Thermal rearrangement benzoxazole-imide membrane and application thereof in hydrogen separation

Abstract

The invention discloses a thermal rearrangement benzoxazole-imide membrane and application thereof in hydrogen separation, and belongs to the technical field of membrane separation, and the thermal rearrangement benzoxazole-imide membrane is characterized in that from the perspective of molecular structure design, commercialized monomer raw materials with specific functional groups are copolymerized to synthesize a thermal rearrangement polyimide precursor. The preparation method comprises the following steps: introducing an ether oxygen chain segment structure to improve the mechanical flexibility of a polymer, and carrying out heat treatment to initiate cyclization rearrangement of ortho-hydroxyl and an imide structure to prepare the benzoxazole-imide gas separation membrane which contains a PBO rigid structure and has good bending flexibility, so as to obtain good gas separation performance and relatively strong H2 enrichment and recovery applicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a thermally rearranged benzoxazole-imide membrane and its application in hydrogen separation. Background Art

[0003] Membrane separation technology has the advantages of low energy consumption, small investment, simple operation and easy coupling with other separation operations. It can be used in both large-scale hydrogen separation processes and small-scale decentralized hydrogen separation processes, and has development potential in the industrial application field. Membrane materials are the core of membrane separation technology. Preparing high-performance (high permeability and high separation selectivity) membrane materials is the key to effectively separating and enriching H 2 gas by using membrane technology. Among many polymer materials, polyimide is widely used in the field of gas separation due to its good chemical stability, thermal stability and easy modification operation. However, the current permeability of polyimide still has a certain gap with the industrial application requirements and needs to be designed and optimized. Although thermal rearrangement modification is an effective means to improve the permeability, it often comes at the cost of the loss of the mechanical properties of the membrane material, which greatly limits its practical application in gas separation. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a thermally rearranged benzoxazole-imide membrane and its application in hydrogen separation.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention:

[0007] The present invention provides a preparation method of a thermally rearranged benzoxazole-imide membrane, using diamine monomers and dianhydride monomers as raw materials to synthesize a thermally rearranged polyimide precursor, forming a membrane from the thermally rearranged polyimide precursor, and baking the thermally rearranged polyimide precursor membrane (coPI) to obtain the thermally rearranged benzoxazole-imide membrane.

[0008] The ether oxygen flexible chain segment can usually improve the rigidity of the polymer molecular chain and enhance the mechanical flexibility of the polymer due to its low cohesive energy and rotational barrier. Thermal rearrangement (TR) modification is a molecular structure rearrangement reaction triggered by the heating of an ortho-hydroxy polyimide precursor. The imide ring breaks and cyclizes and rearranges with the adjacent hydroxyl functional group structure. The formed benzoxazole (PBO) can effectively disrupt the close arrangement of the internal molecular chains of the polymer, obtain a high free volume and generate a microporous structure, which is beneficial to hydrogen (H 2) The rapid and smooth passage of small molecules exhibits the functional characteristics of molecular sieving, effectively improving the permeation selectivity of polyimide. Therefore, in this invention, a thermally rearranged polyimide precursor is synthesized using commercial monomers with specific functional groups, and through high-temperature calcination as the thermal reaction condition, a TR benzoxazole-imide film with good bending flexibility is efficiently and conveniently prepared, and it can efficiently separate H 2 .

[0009] The steps for synthesizing the thermally rearranged polyimide precursor are as follows: Dissolve the diamine monomer in N,N-dimethylacetamide. After complete dissolution, add the dianhydride monomer and N,N-dimethylacetamide under ice-water bath conditions (0 °C). After the reaction, polyamic acid (PAA) is obtained. Then add acetic anhydride and 3-methylpyridine and continue the reaction. The reaction product is precipitated with methanol, washed, and dried to obtain the thermally rearranged polyimide precursor.

[0010] The diamine monomer is 4,4'-(1,4-phenylenedioxy)bis(aniline) (TPEQ) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP). The structural formula of TPEQ is The structural formula of 6FAP is

[0011]

[0012] The dianhydride monomer is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and its structural formula is

[0013]

[0014] The molar ratio of the diamine monomer to the dianhydride monomer is 1:1.

[0015] During the process of synthesizing the thermally rearranged polyimide precursor, both the diamine monomer and the dianhydride monomer have been dried before use.

[0016] The molar ratio of 4,4'-(1,4-phenylenedioxy)bis(aniline) to 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane is (5 - 9):(1 - 5). Exemplarily, when the addition amount of TPEQ is 5 mmol, the addition amount of 6FAP is 5 mmol; when the addition amount of TPEQ is 6 mmol, the addition amount of 6FAP is 4 mmol; when the addition amount of TPEQ is 7 mmol, the addition amount of 6FAP is 3 mmol; when the addition amount of TPEQ is 8 mmol, the addition amount of 6FAP is 2 mmol; when the addition amount of TPEQ is 9 mmol, the addition amount of 6FAP is 1 mmol.

[0017] The structural formula of the PAA is:

[0018]

[0019] Wherein m is an amic acid structure formed by a diamine monomer; n is an amic acid structure formed by a diamine monomer, and m:n (molar ratio) is 9:1, 8:2, 7:3, 6:4 or 5:5.

[0020] The structural formula of coPI is:

[0021]

[0022] Wherein m is an imide structure formed by a diamine monomer; n is an imide structure formed by a diamine monomer, and m:n (molar ratio) is 9:1, 8:2, 7:3, 6:4 or 5:5.

[0023] Taking the molar ratio of TPEQ to 6FAP as 9:1 as an example, the steps of synthesizing the thermally rearranged polyimide precursor are as follows: 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) is placed in a sublimation furnace at 120°C for 12 hours, 4,4'-(1,4-phenylenedioxy) diphenylamine (TPEQ) and 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) are placed in a vacuum drying oven at 60°C for vacuum drying for 12 hours; 2.63 g (9 mmol) of the dried 4,4'-(1,4-phenylenedioxy) diphenylamine and 0.36 g (1 mmol) of the dried 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane are weighed and added into a three-necked flask with argon protective gas at one time, and 18 mL of N,N-dimethylacetamide was dissolved, and after 4,4'-(1,4-phenylenedioxy)dianiline and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane were completely dissolved, 4.44 g 4,4'-(hexafluoroisopropylene) diphthalic anhydride and 7 mL N,N-dimethylacetamide (4,4'-(hexafluoroisopropylene) diphthalic anhydride and N,N-dimethylacetamide were added in five times (15 min interval) under ice-water bath conditions (0°C), and the reaction was carried out for 24 hours to obtain PAA, and 4.73 g acetic anhydride and 0.97 mL 3-methylpyridine were added to continue the reaction for 24 hours. The reaction product was precipitated and washed with methanol, and dried in a vacuum drying oven at 80°C to obtain a thermally rearranged polyimide precursor.

[0024] The step of preparing a film of the thermally rearranged polyimide precursor is as follows: mixing the thermally rearranged polyimide precursor with N,N-dimethylacetamide to obtain a solution, and preparing the thermally rearranged polyimide precursor film by a casting method.

[0025] The mass ratio of the thermally rearranged polyimide precursor to N,N-dimethylacetamide is 1:9.

[0026] Further, the steps for forming a film from the thermally rearranged polyimide precursor are as follows: Weigh 1 g of the thermally rearranged polyimide precursor and place it in a sample bottle. Add 9 g of N,N-dimethylacetamide to prepare a solution with a mass concentration of 10%. After filtration, uniformly coat the solution on a glass dish and dry it at 60 °C to obtain the thermally rearranged polyimide precursor film.

[0027] The roasting is carried out as follows: In an inert gas protection atmosphere, first hold at 300 °C for 1 h, and then hold at 425 °C to 525 °C for 1 h. The first-stage heating process is to achieve the shedding of ester-substituted groups and re-obtain ortho-hydroxy functional groups, providing reaction sites for the thermal rearrangement reaction. The second-stage heating process is to meet the temperature requirements for the thermal rearrangement reaction.

[0028] During the roasting, the heating rate is 5 °C / min.

[0029] The second technical solution of the present invention:

[0030] The present invention also provides a thermally rearranged benzoxazole-imide film prepared according to the above method.

[0031] The third technical solution of the present invention:

[0032] The present invention also provides the application of the thermally rearranged benzoxazole-imide film in H 2 separation. The thermally rearranged benzoxazole-imide film of the present invention is preferably used for hydrogen / methane (H 2 / CH 4 ) separation.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] The present invention provides a new synthetic method for preparing a thermally rearranged polyimide precursor by chemically imidizing and copolymerizing a polyvalent dianhydride and a diamine monomer. By using a tube furnace to carry out roasting heat treatment on the thermally rearranged polyimide precursor film in an inert protective gas atmosphere, a thermal rearrangement reaction is initiated to efficiently prepare a TR benzoxazole-imide film. The material preparation method of the present invention is novel and efficient, with lower consumable costs, the polyimide film material is easy to prepare, and the H 2 separation performance is excellent and can potentially be applied to fields such as chemical by-product recovery of H 2 and so on. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] Figure 1 is the synthesis route of the thermally rearranged polyimide precursor of the present invention.

[0037] Figure 2 This is the preparation process of the thermally rearranged polyimide precursor film of the present invention.

[0038] Figure 3 This is the preparation process of the TR benzoxazole-imide film of the present invention.

[0039] Figure 4 This is the TR structure transformation principle of the TR benzoxazole-imide film of the present invention.

[0040] Figure 5 This is the H of the TR benzoxazole-imide film prepared in Examples 1-15 of the present invention 2 Relationship diagram of the H separation performance and the Robeson trade-off curve of the TR benzoxazole-imide film, where "1991" is the Robeson upper limit defined in 1991, which was obtained by fitting the most excellent gas permeation selectivity data in 1991, and "2008" is the Robeson upper limit defined in 2008, which was obtained by fitting the most excellent gas permeation selectivity data in 2008. Detailed implementation manners

[0041] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be regarded as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0042] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0043] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0044] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0045] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0046] All raw materials used in the examples of the present invention are commercially available.

[0047] An embodiment of the present invention provides a thermally rearranged (TR) benzoxazole-imide film and a preparation method thereof. The preparation method of the TR benzoxazole-imide film is as follows:

[0048] Step 1, preparation of thermally rearranged polyimide precursor:

[0049] 4,4'-(Hexafluoroisopropylene) diphthalic anhydride (6FDA) was placed in a sublimation furnace at 120°C for 12 hours, 4,4'-(1,4-phenylenedioxy) diphenylamine (TPEQ) and 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) were placed in a vacuum drying oven at 60°C for 12 hours; 1.46-2.63g (5-9mmol) of dried 4,4'-(1,4-phenylenedioxy) diphenylamine and 0.36-1.83g (1-5mmol) of dried 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane were weighed and added into a three-necked flask with argon protective gas at one time, and 18mL of N,N-dimethylacetamide was dissolved, and after 4,4'-(1,4-phenylenedioxy) dianiline and 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane were completely dissolved, 4.44 g (10 mmol) of 4,4'-(hexafluoroisopropylene) diphthalic anhydride and 7 mL of N,N-dimethylacetamide (4,4'-(hexafluoroisopropylene) diphthalic anhydride and N,N-dimethylacetamide were added in five times (15 min interval) under ice-water bath conditions (0°C), and the reaction was continued for 24 h to obtain polyamic acid (PAA), and 4.73 g of acetic anhydride and 0.97 mL of The reaction was continued for 24 h with 3-methylpyridine. The reaction product was precipitated and washed with methanol and dried in a vacuum oven at 80 °C to obtain a thermally rearranged polyimide precursor (coPI). In this step, the total molar number of TPEQ and 6FAP was 10 mmol. The synthetic route of the thermally rearranged polyimide precursor is shown in Figure 1 ;

[0050] Step 2, preparation of thermally rearranged polyimide precursor film:

[0051] Weigh 1 g of the thermally rearranged polyimide precursor prepared in step 1 and place it in a sample bottle. Add 9 g of N,N-dimethylacetamide to prepare a solution with a mass concentration of 10%. After filtration, uniformly coat the solution on a glass dish and dry it at 60 °C to obtain a thermally rearranged polyimide precursor film. Calculated by the molar proportion of 6FAP in the diamine monomer, it is named x%-coPI, where x represents the molar ratio of 6FAP in the diamine monomer (for example, when the molar ratio of TPEQ and 6FAP is 9:1, the prepared TR benzoxazole-imide film is denoted as 10%-coPI). The preparation process of the thermally rearranged polyimide precursor film is shown in Figure 2 ;

[0052] Step 3, Preparation of the TR benzoxazole-imide film:

[0053] Clamp and fix the thermally rearranged polyimide precursor film prepared in step 2 with two ceramic sheets, place it in a tube furnace and bake it under an argon protection atmosphere. The heating rate is 5 °C / min, and keep it at 300 °C and in the range of 425 °C - 525 °C for 1 hour respectively to obtain the TR benzoxazole-imide film, named x%-coTR@TEMP (x represents the molar ratio of 6FAP in the diamine monomer, and TEMP represents the final baking temperature of the TR benzoxazole-imide film). The preparation process of the TR benzoxazole-imide film is shown in Figure 3 , and the TR structure transformation principle of the TR benzoxazole-imide film is shown in Figure 4 , at high temperature, the imide ring in the polymer main chain first undergoes a rearrangement reaction with the adjacent hydroxyl functional group (-OH) to form a carboxyl-benzoxazole intermediate, and then the carboxyl group is thermally decomposed to remove CO 2 , and finally form a benzoxazole (PBO) structure.

[0054] Starting from the perspective of molecular structure design, this invention uses commercially available monomer raw materials with specific functional groups (TPEQ - ether oxygen flexible bond, 6FAP - ortho-hydroxy functional group) to copolymerize and synthesize a thermally rearranged polyimide precursor. Then, by specifying the baking temperature, heat treatment initiates the cyclization rearrangement of the ortho-hydroxy group and the imide structure to prepare a TR benzoxazole-imide gas separation membrane containing a PBO rigid structure, in order to obtain higher gas separation performance and potentially be applied to H 2 separation for enrichment and recovery.

[0055] It should be noted that the parts not detailed in this invention are all conventional operation means in the art and are not the focus of this invention.

[0056] The technical solutions of this invention are further described below through examples.

[0057] Example 1

[0058] Step 1, preparation of thermally rearranged polyimide precursor: 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FDA) was placed in a sublimation furnace at 120°C for 12h, 4,4'-(1,4-phenylenedioxy) diphenylamine (TPEQ) and 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) were placed in a vacuum drying oven at 60°C for 12h; 2.63g (9mmol) of dried 4,4'-(1,4-phenylenedioxy) diphenylamine and 0.36g (1mmol) of dried 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane were weighed and added into a three-necked flask with argon protective gas at one time, and 18mL of N,N-dimethylacetamide was dissolved, and after 4,4'-(1,4-phenylenedioxy) dianiline and 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane were completely dissolved, 4.44 g (10 mmol) 4,4'-(hexafluoroisopropylene) diphthalic anhydride and 7 mL N,N-dimethylacetamide (4,4'-(hexafluoroisopropylene) diphthalic anhydride and N,N-dimethylacetamide were added in five times (addition was performed once every 15 minutes) under ice-water bath conditions (0°C), and the reaction was continued for 24 hours to obtain polyamic acid (PAA), and 4.73 g acetic anhydride and 0.97 mL 3-methylpyridine were added to continue the reaction for 24 hours. The reaction product was precipitated and washed with methanol, and dried in a vacuum drying oven at 80°C to obtain a thermally rearranged polyimide precursor (coPI). The structural formula of PAA in this embodiment is

[0059] Wherein m=9, n=1; the structural formula of coPI in this embodiment is

[0060] m=9, n=1;

[0061] Step 2, preparation of thermally rearranged polyimide precursor film: weigh 1 g of the thermally rearranged polyimide precursor prepared in step 1 and place it in a sample bottle, add 9 g of N,N-dimethylacetamide to prepare a solution with a mass concentration of 10%, filter and evenly coat the solution on a glass dish, and dry at 60° C. to obtain a thermally rearranged polyimide precursor film (referred to as 10%-coPI);

[0062] Step 3, preparation of TR benzoxazole-imide film: The thermally rearranged polyimide precursor film obtained in step 2 is clamped and fixed with two ceramic plates, placed in a tubular furnace and calcined under an argon protective atmosphere at a heating rate of 5°C / min, and kept at 300°C and 425°C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 10%-coTR@425).

[0063] Using a gas separation device, the performance of the prepared gas separation membrane (i.e., the TR benzoxazole-imide membrane) was tested. The specific test method is as follows: Under the test conditions of room temperature (25 ± 2 °C) and an upstream pressure of 0.4 MPa, the constant volume variable pressure and time lag method were used to record the permeation fluxes of various pure gases (H 2 、CH 4 etc.). The relationship between the H 2 permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeability coefficient is 34.06 Barrer, and the separation factor is 4.46.

[0064] Example 2

[0065] Same as Example 1, the difference is only that step 3 is: The thermally rearranged polyimide precursor membrane prepared in step 2 was clamped and fixed with two ceramic sheets, placed in a tube furnace and calcined under an argon protection atmosphere. The heating rate was 5 °C / min, and it was kept at 300 °C and 475 °C for 1 hour respectively to obtain the TR benzoxazole-imide membrane (denoted as 10%-coTR@475). Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeability coefficient is 119.98 Barrer, and the separation factor is 11.34.

[0066] Example 3

[0067] Same as Example 1, the difference is only that step 3 is: The thermally rearranged polyimide precursor membrane prepared in step 2 was clamped and fixed with two ceramic sheets, placed in a tube furnace and calcined under an argon protection atmosphere. The heating rate was 5 °C / min, and it was kept at 300 °C and 525 °C for 1 hour respectively to obtain the TR benzoxazole-imide membrane (denoted as 10%-coTR@525). Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeability coefficient is 1501.52 Barrer, and the separation factor is 14.97.

[0068] The results show that the 10% TR benzoxazole-imide membrane (i.e., 10%-coTR@525) prepared by calcination at 525 °C has good H 2 / CH 4 separation performance. The H 2 permeability coefficient can reach 1501.52 Barrer, and the separation factor can reach 14.97.

[0069] Example 4

[0070] Step 1, preparation of thermally rearranged polyimide precursor: 6FDA was placed in a sublimation furnace at 120°C for 12h, TPEQ and 6FAP were placed in a vacuum drying oven at 60°C for 12h; 2.33g (8mmol) of dried TPEQ and 0.73g (2mmol) of dried 6FAP were weighed and added into a three-necked flask with argon protective gas at one time, 18mL of N,N-dimethylacetamide was added to dissolve, and after TPEQ and 6FAP were completely dissolved, 4.44g of 6FDA and 7mL of N,N-dimethylacetamide were added five times (add once every 15min) under ice-water bath conditions (0°C), and PAA was obtained after reaction for 24h, 4.73 acetic anhydride and 0.97mL of 3-methylpyridine were added to continue the reaction for 24h, the reaction product was precipitated and washed with methanol, and dried in a vacuum drying oven at 80°C to obtain a thermally rearranged polyimide precursor. The structural formula of PAA in this embodiment is

[0071] Wherein m=8, n=2; the structural formula of coPI in this embodiment is

[0072] Where m = 8, n = 2;

[0073] Step 2, preparation of thermally rearranged polyimide precursor film: weigh 1 g of the thermally rearranged polyimide precursor in step 1 and place it in a sample bottle, add 9 g of N,N-dimethylacetamide to prepare a solution with a mass concentration of 10%, filter and evenly coat the solution on a glass dish, and dry at 60°C to obtain a thermally rearranged polyimide precursor film (recorded as 20%-coPI).

[0074] Step 3, preparation of TR benzoxazole-imide film: The thermally rearranged polyimide precursor film obtained in step 2 is clamped and fixed with two ceramic plates, placed in a tubular furnace and calcined under an argon protective atmosphere at a heating rate of 5°C / min, and kept at 300°C and 425°C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 20%-coTR@425).

[0075] The performance of the prepared gas separation membrane was tested using a gas separation device. The test process was the same as in Example 1. 2 The relationship between permselectivity and Robeson trade-off curve is shown in Figure 5 .H 2 The permeability coefficient is 50.57 Barrer and the separation factor is 9.06.

[0076] Example 5

[0077] Same as Example 4, except that step 3 is: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic wafers, placed in a tubular furnace and calcined under an argon protection atmosphere, with a heating rate of 5 °C / min, and kept at 300 °C and 475 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 20%-coTR@475).

[0078] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeation coefficient is 175.32 Barrer and the separation factor is 17.29.

[0079] Example 6

[0080] Same as Example 4, except that step 3 is: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic wafers, placed in a tubular furnace and calcined under an argon protection atmosphere, with a heating rate of 5 °C / min, and kept at 300 °C and 525 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 20%-coTR@525).

[0081] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeation coefficient is 2416.50 Barrer and the separation factor is 14.78.

[0082] The results show that the 20% TR benzoxazole-imide film prepared by calcination at 525 °C (i.e., 20%-coTR@525) has good H 2 / CH 4 separation performance, H 2 The permeation coefficient can reach 2416.50 Barrer and the separation factor can reach 14.78.

[0083] Example 7

[0084] Step 1, preparation of thermally rearranged polyimide precursor: 6FDA was placed in a sublimation furnace at 120°C for 12h, TPEQ and 6FAP were placed in a vacuum drying oven at 60°C for 12h; 2.04g (7mmol) of dried TPEQ and 1.09g (3mmol) of dried 6FAP were weighed and added to a three-necked flask with argon protective gas at one time, and 18mL of N,N-dimethylacetamide was added to dissolve. After TPEQ and 6FAP were completely dissolved, 4.44g of 6FDA and 7mL of N,N-dimethylacetamide were added five times (add once every 15min) under ice-water bath conditions (0°C), and PAA was obtained after reacting for 24h. 4.73 acetic anhydride and 0.97mL of 3-methylpyridine were added to continue the reaction for 24h. The reaction product was precipitated and washed with methanol, and dried in a vacuum drying oven at 80°C to obtain coPI. The structural formula of PAA in this embodiment is

[0085] Wherein m=7, n=3; the structural formula of coPI in this embodiment is

[0086] m=7, n=3;

[0087] Step 2, preparation of thermally rearranged polyimide precursor film: weigh 1 g of the thermally rearranged polyimide precursor in step 1 and place it in a sample bottle, add 9 g of N,N-dimethylacetamide to prepare a solution with a mass concentration of 10%, filter and evenly coat the solution on a glass dish, and dry at 60°C to obtain a thermally rearranged polyimide precursor film (recorded as 30%-coPI).

[0088] Step 3, preparation of TR benzoxazole-imide film: The thermally rearranged polyimide precursor film obtained in step 2 is clamped and fixed with two ceramic plates, placed in a tubular furnace and calcined under an argon protective atmosphere at a heating rate of 5°C / min, and kept at 300°C and 425°C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 30%-coTR@425).

[0089] The performance of the prepared gas separation membrane was tested using a gas separation device. The test process was the same as in Example 1. 2 The relationship between permselectivity and Robeson trade-off curve is shown in Figure 5 .H 2 The permeability coefficient is 77.31 Barrer and the separation factor is 14.70.

[0090] Example 8

[0091] Same as Example 7, except that step 3 is as follows: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic wafers, placed in a tube furnace and calcined under an argon protection atmosphere. The heating rate is 5 °C / min, and it is kept at 300 °C and 475 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 30%-coTR@475).

[0092] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The testing process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeability coefficient is 313.86 Barrer, and the separation factor is 22.96.

[0093] Example 9

[0094] Same as Example 7, except that step 3 is as follows: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic wafers, placed in a tube furnace and calcined under an argon protection atmosphere. The heating rate is 5 °C / min, and it is kept at 300 °C and 525 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 30%-coTR@525).

[0095] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The testing process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeability coefficient is 2553.96 Barrer, and the separation factor is 12.26.

[0096] The results show that the 30% TR benzoxazole-imide film prepared by calcination at 525 °C (i.e., 30%-coTR@525) has good H 2 / CH 4 separation performance, H 2 The permeability coefficient can reach 2553.96 Barrer, and the separation factor can reach 12.26.

[0097] Example 10

[0098] Step 1, preparation of thermally rearranged polyimide precursor: 6FDA was placed in a sublimation furnace at 120°C for 12h, TPEQ and 6FAP were placed in a vacuum drying oven at 60°C for 12h; 1.75g ​​(6mmol) of dried TPEQ and 1.46g (4mmol) of dried 6FAP were weighed and added into a three-necked flask with argon protective gas at one time, 18mL of N,N-dimethylacetamide was added to dissolve, and after TPEQ and 6FAP were completely dissolved, 4.44g of 6FDA and 7mL of N,N-dimethylacetamide were added five times (add once every 15min) under ice-water bath conditions (0°C), and the reaction was continued for 24h to obtain PAA, 4.73 acetic anhydride and 0.97mL of 3-methylpyridine were added to continue the reaction for 24h, the reaction product was precipitated and washed with methanol, and placed in a vacuum drying oven at 80°C to obtain coPI. The structural formula of PAA in this embodiment is

[0099] Wherein m=6, n=4; the structural formula of coPI in this embodiment is

[0100] m=6, n=4;

[0101] Step 2, preparation of thermally rearranged polyimide precursor film: weigh 1 g of the thermally rearranged polyimide precursor in step 1 and place it in a sample bottle, add 9 g of N,N-dimethylacetamide to prepare a solution with a mass concentration of 10%, filter and evenly coat the solution on a glass dish, and dry at 60°C to obtain a thermally rearranged polyimide precursor film (recorded as 40%-coPI).

[0102] Step 3, preparation of TR benzoxazole-imide film: The thermally rearranged polyimide precursor film obtained in step 2 is clamped and fixed with two ceramic plates, placed in a tubular furnace and calcined under an argon protective atmosphere at a heating rate of 5°C / min, and kept at 300°C and 425°C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 40%-coTR@425).

[0103] The performance of the prepared gas separation membrane was tested using a gas separation device. The test process was the same as in Example 1. 2 The relationship between permselectivity and Robeson trade-off curve is shown in Figure 5 .H 2 The permeability coefficient is 93.77 Barrer and the separation factor is 22.01.

[0104] Embodiment 11

[0105] Same as Example 10, except that step 3 is as follows: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic sheets, placed in a tube furnace and calcined under an argon protection atmosphere. The heating rate is 5 °C / min, and it is kept at 300 °C and 475 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 40%-coTR@475).

[0106] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeation coefficient is 414.99 Barrer, and the separation factor is 33.12.

[0107] Example 12

[0108] Same as Example 10, except that step 3 is as follows: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic sheets, placed in a tube furnace and calcined under an argon protection atmosphere. The heating rate is 5 °C / min, and it is kept at 300 °C and 525 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 40%-coTR@525).

[0109] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeation coefficient is 3732.76 Barrer, and the separation factor is 11.71.

[0110] The results show that the 40% TR benzoxazole-imide film (i.e., 40%-coTR@525) prepared by calcination at 525 °C has good H 2 / CH 4 separation performance, H 2 The permeation coefficient can reach 3732.76 Barrer, and the separation factor can reach 11.71.

[0111] Example 13

[0112] Step 1, preparation of thermally rearranged polyimide precursor: 6FDA was placed in a sublimation furnace at 120°C for 12h, TPEQ and 6FAP were placed in a vacuum drying oven at 60°C for 12h; 1.46g (5mmol) of dried TPEQ and 1.83g (5mmol) of dried 6FAP were weighed and added into a three-necked flask with argon protective gas at one time, and 18mL of N,N-dimethylacetamide was added to dissolve, and the temperature during the dissolution process was controlled at 0°C. After TPEQ and 6FAP were completely dissolved, 4.44g of 6FDA and 7mL of N,N-dimethylacetamide were added five times (add once every 15min) under ice-water bath conditions (0°C), and the reaction was continued for 24h to obtain PAA, 4.73 acetic anhydride and 0.97mL of 3-methylpyridine were added to continue the reaction for 24h, and the reaction product was precipitated and washed with methanol, and placed in a vacuum drying oven at 80°C to obtain coPI. The structural formula of PAA in this embodiment is

[0113] Wherein m=5, n=5; the structural formula of coPI in this embodiment is

[0114] m=5, n=5;

[0115] Step 2, preparation of thermally rearranged polyimide precursor film: weigh 1 g of the thermally rearranged polyimide precursor in step 1 and place it in a sample bottle, add 9 g of N,N-dimethylacetamide to prepare a solution with a mass concentration of 10%, filter and evenly coat the solution on a glass dish, and dry at 60° C. to obtain a thermally rearranged polyimide precursor film (referred to as 50%-coPI);

[0116] Step 3, preparation of TR benzoxazole-imide film: The thermally rearranged polyimide precursor film obtained in step 2 is clamped and fixed with two ceramic plates, placed in a tubular furnace and calcined under an argon protective atmosphere at a heating rate of 5°C / min, and kept at 300°C and 425°C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 50%-coTR@425).

[0117] The performance of the prepared gas separation membrane was tested using a gas separation device. The test process was the same as in Example 1. 2 The relationship between permselectivity and Robeson trade-off curve is shown in Figure 5 .H 2 The permeability coefficient can reach 121.63 Barrer and the separation factor can reach 20.24.

[0118] Embodiment 14

[0119] Same as Example 13, except that step 3 is as follows: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic wafers, placed in a tubular furnace and calcined under an argon protection atmosphere. The heating rate is 5 °C / min, and it is kept at 300 °C and 475 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 50%-coTR@475).

[0120] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeability coefficient can reach 751.81 Barrer, and the separation factor can reach 38.26.

[0121] Example 15

[0122] Same as Example 13, except that step 3 is as follows: The thermally rearranged polyimide precursor film prepared in step 2 is clamped and fixed with two ceramic wafers, placed in a tubular furnace and calcined under an argon protection atmosphere. The heating rate is 5 °C / min, and it is kept at 300 °C and 525 °C for 1 hour respectively to obtain a TR benzoxazole-imide film (denoted as 50%-coTR@525).

[0123] Using a gas separation device, the performance of the prepared gas separation membrane was tested. The test process was the same as that in Example 1, H 2 The relationship between the permeation selectivity and the Robeson trade-off curve is shown in Figure 5 . H 2 The permeability coefficient is 3198.21 Barrer, and the separation factor is 8.19.

[0124] The results show that the 50% TR benzoxazole-imide film (i.e., 50%-coTR@475) prepared at 475 °C has good H 2 / CH 4 separation performance, H 2 The permeability coefficient can reach 751.81 Barrer, and the separation factor can reach 38.26.

[0125] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing a thermally rearranged benzoxazole-imide film, characterized in that: A thermally rearranged polyimide precursor is synthesized with diamine monomer and dianhydride monomer as raw materials, the thermally rearranged polyimide precursor is formed into a film, and the thermally rearranged polyimide precursor film is calcined to obtain the thermally rearranged benzoxazole-imide film.

2. The method for preparing the thermally rearranged benzoxazole-imide film according to claim 1, characterized in that: The steps of synthesizing the thermally rearranged polyimide precursor are as follows: dissolving a diamine monomer in N,N-dimethylacetamide, adding a dianhydride monomer and N,N-dimethylacetamide under ice-water bath conditions after the diamine monomer is completely dissolved, obtaining polyamic acid after the reaction, adding acetic anhydride and 3-methylpyridine to continue the reaction, precipitating the reaction product with methanol, washing and drying, and obtaining the thermally rearranged polyimide precursor.

3. The method for preparing the thermally rearranged benzoxazole-imide film according to claim 2, characterized in that: The diamine monomers are 4,4'-(1,4-phenylenedioxy) dianiline and 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane; The dianhydride monomer is 4,4'-(hexafluoroisopropylene) diphthalic anhydride.

4. The method for preparing the thermally rearranged benzoxazole-imide film according to claim 3, characterized in that: The molar ratio of the diamine monomer to the dianhydride monomer is 1:

1.

5. The method for preparing the thermally rearranged benzoxazole-imide film according to claim 3, characterized in that: The molar ratio of the 4,4'-(1,4-phenylenedioxy)dianiline to the 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane is (5-9):(1-5).

6. The method for preparing the thermally rearranged benzoxazole-imide film according to claim 1, characterized in that: The step of preparing a film of the thermally rearranged polyimide precursor is as follows: mixing the thermally rearranged polyimide precursor with N,N-dimethylacetamide to obtain a solution, and preparing the thermally rearranged polyimide precursor film by a casting method.

7. The method for preparing the thermally rearranged benzoxazole-imide film according to claim 1, characterized in that: The calcination is as follows: in an inert gas protective atmosphere, firstly keeping the temperature at 300° C. for 1 hour, and then keeping the temperature at 425° C. to 525° C. for 1 hour.

8. The method for preparing the thermally rearranged benzoxazole-imide film according to claim 7, characterized in that: During the calcination, the heating rate is 5°C / min.

9. A thermally rearranged benzoxazole-imide membrane, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the thermally rearranged benzoxazole-imide membrane according to claim 9 in hydrogen separation.

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