Polyamide-imide hollow fiber membrane and helium separation membrane

Abstract

This invention belongs to the field of gas separation membrane technology, specifically relating to a polyamide-imide hollow fiber membrane, and further disclosing its preparation method and its application in preparing helium separation membranes. The method for preparing a polyamide-imide hollow fiber membrane provided by this invention includes the step of preparing a polyamide-imide casting solution, and the step of performing dry-wet spinning on the casting solution to obtain the desired polyamide-imide hollow fiber membrane. The polyamide-imide hollow fiber membrane obtained by this invention has a helium selectivity to nitrogen ratio greater than 5, meeting the requirements of industrial applications, and also exhibits a high helium flux.

Description

Technical Field

[0001] This invention belongs to the field of gas separation membrane technology, specifically relating to a polyamide-imide hollow fiber membrane, and further disclosing its preparation method and its application in preparing helium separation membranes. Background Technology

[0002] Helium, a rare inert gas, possesses unique physicochemical properties that make its applications in nuclear energy, medicine, and the aerospace industry irreplaceable by other substances. It is considered an indispensable strategic material for national defense, military, and technological development. In recent years, the rapid development of nuclear energy, medical, and aerospace industries has led to a significant increase in helium demand. Even though countries with abundant helium resources plan to expand production capacity to meet international market demand, a global helium shortage is expected in the short term, resulting in a rise in the unit price of helium on the international market.

[0003] Currently, the main raw material for industrial helium production comes from helium-containing natural gas. In existing industrial helium production technologies, helium production is divided into three stages: helium recovery, helium upgrading, and helium purification. In the helium recovery stage, traditionally, cryogenic distillation technology is used to recover helium from the outlet gas of the denitrification unit during the liquefaction of helium-containing natural gas, increasing the helium concentration from 1-3 vol% to 50-70 vol%. However, cryogenic distillation technology consumes a large amount of energy, becoming one of the main expenditures in helium production costs.

[0004] Compared to cryogenic distillation, polymer membrane gas separation technology is considered the most promising alternative. It can significantly reduce energy consumption in helium recovery using traditional methods, improve helium recovery efficiency, and effectively lower helium production costs, thus mitigating the impact of anticipated global helium resource shortages on international helium prices. However, existing helium separation membranes, while meeting helium separation selectivity requirements, suffer from low helium flux. Therefore, developing a helium separation membrane that meets both helium separation selectivity requirements and high helium flux is of significant importance. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect of low helium flux in the prior art helium separation membrane while meeting the helium separation selectivity ratio, thereby providing a polyamide-imide hollow fiber membrane, and further disclosing its preparation method and the application of preparing the helium separation membrane.

[0006] This invention provides a method for preparing a polyamide-imide hollow fiber membrane, comprising the steps of preparing a polyamide-imide casting solution and the steps of dry-wet spinning the casting solution to obtain the desired polyamide-imide hollow fiber membrane.

[0007] Preferably, the polyamide-imide casting solution comprises, by total amount: 24-30 wt% polyamide-imide and 70-76 wt% a first polar solvent;

[0008] Preferably, the first polar solvent includes one or a mixture of several of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, or dimethyl sulfoxide.

[0009] Preferably, the temperature for the step of preparing the polyamide-imide casting solution is 75-85°C;

[0010] Preferably, the step of preparing the polyamide-imide casting solution further includes a step of vacuum drying the polyamide-imide at 100-150°C;

[0011] Preferably, the step of preparing the polyamide-imide casting solution further includes the step of letting the polyamide-imide casting solution stand at 60-70°C for 14-18 hours.

[0012] Preferably, the dry-wet spinning step includes mixing the casting solution and the core solution and spinning the resulting spun fibers, which are then subjected to air gap forming and condensation solidification to obtain the desired hollow fiber membrane.

[0013] Preferably, in the dry-wet spinning step, the air gap height in the air gap forming step is 60-80cm;

[0014] Preferably, the ambient temperature for the air gap forming step is 20-30°C and the relative humidity is 20-30%.

[0015] Preferably, in the dry-wet spinning step, the coagulation and solidification step includes immersing the obtained spun yarn in a coagulation solution;

[0016] Preferably, the condensate comprises pure water;

[0017] Preferably, the temperature of the condensate is 20-40°C;

[0018] Preferably, the soaking time is 44-48 hours;

[0019] Preferably, the soaking step further includes changing the water every 20-24 hours.

[0020] Preferably, the core fluid comprises a mixture of deionized water and a second polar solvent;

[0021] Preferably, the mass percentage of deionized water in the core fluid is 5-35 wt%; preferably, the second polar solvent includes one or a mixture of several of N-methylpyrrolidone, dimethylformamide, dimethylacetamide or dimethyl sulfoxide.

[0022] Preferably, in the spinning step, the volumetric flow rate of the polyamide-imide casting solution is 1-3 ml / min, and the volumetric flow rate of the core solution is 0.5-1.5 ml / min;

[0023] Preferably, the temperature of the polyamide-imide casting solution is 20-40°C;

[0024] Preferably, the temperature of the core fluid is 20-40°C.

[0025] Preferably, the dry-wet spinning step further includes drying the hollow fiber membrane at 50-60°C and vacuum evacuation at 160-200°C for 8-12 hours.

[0026] This invention provides a polyamide-imide hollow fiber membrane prepared by the method described above;

[0027] Preferably, the polyamide-imide hollow fiber membrane has an outer diameter of 0.7-1.0 mm, an inner diameter of 0.4-0.7 mm, and a wall thickness of 0.15-0.3 mm.

[0028] Preferably, the polyamide-imide hollow fiber membrane has a tensile strength of 17-20 MPa, a Young's modulus of 550-600 MPa, and a bursting pressure of 9.0-11.0 MPa.

[0029] Preferably, under a single gas permeation test at 25°C, the selectivity ratio of helium to nitrogen is 5.0-10.0; and the permeability of helium is 10-30 GPU, while the permeability of nitrogen is 2.0-5.0 GPU.

[0030] In the invention, the test conditions for the single gas permeation test are that the pressure at the inlet end of the polyamide-imide hollow fiber membrane is 2.0 bar, the pressure at the permeation side is 1.0 bar, and the pressure difference is 1.0 bar.

[0031] This invention provides the use of the polyamide-imide hollow fiber membrane described above for preparing a helium separation membrane.

[0032] The present invention provides a highly selective helium separation membrane, wherein the separation membrane comprises the polyamide-imide hollow fiber membrane described above.

[0033] The present invention provides helium recovery of the outlet gas of the denitrification unit in the natural gas liquefaction process using the polyamide-imide hollow fiber membrane or the helium separation membrane described above.

[0034] In this invention, 1 GPU = 1 × 10 -6 cm 3 (STP) / cm 2 ·s·cmHg.

[0035] The technical solution of this invention has the following advantages:

[0036] The present invention provides a method for preparing a polyamide-imide hollow fiber membrane, which uses a polyamide-imide casting solution and a dry-wet spinning process. The inner surface of the membrane has a porous structure, while the outer surface has a dense structure. This results in a helium-to-nitrogen selectivity ratio of the prepared polyamide-imide hollow fiber membrane greater than 5, meeting the requirements of industrial applications and exhibiting a high helium flux.

[0037] Furthermore, the polyamide-imide casting solution provided by the present invention comprises, by total amount, 24-30 wt% polyamide-imide and 70-76 wt% a first polar solvent. When the content of polyamide-imide is less than 24 wt%, the viscosity of the polyamide-imide casting solution is too low, making it impossible to prepare hollow fiber membranes using a dry-wet phase separation spinning process. When the content of polyamide-imide is greater than 30 wt%, the hollow fiber membranes prepared by dry-wet spinning have an excessively thick outer skin layer, resulting in low gas permeability, and the internal cross-sectional structure is prone to irregular shapes, making it impossible to effectively control the reliability, stability, and reproducibility of hollow fiber membrane preparation.

[0038] Furthermore, in this invention, in the dry-wet spinning step, the air gap height in the air gap forming step is 60-80 cm; the ambient temperature in the air gap forming step is 20-30℃ and the relative humidity is 20-30%. The polyamide-imide hollow fiber membrane prepared using these parameters can remove the inner surface skin layer of the membrane fibers, increasing the gas permeability of the membrane fibers; it can prevent water-air induced phase separation during spinning and inhibit the formation of pores on the outer surface of the membrane fibers, thus preventing the loss of helium and nitrogen separation efficiency. If the air gap height is less than 70 cm, the inner surface skin layer of the membrane fibers cannot be effectively removed, resulting in low gas permeability; if the air gap height is greater than 90 cm, the spinnability is poor, and the membrane fiber wall thickness is too thin, resulting in excessively low mechanical strength of the membrane fibers.

[0039] Furthermore, in this invention, the mass percentage of deionized water in the core liquid is 5-35 wt%. When the mass percentage of deionized water in the core liquid is less than 5 wt%, the phase separation rate in the dry-wet spinning process is too low, and the gas gap height cannot be increased to 60-80 cm. When the mass percentage of deionized water in the core liquid is less than 5 wt%, the phase separation rate in the spinning process is too high when the core liquid is higher than 35 wt%, and the inner surface skin layer of the membrane fibers cannot be effectively removed, resulting in low gas permeability of the hollow fiber membrane.

[0040] Furthermore, in this invention, the volumetric flow rate of the polyamide-imide casting solution is 1-3 ml / min, and the volumetric flow rate of the core solution is 0.5-1.5 ml / min; the high air gap height during the dry-wet spinning process can be controlled to be 60-80 cm, which can effectively control the difference in phase separation speed between the inner and outer surfaces of the membrane fiber and eliminate the risk of irregular shape of the internal cross-sectional structure of the membrane fiber.

[0041] Furthermore, in this invention, the temperature of the polyamide-imide casting solution is 20-40°C, the temperature of the core solution is 20-40°C, and the temperature of the condensate is 20-40°C. This can effectively control the phase separation rate of the inner and outer surfaces of the membrane fibers, reduce the generation of giant pores in the cross-section of the membrane fibers, and improve the mechanical strength of the prepared polyamide-imide hollow fiber membrane.

[0042] Furthermore, the dry-wet spinning step of the present invention also includes a step of drying the hollow fiber membrane at 50-60°C and a step of vacuum pumping at 160-200°C for 8-12 hours. This step can effectively remove the residual solvent inside the membrane fibers, ensuring the reliability and stability of the membrane fibers in gas separation applications. Attached Figure Description

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific 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 from these drawings without creative effort.

[0044] Figure 1 This is a scanning electron microscope image of the outer surface of the polyamide-imide hollow fiber membrane prepared in Example 1 of this invention;

[0045] Figure 2 This is a scanning electron microscope image of the inner surface of the polyamide-imide hollow fiber membrane prepared in Example 1 of this invention;

[0046] Figure 3 This is a scanning electron microscope image of the overall cross-section of the polyamide-imide hollow fiber membrane prepared in Example 1 of this invention;

[0047] Figure 4 This is a scanning electron microscope image of the inner edge cross-section of the polyamide-imide hollow fiber membrane prepared in Example 1 of this invention;

[0048] Figure 5 This is a scanning electron microscope image of the inner edge cross-section of the polyamide-imide hollow fiber membrane prepared in Example 2 of the present invention;

[0049] Figure 6This is a scanning electron microscope image of the inner surface of the polyamide-imide hollow fiber membrane prepared in Example 2 of the present invention;

[0050] Figure 7 This is a scanning electron microscope image of the overall cross-section of the polyamide-imide hollow fiber membrane prepared in Example 2 of this invention;

[0051] Figure 8 This is a scanning electron microscope image of the outer surface of the polyamide-imide hollow fiber membrane prepared in Comparative Example 1 of this invention.

[0052] Figure 9 This is a scanning electron microscope image of the inner surface of the polyamide-imide hollow fiber membrane prepared in Comparative Example 1 of this invention.

[0053] Figure 10 This is a scanning electron microscope image of the overall cross-section of the polyamide-imide hollow fiber membrane prepared in Comparative Example 1 of this invention. Detailed Implementation

[0054] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0055] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0056] The polyamide-imide used in the following examples and comparative examples is Torlon 4000T-LV, Solvay.

[0057] In the following embodiments and comparative examples of the present invention, the model in Cho, YH, Kim, SD, Kim, JF, Choi, HG, Kim, Y., Nam, SE, Park, YI and Park, H., 2019. "Tailoring the porous structure of hollow fiber membranes for osmotic power generation applications via thermally assisted nonsolvent induced phase separation." Journal of Membrane Science, 579, pp. 329-341. was used to calculate the collapse pressure of the polymer hollow fiber membrane using the inner and outer diameters of the membrane fibers and Young's modulus.

[0058] In the following embodiments and comparative examples of the present invention, the gas flux was calculated using the model in Xie, K., Fu, Q., Qiao, GG and Webley, PA, 2019. Recent progress on fabrication methods of polymeric thin film gasseparation membranes for CO2 capture. Journal of Membrane Science, 572, pp. 38-60., through the gas permeance and the pressure difference between the feed and permeate sides of the separation membrane.

[0059] In the following embodiments and comparative examples of the present invention, the standard described in Scholes, CA and Ghosh, U., 2016. Helium separation through polymeric membranes: selectivity targets. Journal of Membrane Science, 520, pp. 221-230 is adopted, that is, the selectivity ratio of helium to nitrogen of the separation membrane is higher than 5, which can be used for helium recovery of the outlet gas of the nitrogen rejection unit (NRU) in the natural gas liquefaction process, thus meeting the selectivity requirements of the present invention.

[0060] In the following embodiments and comparative examples of the present invention, the single gas permeation test conditions are to maintain the inlet pressure of the hollow fiber separation membrane at 2.0 bar and the permeation pressure at 1.0 bar, so that the pressure difference is 1.0 bar.

[0061] Example 1

[0062] This embodiment provides a method for preparing a polyamide-imide hollow fiber membrane, comprising the following steps:

[0063] 27g of polyamide-imide was vacuum dried at 120℃ for 16 hours and then mixed with 73g of N-methylpyrrolidone in a serum bottle. The mixture was stirred and dissolved at 80℃ for 24 hours, and then filtered to obtain a polyamide-imide casting solution. The polyamide-imide casting solution was allowed to stand at 60℃ for 18 hours and then cooled to 25℃. A mixture of N-methylpyrrolidone and deionized water was used as the core solution (the weight percentage of deionized water in the core solution was 35%). The temperature of the core solution and the polyamide-imide casting solution was controlled at 25℃. The polyamide-imide casting solution and the core solution were spun through a spinneret using a syringe pump. The spinneret formed... The spun fibers were solidified in pure water at 25°C using an air gap (the volumetric flow rate of the polyamide-imide casting solution during the spinning process was 2 ml / min, the volumetric flow rate of the core solution was 1 ml / min, the air gap height was 80 cm, the ambient temperature was 25±1°C, and the relative humidity was 25±3%). The solidified fibers were then soaked in pure water at room temperature for 48 hours, with the water changed every 24 hours. The fibers were then dried at 60°C for 24 hours and then vacuum dried at 180°C for 12 hours to obtain the polyamide-imide hollow fiber membrane.

[0064] Scanning electron microscope (SEM) images of the polyamide-imide hollow fiber membranes prepared in this embodiment are attached. Figure 1-4 As shown, where, Figure 1 The outer surface of the membrane fiber has a magnification of 10,000 times. Figure 2 The inner surface of the membrane fiber is shown, with a magnification of 5000x. Figure 3 The cross-section of the membrane fiber is shown, with a magnification of 90x. Figure 4 This is the cross-section of the inner edge of the membrane filament, magnified 1000 times. Figure 1 It is known that the outer surface of the membrane fiber has a defect-free, dense structure. Based on the dissolution-diffusion theory, the different solubility and diffusion coefficients of the membrane material for helium and nitrogen can be utilized to achieve the separation of helium and nitrogen. Figure 2 This demonstrates that the inner surface of the membrane fibers has a connected porous structure. Compared to a dense structure, the porous structure exhibits lower gas permeation mass transfer resistance, thus improving the gas permeability of the separation membrane. Figure 3 It is understood that the polyamide-imide hollow fiber membrane prepared in this embodiment has an outer diameter of 0.8 mm, an inner diameter of 0.48 mm, and a wall thickness of 0.16 mm.

[0065] The hollow fiber membrane described in this embodiment has a tensile strength of 17.3 MPa, a Young's modulus of 573 MPa, and a bursting pressure of 10.0 MPa. The polyamide-imide hollow fiber membrane prepared in this embodiment exhibits high mechanical strength and can withstand an inlet pressure not exceeding 10.0 MPa.

[0066] According to the test results, under a single gas permeation test at 25°C, the helium permeation rate of the hollow separation membrane described in this embodiment is 12.68 GPU, the nitrogen permeation rate is 2.33 GPU, and the helium selectivity to nitrogen ratio is 5.52.

[0067] When the inlet pressure and the permeate pressure are 10.0 MPa and 0.1 MPa respectively, the helium flux of the hollow fiber separator described in this embodiment is 3.73 m³ / s. 3 (STP) / m 2 •h, nitrogen flux is 0.676m 3 (STP) / m 2 ·h.

[0068] Example 2

[0069] The difference between this embodiment and Embodiment 1 is that the air gap height is controlled at 20cm.

[0070] Scanning electron microscope (SEM) images of the polyamide-imide hollow fiber membranes prepared in this embodiment are attached. Figure 5-7 As shown, where Figure 5 The cross-section of the inner edge of the membrane filament is magnified 1,000 times. Figure 6 The inner surface of the membrane fiber is shown, with a magnification of 5,000. Figure 7 The cross-section of the membrane filament is magnified 40 times.

[0071] As can be seen, compared with Example 1 Figure 4 In contrast, during the dry-wet spinning process, the pore size of the inner edge cross-section of the membrane fiber decreases with increasing air gap height, which is beneficial for improving Young's modulus and increasing the membrane fiber rupture pressure. Furthermore, compared to Example 1... Figure 2 In contrast, during the dry-wet spinning process, increasing the air gap height can improve the porosity and pore size of the inner surface of the membrane fiber, which is beneficial to increasing the gas permeability. This is mainly because the phase separation rate on the inner surface of the membrane fiber decreases as the air gap height increases.

[0072] through Figure 7 The results show that the polyamide-imide hollow fiber membrane prepared in this embodiment has an outer diameter of 1.29 mm, an inner diameter of 0.81 mm, and a wall thickness of 0.24 mm.

[0073] The hollow fiber membrane described in this embodiment has a tensile strength of 19.4 MPa, a Young's modulus of 548 MPa, and a bursting pressure of 8.0 MPa.

[0074] According to the test results, under a single gas permeation test at 25°C, the helium permeation rate of the hollow separation membrane described in this embodiment is 9.8 GPU, the nitrogen permeation rate is 1.64 GPU, and the helium selectivity to nitrogen ratio is 5.98.

[0075] When the inlet pressure and the permeate pressure are 8.0 MPa and 0.1 MPa respectively, the helium flux of the hollow fiber separator described in this embodiment is 2.30 m³ / s. 3 (STP) / m 2 •h, nitrogen flux is 0.385m 3 (STP) / m 2 ·h.

[0076] Example 3

[0077] This embodiment provides a method for preparing a polyamide-imide hollow fiber membrane, comprising the following steps:

[0078] 27g of polyamide-imide was vacuum dried at 100℃ for 16 hours and then mixed with 73g of N-methylpyrrolidone in a serum bottle. The mixture was stirred and dissolved at 75℃ for 24 hours, and then filtered to obtain a polyamide-imide casting solution. The polyamide-imide casting solution was allowed to stand at 65℃ for 18 hours and then cooled to 20℃. A mixture of N-methylpyrrolidone and deionized water was used as the core solution (5% by weight of deionized water in the core solution). The temperature of both the core solution and the polyamide-imide casting solution was controlled at 20℃. The polyamide-imide casting solution and the core solution were spun through a spinneret using a syringe pump. The resulting spun yarn... The filaments were solidified in pure water at 20°C using an air gap (the volumetric flow rate of the polyamide-imide casting solution during the spinning process was 1 ml / min, the volumetric flow rate of the core solution was 0.5 ml / min, the air gap height was 60 cm, the ambient temperature was 25 ± 1°C, and the relative humidity was 25 ± 3%). The solidified filaments were then soaked in pure water at room temperature for 48 hours, with the water changed every 24 hours. They were then dried at 50°C for 24 hours and then vacuum dried at 160°C for 12 hours to obtain the polyamide-imide hollow fiber membrane.

[0079] Example 4

[0080] This embodiment provides a method for preparing a polyamide-imide hollow fiber membrane, comprising the following steps:

[0081] 27g of polyamide-imide was vacuum dried at 150℃ for 16 hours and then mixed with 73g of N-methylpyrrolidone in a serum bottle. The mixture was stirred and dissolved at 85℃ for 24 hours, and then filtered to obtain a polyamide-imide casting solution. The polyamide-imide casting solution was allowed to stand at 70℃ for 14 hours, and then cooled to 40℃. A mixture of N-methylpyrrolidone and deionized water was used as the core solution (20% by weight of deionized water in the core solution). The temperature of the core solution and the polyamide-imide casting solution was controlled at 40℃. The polyamide-imide casting solution and the core solution were spun through a spinneret using a syringe pump. The spun fibers formed by the spinneret... The spun fibers are solidified in pure water at 40°C using an air gap (the volumetric flow rate of the polyamide-imide casting solution during the spinning process is 3 ml / min, the volumetric flow rate of the core solution is 1.5 ml / min, the air gap height is 70 cm, the ambient temperature is 25±1°C, and the relative humidity is 25±3%). The solidified fibers are then soaked in pure water at room temperature for 48 hours, with the water changed every 24 hours. They are then dried at 55°C for 24 hours and then vacuum dried at 200°C for 12 hours to obtain the polyamide-imide hollow fiber membrane.

[0082] Comparative Example 1

[0083] The difference between the separation membrane described in this comparative example and that in Example 1 is that it uses wet spinning, that is, the spun yarn formed by the spinneret is directly solidified in pure water at 25°C without passing through an air gap.

[0084] Scanning electron microscope (SEM) images of the polyamide-imide hollow fiber membranes prepared in this comparative example are attached. Figure 8-10 As shown, where Figure 8 The outer surface of the membrane fiber has a magnification of 10,000 times. Figure 9 The inner surface of the membrane fiber is shown, with a magnification of 5,000. Figure 10 The cross-section of the membrane filament is magnified 40 times.

[0085] Figure 9 and 10 The results shown are consistent with those in Example 1. Figure 1 , 2 In contrast, the membrane fibers prepared by wet spinning have a dense inner surface structure, resulting in low gas permeability. This indicates that the dry-wet spinning method used in this invention can prepare a porous inner surface structure without affecting the dense structure of the outer surface of the membrane fibers, thus ensuring the separation efficiency of the membrane fibers for helium and nitrogen.

[0086] through Figure 10 It was found that the polyamide-imide fiber membrane of this comparative example has an outer diameter of 1.54 mm, an inner diameter of 0.94 mm, and a wall thickness of 0.3 mm.

[0087] The tensile strength of the polyamide-imide fiber membrane described in this comparative example was measured to be 22.9 MPa, the Young's modulus was 550 MPa, and the bursting pressure was 8.9 MPa.

[0088] The polyamide-imide fiber membrane of this comparative example was tested at 25°C under a single gas permeation test. The helium permeation rate was 5.81 GPU, the nitrogen permeation rate was 1.07 GPU, and the helium selectivity to nitrogen ratio was 5.43.

[0089] When the inlet pressure and the permeate pressure are 8.9 MPa and 0.1 MPa, respectively, the helium flux of the hollow fiber separator described in this comparative example is 1.52 m³ / s. 3 (STP) / m 2 •h, nitrogen flux is 0.280m 3 (STP) / m 2 ·h.

[0090] In summary, the polyamide-imide hollow fiber membrane of the present invention not only has high mechanical strength, but also has a high helium permeability while ensuring that the helium selectivity to nitrogen ratio is greater than 5, thus effectively guaranteeing its application performance.

Claims

1. A method for preparing a polyamide-imide hollow fiber membrane, characterized in that, The method includes the steps of preparing a polyamide-imide casting solution and the steps of dry-wet spinning the casting solution to obtain the desired polyamide-imide hollow fiber membrane; the polyamide-imide casting solution comprises, by total amount: 24-30 wt% polyamide-imide and 70-76 wt% a first polar solvent; the first polar solvent includes one or a mixture of several of N-methylpyrrolidone, dimethylformamide, dimethylacetamide or dimethyl sulfoxide; The dry-wet spinning step includes spinning polyamide-imide casting solution and core solution through a spinneret using an injection pump. The resulting spun fibers are then formed by air gap and solidified by condensation to obtain the desired hollow fiber membrane. The coagulation and solidification step includes immersing the obtained spun yarn in a coagulation solution. The condensate includes pure water; In the dry-wet spinning step, the air gap height in the air gap forming step is 60-80cm; The ambient temperature for the air gap forming process is 20-30℃, and the relative humidity is 20-30%. The core fluid comprises a mixture of deionized water and a second polar solvent; The core fluid contains 20-35 wt% deionized water; the second polar solvent is N-methylpyrrolidone. The polyamide-imide is designated as Torlon 4000T-LV, Solvay.

2. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, The temperature for preparing the polyamide-imide casting solution is 75-85℃.

3. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, The step of preparing the polyamide-imide casting solution further includes a step of vacuum drying the polyamide-imide at 100-150°C.

4. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, The step of preparing the polyamide-imide casting solution also includes the step of letting the polyamide-imide casting solution stand at 60-70°C for 14-18 hours.

5. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, The temperature of the condensate is 20-40℃.

6. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, In the spinning step, the volumetric flow rate of the polyamide-imide casting solution is 1-3 ml / min, and the volumetric flow rate of the core solution is 0.5-1.5 ml / min.

7. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, The temperature of the polyamide-imide casting solution is 20-40℃.

8. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, The temperature of the core fluid is 20-40℃.

9. The method for preparing the polyamide-imide hollow fiber membrane according to claim 1, characterized in that, The dry-wet spinning step further includes drying the hollow fiber membrane at 50-60°C and vacuum evacuating it at 160-200°C for 8-12 hours.

10. A polyamide-imide hollow fiber membrane prepared by the method according to any one of claims 1-9.

11. The polyamide-imide hollow fiber membrane according to claim 10, characterized in that, The polyamide-imide hollow fiber membrane has an outer diameter of 0.7-1.0 mm, an inner diameter of 0.4-0.7 mm, and a wall thickness of 0.15-0.3 mm.

12. The polyamide-imide hollow fiber membrane according to claim 10, characterized in that, The polyamide-imide hollow fiber membrane has a tensile strength of 17-20 MPa, a Young's modulus of 550-600 MPa, and a bursting pressure of 9.0-11.0 MPa.

13. The polyamide-imide hollow fiber membrane according to claim 10, characterized in that, In a single-gas permeation test at 25℃, the selectivity of helium to nitrogen was 5.0-10.0; and the permeability of helium was 10-30 GPU, while that of nitrogen was 2.0-5.0 GPU.

14. Use of the polyamide-imide hollow fiber membrane of claim 10 for the preparation of a helium separation membrane.

15. A highly selective helium separation membrane, characterized in that, The separation membrane comprises the polyamide-imide hollow fiber membrane of claim 10.

16. The application of the polyamide-imide hollow fiber membrane of claim 10 or the high-selectivity helium separation membrane of claim 15 in the natural gas liquefaction denitrification process.

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