Heterocyclic aramid hollow fiber membrane and preparation method thereof

Abstract

The invention discloses a heterocyclic aramid hollow fiber membrane and a preparation method thereof, the preparation method comprising: S1, removing impurities on the surface of heterocyclic aramid filaments, drying the heterocyclic aramid filaments and PPTA resin; S2, adding a cosolvent to a solvent and making it uniformly dispersed; adding heterocyclic aramid staple fibers, PPTA resin and a porogen to the solution, stirring and swelling at low temperature to obtain a gel premix; S3, adding the gel premix to a twin-screw extruder, further dissolving and degassing, and then quantitatively conveying the gel premix to a hollow spinneret through a booster pump and a metering pump and continuously extruding, and then immersing the gel in a coagulation bath after an air bath to solidify the gel, so as to obtain a primary heterocyclic aramid hollow fiber membrane; S4, winding, washing, neutralizing with alkali solution, and then putting the primary heterocyclic aramid hollow fiber membrane into a normal temperature water bath for extraction and washing, so as to obtain a heterocyclic aramid hollow fiber porous membrane. The method has low cost and high efficiency, and the prepared aromatic polyamide hollow fiber membrane is acid and alkali resistant, high in strength and good in flexibility.

Description

Technical Field

[0001] The invention relates to the field of hollow fiber membranes, and in particular to a heterocyclic aramid hollow fiber membrane and a preparation method thereof. Background Art

[0002] Membrane separation technology is a technology that uses pores of different diameters on the membrane surface to achieve material separation. Compared with traditional separation technologies such as flocculation sedimentation and centrifugation, it is widely used due to its advantages such as high separation accuracy, stability and reliability. In the field of water treatment, hollow fiber membranes have a considerable market share in the fields of printing and dyeing wastewater treatment, domestic sewage, reverse osmosis pretreatment, steel wastewater treatment, chemical wastewater treatment, tap water treatment, etc., and have gradually replaced other water treatment technologies in many application scenarios.

[0003] At present, the membrane materials of hollow fiber membranes mainly include polymer materials such as polyvinylidene fluoride, polyethersulfone, polysulfone, and polytetrafluoroethylene. These materials are generally hydrophobic. In the water treatment process, it is difficult to balance the osmotic separation stability and the pollution resistance is poor. It is necessary to achieve hydrophilic modification during membrane preparation or post-treatment, which is complex and costly.

[0004] Aromatic polyamide is a high-performance film-forming polymer, and its typical representatives are polyisophthalamide (PMIA), polyparaphenylene terephthalamide (PPTA), etc. The separation membrane material made of PPTA has the characteristics of high hydrophilicity, high temperature resistance, solvent resistance, and pollution resistance, and can be widely used in sewage separation and purification in the fields of chemical, pharmaceutical, biological, and food, but its preparation process is difficult and has high requirements for equipment. The Chinese invention patent with publication number CN104353372A discloses a method for preparing an aromatic polyamide hollow fiber porous membrane, which can effectively solve the problems of PPTA spinning film forming difficulty and low porosity. However, the PPTA molecular chain is a rigid straight chain, and the difficulty of high-concentration liquid crystal spinning is large, and the high-temperature acid and alkali resistance needs to be improved. The structure of the obtained membrane is easily destroyed when used for a long time in acid and alkali solution. Summary of the invention

[0005] In view of the shortcomings of the prior art, one object of the present invention is to provide a method for preparing a high-strength, acid- and alkali-resistant heterocyclic aramid hollow fiber membrane. Another object of the present invention is to provide a heterocyclic aramid hollow fiber membrane prepared by the above method.

[0006] To this end, the present invention adopts the following technical solutions:

[0007] A method for preparing a heterocyclic aramid hollow fiber membrane comprises the following steps:

[0008] S1, raw material pretreatment: removing oil impurities on the surface of heterocyclic aramid filaments, cutting the washed and dried heterocyclic aramid filaments to obtain heterocyclic aramid staple fibers; at the same time, drying the PPTA resin;

[0009] S2, preparing heterocyclic aramid gel casting solution: first, adding a cosolvent to the solvent, stirring to make it uniformly dispersed; then adding the heterocyclic aramid staple fiber, the dried PPTA resin and the porogen to the solution, stirring and swelling at low temperature to obtain a gel premixed solution without obvious particles; wherein the mass fraction of each component is as follows:

[0010]

[0011] The sum of the mass fractions of each component is 100%;

[0012] S3, preparing a nascent heterocyclic aramid hollow fiber membrane: adding the gel premix obtained in S2 to a twin-screw extruder, further dissolving and degassing through the high shear action of the twin-screw, then quantitatively transporting to a hollow spinneret through a booster pump and a metering pump and continuously extruding, and then immersing in a coagulation bath after an air bath to solidify the gel, thereby obtaining a nascent heterocyclic aramid hollow fiber membrane;

[0013] S4, post-treatment of the nascent hollow fiber membrane: the nascent heterocyclic aramid hollow fiber membrane is wound, washed with water, neutralized with alkali solution, and then placed in a normal temperature water bath for extraction and washing to obtain a heterocyclic aramid hollow fiber porous membrane.

[0014] Preferably, the heterocyclic aramid filament in S1 is Technora or aramid III, and has a fineness of 200 to 1500D.

[0015] Preferably, the solvent in S2 is concentrated sulfuric acid or fuming sulfuric acid with a concentration of 98±2%; and the auxiliary solvent is LiCl.

[0016] Preferably, the porogen in S2 is a water-soluble polymer, selected from at least one of PEG with a weight average molecular weight of 800 to 10,000 Da or PVP with a weight average molecular weight of 20,000 to 100,000 Da; when PEG and PVP are compounded, the mass ratio of PEG to PVP is 2:1 to 5:1.

[0017] In step S2, the casting liquid is prepared in a dissolving kettle; the low temperature is 25-50°C; during the stirring and swelling process, the speed of the stirrer is 100-300r / min when the stirring starts, and the speed of the stirrer is 20-50r / min after the solution is dissolved without obvious particles, and preliminary degassing is performed.

[0018] Preferably, the feeding pressure of the gel premixed liquid when entering the twin-screw extruder in S3 is 0.5-3 MPa.

[0019] Preferably, the screw speed of the mixing zone of the twin-screw extruder in S3 is 10-50rpm, and the temperature of the melting zone is 40-80°C; the flow rate of the booster pump is 100-400cc / min, and the speed is 5-30r / min; the flow rate of the metering pump is 10-90cc / min, and the speed is 5-30r / min; the metering pump is connected to the hollow spinneret via a spinning pipeline, and the temperature of the spinning pipeline is 30-70°C.

[0020] In step S3, the spinning core liquid of the hollow spinneret is deionized water, and the flow rate of the spinning core liquid is 20-80cc / min; the height of the air bath is 10-100mm; the coagulation bath is deionized water or a NaOH aqueous solution with a concentration of 10-50wt.%, and the acid concentration of the coagulation bath is controlled below 10%; the temperature of the coagulation bath is 20-40°C, and the winding speed is 30-120r / min.

[0021] Preferably, in step S1, the heterocyclic aramid filaments are first soaked in methanol to remove impurities such as spinning oil, then repeatedly washed with clean water, and then vacuum dried, and the dried heterocyclic aramid filaments are cut to obtain heterocyclic aramid staple fibers with a length of 0.5 to 2 cm; the PPTA resin is fully dried in vacuum at 100 to 150°C; in S4, the alkaline washing process uses a weak alkaline solution of NaHCO3 with a concentration of 10 to 30wt.%, and the moisturizing and shaping process is immersed in a glycerol aqueous solution with a concentration of 30 to 50wt.%.

[0022] A heterocyclic aramid hollow fiber membrane prepared by the preparation method has a breaking strength of 3-6 MPa, an elongation at break of 30-50%, and can stably operate in an acid-base solution with a pH of 2-12.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention uses heterocyclic aramid. Compared with PPTA with regular structure, heterocyclic aramid has significantly stronger acid and alkali resistance than PPTA while maintaining ultra-high strength, ultra-high modulus and excellent heat resistance. Due to the addition of the heterocyclic third monomer, the hydrogen bond structure of the original system is destroyed and the intermolecular force is reduced; at the same time, the orderliness and crystallinity of the molecules are reduced, making it easier for the solvent to penetrate into the interior of the molecular chain, and the solubility is improved.

[0025] 2. The present invention adopts twin-screw extrusion technology, which can prepare high-concentration spinning solution and achieve efficient degassing. This not only saves the amount of solvent used, reduces costs, significantly improves spinning efficiency, realizes continuous production of spinning and film making, and avoids low production efficiency and product quality fluctuations caused by intermittent production.

[0026] 3. The molecular structure of heterocyclic aramid contains a heterocyclic structure, which has low activity and is not easy to react with active hydrogen ions or hydroxide ions in acids or bases. This structure has higher chemical stability than the traditional aromatic ring structure and improves the resistance to acid and alkali solutions. The hollow fiber membrane prepared by the present invention can be applied to more severe working environments (such as acid, alkali, and high salt).

[0027] 4. The use of heterocyclic aramid increases the flexibility of the membrane, making the membrane have high strength and high modulus while having a higher elongation at break. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a real photo of the heterocyclic aramid hollow fiber membrane sample prepared in Example 1;

[0029] Figure 2 This is the SEM morphology of the cross-section of the heterocyclic aramid hollow fiber membrane sample prepared in Example 1. DETAILED DESCRIPTION

[0030] The preparation method of the present invention is described in detail below with reference to the examples.

[0031] Example 1

[0032] A method for preparing a heterocyclic aramid hollow fiber membrane comprises the following steps:

[0033] (1) Pretreatment:

[0034] Soak the heterocyclic aramid filament Technora (400D) in methanol to remove impurities such as spinning oil on the fiber surface, then wash it repeatedly with clean water and vacuum dry it. After drying, cut the heterocyclic aramid filament to obtain a short fiber bundle with a length of 0.5 cm. Weigh the PPTA resin according to the proportion and place it in a 120℃ oven to fully dry the water.

[0035] (2) Preparation of casting solution:

[0036] Mix 15wt.% heterocyclic aramid staple fibers, 5wt.% PPTA resin, 17wt.% PEG (molecular weight 4000), 5wt.% LiCl, and 58wt.% solvent (98% concentrated sulfuric acid by mass) in a dissolving kettle, and stir for 2h at a temperature of 40°C and a speed of 180r / min until the solute is completely dissolved. Adjust the stirrer speed to 20r / min, stir for 0.5h, perform preliminary degassing on the casting solution, and then let it stand for 0.5h to obtain the heterocyclic aramid casting solution.

[0037] (3) Preparation of nascent heterocyclic aramid hollow fiber membrane:

[0038] The pressure of the dissolving kettle was set to 1 MPa, and the casting liquid was squeezed from the dissolving kettle into the twin-screw extruder, the speed of the twin-screw extruder was set to 12 r / min, the temperature of the melting zone was set to 70°C, the temperature of the spinning pipeline was set to 50°, the flow rate of the booster pump was 130 cc / min, and the speed was 16.2 r / min; the flow rate of the metering pump was 30 cc / min, and the speed was 12.5 r / min; the flow rate of the spinning core liquid (deionized water) was 50 cc / min, and it was continuously extruded from the hollow spinneret, passed through an air bath (height of 10 mm), a coagulation bath (30 wt.% NaOH solution, temperature of 20°C), and was wound at a speed of 50 r / min to obtain a primary heterocyclic aramid hollow fiber membrane.

[0039] (4) Post-treatment of primary hollow fiber membrane:

[0040] The obtained nascent heterocyclic aramid hollow fiber membrane is treated by post-treatment processes such as alkali washing, spraying, moisturizing and shaping, and ring blowing to obtain a heterocyclic aramid hollow fiber membrane.

[0041] The alkaline washing process uses a 30wt.% NaHCO3 weak alkaline solution, and the moisturizing and shaping process is immersed in a 50wt.% glycerol aqueous solution.

[0042] The actual photo of the heterocyclic aramid hollow fiber membrane prepared in this example is shown in FIG. Figure 1 The cross-sectional morphology of the heterocyclic aramid hollow fiber prepared in this embodiment was observed using a SEM scanning electron microscope, and the results are shown in FIG. Figure 2 shown.

[0043] Depend on Figure 1 It can be seen that the obtained heterocyclic aramid hollow fiber membrane has a complete hollow morphology, the inner and outer diameters have the same wall thickness, and there is no obvious structural defect.

[0044] Depend on Figure 2 It can be seen that the finger-like pores of the obtained heterocyclic aramid hollow fiber membrane have uniform pore size distribution, and the stable pore structure ensures that the heterocyclic aramid hollow fiber membrane has good retention capacity and chemical corrosion resistance.

[0045] Example 2

[0046] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that: the casting solution in step (2) comprises 10wt.% of heterocyclic aramid staple fibers, 10wt.% of PPTA resin, 17wt.% of PEG (molecular weight 4000), 58wt.% of solvent (mass fraction 98% concentrated sulfuric acid), and 5wt.% of LiCl.

[0047] Example 3

[0048] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that: the casting liquid in step (2) comprises 5wt.% of heterocyclic aramid staple fibers, 15wt.% of PPTA resin, 17wt.% of PEG (molecular weight 4000), 58wt.% of solvent (mass fraction 98% concentrated sulfuric acid), and 5wt.% LiCl.

[0049] Example 4

[0050] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as Example 1, except that: the casting liquid in step (2) comprises 15wt.% of heterocyclic aramid staple fibers, 5wt.% of PPTA resin, 7wt.% of PEG (molecular weight 4000), 5wt.% LiCl, and 68wt.% of a solvent (mass fraction 98% concentrated sulfuric acid).

[0051] Example 5

[0052] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that: the casting solution in step (2) comprises 15wt.% heterocyclic aramid staple fibers, 5wt.% PPTA resin, 17wt.% PEG (molecular weight 4000), 1wt.% LiCl, and 62wt.% solvent (mass fraction 98% concentrated sulfuric acid).

[0053] Example 6

[0054] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that: the casting solution in step (2) comprises 15wt.% of heterocyclic aramid staple fibers, 5wt.% of PPTA resin, 17wt.% of PEG and PVP compound (PEG molecular weight is 4000, PVP molecular weight is 20000, and the mass ratio of PEG to PVP is 2:1), 5wt.% LiCl, and 58wt.% of solvent (mass fraction is 98% concentrated sulfuric acid).

[0055] Example 7

[0056] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that: in step 3, the air bath height is 100 mm.

[0057] Example 8

[0058] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that in step (3), the coagulation bath temperature is 40° C. and the NaOH concentration is 10 wt.%.

[0059] Example 9

[0060] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that in step (3), the winding speed is 120 r / min.

[0061] Example 10

[0062] A method for preparing a heterocyclic aramid hollow fiber membrane is basically the same as that of Example 1, except that in step (1), the heterocyclic aramid filament has a fineness of 1200D.

[0063] Comparative Example 1

[0064] A method for preparing a PPTA hollow fiber membrane comprises:

[0065] 1. Preprocessing:

[0066] The PPTA resin was dried in an oven at 120° C. After drying, the PPTA resin was weighed according to the proportion.

[0067] 2. Preparation of casting solution:

[0068] 10wt.% PPTA resin, 17wt.% PEG (molecular weight 4000), 5wt.% LiCl, 68wt.% solvent (98% concentrated sulfuric acid by mass) were mixed in a dissolving kettle, stirred at 40°C and 180r / min for 2h until the solute was completely dissolved. The stirrer speed was adjusted to 20r / min, stirred for 0.5h to preliminarily degas the casting solution, and then left to stand for 0.5h to obtain the heterocyclic aramid casting solution.

[0069] 3. Preparation of PPTA hollow fiber ultrafiltration membrane:

[0070] The temperature and pressure of the dissolving kettle were set to 1MPa. The casting liquid was squeezed from the dissolving kettle into the twin-screw extruder, and the speed of the twin-screw extruder was set to 12r / min; the temperature of the melting zone was 70°C; the temperature of the spinning pipeline was 50°; the flow rate of the booster pump was set to 130cc / min and the speed was 16.2r / min; the flow rate of the metering pump was 30cc / min and the speed was 12.5r / min; the flow rate of the spinning core liquid (deionized water) was 50cc / min, and it was continuously extruded from the hollow spinneret, passed through an air bath (height of 10mm), a coagulation bath (30wt.% NaOH solution, temperature of 20°C), and wound at a speed of 50r / min to obtain a nascent PPTA hollow fiber membrane.

[0071] 4. Post-treatment of hollow fiber membrane:

[0072] The obtained primary PPTA hollow fiber membrane is treated by post-treatment processes such as alkali washing, spraying, moisturizing and shaping, and ring blowing to obtain a PPTA hollow fiber membrane.

[0073] The alkaline washing process uses a 30wt.% NaHCO3 weak alkaline solution, and the moisturizing and shaping process is immersed in a 50wt.% glycerol aqueous solution.

[0074] Comparative Example 2

[0075] A method for preparing an acid- and alkali-resistant heterocyclic aramid hollow fiber membrane, wherein:

[0076] Step (1) pretreatment and step (4) post-treatment of the nascent hollow fiber membrane are the same as those in Example 1.

[0077] (2) Preparation of casting solution:

[0078] 15wt.% heterocyclic aramid staple fibers, 5wt.% PPTA resin, 17wt.% PEG (molecular weight 4000), 5wt.% LiCl, and 58wt.% solvent (98% concentrated sulfuric acid by mass) were mixed in a kettle, stirred with a stirring paddle for 4 hours until the raw materials were completely dissolved, placed in a 60°C vacuum box for degassing for 1 hour, and allowed to stand for 1 hour after sufficient degassing to obtain the heterocyclic aramid casting liquid.

[0079] (3) Preparation of nascent heterocyclic aramid hollow fiber membrane:

[0080] The casting liquid was squeezed from the kettle into the booster pump with a flow rate of 130cc / min and a rotation speed of 16.2r / min. The flow rate of the metering pump was 30cc / min and the rotation speed was 12.5r / min. The spinning core liquid flow rate was 50cc / min, and it was continuously extruded from the hollow spinneret, passed through an air bath (height of 10mm), a coagulation bath (30wt.% NaOH solution, temperature of 20°C), and winding (50r / min) to obtain a primary hollow fiber membrane.

[0081] Membrane performance test experiment:

[0082] Under the conditions of 0.1 MPa and adjusting the pH of the test stock solution to 7, the permeation flux and rejection rate of 1 g / L PEG (molecular weight of 20,000) of the heterocyclic aramid hollow fiber membranes prepared in Examples 1 to 10, the PPTA hollow fiber membranes prepared in Comparative Example 1, and the heterocyclic aramid hollow fiber membranes prepared in Comparative Example 2 were tested, as well as the hollow fiber membrane breaking strength and breaking elongation. The test results for 180 hours are shown in Table 1.

[0083] Under the conditions of 0.1 MPa and adjusting the pH of the test stock solution to 2, the permeation flux and rejection rate of 1 g / L PEG (molecular weight of 20,000) of the heterocyclic aramid hollow fiber membranes prepared in Examples 1 to 10, the PPTA hollow fiber membranes prepared in Comparative Example 1, and the heterocyclic aramid hollow fiber membranes prepared in Comparative Example 2 were tested, and the hollow fiber membrane breaking strength and breaking elongation were measured. The test results for 180 hours are shown in Table 2.

[0084] Under the conditions of 0.1 MPa and adjusting the pH of the test stock solution to 12, the permeation flux and rejection rate of 1 g / L PEG (molecular weight of 20,000) of the heterocyclic aramid hollow fiber membranes prepared in Examples 1 to 10, the PPTA hollow fiber membranes prepared in Comparative Example 1, and the heterocyclic aramid hollow fiber membranes prepared in Comparative Example 2 were tested, and the hollow fiber membrane breaking strength and breaking elongation were measured. The test results for 180 hours are shown in Table 3.

[0085] Table 1 Comparison of performance parameters of the obtained hollow fiber membrane (180 hours)

[0086]

[0087] Table 2 Comparison of acid resistance of hollow fiber membrane obtained (180 hours)

[0088]

[0089]

[0090] Table 3 Comparison of alkali resistance of hollow fiber membrane obtained (180 hours)

[0091]

[0092] From the test results, we can see that:

[0093] (1) The hollow fiber membrane prepared in Comparative Example 1 was tested under acidic and alkaline conditions for 180 h. Compared with the condition of pH = 7, its permeation flux was significantly increased. The main reason is that the molecular chain of PPTA is highly rigid and is composed of benzene rings and terephthaloyl groups connected alternately, forming a tight molecular structure, which makes it swell in an acidic or alkaline environment, increasing the pore size and seriously damaging the membrane structure, resulting in a significant increase in the permeation flux and a decrease in the interception effect.

[0094] (2) Heterocyclic aramid also contains a tight molecular structure and hydrogen bonds, and will swell in an acidic or alkaline environment. The permeation flux of the heterocyclic aramid hollow fiber membrane prepared in Examples 1-10 for polyethylene glycol gradually increases with the change of pH, but the increase is very small, and still retains a good interception effect. This is because the presence of the heterocyclic structure reduces the regularity and order of the molecular chain, but also improves the solubility and the chemical activity and polarity of the fiber surface. This structural feature reduces its swelling degree and helps to enhance the tolerance of the heterocyclic aramid hollow fiber membrane under acidic and alkaline conditions.

[0095] (3) The breaking strength, breaking elongation and attenuation of polyethylene glycol retention performance of the heterocyclic aramid hollow fiber membrane prepared in Examples 1-10 in an acidic or alkaline environment are much lower than those of the PPTA hollow fiber membrane prepared in Comparative Example 1, indicating that the use of heterocyclic aramid as a membrane raw material can enhance the long-term chemical corrosion resistance of the membrane, and the structure itself has strong stability, proving that this method can be used to prepare a hollow fiber membrane with good acid and alkali resistance.

[0096] (4) From the perspective of the whole process from raw material dissolution to hollow fiber membrane formation, the time used in Example 1 is significantly shorter than that used in Comparative Example 2. This is because the premixed dissolution method used in Comparative Example 2 is a single kettle rotary stirring type, which has poor shearing and mixing effects on high-concentration casting liquid, and requires a longer swelling-dissolution time to achieve a relatively uniform gel state. At the same time, long-term concentrated acid solvent conditions will cause partial degradation of aromatic polyamide macromolecules, thereby affecting the mechanical properties of the resulting membrane. The high shear force and mixing capacity of the twin-screw extruder in Example 1 can provide sufficient energy to destroy the high interaction between heterocyclic aramid molecules, which not only accelerates the dissolution of heterocyclic aramid, but also increases the content of heterocyclic aramid in the casting liquid, shortens the preparation time, and improves the performance of the heterocyclic aramid hollow fiber membrane.

Claims

1. A method for preparing a heterocyclic aramid hollow fiber membrane, characterized in that: The following steps are involved: S1, raw material pretreatment: removing oil impurities on the surface of heterocyclic aramid filaments, cutting the cleaned and dried heterocyclic aramid filaments to obtain heterocyclic aramid staple fibers; at the same time, drying the PPTA resin; S2, preparing heterocyclic aramid gel casting solution: first, adding a cosolvent to the solvent, stirring to make it uniformly dispersed; then adding the heterocyclic aramid staple fiber, the dried PPTA resin and the porogen to the solution, stirring and swelling at low temperature to obtain a gel premixed solution without obvious particles; wherein the mass fraction of each component is as follows: The sum of the mass fractions of each component is 100%; S3, preparing a nascent heterocyclic aramid hollow fiber membrane: adding the gel premix obtained in S2 to a twin-screw extruder, further dissolving and degassing through the high shear action of the twin-screw, then quantitatively transporting to a hollow spinneret through a booster pump and a metering pump and continuously extruding, and then immersing in a coagulation bath after an air bath to solidify the gel, thereby obtaining a nascent heterocyclic aramid hollow fiber membrane; S4, post-treatment of the nascent hollow fiber membrane: the nascent heterocyclic aramid hollow fiber membrane is wound, washed, neutralized with alkali solution, and then placed in a normal temperature water bath for extraction and washing to obtain a heterocyclic aramid hollow fiber porous membrane; The co-solvent is LiCl; The heterocyclic aramid filament described in S1 is Technora or aramid III.

2. The preparation method according to claim 1, characterized in that: The heterocyclic aramid filaments described in S1 have a fineness of 200 to 1500D.

3. The preparation method according to claim 1, characterized in that: The solvent in S2 is concentrated sulfuric acid with a concentration of 98±2%.

4. The preparation method according to claim 1, characterized in that: The porogen described in S2 is a water-soluble polymer, selected from at least one of PEG with a weight average molecular weight of 800 to 10,000 Da or PVP with a weight average molecular weight of 20,000 to 100,000 Da; when PEG and PVP are compounded, the mass ratio of PEG to PVP is (2 to 5):

1.

5. The preparation method according to claim 1, characterized in that: The preparation of the casting solution in S2 is carried out in a dissolving kettle; the low temperature is 25-50°C; during the stirring and swelling process, the speed of the stirrer is 100-300r / min when stirring begins, and the speed of the stirrer is 20-50r / min after dissolving until there are no obvious particles, for preliminary degassing.

6. The preparation method according to claim 1, characterized in that: In S3, the feeding pressure of the gel premixed liquid when entering the twin-screw extruder is 0.5-3 MPa.

7. The preparation method according to claim 1, characterized in that: In S3, the screw speed of the mixing zone of the twin-screw extruder is 10-50rpm, and the temperature of the melting zone is 40-80°C; the flow rate of the boost pump is 100-400cc / min, and the rotation speed is 5-30r / min; the flow rate of the metering pump is 10-90cc / min, and the rotation speed is 5-30r / min; the metering pump is connected to the hollow spinneret via a spinning pipeline, and the temperature of the spinning pipeline is 30-70°C.

8. The preparation method according to claim 1, characterized in that: The spinning liquid of the hollow spinneret in S3 is deionized water, and the flow rate of the spinning liquid is 20 to 80 cc / min; the height of the air bath is 10 to 100 mm; the coagulation bath is deionized water or a NaOH aqueous solution with a concentration of 10 to 50 wt.%, and the acid concentration of the coagulation bath is controlled below 10%; the temperature of the coagulation bath is 20 to 40°C, and the winding speed is 30 to 120 r / min.

9. The preparation method according to claim 1, characterized in that: In S1, the heterocyclic aramid filaments are first soaked in methanol, then washed with clean water and vacuum dried, and the dried heterocyclic aramid filaments are cut to obtain heterocyclic aramid staple fibers with a length of 0.5 to 2 cm; the PPTA resin is fully dried in vacuum at 100 to 150°C; in S4, a weak alkaline solution of NaHCO3 with a concentration of 10 to 30 wt.% is used in the alkaline washing process, and the moisturizing and shaping process is immersed in a glycerol aqueous solution with a concentration of 30 to 50 wt.%.

10. A heterocyclic aramid hollow fiber membrane prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The heterocyclic aramid hollow fiber membrane has a breaking strength of 3-6 MPa, a breaking elongation of 30-50%, and can stably operate in an acid-base solution with a pH of 2-12.

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