A method for preparing a heterogeneous fiber-reinforced PPTA hollow fiber membrane

Abstract

The application discloses a preparation method of a heterogeneous fiber reinforced PPTA hollow fiber membrane, and first, a hollow tubular reinforcing body is prepared, then solid sulfuric acid particles are prepared, and high-concentration PPTA casting solution is prepared by taking PPTA resin, a pore-forming agent, nano inorganic particles and the sulfuric acid particles as raw materials; the high-concentration PPTA casting solution is uniformly compounded on the surface of the PPTA hollow tubular reinforcing body through a co-extrusion composite spinning process; and after solidification and shaping, the heterogeneous fiber reinforced PPTA hollow fiber membrane is obtained. The application uses a solvent-free sulfuric acid particle technology to change the casting solution system from a traditional solid-liquid mixed system into a solid-solid mixed system, greatly improves the contact area of sulfuric acid and PPTA resin powder, avoids the caking phenomenon in the PPTA dissolving process, reduces the resin degradation, and further improves the casting solution mixing uniformity, effectively shortens the dissolving time, improves the dissolving rate, realizes the preparation of the homogeneous high-concentration PPTA casting solution, and improves the interface bonding strength of the heterogeneous reinforced PPTA hollow fiber membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane separation, and particularly relates to a preparation method of a heterogeneous fiber-reinforced PPTA hollow fiber membrane. BACKGROUND

[0002] Poly-p-phenyleneterephthalamide (PPTA) is a typical aromatic polyamide. A separation membrane material made of PPTA has the characteristics of high hydrophilicity, high temperature resistance, acid and alkali resistance, solvent resistance, and anti-pollution, and can be widely applied to the separation and purification of wastewater in the fields of chemical industry, medicine, biology, food, and the like. However, the decomposition temperature of PPTA is lower than the melting point, and PPTA cannot be melt-spun into a shape. PPTA is only soluble in concentrated sulfuric acid and the like, and is difficult to be dissolved in most conventional organic solvents, which requires high processing equipment and process control. With the rapid development of the global market of high-performance para-aramid in recent years and the significant increase in market demand, a new round of technical development breakthroughs of membrane products such as separation membranes and battery separators of para-aramid downstream products are accelerating.

[0003] Fiber-reinforced hollow fiber membranes are the most widely used membrane form in the field of water treatment at present, and mainly include fiber filament-reinforced hollow fiber membranes and braided tube-reinforced hollow fiber membranes. The fiber filament-reinforced hollow fiber membrane is extruded by simultaneously extruding a filament fiber bundle and a film-forming polymer solution through the special design of a hollow fiber spinning assembly, and the filament fiber bundle is fixed inside the wall of the homogeneous hollow fiber membrane in the process of forming the homogeneous hollow fiber membrane. The document with the application number 202110406572.X discloses a preparation method of a fiber-reinforced aromatic polyamide hollow fiber membrane, which can effectively improve the tensile breaking strength of the homogeneous hollow fiber membrane and is not limited by specific use of internal pressure or external pressure. However, the film-forming process of the method has high difficulty, needs to accurately control the uniform dispersion and embedding of the filament fibers into the membrane wall, has great control difficulty, and has low production efficiency.

[0004] The fiber braided tube-reinforced hollow fiber membrane is based on the chemical fiber skin / core composite spinning technology, uniformly coats the film-forming polymer solution on the outer surface of a pre-braided hollow braided tube, and makes the film-forming polymer and the hollow braided tube become an integral whole through the non-solvent induced phase inversion method. However, in the prior art, the obtained homogeneous reinforced PPTA hollow fiber membrane has a relatively thick outer diameter (>2 mm), has low packing density of the membrane module, and has poor permeation efficiency. At the same time, the surface separation layer of PPTA has low solid content concentration, and the phenomenon of easy falling off of the surface separation layer still exists in the actual application process. More importantly, the production cost of the homogeneous reinforced PPTA hollow fiber membrane is high, and the application field is greatly limited. SUMMARY

[0005] In view of the deficiencies of the prior art, the technical problem to be solved by the present application is to provide a preparation method of a heterogeneous fiber-reinforced PPTA hollow fiber membrane.

[0006] The technical scheme for solving the technical problem of the present application is to provide a preparation method of a heterogeneous fiber-reinforced PPTA hollow fiber membrane, characterized in that the method comprises the following steps:

[0007] (1) preparing a reinforcing body: preparing a hollow tubular object from a fiber filament;

[0008] (2) preparing sulfuric acid particles: cooling liquid sulfuric acid with a concentration of 98% to 100% to 0 to 10 DEG C, and bubbling a gas into the liquid sulfuric acid, stirring and foaming; then rapidly cooling to below 0 DEG C to freeze and solidify, forming foamed solid sulfuric acid, and crushing the foamed solid sulfuric acid to obtain sulfuric acid particles;

[0009] (3) preparing a high-concentration PPTA casting solution: mixing PPTA resin, a pore-forming agent, nano inorganic particles and the sulfuric acid particles in a solid state; then dissolving and mixing uniformly under stirring at 1500 rpm at a temperature of 70 to 90 DEG C under negative pressure to form a uniform solution, and degassing to obtain a high-concentration PPTA casting solution;

[0010] (4) preparing a heterogeneous fiber-reinforced PPTA hollow fiber membrane: using a co-extrusion composite spinning process, uniformly coating the high-concentration PPTA casting solution on the surface of the PPTA hollow tubular object, and solidifying and shaping to obtain a heterogeneous fiber-reinforced PPTA hollow fiber membrane.

[0011] Compared with the prior art, the present application has the following advantages:

[0012] (1) The present application first prepares a hollow tubular object reinforcing body, then prepares solid sulfuric acid particles, and uses PPTA resin, a pore-forming agent, nano inorganic particles and the sulfuric acid particles as raw materials to prepare a high-concentration PPTA casting solution, and then uniformly coats the high-concentration PPTA casting solution on the surface of the PPTA hollow tubular object through a co-extrusion composite spinning process, and solidifies and shapes to obtain a heterogeneous fiber-reinforced PPTA hollow fiber membrane which has excellent performance and low price (low cost, high permeation flux, high separation precision and high interfacial bonding strength).

[0013] (2) The present application can prepare a high-concentration PPTA surface separation layer casting solution. The use of the solvent-free sulfuric acid particle technology changes the casting solution system from a traditional solid-liquid mixing system to a solid-solid mixing system, greatly increases the contact area of sulfuric acid and PPTA resin powder, avoids the caking phenomenon in the PPTA dissolution process, reduces the degradation of the resin, and thus improves the mixing uniformity of the casting solution, effectively shortens the dissolution time and improves the dissolution rate, realizes the preparation of a homogeneous high-concentration PPTA casting solution, and improves the interfacial bonding strength of the heterogeneous reinforced PPTA hollow fiber membrane.

[0014] (3) The application maintains the characteristics of PPTA separation membrane, such as small pore size and narrow distribution (<20 nm), high temperature resistance (>60℃), super hydrophilicity (contact angle <60°), and the like, while the preparation process is simple, the use cost is low, the control factors are mild, easy to control, and the production efficiency is high, and can be widely applied to complex sewage treatment, such as printing and dyeing wastewater, extraction of viruses and bacteria in water, waste liquid purification in electronic industry, purification and concentration of traditional Chinese medicine liquid.

[0015] (4) The use cost of the reinforced PPTA hollow fiber membrane is reduced by selecting the fiber filaments with large market demand and low cost. At the same time, the hollow fiber has good self-supporting property and high packing density, which can improve the permeation flux of the nanofiltration membrane.

[0016] (5) Compared with the PPTA hollow braided tube with thick outer diameter and poor self-supporting property due to the limitation of fiber fineness, the heterogeneous hollow braided tube with high self-supporting degree and small outer diameter size is prepared by selecting low fine denier fiber filaments and designing different reinforcing structure, which can effectively increase the membrane area. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 SEM morphology of the hollow braided tube of the application;

[0018] Figure 2 SEM morphology of the heterogeneous fiber reinforced PPTA hollow fiber membrane reinforced by the hollow braided tube of the application;

[0019] Figure 3 SEM morphology of the hollow braided tube of the application;

[0020] Figure 4 SEM morphology of the heterogeneous fiber reinforced PPTA hollow fiber membrane reinforced by the hollow braided tube of the application. DETAILED DESCRIPTION

[0021] The specific embodiments of the application are given below. The specific embodiments are only used to further illustrate the application, and do not limit the protection scope of the claims of the application.

[0022] The application provides a preparation method of a heterogeneous fiber reinforced PPTA hollow fiber membrane (referred to as the method), characterized in that the method comprises the following steps:

[0023] (1) preparing a reinforcing body: preparing fiber filaments into a hollow tubular object as a reinforcing body;

[0024] Preferably, step (1) is specifically: adopting two-dimensional braiding technology or knitting technology to prepare fiber filaments into a hollow braided tube or a hollow knitted tube as a reinforcing body.

[0025] Preferably, in step (1), the fiber filaments are low-cost fiber filaments, and one of polyester, nylon, polypropylene, or cellulose acetate fibers is used, with a fineness of 50-400D.

[0026] Preferably, in step (1), the hollow tube has an outer diameter of 1-2 mm and an inner diameter of 0.8-1.8 mm.

[0027] (2) Preparation of sulfuric acid particles: liquid sulfuric acid with a concentration of 98-100% is cooled to 0-10°C (preferably 4-8°C), and a gas is filled into the liquid sulfuric acid while the liquid sulfuric acid is kept at a low temperature, and the liquid sulfuric acid is stirred and foamed; then the liquid sulfuric acid is rapidly cooled to below 0°C to freeze and solidify, forming foamed solid sulfuric acid, which is crushed to obtain solid sulfuric acid particles;

[0028] Preferably, in step (2), the gas is air, nitrogen, argon, or carbon dioxide.

[0029] Preferably, in step (2), the gas filling pressure is 0.5-5 MPa.

[0030] Preferably, in step (2), the stirring and foaming time is 5-20 min, and the stirring speed is 50-200 rpm.

[0031] Preferably, in step (2), the particle size of the sulfuric acid particles is less than a decimeter, preferably less than a centimeter.

[0032] (3) Preparation of high-concentration PPTA casting solution: PPTA resin, pore-forming agent, nano-inorganic particles, and sulfuric acid particles are thoroughly mixed in a solid state (preferably at 0-5°C); then the mixture is dissolved at 70-90°C under negative pressure, and a uniform solution is formed after thorough mixing and degassing, and a high-concentration PPTA casting solution is obtained;

[0033] Preferably, the preparation of the casting solution in step (3) is carried out in a planetary high-speed mixer.

[0034] Preferably, in step (3), the mass fraction of the high-concentration PPTA casting solution is: 3-20 wt.% of PPTA resin (preferably 5-10 wt.%), 1-5 wt.% of pore-forming agent, 0-10 wt.% of nano-inorganic particles, and 65-96 wt.% of sulfuric acid particles, and the sum of the components is 100%.

[0035] Preferably, in step (3), the specific viscosity of the PPTA resin is 3-8 dL / g.

[0036] Preferably, in step (3), the pore-forming agent is a water-soluble polymer selected from at least one of PEG with a weight average molecular weight of 600-20000 or PVP with a weight average molecular weight of 10000-100000; when PEG and PVP are used in combination, the mass ratio of PEG to PVP is 2-8:1.

[0037] Preferably, in step (3), the nano-inorganic particles are selected from at least one of silicon dioxide, titanium dioxide, carbon nanotubes, sodium sulfate, sodium chloride or graphene oxide.

[0038] Preferably, in step (3), the negative pressure condition is -0.1 MPa, and the dissolution condition is stirring at a high speed of greater than 500 rpm (preferably 2000-3000 rpm) for 0.5-2 h.

[0039] (4) Preparation of a heterogeneous fiber-reinforced PPTA hollow fiber membrane: high-concentration PPTA casting solution is injected into a double-screw extruder, and then a high-concentration PPTA casting solution is uniformly compounded on the surface of a PPTA hollow tubular object by using a co-extrusion composite spinning process. After solidification and shaping, a heterogeneous fiber-reinforced PPTA hollow fiber membrane (referred to as a PPTA hollow fiber membrane) is obtained.

[0040] Preferably, step (4) is specifically: high-concentration PPTA casting solution is injected into a double-screw extruder for further mixing and defoaming, and then the high-concentration PPTA casting solution is uniformly compounded on the surface of a PPTA hollow tubular object by using a double-layer composite spinning assembly. Under the traction of an automatic tension-adjusting winding roller, the PPTA casting solution is immersed in a coagulation bath after an air bath for solidification and shaping. After removal of the pore-forming agent and nano-inorganic particles by extraction and washing, a heterogeneous fiber-reinforced PPTA hollow fiber membrane is obtained.

[0041] Preferably, in step (4), the spinning temperature is 70-90°C; the winding roller has a traction speed of 1-30 m / min; the air bath has a height of 1-10 cm; the coagulation bath has a temperature of 0-40°C, and the coagulation bath is a sulfuric acid aqueous solution with a mass concentration of 0-10 wt.%.

[0042] Preferably, in step (4), the extraction and washing process is immersion in a glycerol aqueous solution with a concentration of 30-50 wt.% for more than 48 h; preferably, the glycerol aqueous solution contains formaldehyde with a mass concentration of 1.0-5.0 wt.%.

[0043] Example 1

[0044] (1) Preparation of a reinforcing body: a 200D PET filament is woven into a two-dimensional woven structure PET hollow woven tube by using a two-dimensional weaving technique, and the outer diameter is 1.8 mm;

[0045] (2) Preparation of sulfuric acid particles: liquid sulfuric acid with a concentration of 98% is cooled to 8°C, and nitrogen gas at 1.0 MPa is filled into the liquid sulfuric acid under stirring to form foam; then the temperature is rapidly lowered to below 0°C to freeze and solidify, and the foamed solid sulfuric acid is crushed to obtain sulfuric acid particles;

[0046] (3) Preparation of high-concentration PPTA casting solution: 5.0 wt.% PPTA resin (intrinsic viscosity of 5.0 dL / g), 0.1 wt.% nano-SiO2, 5.0 wt.% pore-forming agent PEG (weight average molecular weight of 2000), and sulfuric acid particles are mixed at 5°C by using a planetary high-speed mixer; then the temperature is raised to 80°C under-0.1 MPa, and the mixture is stirred and dissolved at 2500 rpm for 1 h to form a uniform solution, and the high-concentration PPTA casting solution is obtained after degassing;

[0047] (4) Preparation of heterogeneous fiber-reinforced PPTA hollow fiber membrane: the high-concentration PPTA casting solution is injected into a double-screw extruder for further mixing and degassing, and then uniformly compounded on the surface of the PET hollow braided tube through a double-layer composite spinning assembly, and drawn at a speed of 10 m / min under the traction of an automatic tension-adjusting winder, and then enters a 25°C pure water coagulation bath after passing through a 5 cm air bath to form a heterogeneous fiber-reinforced PPTA hollow fiber nascent membrane (referred to as nascent membrane); the nascent membrane is immersed in a 30 wt.% glycerol aqueous solution (containing 2.0 wt.% formaldehyde) for 72 h to obtain a PPTA hollow fiber membrane.

[0048] The test results show that the obtained PPTA hollow fiber membrane has a pure water flux of 245 L·m -2 ·h -1 ·MPa -1 at 0.1 MPa, and a burst pressure (i.e., the separation strength of the surface separation layer and the reinforcing body) of 0.2 MPa.

[0049] As can be seen from Figure 1 , the two-dimensional braided structure presents a diamond-shaped braided structure.

[0050] As can be seen from Figure 2 , the casting solution of the surface separation layer can penetrate through the diamond-shaped braided nodes and the gaps between the fibers of the two-dimensional braided structure. Due to the tight braided structure and small pore size, only the surface of the fiber reinforcing body is etched by the concentrated sulfuric acid, and the casting solution does not penetrate into the reinforcing body, thereby realizing the tight compounding of the surface separation layer and the fiber braided tube.

[0051] Example 2

[0052] (1) Preparation of the reinforcing body: 200D PET filaments were woven into a two-dimensional woven structure PET hollow braided tube with an outer diameter of 1.8 mm using two-dimensional weaving technology;

[0053] (2) Preparation of sulfuric acid particles: liquid sulfuric acid with a concentration of 98% was cooled to 8°C, and 1.0 MPa of nitrogen was filled into it under the condition of low-temperature liquid state, and stirred and foamed; then rapidly cooled to below 0°C for freezing and coagulation, forming foamed solid sulfuric acid, which was crushed to obtain sulfuric acid particles;

[0054] (3) Preparation of high-concentration PPTA casting solution: 8.0 wt.% PPTA resin (specific viscosity of 5.0 dL / g), 0.1 wt.% nano-SiO2, 5.0 wt.% pore-forming agent PEG (weight average molecular weight of 2000) and sulfuric acid particles were fully mixed at 5°C using a planetary high-speed mixer; then heated to 80°C under-0.1 MPa, stirred and dissolved at a speed of 2500 rpm for 2 h to form a uniform solution, and then degassed to obtain a high-concentration PPTA casting solution;

[0055] (4) Preparation of heterogeneous fiber-reinforced PPTA hollow fiber membrane: the high-concentration PPTA casting solution was injected into a double-screw extruder for further mixing and degassing, and then uniformly compounded on the surface of the PET hollow braided tube through a double-layer composite spinning assembly, and then drawn at a speed of 10 m / min under the traction of an automatic tension-adjusting winding roller, and then passed through an air bath of 5 cm and then entered a 25°C pure water coagulation bath to form a nascent membrane; then the nascent membrane was immersed in a 30 wt.% glycerol aqueous solution (containing 2.0 wt.% formaldehyde) for 72 h to obtain a PPTA hollow fiber membrane.

[0056] The obtained PPTA hollow fiber membrane has a pure water flux of 102 L·m -2 ·h -1 ·MPa -1 and a burst pressure of 0.3 MPa under the condition of 0.1 MPa.

[0057] Example 3

[0058] (1) Preparation of the reinforcing body: 200D PET filaments were woven into a two-dimensional woven structure PET hollow braided tube with an outer diameter of 1.8 mm using two-dimensional weaving technology;

[0059] (2) Preparation of sulfuric acid particles: liquid sulfuric acid with a concentration of 98% was cooled to 8°C, and 1.0 MPa of nitrogen was filled into it under the condition of low-temperature liquid state, and stirred and foamed; then rapidly cooled to below 0°C for freezing and coagulation, forming foamed solid sulfuric acid, which was crushed to obtain sulfuric acid particles;

[0060] (3) Preparation of high-concentration PPTA casting solution: 5.0 wt.% PPTA resin (inherent viscosity of 7.0 dL / g), 0.1 wt.% nano-SiO2, 5.0 wt.% pore-forming agent PEG (weight average molecular weight of 2000) and sulfuric acid particles were mixed at 5°C using a planetary high-speed mixer; then, the temperature was raised to 80°C under -0.1 MPa, and the mixture was stirred and dissolved at 2500 rpm for 1.5 h to form a uniform solution. After degassing, a high-concentration PPTA casting solution was obtained;

[0061] (4) Preparation of heterogeneous fiber-reinforced PPTA hollow fiber membrane: The high-concentration PPTA casting solution was injected into a double-screw extruder for further mixing and degassing. The solution was uniformly compounded on the surface of the PET hollow braided tube through a double-layer composite spinning assembly. Under the traction of the automatic tension-adjusting winding roller, the solution was drawn at a speed of 10 m / min, passed through a 5 cm air bath, and then entered a 25°C pure water coagulation bath to form a primary membrane. The primary membrane was then immersed in a 30 wt.% glycerol aqueous solution (containing 2.0 wt.% formaldehyde) for 72 h to obtain a PPTA hollow fiber membrane.

[0062] The obtained PPTA hollow fiber membrane had a pure water flux of 152 L·m -2 ·h -1 ·MPa -1 and a burst pressure of 0.2 MPa under the condition of 0.1 MPa.

[0063] Example 4

[0064] (1) Preparation of reinforcing body: 200D PET filaments were woven into a two-dimensional woven structure PET hollow braided tube with an outer diameter of 1.8 mm using two-dimensional weaving technology;

[0065] (2) Preparation of sulfuric acid particles: Liquid sulfuric acid with a concentration of 98% was cooled to 8°C, and 1.0 MPa of nitrogen gas was injected into the liquid while stirring to form foam. Then, the foam was rapidly cooled to below 0°C to freeze and coagulate, forming a foamed solid sulfuric acid. After crushing, sulfuric acid particles were obtained;

[0066] (3) Preparation of high-concentration PPTA casting solution: 5.0 wt.% PPTA resin (inherent viscosity of 5.0 dL / g), 0.1 wt.% nano-SiO2, 5.0 wt.% pore-forming agent PEG (weight average molecular weight of 2000) and sulfuric acid particles were mixed at 5°C using a planetary high-speed mixer; then, the temperature was raised to 80°C under -0.1 MPa, and the mixture was stirred and dissolved at 2500 rpm for 1.5 h to form a uniform solution. After degassing, a high-concentration PPTA casting solution was obtained;

[0067] (4) Preparation of heterogeneous fiber reinforced PPTA hollow fiber membrane: high concentration PPTA casting solution was injected into a double screw extruder for further mixing and degassing, and then uniformly compounded on the surface of the PET hollow braided tube through a double-layer composite spinning pack. Under the traction of the automatic tension adjusting winding roller, the nascent membrane was formed by solidifying and shaping in a 25℃ pure water coagulation bath at a drawing speed of 20m / min after passing through a 5cm air bath. The nascent membrane was then immersed in a 30wt.% glycerol aqueous solution (with 2.0wt.% formaldehyde added) for 72h to obtain the PPTA hollow fiber membrane.

[0068] The obtained PPTA hollow fiber membrane has a pure water flux of 340L·m -2 ·h -1 ·MPa -1 and a burst pressure of 0.2MPa under the condition of 0.1MPa.

[0069] Example 5

[0070] (1) Preparation of reinforcing body: a 200D PET filament was knitted into a knitted structure PET hollow knitted tube with an outer diameter of 1.4mm by using knitting technology;

[0071] (2) Preparation of sulfuric acid particles: liquid sulfuric acid with a concentration of 98% was cooled to 8℃, and nitrogen gas at 3.0MPa was injected into the liquid under low temperature to stir and foam. Then, the temperature was rapidly lowered to below 0℃ for freezing and coagulation to form foamed solid sulfuric acid, which was crushed to obtain sulfuric acid particles;

[0072] (3) Preparation of high concentration PPTA casting solution: 5.0wt.% PPTA resin (intrinsic viscosity of 5.0dL / g), 0.1wt.% nano-SiO2, 5.0wt.% porogen PEG (weight average molecular weight of 2000) and sulfuric acid particles were mixed at 5℃ by using a planetary high-speed mixer. Then, the mixture was stirred and dissolved at 80℃ under-0.1MPa for 0.5h at a rotation speed of 2500r / min to form a uniform solution. After degassing, the high concentration PPTA casting solution was obtained;

[0073] (4) Preparation of heterogeneous fiber reinforced PPTA hollow fiber membrane: the high concentration PPTA casting solution was injected into a double screw extruder for further mixing and degassing, and then uniformly compounded on the surface of the PET hollow braided tube through a double-layer composite spinning pack. Under the traction of the automatic tension adjusting winding roller, the nascent membrane was formed by solidifying and shaping in a 25℃ pure water coagulation bath at a drawing speed of 15m / min after passing through a 5cm air bath. The nascent membrane was then immersed in a 30wt.% glycerol aqueous solution (with 2.0wt.% formaldehyde added) for 72h to obtain the PPTA hollow fiber membrane.

[0074] The obtained PPTA hollow fiber membrane, under a pressure of 0.1 MPa, exhibited a pure water flux of 238 L·m⁻¹. -2 ·h -1 ·MPa -1 The burst pressure is 0.3 MPa.

[0075] Depend on Figure 3 It can be seen that the reinforcement adopts a single-sided weft flat needle coil structure, and the surface separation layer casting liquid can fill the pores through the coil and seep in from the fiber gaps.

[0076] Depend on Figure 4 It can be seen that, compared with the two-dimensional braided structure, the knitted structure has a larger pore size and higher porosity, which makes it easier for the surface separation layer casting liquid to penetrate into the fiber reinforcement and form a through-type reinforcement structure.

[0077] Example 6

[0078] (1) Preparation of reinforcement: 200D PET filaments were knitted into PET hollow knitted tubes with an outer diameter of 1.4mm using knitting technology;

[0079] (2) Preparation of sulfuric acid particles: Cool 98% liquid sulfuric acid to 8°C, and introduce 3.0 MPa of nitrogen gas into it while maintaining the low temperature liquid state, and stir to foam; then quickly cool it to below 0°C to freeze and solidify, forming foamed solid sulfuric acid, which is then crushed to obtain sulfuric acid particles;

[0080] (3) Preparation of high-concentration PPTA casting solution: 5.0 wt.% PPTA resin (specific logarithmic viscosity of 5.0 dL / g), 0.1 wt.% nano SiO2, and 5.0 wt.% porogen PEG / PVP (PEG weight average molecular weight of 2000, PVP weight average molecular weight of 30000, PEG to PVP mass ratio of 4:1) and sulfuric acid particles were thoroughly mixed at 5°C using a planetary high-speed mixer; then the temperature was raised to 80°C at -0.1 MPa and stirred at 2500 rpm for 0.5 h to dissolve the solution, and the mixture was stirred until a homogeneous solution was formed. After degassing, a high-concentration PPTA casting solution was obtained.

[0081] (4) Preparation of heterogeneous fiber reinforced PPTA hollow fiber membrane: High concentration PPTA casting solution was injected into a twin-screw extruder for further mixing and degassing. It was then uniformly composited onto the surface of a PET hollow braided tube through a double-layer composite spinneret. Under the traction of an automatic tension-adjusting winding roller, the membrane was stretched at a speed of 15 m / min and then immersed in a 25°C pure water coagulation bath after passing through a 5 cm air bath to solidify and form a nascent membrane. The nascent membrane was then immersed in a 30 wt.% glycerol aqueous solution (with 2.0 wt.% formaldehyde added) for 72 h to obtain a PPTA hollow fiber membrane.

[0082] The pure water flux of the obtained PPTA hollow fiber membrane is 294 L-m -2 ·h -1 ·MPa -1 , and the burst pressure is 0.3 MPa.

[0083] Example 7

[0084] (1) Preparation of the reinforcing body: 200D PET filaments are knitted into a knitted structure PET hollow knitted tube with an outer diameter of 1.4 mm by using a knitting technology;

[0085] (2) Preparation of sulfuric acid particles: liquid sulfuric acid with a concentration of 98% is cooled to 8°C, and nitrogen gas at 3.0 MPa is filled into the liquid sulfuric acid under the condition of keeping the low-temperature liquid state and stirring to foam; then, the temperature is rapidly lowered to below 0°C for freezing and solidification, and foamed solid sulfuric acid is formed, which is crushed to obtain sulfuric acid particles;

[0086] (3) Preparation of high-concentration PPTA casting solution: 5.0 wt.% PPTA resin (intrinsic viscosity of 5.0 dL / g), 0.1 wt.% nano-SiO2, 5.0 wt.% porogen PEG / PVP (weight average molecular weight of PEG is 2000, weight average molecular weight of PVP is 30000, and the mass ratio of PEG to PVP is 4:1) and sulfuric acid particles are fully mixed at 5°C by using a planetary high-speed mixer; then, the temperature is raised to 80°C under-0.1 MPa, and the mixture is stirred and dissolved at a speed of 2500 rpm for 0.5 h to form a uniform solution, and the high-concentration PPTA casting solution is obtained after degassing;

[0087] (4) Preparation of heterogeneous fiber-reinforced PPTA hollow fiber membrane: the high-concentration PPTA casting solution is injected into a double-screw extruder for further mixing and degassing, and is uniformly compounded on the surface of the PET hollow knitted tube by using a double-layer composite spinning assembly; under the traction of an automatic tension-adjusting winding roller, the stretching speed is 15 m / min, the nascent membrane is formed after passing through an air bath of 5 cm and then being immersed in a 25°C sulfuric acid water coagulation bath with a concentration of 5.0 wt.%; and the PPTA hollow fiber membrane is obtained after being immersed in a glycerol aqueous solution with a concentration of 30 wt.% (2.0 wt.% formaldehyde is added) for 72 h of extraction and washing.

[0088] The pure water flux of the obtained PPTA hollow fiber membrane is 276 L-m -2 ·h -1 ·MPa -1 , and the burst pressure is 0.3 MPa.

[0089] Example 8

[0090] (1) Preparation of reinforcing body: 200D PET filaments are knitted into a knitted structure PET hollow knitted tube with an outer diameter of 1.4 mm by using knitting technology;

[0091] (2) Preparation of sulfuric acid particles: liquid sulfuric acid with a concentration of 98% is cooled to 8°C, and nitrogen gas at 3.0 MPa is filled into the liquid under low temperature to stir and foam; then it is quickly cooled to below 0°C to freeze and solidify, forming foamed solid sulfuric acid, which is crushed to obtain sulfuric acid particles;

[0092] (3) Preparation of high-concentration PPTA casting solution: 5.0 wt.% PPTA resin (intrinsic viscosity of 5.0 dL / g), 0.1 wt.% nano-SiO2, 5.0 wt.% porogen PEG / PVP (weight average molecular weight of PEG is 2000, weight average molecular weight of PVP is 30000, mass ratio of PEG to PVP is 4:1) and sulfuric acid particles are mixed at 5°C by using a planetary high-speed mixer; then it is dissolved at 80°C under -0.1 MPa for 0.5 h at a stirring speed of 2500 rpm to form a uniform solution, and the high-concentration PPTA casting solution is obtained after degassing;

[0093] (4) Preparation of heterogeneous fiber-reinforced PPTA hollow fiber membrane: the high-concentration PPTA casting solution is further mixed and degassed by a double-screw extruder, and then uniformly compounded on the surface of the PET hollow knitted tube by a double-layer composite spinning assembly. Under the traction of the automatic tension adjusting winding roller, the nascent membrane is formed by immersing the nascent membrane into a 5.0 wt.% sulfuric acid water coagulation bath at 35°C after passing through a 5 cm air bath at a drawing speed of 15 m / min. The PPTA hollow fiber membrane is obtained by immersing the nascent membrane in a 30 wt.% glycerol aqueous solution (containing 2.0 wt.% formaldehyde) for 72 h.

[0094] The test results show that the PPTA hollow fiber membrane has a pure water flux of 316 L·m -2 ·h -1 ·MPa -1 and a burst pressure of 0.3 MPa under the condition of 0.1 MPa.

[0095] Comparative Example 1

[0096] (1) Preparation of reinforcing body: 200D PET filaments are knitted into a two-dimensional knitted structure PET hollow knitted tube with an outer diameter of 1.8 mm by using two-dimensional knitting technology;

[0097] (2) Preparing PPTA casting solution: 1.5 wt.% of PPTA resin (inherent viscosity of 5.0 dL / g), 0.1 wt.% of nano-SiO2, and 5.0 wt.% of pore-forming agent PEG (weight average molecular weight of 2000) were dissolved in a concentrated sulfuric acid solvent with a concentration of 98%, stirred at 80°C for 3h until mixed uniformly, and then deaerated to obtain a PPTA casting solution;

[0098] (3) Preparing heterogeneous fiber-reinforced PPTA hollow fiber membrane: The PPTA casting solution was injected into a double screw extruder for further mixing and deaeration, and then uniformly coated on the surface of a PET hollow braided tube through a double-layer composite spinning assembly. The nascent membrane was formed by solidification in a 35°C pure water coagulation bath after being drawn at a speed of 10 m / min through a 5cm air bath under the traction of an automatic tension-adjusting winder. The nascent membrane was then immersed in a glycerol aqueous solution (with a concentration of 30 wt.%) containing 2.0 wt.% of formaldehyde for 72h for extraction and washing to obtain a PPTA hollow fiber membrane.

[0099] The obtained PPTA hollow fiber membrane had a pure water flux of 436 L·m -2 ·h -1 ·MPa -1 and a burst pressure of 0.1 MPa under the condition of 0.1 MPa.

[0100] Performance of PPTA hollow fiber membranes prepared in Examples 1-8 and Comparative Example 1

[0101]

[0102]

[0103] From the preparation parameters shown in the examples and comparative examples and the data in Table 1, it can be seen that: (1) as the PPTA solid content increases and the specific concentration logarithmic viscosity of PPTA increases, and the solvent content in the coagulation bath increases, the porosity of the obtained membrane decreases, the density of the separation layer on the surface of the membrane increases, the pure water flux of the obtained heterogeneous fiber-reinforced PPTA hollow fiber membrane significantly decreases, and the interfacial bonding strength increases; (2) the faster the winding rate, the thinner the wall thickness of the separation layer on the surface of the obtained membrane; the higher the content of the pore-forming agent, the higher the porosity of the obtained membrane, the pure water flux of the obtained heterogeneous fiber-reinforced PPTA hollow fiber membrane significantly increases, and the interfacial bonding strength decreases; (3) compared with the two-dimensional woven structure, the knitted structure has a large pore size and high porosity, which is beneficial to the penetration of the surface separation layer into the fiber reinforcement, and the interfacial bonding strength is improved; (4) from Comparative Example 1, it can be seen that the solid-solid dissolution process of PPTA resin-solid sulfuric acid particles can obtain a high-concentration PPTA casting solution, and at the same time, high-pressure gas is beneficial to obtain sulfuric acid particles with appropriate particle size, thereby improving the mixing uniformity of the casting solution, effectively shortening the dissolution time, and improving the interfacial bonding strength of the heterogeneous fiber-reinforced PPTA hollow fiber membrane. In summary, by comprehensively regulating the woven structure of the fiber hollow woven tube, the PPTA dissolution method, and the corrosion time of the surface separation layer and the surface of the hollow woven tube, the optimal state of permeation efficiency and two-phase interfacial bonding can be achieved.

[0104] The unmentioned parts of the present application apply to the prior art.

Claims

1. A method for preparing a heterogeneous fiber-reinforced PPTA hollow fiber membrane, characterized in that, The method includes the following steps: (1) Preparation of reinforcement: The fiber filament is made into a hollow tubular structure; the fiber filament is one of polyester, nylon, polypropylene or cellulose acetate fiber; (2) Preparation of sulfuric acid particles: Cool liquid sulfuric acid with a concentration of 98%~100% to 0~10℃, and introduce gas into it, stir and foam; then quickly cool it to below 0℃ to freeze and solidify it to form foamed solid sulfuric acid, which is then crushed to obtain sulfuric acid particles; (3) Preparation of high-concentration PPTA casting solution: PPTA resin, pore-forming agent, nano-inorganic particles and sulfuric acid particles are thoroughly mixed in solid state; then the temperature is raised to 70~90℃ under negative pressure to dissolve and mix evenly to form a homogeneous solution. After degassing, a high-concentration PPTA casting solution is obtained. The mass composition of the high-concentration PPTA casting solution is as follows: 3~20 wt.% PPTA resin, 1~5 wt.% pore-forming agent, 0~10 wt.% (excluding 0 wt.% nano-inorganic particles), and 65~96 wt.% sulfuric acid particles, with the sum of all components being 100%. (4) Preparation of heterogeneous fiber reinforced PPTA hollow fiber membrane: The high-concentration PPTA casting solution is uniformly coated on the surface of the hollow tube by a twin-screw co-extrusion composite spinning process. After solidification, a heterogeneous fiber reinforced PPTA hollow fiber membrane is obtained.

2. The method for preparing heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 1, characterized in that, Step (1) specifically involves using two-dimensional weaving or knitting techniques to make hollow braided tubes or hollow knitted tubes from fiber filaments.

3. The method for preparing heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 1, characterized in that, In step (1), the fineness of the fiber filament is 50~400D.

4. The method for preparing heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 1, characterized in that, In step (2), the gas used is air, nitrogen, argon or carbon dioxide, and the filling pressure is 0.5~5MPa.

5. The method for preparing heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 1, characterized in that, In step (2), the stirring and foaming time is 5~20 min and the stirring speed is 50~200 rpm.

6. The method for preparing heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 1, characterized in that, In step (3), the specific logarithmic viscosity of the PPTA resin is 3~8 dL / g; The pore-forming agent is a water-soluble polymer selected from at least one of PEG with a weight average molecular weight of 600-20000 or PVP with a weight average molecular weight of 10000-100000; when PEG and PVP are used in combination, the mass ratio of PEG to PVP is 2-8:

1. The nano-inorganic particles are selected from at least one of silicon dioxide, titanium dioxide, carbon nanotubes, sodium sulfate, sodium chloride, or graphene oxide.

7. The method for preparing heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 1, characterized in that, In step (3), the negative pressure condition is -0.1 MPa, and the dissolution condition is: stirring at a high speed of more than 500 rpm for 0.5~2 h.

8. The method for preparing heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 1, characterized in that, Step (4) specifically involves: injecting high-concentration PPTA casting liquid into a twin-screw extruder for mixing and degassing; then uniformly coating the high-concentration PPTA casting liquid onto the surface of a hollow tube through a double-layer composite spinneret; under the traction of an automatic tension-adjusting winding roller, after passing through an air bath, immersing it in a coagulation bath to solidify and form a shape; and then extracting and washing to remove the pore-forming agent and nano-inorganic particles to obtain a heterogeneous fiber-reinforced PPTA hollow fiber membrane.

9. The method for preparing the heterogeneous fiber reinforced PPTA hollow fiber membrane according to claim 8, characterized in that, In step (4), the spinning temperature is 70~90℃; the traction speed of the winding roller is 1~30m / min; the air bath height is 1~10cm; the coagulation bath temperature is 0~40℃, and the coagulation bath is a sulfuric acid aqueous solution with a mass concentration of 0~10wt.%; the extraction process is to soak in a glycerol aqueous solution with a concentration of 30~50wt.% for more than 48 hours.

Images