiimide (DCC) (activator), 4-dimethylaminopyridine (DMAP) (catalyst) and PFSA in DMSO solution were added to the solution to obtain a mixture. The mixture was then reacted at 50℃ for 72 h. Finally, the mixture was centrifuged, washed with acetone, washed with ethanol aqueous solution at 95℃, and dried to obtain PFSA-g-GO nanocomposite. The concentration of PFSA in DMSO solution was 0.05 g / mL. The mass ratio of DCC to GO nanoparticles was 46:1, and the mass ratio of DMAP to DCC was 1:135.

[0080] Example 2

[0081] The preparation method of the composite pervaporation desalination membrane is as follows:

[0082] First, 40g of solid PVA was mixed with 360g of deionized water and heated and stirred at 90℃ for 6 hours. The insoluble matter was filtered off to obtain a 10wt% PVA aqueous solution. Then, 30g of PVA solution was weighed using a pipette, and 70g of deionized water and 15mg of PFSA-g-GO nanocomposite were added. After stirring at room temperature for 6 hours, a PVA solution with a nano-additive content of 0.5wt% was obtained. Then, 150mg of maleic acid was added, and the mixture was stirred at room temperature for another 4 hours to finally obtain a PVA coating solution with a nano-additive content of 0.5wt% and a crosslinking agent content of 5%. The coating solution was allowed to stand overnight to remove bubbles.

[0083] Dissolve 80g of sodium hydroxide in 2L of water to obtain a 1mol / L sodium hydroxide aqueous solution. Immerse the cut PAN film in the sodium hydroxide aqueous solution and soak for 1 hour. Then take it out, rinse it until the surface is neutral, and then air dry it for later use.

[0084] Secure the PAN film with waterproof tape. Weigh 20g of coating solution and pour it evenly onto one side of the film. Then, quickly scrape the film surface with a casting knife to remove excess coating solution, leaving a thin layer. To avoid large air bubbles on the active layer surface caused by human error, apply a second coating after the first coating has dried, following the same steps. After both coatings are complete and the surface is dry, place the film in a vacuum oven for thermal crosslinking at 60℃ for 24 hours. Remove and allow to cool before use; this film is designated M1.

[0085] Blank control group and Examples 4-6

[0086] The specific steps are basically the same as in Example 2, except that the content of the added PFSA-g-GO nanocomposite is different. The specific differences are shown in Table 1.

[0087] Table 1

[0088]

[0089] The pervaporation desalination performance of the blank control group and Examples 2-5 is shown in Table 2. The salt solution used was an aqueous sodium chloride solution, and the minimum pressure on the vacuum pump side was 2 kPa.

[0090] Table 2

[0091] Example Blank control group Example 2 Example 3 Example 4 Example 5 Membrane number M0 M1 M2 M3 M4 Salt solution concentration 3.5wt% 3.5wt% 3.5wt% 3.5wt% 3.5wt% Solution temperature 30℃ 30℃ 30℃ 30℃ 30℃ water flux <![CDATA[4.46kg / m 2 ·h]]> <![CDATA[5.06kg / m 2 ·h]]> <![CDATA[5.61kg / m 2 ·h]]> <![CDATA[6.14kg / m 2 ·h]]> <![CDATA[7.86kg / m 2 ·h]]> Desalination rate 92.48％ 99.83％ 99.99％ 99.99％ 97.46％

[0092] Comparing the blank control group with Examples 2-5, it was found that as the content of PFSA-g-GO nanocomposite in the membrane increased, the water flux of the composite membrane gradually increased, and the desalination rate remained above 95%. However, the desalination rate decreased after the content of PFSA-g-GO nanocomposite reached 4 wt%. This is because a large amount of PFSA-g-GO nanocomposite could not be completely dispersed in the PVA layer, and the PFSA-g-GO nanocomposite aggregated in the membrane layer, resulting in larger diffusion channels inside the membrane layer and easier salt penetration. Therefore, selecting an appropriate amount of PFSA-g-GO nanocomposite is crucial.

[0093] Examples 6-7

[0094] The specific steps are basically the same as in Example 2, the difference being the use of different crosslinking agents. Details and the pervaporation desalination performance of different examples are shown in Table 3.

[0095] Table 3

[0096] Example Example 2 Example 6 Example 7 Membrane number M1 M5 M6 Salt solution concentration 3.5wt% 3.5wt% 3.5wt% Solution temperature 30℃ 30℃ 30℃ Types of crosslinking agents Maleic acid tartaric acid 4-Sulfophthalic acid Crosslinking agent dosage 5％ 5％ 5％ water flux <![CDATA[5.06kg / m 2 ·h]]> <![CDATA[4.66kg / m 2 ·h]]> <![CDATA[6.43kg / m 2 ·h]]> Desalination rate 99.83％ 99.99％ 99.99％

[0097] Comparing Example 2 with Examples 6-7, it was found that different types of crosslinking agents also affect the pervaporation and desalination performance of the composite membrane. Among them, the composite membrane crosslinked with 4-sulfophthalic acid had the highest water flux and better desalination rate under the same test conditions. This is because the sulfonic acid group of the crosslinking agent 4-sulfophthalic acid itself is a hydrophilic group, which can assist water molecules in transport within the membrane and accelerate the water molecule permeation rate.

[0098] Example 8

[0099] The specific steps are basically the same as in Example 7, except that the amount of PFSA-g-GO nanocomposite added is 2wt%.

[0100] The pervaporation desalination performance of Example 8 is shown in Tables 4 and 5.

[0101] Table 4

[0102] Salt solution temperature 30℃ 40℃ 50℃ 60℃ 70℃ Salt solution concentration 3.5wt% 3.5wt% 3.5wt% 3.5wt% 3.5wt% water flux <![CDATA[7.55kg / m 2 ·h]]> <![CDATA[10.27kg / m 2 ·h]]> <![CDATA[14.56kg / m 2 ·h]]> <![CDATA[22.24kg / m 2 ·h]]> <![CDATA[30.58kg / m 2 ·h]]> Desalination rate 99.99％ 99.99％ 99.99％ 99.99％ 99.99％

[0103] Table 5

[0104] Salt solution temperature 40℃ 40℃ 40℃ 40℃ 40℃ Salt solution concentration 0.5wt% 3.5wt% 5wt% 10wt% 20wt% water flux <![CDATA[12.41kg / m 2 ·h]]> <![CDATA[10.27kg / m 2 ·h]]> <![CDATA[9.42kg / m 2 ·h]]> <![CDATA[6.82kg / m 2 ·h]]> <![CDATA[4.56kg / m 2 ·h]]> Desalination rate 99.99％ 99.99％ 99.99％ 99.99％ 99.99％

[0105] Comparative Example 1

[0106] Except for replacing the PFSA-g-GO nanocomposite with the OA-g-GO nanocomposite (oxalic acid-modified graphene oxide), all other operations and conditions were the same as in Example 8.

[0107] The preparation process of OA-g-GO is as follows:

[0108] The prepared GO nanoparticles were ultrasonically dispersed in water to obtain a 0.2 g / L GO aqueous dispersion. 50 mL of the GO aqueous dispersion was taken, and 5 mL of hydrobromic acid was added. Hydrobromic acid can open the rings of the epoxides on the GO plane and convert them into hydroxyl groups, which is beneficial for subsequent OA grafting. After adding hydrobromic acid, the entire system was stirred for 16 h, with the system temperature controlled at 30 °C during stirring. After the predetermined stirring time, 10 g of OA was added to the system, and stirring was continued for another 10 h. After stirring, the entire system was continuously washed with deionized water until the filtrate became neutral. The obtained solid was then freeze-dried to obtain OA-g-GO. The mass ratio of GO to OA was 1:1000.

[0109] Comparative Example 2

[0110] Except for replacing the PFSA-g-GO nanocomposite with the ODA-g-GO nanocomposite (octadecylamine-modified graphene oxide), all other operations and conditions were the same as in Example 8.

[0111] The preparation process of ODA-g-GO is as follows:

[0112] The prepared GO nanoparticles were ultrasonically dispersed in water to obtain a 0.2 g / L GO aqueous dispersion. 500 mL of the GO aqueous dispersion was added to an ethanol solution of ODA (1.5 g ODA dissolved in 150 mL ethanol), resulting in a GO to ODA mass ratio of 1:15 in the mixed solution. The mixture was stirred thoroughly and then sealed in a vacuum oven at atmospheric pressure for 16 hours. The resulting solution was filtered, vacuum dried, and then ground to obtain ODA-g-GO.

[0113] Comparative Example 3

[0114] Except for replacing the PFSA-g-GO nanocomposite with the CS-g-GO nanocomposite (chitosan-modified graphene oxide), all other operations and conditions were the same as in Example 8.

[0115] The preparation process of CS-g-GO is as follows:

[0116] The prepared GO nanoparticles were ultrasonically dispersed in water to obtain a 1 g / L GO aqueous dispersion. 100 mL of the GO aqueous dispersion was then taken, followed by the addition of 5 g chitosan and 2 g sodium borohydride. The mixture was ultrasonically in a water bath at room temperature for 4 hours, and then the entire system was refluxed at 100 °C for 4 hours. The mixture was then filtered and separated, and the resulting material was washed with distilled water until neutral. Finally, it was dried in an oven at 60 °C for 5 hours to obtain the final product.

[0117] Table 6

[0118] Example 8 Comparative Example 1 Comparative Example 2 Comparative Example 3 Nanocomposite used PFSA-g-GO OA-g-GO ODA-g-GO CS-g-GO Salt solution concentration 3.5wt% 3.5wt% 3.5wt% 3.5wt% Solution temperature 70℃ 70℃ 70℃ 70℃ water flux <![CDATA[30.58kg / m 2 ·h]]> <![CDATA[22.41kg / m 2 ·h]]> <![CDATA[20.56kg / m 2 ·h]]> <![CDATA[25.48kg / m 2 ·h]]> Desalination rate 99.99％ 99.99％ 99.99％ 99.99％

[0119] The pervaporation desalination performance of Example 8 and Comparative Examples 1, 2, and 3 is shown in Table 6. According to the data in Table 6, when other types of nanocomposites are used, their pervaporation desalination performance is worse than that of the examples of the present invention.

Claims

1. A composite pervaporation desalination membrane, characterized in that, It includes a separation layer with separation function and an organic porous base membrane layer that provides support; The separation layer is made of polyvinyl alcohol aqueous solution, PFSA-g-GO nanocomposite and crosslinking agent. The amount of PFSA-g-GO nanocomposite added is 0.5-2 mass%, and the amount of crosslinking agent added is 1-10 mass%. mass% is the percentage of the mass of each component to the mass of polyvinyl alcohol. The organic porous base membrane layer is a polyacrylonitrile membrane or a polyethersulfone membrane; The crosslinking agent is 4-sulfophthalic acid.

2. The composite pervaporation desalination membrane as described in claim 1, characterized in that, The thickness of the separation layer is 0.2-1 μm.

3. The composite pervaporation desalination membrane as described in claim 1, characterized in that, The amount of PFSA-g-GO nanocomposite added is 1 mass% or 2 mass%.

4. The composite pervaporation desalination membrane as described in claim 1, characterized in that, The amount of crosslinking agent added is 2-6 mass.

5. The composite pervaporation desalination membrane as described in claim 4, characterized in that, The amount of crosslinking agent added is 5 mass.

6. The composite pervaporation desalination membrane as described in claim 1, characterized in that, The mass concentration of the polyvinyl alcohol aqueous solution is 2-4%.

7. The composite pervaporation desalination membrane as described in claim 6, characterized in that, The mass concentration of the polyvinyl alcohol aqueous solution is 3%.

8. The composite pervaporation desalination membrane as described in claim 1, characterized in that, The PFSA-g-GO nanocomposite was prepared by esterification reaction of PFSA resin and GO nanoparticles.

9. The composite pervaporation desalination membrane as described in claim 1, characterized in that, The preparation process of the PFSA-g-GO nanocomposite includes: firstly, adding an activator, a catalyst and a PFSA solution to a DMSO solution containing GO nanoparticles to obtain a mixture; then reacting the mixture at a temperature of 30-50℃ for 48-72h; and finally, obtaining the PFSA-g-GO nanocomposite after post-treatment.

10. A method for preparing a composite pervaporation desalination membrane as described in any one of claims 1 to 9, characterized in that, It includes the following steps: A coating solution containing the polyvinyl alcohol aqueous solution, the PFSA-g-GO nanocomposite and the crosslinking agent is coated onto an organic porous base membrane layer, and then heat-treated to obtain a composite pervaporation desalination membrane.

11. The method for preparing the composite pervaporation desalination membrane as described in claim 10, characterized in that, The heat treatment temperature is 40-140℃; And / or, the heat treatment time is 6-36 hours; And / or, the preparation method of the coating solution includes the following steps: first, mixing the PFSA-g-GO nanocomposite and the polyvinyl alcohol aqueous solution for the first time to obtain solution A; then, mixing the crosslinking agent and solution A for the second time; And / or, the organic porous base film layer is first soaked in an alkaline solution before coating.

12. The method for preparing the composite pervaporation desalination membrane as described in claim 11, characterized in that, The heat treatment temperature is 40-80℃; And / or, the heat treatment time is 15-30 hours.

13. The method for preparing the composite pervaporation desalination membrane as described in claim 11, characterized in that, The heat treatment temperature is 60°C; And / or, the heat treatment time is 24 hours.

14. The method for preparing the composite pervaporation desalination membrane as described in claim 11, characterized in that, The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution; And / or, the concentration of the alkaline solution is 0.5 mol / L to 4 mol / L; And / or, the soaking time is 0.5-2 hours.

15. The method for preparing the composite pervaporation desalination membrane as described in claim 14, characterized in that, The concentration of the alkaline solution is 1.0 mol / L; And / or, the soaking time is 1 hour.

16. The application of a composite pervaporation desalination membrane as described in any one of claims 1 to 9 in the fields of chemical industry, pharmaceutical industry, seawater desalination and wastewater reuse treatment.

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