Industrial preparation process of low-cost, high-flux, acid-resistant, alkali-resistant and high-conductivity carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane

Abstract

The invention relates to an industrial preparation process of a low-cost high-flux acid and alkali resistant high-conductivity carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane, which comprises the following steps: mixing and crushing carbon nanotubes and polyvinylpyrrolidone to obtain mixed powder; dispersing the mixed powder, polyvinylidene fluoride and polyethylene glycol in an organic solvent, heating, stirring and defoaming to obtain a spinning solution; adjusting the air gap distance between a spinneret plate and the liquid level of the coagulating bath, and spinning by taking the spinning solution as a shell solution and an organic solvent / aqueous solution as a core solution to obtain membrane filaments; and putting the membrane filaments into hot water for hot washing, naturally airing, carrying out hot washing again, soaking the membrane filaments in a glycerol aqueous solution, and naturally airing after soaking to obtain the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane. The treatment before crushing can improve the dispersibility of the carbon nanotube powder, shorten the stirring time and improve the membrane preparation efficiency. The post-treatment of the membrane filaments can enable the membrane filaments to have stable high-purity water flux, the conductivity of the membrane filaments in a wet state is improved, and the electrochemical performance of the membrane filaments is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membrane preparation, and in particular to an industrial preparation process for a low-cost, high-throughput, acid- and alkali-resistant, highly conductive carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane. Background Art

[0002] Membrane separation technology, due to its high efficiency, space-saving design, and ease of assembly, has been widely used in industrial wastewater treatment, drinking water purification, and seawater desalination, playing a vital role in controlling water pollution and alleviating water shortages. However, conventional separation membranes still face challenges such as severe membrane fouling and the trade-off between permeability and selectivity. In recent years, conductive separation membranes have emerged as a rapidly developing new type of separation membrane. These membranes not only retain their separation capabilities but also utilize electrochemical principles to enhance their performance and enable new functions not possible with conventional membranes.

[0003] Among many conductive materials, carbon nanotubes have been industrialized and commercialized with low cost. At the same time, carbon nanotubes are one-dimensional hollow tubular structures with excellent conductivity and mechanical strength. 2 Hybridized carbon surfaces allow for rapid, frictionless transport of water molecules, demonstrating significant potential for the construction of high-performance conductive separation membranes. Patent CN104028112A discloses a method for the large-scale preparation of pure carbon nanotube hollow fiber membranes. This method utilizes large amounts of concentrated nitric acid and sulfuric acid, resulting in high operational risks and the generation of secondary pollutants such as waste acid. It also requires a high-temperature calcination process, which consumes a lot of energy. The long preparation cycle results in low yields, making it difficult to meet the efficiency requirements of industrial continuous production. The resulting pure carbon nanotube hollow fiber membranes are brittle and prone to breakage, exhibiting poor flexibility and difficulty meeting practical application requirements. Patent CN116571101A discloses a method for the preparation of carbon nanotube-polyvinylidene fluoride composite hollow fiber membranes. This method utilizes surface-modified carbon nanotubes and utilizes a dispersant to enhance the dispersion of the carbon nanotubes in the polyvinylidene fluoride, resulting in high raw material costs. Furthermore, due to the moderate swelling of polyvinylidene fluoride in water, the conductivity of the resulting membrane fibers in their wet state is limited. Therefore, it is of great value and significance to develop an industrial preparation process for low-cost, high-throughput, and highly conductive carbon nanotube-based hollow fiber membranes. Summary of the Invention

[0004] In order to solve the problems of existing hollow fiber membranes such as brittleness, poor flexibility, poor conductivity, low flux, high preparation cost and long cycle, a low-cost, high-flux, acid- and alkali-resistant, and highly conductive carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane industrial preparation process is proposed. The preparation process is designed to meet the higher requirements for the performance of conductive hollow fiber membranes in practical applications.

[0005] According to one aspect of the present invention, a low-cost, high-throughput, acid- and alkali-resistant, highly conductive industrial preparation process for a carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane is provided. The industrial preparation process comprises the following steps: Step (1), raw material pretreatment: mixing carbon nanotubes and polyvinyl pyrrolidone, and crushing to obtain a mixed powder; Step (2), preparation of spinning solution: dispersing the mixed powder obtained in step (1), polyvinylidene fluoride and polyethylene glycol in an organic solvent, heating and stirring, and degassing in a vacuum or standing state to obtain a spinning solution; Step (3), dry-wet spinning: adjusting the air gap between the spinneret and the coagulation bath liquid surface, the spinning solution obtained in step (2) is the shell liquid, and the organic solvent / water solution is the core liquid. The shell liquid and the core liquid pass through the spinneret and then enter the coagulation bath through the air gap, and then are wound on a winding wheel for spinning to obtain a primary carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane; Step (4), post-treatment of the membrane fibers: placing the nascent carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane fibers prepared in step (3) in hot water for heat washing, naturally drying, placing them in hot water again for heat washing, soaking them in a glycerol aqueous solution after hot washing, and naturally drying them after soaking to obtain a carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane.

[0006] Furthermore, the dry-wet spinning in step (3) also includes coating the spinning solution onto the hollow nylon braided tube substrate through a spinneret, and then entering the spinning solution into a coagulation bath together, spinning after preliminary phase transformation and soaking in water for 6 to 24 hours, thereby obtaining a carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane with the nylon braided tube as the substrate.

[0007] Furthermore, the polyvinyl pyrrolidone in step (1) has a model of K12 to K96, preferably K30; The carbon nanotubes in step (1) are selected from at least one of unmodified carbon nanotubes, carboxylated carbon nanotubes, hydroxylated carbon nanotubes, and amino carbon nanotubes, preferably unmodified carbon nanotubes; The crushing time in step (1) is 30 s to 2 min.

[0008] Furthermore, the organic solvent in step (2) is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide, preferably N,N-dimethylacetamide; The model of the polyethylene glycol in step (1) is PEG200-600, preferably PEG400; The conditions for heating and stirring in step (2) are as follows: The heating and stirring temperature is 40-80°C; The heating and stirring time is 6 to 12 hours; The heating and stirring speed is 500-800 rpm; The mass ratio of polyvinylidene fluoride, carbon nanotubes, polyvinyl pyrrolidone and polyethylene glycol in the spinning solution in step (2) is 1:0.1~0.5:0.2~1:0~1.

[0009] Furthermore, the air gap spacing in step (3) is 2 to 20 cm.

[0010] The type of organic solvent in the spinning solution of step (2) is the same as the type of organic solvent in the core solution of step (3), and the mass fraction is 50-90%; The volume flow ratio of the shell liquid to the core liquid is 2 to 6:1, preferably 4:1; The spinning conditions are as follows: The rotation speed ratio of the shell liquid to the core liquid is 10-30:5-15; The winding speed during spinning is 5-30 m / min; Furthermore, the temperature of the hot water in the membrane filament post-treatment in step (4) is 50-100°C, preferably 70°C; The hot washing time is 2 to 6 hours.

[0011] Furthermore, the mass fraction of the glycerol aqueous solution in step (4) is 30-70%, preferably 50%; The soaking time in the glycerol aqueous solution in step (4) is 8 to 24 hours.

[0012] Furthermore, the inner surface of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane obtained in step (4) presents a macroporous morphology, the cross section is a typical hollow structure, the cross section presents a semi-finger-like, semi-sponge structure, the average pore size is 50~60 nm, the porosity is 90%~95%, and the pore size distribution is narrow.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane disclosed in the present invention has low production cost. The preparation process utilizes the shear force of the crusher at high speed to make the carbon nanotubes and polyvinyl pyrrolidone fully contact and evenly disperse. First, mechanical crushing can destroy the structure of carbon nanotube aggregates and release single or small bundles of carbon nanotubes. At the same time, polyvinyl pyrrolidone is an amphiphilic polymer. Its hydrophobic groups are adsorbed on the surface of carbon nanotubes through π-π conjugation, and the hydrophilic groups form steric hindrance outward to prevent re-agglomeration. The shear force can promote the uniform combination of polyvinyl pyrrolidone and carbon nanotubes. Secondly, the carbon nanotubes modified with polyvinyl pyrrolidone can be evenly dispersed in the solvent and matrix after crushing. On the one hand, it can reduce the sedimentation or aggregation of carbon nanotubes in the subsequent spinning solution. On the other hand, the evenly dispersed carbon nanotubes can construct a continuous conductive network and improve the conductivity of the membrane. Finally, mechanical crushing can quickly destroy carbon nanotube agglomerates, shorten the dispersion time, further reduce the time required for subsequent stirring, and optimize process efficiency. The process method has a short cycle and is simple, does not require expensive chemical reagents and equipment, and is suitable for industrial production.

[0014] (2) The carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane disclosed in the present invention has high flux, strong acid and alkali resistance, good electrical conductivity, uniform and smooth surface, and good flexibility; the preparation process adopts a post-treatment process of "hot washing - drying - re-hot washing - soaking in glycerol - natural drying" to improve the comprehensive performance of the membrane: 1. "Hot washing membrane wire", using hot water and water vapor to accelerate the rapid diffusion and dissolution of organic solvents and pore-forming agents on the surface and in the pores of the membrane wire; 2. "Drying membrane wire", due to the rigid support of carbon nanotubes, the membrane wire will produce micro-contraction in the axial direction during the drying process, and the micro-contraction will occur in the membrane wire. While ensuring the pores and porosity of the membrane wire, the bonding force between the carbon nanotubes is strengthened to form a denser conductive network channel, thereby greatly improving the conductivity of the wet membrane wire; 3. "Reheat washing the membrane wire" uses the active water molecules of high-temperature hot water and water vapor to accelerate the water infiltration of the dry membrane wire; 4. After "immersing in glycerol aqueous solution", small glycerol molecules are adsorbed onto the surface of the membrane wire and the membrane pores. Its strong hygroscopicity can maintain the wetting environment of the membrane wire, forming a stable hydrated molecular layer to ensure hydrophilicity; 5. After "natural drying", glycerol as a moisturizer can maintain the flexibility of the membrane wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a process flow chart for preparing the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane described in Examples 1 to 3 of the present invention; Figure 2Scanning electron microscope images of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane prepared in Example 3 of the present invention at different magnifications ((A) outer surface 30 times, (B) outer surface 20,000 times, (C) outer surface 60,000 times, (D) inner surface 2000 times, (E) inner surface 10,000 times, (F) inner surface 50,000 times, (G) cross section 50 times, (H) cross section 300 times, (I) cross section 600 times); Figure 3 This is a pore size distribution diagram of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane prepared in Example 3 of the present invention; Figure 4 These are scanning electron micrographs of the outer surface and cross-section of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane based on hollow crocheted rope in Example 5 of the present invention (A, 50,000 times; B, 60,000 times; C, 50 times). DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0017] Unless otherwise specified, the reagents and raw materials used in the examples and comparative examples of the present invention were purchased.

[0018] Example 1 (1) Raw material pretreatment: 33 g of carboxylated carbon nanotubes and 110 g of polyvinylpyrrolidone K30 (PVP) were mixed evenly and placed in a grinder. The mechanical grinding time was set to 30 s to obtain a mixed powder of crushed carbon nanotubes and polyvinylpyrrolidone K30.

[0019] (2) Preparation of spinning solution: The crushed carbon nanotubes and polyvinylpyrrolidone K30 mixed powder described in step (1) and 134.6 g of polyvinylidene fluoride (PVDF) were poured into the spinning reactor in sequence, and then 645 g of N,N-dimethylformamide (mass fraction 61%, DMAc) and 134.6 g of polyethylene glycol PEG-600 (PEG) were poured into the reactor. The stirring speed was set to 800 r / min and the heating temperature was set to 70 °C. The mixture was stirred for 12 h to mix evenly and deaerate to obtain the spinning solution.

[0020] (3) Dry-wet spinning: The air gap between the spinneret and the coagulation bath liquid surface was adjusted to 15 cm, the spinning solution obtained in step (2) was used as the shell liquid, and the 70% N,N-dimethylformamide aqueous solution was used as the core liquid. The displacements of the spinning solution gear pump and the core liquid gear pump were 1.2 CC and 0.6 CC, respectively. The spinning solution (rotation speed of 10 rpm) and the core liquid (rotation speed of 5 rpm) obtained in step (2) passed through the spinneret at a rotation speed ratio of 10:5, and then passed through an air gap of 15 cm and entered the coagulation bath at 50°C. Subsequently, the spinning was wound on a winding wheel at a speed of 10 m / min for spinning. After the spinning was completed, the obtained membrane filaments were immersed in pure water for 24 h to remove the organic solvent and the pore-forming agent, thereby obtaining the primary carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane filaments. (4) Post-treatment of membrane fibers: The nascent carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane fibers obtained in step (3) are placed in 80°C pure water for hot washing for 5 h (hot washing membrane fibers), and then the membrane fibers are naturally dried to obtain air-dried membrane fibers. The air-dried membrane fibers are again placed in 80°C pure water for hot washing for 5 h (re-hot washing), and then soaked in a 30% glycerol aqueous solution for 24 h (soaking in glycerol aqueous solution). Finally, the soaked membrane fibers are hung to dry naturally to obtain carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membranes (membrane fiber products). The process flow chart of the membrane fiber products is as follows: Figure 1 shown.

[0021] Example 2 (1) Raw material pretreatment: 24 g of hydroxylated multi-walled carbon nanotubes and 80 g of polyvinylpyrrolidone K30 (PVP) were mixed evenly and placed in a grinder. The mechanical grinding time was set to 2 min to obtain a mixed powder of crushed carbon nanotubes and polyvinylpyrrolidone K30.

[0022] (2) Preparation of spinning solution: The crushed carbon nanotubes and polyvinylpyrrolidone K30 mixed powder described in step (1) and 80.8 g of polyvinylidene fluoride (PVDF) were poured into the spinning reactor in sequence, and then 490.8 g of N,N-dimethylacetamide (mass fraction of 70.6%, DMAc) and 20 g of polyethylene glycol PEG-400 (PEG) were poured into the reactor. The stirring speed was set to 800 r / min and the heating temperature was set to 60 °C. The mixture was stirred for 8 h to mix evenly and deaerate to obtain the spinning solution.

[0023] (3) Dry-wet spinning: The air gap between the spinneret and the coagulation bath liquid surface was adjusted to 10 cm, the spinning solution obtained in step (2) was used as the shell liquid, and the N,N-dimethylacetamide aqueous solution with a mass fraction of 80% was used as the core liquid. The displacements of the spinning solution gear pump and the core liquid gear pump were 1.2 CC and 0.6 CC, respectively. The spinning solution (rotation speed of 10 rpm) and the core liquid (rotation speed of 5 rpm) obtained in step (2) passed through the spinneret at a rotation speed ratio of 10:5 and entered the coagulation bath at 60°C. They were then wound on the winding wheel at a speed of 10 m / min. After the spinning was completed, the obtained membrane filaments were immersed in pure water for 24 h to remove the organic solvent and pore-forming agent, thereby obtaining the primary carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane filaments. (4) Post-treatment of membrane fibers: The nascent carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane fibers obtained in step (3) are placed in 70°C pure water for hot washing for 4 hours (hot washing membrane fibers), and naturally dried to obtain air-dried membrane fibers. Subsequently, the air-dried membrane fibers are placed in 70°C pure water for hot washing for 4 hours again (re-hot washing), and then soaked in a 40% glycerol aqueous solution for 12 hours (soaking in glycerol aqueous solution). Finally, the soaked membrane fibers are hung to dry naturally to obtain carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membranes (membrane fiber products). The process flow chart of the membrane fiber product is shown below. Figure 1 shown.

[0024] Example 3 (1) Raw material pretreatment: 40.4 g of unmodified carbon nanotubes and 134.6 g of polyvinyl pyrrolidone K30 were mixed evenly and placed in a grinder. The mechanical grinding time was set to 1 min to obtain a mixed powder of crushed carbon nanotubes and polyvinyl pyrrolidone K30.

[0025] (2) Preparation of spinning solution: The crushed carbon nanotubes and polyvinylpyrrolidone K30 mixed powder described in step (1) and 134.6 g of polyvinylidene fluoride (PVDF) were poured into the spinning reactor in sequence, and then 825 g of N,N-dimethylacetamide (mass fraction of 65%, DMAc) and 134.6 g of polyethylene glycol PEG-400 (PEG) were poured into the reactor. The stirring speed was set to 500 r / min and the heating temperature was set to 60 °C. The mixture was stirred for 6 h to mix evenly and deaerate to obtain the spinning solution.

[0026] (3) Dry-wet spinning: The air gap between the spinneret and the coagulation bath liquid surface was adjusted to 8 cm, the spinning solution obtained in step (2) was used as the shell liquid, and the aqueous solution of N,N-dimethylacetamide with a mass fraction of 70% was used as the core liquid. The displacements of the spinning solution gear pump and the core liquid gear pump were 1.2 CC and 0.6 CC, respectively. The spinning solution (rotation speed of 10 rpm) and the core liquid (rotation speed of 5 rpm) obtained in step (2) passed through the spinneret at a rotation speed ratio of 10:5 and entered the coagulation bath at 70°C. The spinning was then wound on the winding wheel at a speed of 10 m / min. After the spinning was completed, the obtained membrane filaments were immersed in pure water for 24 h to remove the organic solvent and the pore-forming agent, thereby obtaining the primary carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane filaments. (4) Post-treatment of membrane fibers: The nascent carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane fibers obtained in step (3) are placed in 70°C pure water for hot washing for 4 hours (hot washing membrane fibers), and naturally dried to obtain dried membrane fibers. Subsequently, the dried membrane fibers are again placed in 70°C pure water for hot washing for 4 hours (re-hot washing), and then soaked in a 50% glycerol aqueous solution for 12 hours (soaking in glycerol aqueous solution). Finally, the soaked membrane fibers are hung to dry naturally to obtain carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membranes (membrane fiber products). The process flow chart of the membrane fiber product is shown below. Figure 1 The scanning electron microscopy characterization results of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane are shown as follows: Figure 2 As shown (where (A): outer surface 30 times, (B): outer surface 20,000 times, (C): outer surface 60,000 times, (D): inner surface 2000 times, (E): inner surface 10,000 times, (F): inner surface 50,000 times, (G): cross section 50 times, (H): cross section 300 times and (I): cross section 600 times), the results show that the outer surface electron microscope photos are as follows Figure 2 As shown in (A, B, C), the outer surface of the membrane is uniform and smooth, with a high surface porosity and uniform pore size; the electron microscope photos of the inner surface are shown in Figure 2 As shown in (D, E, F), the inner surface presents a macroporous morphology, which can reduce the water transmission resistance. At high magnification, carbon nanotubes can be observed to be intertwined and coiled with each other; cross-sectional electron microscopy photos are shown in Figure 2 As shown in (G, H, I), the cross section is a typical hollow structure, with a semi-finger-like, semi-sponge structure and ultra-high porosity. The pore size distribution results of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane are shown in Figure 3 As shown in the figure, the results show that the average pore size measured by capillary flow pore size analyzer is 50 nm, accounting for more than 90%, and the pore size distribution is narrow.

[0027] The prepared carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane was immersed in a pH 1 HCl solution (i.e., acid treatment) and a pH 13 sodium hydroxide aqueous solution (i.e., alkali treatment) for 24 h. The test results of its performance (dry and wet conductivity, tensile strength at break, and pure water flux) are shown in Table 2. The test results show that the membrane fibers have stable performance and exhibit excellent acid and alkali resistance. This shows that the production process of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fibers proposed in this embodiment of the present invention is simple, has a short cycle time, and is low in cost. The prepared membrane fibers have uniform inner and outer diameters, good electrical conductivity, and excellent pure water flux. In addition, they have good acid and alkali resistance and are suitable for complex working conditions such as strong acids and strong bases. The process method significantly improves the electrical conductivity, tensile strength at break, and pure water flux of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fibers.

[0028] The production cost of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane is shown in Table 1. 2 The cost of raw materials required for carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane is 15.22 yuan. Table 1 is the preparation of 1 m 2 Raw material quantity and cost required for carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane

[0029] Example 4 The difference from Example 3 is that in step (3), no core liquid is used in the dry-wet spinning process, and a nylon braided tube is used instead of the core liquid. The specific steps are as follows: The nylon braided tube is passed through the spinneret, passed through the coagulation bath by the fixed pulley, and then wound on the winding roller. The air gap between the spinneret and the coagulation bath liquid surface is adjusted to 15 cm. The speed of the spinning solution extrusion pump is set to 15 rpm. At the same time, the spinning solution extrusion pump, the winding wheel and the wire arrangement device are started. The spinning solution is evenly coated on the outer surface of the nylon braided tube through the spinneret, and then enters the coagulation bath with a temperature of 60 ° C. After the initial phase transformation and molding, it is wound on the winding wheel at a linear speed of 15 m / min for spinning. After the spinning is completed, the membrane fiber is soaked in pure water for 12 hours to remove the organic solvent and pore-forming agent to obtain the primary carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane fiber. The remaining steps are consistent with Example 3, and the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane (membrane fiber product) with nylon braided tube as the substrate is obtained. The electron microscope photo of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane with nylon braided tube as the substrate is shown in FIG. Figure 4As shown in (A, B, C), it can be clearly seen that the carbon nanotubes on the membrane surface are intertwined and embedded in polyvinylidene fluoride, and the membrane pores are about 50 nm; the cross-section shows a typical hollow structure, in which the inner layer is a support layer with a hollow crocheted rope as the base, and the outer layer is a separation layer with a mixture of carbon nanotubes and polyvinylidene fluoride as the functional layer, and the base and separation layer are tightly combined.

[0030] Comparative Example 1 The difference from Example 3 is that step (1) raw material pretreatment (i.e., mechanical blending and crushing of raw materials) is not performed, step (4) membrane filament post-treatment process is different (i.e., the membrane filament post-treatment process of "hot washing - drying - re-hot washing - soaking in glycerol - natural drying" is not adopted), and step (2) the stirring time in the preparation of the spinning solution is different. The specific steps are as follows: (1) Preparation of spinning solution: 134.6 g of polyvinylidene fluoride, 40.4 g of unmodified carbon nanotubes, 134.6 g of polyvinylpyrrolidone K30 (PVP) and 134.6 g of polyethylene glycol PEG-400 (PEG) were added to 825 g of N,N-dimethylacetamide (65% by mass, DMAc) in sequence. The stirring speed was set to 500 r / min and the heating temperature was set to 60 °C. The mixture was stirred for 24 h to mix evenly and deaerate to obtain the spinning solution.

[0031] (2) Dry-wet spinning: The air gap between the spinneret and the coagulation bath liquid surface was adjusted to 8 cm, the spinning solution obtained in step (1) was used as the shell liquid, and the aqueous solution of N,N-dimethylacetamide with a mass fraction of 80% was used as the core liquid. The displacements of the spinning solution gear pump and the core liquid gear pump were 1.2 CC and 0.6 CC, respectively. The spinning solution (rotation speed of 10 rpm) and the core liquid (rotation speed of 5 rpm) obtained in step (2) passed through the spinneret at a rotation speed ratio of 10:5 and entered into the coagulation bath at 70°C. The spinning solution was then wound on the winding wheel at a speed of 7.5 m / min. After the spinning was completed, the obtained membrane filaments were immersed in pure water for 24 h to remove the organic solvent and pore-forming agent, thereby obtaining the primary carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane filaments. (3) Post-treatment of membrane fibers: The nascent carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane fibers obtained in step (2) were placed in 70°C pure water for 4 hours and then naturally dried. The dried membrane fibers were then immersed in a 50% glycerol aqueous solution for 12 hours. Finally, the immersed membrane fibers were hung and naturally dried to obtain polyvinylidene fluoride mixed matrix hollow fiber membranes (membrane fiber products). The conductivity, tensile strength at break, acid and alkali resistance, and pure water flux test results of the polyvinylidene fluoride mixed matrix hollow fiber membranes are shown in Table 2.

[0032] Table 2 shows the test results of dry and wet conductivity, tensile strength at break and pure water flux of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane prepared in Example 3 and Comparative Example 1

[0033] The above descriptions are merely several embodiments of the present invention and do not constitute any form of limitation to the present invention. Although the present invention is disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Any technician familiar with the present profession who, without departing from the scope of the technical solution of the present invention, makes slight changes or modifications using the technical contents disclosed above are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A low-cost, high-throughput, acid- and alkali-resistant, highly conductive carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane industrial preparation process, characterized in that: The industrial preparation process comprises the following steps: Step (1), raw material pretreatment: mixing carbon nanotubes and polyvinyl pyrrolidone, and crushing to obtain a mixed powder; Step (2), preparation of spinning solution: dispersing the mixed powder obtained in step (1), polyvinylidene fluoride and polyethylene glycol in an organic solvent, heating and stirring, and degassing in a vacuum or standing state to obtain a spinning solution; Step (3), dry-wet spinning: adjusting the air gap between the spinneret and the coagulation bath liquid surface, the spinning solution obtained in step (2) is the shell liquid, and the organic solvent / water solution is the core liquid. The shell liquid and the core liquid pass through the spinneret and then pass through the air gap into the coagulation bath, and then are wound on a winding wheel for spinning to obtain a primary carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane; Step (4), post-treatment of the membrane fibers: placing the nascent carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane fibers prepared in step (3) in hot water for heat washing, naturally drying, placing them in hot water again for heat washing, soaking them in a glycerol aqueous solution after hot washing, and naturally drying them after soaking to obtain a carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane.

2. The industrial preparation process according to claim 1, characterized in that: The dry-wet spinning in step (3) also includes coating the spinning solution onto the hollow nylon braided tube substrate through a spinneret, and then entering the spinning solution into a coagulation bath together, spinning after preliminary phase transformation and soaking in water for 6 to 24 hours to obtain a carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane with the nylon braided tube as the substrate.

3. The industrial preparation process according to claim 1, characterized in that: The polyvinyl pyrrolidone in step (1) is of a type K12 to K96, preferably K30; The carbon nanotubes in step (1) are selected from at least one of unmodified carbon nanotubes, carboxylated carbon nanotubes, hydroxylated carbon nanotubes, and amino carbon nanotubes, preferably unmodified carbon nanotubes; The crushing time in step (1) is 30 s to 2 min.

4. The industrial preparation process according to claim 1, characterized in that: The organic solvent in step (2) is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide, preferably N,N-dimethylacetamide; The model of the polyethylene glycol in step (1) is PEG200-600, preferably PEG400; The conditions for heating and stirring in step (2) are as follows: The heating and stirring temperature is 40-80°C; The heating and stirring time is 6 to 12 hours; The heating and stirring speed is 500-800 rpm; The mass ratio of polyvinylidene fluoride, carbon nanotubes, polyvinyl pyrrolidone and polyethylene glycol in the spinning solution in step (2) is 1:0.1~0.5:0.2~1:0~1.

5. The industrial preparation process according to claim 1, characterized in that: The air gap distance in step (3) is 2 to 20 cm; The temperature of the coagulation bath is 20-80°C; The type of organic solvent in the spinning solution of step (2) is the same as the type of organic solvent in the core solution of step (3), and the mass fraction is 50-90%; The volume flow ratio of the shell liquid to the core liquid is 2 to 6:1, preferably 4:1; The spinning conditions are as follows: The rotation speed ratio of the shell liquid to the core liquid is 10-30:5-15; The winding speed during the spinning is 5-30 m / min.

6. The industrial preparation process according to claim 1, characterized in that: The temperature of the hot water in the membrane filament post-treatment in step (4) is 50-100°C, preferably 70°C; The hot washing time is 2 to 6 hours.

7. The industrial preparation process according to claim 1, characterized in that: The mass fraction of the glycerol aqueous solution in step (4) is 30-70%, preferably 50%; The soaking time in the glycerol aqueous solution in step (4) is 8 to 24 hours.

8. The industrial preparation process according to claim 1, characterized in that: The inner surface of the carbon nanotube / polyvinylidene fluoride mixed matrix hollow fiber membrane obtained in step (4) presents a macroporous morphology, a typical hollow structure in cross section, a semi-finger-like, semi-sponge structure in cross section, an average pore size of 50-60 nm, a porosity of 90-95%, and a narrow pore size distribution.

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