Blended gas separation membrane containing benzocyclobutene polyimide and preparation method thereof

Abstract

The invention belongs to the technical field of gas separation membranes, and relates to a blended gas separation membrane containing benzocyclobutene polyimide and a preparation method of the blended gas separation membrane. The blended composite gas separation membrane comprises benzocyclobutenyl polyimide and polybenzimidazole, wherein the polybenzimidazole contains a Troger base. The blended composite gas separation membrane provided by the invention has excellent gas permeability coefficient and gas selectivity, is easy to process and form and simple in preparation process, and has a wide application prospect in the field of gas separation membranes.

Description

Technical Field

[0001] This invention belongs to the field of gas separation membrane technology, and particularly relates to a blended gas separation membrane containing benzocyclobutene polyimide and its preparation method. Background Technology

[0002] Membrane separation technology, as a powerful means to solve environmental problems, has excellent economic advantages such as small size, short process, low energy consumption, easy operation, sustainability, and no phase change. Among various materials for gas separation membranes, polyimide (PI) is an engineering polymer with thermal stability, mechanical properties, and chemical resistance. However, it has a relatively low gas permeability under high gas selectivity and vice versa, thus limiting its application.

[0003] To address the aforementioned problems, existing technologies have proposed various modification methods. For example, CN115463561A discloses a blended composite gas separation membrane and its preparation method. This method introduces trifluoromethyl large side groups and non-planar benzo[a]carbazole onto the main chain of a polyimide material, and adds a metal-organic cage with tetrahedral Ti4L6 as the structural unit to form a mixed matrix membrane. The combination of these two factors improves both gas permeability and selectivity, and the membrane is easy to process and mold. However, the separation performance of the blended composite membrane is relatively poor.

[0004] CN115970524A discloses a mixed matrix membrane for gas separation, its preparation method, and its application, yielding a membrane with β... TpTta, a covalent framework polymer with a ketene-enamine structure COF; will TpTta COF is added to a solution of ionic liquid [Bmim][Tf₂N] or [BCNtz][HFP] and heated to react. The ionic liquid is then introduced into Tp and Tta using an impregnation method. The ionic liquid-intercalated modified composite was prepared by inserting PIM into the pore cavity of COF. A mixed matrix membrane was prepared by dispersing a composite material modified by ionic liquid in solution and then using a solution casting evaporation method. This filler material, after being cleaved by the ionic liquid, has a pore size that better matches the kinetic dimensions of the gas molecules to be separated, thus significantly improving gas separation efficiency and selectivity. However, the preparation process of this mixed matrix membrane is relatively complex and is only suitable for the separation of a specific single gas. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a blended gas separation membrane containing benzocyclobutene polyimide and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A blended composite gas separation membrane containing benzocyclobutenyl polyimide comprises benzocyclobutenyl polyimide and polybenzimidazole, wherein the polybenzimidazole contains a Choger base.

[0007] Preferably, the blended composite gas separation membrane is obtained by blending benzocyclobutene-based polyimide and polybenzimidazole.

[0008] The blended composite gas separation membrane described in this invention has good mechanical properties and dimensional stability, maintains high gas selectivity in high gas permeability, and has excellent anti-aging properties, making it suitable for the gas separation field.

[0009] Specifically, benzocyclobutene groups have low curing temperatures and do not generate other small molecules during curing. Introducing benzocyclobutene groups into the polyimide molecule enables the polyimide to maintain excellent gas separation performance. However, a single polyimide membrane cannot maintain high gas selectivity under conditions of high gas permeability. Based on the excellent characteristics of benzocyclobutene-based polyimide, this invention introduces polybenzimidazole as a filler material into the polyimide membrane matrix. The prepared blended composite gas separation membrane exhibits excellent gas separation performance and is suitable for gas separation applications.

[0010] Preferably, the mass ratio of the benzocyclobutenyl polyimide to the polybenzimidazole is (1-10):(1-10), for example, it can be 8:1, 6:1, 4:1, 2:1, 1:2, 1:4, 1:6, 1:8, etc., as well as any specific ratio or range between the above ratios.

[0011] Preferably, the thickness of the blended composite gas separation membrane is 5-100 µm, more preferably 10-90 µm, such as 10 µm, 20 µm, 30 µm, 40 µm, 45 µm, 60 µm, 70 µm, 80 µm, 90 µm, etc., as well as any specific value or range between the above values.

[0012] The benzocyclobutenyl polyimide has the structure shown in Formula I: Formula I; Wherein, R1 is an aromatic dianhydride residue, and n is 10-1000000, for example, 10, 100, 500, 1000, 5000, 10000, 50000, 100000, 100000, 1000000, and any value between the above values.

[0013] Preferably, the optimal range of n is 50000-500000, for example 50000, 100000, 200000, 300000, 400000, 500000, and any value between the above points.

[0014] Preferably, R1 is selected from any one of the following groups, whether substituted or unsubstituted: ; The dashed lines indicate the locations where the functional groups are attached. The substituted groups of R1 are independently selected from one of methyl, methoxy, halogen, hydroxy, cyano, heteroaryl, heterocycloalkyl, and amino.

[0015] More preferably, R1 is selected from... or .

[0016] Preferably, the polybenzimidazole has the structure shown in Formula II: Formula II; The ratio of y to x is (0-9):1, where 0-9 can be 0, 1, 2, 3, 4, 5, 6, 7, 8, etc. The values ​​of x and y range from 10 to 1,000,000, and the preferred ratio of y to x is 0.5 to 2:1.

[0017] Preferably, R2 and Ar are each selected from any one of the following groups, whether substituted or unsubstituted: .

[0018] Preferably, R3 is selected from any one of the following groups, whether substituted or unsubstituted: .

[0019] Preferably, R2, Ar and R3 may contain substituents, each of which is independently selected from any one of halogens, -OH, -SO3H, -NO2, -H2PO4, unsubstituted or halogenated C1~C10 straight-chain or branched alkyl groups.

[0020] The present invention also provides a method for preparing the above-mentioned blended composite gas separation membrane, comprising the following steps: A benzocyclobutene-based polyimide solution was blended with a polybenzimidazole solution. The blended solution was then subjected to ultrasonic degassing treatment, followed by a film-forming process to obtain a gas separation membrane containing a blend of benzocyclobutene-based polyimide and polybenzimidazole.

[0021] Preferably, the content of polybenzimidazole in the blend solution is 1-30 wt%, for example 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 13 wt%, 15 wt%, 18 wt%, 20 wt%, 23 wt%, 25 wt%, 28 wt%, 30 wt%, and any value between the above points.

[0022] Preferably, the film-forming method includes solution casting, spin coating, blade coating, and casting.

[0023] Preferably, the solvents used for the benzocyclobutene polyimide solution and the polybenzimidazole solution are the same polar solvents.

[0024] Preferably, the polar solvent is selected from one of trifluoroacetic acid, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and sulfolane. Trifluoroacetic acid is further preferred.

[0025] The present invention also provides the application of the above-mentioned blended composite gas separation membrane in gas separation. Particularly, it is used in the separation of H2 / CH4, H2 / N2, and CO2 / CH4, and more preferably in the separation of H2 / CH4.

[0026] The beneficial effects of this invention are: (1) By introducing a benzocyclobutene structure into the polyimide molecular chain, the polyimide possesses excellent mechanical properties and heat resistance. The polybenzimidazole material contains -NH groups, which can increase the affinity for gas molecules, increase adsorption capacity, and improve gas separation performance and industrial application value. The blended composite gas separation membrane has good mechanical properties, good heat resistance, good selectivity, high separation efficiency, and a simple preparation process.

[0027] (2) The blended gas separation membrane of the present invention contains benzocyclobutene-based polyimide. The benzocyclobutene-based molecular structure has a long length and side group length, which are large hanging groups. The polymer molecular chains formed are loosely stacked, which is conducive to gas permeation. Furthermore, it can be cross-linked to generate a six-membered ring structure, which is suitable for the passage of small molecule gases, such as H2 and CO2, and the permeability coefficient increases.

[0028] (3) The blended gas separation membrane of the present invention contains polybenzimidazole containing the Choger base, which forms a microporous structure in the polymer molecular chain stacking, and significantly improves the gas separation performance. The blended gas separation membrane of the present invention, through polybenzimidazole and polyimide with specific structures, can efficiently separate H2 / CH4, H2 / N2, and CO2 / CH4, especially H2 / CH4. (4) The present invention does not require the use of modifiers or the preparation of precursors. The benzocyclobutene structure itself can undergo low-temperature crosslinking without the release of small molecules and also has very favorable solubility, which simplifies the preparation process. Detailed Implementation

[0029] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0030] Example 1 This embodiment provides a blended composite gas separation membrane, which comprises benzocyclobutene-containing polyimide and polybenzimidazole in a mass ratio of 2:1.

[0031] The preparation method of polybenzimidazole is as follows: (1) Prepare aromatic dicarboxylic acid containing choger base according to Example 13 of CN113717177A .

[0032] (2) Prepare the following reaction in a polyphosphoric acid system: 81g of polyphosphoric acid and 9g of phosphorus pentoxide were added to the reaction vessel and heated to 100°C with stirring until all the phosphorus pentoxide was dissolved and the solution was clear and transparent. Then, 11.8370g of the chogel-containing aromatic dicarboxylic acid, 14.9989g of 3,3'-diaminobenzidine and 5.8146g of terephthalic acid were added to the reaction vessel and stirred for 4h. The temperature was then raised to 180°C and reacted for 24h.

[0033] The reaction formula is as follows: x=50000, y=50000.

[0034] Preparation method of polyimide containing benzocyclobutene: (1) Preparation of diamine monomers containing benzocyclobutene (1.1) 4-Aminobenzocyclobutene (1.2450 g, 0.0080 mol) and p-fluoronitrobenzene (3.3864 g, 0.0240 mol) were added to a three-necked flask containing 50 mL of dimethyl sulfoxide. After complete dissolution under magnetic stirring, cesium fluoride (3.6456 g, 0.0240 mol) was added to the reaction mixture. The temperature was then slowly raised to 120 °C, and the reaction was continued for 12 hours. After the reaction was completed, the reaction solution was poured into a beaker containing 300 mL of deionized water to precipitate the product. After washing with water and methanol 2-3 times, the product was dried under vacuum at 80 °C to obtain 2.2 g of crude product, which was then recrystallized from DMF / deionized water (volume ratio 1:3) to obtain 1.8 g of the final orange-yellow product.

[0035] (1.2) The 1.8000 g (0.0049 mol) obtained in step (1.1) and palladium on carbon (0.18 g) were added to a three-necked flask containing 54 mL of ethanol. Under a nitrogen atmosphere, the temperature was raised to 78°C and the mixture was magnetically stirred for 0.5 h. The solution formed a homogeneous system, and then hydrazine hydrate (9 mL, 0.2770 mol) was added stepwise using a constant pressure dropper. The reaction was then refluxed for another 24 h. The hot Pd / C was then filtered off, and the solution was poured into deionized water to precipitate a white powder. The crude product was collected by suction filtration and recrystallized from ethanol to obtain 0.9 g of the product, a diamine monomer containing benzocyclobutene.

[0036] (2) Preparation of benzocyclobutene-containing polyimide 0.5 g of a benzocyclobutene-containing diamine monomer was dissolved in NMP, and a dianhydride monomer (6FDA) with the same molar mass ratio as the diamine monomer was added. The mixture was reacted in an ice-water bath for 12 h. Then, a 1:1 molar mixture of acetic anhydride and triethylamine was added, and the mixture was heated to 90 °C and reacted for another 12 h. After the solution was cooled to room temperature, it was washed in a 1:1 methanol / water mixture. The washing was repeated 2-3 times, and the solution was dried under vacuum at 120 °C to finally obtain benzocyclobutene-containing polyimide PI-1.

[0037] The reaction equation is: n=100000.

[0038] The method for preparing the blended gas separation membrane is as follows: (1) Preparation of polybenzimidazole casting solution: Dissolve 1g of polybenzimidazole in 10mL of trifluoroacetic acid (TFA), stir at room temperature for 2h until completely dissolved, and obtain polybenzimidazole casting solution.

[0039] (2) The benzocyclobutene polyimide was purified and dissolved in trifluoroacetic acid. At the same time, the above-mentioned polybenzimidazole casting solution was added and stirred at 35°C for 96 hours to obtain a blended film casting solution of benzocyclobutene-containing polyimide and polybenzimidazole material with a mass ratio of 2:1, and the solid content was controlled to be 10%.

[0040] (3) Allow the mixture to cool naturally to room temperature. Use a syringe to draw the mixture from the casting solution of the blended membrane. Then use a 25-0.45 µm polytetrafluoroethylene filter head for squeezing and filtration. Collect the filtrate and let it stand for 30 minutes to remove bubbles.

[0041] (4) The casting solution of the blended membrane was coated onto a smooth, flat-bottomed petri dish that had been leveled beforehand. The dish was then placed in a preheated drying oven at 60°C and dried at normal pressure for about 24 hours to remove most of the solvent. The thickness of the liquid membrane after solvent evaporation was controlled to be 50 µm. The membrane was then placed in a vacuum drying oven at 120°C and dried under vacuum for 4 hours to completely remove the solvent. After the vacuum drying oven cooled naturally to room temperature, the membrane was demolded to obtain a blended composite gas separation membrane containing benzocyclobutene, polyimide, and polybenzimidazole. The final membrane thickness was 45 µm.

[0042] Example 2 This embodiment provides a blended composite gas separation membrane, which comprises polybenzimidazole and benzocyclobutene-containing polyimide in a mass ratio of 1:1.

[0043] The structural formula and preparation method of polybenzimidazole are the same as in Example 1.

[0044] Preparation of benzocyclobutene-containing polyimide: (1) The preparation method of the diamine monomer containing benzocyclobutene is as described in Example 1.

[0045] (2) Dissolve 0.5 g of the benzocyclobutene-containing diamine monomer prepared in step (1) in NMP, add dianhydride monomer (BTDA) with the same molar mass ratio as the diamine monomer, react in an ice-water bath for 12 h, then add a 1:1 molar ratio acetic anhydride / triethylamine mixed solution, continue the reaction at 90 ℃ for 12 h, and after the solution is cooled to room temperature, pour it into a 1:1 mass ratio methanol / water mixed solution for washing, repeat the washing 2-3 times, and then vacuum dry at 120 ℃ to finally obtain benzocyclobutene-based polyimide PI-2.

[0046] The reaction equation is:

[0047] n=100000.

[0048] The preparation method of the blended gas separation membrane is as follows: (1) Preparation of polybenzimidazole casting solution: Dissolve 1g of polybenzimidazole in 10mL of trifluoroacetic acid (TFA), stir at room temperature for 2h until completely dissolved, and obtain polybenzimidazole casting solution.

[0049] (2) The benzocyclobutene polyimide was purified and dissolved in trifluoroacetic acid. At the same time, the above-mentioned polybenzimidazole casting solution was added and stirred at 35°C for 96 hours to obtain a blended film casting solution of benzocyclobutene-containing polyimide and polybenzimidazole material with a mass ratio of 1:1, and the solid content was controlled to be 10%.

[0050] (3) Allow the mixture to cool naturally to room temperature. Use a syringe to draw the mixture from the casting solution of the blended membrane. Then use a 25-0.45 µm polytetrafluoroethylene filter head for squeezing and filtration. Collect the filtrate and let it stand for 30 minutes to remove bubbles.

[0051] (4) The casting solution of the blended membrane was coated onto a smooth, flat-bottomed petri dish that had been leveled beforehand. The dish was then placed in a preheated drying oven at 60°C and dried at normal pressure for about 24 hours to remove most of the solvent. The thickness of the liquid membrane after solvent evaporation was controlled to be 50 µm. The membrane was then placed in a vacuum drying oven at 120°C and dried under vacuum for 4 hours to completely remove the solvent. After the vacuum drying oven cooled naturally to room temperature, the membrane was demolded to obtain a blended composite gas separation membrane containing benzocyclobutene, polyimide, and polybenzimidazole. The final thickness of the membrane was 40 µm.

[0052] Comparative Example 1 This comparative example provides a gas separation membrane, which differs from Example 1 only in that the gas separation membrane does not contain polybenzimidazole material, while the other raw materials and amounts are the same as in Example 1.

[0053] Comparative Example 2 This comparative example provides a gas separation membrane, which differs from Example 1 only in that the gas separation membrane does not contain benzocyclobutene-based polyimide material, while the other raw materials and amounts are the same as in Example 1.

[0054] Comparative Example 3 This comparative example provides a gas separation membrane, which is Matrimid 5218 (Reference: Prog. Polym. Sci. , 2019, 92, 35). 88; RSC Adv., 2016, 6, 23746 23759).

[0055] Comparative Example 4 This comparative example provides a gas separation membrane, which is P84 (Reference: Prog. Polym. Sci., 2019, 92, 35). 88; J. Membr. Sci., 2013, 428, 445 453).

[0056] Comparative Example 5 This comparative example provides a gas separation membrane, which is PI-1.00 (Reference Sep. Purif. Technol., Volume 282, Part B, 2022, 120091).

[0057] Performance testing The blended composite gas separation membranes described in Examples 1-2 and Comparative Examples 1-4 were tested as follows: (1) Gas separation performance: using constant volume The pressure swing method was used to evaluate the gas separation performance of the gas separation membranes provided in Examples 1-2 and Comparative Examples 1-5 for different single-component pure gases (H2, N2, O2, CO2, CH4) under the conditions of 35 °C and 1 bar feed gas pressure. During the test, a high-pressure chamber and a low-pressure chamber were located on opposite sides of the membrane, with the volume of the low-pressure chamber known. Before the test, both the high-pressure and low-pressure chambers were evacuated to a vacuum. Then, feed gas was introduced into the high-pressure chamber according to the test conditions. The test began when the pressure valve reading reached 1 bar. Gas permeated through the membrane into the low-pressure chamber, and the pressure change of the gas in the low-pressure chamber over time was recorded to calculate the permeability coefficient P. The ideal selectivity α was calculated by the ratio of the permeability coefficients of different gases. Detailed test steps and calculation formulas can be found in the reference (Macromolecules, 2014, 47, 7947). 7957).

[0058] (2) Mechanical properties: The prepared blended gas separation membrane was dried in an oven at 120 ℃, and the membrane was cut into 5 mm × 30 mm. The mechanical properties of the membrane were tested using an electronic universal testing machine (AGS-X-10kN).

[0059] The test results are summarized in Tables 1 and 2.

[0060] Table 1. Permeability and selectivity of gas separation membranes

[0061] Table 2 Glass transition temperature and tensile strength of gas separation membranes

[0062] As shown in Tables 1 and 2, the blended composite gas separation membrane provided by the present invention, by introducing benzocyclobutene and blending it with polybenzimidazole material, gives the blended composite gas separation membrane excellent mechanical properties, thermal stability and separation performance.

[0063] As shown in Examples 1-2, the blended composite gas separation membrane has high permeability coefficients for conventional gases H2 and CO2, high selectivity for H2 / CH4, H2 / N2, and CO2 / CH4, and a glass transition temperature >400 ℃, exhibiting excellent heat resistance; the tensile strength is 130~150 MPa. As shown in Examples 1-2 and Comparative Examples 1-2 and 3-4, the gas permeability and gas selectivity of the blended composite gas separation membrane provided by the present invention are significantly higher than those of membranes made from polyimide materials before blending, and it also has excellent heat resistance stability. The blended composite gas separation membrane is superior to commercially available polyimide separation membranes.

[0064] In summary, the blended composite gas separation membrane provided by this invention, by introducing benzocyclobutene groups into polyimide and then blending it with polybenzimidazole material, not only possesses excellent mechanical properties and thermal stability, but also high permeability and selectivity, making it suitable for the separation of conventional gases.

Claims

1. A blended composite gas separation membrane comprising a benzocyclobutene-based polyimide, characterized by, The benzocyclobutene-based polyimide and the polybenzimidazole contain chrysene base.

2. The blended composite gas separation membrane of claim 1, wherein, The blended composite gas separation membrane is obtained by blending a benzocyclobutene-based polyimide and a polybenzimidazole material. The mass ratio of the benzocyclobutene-based polyimide to the polybenzimidazole material is (1-10):(1-10). The thickness of the blended composite gas separation membrane is 5-100 µm.

3. The blended composite gas separation membrane according to claim 1 or 2, wherein, The benzocyclobutene-based polyimide has a structure shown in Formula I: Formula I; wherein R1 is an aromatic dianhydride residue, and n is an integer of 10-1,000,000.

4. The blended composite gas separation membrane of claim 3, wherein, The R1 is selected from any one of the following groups which are substituted or unsubstituted: 、 、 、 、 、 、 、 、 、 、 ； wherein the dotted line indicates the access position of the group; The substituted group of the R1 is independently selected from one of methyl, methoxy, halogen, hydroxyl, cyano, heteroaryl, heterocycloalkyl and amino.

5. The blended composite gas separation membrane according to any one of claims 1-2, wherein, The polybenzimidazole has a structure shown in Formula II: , formula II; The number ratio of y to x is (0-9):1; The R2, Ar are respectively selected from any one of the following groups which are substituted or unsubstituted: ； The R3 is selected from any one of the following groups which are substituted or unsubstituted: ； The substituted group of the R2, Ar and R3 is each independently selected from any one of halogen, -OH, -SO3H, -NO2, -H2PO4, unsubstituted or halogenated C1-C10 straight chain or branched alkyl.

6. The method of claim 1-5 for making a blended composite gas separation membrane, characterized in that, The method comprises the following steps: The benzocyclobutene-based polyimide solution and the polybenzimidazole solution are blended, the blended solution is subjected to ultrasonic degassing bubble treatment, and then is subjected to a film forming process to obtain a blended gas separation membrane containing benzocyclobutene-based polyimide and polybenzimidazole.

7. The production method according to claim 6, wherein The content of the polybenzimidazole in the blended solution is 1-30 wt%.

8. The preparation method according to claim 6, characterized in that, The solvent used for the solution of the benzocyclobutene-based polyimide material and the solution of the polybenzimidazole material is the same polar solvent; The polar solvent is selected from one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide and sulfolane.

9. The blended composite gas separation membrane of claims 1-5 or the blended composite gas separation membrane prepared by the method of claims 6-8 is used in gas separation.

10. Use according to claim 9, characterized in that, The application is for separating H2 / CH4, H2 / N2 and CO2 / CH4.

Images