阅读说明：本技术 一种大通量除病毒聚偏氟乙烯中空纤维微孔膜及制备方法 (Large-flux virus-removing polyvinylidene fluoride hollow fiber microporous membrane and preparation method thereof ) 是由 田野 金宇涛 林亚凯 吴红梅 于 2020-04-28 设计创作，主要内容包括：本发明涉及一种具有多层过滤结构的大通量、高效除病毒聚偏氟乙烯中空纤维微孔膜及制备方法。为提高中空纤维微孔膜病毒截留性能及纯水通量,本发明的聚偏氟乙烯中空纤维微孔膜,膜丝外径1.1～1.4mm,内径0.6～0.8mm,壁厚0.2～0.4mm；膜丝外表面具有明显的开孔；从外到内形成具有显著分界的三层膜孔结构层。制备方法包括：制备铸膜液；中空纤维膜的挤出；外层喷雾溶剂交换成膜；中间层低温分相成膜；内层低温分相成膜；萃取。本发明在热致相分离制膜法的基础上,结合浅层溶剂-非溶剂快速交换成膜、分级温度梯度分相成孔等技术,制得具有明显不同分界的三层孔结构的中空纤维膜,在保证大的过滤通量的前提下,可对病毒等致病性微生物形成高效多层过滤,截留性能达到了99.99%,第三方检测的平均截留率更是达到了99.999%。(The invention relates to a large-flux and high-efficiency virus-removing polyvinylidene fluoride hollow fiber microporous membrane with a multi-layer filtering structure and a preparation method thereof. In order to improve the virus interception performance and the pure water flux of the hollow fiber microporous membrane, the polyvinylidene fluoride hollow fiber microporous membrane has membrane filaments with the outer diameter of 1.1-1.4 mm, the inner diameter of 0.6-0.8 mm and the wall thickness of 0.2-0.4 mm; the outer surface of the membrane silk is provided with obvious openings; three membrane pore structure layers with obvious boundaries are formed from outside to inside. The preparation method comprises the following steps: preparing a membrane casting solution; extruding a hollow fiber membrane; solvent exchange film formation is carried out on the outer layer; the middle layer is split into phases at low temperature to form a film; the inner layer is split into phases at low temperature to form a film; and (4) extracting. On the basis of a thermally-induced phase separation membrane preparation method, the hollow fiber membrane with a three-layer pore structure with obviously different boundaries is prepared by combining technologies such as shallow solvent-non-solvent rapid exchange membrane formation, graded temperature gradient phase separation pore formation and the like, on the premise of ensuring large filtration flux, efficient multilayer filtration can be formed on pathogenic microorganisms such as viruses and the like, the retention performance reaches 99.99%, and the average retention rate detected by a third party further reaches 99.999%.)

1. The large-flux virus-removing polyvinylidene fluoride hollow fiber microporous membrane is characterized in that: the outer diameter of the membrane wire is 1.1-1.4 mm, the inner diameter is 0.6-0.8 mm, and the wall thickness is 0.2-0.4 mm; the outer surface of the membrane silk is provided with obvious openings; three membrane pore structure layers with obvious boundaries are formed from outside to inside.

2. The polyvinylidene fluoride hollow fiber microporous membrane of claim 1, wherein: the outer layer of the membrane wire is an outer surface and a compact layer close to the outer surface, the outer surface is provided with obvious openings, the compact layer is a compact cellular cavity-shaped pore structure with good sealing performance, the thickness of the outer layer is 5-10 mu m, and the pore diameter is 0.02-0.03 mu m; the membrane silk intermediate layer is a larger closed cell-shaped pore structure layer, the thickness is 20-40 mu m, and the pore diameter is 0.1-0.2 mu m; the inner layer of the membrane silk is a typical bicontinuous through-hole structural layer, the thickness is 150-370 mu m, and the aperture is 0.2-0.4 mu m.

3. A method of making a high flux virus-removing polyvinylidene fluoride hollow fiber microporous membrane of claim 1, comprising the steps of:

(1) preparing a casting solution: heating the diluent and the polyvinylidene fluoride copolymer to 200-250 ℃ to form a homogeneous solution, standing, defoaming and uniformly mixing to obtain a casting solution;

(2) extrusion of hollow fiber membranes: the casting solution is further sheared, melted and mixed at high temperature through a double-screw extruder, finally, the casting solution is sprayed and converged with inner core solution and outer layers at a spinning nozzle, and the inner core solution and the outer layers are extruded through the spinning nozzle to form hollow fibrous homogeneous high-temperature casting solution, the inner cavity of which contains the high-temperature core solution and the outer part of which surrounds a low-temperature spraying layer; the outer layer spray is hydrous ethanol; the inner core liquid is one or more of glycerol, 1, 2-propylene glycol or 2, 3-butanediol;

(3) outer layer spraying-solvent exchange film forming: the hollow fibrous homogeneous phase high-temperature solution coexists with the spray for 0.01-0.05 second, a surface layer diluent exchanges solvents with a small amount of ethanol in the spray to form a compact outer surface with tiny open pores, meanwhile, a casting solution with the thickness of 5-10 mu m below the outer surface is affected by the low temperature of the spray, PVDF in the casting solution is separated from the diluent and is rapidly cured to form a compact layer with a very small closed cell-shaped pore structure, and the outer surface and the shallow cell-shaped compact layer form an outer layer together;

(4) and (3) low-temperature phase separation and film formation of the middle layer: in the area 10-50 microns below the outer surface of the casting solution, the PVDF and the diluent are also affected by low temperature of spraying, phase separation is carried out for a longer time, the pore structure is obviously increased, low-permeability closed cell-shaped pores are formed, and an intermediate layer is formed;

(5) and (3) low-temperature phase separation and film formation of the inner layer: after the hollow fibrous homogeneous high-temperature membrane casting solution is cooled by spraying, directly immersing the membrane casting solution into a water bath with the temperature 30-50 ℃ higher than the spraying temperature for cooling, staying for 1-2 seconds, performing typical thermally induced phase separation on PVDF and a diluent, and fully coarsening and growing the PVDF-rich and diluent-rich phases before curing to form a bicontinuous through hole structure until the membrane casting solution is completely cured and stopped to form an inner layer;

(6) extracting and removing a diluent: and (5) removing the diluent in the membrane filaments obtained in the step (5) by using an extracting agent to obtain the polyvinylidene fluoride hollow fiber microporous membrane with a three-layer pore structure.

4. The production method according to claim 3, characterized in that: the casting solution in the step (1) comprises 20-30 wt% of polyvinylidene fluoride copolymer, the weight average molecular weight of the polyvinylidene fluoride is 60-80 ten thousand, and the balance is diluent.

5. The production method according to claim 3 or 4, characterized in that: the spinning head special for the step (2) is of a three-layer structure, the diameter of an inner layer is 0.6-0.8 mm, and the spinning head is a core liquid flow channel; the diameter of the middle layer is 1.2-2.0 mm, and the middle layer is a casting solution flow channel; the two layers accurately measure the flow of the solution entering the spinning nozzle through high-temperature metering pumps respectively; the third layer is a heat-insulating spraying layer with the diameter of 2.0-3.0 mm; the front end is connected with a spray generator with a heat exchange device.

6. The production method according to claim 3 or 4, characterized in that: the diluent in the step (1) is one or a mixture of more of benzophenone, diphenyl carbonate, diethyl phthalate, glyceryl triacetate, methyl benzoate, ethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, diethylene glycol, triethylene glycol, dioctyl adipate, dioctyl phthalate, tetraethylene glycol and n-octanol.

7. The production method according to claim 3 or 4, characterized in that: the spraying temperature is controlled to be 5-10 ℃, and the water bath cooling liquid is controlled to be 40-60 ℃.

8. The production method according to claim 3 or 4, characterized in that: the extractant in the step (5) is ethanol.

Technical Field

The invention relates to a hollow fiber microporous membrane, in particular to a polyvinylidene fluoride (PVDF) hollow fiber microporous membrane with a multi-layer filtering structure and a preparation method thereof, which has high flux and high efficiency for removing viruses.

Background

Pathogenic microorganisms refer to pathogenic bacteria, viruses and protozoa (protozoa and worms) widely existing in water body and can cause various diseases such as gastroenteritis, diarrhea, dysentery, hepatitis, cholera, typhoid and the like. Therefore, controlling the risk of pathogenic microorganisms in drinking water is an important part of the work of drinking water safety assurance. Among all pathogenic microorganisms, viruses tend to have more serious consequences, but are also more difficult to handle due to their smaller size, ranging from about 20 to 300 nm. The water quality standards of drinking water in the united states, canada, and other countries stipulate that the virus removal/inactivation rate is not less than 99.99%. Although the drinking water sanitary standard in China has no virus index, the drinking water disinfection treatment and the specific control requirements on disinfection are provided, and the limit value of turbidity is specified.

The traditional drinking water treatment process is coagulation-precipitation-filtration-disinfection, which is still the mainstream water treatment process of water works taking surface water as a water source in China at present. The disinfection link is an important barrier for guaranteeing the biological safety of drinking water. However, since different viruses have different structures, compositions, nucleic acid compositions and forms, the survival ability in environmental media and the tolerance to water purification and disinfectants are different. There is therefore still an unknown risk of killing viruses by means of disinfectants alone.

The membrane treatment technology is a membrane separation technology taking pressure as a driving force, microorganisms, particles and even dissolved salt in water are separated from the water through membranes with different pore sizes, chemical agents are not basically needed, the quality of produced water is relatively stable, and the influence of inlet water fluctuation is small. The ultra/micro filtration technology is the most commonly used membrane treatment technology for removing microorganisms, and the main mechanism of the technology is sieving, wherein the sieving is to retain microorganism particles which are larger than the pore size of the micro filtration technology or are equivalent to the pore size of the micro filtration technology through a membrane. In addition, when microorganisms penetrate through the surface of the membrane and enter the interior of the membrane, part of the separation membrane deposits on the side wall of the membrane hole or the matrix in the membrane under the influence of the physical and chemical properties, the electrostatic attraction and the like, so that the aim of removing viruses is fulfilled.

Currently available ultrafiltration membrane products are mostly prepared by Non-Solvent Induced phase separation (NIPS) method. The film-making method mainly relies on the exchange between the solvent and the non-solvent of the film material, so as to form pores. The obtained membrane product is mainly characterized in that the surface of the membrane is provided with a compact skin layer with the thickness of about 1 mu m, and the section of the membrane is of a big finger-shaped pore structure. The retention of the virus can only be realized by a compact cortex on the surface. In case the surface compact cortex is abraded, the virus interception performance is greatly reduced, and the water safety is affected.

Thermal Induced Phase Separation (TIPS) is an emerging microporous membrane manufacturing technique. Is a method of forming a pore structure by causing the membrane material to phase separate from the diluent by a change in temperature. Then the diluent is extracted out, and finally the microporous structure is obtained. The microporous membrane prepared by the TIPS method has the characteristics of high strength, uniform pore size distribution from outside to inside, large pure water flux and the like. However, it is generally believed that the common TIPS microporous membrane has no compact skin layer on the surface layer, has a high aperture ratio, and has poor virus retention performance.

Among numerous high polymers, Polyvinylidene Fluoride (PVDF) has the characteristics of strong biological decomposition resistance, good thermal stability, high mechanical strength of a matrix, chemical oxidation resistance, ultraviolet aging resistance and the like, meets the safety certification of the FDA, can meet the requirements of water treatment technology on membranes, and is a well-known membrane material with excellent performance. The hollow fiber membrane can improve the packing density of unit area, is beneficial to realizing high flux, is easy to carry out on-line drug washing, is convenient to clean the membrane, and is the first choice of the ultra/micro filtration membrane form.

The utility model patent with publication number CN204638007U discloses an antibacterial ultrafiltration membrane, which integrates the technologies of a supporting layer, an ultrafiltration membrane layer, an ultraviolet antibacterial layer, coarse-hole filtration and the like, and strengthens the filtration effect by installing two layers of ultrafiltration membranes. The utility model discloses a there is the technology too complicated, lacks practical competitiveness. And the patent rights are terminated in 2018, 6, month and 12.

The invention patent with the publication number of CN104437139A discloses an inorganic-organic hybrid antibacterial ultrafiltration membrane and a preparation method thereof. On the basis of preparing copper nanoparticles, copper nanoparticles and self-made hydrophilic sulfonated polyarylethersulfone are blended into a polyether sulfone matrix, the preparation process is simple, the antibacterial property is achieved, and loss of copper substances can be effectively inhibited. The disadvantage is that the pure water flux is very low and is only 40-200L/m²·h·bar。

The invention patent with the publication number of CN106794431A discloses a novel ultrafiltration membrane, which consists of a cavity formed by a sulfone polymer membrane matrix and an organic polymer packaging layer, wherein the cavity contains a nano adsorbent. The preparation method comprises the steps of preparing a sulfone polymer membrane matrix by an NIPS method, reversely filling the nano adsorbent from the bottom of the sulfone polymer membrane matrix, and encapsulating by using an organic polymer after filling to obtain the multifunctional ultrafiltration membrane, wherein the multifunctional ultrafiltration membrane has a good removal effect on simulated viruses, macromolecules and lead ions. But the manufacturing method is also complicated. And the pure water flux is low and is only 200-400L/m²·h·bar。

Disclosure of Invention

The invention aims to: the defects that virus interception performance is greatly reduced due to abrasion of a membrane surface filtering layer, or viruses cannot be effectively intercepted due to overhigh opening rate, water safety is influenced, pure water flux is low, and a preparation method is complex in the prior art are overcome, and the polyvinylidene fluoride hollow fiber microporous membrane capable of efficiently removing the viruses with high flux and the preparation method thereof are provided. The method combines the technologies of shallow solvent-non-solvent rapid exchange film formation, graded temperature gradient phase separation pore formation and the like on the basis of a thermal phase separation film forming method to form a hollow fiber film with three-layer pore structures with obviously different boundaries, and can form a high-efficiency multi-layer filtering microporous film for pathogenic microorganisms such as viruses and the like on the premise of ensuring large filtering flux.

The invention is realized by the following steps:

the large-flux virus-removing polyvinylidene fluoride hollow fiber microporous membrane has membrane filaments with the outer diameter of 1.1-1.4 mm, the inner diameter of 0.6-0.8 mm and the wall thickness of 0.2-0.4 mm; the outer surface of the membrane silk is provided with obvious openings; three membrane pore structure layers with obvious boundaries are formed from outside to inside.

Preferably, the outer layer of the membrane wire is an outer surface and a compact layer close to the outer surface, the outer surface is provided with obvious open pores, the compact layer is a compact cellular cavity-shaped pore structure with good sealing performance, the thickness of the outer layer is 5-10 mu m, and the pore diameter is 0.02-0.03 mu m; the membrane silk intermediate layer is a larger closed cell-shaped pore structure layer, the thickness is 20-40 mu m, and the pore diameter is 0.1-0.2 mu m; the inner layer of the membrane silk is a typical bicontinuous through-hole structural layer, the thickness is 150-370 mu m, and the aperture is 0.2-0.4 mu m.

A method for preparing the large-flux virus-removing polyvinylidene fluoride hollow fiber microporous membrane comprises the following steps:

(1) preparing a casting solution: heating the diluent and the polyvinylidene fluoride copolymer to 200-250 ℃ to form a homogeneous solution, standing, defoaming and uniformly mixing to obtain a casting solution;

(2) extrusion of hollow fiber membranes: the casting solution is further sheared, melted and mixed at high temperature through a double-screw extruder, finally, the casting solution is sprayed and converged with inner core solution and outer layers at a spinning nozzle, and the inner core solution and the outer layers are extruded through the spinning nozzle to form hollow fibrous homogeneous high-temperature casting solution, the inner cavity of which contains the high-temperature core solution and the outer part of which surrounds a low-temperature spraying layer; the outer layer spray is hydrous ethanol; the inner core liquid is one or more of glycerol, 1, 2-propylene glycol or 2, 3-butanediol;

(3) outer layer spraying-solvent exchange film forming: the hollow fibrous homogeneous phase high-temperature solution coexists with the spray for 0.01-0.05 second, a surface layer diluent exchanges solvents with a small amount of ethanol in the spray to form a compact outer surface with tiny open pores, meanwhile, a casting solution with the thickness of 5-10 mu m below the outer surface is affected by the low temperature of the spray, PVDF in the casting solution is separated from the diluent and is rapidly cured to form a compact layer with a very small closed cell-shaped pore structure, and the outer surface and the shallow cell-shaped compact layer form an outer layer together;

(4) and (3) low-temperature phase separation and film formation of the middle layer: in the area 10-50 microns below the outer surface of the casting solution, the PVDF and the diluent are also affected by low temperature of spraying, phase separation is carried out for a longer time, the pore structure is obviously increased, low-permeability closed cell-shaped pores are formed, and an intermediate layer is formed;

(5) and (3) low-temperature phase separation and film formation of the inner layer: after the hollow fibrous homogeneous high-temperature membrane casting solution is cooled by spraying, directly immersing the membrane casting solution into a water bath with the temperature 30-50 ℃ higher than the spraying temperature for cooling, staying for 1-2 seconds, performing typical thermally induced phase separation on PVDF and a diluent, and fully coarsening and growing the PVDF-rich and diluent-rich phases before curing to form a bicontinuous through hole structure until the membrane casting solution is completely cured and stopped to form an inner layer;

(6) extracting and removing a diluent: and (5) removing the diluent in the membrane filaments obtained in the step (5) by using an extracting agent to obtain the polyvinylidene fluoride hollow fiber microporous membrane with a three-layer pore structure.

Preferably, the casting solution in the step (1) of the preparation method comprises 20-30 wt% of polyvinylidene fluoride copolymer, the weight average molecular weight of the polyvinylidene fluoride is 60-80 ten thousand, and the balance is diluent.

Preferably, the special spinning nozzle in the step (2) of the preparation method is of a three-layer structure, the diameter of an inner layer is 0.6-0.8 mm, and the special spinning nozzle is a core liquid flow channel; the diameter of the middle layer is 1.2-2.0 mm, and the middle layer is a casting solution flow channel; the two layers accurately measure the flow of the solution entering the spinning nozzle through high-temperature metering pumps respectively; the third layer is a heat-insulating spraying layer with the diameter of 2.0-3.0 mm; the front end is connected with a spray generator with a heat exchange device.

Preferably, the diluent in step (1) of the preparation method is one or a mixture of benzophenone, diphenyl carbonate, diethyl phthalate, glyceryl triacetate, methyl benzoate and ethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, diethylene glycol, triethylene glycol, dioctyl adipate, dioctyl phthalate, tetraethylene glycol and n-octanol.

Preferably, the spraying temperature is controlled to be 5-10 ℃, and the water bath cooling liquid is controlled to be 40-60 ℃.

Preferably, the extractant in the step (5) of the preparation method is ethanol.

After the multifunctional ultrafiltration membrane is prepared, viruses are simulated by using nonhazardous phages (22-24 nm), and the rejection rate of the antiviral membrane to the phages is more than 99.99%. Meanwhile, the average retention rate of the phage is 99.999 percent as proved by a third-party test of the American NSF.

On the basis of a thermally-induced phase separation membrane making method, the invention combines the technologies of shallow solvent-non-solvent rapid exchange membrane forming, graded temperature gradient phase separation pore forming and the like to form three-layer pore hollow fiber membranes with obviously different structures, and can prepare microporous membranes for forming efficient multi-layer filtration on pathogenic microorganisms such as viruses and the like on the premise of ensuring large filtration flux. The preparation method of the invention forms a large-flux and high-efficiency virus-removing polyvinylidene fluoride hollow fiber microporous membrane with a three-layer filtering structure at one time by a multi-layer spinneret structure and a multi-stage thermally induced phase separation method. The outermost layer is provided with the holes, and the shallow layer is provided with the closed cellular pore structure compact layer with multiple folds, so that the effective filtration area is expanded by multiple times on the premise of ensuring the filtration precision, and the pure water flux of the microporous membrane is greatly improved to reach more than 1500L/m2 h.bar; the second layer structure further greatly improves the removal rate of the virus through layer-by-layer adsorption. The common ultrafiltration membrane for intercepting the virus by depending on the surface layer has the interception performance of about 99-99.9% on the virus, the interception performance of the ultrafiltration membrane is as high as 99.99%, the average interception rate of third-party detection is more 99.999%, and the virus removal effect is far higher than that of the common ultrafiltration membrane; the third layer of bicontinuous through-hole structure provides strength for the microporous membrane and ensures large flux.

Drawings

FIG. 1 is a cross-sectional view of a hollow fiber ultrafiltration membrane of example 1.

FIG. 2 is a graph showing the effect of the outer surface layer of the hollow fiber ultrafiltration membrane of example 1.

FIG. 3 is a schematic diagram showing the structure of the outer surface layer and the intermediate layer of the hollow fiber ultrafiltration membrane of example 1.

FIG. 4 is a schematic diagram of the inner layer structure of the hollow fiber ultrafiltration membrane of example 1.

Detailed Description

The invention will be further explained with reference to the drawings. FIG. 1 is a sectional view of a PVDF hollow fiber ultrafiltration membrane obtained in example 1. As shown in the figure, 1 is a compact cellular pore structure layer of the outer surface layer of the membrane silk, 2 is a closed cellular pore structure layer of the middle layer of the membrane silk, and 3 is a bicontinuous through hole structure of the inner layer of the membrane silk.

Figure 3 shows that the outer surface layer and the middle layer of the membrane yarn have very sharp boundaries.

The mesh structure of the middle and inner layers can be seen in fig. 3 and 4, respectively, and the structures of the two layers are also clearly different.