Polymer, chlorine-containing polyimide gas separation composite membrane as well as preparation method and application of polymer and chlorine-containing polyimide gas separation composite membrane

Abstract

The invention discloses a polymer, a chlorine-containing polyimide gas separation composite membrane as well as a preparation method and application of the polymer and the chlorine-containing polyimide gas separation composite membrane. The structural unit of the polymer is shown as a formula I, the polymer can be dissolved in weak aprotic solvents (such as acetone and methylbenzene), and the characteristic provides convenient conditions for secondary processing. The polyimide is used as a coating material, and a base membrane cannot be dissolved by selecting a weak aprotic solvent. The difficulty that the polyimide gas separation membrane can only be prepared through a phase inversion method at present is solved. The method for preparing the gas separation composite membrane from polyimide disclosed by the invention is convenient and fast, greatly saves the material consumption of the separation layer, and has a wide application prospect.

Description

Technical Field

[0001] This application relates to a polymer, a chlorinated polyimide gas separation composite membrane, its preparation method and application, and belongs to the field of gas separation membranes. Background Technology

[0002] Membrane separation technology boasts advantages such as no phase change and low energy consumption, demonstrating immense industrial application potential in gas separation. Among numerous membrane materials, polyimide, as a polymer, exhibits superior comprehensive performance: excellent gas selectivity, high glass transition temperature, good thermal stability, and excellent chemical resistance. It can be processed and molded using various methods, making it a suitable membrane material. Since the mid-1980s, polyimide has begun to achieve excellent results in separation systems with strong industrial applications, such as H2 / N2, O2 / N2, He / CH4, CO2 / N2, and CO2 / CH4.

[0003] Polyimides are diverse in variety and form, and their synthesis involves multiple pathways, allowing for selection based on various applications. This synthetic flexibility is unmatched by other polymers. Polyimides are primarily aromatic heterocyclic polymers obtained through the condensation polymerization of dianhydrides and diamines. Compared to other heterocyclic polymers such as polybenzimidazole, polybenzoxazole, polybenzothiazole, and polyquinoline, these two monomers have a wider range of raw material sources and are easier to synthesize. Dihydrides and diamines are numerous, and different combinations can yield polyimides with varying properties. Aromatic polyimides, due to their rigid backbone's sieving effect on different molecules, exhibit high separation performance for a wide range of gases, making them promising for applications in gas separation. For polymeric gas separation membranes, permeability and selectivity are contradictory (trade-off phenomenon): highly permeable membranes often have low separation selectivity, while highly selective membranes often have very low permeability. Polyimide gas separation membranes exhibit good selectivity but low permeability, which hinders their ideal performance and significantly limits their application value in gas separation. Polyimide macromolecules offer diverse structures, and high-performance gas separation membrane materials can be obtained through molecular structure design. Based on this, many researchers have focused on molecular design, introducing special groups into the main chain of polyimide molecules (which have poor permeability but good separation selectivity) to disrupt the symmetry and regularity of the molecular structure. This reduces the intermolecular forces between rigid polyimide molecular chains, increases the free volume of the membrane, and improves permeability, aiming to obtain membrane materials with high selectivity and permeability.

[0004] Industrially applied polymer gas separation membranes are typically asymmetric structures. Currently, obtaining defect-free asymmetric polyimide membranes often involves using phase inversion methods to prepare gas separation membranes with dense functional layers. Polyimide types soluble in organic solvents are selected as membrane materials. A good solvent / additive mixture is used to prepare the casting solution, and a dry-wet phase inversion method is employed to obtain defect-free asymmetric polyimide membranes. However, the surface skin of such membranes is often too thick, resulting in low gas permeation rates. In the 1880s, Peinenann et al. used chlorinated hydrocarbons as solvents and acetone or toluene as coagulation baths to prepare defect-free asymmetric polyetherimide (Ultem) membranes using a dry-wet phase inversion method, achieving a He / CH4 separation coefficient higher than that of homogeneous membranes. However, chlorinated hydrocarbons are toxic, and the viscosity of Ultem in chlorinated hydrocarbons is too low, which is detrimental to practical operation. Composite membranes, with separate dense and porous support layers, have become an effective way to improve the permeation performance of gas separation membranes. Compared with asymmetric membranes prepared by phase inversion methods, composite membranes have the following characteristics:

[0005] (1) When the selected separation membrane material is expensive, the support layer material of the composite membrane can be made of inexpensive material, saving a lot of expensive materials.

[0006] (2) It broadens the range of asymmetric membrane materials. Some materials are difficult to make into asymmetric membranes by phase transformation, such as materials that are brittle. In this case, they can be made into composite membranes to achieve asymmetric forms.

[0007] (3) It is easier to obtain defect-free asymmetric films than the phase transformation method.

[0008] However, when polyimide is used as a functional layer gas separation membrane material, the biggest problem faced by using composite membrane fabrication is that traditional polyimide either has poor solubility or is only soluble in aprotic polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. These solvents are usually also good solvents for the support layer material, making it impossible to obtain a defect-free composite membrane by solution coating, thus limiting its application range.

[0009] Aromatic polyimides are poorly soluble in most solvents, making them difficult to process. The secondary processing of insoluble aromatic polyimides into films, coatings, and other components requires complex processes, such as agglomerating them into powders. Another approach to secondary processing involves using polyamic acid, a soluble precursor of insoluble polyimides, followed by thermal or chemical imidization to convert it into polyimide. This route is not only lengthy but also prone to defects due to the evaporation of water as a byproduct during imidization. Summary of the Invention

[0010] The purpose of this application is to provide a chlorinated polyimide gas separation membrane, which is prepared by solution coating to overcome the above-mentioned shortcomings. The polyimide has better solubility than ordinary polyimides. The introduction of halogen atoms into the polyimide molecular chain makes this type of polyimide soluble in a wide range of aprotic solvents, from N-methylpyrrolidone to toluene.

[0011] According to one aspect of this application, a polymer is provided, the structural unit of which is shown in Formula I:

[0012]

[0013] Where n is 1 to 1000;

[0014] Optionally, n can be 1 to 500;

[0015] Optionally, n can be 10 to 100;

[0016] R is a straight chain with a carbon chain length between 50 and 200;

[0017] The straight chain is composed of groups having a structure of formula A and groups having a structure of formula B;

[0018]

[0019]

[0020] In the straight chain, the content of groups having the structure of formula A is 50-100 mol%, excluding 50 mol%; when the content of groups having the structure of formula A is 100 mol%, groups having the structure of formula B are not present.

[0021] Optionally, the content of groups having the structure of formula A in the straight chain is 70-100 mol%.

[0022] Optionally, the content of groups having the structure of formula A in the straight chain is 80-100 mol%.

[0023] The number-average molecular weight (based on polystyrene standards) of the polymer is 10,000 to 200,000 g / mol;

[0024] Optionally, the number-average molecular weight of the polymer is 20,000 to 120,000 g / mol;

[0025] Optionally, the number-average molecular weight of the polymer is 20,000 to 100,000 g / mol;

[0026] The weight-average molecular weight of the polymer is 10,000 to 500,000 g / mol;

[0027] Optionally, the weight-average molecular weight of the polymer is 30,000 to 400,000 g / mol;

[0028] Optionally, the weight-average molecular weight of the polymer is 50,000 to 300,000 g / mol;

[0029] The polydispersity index of the polymer is 1 to 10.

[0030] Optionally, the polydispersity index of the polymer is 1.5 to 3.5.

[0031] Optionally, the polydispersity index of the polymer is 1.5 to 3.

[0032] According to another aspect of this application, a method for preparing the above-mentioned polymer is provided, comprising the following steps:

[0033] 4,4'-methylenebis(2-methyl-6-ethylaniline), 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and N-methylpyrrolidone were mixed, reacted, heated under reflux, washed, and dried to obtain the polymer.

[0034] The molar ratio of 4,4'-methylenebis(2-methyl-6-ethylaniline) to 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride is 1:0.9-1;

[0035] The ratio of 4,4'-methylenebis(2-methyl-6-ethylaniline) to N-methylpyrrolidone is 1 mol: 2500-3000 ml;

[0036] The reaction temperature is 20–200°C;

[0037] The reaction time is 16–24 hours;

[0038] The temperature of the heating reflux is 180–200°C;

[0039] The heating reflux time is 8–16 hours;

[0040] The drying temperature is 150–250°C;

[0041] The drying time is 24 to 48 hours.

[0042] The polymer can be dissolved in at least one of trichloroethylene, acetone, benzene, and toluene.

[0043] According to another aspect of this application, a chlorinated polyimide gas separation composite membrane is provided, containing the aforementioned polymer.

[0044] According to another aspect of this application, a method for preparing the above-mentioned chlorinated polyimide gas separation composite membrane is provided, comprising the following steps:

[0045] The polymer is mixed with a solvent to obtain a coating liquid. The coating liquid is then applied to the surface of a base membrane by dip coating and dried to obtain the chlorinated polyimide gas separation composite membrane.

[0046] The solvent is selected from at least one of trichloroethylene, acetone, benzene, and toluene;

[0047] In the coating liquid, the concentration of the polymer is 1-10 wt%;

[0048] Optionally, the concentration of the polymer in the coating liquid is 1 to 5 wt%.

[0049] Optionally, the concentration of the polymer in the coating liquid is 1 to 3 wt%.

[0050] The coating temperature is 25–30°C;

[0051] The coating time is 5 to 60 seconds;

[0052] Optionally, the coating time is 5 to 30 seconds;

[0053] Optionally, the coating time is 5 to 20 seconds;

[0054] The vacuum degree of the coating is 0 to -0.08 MPa;

[0055] Optionally, the vacuum degree of the coating is 0 to -0.06 MPa;

[0056] The drying temperature is 25–30°C;

[0057] The drying time is 0.5 to 2 hours.

[0058] The material of the base film is selected from at least one of polysulfone, polyvinylidene fluoride, polyacrylonitrile, and polyetherimide;

[0059] The base membrane is an ultrafiltration membrane or a microfiltration membrane;

[0060] The pore size of the base film is 0.001–1 μm;

[0061] Optionally, the pore size of the base film is 0.01–0.2 μm;

[0062] Optionally, the pore size of the base film is 0.01 to 0.05 μm.

[0063] According to another aspect of this application, an application of the above-mentioned chlorinated polyimide gas separation composite membrane is provided for air separation, hydrogen separation, decarbonization, and rare gas concentration.

[0064] The beneficial effects that this application can produce include:

[0065] The polyimide involved in this application is soluble in weakly aprotic solvents (such as acetone and toluene), a property that facilitates secondary processing. Using this type of polyimide as a coating material, weakly aprotic solvents will not dissolve the base membrane. This solves the current difficulty of preparing polyimide gas separation membranes only through phase inversion methods. The method for preparing gas separation composite membranes using the polyimide disclosed in this application is not only convenient but also significantly reduces the amount of separation layer material used, showing broad application prospects. Attached Figure Description

[0066] Figure 1 Infrared spectrum of 6FDA-MCDEA polyimide;

[0067] Figure 2 Results of 6FDA-MCDEA polyimide gel chromatography analysis;

[0068] Figure 3 The results are from the gel chromatography analysis of 6FDA / BTDA-MCDEA copolyimide. Detailed Implementation

[0069] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0070] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0071] Example 1

[0072] Under nitrogen protection, 0.2 mol of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) was added in portions to a stirred solution of 0.2 mol of 4,4'-methylenebis(2-methyl-6-ethylaniline) (MCDEA) and N-methylpyrrolidone (NMP) (500 ml). The reaction was carried out at 25 °C for 4 h, followed by slow heating to 190 °C and reflux for 6 h. The mixture was then slowly cooled to room temperature, and the product was precipitated in methanol. The precipitate was washed three times with anhydrous methanol, air-dried at room temperature for 1 h, and then further dried in a vacuum oven at 250 °C for 24 h to remove residual moisture and solvent. The product was then obtained after the oven cooled naturally to room temperature.

[0073] This polyimide is soluble in N-methylpyrrolidone, N,N-dimethylamide, dichloromethane, m-cresol, acetone, and toluene. The gas permeation properties of the polyimide were tested according to the method specified in GB / T 40260-2021. Gas permeation properties at 25℃ and 0.2 MPa: PH2 = 237.440 Barrer, PO2 = 14.637 Barrer, PHe = 240.877 Barrer, PCO2 = 79.875 Barrer; ideal separation coefficients αH2 / N2 = 56.01, αO2 / N2 = 3.45, αHe / CH4 = 67.85, αCO2 / CH4 = 22.51.

[0074] Figure 1 Infrared spectrum of 6FDA-MCDEA polyimide;

[0075] Depend on Figure 1 As can be seen, the formation of imide is confirmed by the absorption peaks at 1787 cm⁻¹ (C=O asymmetric stretching peak), 1728 cm⁻¹ (C=O symmetric stretching peak), 1358 cm⁻¹ (CN stretching peak), and 1064 cm⁻¹ (imine ring bending peak). Furthermore, the absence of a significant absorption peak near 3300 cm⁻¹ (NH and -OH stretching peaks) confirms that the imidization process was relatively complete.

[0076] Figure 2 The results of 6FDA-MCDEA polyimide gel chromatography analysis are as follows:

[0077]

[0078] (Relevance factor: 0.998880)

[0079] Depend on Figure 2 As can be seen, the Mn of 6FDA-MCDEA polyimide is 84010, Mw is 236229, and PD is 2.812.

[0080] Comparative Example 1

[0081] A 100ml dry four-necked flask equipped with a mechanical stirrer, thermometer, nitrogen inlet, and water separator was placed in a 20℃ constant temperature water bath. Under nitrogen protection, 50ml of N-methylpyrrolidone (NMP) was added, followed by 0.02mol of 4,4'-methylenebis(2-methyl-6-ethylaniline) (MMEA) with mechanical stirring. After complete dissolution, 0.02mol of 6FDA was added. The reaction was carried out at 20℃ for 4-24h to obtain a polyamic acid solution. 0.1mol of acetic anhydride and 0.1mol of triethylamine were added for chemical imidization. The reaction was stopped after 24h at room temperature, and the polymerization product was allowed to precipitate in anhydrous methanol. The product was then washed three times with anhydrous methanol, air-dried at room temperature for 1h, and further dried in a vacuum oven at 250℃ for 24h to remove residual moisture and solvent. The product was then removed after the oven had cooled naturally to room temperature.

[0082] This polyimide, 6FDA-MMEA, is soluble in N-methylpyrrolidone, N,N-dimethylamide, dichloromethane, and m-cresol, but insoluble in acetone and toluene. Compared to the 6FDA-MCDEA polyimide in Example 1, the 6FDA-MMEA polyimide structural unit does not contain chlorine atoms, while the other structures are identical. This indicates that the wide range of solubility of the 6FDA-MCDEA polyimide is due to the addition of chlorine atoms. The gas permeability of the polyimide was tested using the method specified in GB / T 40260-2021. Gas permeability at 25°C and 0.2 MPa: PO2 = 17.340 Barrer (1 Barrer = 1 × 10⁻⁶). -10 cm 3 (STP)·cm·cm -2 ·s -1 cmHg -1 The ideal separation coefficient αO2 / N2 = 3.80. Compared with the polyimide in Example 1, the polyimide in Comparative Example 1 lacks only chlorine atoms in its structure, resulting in a slightly higher permeability coefficient and similar separation coefficient.

[0083] Example 2

[0084] Under nitrogen protection, 0.02 mol of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added to a stirred solution of 0.2 mol of 4,4'-methylenebis(2-methyl-6-ethylaniline) (MCDEA) and N-methylpyrrolidone (NMP) (500 ml), followed by the addition of 0.18 mol of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA). The reaction was carried out at 25 °C for 4 h, followed by slow heating to 190 °C and reflux for 6 h. The mixture was then slowly cooled to room temperature, and the product was precipitated in methanol. The precipitate was washed three times with anhydrous methanol, air-dried at room temperature for 1 h, and then further dried in a vacuum oven at 250 °C for 24 h to remove residual moisture and solvent. The product was then obtained after the oven cooled naturally to room temperature.

[0085] This polyimide is soluble in N-methylpyrrolidone, N,N-dimethylamide, dichloromethane, m-cresol, acetone, and toluene. The gas permeation properties of the polyimide were tested according to the method specified in GB / T 40260-2021. Gas permeation properties at 25℃ and 0.2 MPa: PO2 = 10.116 Barrer, PHe = 199.671 Barrer, PCO2 = 57.158 Barrer; ideal separation coefficients αO2 / N2 = 3.51, αHe / CH4 = 87.58, αCO2 / CH4 = 25.07.

[0086] Figure 3 The results of gel chromatography analysis of 6FDA / BTDA-MCDEA copolyimide are as follows:

[0087]

[0088] (Relevance factor: 0.999612)

[0089] Depend on Figure 3 As can be seen, the Mn of the 6FDA / BTDA-MCDEA copolyimide is 51535, the Mw is 118187, and the PD is 2.293.

[0090] Example 3

[0091] 0.3 g of polyimide and 10 g of toluene from Example 1 were stirred at room temperature for 30 min, filtered, and allowed to stand for 2 h. A flat composite membrane was then prepared using a dip-coating method. After draining the water from the surface of the polyetherimide-based membrane (pore size 0.02–0.04 μm), it was placed in a mold on a glass plate. The coating liquid was poured into the mold for 10 s, and then the outlet valve at the bottom of the mold was opened to allow excess casting liquid to flow out. After drying at room temperature for 12 h, the coating process was repeated. The gas permeability of the composite membrane was tested after drying at room temperature for 12 h. Gas permeability at 25℃ and 0.2 MPa: P / L O2 = 90.3 GPUs (1 GPU = 1 × 10 -6 cm 3 (STP)·cm -2 ·s -1 cmHg -1 The ideal separation coefficient αO2 / N2 = 3.33.

[0092] Example 4

[0093] 10g of polyimide and 300g of toluene from Example 1 were stirred at room temperature for 30 minutes, filtered, and allowed to stand for 2 hours. A hollow fiber composite membrane was then prepared using a dip-coating method. Water was drained from the surface of the polyetherimide hollow fiber base membrane (pore size 0.02–0.04 μm, outer diameter 0.8 mm, inner diameter 0.5 mm), and the membrane was cut into 30 cm lengths. Twenty pieces were then used to fabricate U-shaped components using rapid epoxy coating. After 30 minutes, the components were installed in a vacuum coating fixture, and the entire fixture was immersed in the coating solution. The vacuum valve was opened, and the vacuum level was rapidly adjusted to -0.06 MPa. After 20 seconds, the membrane was removed and dried at room temperature for 6 hours. The gas permeability of the hollow fiber composite membrane was then tested. Gas permeability at 25℃ and 0.2 MPa: P / L O2 =88.4 GPUs, P / L He =1460 GPU, P / L CO2 =499.5 GPU; ideal separation coefficient αO2 / N2 = 3.58. αHe / CH4 = 70.25, αCO2 / CH4 = 24.03.

[0094] Comparative Example 2

[0095] In Example 1, 10g of polyimide and 300g of toluene were stirred at room temperature for 30 minutes, filtered, and allowed to stand for 2 hours. A hollow fiber composite membrane was then prepared using a dip-coating method. After draining the water from the surface of the polyetherimide hollow fiber base membrane (pore size 0.02–0.04 μm, outer diameter 0.8 mm, inner diameter 0.5 mm), it was cut into 30cm lengths. Twenty pieces were then used to fabricate U-shaped components using rapid epoxy coating. After 30 minutes, the components were immersed in the coating solution for 10 seconds, removed, and dried at room temperature for 6 hours. The coating process was repeated. After drying at room temperature for 6 hours, the gas permeability of the hollow fiber composite membrane was tested. Gas permeability at 25℃ and 0.2 MPa: P / L O2 =105.7 GPU; Ideal separation coefficient αO2 / N2 = 3.05.

[0096] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A polymer, characterized in that, The structural unit of the polymer is shown in Formula I: Where n is 1 to 1000; R is a straight chain with a carbon chain length between 50 and 200; The straight chain is composed of groups having a structure of formula A and groups having a structure of formula B; In the straight chain, the content of groups having the structure of formula A is 50-100 mol%, excluding 50 mol%. When the content of the group with the structure of formula A is 100 mol%, the group with the structure of formula B is not present; The number-average molecular weight of the polymer is 10,000 to 200,000 g / mol; The weight-average molecular weight of the polymer is 10,000 to 500,000 g / mol; The polydispersity index of the polymer is 1 to 10.

2. The polymer according to claim 1, characterized in that, n is 1 to 500; In the straight chain, the content of groups having the structure of formula A is 70-100 mol%. The number-average molecular weight of the polymer is 20,000 to 120,000 g / mol; The weight-average molecular weight of the polymer is 30,000 to 400,000 g / mol; The polydispersity index of the polymer is 1.5 to 3.

5.

3. The polymer according to claim 1, characterized in that, n is between 10 and 100; The linear chain contains 80–100 mol% groups having the structure of formula A. The number-average molecular weight of the polymer is 20,000 to 100,000 g / mol; The weight-average molecular weight of the polymer is 50,000 to 300,000 g / mol; The polydispersity index of the polymer is 1.5 to 3.

4. A method for preparing the polymer according to any one of claims 1 to 3, characterized in that, Includes the following steps: 4,4'-methylenebis(2-methyl-6-ethylaniline), 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and N-methylpyrrolidone were mixed, reacted, heated under reflux, washed, and dried to obtain the polymer.

5. The preparation method according to claim 4, characterized in that, The molar ratio of 4,4'-methylenebis(2-methyl-6-ethylaniline) to 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride is 1:0.9-1; The ratio of 4,4'-methylenebis(2-methyl-6-ethylaniline) to N-methylpyrrolidone is 1 mol: 2500-3000 ml; The reaction temperature is 20–200°C; The reaction time is 16–24 hours; The temperature of the heating reflux is 180–200°C; The heating reflux time is 8–16 hours; The drying temperature is 150–250°C; The drying time is 24 to 48 hours.

6. A chlorinated polyimide gas separation composite membrane, characterized in that, Contains the polymer according to any one of claims 1 to 3.

7. A method for preparing the chlorinated polyimide gas separation composite membrane according to claim 6, characterized in that, Includes the following steps: The polymer is mixed with a solvent to obtain a coating liquid. The coating liquid is then applied to the surface of a base membrane by dip coating and dried to obtain the chlorinated polyimide gas separation composite membrane.

8. The preparation method according to claim 7, characterized in that, The solvent is selected from at least one of trichloroethylene, acetone, benzene, and toluene; In the coating liquid, the concentration of the polymer is 1-10 wt%; Preferably, the concentration of the polymer in the coating liquid is 1-5 wt%. Preferably, the concentration of the polymer in the coating liquid is 1-3 wt%. The coating temperature is 25–30°C; The coating time is 5 to 60 seconds; Preferably, the coating time is 5 to 30 seconds; Preferably, the coating time is 5 to 20 seconds; The vacuum degree of the coating is 0 to -0.08 MPa; Preferably, the vacuum degree of the coating is 0 to -0.06 MPa; The drying temperature is 25–30°C; The drying time is 0.5 to 2 hours.

9. The preparation method according to claim 7, characterized in that, The material of the base film is selected from at least one of polysulfone, polyvinylidene fluoride, polyacrylonitrile, and polyetherimide; The base membrane is an ultrafiltration membrane or a microfiltration membrane; The pore size of the base film is 0.001–1 μm; Preferably, the pore size of the base film is 0.01–0.2 μm; Preferably, the pore size of the base film is 0.01 to 0.05 μm.

10. An application of the chlorinated polyimide gas separation composite membrane according to claim 6, characterized in that, Used for air separation, hydrogen separation, decarbonization, and rare gas concentration.

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