A gas separation membrane and a method of making the same

Abstract

The application belongs to the technical field of film material preparation, and provides a gas separation film and a preparation method thereof.The method comprises the following steps: S1, preparing a soluble polyimide into a polyimide solution with a mass fraction of 10% by using N-methyl pyrrolidone; S2, mixing 1.4-1.6 parts of mesoporous silica, 1.7-1.9 parts of polyaniline-coated carbon nanotubes and 65-67 parts of 15wt% nanometer titanium dioxide sol according to weight fractions to obtain a mixture; S3, adding the mixture obtained in S2 into 860-870 parts of the polyimide solution obtained in S1 under stirring, stirring for 24-26 hours at room temperature, filtering, degassing, film preparation, vacuum drying, water boiling demolding and drying, so that the gas separation film is obtained. By keeping a high addition amount of inorganic particles, the application ensures that the prepared composite film has excellent gas permeability (hydrogen permeability coefficient) and further improves the mechanical property (breaking strength).

Description

Technical Field

[0001] This invention belongs to the field of membrane material preparation technology, specifically relating to a gas separation membrane and its preparation method. Background Technology

[0002] The selectivity and permeability of gas separation membranes are the main performance parameters that determine the quality of gas separation membranes. Good membrane permeability can improve production efficiency and reduce costs, while high membrane selectivity can improve separation efficiency and product recovery rate.

[0003] In existing technologies, to improve the performance of polyimide membranes, a sol-gel method is used to composite nano-titanium dioxide with polyimide. This method controls the inorganic material structure at the nanoscale while enabling the formed inorganic network to chemically bond with the polymer, thus creating a stable organic-inorganic interpenetrating network and preparing an organic-inorganic nanocomposite material (composite membrane). It is known that increasing the titanium dioxide content within a certain range can improve the air permeability (e.g., hydrogen permeability coefficient) of the prepared composite material (composite membrane). Therefore, increasing the titanium dioxide content is an effective technical means to improve the air permeability of the prepared composite membrane.

[0004] However, at the same time, due to the high addition / content of titanium dioxide inorganic particles, the composite material (composite film) exhibits the mechanical properties of inorganic materials, and its mechanical properties (such as fracture strength) need to be improved. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a gas separation membrane and its preparation method, which, by maintaining a high amount of inorganic particles, ensures that the composite membrane has excellent air permeability (H2 air permeability coefficient) while further improving its mechanical properties (tensile strength).

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a gas separation membrane, comprising the following steps: S1. Prepare a 10% (w / w) polyimide solution using N-methylpyrrolidone; S2. By weight, mix 1.4-1.6 parts of mesoporous silica, 1.7-1.9 parts of polyaniline-coated carbon nanotubes and 65-67 parts of 15wt% nano-titanium dioxide sol to obtain a mixture; S3. The mixture obtained in S2 is added dropwise to 860-870 parts of the polyimide solution obtained in S1 under stirring. After stirring at room temperature for 24-26 hours, the mixture is filtered and degassed. A membrane is formed by coating with a blade, dried under reduced pressure at 150°C for 24 hours, and then desorbed by boiling in water and dried to obtain the gas separation membrane.

[0007] Furthermore, the preparation method of the polyaniline-coated carbon nanotubes is as follows: A1. Add 385-400 mL of 1 mol / L hydrochloric acid solution to a three-necked flask, then add 3 g of carbon nanotubes, and sonicate at 25 °C for 1 h; then add 1.5-1.6 g of aniline, and sonicate at 0-5 °C for 1 h to obtain a miscible solution. A2. Dissolve 2-2.2g of ammonium persulfate in 205-215mL of 1mol / L hydrochloric acid solution and sonicate for 1h to obtain ammonium persulfate solution; A3. At 0-5℃, add the ammonium persulfate solution obtained in A2 dropwise to the mixed solution obtained in A1, keeping the temperature constant. After the dropwise addition is completed, continue stirring for 8 hours, filter, wash the obtained product with anhydrous ethanol 3-5 times, and then dry it in an electric heating drying oven at 80℃ to obtain the polyaniline-coated carbon nanotubes.

[0008] Furthermore, in A3, the dropping time is 20-25 minutes.

[0009] Furthermore, in A3, the drying temperature is 80±2℃ and the drying time is 8-12h.

[0010] Furthermore, the method for preparing the soluble polyimide is as follows: B1. Add 0.1 mol of 3,3'-dimethyl-4,4'-diaminodiphenylmethane and 0.1 mol of 4,4'-terephthalodioxydiphthalic anhydride to 300 mL of N-methylpyrrolidone, and stir the mixture at 0-4 °C for 24-25 h to obtain a polyamic acid solution. B2. After chemical imidization of the polyamic acid solution obtained in B1, the polymer is precipitated with ethanol to obtain the polymer. After washing with ethanol and deionized water, the polymer is dried under reduced pressure at 150±5℃ for 24-25h to obtain the soluble polyimide.

[0011] Furthermore, in B2, chemical imidization is carried out using acetic anhydride and triethylamine for 45-48 hours.

[0012] Furthermore, the amount of acetic anhydride used is 50.5-51.2g, and the amount of triethylamine used is 25.2-25.5g.

[0013] Furthermore, the temperature for chemical imidization is 30-35℃.

[0014] Secondly, the present invention provides a gas separation membrane prepared by the above-described preparation method.

[0015] This application has the following beneficial effects: In the preparation of the gas separation membrane of this invention, polyaniline-coated carbon nanotubes and mesoporous silica are introduced simultaneously. The polyaniline coating layer of the polyaniline-coated carbon nanotubes preferentially forms hydrogen bonds with the hydroxyl groups on the surface of the mesoporous silica, and can further form covalent bonds. At the same time, the amino groups of the polyaniline coating layer can react with the terminal carboxyl groups of the polyimide matrix to form amide bonds, and hydrogen bonds are formed between the amino / imide groups and the carbonyl groups of the polyimide. The aromatic ring structures of the two undergo π-π stacking. In addition, a strong interfacial interaction is formed between the carbon nanotubes and titanium dioxide through the bridging effect of polyaniline. The polyaniline coating layer further enables the mesoporous silica and carbon nanotubes to overlap and construct an inorganic-organic interpenetrating reinforcement network, which jointly bears external forces and effectively prevents crack propagation. Through the above effects, the originally weak interface between the mesoporous silica and the polyimide matrix is ​​effectively strengthened, the interfacial voids are eliminated, and the stress concentration is alleviated, so that the mesoporous silica is transformed from a "defect source" into a "stress transmission point", thereby synergistically improving the fracture strength of the prepared composite membrane.

[0016] Mesoporous silica provides a transport path for H2 through its own mesoporous channels, ensuring H2 permeability; the interpenetrating network constructed by polyaniline-coated carbon nanotubes is mainly distributed at the mesoporous pore wall interface, without blocking the main mesoporous channels, thus strengthening the pore wall interface while fully preserving the gas transport path; together they maintain the high H2 permeability coefficient of the prepared composite membrane. Attached Figure Description

[0017] Figure 1 This is a comparative trend chart of the H2 permeability coefficient test data of the composite membrane material samples prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention. Figure 2 This is a comparative trend chart of the fracture strength test data of the composite membrane material samples prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0018] The present application will be further described in detail below with reference to the embodiments.

[0019] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0020] The preparation method of polyaniline-coated carbon nanotubes involved in the embodiments / comparative examples of this invention is as follows: A1. Add 395 mL of 1 mol / L hydrochloric acid solution to a three-necked flask, then add 3 g of carbon nanotubes, and sonicate at 25 °C for 1 h; then add 1.55 g of aniline, and sonicate at 3 °C for 1 h to obtain a mixed solution.

[0021] A2. Dissolve 2.1g of ammonium persulfate in 210mL of 1mol / L hydrochloric acid solution and sonicate for 1h to obtain ammonium persulfate solution.

[0022] A3. At 3℃, add the ammonium persulfate solution obtained in A2 dropwise to the mixed solution obtained in A1, keeping the temperature constant. The total dropwise addition time is 23 min. After the dropwise addition process is completed, continue stirring and reacting for 8 h. Filter the solution, wash the product four times with anhydrous ethanol, and then dry it in an electric heating drying oven at 80℃ for 11 h to obtain polyaniline-coated carbon nanotubes.

[0023] The mesoporous silica (99.9% effective content) involved in the embodiments / comparative examples of this invention was purchased from Qinghe County Ruijiang Metal Materials Co., Ltd.

[0024] The nano-titanium dioxide sol (model CY-TA33) involved in the embodiments / comparative examples of this invention, with a content of 15wt%, was purchased from Hangzhou Jiupeng New Materials Co., Ltd.

[0025] The preparation method of the soluble polyimide involved in the embodiments / comparative examples of this invention is as follows: B1. Add 0.1 mol of 3,3'-dimethyl-4,4'-diaminodiphenylmethane and 0.1 mol of 4,4'-terephthalodioxydiphthalic anhydride to 300 mL of N-methylpyrrolidone, and stir the mixture at 3 °C for 24.5 h to obtain a polyamic acid solution.

[0026] B2. The polyamic acid solution obtained in B1 was chemically imidized for 47 hours with 50.8 g of acetic anhydride and 25.3 g of triethylamine at a temperature of 32 °C. Then, it was precipitated with ethanol to obtain the polymer. After washing with ethanol and deionized water, it was dried under reduced pressure at 150 °C for 24.5 hours to obtain soluble polyimide.

[0027] Other specific details of the embodiments / comparative examples of the present invention are as follows.

[0028] Example 1: A method for preparing a gas separation membrane, comprising the following steps: S1. Prepare a 10% polyimide solution using N-methylpyrrolidone.

[0029] S2. By weight, 1.5 parts of mesoporous silica, 1.8 parts of polyaniline-coated carbon nanotubes and 66 parts of 15wt% nano-titanium dioxide sol are mixed to obtain a mixture equivalent to 9.9 parts of nano-titanium dioxide.

[0030] S3. The mixture obtained in S2 is added dropwise to 868 parts of the polyimide solution obtained in S1 under stirring, which is equivalent to 86.8 parts of polyimide. After stirring at room temperature for 25 hours, the mixture is filtered and degassed. A membrane is formed by coating with a blade, dried under reduced pressure at 150℃ for 24 hours, demembranes by boiling in water, and dried to obtain the gas separation membrane.

[0031] Example 2: A method for preparing a gas separation membrane, comprising the following steps: S1. Prepare a 10% polyimide solution using N-methylpyrrolidone.

[0032] S2. By weight, 1.4 parts of mesoporous silica, 1.7 parts of polyaniline-coated carbon nanotubes and 65 parts of 15wt% nano-titanium dioxide sol are mixed to obtain a mixture.

[0033] S3. The mixture obtained in S2 is added dropwise to 860 parts of the polyimide solution obtained in S1 under stirring. After stirring at room temperature for 25 hours, the mixture is filtered and degassed. A membrane is formed by coating with a blade and dried under reduced pressure at 150°C for 24 hours. The membrane is then removed by boiling in water and dried to obtain the gas separation membrane.

[0034] Example 3: A method for preparing a gas separation membrane, comprising the following steps: S1. Prepare a 10% polyimide solution using N-methylpyrrolidone.

[0035] S2. By weight, 1.6 parts of mesoporous silica, 1.9 parts of polyaniline-coated carbon nanotubes and 67 parts of 15wt% nano-titanium dioxide sol are mixed to obtain a mixture.

[0036] S3. The mixture obtained in S2 is added dropwise to 870 parts of the polyimide solution obtained in S1 under stirring. After stirring at room temperature for 25 hours, the mixture is filtered and degassed. A membrane is formed by coating with a blade and dried under reduced pressure at 150°C for 24 hours. The membrane is then removed by boiling in water and dried to obtain the gas separation membrane.

[0037] Comparative Example 1: The difference between this comparative example and Example 1 is that in the preparation of the gas separation membrane, the amounts of mesoporous silica and polyaniline-coated carbon nanotubes are replaced with the amounts of nano-titanium dioxide. That is, 1.5 parts of mesoporous silica and 1.8 parts of polyaniline-coated carbon nanotubes are replaced with 22 parts of 15wt% nano-titanium dioxide sol (equivalent to 3.3 parts of nano-titanium dioxide).

[0038] Specifically, a method for preparing a gas separation membrane includes the following steps: S1. Prepare a 10% polyimide solution using N-methylpyrrolidone.

[0039] S2. By weight, take 88 parts of 15wt% nano titanium dioxide sol, which is equivalent to 13.2 parts of nano titanium dioxide.

[0040] S3. Add 88 parts of 15wt% nano titanium dioxide sol obtained in S2 dropwise to 868 parts of polyimide solution obtained in S1 under stirring, which is equivalent to 86.8 parts of polyimide. After stirring at room temperature for 25 hours, filter and degas, form a membrane by scraping, dry under reduced pressure at 150℃ for 24 hours, boil in water to remove the membrane, and dry to obtain the gas separation membrane.

[0041] Comparative Example 2: The difference between this comparative example and Example 1 is that in the preparation of the gas separation membrane, the amount of polyaniline-coated carbon nanotubes is replaced with the amount of nano-titanium dioxide. That is, 1.8 parts of polyaniline-coated carbon nanotubes are replaced with 12 parts of 15wt% nano-titanium dioxide sol (equivalent to 1.8 parts of nano-titanium dioxide).

[0042] Specifically, a method for preparing a gas separation membrane includes the following steps: S1. Prepare a 10% polyimide solution using N-methylpyrrolidone.

[0043] S2. By weight, 1.5 parts of mesoporous silica and 78 parts of 15wt% nano-titanium dioxide sol are mixed, which is equivalent to 11.7 parts of nano-titanium dioxide, to obtain a mixture.

[0044] S3. The mixture obtained in S2 is added dropwise to 868 parts of the polyimide solution obtained in S1 under stirring, which is equivalent to 86.8 parts of polyimide. After stirring at room temperature for 25 hours, the mixture is filtered and degassed. A membrane is formed by coating with a blade, dried under reduced pressure at 150℃ for 24 hours, demembranes by boiling in water, and dried to obtain the gas separation membrane.

[0045] Comparative Example 3: The difference between this comparative example and Example 1 is that in the preparation of the gas separation membrane, the amount of mesoporous silica is replaced with the amount of nano-titanium dioxide. That is, 1.5 parts of mesoporous silica are replaced with 10 parts of 15wt% nano-titanium dioxide sol (equivalent to 1.5 parts of nano-titanium dioxide).

[0046] Specifically, a method for preparing a gas separation membrane includes the following steps: S1. Prepare a 10% polyimide solution using N-methylpyrrolidone.

[0047] S2. By weight, 1.8 parts of polyaniline-coated carbon nanotubes and 76 parts of 15wt% nano-titanium dioxide sol are mixed, which is equivalent to 11.4 parts of nano-titanium dioxide, to obtain a mixture.

[0048] S3. The mixture obtained in S2 is added dropwise to 868 parts of the polyimide solution obtained in S1 under stirring, which is equivalent to 86.8 parts of polyimide. After stirring at room temperature for 25 hours, the mixture is filtered and degassed. A membrane is formed by coating with a blade, dried under reduced pressure at 150℃ for 24 hours, demembranes by boiling in water, and dried to obtain the gas separation membrane.

[0049] Experimental Example: Test Subjects: Composite membrane material samples prepared in Examples 1-3 and Comparative Examples 1-3. Test Items: ① H2 permeability coefficient (25℃); ② Tensile strength. Test Results: See Table 1.

[0050] Table 1. Experimental Results Data

[0051] Results Analysis: Combining the data in Table 1 and... Figures 1-2 Analysis of Examples 1-3 shows that the H2 permeability coefficient of the composite membrane material samples prepared by the present invention (Examples 1-3) reaches 4.42 × 10⁻⁶. -15 m 3 ·m / (m 2 The strength of the fracture strength test data is above 99.8 MPa (·s·Pa) and the fracture strength test data is above 99.8 MPa.

[0052] Combining the data in Table 1 and Figures 1-2 The analysis focused on Example 1 and Comparative Examples 1-3: Specifically, by comparing Comparative Example 1 and Comparative Example 2, it can be seen that, compared with Comparative Example 1, the addition of mesoporous silica in Comparative Example 2 alone improved the air permeability (H2 air permeability coefficient) of the composite membrane material sample, but reduced the mechanical properties (fracture strength).

[0053] This is mainly because, when mesoporous silica is introduced alone, on the one hand, its mesoporous channels can further improve the gas transport path and maintain / increase the H2 permeability. On the other hand, mesoporous silica itself is a rigid inorganic particle with weak interfacial bonding with the polyimide matrix, making it easier to form interfacial voids and stress concentration points; moreover, the mesoporous silica itself is rich in mesoporous structures, which will disrupt the continuous stacking / entanglement of polyimide molecular chains, reducing the overall load-bearing capacity of the membrane; thus leading to a decrease in the tensile strength of the prepared composite membrane.

[0054] Specifically, by comparing Comparative Example 1 and Comparative Example 3, it can be seen that, compared with Comparative Example 1, Comparative Example 3, by simply adding polyaniline-coated carbon nanotubes, resulted in improved air permeability (H2 air permeability coefficient) and mechanical properties (fracture strength) of the composite membrane material sample.

[0055] By comparing with Example 1, it can be seen that the present invention simultaneously introduces mesoporous silica and polyaniline-coated carbon nanotubes, which can produce a synergistic effect and synergistically improve the mechanical properties (fracture strength) of the prepared composite membrane material sample.

[0056] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0057] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a gas separation membrane, characterized in that, Includes the following steps: S1. Prepare a 10% (w / w) polyimide solution using N-methylpyrrolidone; S2. By weight, mix 1.4-1.6 parts of mesoporous silica, 1.7-1.9 parts of polyaniline-coated carbon nanotubes and 65-67 parts of 15wt% nano-titanium dioxide sol to obtain a mixture; S3. The mixture obtained in S2 is added dropwise to 860-870 parts of the polyimide solution obtained in S1 under stirring. After stirring at room temperature for 24-26 hours, the mixture is filtered, degassed, membrane-formed, dried, demembranes removed by boiling in water, and dried again to obtain the gas separation membrane.

2. The method for preparing the gas separation membrane according to claim 1, characterized in that, The preparation method of the polyaniline-coated carbon nanotubes is as follows: A1. Add 385-400 mL of 1 mol / L hydrochloric acid solution to a three-necked flask, then add 3 g of carbon nanotubes and sonicate at 25 °C; then add 1.5-1.6 g of aniline and sonicate at 0-5 °C to obtain a miscible solution. A2. Dissolve 2-2.2g of ammonium persulfate in 205-215mL of 1mol / L hydrochloric acid solution and sonicate to obtain ammonium persulfate solution; A3. At 0-5℃, add the ammonium persulfate solution obtained in A2 dropwise to the mixed solution obtained in A1. After stirring and reacting for 8 hours, filter the solution and wash the product with anhydrous ethanol 3-5 times. Then dry the product to obtain the polyaniline-coated carbon nanotubes.

3. The method for preparing the gas separation membrane according to claim 2, characterized in that, In A3, the dropping time is 20-25 minutes.

4. The method for preparing the gas separation membrane according to claim 2, characterized in that, In A3, the drying temperature is 80±2℃ and the drying time is 8-12h.

5. The method for preparing the gas separation membrane according to claim 1, characterized in that, The method for preparing the soluble polyimide is as follows: B1. Add 0.1 mol of 3,3'-dimethyl-4,4'-diaminodiphenylmethane and 0.1 mol of 4,4'-terephthalodioxydiphthalic anhydride to 300 mL of N-methylpyrrolidone, and stir the mixture at 0-4 °C for 24-25 h to obtain a polyamic acid solution. B2. After chemical imidization of the polyamic acid solution obtained in B1, the polymer is precipitated with ethanol to obtain the polymer. After washing with ethanol and deionized water, the polymer is dried to obtain the soluble polyimide.

6. The method for preparing the gas separation membrane according to claim 5, characterized in that, In B2, chemical imidization was carried out using acetic anhydride and triethylamine for 45-48 hours.

7. The method for preparing the gas separation membrane according to claim 6, characterized in that, The dosage of acetic anhydride is 50.5-51.2g, and the dosage of triethylamine is 25.2-25.5g.

8. The method for preparing the gas separation membrane according to claim 5 or 6, characterized in that, The temperature for chemical imidization is 30-35℃.

9. A gas separation membrane, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

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