Pdms / polyacrylonitrile (pan) composite membrane based on chemically modified pan membrane

Abstract

This invention relates to a PDMS / PAN composite membrane based on a chemically modified PAN membrane, which is composed of a PAN substrate membrane sequentially modified with NaOH and GMA and grafted with methacrylate-functionalized PDMS. The invention also relates to a method for preparing the above membrane, which involves sequentially chemically modifying the PAN substrate membrane with NaOH and GMA in two steps to introduce acrylate double bonds onto the surface of the PAN membrane, followed by further photopolymerization grafting of a PDMS selective layer to prepare the PDMS / PAN composite membrane. This improves the adhesion of the PDMS selective layer, effectively mitigating cracking and delamination phenomena in practical applications of the PDMS / PAN composite membrane. Simultaneously, the membrane's performance in pervaporation and ethanol separation is significantly enhanced, greatly improving the application prospects of PDMS membranes in actual pervaporation processes.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing and applying a PDMS / PAN composite membrane based on a chemically modified PAN membrane and a PDMS selective layer grafted thereon. Background Technology

[0002] Bioethanol, as a novel biofuel, has an energy content similar to gasoline and emits fewer toxic pollutants than fossil fuels, potentially alleviating the energy crisis caused by fossil fuel shortages. Pervaporation technology, with its high selectivity, low energy consumption, and non-toxic microorganisms, shows great promise in the separation of bioethanol. Polydimethylsiloxane (PDMS), with its low raw material cost and good processing performance, is widely used in ethanol separation. Polyacrylonitrile (PAN), with its thermal stability and mechanical stability, is widely used in the preparation of pervaporation membrane materials.

[0003] During the separation process, the strength of the bond between the PDMS selective layer and the base membrane directly determines the membrane's lifespan. However, in practical applications of PDMS membranes for pervaporation separation of ethanol, the problem of weak selective layer adhesion is frequently encountered. Cracks and delamination of the selective layer severely restrict the widespread application of PDMS membranes in pervaporation processes and the stability of the pervaporation process.

[0004] Therefore, it is crucial to prepare a PDMS / PAN membrane with high PDMS selective layer adhesion and excellent pervaporation performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a PDMS / PAN composite membrane based on chemically modified PAN membrane, which addresses the problems of weak selective layer adhesion, selective layer cracking and delamination encountered when using PDMS membrane for pervaporation separation of ethanol. This PDMS / PAN composite membrane has strong PDMS selective layer adhesion and excellent pervaporation performance, and can be used in actual pervaporation processes.

[0006] Therefore, the first aspect of the present invention provides a PDMS / PAN composite membrane based on a chemically modified PAN membrane, which is composed of PAN mulch film modified sequentially by NaOH and GMA and grafted with methacrylate-functionalized PDMS, and its molecular structure is shown in formula (IX):

[0007]

[0008] In formula (IX), m represents the number of -CH2-CHCN- groups;

[0009] n represents the number of -CH2CH- groups;

[0010] x represents the number of -Si-O- groups.

[0011] In some embodiments of the present invention, the L of the PDMS / PAN composite film C1 The critical load is 8.3 mN; and / or, the L of the PDMS / PAN composite film... C2 The critical load is 11.9 mN; and / or, the permeation flux of the PDMS / PAN composite membrane is 1297.5-1413.5 g·m³. -2 ·h -1 The separation factor was 8.57-9.13.

[0012] A second aspect of the present invention provides a method for preparing a PDMS / PAN composite film based on a chemically modified PAN film, comprising:

[0013] Step A: After rinsing the PAN substrate with water, soak it in NaOH aqueous solution, and then rinse it with water to obtain the sodium hydroxide modified PAN substrate.

[0014] Step B: Immerse the sodium hydroxide-modified PAN substrate in GMA / MeOH solution, then rinse it with water to obtain the GMA-modified PAN substrate.

[0015] Step C: After vacuum degassing the PDMS casting solution, pour it onto the GMA-modified PAN substrate and perform film scraping. Immediately after film scraping, transfer the coating to a UV lamp for irradiation to produce a PDMS / PAN composite film based on a chemically modified PAN film.

[0016] In some embodiments of the present invention, in step A, the concentration of the NaOH aqueous solution is 0.0125 mol / L; and / or, the soaking time is 3 min.

[0017] In some embodiments of the present invention, in step B, the concentration of the GMA / MeOH solution is 0.003 mol / L; and / or, the soaking time is 0.5 h.

[0018] According to the present invention, the PDMS casting solution is prepared by adding dodecafluoroheptyl methacrylate to a heptane solution of methacrylate-functionalized PDMS, followed by the addition of photoinitiator 2-hydroxy-2-methylphenylacetone, and stirring at room temperature.

[0019] In some embodiments of the present invention, during the PDMS casting process, the mass ratio of methacrylate-functionalized PDMS to dodecafluoroheptyl methacrylate is 1:0.1; and / or, the mass ratio of methacrylate-functionalized PDMS to photoinitiator is 3:1; and / or, the stirring time is 24 h.

[0020] According to the present invention, the preparation method of methacrylate-functionalized PDMS includes: mixing PDMS, silane coupling agent KH570, dibutyltin dilaurate, water and n-heptane, weighing and recording the mixture, stirring at room temperature, weighing again and adding n-heptane to the original weight, stirring again until homogeneous, and preparing methacrylate-functionalized PDMS.

[0021] In some embodiments of the present invention, during the preparation of methacrylate-functionalized PDMS, the mass ratio of 5000 cP PDMS to silane coupling agent KH570 is 11:0.12; and / or, the mass ratio of PDMS to dibutyltin dilaurate is 11:0.1, the mass ratio of PDMS to water is 11:0.1, and the mass ratio of PDMS to n-heptane is 1:1.

[0022] The third aspect of the present invention provides the application of PDMS / PAN composite membranes as described in the first aspect of the present invention or PDMS / PAN composite membranes prepared by the method described in the second aspect of the present invention in separation processes.

[0023] In some embodiments of the present invention, the separation process includes a pervaporation separation process and / or a nanofiltration separation process.

[0024] This invention uses a PAN membrane as the base membrane and PDMS as the selective layer. A PDMS / PAN composite membrane is prepared through a two-step chemical modification of PAN followed by PDMS grafting. This effectively improves the problem of weak adhesion of the selective layer during pervaporation. The modified PDMS / PAN membrane exhibits excellent adhesion between the PAN and PDMS layers, helping to prevent cracking and delamination of the PDMS selective layer. With the increase in the adhesion of the PDMS selective layer, cracking and delamination phenomena in the PDMS / PAN composite membrane are effectively alleviated in practical applications. Simultaneously, the performance of pervaporation for ethanol separation is significantly improved, greatly enhancing the application prospects of PDMS membranes in practical pervaporation processes. Attached Figure Description

[0025] To make the present invention easier to understand, the present invention will be described in detail below with reference to the accompanying drawings.

[0026] Figure 1 The NaOH modification pathway of PAN is shown.

[0027] Figure 2 The GMA modification pathway of PAN is shown.

[0028] Figure 3 The preparation route of methacrylate-functionalized PDMS is shown.

[0029] Figure 4This paper illustrates the preparation route for PDMS / PAN composite films by photopolymerization and grafting of PDMS onto modified PAN films.

[0030] Figure 5 The results show a comparison of the Fourier transform infrared spectra of the PAN film surface before and after NaOH modification.

[0031] Figure 6 The results show a comparison of the Fourier transform infrared spectra of the PAN film surface before and after GMA modification.

[0032] Figure 7 Typical results of nano-scratch tests on PDMS / PAN composite films before and after modification are shown: (a) scratch profile, (b) friction profile of unmodified PDMS / PAN composite film and (c) scratch profile, (d) friction profile of modified PDMS / PAN composite film.

[0033] Figure 8 This is a schematic diagram of a pervaporation device. Detailed Implementation

[0034] To facilitate understanding of the present invention, it will be described in detail below with reference to the accompanying drawings. However, before describing the present invention in detail, it should be understood that the present invention is not limited to the specific embodiments described. It should also be understood that the terminology used herein is for describing specific embodiments only and is not intended to be restrictive.

[0035] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While any methods and materials similar to or equivalent to those described herein may also be used in the practice or testing of this invention, preferred methods and materials are now described.

[0036] In this invention, the range of dosage concentration, temperature or other physical or chemical properties or characteristics, unless otherwise specified, covers or includes the upper and lower limits of that range.

[0037] I. Terminology

[0038] In this invention, the term "GMA" represents glycidyl methacrylate, with the chemical formula C7H. 10 O3.

[0039] In this invention, the term "1173" refers to 1173 photoinitiator, namely 2-hydroxy-2-methyl-1-phenyl-1-propanone photoinitiator.

[0040] In this invention, the term "PDMS" refers to polydimethylsiloxane, with the chemical formula (C2H6OSi).n Accordingly, the “PDMS membrane” refers to a polydimethylsiloxane membrane.

[0041] In this invention, the term "PAN" refers to polyacrylonitrile, with the chemical formula (C3H3N). n Accordingly, the “PAN film” refers to a polyacrylonitrile film.

[0042] Unless otherwise specified, the term "water" in this invention refers to one or more of deionized water, distilled water, and ultrapure water.

[0043] II. Implementation Plan

[0044] As mentioned earlier, the strength of the bond between the PDMS selective layer and the base membrane directly determines the membrane's service life during the separation process. Currently used PDMS / PAN membranes often face problems such as weak adhesion of the PDMS selective layer, selective layer cracking, and delamination during actual pervaporation. In view of this, the inventors have conducted extensive research on PAN membranes and PDMS membranes.

[0045] The inventors have discovered that by performing a two-step chemical modification of a PAN membrane with NaOH and GMA followed by photopolymerization and grafting of PDMS, a PDMS / PAN composite membrane based on a chemically modified PAN membrane can be prepared. This composite membrane exhibits strong PDMS selective layer adhesion and excellent pervaporation performance, making it suitable for use in practical pervaporation processes.

[0046] To achieve the present invention, the present invention employs the following method to prepare a PDMS / PAN composite membrane based on a chemically modified PAN membrane, comprising:

[0047] (1) NaOH modification of PAN film: After rinsing the PAN substrate with dewatering water, it is immersed in a 0.0125 mol / L NaOH aqueous solution for 3 min, and then rinsed with dewatering water to obtain a sodium hydroxide modified PAN substrate; the NaOH solution is formed by dissolving NaOH in water;

[0048] (2) GMA modification of PAN film: The PAN substrate film modified with sodium hydroxide was immersed in a GMA / MeOH solution with a concentration of 0.003 mol / L for 0.5 h, and then rinsed with water to obtain the GMA-modified PAN substrate film; the GMA / MeOH solution was formed by dissolving GMA in MeOH;

[0049] (3) Photopolymerization of modified PAN film to graft PDMS to prepare PDMS / PAN composite film: After vacuum degassing of PDMS casting solution, it is poured onto the GMA modified PAN substrate film and coated. After coating is completed, the coating is immediately transferred to a UV lamp for irradiation to prepare PDMS / PAN composite film based on chemically modified PAN film.

[0050] According to the present invention, the preparation method of the above-mentioned PDMS casting solution includes:

[0051] S1, PDMS, silane coupling agent KH570, dibutyltin dilaurate, water and n-heptane are mixed, weighed and recorded, stirred at room temperature, weighed again, n-heptane is added to the original weight, and stirred again until homogeneous to prepare methacrylate-functionalized PDMS.

[0052] S2, methacrylate-functionalized PDMS was diluted with n-heptane to form a methacrylate-functionalized PDMS diluent, dodecafluoroheptyl methacrylate was added, and then the photoinitiator 2-hydroxy-2-methylphenylacetone was added. After stirring at room temperature for 24 hours, PDMS casting solution was obtained.

[0053] In step S2 above, the mass ratio of methacrylate-functionalized PDMS to dodecafluoroheptyl methacrylate is 1:0.1; and / or, the mass ratio of methacrylate-functionalized PDMS to photoinitiator is 3:1.

[0054] In step S1 above, the mass ratio of 5000 cP PDMS to silane coupling agent KH570 is 11:0.12; and / or, the mass ratio of PDMS to dibutyltin dilaurate is 11:0.1, the mass ratio of PDMS to water is 11:0.1, and the mass ratio of PDMS to n-heptane is 1:1.

[0055] As can be seen from the above, the specific preparation route for preparing PDMS / PAN composite membrane based on chemically modified PAN membrane according to the present invention is as follows:

[0056] (1) The NaOH modification path for PAN substrate is as follows: Figure 1 As shown, from Figure 1 It can be seen that after hydrolysis modification with NaOH solution, the cyano functional groups on the surface of the PAN film are partially transformed into amino functional groups;

[0057] (2) The GMA modification pathway of PAN bottom film is as follows: Figure 2 As shown, from Figure 2 It can be seen that after modification with GMA solution, the amino functional groups on the surface of the PAN substrate react with GMA to produce acrylate double bonds, that is, the acrylate functional groups grafted onto the surface of the PAN film.

[0058] (3) The preparation route of methacrylate-functionalized PDMS is as follows: Figure 3 As shown, from Figure 3 It can be seen that the acrylate double bond is introduced into PDMS through the reaction of PDMS with silane coupling agent KH570;

[0059] (4) The preparation route of PDMS / PAN composite film by photopolymerization and grafting of PDMS onto modified PAN film is as follows: Figure 4 As shown, from Figure 4 It can be seen that the acrylate double bonds on the surface of the modified PAN film and the acrylate double bonds in PDMS undergo photopolymerization under ultraviolet light irradiation, and a PDMS selective layer is grafted onto the surface of the PAN film, thus successfully preparing a PDMS / PAN composite film.

[0060] It is easy to understand that the PDMS / PAN composite membrane based on chemically modified PAN membrane prepared by the above preparation method or route is composed of a PAN membrane chemically modified in two steps with sodium hydroxide and glycidyl methacrylate (GMA) and grafted with a PDMS selective layer. The molecular structure of the membrane material constituting the PDMS / PAN composite membrane is shown in formula (IX):

[0061]

[0062] In formula (IX), m is the number of -CH2-CHCN- groups, and its value is a positive integer;

[0063] n is the number of -CH2CH- groups, and its value is a positive integer;

[0064] x represents the number of -Si-O- groups, and its value is a positive integer.

[0065] This invention involves a two-step chemical modification of the PAN substrate membrane: NaOH modification and GMA modification, introducing acrylate double bonds onto the PAN membrane surface. Further photopolymerization grafting of a PDMS selective layer completes the process, preparing a PDMS / PAN composite membrane. This improves the adhesion and pervaporation performance of the PDMS selective layer. Nano-scratch testing revealed that cracking and delamination of the PDMS selective layer are effectively mitigated, and adhesion is significantly enhanced. Pervaporation testing showed that the PDMS / PAN composite membrane prepared based on the chemically modified PAN membrane and PDMS grafting improves the ethanol separation factor.

[0066] The research results indicate that, in this invention, the L... C1 The critical load is 8.3 mN; and / or, the L of the PDMS / PAN composite film... C2 The critical load is 11.9 mN; and / or, the permeation flux of the PDMS / PAN composite membrane is 1297.5-1413.5 g·m³. -2·h -1 The separation factor was 8.57-9.13.

[0067] The present invention also provides the application of the above-mentioned PDMS / PAN composite membrane or the PDMS / PAN composite membrane prepared by the above-mentioned preparation method in the separation process.

[0068] In some embodiments of the present invention, the separation process includes a pervaporation separation process and / or a nanofiltration separation process.

[0069] Example

[0070] To make the present invention easier to understand, the present invention will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained commercially or by conventional methods.

[0071] Example 1: Preparation of PDMS / PAN composite membrane based on chemically modified PAN membrane

[0072] (1) NaOH modification of PAN membrane: Weigh 0.5g NaOH and dissolve it in 1L of water to prepare a 0.0125mol / L NaOH solution. After rinsing the PAN substrate with deionized water, immerse it in the 0.0125mol / L NaOH solution for 3min, and then rinse it with deionized water to complete the sodium hydroxide modification of the PAN substrate.

[0073] (2) GMA modification of PAN membrane: Weigh 0.426g GMA and dissolve it in 1L of anhydrous methanol to prepare a 0.003mol / L GMA / MeOH solution. Stir well and immerse the PAN substrate membrane modified with 0.0125mol / L sodium hydroxide solution for 3min in the 0.003mol / L GMA / MeOH solution for 0.5h. Then rinse it with deionized water to complete the GMA modification of PAN substrate membrane.

[0074] (3) Preparation of methacrylate-functionalized PDMS: 11 g of 5000 cP PDMS, 0.12 g of silane coupling agent KH570, 0.1 g of dibutyltin dilaurate, 0.1 g of deionized water, and 11 g of n-heptane (PDMS:KH570:dibutyltin dilaurate:deionized water:n-heptane = 110:1.2:1:1:110) were mixed in a 50 ml beaker, weighed, and the weight was recorded. The mixture was stirred at 800 rpm for 24 h at room temperature, weighed again, and n-heptane was added to bring the weight back to the original level. The mixture was stirred again until homogeneous, thus completing the preparation of methacrylate-functionalized PDMS.

[0075] (4) Preparation of PDMS / PAN film: Take 3g of methacrylate-functionalized PDMS, add 0.75g of n-heptane to dilute it to a solvent content of 70%, add 0.3g of dodecafluoroheptyl methacrylate, and then add 1g of photoinitiator 2-hydroxy-2-methylphenylacetone. Stir at 800rpm for 20min at room temperature. Then, vacuum degas the stirred PDMS casting solution. The thickness of the scraper is 60μm. Then, pour the PDMS casting solution onto the modified PAN substrate and scrape the film using an Elcometer-4340 automatic coating machine. Immediately after the film is scraped, transfer the coating to a 365nm ultraviolet lamp for irradiation for 3min, with the film 10cm away from the ultraviolet lamp. The preparation of PDMS / PAN film is completed.

[0076] The NaOH and GMA-modified PAN films were characterized by Fourier transform infrared spectroscopy (model 3, manufacturer: PerkinElmer). The results for the NaOH-modified films are as follows: Figure 5 As shown: Figure 5 The significantly enhanced peak of -NH2 indicates that hydrolysis modification produced some amino functional groups; the results after GMA modification are as follows: Figure 6 As shown: Figure 6 The characteristic peak of GMA in the middle is 1168 cm⁻¹ -1 The increase in peak area proves that the PAN surface modified by NaOH solution hydrolysis was modified by GMA / MeOH solution, and GMA reacted with the amino groups on the surface, so that acrylate groups were successfully grafted onto the surface of the PAN film.

[0077] Through nano scratch test (model Nst) 3 The test (manufactured by Anton Paar) characterizes the adhesion of the PDMS selective layer in the PDMS / PAN composite film. The test conditions involve gradually increasing the applied load from an initial 3 mN to a maximum load of 60 mN, at a rate of approximately 57 mN / min.

[0078] In nano-scratch testing, the critical load of the membrane is determined by observing the friction between the indenter and the membrane during the scratch test loading process. The failure critical load is a quantitative standard for the adhesive strength of composite membranes. C1 The critical load represents the PDMS layer's ability to withstand lateral loads, reflecting its resistance to crack initiation; it is also known as the "lower critical load." C2 The critical load represents the transverse critical load corresponding to the total peeling of the PDMS layer from the PVDF substrate, also known as the "higher critical load".

[0079] Figure 7 Typical scratch results of PDMS / PAN composite films before and after modification are presented to compare the adhesion of the PDMS selective layer before and after modification. Figure 7Demonstrates the critical load (L) at the PDMS-PAN interface. C The determination of ).

[0080] The test results show that the L of the modified PDMS / PAN composite film... C1 and L C2 The modified PDMS / PAN interface exhibits significantly enhanced adhesion between the PAN and PDMS layers, which helps prevent cracking and delamination of the film coating. The increased adhesion of the modified PDMS / PAN composite film is attributed to the photopolymerization grafting of acrylate bonds between the chemically modified PDMS selective layer and the PAN substrate, which generates partial chemical bonds that significantly enhance the adhesion of the PDMS selective layer.

[0081] Example 2:

[0082] Pervaporation tests were performed on the PDMS / PAN composite membrane prepared in Example 1.

[0083] Pervaporation test: The separation performance of the obtained cured membrane with 5wt% ethanol was tested using a pervaporation device under heating conditions of 60℃.

[0084] The pervaporation performance of ethanol was tested using a self-made laboratory apparatus at a temperature of 60°C and an ethanol concentration of 5 wt%. The specific testing apparatus is as follows: Figure 8 As shown.

[0085] Pervaporation results showed that the separation factor of the PDMS / PAN membrane modified with 0.0125 mol / L sodium hydroxide solution for 3 min was 8.85. After NaOH modification, amino functional groups were generated on the PAN membrane surface. Following reaction with GMA, acrylate groups were grafted onto the PAN membrane surface. After photopolymerization, a denser PDMS selective layer was formed, leading to improved pervaporation performance. The water flux of the NaOH-modified PDMS / PAN membrane was 924.8 g·m³. -2 ·h -1 However, the ethanol flux is as high as 430.7 g·m³. -2 ·h -1 With a total flux of 1355.5, it exhibits excellent pervaporation performance.

[0086] Comparative Example 1:

[0087] (1) Preparation of methacrylate-functionalized PDMS: 11 g of 5000 cP PDMS, 0.12 g of silane coupling agent KH570, 0.1 g of dibutyltin dilaurate, 0.1 g of deionized water, and 11 g of n-heptane were mixed in a 50 ml beaker, weighed, and the weight was recorded. The mixture was stirred at 800 rpm for 24 h at room temperature, weighed again, and n-heptane was added to bring the weight back to the original level. The mixture was stirred until homogeneous.

[0088] (2) Preparation of PDMS / PAN film: Take 3g of methacrylate-functionalized PDMS, add 0.75g of n-heptane to dilute it to a solvent content of 70%, add 0.3g of dodecafluoroheptyl methacrylate, and then add 1g of photoinitiator 2-hydroxy-2-methylphenylacetone. Stir at 800rpm for 20min at room temperature. Then, vacuum degas the stirred PDMS casting solution. The thickness of the scraper is 60μm. Then, pour the PDMS casting solution onto the unmodified PAN substrate and scrape the film using an Elcometer-4340 automatic coating machine. Immediately after the film is scraped, transfer the coating to a 365nm ultraviolet lamp for irradiation for 3min, with the film 10cm away from the ultraviolet lamp. The preparation of PDMS / PAN film is completed.

[0089] (3) Pervaporation Test: The separation performance of the obtained PDMS / PAN composite membrane for 5 wt% ethanol was tested using a pervaporation device under heating conditions at 60℃. The pervaporation test results showed that the separation factor of the unmodified PDMS / PAN composite membrane for separating 5 wt% ethanol at 60℃ was 8.29, and the flux was 1283.5 g·m³. -2 ·h -1 .

[0090] (4) Nanoscratch test: The nanoscratch test results of the unmodified PDMS / PAN composite film are as follows: Figure 7 As shown, the critical load L C1 =6.1mN, L C2 =7.5mN.

[0091] As can be seen from the above, compared with Comparative Example 1, the modified PDMS / PAN membrane provided by the present invention has superior PDMS selective layer adhesion, and the selective layer has stronger resistance to cracking and delamination, indicating that it has superior stability during pervaporation. Furthermore, at a certain temperature, the permeation flux of the PDMS membrane obtained in the examples is 1297.5-1413.5 g·m³. -2 ·h -1 The separation factor was 8.57-9.13. According to the test results, the PDMS / PAN composite membrane prepared by chemical modification of PAN membrane showed corresponding improvements in the separation factor of ethanol, the ethanol concentration of the permeate, and the selectivity of ethanol. After chemical modification of PAN membrane, the separation factor and permeate flux in the pervaporation test were both improved compared with the unmodified membrane.

[0092] It should be noted that the embodiments described above are merely preferred embodiments of the present invention, used to explain the present invention, and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the terms used herein are descriptive and explanatory, not limiting. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from its scope and spirit. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications having the same function.

Claims

1. A PDMS / PAN composite membrane based on chemically modified PAN membrane, which is composed of a PAN base membrane sequentially modified by NaOH and GMA to graft methacrylate functionalized PDMS, and the molecular structure is shown in formula (IX) : In formula (IX), m is the number of -CH2-CHCN- groups; n is the number of -CH2CH- groups; and x is the number of -Si-O- groups. 3.A method for preparing the PDMS / PAN composite membrane based on chemically modified PAN membrane according to claim 1 or 2, which comprises: Step A, after the PAN base membrane is washed with deionized water, it is immersed in a NaOH aqueous solution, and then washed with deionized water to obtain a PAN base membrane modified by NaOH; 2. The PDMS / PAN composite membrane according to claim 1, wherein, The PDMS / PAN composite film has a L C1 critical load of 8.3 mN; the PDMS / PAN composite film has a L C2 critical load of 11.9 mN; the PDMS / PAN composite film has a permeation flux of 1297.5-1413.5 g·m −2 ·h −1 , and a separation factor of 8.57-9.

13. Step B, the PAN base membrane modified by NaOH is immersed in a GMA / MeOH solution, and then washed with deionized water to obtain a PAN base membrane modified by GMA; Step C, after the PDMS casting solution is vacuum degassed, it is poured onto the PAN base membrane modified by GMA, and then coated by a doctor blade, and the coating is immediately transferred to a UV lamp for irradiation to prepare the PDMS / PAN composite membrane based on chemically modified PAN membrane. In step A, the concentration of the NaOH aqueous solution is 0.0125 mol / L; and the immersion time is 3 min. In step B, the concentration of the GMA / MeOH solution is 0.003 mol / L; and the immersion time is 0.5 h.

4. The production method according to claim 3, characterized by, The PDMS casting solution is prepared by stirring a methacrylate functionalized PDMS n-heptane solution, adding dodecafluoroheptyl methacrylate, and then adding a photoinitiator 2-hydroxy-2-methylpropiophenone at room temperature.

5. The preparation method according to claim 3, characterized in that, In the process of preparing the PDMS casting solution, the mass ratio of the methacrylate functionalized PDMS to dodecafluoroheptyl methacrylate is 1:0.1; the mass ratio of the methacrylate functionalized PDMS to the photoinitiator is 3:1; and the stirring time is 24 h.

6. The method of any one of claims 3-5, wherein, The preparation method of the methacrylate functionalized PDMS comprises: blending PDMS, silane coupling agent KH570, dibutyltin dilaurate, water and n-heptane, weighing and recording, stirring at room temperature, adding n-heptane to the original weight again, stirring again until uniform, and preparing the methacrylate functionalized PDMS.

7. The production method according to claim 6, characterized by, In the process of preparing the methacrylate functionalized PDMS, the mass ratio of 5000 cP PDMS to silane coupling agent KH570 is 11:0.12; the mass ratio of PDMS to dibutyltin dilaurate is 11:0.1; the mass ratio of PDMS to water is 11:0.1; and the mass ratio of PDMS to n-heptane is 1:

1.

8. The production method according to claim 6, characterized by, 10.The PDMS / PAN composite membrane according to claim 1 or 2 or prepared by the method according to any one of claims 3-9 is used in a separation process.

9. The production method according to claim 8, characterized by, The separation process comprises a pervaporation separation process and / or a nanofiltration separation process. ​ 11. Use according to claim 10, characterized in that, ​

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