Zinc halide modified carbon nanotube composite polyimide film as well as preparation method and application thereof

Abstract

The invention discloses a zinc halide modified carbon nanotube composite polyimide film and a preparation method and application thereof, and relates to the technical field of film materials, the zinc halide modified carbon nanotube composite polyimide film comprises a zinc halide modified carbon nanotube and polyimide, the zinc halide in the zinc halide modified carbon nanotube accounts for 10-40% of the mass of the carbon nanotube, and the polyimide accounts for 10-40% of the mass of the carbon nanotube. The zinc halide modified carbon nanotube accounts for 10-30% of the mass of the polyimide, the zinc halide is one of ZnCl2, ZnBr2 and ZnI2, and the polyimide is one of P84 and Matrimid 5218. According to the prepared zinc halide modified carbon nanotube composite polyimide film, after the zinc halide modified carbon nanotube is introduced, the film selectivity and flux are remarkably improved, the film flux is improved to the maximum 1537 Barrer from 52 Barrer, the film selectivity is improved again after the zinc halide modified film is adopted, and the He / CH4 selectivity is improved to the maximum 286 from the original 97.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and in particular to a zinc halide-modified carbon nanotube composite polyimide membrane, its preparation method, and its application. Background Technology

[0002] Helium is an indispensable rare strategic material for national defense, military industry, and high-tech industrial development, with wide applications in scientific research, refrigeration, metal manufacturing, medical treatment, aerospace, superconducting experiments, optical fibers, deep-sea diving, and welding production. Currently, shale gas remains the sole source of industrial helium production. However, my country's energy structure is characterized by abundant coal, scarce oil, and limited gas reserves, resulting in low shale gas reserves, particularly helium. Only small amounts of helium are found in regions like Sichuan and Chongqing, and helium purification is extremely difficult. my country relies heavily on imports for helium, which has become a major bottleneck for the country. Therefore, developing advanced shale gas helium extraction and recovery technologies is crucial for reducing helium purification costs and promoting the development of my country's shale gas helium extraction industry.

[0003] Traditional helium purification methods mainly involve cryogenic distillation and pressure swing adsorption, both of which are energy-intensive, increasing the cost of helium extraction. Membrane separation technology, as an emerging separation method, has enormous application potential in gas separation, offering advantages such as low cost, low energy consumption, and being environmentally friendly. However, membrane separation technology often suffers from the "trade-off" effect, meaning that increasing gas flux leads to decreased selectivity. Therefore, developing high-flux and high-selectivity membranes is of great significance. Patent CN115945079A discloses a method for preparing polyimide-based carbon molecular sieve membranes, applied to CO2 purification. The maximum CO2 flux reaches 3580 Barrer, with a CO2 / N2 selectivity of 9 and a CO2 / CH4 selectivity of 32. Membranes prepared by this method have high flux but low selectivity. The literature [Chemical Engineering & Processing: Process Intensification 148(2020)107804] reports a method for preparing a mixed matrix membrane of MOF modified polyimide. The selectivity of He / CH4 and He / N2 is as high as 257 and 193, respectively, but the flux is only 51.8 Barrer. Although the membrane prepared by this method has excellent selectivity, the low flux limits its industrial application. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a zinc halide-modified carbon nanotube composite polyimide membrane, its preparation method and application, so as to improve the flux and selectivity of the polyimide membrane, enhance the membrane stability, and promote the application of the polyimide membrane in helium purification.

[0005] In a first aspect, the present invention provides a zinc halide-modified carbon nanotube composite polyimide film, characterized in that the zinc halide-modified carbon nanotube composite polyimide film comprises zinc halide-modified carbon nanotubes and polyimide, wherein the zinc halide accounts for 10-40% of the mass of the carbon nanotubes, and the zinc halide-modified carbon nanotubes account for 10-30% of the mass of the polyimide, wherein the zinc halide is one of ZnCl2, ZnBr2 and ZnI2, and the polyimide is one of P84 and Matrimid 5218.

[0006] Secondly, the present invention provides a method for preparing a zinc halide-modified carbon nanotube composite polyimide film, comprising the following steps:

[0007] 1) Preparation of zinc halide-modified carbon nanotubes

[0008] Carbon nanotubes were placed in a ball mill and milled at 4000-8000 r / min for 8-24 h. Zinc halide was then poured into a solvent and stirred to dissolve. The carbon nanotubes were then added to the solvent and stirred at room temperature for 1-2 h. The mixture was then sonicated for 30-60 min and vacuum dried at 60-80℃ for 8-12 h to obtain zinc halide-modified carbon nanotubes.

[0009] 2) Preparation of casting solution

[0010] Take polyimide and dry it in a vacuum drying oven at 80-110℃ for 12-24 hours. Then pour it into a solvent to dissolve it and stir it at 30-120℃ for 6-8 hours. Then add polyvinylpyrrolidone (PVP) and zinc halide-modified carbon nanotubes in sequence and continue stirring for 12-24 hours. Then degas it under vacuum for 1-4 hours to obtain the casting solution.

[0011] 3) Preparation of zinc halide-modified carbon nanotube composite polyimide membranes

[0012] The casting solution was poured onto a glass plate, and a film was scraped out using a film scraper. The glass plate was then quickly placed in an oven to dry. The film was then peeled off and finally placed in a vacuum drying oven to dry at 200-230℃ for 8-12 hours to obtain a zinc halide modified carbon nanotube composite polyimide film.

[0013] In conjunction with the second aspect, in some embodiments, the solvent mentioned in step 1) is any one of methanol, ethanol, and acetone.

[0014] In conjunction with the second aspect, in some embodiments, the mass ratio of the carbon nanotubes to the solvent in step 1) is 1:1-2.

[0015] In conjunction with the second aspect, in some embodiments, the solvent mentioned in step 2) is one of nitrogen-methylpyrrolidone (NMP) and chloroform.

[0016] In conjunction with the second aspect, in some embodiments, the polyimide described in step 2) accounts for 15-20% of the solvent mass.

[0017] In conjunction with the second aspect, in some embodiments, the molecular weight of the polyvinylpyrrolidone (PVP) in step 2) is between 3,500 and 220,000, and the PPVP accounts for 1% to 10% of the mass of the polyimide.

[0018] In conjunction with the second aspect, in some embodiments, the thickness of the zinc halide-modified carbon nanotube composite polyimide film described in step 3) is between 50 μm and 100 μm.

[0019] In conjunction with the second aspect, in some embodiments, the drying conditions in the oven in step 3) are: drying at 60-80℃ for 2-4 hours, and then raising the temperature to 150-180℃ for another 8-12 hours.

[0020] Thirdly, the present invention provides the application of the above-mentioned zinc halide-modified carbon nanotube composite polyimide membrane or the zinc halide-modified carbon nanotube composite polyimide membrane prepared by the above preparation method in helium extraction from natural gas.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention prepares a zinc halide-modified carbon nanotube composite polyimide membrane. After introducing zinc halide-modified carbon nanotubes, the membrane selectivity and flux are significantly improved. The membrane flux increases from 52 Barrer to a maximum of 1537 Barrer. The membrane selectivity after zinc halide modification is further improved, with the He / CH4 selectivity increasing from the original 97 to a maximum of 286.

[0023] 2. The prepared zinc halide-modified carbon nanotube composite polyimide membrane exhibits strong stability, with only a slight decrease in selectivity and permeability after 350 hours of normal operation.

[0024] 3. Low cost and simple preparation process, which can effectively solve the current problems of high difficulty and cost in the preparation of domestic natural gas helium extraction membranes, low membrane selectivity and stability, and the reliance on imports for commonly used separation membrane materials such as polyacetate fiber membranes. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the principle of testing the gas separation performance of the membrane in an embodiment of the present invention.

[0026] Figure 2 This is a stability diagram of the zinc halide-modified carbon nanotube composite polyimide film prepared in Example 4 of the present invention.

[0027] Figure 3This is a stability diagram of the composite polyimide film prepared in Comparative Example 1 of the present invention.

[0028] Figure 4 This is a stability diagram of the composite polyimide film prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified in the following examples, the conditions are as per standard conditions or the manufacturer's recommendations. Raw materials, equipment, or instruments whose manufacturers are not specified are all commercially available products.

[0031] This invention proposes a zinc halide-modified carbon nanotube composite polyimide membrane, its preparation method, and its application. The high specific surface area and special pore structure of carbon nanotubes can significantly improve the membrane flux, while the introduction of zinc halides will further enhance gas selectivity. This method overcomes the "trade-off" effect to a certain extent and has important potential in helium purification.

[0032] The preparation method of a zinc halide-modified carbon nanotube composite polyimide film of the present invention includes the following steps:

[0033] 1) Preparation of zinc halide-modified carbon nanotubes: Carbon nanotubes were placed in a ball mill and milled at 4000-8000 r / min for 8-24 h. Zinc halide was dissolved in a solvent by stirring, and then the carbon nanotubes were added to the solvent. The mixture was stirred at room temperature for 1-2 h, followed by ultrasonication for 30-60 min and vacuum drying at 60-80℃ for 8-12 h to obtain zinc halide-modified carbon nanotubes. The solvent used was any one of methanol, ethanol, or acetone, and the mass ratio of carbon nanotubes to solvent was 1:1-2.

[0034] 2) Preparation of casting solution: Dry polyimide in a vacuum drying oven at 80-110℃ for 12-24 hours, then dissolve it in a solvent and stir at 30-120℃ for 6-8 hours. Next, add polyvinylpyrrolidone (PVP) and zinc halide-modified carbon nanotubes sequentially, and continue stirring for 12-24 hours. Then, degas under vacuum for 1-4 hours to obtain the casting solution. The solvent used is either N-methylpyrrolidone (NMP) or chloroform, with polyimide accounting for 15-20% of the solvent mass. The PVP molecular weight is between 3500-220000, and the PVP accounts for 1%-10% of the polyimide mass.

[0035] 3) Preparation of zinc halide-modified carbon nanotube composite polyimide film: The casting solution was poured onto a glass plate, and the film was scraped out using a film scraper. Then, the glass plate was quickly placed in an oven and dried at 60-80℃ for 2-4 hours. Then, the temperature was raised to 150-180℃ and dried for another 8-12 hours. The film was peeled off and finally placed in a vacuum drying oven and dried at 200-230℃ for 8-12 hours to obtain a zinc halide-modified carbon nanotube composite polyimide film with a thickness between 50μm and 100μm.

[0036] The following examples 1-3 provide a detailed description of a zinc halide-modified carbon nanotube composite polyimide film of the present invention, its preparation method, and its application.

[0037] Example 1

[0038] This embodiment provides a method for preparing a ZnCl2-modified carbon nanotube composite polyimide film, the steps of which are as follows:

[0039] 40g of carbon nanotubes were placed in a ball mill and ball-milled at 4000r / min for 8h. 0.2g of ZnCl2 was poured into 2g of methanol and stirred to dissolve. Then, 2g of carbon nanotubes were added to the methanol and stirred at room temperature for 1h. The mixture was then sonicated for 30min and vacuum dried at 60℃ for 8h to obtain ZnCl2-modified carbon nanotubes.

[0040] P84 was dried in a vacuum drying oven at 80℃ for 12 hours. Then, 3g of P84 was added to 20g of NMP solvent and stirred at 120℃ for 6 hours. Next, 0.03g of 3500-PVP and 0.3g of ZnCl2-modified carbon nanotubes were added sequentially, and stirring was continued for 12 hours. Then, vacuum degassing was performed for 1 hour to obtain the casting solution. The casting solution was poured onto a glass plate, and a film was scraped out using a film scraper. The glass plate was then quickly placed in an oven and dried at 60℃ for 2 hours, followed by drying at 150℃ for another 8 hours. The film was then peeled off and finally dried in a vacuum drying oven at 200℃ for 8 hours to obtain a 50μm ZnCl2-modified carbon nanotube composite polyimide film.

[0041] Example 2

[0042] This embodiment provides a method for preparing a ZnBr2-modified carbon nanotube composite polyimide film, the steps of which are as follows:

[0043] 40g of carbon nanotubes were placed in a ball mill and milled at 6000r / min for 24h. 0.8g of ZnBr2 was poured into 4g of ethanol and stirred to dissolve. Then, 2g of carbon nanotubes were added to the solution and stirred at room temperature for 2h. The mixture was then sonicated for 60min and vacuum dried at 80℃ for 12h to obtain ZnBr2-modified carbon nanotubes.

[0044] Matrimid 5218 was dried in a vacuum drying oven at 110℃ for 24 hours. Then, 3g of Matrimid 5218 was added to 15g of chloroform solvent and stirred at 30℃ for 8 hours. Next, 0.3g of 220000-PVP and 0.9g of ZnBr2-modified carbon nanotubes were added sequentially, and stirring was continued for 24 hours. After vacuum degassing for 4 hours, a casting solution was obtained. The casting solution was poured onto a glass plate, and a film was scraped out using a film scraper. The glass plate was then quickly placed in an oven and dried at 80℃ for 4 hours, followed by drying at 180℃ for another 12 hours. The film was then peeled off and finally dried in a vacuum drying oven at 230℃ for 12 hours to obtain a 100μm ZnBr2-modified carbon nanotube composite polyimide film.

[0045] Example 3

[0046] This embodiment provides a method for preparing a ZnI2-modified carbon nanotube composite polyimide film, the steps of which are as follows:

[0047] 40g of carbon nanotubes were placed in a ball mill and milled at 8000r / min for 24h. 0.8g of ZnI2 was poured into 4g of acetone and stirred to dissolve. Then, 2g of carbon nanotubes were added to the mixture and stirred at room temperature for 2h. The mixture was then sonicated for 60min and vacuum dried at 80℃ for 12h to obtain ZnI2-modified carbon nanotubes.

[0048] Matrimid 5218 was dried in a vacuum drying oven at 110℃ for 24 hours. Then, 3g of Matrimid 5218 was added to 15g of chloroform solvent and stirred at 30℃ for 8 hours. Next, 0.3g of 220000-PVP and 0.9g of ZnI2-modified carbon nanotubes were added sequentially, and stirring was continued for 24 hours. Then, vacuum degassing was performed for 4 hours to obtain the casting solution. The casting solution was poured onto a glass plate, and a film was scraped out using a film scraper. The glass plate was then quickly placed in an oven and dried at 80℃ for 4 hours, followed by drying at 180℃ for another 12 hours. The film was then peeled off and finally dried in a vacuum drying oven at 230℃ for 12 hours to obtain a 50μm ZnI2-modified carbon nanotube composite polyimide film.

[0049] Example 4

[0050] This embodiment provides a method for preparing a ZnBr2-modified carbon nanotube composite polyimide film, the steps of which are as follows:

[0051] 40g of carbon nanotubes were placed in a ball mill and milled at 8000r / min for 12h. 0.6g of ZnBr2 was poured into 3g of ethanol and stirred to dissolve. Then, 2g of carbon nanotubes were added to the solution and stirred at room temperature for 2h. The mixture was then sonicated for 60min and vacuum dried at 80℃ for 12h to obtain ZnBr2-modified carbon nanotubes.

[0052] Matrimid 5218 was dried in a vacuum drying oven at 110℃ for 24 hours. Then, 3g of Matrimid 5218 was added to 15g of chloroform solvent and stirred at 30℃ for 8 hours. Next, 0.3g of 58000-PVP and 0.6g of ZnBr2-modified carbon nanotubes were added sequentially, and stirring was continued for 24 hours. After vacuum degassing for 4 hours, a casting solution was obtained. The casting solution was poured onto a glass plate, and a film was scraped out using a film scraper. The glass plate was then quickly placed in an oven and dried at 80℃ for 4 hours, followed by drying at 180℃ for another 12 hours. The film was then peeled off and finally dried in a vacuum drying oven at 230℃ for 12 hours to obtain a 50μm ZnBr2-modified carbon nanotube composite polyimide film.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 4 is that carbon nanotubes were not added in this comparison.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 4 is that the ZnBr2-modified carbon nanotubes in this comparison are replaced with ordinary carbon nanotubes.

[0057] The zinc halide-modified carbon nanotube composite polyimide films prepared in Examples 1, 2, 3, and 4, and the composite polyimide films prepared in Comparative Examples 1 and 2, were tested as follows:

[0058] Test the gas separation performance of the membrane:

[0059] The zinc halide-modified carbon nanotube composite polyimide membranes prepared in Examples 1, 2, 3, and 4, and the composite polyimide membranes prepared in Comparative Examples 1 and 2, were assembled into membrane modules, and their helium separation performance was tested at room temperature. The feed gases were He, CH4, and N2, and the pressure was 0.1 MPa. Figure 1 As shown in the figure. The test results are shown in Table 1.

[0060] Table 1 Membrane separation performance

[0061]

[0062] As shown in Table 1, compared to the membrane without carbon nanotubes in Comparative Example 1, the membrane flux and selectivity of Examples 1, 2, 3, and 4, after the addition of zinc halide-modified carbon nanotubes, were significantly improved. The membrane flux increased from 52 Barrer to over 900 Barrer, especially in Example 4, which increased to 1358 Barrer. The selectivity of the membrane after zinc halide modification was further improved, with the He / CH4 selectivity increasing from 97 to over 210 and the He / N2 selectivity increasing from 104 to a maximum of over 220. In contrast, Comparative Example 2, which replaced the ZnBr2-modified carbon nanotubes with ordinary carbon nanotubes, achieved a membrane flux of 1537 Barrer, but the selectivities for He / N2 and He / CH4 were both below 170. Therefore, the zinc halide-modified carbon nanotube composite polyimide membrane of this invention can selectively pass helium, showing significant potential in helium purification.

[0063] The stability tests of the zinc halide-modified carbon nanotube composite polyimide film prepared in Example 4, and the composite polyimide films prepared in Comparative Examples 1 and 2 are as follows:

[0064] The prepared composite polyimide membrane was placed in a membrane cell, and its He separation performance was tested at room temperature. The inlet gas consisted of He, CH4, and N2 at a pressure of 0.2 MPa, while the permeate side was purged with argon gas for 20 min at a flow rate of 20 mL / min. The test results are shown below. Figure 2 , Figure 3 and Figure 4 .Depend on Figure 2 The data show that the helium flux and selectivity of the zinc halide-modified carbon nanotube composite polyimide membrane prepared in this invention remained generally stable after 350 hours of operation. Figure 3 The composite polyimide membrane prepared in Comparative Example 1 began to show a continuous decrease in helium flux and selectivity after 120 hours of operation. Figure 4 Although the composite polyimide membrane prepared in Comparative Example 2 maintained stable helium flux and selectivity after 350 hours of operation, its He selectivity was too poor, which was not conducive to improving the efficiency of natural gas helium extraction. Therefore, the zinc halide-modified carbon nanotube composite polyimide membrane prepared in this invention exhibits strong operational stability, can effectively improve the efficiency of natural gas helium extraction, and reduce the cost of membrane materials.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention. Technologies not described in detail in this invention are known technologies.

Claims

1. A zinc halide-modified carbon nanotube composite polyimide film, characterized by, The zinc halide-modified carbon nanotube composite polyimide film comprises zinc halide-modified carbon nanotubes and polyimide. The zinc halide accounts for 10-40% of the mass of the carbon nanotubes, and the zinc halide accounts for 10-30% of the mass of the polyimide. The zinc halide is one of ZnCl2, ZnBr2, and ZnI2, and the polyimide is one of P84 and Matrimid 5218.

2. A method for preparing a zinc halide-modified carbon nanotube composite polyimide film, characterized in that, Includes the following steps: 1) Preparation of zinc halide-modified carbon nanotubes Carbon nanotubes were placed in a ball mill and milled at 4000-8000 r / min for 8-24 h. Zinc halide was then poured into a solvent and stirred to dissolve. The carbon nanotubes were then poured into the solvent and stirred at room temperature for 1-2 h. The mixture was then sonicated for 30-60 min and vacuum dried at 60-80℃ for 8-12 h to obtain zinc halide-modified carbon nanotubes. 2) Preparation of casting solution Take polyimide and dry it in a vacuum drying oven at 80-110℃ for 12-24h. Then pour it into a solvent to dissolve it and stir it at 30-120℃ for 6-8h. Then add polyvinylpyrrolidone and zinc halide to modify carbon nanotubes in sequence, continue stirring for 12-24h, and then degas under vacuum for 1-4h to obtain the casting solution. 3) Preparation of zinc halide-modified carbon nanotube composite polyimide membranes The casting solution was poured onto a glass plate, and a film was scraped out using a film scraper. The glass plate was then quickly placed in an oven to dry. The film was then peeled off and finally placed in a vacuum drying oven to dry at 200-230℃ for 8-12 hours to obtain a zinc halide-modified carbon nanotube composite polyimide film.

3. The production method according to claim 2, wherein The solvent mentioned in step 1) is any one of methanol, ethanol, and acetone.

4. The production method according to claim 3, wherein The mass ratio of carbon nanotubes to solvent in step 1) is 1:1-2.

5. The production method according to claim 4, wherein The solvent mentioned in step 2) is one of nitrogen-methylpyrrolidone (NMP) and chloroform.

6. The production method according to claim 5, wherein The polyimide mentioned in step 2) accounts for 15-20% of the solvent mass.

7. The production method according to claim 5, wherein The molecular weight of the polyvinylpyrrolidone mentioned in step 2) is between 3,500 and 220,000, and the polyvinylpyrrolidone accounts for 1% to 10% of the mass of the polyimide.

8. The production method according to claim 5, wherein The thickness of the zinc halide-modified carbon nanotube composite polyimide film described in step 3) is between 50 μm and 100 μm.

9. The production method according to claim 5, wherein In step 3), the drying conditions in the oven are: drying at 60-80℃ for 2-4 hours, then raising the temperature to 150-180℃ and drying for another 8-12 hours.

10. The application of the zinc halide-modified carbon nanotube composite polyimide membrane as described in claim 1 or the zinc halide-modified carbon nanotube composite polyimide membrane prepared by any one of the preparation methods described in claims 2-9 in helium extraction from natural gas.

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