CN103877869A - Porous membrane made of polytetrafluoroethylene hollow fibers, preparation method and application thereof in membrane contactor - Google Patents

Abstract

The invention relates to a preparation method of a polytetrafluoroethylene hollow fiber porous membrane and its application in a membrane contactor. The method is based on the in-situ generation of silica nanoparticles by the reaction of the silica precursor in the polytetrafluoroethylene spinning solution, and the use of a silane coupling agent to make them uniformly dispersed, and then used as a catalyst in the process of forming the hollow fiber membrane. Pore agent. The spun membrane filaments can be properly dried, sintered, stretched, extracted and washed to obtain a hydrophobic polytetrafluoroethylene hollow fiber membrane with a certain microporous structure. The polytetrafluoroethylene hollow fiber porous membrane of the invention has good application prospects in the field of membrane contactors.

Description

PTFE Hollow Fiber Porous Membrane and Its Preparation and Application in Membrane Contactor

technical field

The invention relates to a preparation method of a polytetrafluoroethylene hollow fiber porous membrane and its application in a membrane contactor.

Background technique

Polytetrafluoroethylene (PTFE) material has outstanding chemical stability, excellent high and low temperature resistance and good corrosion resistance, so filter materials made of PTFE can be widely used in the separation of fine particles under harsh conditions. At the same time, due to its strong hydrophobicity, PTFE has also become an ideal membrane material for the preparation of waterproof and breathable, membrane distillation, osmotic distillation and membrane contactor processes. However, PTFE is insoluble in general solvents, has high viscosity and poor fluidity at high temperatures, and its "insoluble and infusible" characteristics make its processing performance poor, and it cannot be wet-spun like polysulfone, polypropylene and polyvinylidene fluoride. Or melt spinning to prepare hollow fiber membrane material.

As early as 1953, the manufacturing process of PTFE fiber was developed by DuPont Company of the United States, and industrial production was realized in 1957. However, due to the special structure of PTFE, it is not suitable for making fibers by the usual solution method and melting method. Therefore, although PTFE fiber has been industrially produced for nearly 50 years, only a few companies have produced PTFE fiber products so far. Carrier spinning, paste extrusion spinning, melt spinning, and membrane split spinning are four developed spinning process routes. Among them, carrier spinning is the main method for industrial production of PTFE fibers. Generally, PTFE emulsion is mixed with fibrous carriers such as viscose or polyvinyl alcohol aqueous solution to make spinning solution, and the spinning solution is injected into the spinning head after passing through the filter. Perform wet spinning. The spinning head is placed in a coagulation bath such as sodium sulfate, and the mixed solution is condensed into fibers in the coagulation bath. After the shaped fibers are washed and dried, they are sintered at high temperature to carbonize and remove the carrier, and then the sintered fibers are properly stretched to obtain finished fibers.

At present, there are few reports on the preparation of PTFE hollow fiber porous membranes by the carrier method, and the manufacturing methods are mainly improved on the manufacturing process of PTFE fibers. For example, JP2012132120-A discloses that PTFE as-spun fibers prepared by carrier method can be used in the production of bag filters after sintering and stretching process. Patent JP2010047859-A uses cellulose and its derivatives as carriers to prepare fluorine-containing hollow fibers, and the unsintered hollow fibers can be used in the textile industry. Guo Yuhai developed a simplified process for the preparation of polytetrafluoroethylene fibers by improving the spinning solution formula (CN1970847A). The added boric acid reacts with the carrier polyvinyl alcohol as a cross-linking agent, reduces the amount of the carrier, and helps the removal of the carrier through the oxidant, and obtains a tea-brown PTFE fiber; The method for manufacturing polytetrafluoroethylene porous membrane by blending inorganic particles in silk liquid, the test results show that the proportion of inorganic micropowder has a very significant effect on water flux, and the flux increases more obviously after stretching.

Compared with other preparation methods, the preparation of PTFE microporous membranes by the carrier method usually requires the addition of an appropriate amount of porogens to obtain high porosity. Commonly used porogens can be divided into soluble salts and insoluble particles (inorganic particles), relatively The porogenic effect of non-soluble particles is more significant. The insoluble particle porogens disclosed in current patents are basically added by blending. Since the insoluble particles are insoluble in water, they are suspended and dispersed in the spinning solution only by mechanical stirring, so there are usually particles Phenomena such as agglomeration or uneven dispersion are not conducive to spinning and stretching, and are likely to cause defects.

Contents of the invention

The technical problem to be solved by the present invention is the problem of agglomeration or uneven dispersion caused by insoluble particles.

In order to solve the above-mentioned problems, the present invention adopts the addition method of in-situ synthesized particles on the basis of carrier spinning to prepare PTFE microporous membrane, and overcomes the shortcomings of particle agglomeration and uneven dispersion.

Specifically, the present invention provides a preparation method for a PTFE hollow fiber porous membrane used in a membrane contactor, which uses polytetrafluoroethylene emulsion as a raw material, uses polyvinyl alcohol as a carrier, and adds silicon dioxide to the spinning solution Silica nanoparticles were synthesized in situ from the precursor as a porogen in the membrane-forming process, and silane coupling agent was used to uniformly disperse them, and the polytetrafluoroethylene hollow fiber membrane was prepared by solution spinning method. The spun membrane filaments can be properly dried, sintered, stretched, extracted and washed to obtain a hydrophobic polytetrafluoroethylene hollow fiber membrane with a certain microporous structure.

Using the above method, the PTFE hollow fiber membrane with a certain microporous structure is prepared by using the silica nanoparticles generated in situ in the PTFE spinning solution as a porogen, and then the carrier spinning method, which can significantly improve the traditional physical co-existence. The phenomenon of uneven dispersion and easy agglomeration of nanoparticles during the mixing process, and the process is simple, easy to operate, mild conditions, requires specific instruments, and is easy to scale up and industrial applications.

The invention also provides a membrane contactor prepared by polytetrafluoroethylene hollow fiber porous membrane. The hollow fiber membrane contactor can be applied to natural gas purification, biogas purification, flue gas treatment, water deoxygenation and the like.

In the invention, silicon dioxide precursors are hydrolyzed in PTFE spinning solution to generate silicon dioxide nanoparticles with good distribution, and the dispersibility in spinning solution is further improved by silane coupling agent. The resulting spinning solution is uniform, has good spinnability, and has no agglomeration or agglomeration. After the spun membrane filaments are properly dried, sintered, stretched, extracted and washed, a hydrophobic PTFE hollow fiber membrane with a certain microporous structure and suitable for membrane contactors can be obtained.

To achieve the above object, the technical solution adopted in the present invention is:

(1) Preparation of PTFE spinning solution: uniformly mix PTFE emulsion and polyvinyl alcohol aqueous solution, add boric acid and other cross-linking agents to obtain spinning solution;

(2) In-situ synthesis of silica nanoparticles in the spinning solution: add an appropriate amount of silane coupling agent to the above spinning solution, add silicon precursor and a small amount of catalyst after the reaction is completed, and react for a certain period of time;

(3) Preparation of nascent PTFE hollow fiber: After the spinning solution is vacuum degassed, wet spinning is used to make PTFE nascent fiber in a coagulation bath;

(4) Post-treatment of nascent PTFE hollow fibers: After the nascent PTFE hollow fibers are dried, they are subjected to post-treatments such as sintering, stretching, extraction and washing to obtain PTFE hollow fiber porous membranes with a certain microporous structure.

The preparation of described PTFE spinning solution, wherein the mass fraction of PTFE emulsion is 30-70%, pH value is 8-10, can adopt commercial product or self-made;

The preparation of the PTFE spinning solution, wherein the degree of polymerization of polyvinyl alcohol is 1700-2800, the degree of alcoholysis is 88-99%, commercial products can be used, and its quality is 5%-20% of PTFE;

The silica nanoparticles are synthesized in situ in the spinning solution, wherein the silane coupling agent is: vinyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropylene Trimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, its addition accounts for 1%-10% of the weight of the silica precursor, and the reaction temperature is 20-60℃, the reaction time is 2-8h;

The silica nanoparticles are synthesized in situ in the spinning solution, wherein the silica precursor is methyl orthosilicate (TMOS) or tetraethyl orthosilicate (TEOS), and its added amount accounts for 4% of polytetrafluoroethylene 5%-30% by weight; the hydrolysis condition is acid catalysis or base catalysis, the catalyst can be ammonia water, hydrochloric acid or acetic acid, etc., the reaction pH value is 3-11, the reaction temperature is 20-60°C, and the reaction time is 5-30 hours ;

The preparation of the nascent PTFE hollow fiber, wherein the temperature of the spinning solution is 20-50°C; the coagulation bath and the core liquid are sodium sulfate solution, the pH is 9-13, and the temperature is 20-60°C;

The post-treatment of the nascent PTFE hollow fiber, wherein the drying method is natural drying or drying after replacement, the sintering temperature is 340-400°C, the sintering time is 1-10min, the stretching temperature is 200-300°C, and the stretching ratio 1-3 times; the extraction and washing liquid is 5-20% aqueous solution of sodium hydroxide or potassium hydroxide, and the extraction and washing time is 24-72h. The porosity of the obtained PTFE hollow fiber porous membrane is 20-60%, the average pore diameter is 0.05-2.0 μm, and the contact angle is 100-120°.

The membrane filaments prepared according to the above method are suitable for being prepared into hollow fiber membrane contactors, which are applied in natural gas purification, biogas purification, flue gas treatment, water deoxygenation and the like.

Detailed ways

The present invention is described in detail below in conjunction with embodiment.

Example 1

Dissolve 100g of PVA1788 in 400g of water, add 1660g of PTFE emulsion (60wt%) after completely dissolving, stir well, then add 10g of γ-aminopropyl triethoxysilane, 100g of ethyl orthosilicate in turn, at room temperature Under mechanical stirring for about 4 hours, after vacuum defoaming, wet spinning. The obtained as-spun fibers are subjected to processes such as natural drying, sintering and stretching, and then extracted and washed in 5% sodium hydroxide aqueous solution for 48 hours to obtain a PTFE hollow fiber porous membrane. Sintering conditions: 380°C, 5min, stretching temperature: 300°C, stretching ratio: 1.5 times. The porosity of the obtained membrane filament is 30%, the average pore diameter is 0.2 μm, and the contact angle is 105°. The PTFE hollow fiber porous membrane was processed into a membrane contactor module, and the CO ₂ removal effect was tested with 15% CO ₂ /N ₂ mixed gas as the feed gas and 30% diethanolamine aqueous solution as the absorbent. When the operating pressure is 1.0MPa, the _CO2 removal rate reaches 76%.

Example 2

Dissolve 100g of PVA2488 in 400g of water, add 1660g of PTFE emulsion (60wt%) after completely dissolving, stir evenly, then add 20g of γ-aminopropyltriethoxysilane as silane coupling agent, 200g of ethyl orthosilicate, at room temperature Mechanical stirring for about 8 hours, vacuum defoaming, wet spinning. The obtained as-spun fibers are subjected to processes such as natural drying, sintering and stretching, and then extracted and washed in 20% sodium hydroxide aqueous solution for 48 hours to obtain a PTFE hollow fiber porous membrane. Sintering conditions: 380°C, 5min, stretching temperature: 300°C, stretching ratio: 1.5 times, the porosity of the obtained membrane filament is 42%, the average pore diameter is 0.7μm, and the contact angle is 115°. The PTFE hollow fiber porous membrane was processed into a membrane contactor module, and the CO ₂ removal effect was tested with 15% CO ₂ /N ₂ mixed gas as the feed gas and 30% diethanolamine aqueous solution as the absorbent. When the operating pressure is 1.0MPa, the _CO2 removal rate reaches 87%.

Example 3

Dissolve 100g of PVA1799 in 400g of water, add 1660g of PTFE emulsion (60wt%) after completely dissolving, stir evenly, then add 10g of γ-glycidoxypropyltrimethoxysilane, 100g of methyl orthosilicate in sequence, Stir mechanically at room temperature for about 8 hours. After vacuum defoaming, wet spinning. The obtained as-spun fibers are subjected to processes such as natural drying, sintering and stretching, and then extracted and washed in 20% sodium hydroxide aqueous solution for 48 hours to obtain a PTFE hollow fiber porous membrane. Sintering conditions: 360°C, 8min, stretching temperature: 300°C, stretching ratio: 2 times, the porosity of the obtained membrane filament is 48%, the average pore diameter is 1.0 μm, and the contact angle is 108°. The PTFE hollow fiber porous membrane was processed into a membrane contactor module, and the CO ₂ removal effect was tested with 15% CO ₂ /N ₂ mixed gas as the feed gas and 30% diethanolamine aqueous solution as the absorbent. When the operating pressure is 1.0MPa, the _CO2 removal rate reaches 90%.

The invention has the following advantages: the reaction conditions are mild and easy to control, the operation is simple and safe, there is no special requirement for equipment, and continuous production is easily realized. The method of in-situ synthesis of the porogen enables the silica nanoparticles to be uniformly dispersed in the spinning solution, which overcomes the disadvantages of easy agglomeration, agglomeration and uneven distribution of the porogen in the blending method. The PTFE hollow fiber membrane prepared by this method has a uniform microporous structure, good mechanical properties and chemical stability, and maintains the strong hydrophobicity of the PTFE material itself, and has a good application prospect in the field of membrane contactors.

Claims (10)

1. a preparation method of polytetrafluoroethylene hollow fiber porous membrane, is characterized in that: Using polytetrafluoroethylene emulsion as raw material, using polyvinyl alcohol as carrier, adding silica precursor to the spinning solution to synthesize silica nanoparticles in situ as porogen in the film forming process, and using silane coupling agent to make it evenly dispersed, and prepare polytetrafluoroethylene hollow fiber membrane by solution spinning method; The spun polytetrafluoroethylene hollow fiber membrane is properly post-treated to prepare a hydrophobic polytetrafluoroethylene hollow fiber membrane with a microporous structure. 2. a preparation method of polytetrafluoroethylene hollow fiber porous membrane described in claim 1, is characterized in that: Using polytetrafluoroethylene emulsion as raw material, using polyvinyl alcohol as carrier, adding silica precursor to the spinning solution to synthesize silica nanoparticles in situ as porogen in the film forming process, and using silane coupling agent to make it evenly dispersed, and prepare polytetrafluoroethylene hollow fiber membrane by solution spinning method; The spun polytetrafluoroethylene hollow fiber membrane is properly post-treated to prepare a hydrophobic polytetrafluoroethylene hollow fiber membrane with a microporous structure. 3. according to the preparation method of the polytetrafluoroethylene hollow fiber porous membrane described in claim 2, it is characterized in that: The mass fraction of the polytetrafluoroethylene emulsion used is 30-70%, and the pH value is 8-10; The degree of polymerization of the polyvinyl alcohol used is 1700-2800, the degree of alcoholysis is 88-99%, and its mass is 5%-20% of the mass of PTFE. 4. The preparation method of polytetrafluoroethylene hollow fiber porous membrane according to claim 2, characterized in that: the silica precursor is methyl orthosilicate (TMOS) or tetraethyl orthosilicate (TEOS); The added amount of the silicon dioxide precursor accounts for 5%-30% of the mass of the polytetrafluoroethylene. 5. according to the preparation method of polytetrafluoroethylene hollow fiber porous membrane described in claim 2, it is characterized in that: the silane coupling agent used to improve the dispersibility of silicon dioxide is: vinyltriethoxysilane, gamma-ammonia Propyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane or γ-mercaptopropyltrimethoxysilane; silane coupling agent The added amount accounts for 1%-10% of the mass of the silicon dioxide precursor. 6. According to the preparation method of polytetrafluoroethylene hollow fiber porous membrane according to claim 2 or 4, it is characterized in that: the hydrolysis condition of the silicon dioxide precursor is acid catalysis or alkali catalysis, and the catalyst can be ammonia water, hydrochloric acid or acetic acid; The pH value of the reaction for in-situ synthesis of silicon dioxide nanoparticles is 3-11, the reaction temperature is 20-60° C., and the reaction time is 5-30 hours. 7. according to the preparation method of polytetrafluoroethylene hollow fiber porous membrane according to claim 2, it is characterized in that: Post-treatment means that the spun PTFE hollow fiber membrane is dried, sintered, stretched, extracted and washed; The drying method of the spun membrane yarn is natural drying or drying after solvent replacement. The solvent used for the replacement is ethanol or n-hexane; the sintering temperature is 340-400°C, the sintering time is 1-10min, and the stretching temperature is 200-300°C. The stretching ratio is 1-3 times, the extraction and washing solution is an aqueous solution of sodium hydroxide or potassium hydroxide with a mass concentration of 5-20%, and the extraction and washing time is 24-72 hours. 8. according to the preparation method of polytetrafluoroethylene hollow fiber porous membrane described in claim 2, it is characterized in that: the porosity of polytetrafluoroethylene hollow fiber porous membrane is 20-60%, and average aperture is 0.05-2.0 μ m, contact The angle is 100-120°. 9. The application of the polytetrafluoroethylene hollow fiber porous membrane as claimed in claim 1, which is used as a membrane contactor assembly to make a membrane contactor, and the membrane contactor assembly is mainly composed of a contactor housing, an epoxy sealing head, claim 1. The polytetrafluoroethylene hollow fiber membrane is formed. 10. According to the application of claim 9, it is characterized in that: the polytetrafluoroethylene hollow fiber membrane contactor can be used in the membrane absorption process to remove acidic components in the mixed gas or trace gases in the water; the contactor is a closed cavity , the contactor shell is provided with the inlet and outlet of gas and liquid two-phase fluid, more than two PTFE hollow fiber membranes are filled in the cavity of the contactor shell, and more than two PTFE hollow fiber membranes Both ends of the fiber membrane extend out of the contactor through the contactor housing respectively, and more than two PTFE hollow fiber membranes are sealed and connected with the contactor housing through the epoxy seal head.