Thermally modified polyimide gas separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a thermally modified polyimide gas separation membrane as well as a preparation method and application thereof, and relates to the technical field of gas separation membranes. The preparation method of the thermally modified polyimide gas separation membrane comprises the following steps: step 1, stirring and dissolving a mixed diamine monomer of 6FDA and MDA in NMP, adding DABA and NMP after the mixed diamine monomer is fully dissolved, carrying out ice-water bath at the initial stage of reaction, and then stirring and reacting at room temperature to obtain a high-viscosity polyamide acid solution; step 2, adding Ac2O and TEA into the polyamide acid solution, adding NMP to dilute the polyamide acid solution, and reacting at room temperature under the condition of N2 to obtain a PI solution; according to the thermally modified polyimide gas separation membrane as well as the preparation method and the application thereof, polyimide is modified at high temperature, so that the polyimide gas separation membrane has excellent mechanical properties and also has excellent gas permeability and selective separation coefficient.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation membranes, and in particular to a thermally modified polyimide gas separation membrane and a preparation method and application thereof. Background Art

[0002] With the development of industry, the expectations and requirements for materials in the field of gas separation are getting higher and higher. Developing a gas separation membrane material with high efficiency and low loss, high safety factor in the operating process, long life and good mechanical properties has become a research hotspot. Polyimide (PI) has good stability, radiation resistance, high and low temperature resistance, good chemical stability, good mechanical properties, small dielectric constant, non-toxicity, good transparency and flexibility, and is widely used in various fields. PI has extremely high application prospects in the field of gas separation because of its high gas selectivity, excellent physical properties, and the best comprehensive performance as an organic polymer material.

[0003] The molecular structure of PI is diverse, and new molecules with different synthetic structures can be designed and synthesized according to different applications and requirements to meet diverse industrial needs; and the molecular structure of PI is highly variable, which is conducive to the design and synthesis of molecules according to the needs of different actual situations to complete the modification of certain performance. When some gas separation membranes are used, plasticization is prone to occur when the CO2 partial pressure is high. For example, in the natural gas purification process, when the separation factor of carbon dioxide and methane reaches 40 or more, the presence of carbon dioxide or other acidic gases will cause the membrane to induce plasticization and swelling, which makes the gas separation membrane face huge problems during use, so it is urgent to improve the mechanical properties of the membrane. The present application modifies polyimide by high temperature, so that the polyimide gas separation membrane has excellent mechanical properties and excellent gas permeability and selective separation coefficient. Summary of the invention

[0004] The purpose of the present invention is to provide a thermally modified polyimide gas separation membrane and its preparation method and application. By modifying the polyimide at high temperature, the polyimide gas separation membrane has excellent mechanical properties, as well as excellent gas permeability and selective separation coefficient.

[0005] To achieve the above object, the present invention provides a method for preparing a thermally modified polyimide gas separation membrane, comprising the following steps:

[0006] Step 1, stirring and dissolving the mixed diamine monomers of 6FDA and MDA in NMP, adding DABA and NMP after fully dissolving, ensuring that the solid content is 14-16wt%, ice water bath at the initial stage of the reaction, maintaining the temperature at 3-5°C, and then stirring and reacting at room temperature for 20-28h to obtain a high viscosity polyamic acid solution;

[0007] Step 2, then adding Ac2O and TEA to the polyamic acid solution, and adding NMP to dilute the polyamic acid solution by 1-1.5 times, and reacting at room temperature for 20-28h under N2 conditions to obtain a PI solution;

[0008] Step 3, remove impurities by suction filtration, add methanol aqueous solution to precipitate PI, filter by suction, wash with methanol, and dry overnight in vacuum at 150° C. to obtain FMD solid;

[0009] Step 4: Dissolve the FMD solid in DMF to prepare a solution, filter it with suction and let it stand for 12 hours to remove bubbles;

[0010] Step 5, then coating the solution on a clean and flat glass substrate with a scraper, and immediately placing it in a vacuum box for vacuum drying to obtain an FMD film;

[0011] Step 6, placing the FMD membrane in a vacuum muffle furnace and sintering it at high temperature in a nitrogen atmosphere to obtain a thermally modified FMD membrane.

[0012] Furthermore, in step 1, the molar ratio of 6FDA, DABA and MDA is 6FDA:DABA:MDA=10:3:7.

[0013] Furthermore, in step 1, the solid content is ensured to be 15 wt %, an ice-water bath is used at the initial stage of the reaction to maintain the temperature at 5° C., and then the reaction is stirred at room temperature for 24 h.

[0014] Furthermore, in step 2, the molar ratio of Ac2O, TEA and 6FDA is Ac2O:TEA:6FDA=4:1:1.

[0015] Furthermore, in step 2, NMP is added to dilute the polyamic acid solution by 1 times, and the reaction is carried out at room temperature for 24 hours under N2 conditions to obtain a PI solution.

[0016] Furthermore, in step 5, the scraper is 200 μm, and the specific operation of vacuum drying is to vacuum dry at 50° C. for 16-18 hours, then increase the temperature to 180-220° C., dry for 4 hours, remove the residual solvent, and then peel off from the glass substrate to obtain the FMD film.

[0017] Furthermore, the thickness of the FMD film in step 5 is 13-17 μm.

[0018] Furthermore, in step 6, the high temperature sintering is to increase the temperature to a set temperature at a rate of 5°C / min, and then keep it warm for 0.5h. After the reaction is completed, it is naturally cooled to room temperature and sealed for storage. The set temperature is 250°C, 300°C, 350°C or 400°C.

[0019] The present invention also provides a thermally modified polyimide gas separation membrane, which is prepared by the above preparation method.

[0020] The present invention also provides application of the thermally modified polyimide gas separation membrane in gas separation.

[0021] The advantages and positive effects of the thermally modified polyimide gas separation membrane and its preparation method and application described in the present invention are:

[0022] The present application modifies polyimide by high temperature so that the polyimide gas separation membrane has excellent mechanical properties, and determines the optimal modification temperature to be 350°C. At this temperature, the polyimide gas separation membrane also has excellent gas permeability and selective separation coefficient. It can be summarized that at a modification temperature of 350°C, a polyimide gas separation membrane with optimal performance can be obtained, which is very practical.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The invention discloses a thermally modified polyimide gas separation membrane and its preparation method and synthesis and thermal cross-linking mechanism in application examples. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0026] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0027] Unless otherwise defined, the instruments, equipment and reagents used in the present invention are conventionally commercially available.

[0028] Comparison table of Chinese and English abbreviations

[0029] 3,3',4,4'-(Hexafluoroisopropylene) dianhydride (6FDA)

[0030] 4,4'-Diaminodiphenylmethane (MDA)

[0031] 3,5-Diaminobenzoic acid (DABA)

[0032] N-Methylpyrrolidone (NMP)

[0033] Acetic anhydride (Ac2O)

[0034] Triethylamine (TEA)

[0035] N,N'-Dimethylformamide (DMF)

[0036] 6FDA-MDA / DABA membrane (FMD membrane)

[0037] Example 1

[0038] A method for preparing a thermally modified polyimide gas separation membrane comprises the following steps:

[0039] Step 1, stirring and dissolving the mixed diamine monomers of 6FDA and MDA in NMP, adding DABA and NMP after fully dissolving, ensuring that the solid content is 15wt%, keeping the temperature at 5°C in an ice water bath at the initial stage of the reaction, and then stirring and reacting at room temperature for 24h to obtain a high-viscosity polyamic acid solution; the molar ratio of 6FDA, DABA and MDA is 6FDA:DABA:MDA=10:3:7.

[0040] Step 2, then add Ac2O and TEA to the polyamic acid solution, add NMP to dilute the polyamic acid solution by 1 times, react at room temperature for 24 hours under N2 conditions to obtain a PI solution; the molar ratio of Ac2O, TEA and 6FDA is Ac2O:TEA:6FDA=4:1:1.

[0041] Step 3, remove impurities by suction filtration, add methanol aqueous solution to precipitate PI, filter by suction, wash thoroughly with methanol, and dry overnight in vacuum at 150° C. to obtain FMD solid.

[0042] Step 4: Dissolve the FMD solid in DMF to prepare a solution, filter it with suction and let it stand for 12 hours to remove bubbles.

[0043] Step 5, then use a scraper (200 μm) to coat the solution on a clean and flat glass substrate, immediately put it into a vacuum box, vacuum dry it at 50°C for 16 hours, then raise the temperature to 200°C and dry it for 4 hours to remove the residual solvent, and then peel it off from the glass substrate to obtain FMD film I with a thickness of 16.5 μm.

[0044] Example 2

[0045] A method for preparing a thermally modified polyimide gas separation membrane comprises the following steps:

[0046] Step 1, stirring and dissolving the mixed diamine monomers of 6FDA and MDA in NMP, adding DABA and NMP after fully dissolving, ensuring that the solid content is 15wt%, keeping the temperature at 5°C in an ice water bath at the initial stage of the reaction, and then stirring and reacting at room temperature for 24h to obtain a high-viscosity polyamic acid solution; the molar ratio of 6FDA, DABA and MDA is 6FDA:DABA:MDA=10:3:7.

[0047] Step 2, then add Ac2O and TEA to the polyamic acid solution, add NMP to dilute the polyamic acid solution by 1 times, react at room temperature for 24 hours under N2 conditions to obtain a PI solution; the molar ratio of Ac2O, TEA and 6FDA is Ac2O:TEA:6FDA=4:1:1.

[0048] Step 3, remove impurities by suction filtration, add methanol aqueous solution to precipitate PI, filter by suction, wash thoroughly with methanol, and dry overnight in vacuum at 150° C. to obtain FMD solid.

[0049] Step 4: Dissolve the FMD solid in DMF to prepare a solution, filter it with suction and let it stand for 12 hours to remove bubbles.

[0050] Step 5, then use a scraper (200 μm) to coat the solution on a clean and flat glass substrate, immediately put it into a vacuum box, vacuum dry it at 50°C for 16 hours, then raise the temperature to 200°C and dry it for 4 hours to remove the residual solvent, and then peel it off from the glass substrate to obtain the FMD film.

[0051] Step 6, place the FMD membrane in a vacuum muffle furnace, heat it to 250°C at a rate of 5°C / min in a nitrogen atmosphere, and then keep it warm for 0.5h. After the reaction is completed, naturally cool it to room temperature and seal it for storage to obtain a thermally modified FMD membrane II with a thickness of 16μm.

[0052] Example 3

[0053] A method for preparing a thermally modified polyimide gas separation membrane comprises the following steps:

[0054] Step 1, stirring and dissolving the mixed diamine monomers of 6FDA and MDA in NMP, adding DABA and NMP after fully dissolving, ensuring that the solid content is 15wt%, keeping the temperature at 5°C in an ice water bath at the initial stage of the reaction, and then stirring and reacting at room temperature for 24h to obtain a high-viscosity polyamic acid solution; the molar ratio of 6FDA, DABA and MDA is 6FDA:DABA:MDA=10:3:7.

[0055] Step 2, then add Ac2O and TEA to the polyamic acid solution, add NMP to dilute the polyamic acid solution by 1 times, react at room temperature for 24 hours under N2 conditions to obtain a PI solution; the molar ratio of Ac2O, TEA and 6FDA is Ac2O:TEA:6FDA=4:1:1.

[0056] Step 3, remove impurities by suction filtration, add methanol aqueous solution to precipitate PI, filter by suction, wash thoroughly with methanol, and dry overnight in vacuum at 150° C. to obtain FMD solid.

[0057] Step 4: Dissolve the FMD solid in DMF to prepare a solution, filter it with suction and let it stand for 12 hours to remove bubbles.

[0058] Step 5, then use a scraper (200 μm) to coat the solution on a clean and flat glass substrate, immediately put it into a vacuum box, vacuum dry it at 50°C for 16 hours, then raise the temperature to 200°C and dry it for 4 hours to remove the residual solvent, and then peel it off from the glass substrate to obtain the FMD film.

[0059] Step 6, place the FMD membrane in a vacuum muffle furnace, heat it to 300°C at a rate of 5°C / min in a nitrogen atmosphere, and then keep it warm for 0.5h. After the reaction is completed, naturally cool it to room temperature and seal it for storage to obtain a thermally modified FMD membrane III with a thickness of 15μm.

[0060] Example 4

[0061] A method for preparing a thermally modified polyimide gas separation membrane comprises the following steps:

[0062] Step 1, stirring and dissolving the mixed diamine monomers of 6FDA and MDA in NMP, adding DABA and NMP after fully dissolving, ensuring that the solid content is 15wt%, keeping the temperature at 5°C in an ice water bath at the initial stage of the reaction, and then stirring and reacting at room temperature for 24h to obtain a high-viscosity polyamic acid solution; the molar ratio of 6FDA, DABA and MDA is 6FDA:DABA:MDA=10:3:7.

[0063] Step 2, then add Ac2O and TEA to the polyamic acid solution, add NMP to dilute the polyamic acid solution by 1 times, react at room temperature for 24 hours under N2 conditions to obtain a PI solution; the molar ratio of Ac2O, TEA and 6FDA is Ac2O:TEA:6FDA=4:1:1.

[0064] Step 3, remove impurities by suction filtration, add methanol aqueous solution to precipitate PI, filter by suction, wash thoroughly with methanol, and dry overnight in vacuum at 150° C. to obtain FMD solid.

[0065] Step 4: Dissolve the FMD solid in DMF to prepare a solution, filter it with suction and let it stand for 12 hours to remove bubbles.

[0066] Step 5, then use a scraper (200 μm) to coat the solution on a clean and flat glass substrate, immediately put it into a vacuum box, vacuum dry it at 50°C for 16 hours, then raise the temperature to 200°C and dry it for 4 hours to remove the residual solvent, and then peel it off from the glass substrate to obtain the FMD film.

[0067] Step 6, place the FMD membrane in a vacuum muffle furnace, heat it to 350°C at a rate of 5°C / min in a nitrogen atmosphere, and then keep it warm for 0.5h. After the reaction is completed, naturally cool it to room temperature and seal it for storage to obtain a thermally modified FMD membrane IV with a thickness of 15.5μm.

[0068] Example 5

[0069] A method for preparing a thermally modified polyimide gas separation membrane comprises the following steps:

[0070] Step 1, stirring and dissolving the mixed diamine monomers of 6FDA and MDA in NMP, adding DABA and NMP after fully dissolving, ensuring that the solid content is 15wt%, keeping the temperature at 5°C in an ice water bath at the initial stage of the reaction, and then stirring and reacting at room temperature for 24h to obtain a high-viscosity polyamic acid solution; the molar ratio of 6FDA, DABA and MDA is 6FDA:DABA:MDA=10:3:7.

[0071] Step 2, then add Ac2O and TEA to the polyamic acid solution, add NMP to dilute the polyamic acid solution by 1 times, react at room temperature for 24 hours under N2 conditions to obtain a PI solution; the molar ratio of Ac2O, TEA and 6FDA is Ac2O:TEA:6FDA=4:1:1.

[0072] Step 3, remove impurities by suction filtration, add methanol aqueous solution to precipitate PI, filter by suction, wash thoroughly with methanol, and dry overnight in vacuum at 150° C. to obtain FMD solid.

[0073] Step 4: Dissolve the FMD solid in DMF to prepare a solution, filter it with suction and let it stand for 12 hours to remove bubbles.

[0074] Step 5, then use a scraper (200 μm) to coat the solution on a clean and flat glass substrate, immediately put it into a vacuum box, vacuum dry it at 50°C for 16 hours, then raise the temperature to 200°C and dry it for 4 hours to remove the residual solvent, and then peel it off from the glass substrate to obtain the FMD film.

[0075] Step 6, place the FMD membrane in a vacuum muffle furnace, heat it to 400°C at a rate of 5°C / min in a nitrogen atmosphere, and then keep it warm for 0.5h. After the reaction is completed, naturally cool it to room temperature and seal it for storage to obtain a thermally modified FMD membrane V with a thickness of 13.5μm.

[0076] Performance Test:

[0077] The tensile strength and elongation at break of the FMD film prepared above were tested, and the results are shown in Table 1:

[0078] Table 1 Mechanical properties of FMD membrane

[0079] Elongation at break (%) Tensile strength (%) FMD membrane Ⅰ 10.6±1.1 88.4±3.4 FMD membrane Ⅱ 7.9±0.8 91.5±6.0 FMD membrane Ⅲ 9.6±0.4 116.0±7.7 FMD membrane Ⅳ 10.3±1.4 122.3±4.5 FMD membrane Ⅴ 6.3±0.5 87.1±5.2

[0080] As shown in Table 1, as the heat treatment temperature increases, the tensile strength first increases and then decreases, reaching a maximum at a heat treatment temperature of 350°C. After analysis, it is found that when the heat treatment temperature is low, thermal annealing plays a major role, resulting in tighter chain stacking, thereby improving the tensile strength; when the heat temperature becomes higher, heat-induced chemical crosslinking plays a leading role, resulting in increased brittleness of the film and lower tensile strength. In general, when heat treatment is performed at a relatively high temperature, the mechanical properties of the film can be significantly improved; in the present application, the mechanical properties of the FMD film are best when it is heat treated at 350°C (Example 4).

[0081] The permeability and separation coefficient of the FMD membrane prepared in the above Example 4 (heat treatment temperature 350° C.) were measured.

[0082] At 35°C and 50 Psig, the gas permeability of the gas separation membrane prepared in Example 4 was measured using a gas permeability meter and the selective separation coefficients for different gases were calculated. The results are shown in Tables 2 and 3, respectively, where the unit of gas permeability is: (10 -10 cm 3 (STP) cm cm -2 s cm Hg).

[0083] Table 2 Gas permeability of gas separation membranes for different pure gases

[0084] <![CDATA[N2]]> <![CDATA[O2]]> <![CDATA[CO2]]> <![CDATA[H2]]> He <![CDATA[CH4]]> FMD membrane Ⅳ 543 1407 3603 6315 13773 30

[0085] Table 3 Selective separation coefficients of gas separation membranes for different pure gases

[0086] <![CDATA[N2 / CH4]]> <![CDATA[O2 / CH4]]> <![CDATA[CO2 / CH4]]> <![CDATA[H2 / CH4]]> <![CDATA[He / CH4]]> FMD membrane Ⅳ 18.1 46.9 120.1 210.5 459.1

[0087] It can be seen from Table 2 and Table 3 that under the condition that the mechanical properties of FMD membrane IV are relatively excellent, FMD membrane IV has excellent gas permeability and selective separation coefficient, and can be used as a gas separation membrane.

[0088] Therefore, the present invention adopts the above-mentioned thermally modified polyimide gas separation membrane and its preparation method and application, and modifies the polyimide by high temperature so that the polyimide gas separation membrane has excellent mechanical properties, as well as excellent gas permeability and selective separation coefficient.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a thermally modified polyimide gas separation membrane, characterized in that: The following steps are involved: Step 1, stirring and dissolving the mixed diamine monomers of 6FDA and MDA in NMP, adding DABA and NMP after fully dissolving, ensuring that the solid content is 14-16wt%, ice water bath at the initial stage of the reaction, maintaining the temperature at 3-5°C, and then stirring and reacting at room temperature for 20-28h to obtain a high viscosity polyamic acid solution; Step 2, then adding Ac2O and TEA to the polyamic acid solution, and adding NMP to dilute the polyamic acid solution by 1-1.5 times, and reacting at room temperature for 20-28h under N2 conditions to obtain a PI solution; Step 3, remove impurities by suction filtration, add methanol aqueous solution to precipitate PI, filter by suction, wash with methanol, and dry overnight in vacuum at 150° C. to obtain FMD solid; Step 4: Dissolve the FMD solid in DMF to prepare a solution, filter it with suction and let it stand for 12 hours to remove bubbles; Step 5, then coating the solution on a clean and flat glass substrate with a scraper, and immediately placing it in a vacuum box for vacuum drying to obtain an FMD film; Step 6, placing the FMD membrane in a vacuum muffle furnace and sintering it at high temperature in a nitrogen atmosphere to obtain a thermally modified FMD membrane.

2. A thermally modified polyimide gas separation membrane and a preparation method and application thereof according to claim 1, characterized in that: The molar ratio of 6FDA, DABA and MDA in step 1 is 6FDA:DABA:MDA=10:3:

7.

3. The thermally modified polyimide gas separation membrane and its preparation method and application according to claim 1, characterized in that: In step 1, the solid content is ensured to be 15 wt %. In the initial stage of the reaction, an ice-water bath is used to maintain the temperature at 5° C., and then the reaction is stirred at room temperature for 24 h.

4. A thermally modified polyimide gas separation membrane and a preparation method and application thereof according to claim 1, characterized in that: The molar ratio of Ac2O, TEA and 6FDA in step 2 is Ac2O:TEA:6FDA=4:1:

1.

5. The thermally modified polyimide gas separation membrane and its preparation method and use according to claim 1, characterized in that: In step 2, NMP was added to dilute the polyamic acid solution by 1 times, and the PI solution was obtained by reacting at room temperature for 24 hours under N2 conditions.

6. A thermally modified polyimide gas separation membrane and a preparation method and application thereof according to claim 1, characterized in that: In step 5, the scraper is 200 μm, and the specific operation of vacuum drying is to vacuum dry at 50° C. for 16-18 hours, then increase the temperature to 180-220° C., dry for 4 hours, remove the residual solvent, and then peel off from the glass substrate to obtain the FMD film.

7. The thermally modified polyimide gas separation membrane and its preparation method and application according to claim 1, characterized in that: The thickness of the FMD film in step 5 is 13-17 μm.

8. The thermally modified polyimide gas separation membrane and its preparation method and use according to claim 1, characterized in that: In step 6, the high temperature sintering is to heat up to the set temperature at a rate of 5°C / min, and then keep it warm for 0.5h. After the reaction is completed, it is naturally cooled to room temperature and sealed for storage. The set temperature is 250°C, 300°C, 350°C or 400°C.

9. A thermally modified polyimide gas separation membrane, characterized in that: The preparation method is described in any one of claims 1 to 8.

10. Use of the thermally modified polyimide gas separation membrane according to claim 9 in gas separation.

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