LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane and its preparation method and application

Abstract

The present invention relates to the technical field of separation membrane materials, and in particular to LaFe perovskite @ ZIF‑8 modified polyimide hollow fiber membrane and its preparation method and application, wherein the modified polyimide hollow fiber membrane includes LaFe perovskite, ZIF‑8 and polyimide, and the mass ratio of LaFe perovskite, ZIF‑8 and polyimide is 1:(1-4):(30-50). The LaFe perovskite @ ZIF‑8 modified polyimide hollow fiber membrane of the present invention can efficiently separate helium by utilizing the excellent molecular sieving effect of ZIF‑8, and the perovskite itself has excellent stability, which can effectively prevent the movement of polymer segments, thereby inhibiting the plasticization of the membrane. LaFe perovskite and ZIF‑8 synergistically improve membrane permeability and anti-plasticization performance, and have great potential for industrial application in natural gas helium extraction.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membrane materials, and in particular to a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane and a preparation method and application thereof. Background Art

[0002] Helium is a rare, non-renewable gas that is widely used in cryogenics (especially cooling of superconducting magnets), military industry, scientific research, petrochemicals, refrigeration, medical treatment, semiconductors, pipeline leak detection, superconducting experiments, metal manufacturing, deep-sea diving, high-precision welding, optoelectronic products, and magnetic resonance imaging scanning technology. The main source of helium is natural gas, which is usually at a low concentration. The concentration of helium in my country is less than 0.2%. If traditional separation technology (such as cryogenic distillation and pressure swing adsorption) is used, the energy consumption will be very high, greatly increasing the cost of helium extraction, which has an adverse effect on medical, industrial applications, and basic research. At present, the application of membrane separation technology is becoming more and more widespread. It can also be used for helium separation. It can separate high-purity helium under mild conditions, is easy to industrialize, is environmentally friendly, and has low energy consumption. It has great potential in gas separation applications.

[0003] Membrane separation technology can purify high-purity gas at low energy consumption, but there are also many problems in practical applications, such as plasticization, low flux and being subject to Robeson upper limit. Chinese patent CN102892485A discloses a polyimide hollow fiber membrane for air separation. The hollow fiber membrane has an O2 permeability of more than 300 GPU and an O2 / N2 selectivity of more than 3 at 308 kPa and 60 ° C, and a CO2 permeability of more than 1000 GPU and a CO2 / CH4 gas selectivity of more than 20 at 791 kPa and 50 ° C. Although this method has a high flux, it has a low selectivity. The literature [Journal of Materials Processing Technology 186 (2007) 102–110] developed a carbon hollow fiber membrane with a helium flux of up to 24 GPU and a He / CH4 selectivity of up to 137. The selectivity is good, but the helium flux is low and the preparation process is cumbersome. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane and a preparation method and application thereof, so as to at least solve the problems of low selectivity and low helium flux existing in the prior art.

[0005] The present invention solves the above technical problems by the following technical means:

[0006] In a first aspect, the present invention provides a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane, comprising LaFe perovskite, ZIF-8 and polyimide, wherein the mass ratio of the LaFe perovskite, ZIF-8 and polyimide is 1:(1-4):(30-50).

[0007] The present invention sets the mass ratio of LaFe perovskite, ZIF-8 and polyimide so as to give full play to the synergistic effect between perovskite and ZIF-8 and improve the membrane separation effect. The LaFe perovskite in the present invention itself has a stable structure, which can prevent the movement of the polyimide chain segment, prevent it from plasticizing, and improve its performance stability. Moreover, there is a synergistic effect between perovskite and ZIF-8, which further improves the separation effect.

[0008] In a second aspect, the present invention provides a method for preparing a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane, comprising the following steps:

[0009] Preparation of LaFe perovskite: lanthanum nitrate hexahydrate, iron nitrate nonahydrate and citric acid are weighed and added into a ball mill, and then dried and calcined at 700-900° C. for 8-12 hours to obtain LaFe perovskite;

[0010] Preparation of casting solution: weigh the dried polyimide and pour it into the solvent, stir it at 25-80° C. for 12-24 hours, add LaFe perovskite and ZIF-8 in sequence, stir it at 60-100° C. for 8-12 hours, cool it and let it stand for degassing to obtain LaFe perovskite@ZIF-8 modified polyimide casting solution, wherein the mass ratio of LaFe perovskite, ZIF-8 and polyimide is 1:(1-4):(30-50);

[0011] The preparation of the hollow fiber membrane comprises the following steps: taking nitrogen-methylpyrrolidone and deionized water in a mass ratio of (8-19):1 and stirring to obtain a core liquid; pouring the core liquid and the casting liquid into a spinning machine kettle; and then controlling the flow rate to simultaneously flow through the spinneret into a condensation tank; the mass flow rate ratio of the core liquid to the casting liquid is 1:(1-3); spinning to obtain a hollow fiber membrane; and then soaking it in pure water or ethanol for 2-3 days and drying it to obtain a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane.

[0012] In combination with the second aspect, in some embodiments, the molar ratio of the lanthanum nitrate hexahydrate, the ferric nitrate nonahydrate and the citric acid is 1:1:1-3.

[0013] In combination with the second aspect, in some embodiments, in the preparation of the LaFe perovskite, lanthanum nitrate hexahydrate, ferric nitrate nonahydrate and citric acid are weighed and added to a ball mill, the ball mill is operated at a speed of 500 to 2000 r / min for 12 to 24 hours, and then dried at 80 to 100° C. for 12 to 24 hours.

[0014] In combination with the second aspect, in some embodiments, the drying conditions of the polyimide are as follows: the polyimide is vacuum dried at 80 to 110° C. for 8 to 24 hours.

[0015] In combination with the second aspect, in some embodiments, the polyimide is any one of Matrimid 5218 or P84, the solvent is any one of nitrogen-methylpyrrolidone, N,N-dimethylacetamide, and chloroform, and the mass of the polyimide accounts for 10 to 30 wt % of the mass of the solvent.

[0016] In combination with the second aspect, in some embodiments, the preparation method of ZIF-8 is as follows: weigh zinc nitrate hexahydrate and dissolve it in methanol to form solution A, weigh 2-methylimidazole and dissolve it in methanol to form solution B, mix solution A and solution B and stir at room temperature for 1 to 2 hours, centrifuge, wash with methanol 2 to 3 times, and then dry at 60 to 80°C for 12 to 24 hours to obtain ZIF-8.

[0017] In combination with the second aspect, in some embodiments, the mass concentration of solution A is 0.02-0.03 g / mL, the mass concentration of solution B is 0.04-0.06 g / mL, and the mass ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:(2-4).

[0018] In combination with the second aspect, in some embodiments, the temperature of the spinneret is controlled at 50-70° C., the temperature of the condensation tank is controlled at 0-10° C., and the distance between the spinneret and the condensation tank is 1-5 cm.

[0019] In a third aspect, the present invention further provides the use of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane described in the first aspect or the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane prepared by the preparation method described in the second aspect in helium separation.

[0020] The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane of the present invention can efficiently separate helium by utilizing the excellent molecular sieving effect of ZIF-8. The perovskite itself has excellent stability and can effectively prevent the movement of polymer segments, thereby inhibiting the plasticization of the membrane and improving the membrane stability. LaFe perovskite and ZIF-8 synergistically improve the membrane permeability and anti-plasticization performance, and have great potential for industrial application in natural gas helium extraction.

[0021] The preparation method of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane of the present invention is simple and easy to operate, the raw materials are easily available and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of a hollow fiber membrane module;

[0023] Figure 2 is a stability diagram of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane prepared in Example 1;

[0024] Figure 3 This is a stability diagram of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane prepared in Example 4. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The raw materials, equipment or instruments used, if no manufacturer is specified, are all conventional products that can be purchased on the market.

[0027] The present invention provides a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane and a preparation method thereof. The excellent molecular sieving effect of ZIF-8 can be used to efficiently separate helium. The perovskite itself has excellent stability and can effectively prevent the movement of polymer chain segments, thereby inhibiting the plasticization of the membrane. The membrane has great potential for industrial application in natural gas helium extraction.

[0028] Specifically, the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane of the present invention comprises LaFe perovskite, ZIF-8 and polyimide, and the mass ratio of the LaFe perovskite, ZIF-8 and polyimide is 1:(1-4):(30-50).

[0029] The preparation method of LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane is as follows:

[0030] Preparation of LaFe perovskite: lanthanum nitrate hexahydrate, iron nitrate nonahydrate and citric acid are weighed and added into a ball mill, and then dried and calcined at 700-900° C. for 8-12 hours to obtain LaFe perovskite;

[0031] Preparation of casting solution: weigh the dried polyimide and pour it into the solvent, stir it at 25-80° C. for 12-24 hours, add LaFe perovskite and ZIF-8 in sequence, stir it at 60-100° C. for 8-12 hours, cool it and let it stand for degassing to obtain LaFe perovskite@ZIF-8 modified polyimide casting solution, wherein the mass ratio of LaFe perovskite, ZIF-8 and polyimide is 1:(1-4):(30-50);

[0032] The preparation of the hollow fiber membrane comprises the following steps: taking nitrogen-methylpyrrolidone and deionized water in a mass ratio of (8-19):1 and stirring to obtain a core liquid; pouring the core liquid and the casting liquid into a spinning machine kettle; and then controlling the flow rate to simultaneously flow through the spinneret into a condensation tank; the mass flow rate ratio of the core liquid to the casting liquid is 1:(1-3); spinning to obtain a hollow fiber membrane; and then soaking it in pure water or ethanol for 2-3 days and drying it to obtain a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane.

[0033] The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane and its preparation method of the present invention are described in detail below through implementation 1-4:

[0034] Example 1

[0035] The preparation method of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane of this embodiment is as follows:

[0036] (1) Preparation of LaFe perovskite: LaFe perovskite was prepared by ball milling. 20 g of lanthanum nitrate hexahydrate, 18.6 g of ferric nitrate nonahydrate and 8.9 g of citric acid were weighed in sequence and placed in a ball mill. The mill was operated at 500 r / min for 12 h, then dried at 80 °C for 12 h, and then calcined at 700 °C for 8 h to obtain LaFeO3 perovskite.

[0037] (2) Preparation of ZIF-8

[0038] Weigh 20 g of zinc nitrate hexahydrate and dissolve it in 1000 mL of methanol to form solution A, weigh 40 g of 2-methylimidazole and dissolve it in 1000 mL of methanol to form solution B, mix solutions A and B, stir at room temperature for 1 h, then centrifuge, wash twice with methanol, and then dry at 60° C. for 12 h to obtain ZIF-8.

[0039] (3) Preparation of LaFe perovskite@ZIF-8 modified polyimide film solution

[0040] The polyimide was vacuum dried at 80°C for 8h, then 300g of Matrimid 5218 was weighed and poured into 3000g of NMP, stirred at 80°C for 12h, and then 30g of LaFe perovskite and 30g of ZIF-8 were added to the Matrimid 5218 solution in sequence, stirred at 60°C for 8h, cooled and allowed to stand for degassing for 2 days to obtain LaFe perovskite-ZIF-8 modified polyimide casting solution.

[0041] (4) Preparation of core fluid

[0042] Weigh NMP and deionized water, mix and stir at room temperature for 1 h to obtain core liquid, and the mass ratio of NMP to water is 8:1.

[0043] (5) Preparation of LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane

[0044] LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane was prepared by dry-wet method. The core liquid and casting liquid were poured into the spinning machine kettle, and then the mass flow rate was controlled to be 1:1. At the same time, it flowed through the spinneret into the condensation tank. The temperature of the spinneret was controlled at 50°C, the distance between the spinneret and the condensation tank was 1 cm, and the temperature of the condensation tank was controlled at 0°C to obtain a hollow fiber membrane. It was then soaked in pure water for 2 days and dried at room temperature for 1 week to obtain a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane.

[0045] Example 2

[0046] The preparation method of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane of this embodiment is as follows:

[0047] (1) Preparation of LaFe perovskite

[0048] LaFe perovskite was prepared by ball milling. 20 g of lanthanum nitrate hexahydrate, 18.6 g of ferric nitrate nonahydrate and 26.6 g of citric acid were weighed in turn and put into a ball mill. The mill was operated at 2000 r / min for 24 h, then dried at 100 °C for 24 h, and then calcined at 900 °C for 8 h to obtain LaFeO3 perovskite.

[0049] (2) Preparation of ZIF-8

[0050] Weigh 20 g of zinc nitrate hexahydrate and dissolve it in 667 mL of methanol to form solution A, weigh 80 g of 2-methylimidazole and dissolve it in 1333 mL of methanol to form solution B, mix solutions A and B and stir at room temperature for 2 h, then centrifuge, wash with methanol three times, and then dry at 80° C. for 24 h to obtain ZIF-8.

[0051] (3) Preparation of LaFe perovskite@ZIF-8 modified polyimide film solution

[0052] The polyimide was vacuum dried at 110°C for 24 hours, then 300g of P84 was weighed and poured into 1000g of chloroform, stirred at 60°C for 24 hours, and then 6g of LaFe perovskite and 24g of ZIF-8 were added to the P84 solution in sequence, stirred at 100°C for 12 hours, cooled and allowed to stand for degassing for 3 days to obtain LaFe perovskite@ZIF-8 modified polyimide casting solution.

[0053] (4) Preparation of core fluid

[0054] Weigh NMP and deionized water, mix and stir at room temperature for 1 h to obtain core liquid, and the mass ratio of NMP to water is 19:1.

[0055] (5) Preparation of LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane

[0056] LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane was prepared by dry-wet method. The core liquid and casting liquid were poured into the spinning machine kettle, and then the mass flow rate was controlled at 1:3. At the same time, it flowed through the spinneret into the condensation tank. The temperature of the spinneret was controlled at 70°C, the distance between the spinneret and the condensation tank was 5 cm, and the temperature of the condensation tank was controlled at 10°C to obtain a hollow fiber membrane. It was then soaked in pure water for 3 days and dried at room temperature for 2 weeks to obtain LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane.

[0057] Example 3

[0058] The preparation method of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane of this embodiment is as follows:

[0059] (1) Preparation of LaFe perovskite

[0060] LaFe perovskite was prepared by ball milling. 20 g of lanthanum nitrate hexahydrate, 18.6 g of ferric nitrate nonahydrate and 26.6 g of citric acid were weighed in turn and put into a ball mill. The mill was operated at 2000 r / min for 24 h, then dried at 100 °C for 24 h, and then calcined at 900 °C for 8 h to obtain LaFeO3 perovskite.

[0061] (2) Preparation of ZIF-8

[0062] Weigh 20 g of zinc nitrate hexahydrate and dissolve it in 667 mL of methanol to form solution A, weigh 80 g of 2-methylimidazole and dissolve it in 1333 mL of methanol to form solution B, mix solutions A and B and stir at room temperature for 2 h, then centrifuge, wash with methanol three times, and then dry at 80° C. for 24 h to obtain ZIF-8.

[0063] (3) Preparation of LaFe perovskite@ZIF-8 modified polyimide film solution

[0064] The polyimide was vacuum dried at 110°C for 24 hours, then 300g of P84 was weighed and poured into 1000g of NMP and stirred at 60°C for 24 hours. Then 6g of LaFe perovskite and 24g of ZIF-8 were added to the P84 solution in sequence and stirred at 100°C for 12 hours. After cooling, it was allowed to stand and degas for 3 days to obtain LaFe perovskite@ZIF-8 modified polyimide casting solution.

[0065] (4) Preparation of core fluid

[0066] Weigh NMP and deionized water, mix and stir at room temperature for 4 hours to obtain core liquid, and the mass ratio of NMP to water is 19:1.

[0067] (5) Preparation of LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane

[0068] LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane was prepared by dry-wet method. The core liquid and casting liquid were poured into the spinning machine kettle, and then the mass flow rate was controlled at 1:3. At the same time, it flowed through the spinneret into the condensation tank. The temperature of the spinneret was controlled at 70°C, the distance between the spinneret and the condensation tank was 1 cm, and the temperature of the condensation tank was controlled at 5°C to obtain a hollow fiber membrane. It was then soaked in pure water for 3 days and dried at room temperature for 2 weeks to obtain LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane.

[0069] Example 4

[0070] The preparation method of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane of this embodiment is as follows:

[0071] (1) Preparation of LaFe perovskite

[0072] LaFe perovskite was prepared by ball milling. 20 g of lanthanum nitrate hexahydrate, 18.6 g of ferric nitrate nonahydrate and 26.6 g of citric acid were weighed in turn and placed in a ball mill. The mill was operated at 1800 r / min for 23 h, then dried at 95 °C for 23 h, and then calcined at 800 °C for 10 h to obtain LaFeO3 perovskite.

[0073] (2) Preparation of ZIF-8

[0074] Weigh 20 g of zinc nitrate hexahydrate and dissolve it in 667 mL of methanol to form solution A, weigh 60 g of 2-methylimidazole and dissolve it in 1000 mL of methanol to form solution B, mix solutions A and B, stir at room temperature for 1.5 h, then centrifuge, wash with methanol three times, and then dry at 70° C. for 22 h to obtain ZIF-8.

[0075] (3) Preparation of LaFe perovskite@ZIF-8 modified polyimide film solution

[0076] The polyimide was vacuum dried at 100°C for 20 h, then 300 g of P84 was weighed and poured into 1000 g of DMAc, stirred at 60°C for 22 h, and then 6 g of LaFe perovskite and 24 g of ZIF-8 were added to the P84 solution in sequence, stirred at 90°C for 10 h, cooled and allowed to stand for degassing for 3 days to obtain LaFe perovskite@ZIF-8 modified polyimide casting solution.

[0077] (4) Preparation of core fluid

[0078] Weigh NMP and deionized water, mix and stir at room temperature for 3 hours to obtain core liquid, and the mass ratio of NMP to water is 15:1.

[0079] (5) Preparation of LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane

[0080] LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane was prepared by dry-wet method. The core liquid and casting liquid were poured into the spinning machine kettle, and then the mass flow rate was controlled at 1:2. At the same time, it flowed through the spinneret into the condensation tank. The temperature of the spinneret was controlled at 60°C, the distance between the spinneret and the condensation tank was 3 cm, and the temperature of the condensation tank was controlled at 5°C to obtain a hollow fiber membrane. It was then soaked in pure water for 3 days and dried at room temperature for 2 weeks to obtain LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane.

[0081] Comparative Example 1

[0082] The polyimide hollow fiber membrane of this embodiment is different from that of Embodiment 1 in that LaFe perovskite is not added during the preparation process.

[0083] Comparative Example 2

[0084] The polyimide hollow fiber membrane of this embodiment is different from that of Embodiment 1 in that ZIF-8 is not added during the preparation process.

[0085] The LaFe perovskite @ ZIF-8 modified polyimide hollow fiber membrane prepared in Example 1-4 and the polyimide hollow fiber membrane prepared in Comparative Example 1-2 were tested for gas separation ability. Specifically, the LaFe perovskite @ ZIF-8 modified polyimide hollow fiber membrane prepared in Example 1-4 was sealed in the assembly, and then the He separation performance of the membrane was tested at room temperature. The gas on the inlet side was He, CO2, CH4 and N2, the pressure was 1Mpa, and the retentate side was purged with argon for 30min at a flow rate of 50mL / min. The screening ability test results are shown in Table 1.

[0086] Table 1 Hollow fiber membrane gas separation performance test

[0087]

[0088] From the data in Table 1, it can be seen that the LaFe perovskite @ ZIF-8 modified polyimide hollow fiber membrane of the present invention has excellent permeability to helium, with a permeability of up to 218 GPU, and exhibits good selectivity in He / CO2, He / N2, and He / CH4 systems. It can be seen that the LaFe perovskite @ ZIF-8 modified polyimide hollow fiber membrane of the present invention can be used in the separation and purification of helium.

[0089] The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membranes prepared in Example 4 and Comparative Example 1 were tested for anti-plasticization stability. Figure 1 The prepared hollow fiber membrane was encapsulated in Figure 1 In the component, mixed gas is used for feeding, the test pressure is 1MPa, the temperature is room temperature, and the retentate side is purged with argon for 30min at a flow rate of 50mL / min. The raw gas enters the component from the raw material side, the retentate side is the raw gas, and the permeate side is the separated gas. The separated gas enters the chromatogram to measure the content and obtain relevant performance data. The anti-plasticization stability diagram of the LaFe perovskite @ ZIF-8 modified polyimide hollow fiber membrane prepared in Example 4 is shown in Figure 2 The anti-plasticization stability of the ZIF-8 modified polyimide hollow fiber membrane prepared in Comparative Example 1 is shown in FIG. Figure 3 . It can be seen that the introduction of LaFe perovskite enhances the anti-plasticization performance of the hollow fiber membrane. After 115 days of operation, the helium flux and helium selectivity did not change much, the helium flux decreased by 5%, the helium / methane selectivity decreased by 4%, the helium / nitrogen selectivity decreased by 4%, and the helium / carbon dioxide selectivity decreased by 7%. The performance of the hollow fiber membrane is better. However, the performance of the hollow fiber membrane without the addition of LaFe perovskite decreased rapidly, with the helium flux decreased by 56%, the helium / methane selectivity decreased by 40%, the helium / nitrogen selectivity decreased by 48%, and the helium / carbon dioxide selectivity decreased by 38%. Therefore, it illustrates the significant role of LaFe perovskite in the anti-plasticization of the hollow fiber membrane.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention. The techniques, shapes, and structural parts not described in detail in the present invention are all known technologies.

Claims

1. LaFe perovskite @ ZIF-8 modified polyimide hollow fiber membrane, characterized in that: The invention relates to a method for preparing a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane, comprising the following steps: Preparation of LaFe perovskite: lanthanum nitrate hexahydrate, iron nitrate nonahydrate and citric acid are weighed and added into a ball mill, and then dried and calcined at 700-900° C. for 8-12 hours to obtain LaFe perovskite; Preparation of casting solution: weigh the dried polyimide and pour it into the solvent, stir it at 25-80° C. for 12-24 hours, add LaFe perovskite and ZIF-8 in sequence, stir it at 60-100° C. for 8-12 hours, cool it and let it stand for degassing to obtain LaFe perovskite@ZIF-8 modified polyimide casting solution, wherein the mass ratio of LaFe perovskite, ZIF-8 and polyimide is 1:(1-4):(30-50); The preparation of the hollow fiber membrane comprises the following steps: taking nitrogen-methylpyrrolidone and deionized water in a mass ratio of (8-19):1 and stirring to obtain a core liquid; pouring the core liquid and the casting liquid into a spinning machine kettle; and then controlling the flow rate to simultaneously flow through the spinneret into a condensation tank; the mass flow rate ratio of the core liquid to the casting liquid is 1:(1-3); spinning to obtain a hollow fiber membrane; and then soaking it in pure water or ethanol for 2-3 days and drying it to obtain a LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane.

2. The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to claim 1, characterized in that: The molar ratio of the lanthanum nitrate hexahydrate, the ferric nitrate nonahydrate and the citric acid is 1:1:1-3.

3. The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to claim 2, characterized in that: In the preparation of the LaFe perovskite, lanthanum nitrate hexahydrate, iron nitrate nonahydrate and citric acid are weighed and added into a ball mill respectively, and the ball mill is operated at a speed of 500 to 2000 r / min for 12 to 24 hours, and then dried at 80 to 100° C. for 12 to 24 hours.

4. The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to claim 3, characterized in that: The drying conditions of the polyimide are as follows: the polyimide is vacuum dried at 80-110° C. for 8-24 hours.

5. The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to claim 4, characterized in that: The polyimide is any one of Matrimid 5218 and P84, the solvent is any one of nitrogen-methylpyrrolidone, N,N-dimethylacetamide and chloroform, and the mass of the polyimide accounts for 10-30wt% of the mass of the solvent.

6. The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to claim 5, characterized in that: The preparation method of ZIF-8 is as follows: zinc nitrate hexahydrate is weighed and dissolved in methanol to form a solution A, 2-methylimidazole is weighed and dissolved in methanol to form a solution B, solution A and solution B are mixed and stirred at room temperature for 1 to 2 hours, centrifuged, washed with methanol for 2 to 3 times, and then dried at 60 to 80° C. for 12 to 24 hours to obtain ZIF-8.

7. The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to claim 6, characterized in that: The mass concentration of the solution A is 0.02-0.03 g / mL, the mass concentration of the solution B is 0.04-0.06 g / mL, and the mass ratio of the zinc nitrate hexahydrate to 2-methylimidazole is 1:(2-4).

8. The LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to claim 7, characterized in that: The temperature of the spinneret is controlled at 50-70° C., the temperature of the condensation tank is controlled at 0-10° C., and the distance between the spinneret and the condensation tank is 1-5 cm.

9. Use of the LaFe perovskite@ZIF-8 modified polyimide hollow fiber membrane according to any one of claims 1 to 8 in helium separation.

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