Repair method of low-selectivity polyimide gas separation membrane, polyimide gas separation membrane and application of polyimide gas separation membrane

Abstract

The invention discloses a repairing method of a low-selectivity polyimide gas separation membrane, the polyimide gas separation membrane and application of the low-selectivity polyimide gas separation membrane, and the repairing method comprises the steps that the low-selectivity polyimide membrane serves as a repairing object to be soaked in a swelling agent, after 1-12 h, the swelling agent is discharged, and the polyimide membrane is obtained; and drying the polyimide film by using a gradient heating method to finish repairing. According to the method, the organic solvent which has a swelling effect on polyimide acts on the selective layer of the membrane, so that the selective layer is promoted to swell, macromolecular chain segment rearrangement is realized, further pores of the selective layer are shrunk until being closed, the selectivity of the membrane is remarkably improved, and the industrial application requirements are met. The method successfully overcomes the defect that high selectivity of the low-selectivity polyimide film cannot be achieved through traditional PDMS secondary treatment, fills the blank of the prior art, has the advantages of being low in cost and easy to control, can be widely applied to the field of gas separation film preparation, and has good industrialization prospects and practical value.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology, and in particular to a method for repairing a low-selectivity polyimide gas separation membrane, the polyimide gas separation membrane, and its applications. Background Technology

[0002] In 1979, Monsanto's Prism membrane was successfully applied to hydrogen recovery in the ammonia synthesis process, marking the first industrial-scale application of gas separation membranes. Currently, the mainstream membrane materials in hydrogen recovery include cellulose acetate, polysulfone, polyimide, and polyarylamide. Among these, polyimide is the most widely used membrane material due to its excellent thermal stability, mechanical properties, solvent resistance, chemical stability, good film-forming properties, and diverse structures and properties.

[0003] From the perspective of practical application needs, gas separation membranes must exist in the form of asymmetric membranes. These membranes consist of a thin, dense separation layer (core separation functional layer) and a much thicker porous support layer (providing mechanical support). In order for polyimide materials to be transformed into gas separation membranes with practical application value, they must also be processed into asymmetric membrane structures.

[0004] Currently, the mainstream method for preparing polyimide asymmetric membranes in industry is the immersion gel phase inversion method, which is simple to operate and widely used. The asymmetric membranes prepared by this method have a dense selective layer thickness of only 0.02~0.1μm and a porous support layer thickness of 100~150μm. However, due to the characteristics of the preparation process, defects are easily generated in the selective layer, which directly leads to a decrease in the membrane separation efficiency. To compensate for this problem, secondary treatment methods such as PDMS pore plugging are often used in the industry. However, such traditional secondary treatments have strict requirements on the size and number of defects in the selective layer: if there are many defects in the selective layer and their size is large (i.e., the membrane selectivity is too low), it is impossible to achieve the optimization effect of high selectivity through traditional secondary treatment (JMS Henis, MKTripodi, Journal of Membrane Science, 8(1981)233-246).

[0005] Furthermore, with the increasing demand for energy conservation and emission reduction in the industrial sector, one of the core directions for the competitiveness of membrane technology is to make the selective layer thinner. This trend has significantly increased the difficulty of quality control of membrane products, making it easier for the selectivity to be too low during the production process. As a result, even after secondary treatment with traditional PDMS, it is still difficult to obtain a high-selectivity polyimide gas separation membrane. This technical bottleneck urgently needs to be overcome. Summary of the Invention

[0006] This invention addresses the problem of low selectivity in existing polyimide gas separation membranes, which persists even after secondary treatments such as silicone rubber plugging, failing to achieve high-selectivity polyimide membranes. It provides a method for repairing low-selectivity polyimide gas separation membranes, the resulting polyimide gas separation membrane, and its applications. Specifically, it uses an organic solvent with swelling properties to treat the selective layer of the membrane, causing swelling, polymer chain rearrangement, and reduction or even closure of the pores, thus significantly improving selectivity. This method effectively repairs low-selectivity polyimide membranes, giving them high selectivity to meet the needs of industrial applications.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: The present invention provides a method for repairing a low-selectivity polyimide gas separation membrane, comprising the steps of: immersing the low-selectivity polyimide membrane as the repair target in a swelling agent for 1-12 hours, removing the swelling agent to obtain the polyimide membrane, and drying the polyimide membrane using a gradient heating method to achieve the repair of the low-selectivity polyimide gas separation membrane.

[0008] Furthermore, the swelling agent is at least one selected from methanol, ethanol, propanol, isopropanol, butanol, ethyl acetate, and ethyl propionate.

[0009] Furthermore, the polyimide is a polymeric material containing an imide ring in its structure.

[0010] Furthermore, the oxygen and nitrogen selectivity of the low-selectivity polyimide film is less than 2.0.

[0011] Furthermore, the polyimide film is of the flat sheet type or the hollow fiber type.

[0012] Furthermore, the specific method of gradient heating is as follows: A polyimide gas separation membrane with significantly improved selectivity was obtained by purging with nitrogen at room temperature for 10~100 min, at 40℃ for 10~100 min, at 60℃ for 10~100 min, at 80℃ for 10~100 min, and at 100℃ for 10~100 min, followed by slow cooling at room temperature.

[0013] In another aspect, the present invention provides a polyimide gas separation membrane, which is obtained by repairing a low-selectivity polyimide gas separation membrane using the aforementioned repair method.

[0014] The final aspect of this invention provides the application of the aforementioned polyimide gas separation membrane in gas separation and recovery.

[0015] Furthermore, the specific applications include recovering hydrogen from hydrogen-containing gas mixtures, separating oxygen and nitrogen, separating CO2 and CH4, extracting helium from natural gas, or dehumidifying gases.

[0016] The beneficial effects of this invention are: (1) The present invention discloses a method for repairing a low-selectivity polyimide gas separation membrane. The selective layer of the low-selectivity polyimide gas separation membrane is treated with an organic solvent that has a swelling effect on polyimide, which causes the selective layer to swell and realize the rearrangement of polymer chain segments, thereby reducing and even closing the pores in the selective layer, and finally achieving a significant improvement in the selectivity of the low-selectivity polyimide gas separation membrane, so that it meets the high selectivity requirements required for industrial applications. (2) This repair method successfully overcomes the drawback that traditional PDMS secondary treatment cannot make low-selectivity polyimide gas separation membranes obtain high selectivity, and fills the technical gap in the field of low-selectivity polyimide membrane repair. (3) This repair method has the advantages of low cost and easy control, and can be widely used in the preparation of gas separation membranes. It has good industrialization prospects and practical value. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a testing device for the gas separation membrane used in this invention.

[0019] In the diagram: 1. Gas cylinder; 2. Pressure reducing valve; 3. First pressure gauge; 4. Second pressure gauge; 5. Membrane evaluation tank; 6. Temperature control system; 7. Soap bubble flow meter. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The permeation and separation performance of the gas separation membranes prepared in the embodiments and comparative examples of this invention are based on the permeation rate of pure gas. Jand separation coefficient α To characterize.

[0022] The testing apparatus for the gas separation membrane used in this invention is as follows: Figure 1 As shown, gas cylinder 1 is connected to membrane evaluation cell 5 via pressure reducing valve 2. A first pressure gauge 3 is also installed between pressure reducing valve 2 and membrane evaluation cell 5. A second pressure gauge 4 is installed at the end of membrane evaluation cell 5. Membrane evaluation cell 5 is connected to soap bubble flow meter 7 via pipeline. Membrane evaluation cell 5 is also equipped with temperature control system 6. Membrane evaluation cell 5 contains the prepared hollow fiber membrane test assembly or sample hollow fiber membrane test sheet for testing. The equipment is also equipped with conventional devices such as temperature sensors and pressure sensors to monitor the temperature and pressure of the device in real time.

[0023] The procedure for preparing the hollow fiber membrane test assembly is as follows: Take a hollow fiber membrane sample to be tested, approximately 150 mm in length, bundle 10 strands together, cast the open end with epoxy resin onto an aluminum end cap, and seal the other end with epoxy resin. For example... Figure 1 As shown, the test assembly was fixed in a stainless steel membrane evaluation cell 5. The raw material gas used in the test was passed outside the hollow fiber membrane, and the volumetric flow rate of the gas was measured using a soap bubble flow meter 7. The membrane permeate side pressure was maintained at atmospheric pressure, and the temperature of the test system was 25 °C.

[0024] Before the experiment, the testing device needs to be stabilized under the selected conditions for at least 2 hours before use. The gas flow rate is measured by the soap bubble flow meter 7, and the permeation rate (J) is calculated by equation (1): (1) In formula (1): V—Permeate gas flux under test conditions (cm³) 3 ); A—Effective membrane area (cm²) 2 ); Δp — membrane pressure difference (cm Hg); T0, p0 — Temperature (K) and pressure (cm Hg) under the test conditions; Ideal selectivity of the membrane α i / j Defined as the permeation rate of the two gases in the gas to be separated. Ji and Jj The ratio is calculated using the formula (2): (2) In equation (2), i and j represent two different gases to be separated.

[0025] The raw material information involved in the embodiments of this solution is as follows: Polyimide (P84): Purchased from Evonik; N-methylpyrrolidone (NMP), n-hexane, ethanol, isopropanol, ethyl acetate, analytical grade, Tianjin Kemeio; PDMS silicone rubber, Sylgard 184, Dow Corning.

[0026] Example 1: A method for repairing a low-selectivity polyimide gas separation membrane includes the following steps: S1: Preparation of polyimide hollow fiber membrane P84 was dissolved in NMP at a concentration of 28.5 wt.%, and heated and stirred at 50°C to form a mixed solution. After vacuum degassing, a dry-wet spinning process was used for spinning. The spinning solution was filtered and extruded through a nozzle. A water and NMP mixed solution (NMP / H2O = 90 / 10) was used as the core solution. The spinning temperature was 50°C, the dry spinning distance was 5 cm, the spinning solution flow rate was 2.0 mL / min, the nozzle size was 0.2 / 0.4 / 0.6 mm, the core solution flow rate at room temperature was 0.6 mL / min, the traction speed was 18 m / min, and a pure hydrogel bath was used. After collection with a winding wheel, residual solvent was removed by washing with flowing water in a water tank. After 2 days, the membrane was removed, solvent exchanged with methanol for 2 h, and then dried in air for 12 h, followed by drying at 120°C for 2 h to obtain a polyimide hollow fiber membrane.

[0027] S2: Separation layer repair: S21: The polyimide gas separation membrane from step S1 is encapsulated to form a hollow fiber membrane module. Isopropanol is injected into the shell side of the module and kept for 2 hours after filling. Then the isopropanol is discharged. S22: Gradient Temperature Drying: The polyimide hollow fiber membrane module obtained in step S21 was dried using a gradient temperature method. Specifically, the process was as follows: nitrogen purging at room temperature for 60 min, nitrogen purging at 40℃ for 60 min, nitrogen purging at 60℃ for 60 min, nitrogen purging at 80℃ for 60 min, and nitrogen purging at 100℃ for 60 min. The temperature was then slowly lowered to room temperature. The test results were: J N2 =2.3 GPU, J O2 =9.4 GPU, α O2 / N2 =4.1.

[0028] S3: PDMS post-treatment: The two-component PDMS was dissolved in n-hexane at a ratio of 10:1, with a mass concentration of 5 wt.%. The permeate side of the hollow fiber membrane obtained in step (1) was vacuum-immersed in the PDMS solution for 15 min, removed, air-dried at room temperature, and then dried at 80℃ for 1 h. The PDMS-post-treated polyimide hollow fiber membrane was obtained, and the test results were as follows: J N2 =0.73 GPU, J O2 =7.1 GPU, α O2 / N2 =9.6.

[0029] The above results show that the selectivity of the polyimide gas separation membrane repaired by this method is improved from 1.6 to 4.1. After PDMS post-treatment to remove organic fluids, the selectivity of the membrane is close to the intrinsic value of the material.

[0030] Example 2: A method for repairing a low-selectivity polyimide gas separation membrane includes the following steps: S1: The preparation method of the polyimide hollow fiber membrane is the same as in Example 1; S2: Separation layer repair: S21: The polyimide gas separation membrane of S1 is encapsulated to form a hollow fiber membrane module. Ethyl acetate is injected into the shell side of the module and kept for 4 hours after filling. Then the ethyl acetate is discharged. S22: Gradient Temperature Drying: The polyimide hollow fiber membrane module obtained in S21 was dried using a gradient temperature method. Specifically: nitrogen purging at room temperature for 60 min, nitrogen purging at 40℃ for 60 min, nitrogen purging at 60℃ for 60 min, nitrogen purging at 80℃ for 60 min, and nitrogen purging at 100℃ for 60 min. The temperature was then slowly lowered to room temperature. The test results were: J N2 =1.8 GPU, J O2 =10.3 GPUs, α O2 / N2 =5.7.

[0031] S3: PDMS post-treatment is the same as in Example 1; a polyimide hollow fiber membrane post-treated with PDMS is obtained, and the test results are: J N2 =0.86 GPU, J O2 =8.1 GPU, α O2 / N2 =9.4.

[0032] The above results show that the selectivity of the polyimide gas separation membrane repaired by this method is improved from 1.6 to 5.7, and after PDMS post-treatment, the selectivity is close to the intrinsic value of the material.

[0033] Comparative Example 1: A traditional method for preparing a polyimide gas separation membrane involves the following steps: S1: The preparation method of the polyimide hollow fiber membrane is the same as in Example 1; after obtaining the polyimide hollow fiber membrane, it was made into a small component and tested. The test results are: J N2 =32.6 GPU, J O2 =52.7 GPU, α O2 / N2 =1.6.

[0034] S2: PDMS post-treatment: Two-component PDMS was dissolved in n-hexane at a ratio of 10:1, with a mass concentration of 5 wt.%. The hollow fiber membrane obtained in S1 was immersed in the PDMS solution under vacuum for 15 min, then removed, air-dried at room temperature, and finally dried at 80℃ for 1 h. The resulting polyimide hollow fiber membrane after PDMS post-treatment was obtained. The test results are as follows: J N2 =3.1 GPU, J O2 =11.6 GPUs, α O2 / N2 =3.7.

[0035] The above results show that the selectivity of the polyimide gas separation membrane prepared in method S1 of Comparative Example 1 is much lower than the intrinsic selectivity of P84 material, and there are too many defects. Even after the repair in step (2), the selectivity (3.7) is still significantly lower than its intrinsic selectivity (10.0, Journal of Membrane Science 216 (2003) 195-205).

[0036] Comparative Example 2: A traditional method for preparing a polyimide gas separation membrane involves the following steps: S1: Preparation of polyimide hollow fiber membrane: P84 and ethanol were dissolved in NMP, with a P84 concentration of 28.5 wt.% and an ethanol concentration of 1.5 wt.%. The mixture was heated and stirred at 50°C to form a mixed solution. After vacuum degassing, the solution was spun using a dry-wet spinning process. The spinning solution was filtered and extruded through a nozzle. A mixed solution of water and NMP (NMP / H2O = 90 / 10) was used as the core solution. The spinning temperature was 50°C, the dry spinning distance was 10 cm, the spinning solution flow rate was 2.0 mL / min, the nozzle size was 0.2 / 0.4 / 0.6 mm, the core solution flow rate at room temperature was 0.6 mL / min, the traction speed was 18 m / min, and a pure hydrogel bath was used. After collection with a winding wheel, the membrane was washed with flowing water in a water tank to remove residual solvent. After 2 days, the membrane was removed, subjected to methanol solvent exchange for 2 h, and then air-dried for 12 h, followed by drying at 120°C for 2 h to obtain the polyimide hollow fiber membrane. After creating the widget and testing it, the test result was: J N2 =3.1 GPU, J O2 =7.1 GPU, α O2 / N2 =2.3.

[0037] S2: PDMS post-treatment: Two-component PDMS was dissolved in n-hexane at a ratio of 10:1, with a mass concentration of 5 wt.%. The hollow fiber membrane obtained in S1 was immersed in the PDMS solution under vacuum for 15 min, then removed, air-dried at room temperature, and finally dried at 80℃ for 1 h. The resulting polyimide hollow fiber membrane after PDMS post-treatment was obtained. The test results are as follows: J N2 =0.51 GPU, JO2 =4.8 GPUs, α O2 / N2 =9.4.

[0038] Using the method of Comparative Example 2, the gas separation membrane obtained in S1 has a higher selectivity than that of Comparative Example 1, but is much lower than the gas separation membranes obtained in S1 of Examples 1 and 2. After PDMS repair, the selectivity of the polyimide hollow fiber membrane in Comparative Example 2 is 9.4, which is close to the intrinsic selectivity of P84 material, but its nitrogen permeation flux J is lower. N2 Oxygen osmotic flux J O2 All were lower than the corresponding permeation flux of the membranes repaired by the methods in Examples 1 and 2.

[0039] Example 3 This embodiment provides a method for a refinery to recover hydrogen from a hydrogen-containing gas mixture. The polyimide gas separation membrane of Example 2 is used in this embodiment.

[0040] The hydrogen-containing gas mixture has a pressure of 13.8 barG, a temperature of 30.2℃, and a flow rate of 13458.95 Nm³. 3 / hr, the composition is shown in Table 1.

[0041] Table 1 Composition of hydrogen-containing gas mixture

[0042] The specific process for recovering hydrogen from a hydrogen-containing gas mixture is as follows: The gas mixture to be separated first enters a gas-liquid separator to remove liquid hydrocarbons, then passes through a coalescing filter to remove any entrained droplets and dust, and then enters a heater to be heated to 80°C to ensure that the gas entering the membrane separator is far from the dew point and to prevent droplet condensation on the membrane surface. The heated gas then enters the membrane separator for hydrogen enrichment. The membrane separator is filled with a polyimide gas separation membrane prepared according to the method in Example 2. After passing through the membrane separator, hydrogen is enriched at a relatively fast rate; this gas is called product hydrogen, with a purity of 72.2%, a hydrogen yield of 82.5%, a pressure of 0.5 barG, and a flow rate of 3715.72 Nm³. 3 / hr, can enter the PSA adsorption unit for further purification, and the specific composition of the product hydrogen is shown in Table 2.

[0043] Table 2 Composition of Hydrogen in the Product

[0044] The remaining gas after passing through the membrane separator is called permeate or tail gas. The hydrogen purity in the permeate is 5.82%, the pressure is 11.9 barG, and the flow rate is 9743.23 Nm³. 3 / hr. It can be introduced into the fuel gas pipeline network and used as fuel gas. The specific composition of the residual gas is shown in Table 3.

[0045] Table 3 Composition of residual gas

[0046] The above data shows that the polyimide gas separation membrane prepared in Example 2 can effectively concentrate and recover hydrogen in a refinery mixture containing 24.14% hydrogen through membrane separation. The product has a hydrogen purity of 72.17% and a hydrogen recovery rate of 82.5%, which can be further purified in the PSA unit. The residual gas is then used as fuel gas for resource utilization, significantly improving the resource value and utilization efficiency of hydrogen in the mixture.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for repairing a low-selectivity polyimide gas separation membrane, characterized in that, The steps include: immersing a low-selectivity polyimide membrane as the object of repair in a swelling agent for 1-12 hours, then removing the swelling agent to obtain the polyimide membrane, and drying the polyimide membrane using a gradient heating method to achieve the repair of the low-selectivity polyimide gas separation membrane.

2. The method for repairing the low-selectivity polyimide gas separation membrane according to claim 1, characterized in that, The swelling agent is at least one of methanol, ethanol, propanol, isopropanol, butanol, ethyl acetate, and ethyl propionate.

3. The method for repairing the low-selectivity polyimide gas separation membrane according to claim 1, characterized in that, The polyimide is a polymeric material containing an imide ring in its structure.

4. The method for repairing the low-selectivity polyimide gas separation membrane according to claim 1, characterized in that, The oxygen and nitrogen selectivity of the low-selectivity polyimide film is less than 2.

0.

5. The method for repairing the low-selectivity polyimide gas separation membrane according to claim 1, characterized in that, The polyimide film is of either flat sheet type or hollow fiber type.

6. The method for repairing the low-selectivity polyimide gas separation membrane according to claim 1, characterized in that, The specific method of gradient heating is as follows: Purge with nitrogen at room temperature for 10-100 min, at 40℃ for 10-100 min, at 60℃ for 10-100 min, at 80℃ for 10-100 min, and at 100℃ for 10-100 min, then slowly cool down at room temperature.

7. A polyimide gas separation membrane, characterized in that, It is obtained by repairing the low-selectivity polyimide gas separation membrane using the repair method described in claim 1.

8. The application of the polyimide gas separation membrane as described in claim 7 in gas separation and recovery.

9. The application according to claim 8, characterized in that, The specific applications include recovering hydrogen from hydrogen-containing gas mixtures, separating oxygen and nitrogen, separating CO2 and CH4, extracting helium from natural gas, or dehumidifying gases.

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