CN116236919A

CN116236919A - Double-layer structure hollow fiber membrane spun by using new and old PVDF resin, preparation method and preparation device

Info

Publication number: CN116236919A
Application number: CN202310089172.XA
Authority: CN
Inventors: 孙广东; 史继岩; 陈亦力; 莫恒亮; 李锁定; 彭兴峥; 宋冠军; 侯琴; 刘丽霞; 赵昕
Original assignee: Oseco Membrane Technology Tianjin Co ltd
Current assignee: Oseco Membrane Technology Tianjin Co ltd
Priority date: 2023-02-02
Filing date: 2023-02-02
Publication date: 2023-06-09

Abstract

The invention relates to a double-layer hollow fiber membrane spun by using new and old PVDF resin, a preparation method and a preparation device thereof; the preparation method comprises the steps of mixing new polyvinylidene fluoride, a pore-forming agent and a solvent, uniformly stirring, pumping air and defoaming to obtain PVDF resin spinning solution A; mixing the recycled polyvinylidene fluoride, the pore-forming agent and the solvent, uniformly stirring, and then pumping and defoaming to obtain an old PVDF resin spinning solution B; taking old PVDF resin spinning solution B as spinning inner layer solution, taking PVDF resin spinning solution A as spinning outer layer solution, taking PET material woven tube as lining, spinning by a hollow fiber membrane wet spinning process, and obtaining membrane filaments; the membrane filaments are soaked in pure water, then soaked in glycerol and dried to obtain the hollow fiber membrane with the double-layer structure, and the preparation method can reduce the use amount of PVDF resin and realize the recycling of the old PVDF membrane filaments.

Description

Double-layer structure hollow fiber membrane spun by using new and old PVDF resin, preparation method and preparation device

Technical Field

The invention relates to the technical field of hollow fiber membrane preparation, in particular to a double-layer structure hollow fiber membrane spun by using new and old PVDF resin, a preparation method and a preparation device.

Background

There are many kinds of resins for preparing hollow fiber ultrafiltration membranes, including polyvinylidene fluoride, polyethylene, polypropylene, polymethyl methacrylate, polyvinyl butyral, polyvinyl chloride, polycarbonate, polysulfone, etc.; the selection of the resin type needs to consider not only the molecular structure of the resin itself, but also pore-forming and film-forming properties of the resin; among the above materials, polyvinylidene fluoride (PVDF) has both the characteristics of a fluororesin and a general-purpose resin, has excellent chemical resistance, oxidation resistance, weather resistance, and the like, and is widely used in various fields based on excellent properties of PVDF. PVDF hollow fiber membranes also exhibit excellent performance in the field of water treatment membranes.

However, with a great deal of application of PVDF hollow fiber membranes, waste polyvinylidene fluoride (PVDF) hollow fiber membrane filaments are produced each year, PVDF belongs to high molecular polymers, is difficult to degrade in natural environment, occupies land resources when being directly buried, can cause soil slagging and the like when being improperly buried, releases fluorine-containing compounds when the waste membrane filaments are burnt, and seriously pollutes the atmosphere; the existing degradation technology for industrially reducing environmental pollution is immature and has complex technological process. The reduction of the use of PVDF resins to make hollow fiber membranes and how to effectively recycle the use of waste membrane filaments is a major problem to be solved at present.

Of the hollow fiber membranes of the double-layer structure, most of the patents are directed only to self-supporting hollow fiber membranes without a liner, but are not so much directed to double-layer hollow fiber membranes having such a woven tube as a liner structure. At present, patent 'manufacturing method of hollow fiber membrane and nozzle for spinning hollow fiber membrane' published by Mitsubishi chemical corporation propose a solution to the problem of abnormal extrusion during the spinning process, and the mentioned resin is resin material such as polysulfone, polyethersulfone, sulfonized polysulfone, polyvinylidene fluoride, polyacrylonitrile, etc., and the hollow fiber membrane is prepared by using PVDF resin recovered from waste membrane yarn with the end of the engineering application life as the inner layer resin; the patent 'a preparation method of a hollow fiber asymmetric composite membrane' prepares a self-supporting hollow fiber membrane, PVDF resin is not used, and the used resin materials are polysulfone and polyether; the patent three-layer composite hollow fiber nanofiltration membrane, the preparation method and the special tool thereof are mainly based on non-PVDF resin, three-layer hollow fibers with nanofiltration level separation capability are prepared, the pore diameter structure of the nanofiltration membrane is different from that of the ultra-micro filtration membrane. The patent 'a method for preparing a nano-composite polyvinylidene fluoride hollow fiber membrane by three-layer coextrusion and coextrusion equipment thereof' adopts PVDF resin as an inner layer material, and adopts a blending nano-material as an outer layer, which is mainly used for improving the hydrophilicity of the PVDF surface, wherein two resin structures are not involved; the article A Facile Method to Prepare Double-Layer Isoporous Hollow Fiber Membrane by In Situ Hydrogen Bond Formation in the Spinning Line uses a synthetic diblock copolymer PS-b-P4VP as the outer resin and uses a uniform, blended polymer or random copolymer as the inner resin to prepare a three-layer hollow fiber membrane which is still of a lining-free structure, and meanwhile, the block copolymer needs to be synthesized, so that the process is complex. The above-mentioned studies have not seen a study of preparing a double-layered hollow fiber membrane using a recycled waste membrane yarn PVDF resin.

Accordingly, in order to solve the above problems, the present invention is directed to providing a hollow fiber membrane of a double-layer structure, a preparation method and a preparation apparatus using the spinning of new and old PVDF resins.

Disclosure of Invention

The invention aims to provide a preparation method of a double-layer structure hollow fiber membrane by using new and old PVDF resin spinning, which solves the technical problems of how to reduce the use of PVDF resin to prepare the hollow fiber membrane and how to effectively recycle and use waste membrane yarns in the prior art by using the structural design of the preparation method of the double-layer structure hollow fiber membrane by using the new and old PVDF resin spinning.

The invention provides a preparation method of a double-layer structure hollow fiber membrane spun by using new and old PVDF resin, which comprises the following preparation steps:

mixing new polyvinylidene fluoride (new PVDF), a pore-forming agent and a solvent, uniformly stirring, and obtaining PVDF resin spinning solution A after steam extraction and defoaming;

mixing the recycled polyvinylidene fluoride (old PVDF), the pore-forming agent and the solvent, uniformly stirring, and then pumping and defoaming to obtain an old PVDF resin spinning solution B;

taking old PVDF resin spinning solution B as spinning inner layer solution, taking PVDF resin spinning solution A as spinning outer layer solution, taking PET material woven tube as lining, and spinning by adopting a hollow fiber membrane wet spinning process to obtain membrane filaments;

and (3) soaking the membrane filaments in pure water, then soaking the membrane filaments in glycerol, and airing to obtain the hollow fiber membrane with the double-layer structure.

Preferably, in the process of the hollow fiber membrane wet spinning technology, a three-way spinneret plate is adopted for spinning;

the spinning temperature is 60-80 ℃;

the traction speed of the PET material braided tube is 5-30m/min;

pumping the PVDF resin spinning solution A and the old PVDF resin spinning solution B into a three-way spinneret plate by adopting a metering pump, wherein the pumping speed is 5-50Hz/min, and the pumping speed ratio of the PVDF resin spinning solution A to the old PVDF resin spinning solution B is 1 (1.5-2);

the temperature of the pure water gel bath is 50-70 ℃;

the length of the air bath is 0.1-1m.

Preferably, the PVDF resin spinning solution A comprises 15-25 parts by weight of polyvinylidene fluoride (PVDF), 8-38 parts by weight of pore-forming agent and 70 parts by weight of solvent, wherein the viscosity of the PVDF resin spinning solution A is 50000-150000 mPa.s;

the old PVDF resin spinning solution B comprises 15-25 parts by weight of recovered old polyvinylidene fluoride (PVDF), 8-38 parts by weight of pore-forming agent and 70 parts by weight of solvent, wherein the viscosity of the old PVDF resin spinning solution B is 30000-60000 mPa.s.

Preferably, the porogens are polyethylene glycol 400 (PEG 400), polyethylene glycol 20000 (PEG 20000), polyvinylpyrrolidone (PVPK 60) and ethylene glycol;

the solvent was azodicarbonamide (DMAC).

Preferably, in the PVDF resin spinning solution A, the pore-foaming agent comprises 2-8 parts of polyethylene glycol 400 (PEG 400), 1-10 parts of polyethylene glycol 20000 (PEG 20000), 3-10 parts of polyvinylpyrrolidone (PVPK 60) and 2-10 parts of ethylene glycol according to parts by weight;

the old PVDF resin spinning solution B comprises, by mass, 2-8 parts of a pore-forming agent including polyethylene glycol 400 (PEG 400), 1-10 parts of polyethylene glycol 20000 (PEG 20000), 3-10 parts of polyvinylpyrrolidone (PVPK 60) and 2-10 parts of ethylene glycol.

Preferably, the old polyvinylidene fluoride preparation process comprises: cutting the waste film yarn into short yarns with the length of 5-10cm, placing the short yarns in a water tank, flushing with clear water for 2 hours, removing sludge on the surface of the waste film yarn, cleaning the waste film yarn with the sludge removed by using oxalic acid solution with the mass fraction of 1% and soaking the waste film yarn for 2.0 hours, and cleaning the waste film yarn with 10000mg/L sodium hypochlorite and soaking the waste film yarn for 2.0 hours.

Preferably, after the membrane filaments are obtained, the membrane filaments are soaked in pure water for 8-24 hours, then the membrane filaments are heat treated in pure water at 60 ℃ for 45min, then soaked in 10-20wt% of glycerol for 0.5-1.0 hour, taken out, hung and dried.

The invention provides a double-layer structure hollow fiber membrane based on the preparation method of the double-layer structure hollow fiber membrane spun by using new and old PVDF resin, which is characterized in that: the lining comprises a lining, an old PVDF resin layer B is wrapped outside the lining, and a PVDF resin layer A is wrapped outside the old PVDF resin layer.

Preferably, the total thickness of the old PVDF resin layer B and PVDF resin layer A is 50-100um;

the diameter range of the hollow fiber membrane with the double-layer structure is 2.0 plus or minus 0.2mm;

the old PVDF resin layer B has a thickness greater than that of PVDF resin layer a.

The invention also provides a preparation device based on the double-layer structure hollow fiber membrane, which is characterized in that: the device comprises a first liquid storage tank, a second liquid storage tank, a first metering pump, a second metering pump, a three-way spinneret plate, a traction roller set, a water bath and a filament collecting roller;

the three-channel spinneret plate comprises a hollow inner sleeve, an intermediate sleeve sleeved outside the inner sleeve, and an outer sleeve sleeved outside the intermediate sleeve, wherein a first liquid circulation channel is arranged between the inner sleeve and the intermediate sleeve, and a second liquid circulation channel is arranged between the intermediate sleeve and the outer sleeve;

the first liquid storage tank is communicated with the first metering pump through a pipeline, the second liquid storage tank is communicated with the second metering pump through a pipeline, the first metering pump is communicated with the first liquid circulation channel of the three-way spinneret through a pipeline, and the second metering pump is communicated with the second liquid circulation channel through a pipeline.

Compared with the prior art, the preparation method of the double-layer structure hollow fiber membrane spun by using the new and old PVDF resin has the following steps:

1. according to the preparation method of the hollow fiber membrane with the double-layer structure by utilizing the new PVDF resin spinning, the PET material woven tube is used as the inner lining, the old PVDF resin recovered from the waste membrane yarn is used as the inner layer, the new PVDF resin is used as the outer layer, the consumption of the raw material PVDF resin is effectively reduced, the cost of the raw material is reduced, meanwhile, the PVDF resin of the outer layer can play a good filtering and screening effect, the old PVDF resin of the inner layer can permeate water rapidly, the performance of the whole composite membrane is not reduced, and the appearance is consistent with that of the membrane yarn prepared from the new PVDF resin.

2. According to the preparation method of the hollow fiber membrane with the double-layer structure by utilizing the new and old PVDF resin spinning, the incompatibility of the inner and outer resins and the shrinkage difference problem generated in the exchange process of the old PVDF resin solvent and the non-solvent of the waste membrane yarn are not required to be considered, and only the addition amount of the old PVDF resin recovered by the whole inner waste membrane yarn and the new PVDF resin material of the outer raw material, the types and the concentration of the additive and the composition and the temperature of the gel bath are required to be adjusted, so that the membrane pore structure is adjusted, the method is simple and easy to obtain.

3. The invention recycles the spinning polarity of the old PVDF resin, reduces the emission of fluorine-containing substances, and has important significance for environmental protection.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.

FIG. 1 is a block diagram of steps of a method for preparing a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning;

FIG. 2 is a scanning electron microscope image of the hollow fiber single-layer membrane produced in comparative example 2 described in example one, wherein (a) the hollow fiber single-layer membrane surface was produced for the old PVDF resin dope B, and (B) the hollow fiber single-layer membrane cross-section was produced for the old PVDF resin dope B;

FIG. 3 is a scanning electron microscope image of the hollow fiber single-layer membrane produced in comparative example 1 described in example one, wherein (a) the hollow fiber single-layer membrane surface was produced for PVDF resin dope A, and (b) the cross section of the hollow fiber single-layer membrane was produced for PVDF resin dope A;

FIG. 4 is a scanning electron microscope image of a hollow fiber membrane of a double-layer structure obtained in example one, wherein (a) is the surface of the hollow fiber membrane of the double-layer structure, and (b) is the cross section of the hollow fiber membrane of the double-layer structure;

FIG. 5 is a graph of the contamination resistant operating pressures of a hollow fiber membrane module of example one double layer structure, a module of comparative example 1 and a module of comparative example 2;

FIG. 6 is a scanning electron microscope image of a hollow fiber membrane of a double-layer structure obtained in example two, wherein (a) is the surface of the hollow fiber membrane of the double-layer structure, and (b) is the cross section of the hollow fiber membrane of the double-layer structure;

FIG. 7 is a scanning electron microscope image of a hollow fiber membrane of a double-layer structure obtained in example three, wherein (a) is the surface of the hollow fiber membrane of the double-layer structure, and (b) is the cross section of the hollow fiber membrane of the double-layer structure;

FIG. 8 is a schematic structural view of a device for producing a hollow fiber membrane with a double-layer structure according to the third embodiment;

fig. 9 is a schematic structural view of the three-way spinneret plate in the third embodiment.

Detailed Description

The following description of the present invention will be made clearly and fully, and it is apparent that the embodiments described are some, but not all, of the embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

s1) mixing new polyvinylidene fluoride (new PVDF), a pore-forming agent and a solvent, uniformly stirring, and obtaining PVDF resin spinning solution A after air suction and defoaming;

s2) mixing the recycled old polyvinylidene fluoride (old PVDF), the pore-forming agent and the solvent, uniformly stirring, and then pumping and defoaming to obtain an old PVDF resin spinning solution B;

s3) taking the old PVDF resin spinning solution B as spinning inner layer solution, taking the PVDF resin spinning solution A as spinning outer layer solution, taking a PET material woven tube as a lining, and spinning by adopting a hollow fiber membrane wet spinning process to obtain membrane filaments;

s4) soaking the membrane filaments in pure water, then soaking the membrane filaments in glycerol, and airing to obtain the hollow fiber membrane with the double-layer structure.

Specifically, in the process of the hollow fiber membrane wet spinning technology, spinning is carried out by adopting a three-way spinneret plate;

the spinning temperature is 60-80 ℃;

the traction speed of the PET material braided tube is 5-30m/min;

the temperature of the pure water gel bath is 50-70 ℃;

the length of the air bath is 0.1-1m.

Specifically, the PVDF resin spinning solution A comprises, by weight, 15-25 parts of polyvinylidene fluoride (PVDF), 8-38 parts of a pore-forming agent and 70 parts of a solvent, wherein the viscosity of the PVDF resin spinning solution A is 50000-150000 mPa.s;

Specifically, the pore-forming agent is polyethylene glycol 400 (PEG 400), polyethylene glycol 20000 (PEG 20000), polyvinylpyrrolidone (PVPK 60) and ethylene glycol;

the solvent was azodicarbonamide (DMAC).

Specifically, the preparation process of the old polyvinylidene fluoride comprises the following steps: cutting the waste film yarn into short yarns with the length of 5-10cm, placing the short yarns in a water tank, flushing with clear water for 2 hours, removing sludge on the surface of the waste film yarn, cleaning the waste film yarn with the sludge removed by using oxalic acid solution with the mass fraction of 1% and soaking the waste film yarn for 2.0 hours, and cleaning the waste film yarn with 10000mg/L sodium hypochlorite and soaking the waste film yarn for 2.0 hours.

Specifically, after the membrane silk is obtained, the membrane silk is soaked in pure water for 8-24 hours, then the membrane silk is subjected to heat treatment in pure water at 60 ℃ for 45min, then soaked in 10-20wt% of glycerol for 0.5-10 hours, taken out, hung and dried.

The invention also provides a double-layer hollow fiber membrane obtained based on the preparation method of the double-layer hollow fiber membrane spun by using the new and old PVDF resin, which is characterized in that: the lining comprises a lining, an old PVDF resin layer B is wrapped outside the lining, and a PVDF resin layer A is wrapped outside the old PVDF resin layer.

Specifically, the total thickness of the old PVDF resin layer B and the PVDF resin layer A is 50-100um;

The invention also provides a preparation device based on the double-layer hollow fiber membrane, which comprises a first liquid storage tank, a second liquid storage tank, a first metering pump, a second metering pump, a three-way spinneret plate, a traction roller set, a water bath and a filament collecting roller;

According to the preparation method of the hollow fiber membrane with the double-layer structure by utilizing the new PVDF resin spinning, the PET material woven tube is used as the inner lining, the old PVDF resin recovered from the waste membrane yarn is used as the inner layer, the new PVDF resin is used as the outer layer, the consumption of the raw material PVDF resin is effectively reduced, the cost of the raw material is reduced, meanwhile, the PVDF resin of the outer layer can play a good filtering and screening effect, the old PVDF resin of the inner layer can permeate water rapidly, the performance of the whole composite membrane is not reduced, and the appearance is consistent with that of the membrane yarn prepared from the new PVDF resin.

According to the preparation method of the hollow fiber membrane with the double-layer structure by utilizing the new and old PVDF resin spinning, the incompatibility of the inner and outer resins and the shrinkage difference problem generated in the exchange process of the old PVDF resin solvent and the non-solvent of the waste membrane yarn are not required to be considered, and only the addition amount of the old PVDF resin recovered by the whole inner waste membrane yarn and the new PVDF resin material of the outer raw material, the types and the concentration of the additive and the composition and the temperature of the gel bath are required to be adjusted, so that the membrane pore structure is adjusted, the method is simple and easy to obtain.

The invention recycles the spinning polarity of the old PVDF resin, reduces the emission of fluorine-containing substances, and has important significance for environmental protection.

Example 1

101 15 parts of new polyvinylidene fluoride (PVDF), 4 parts of polyethylene glycol 400 (PEG 400), 10 parts of polyethylene glycol 20000 (PEG 20000), 5 parts of polyvinylpyrrolidone (PVPK 60), 5 parts of ethylene glycol and 70 parts of azomethide (DMAC) are mixed, stirred uniformly, stirred for 5 hours, pumped and defoamed to obtain PVDF resin spinning solution A.

102 20 parts of recycled old polyvinylidene fluoride (old PVDF), 2 parts of polyethylene glycol 400 (PEG 400), 8 parts of polyethylene glycol 20000 (PEG 20000), 3 parts of polyvinylpyrrolidone (PVPK 60), 5 parts of ethylene glycol and 70 parts of azomethine formamide (DMAC) are mixed, stirred uniformly for 5 hours, and air-extracted and defoamed to obtain the old PVDF resin spinning solution B.

103 Taking the old PVDF resin spinning solution B as spinning inner layer solution, taking the PVDF resin spinning solution A as spinning outer layer solution, taking a PET material woven tube as an inner lining, spinning under a hollow fiber membrane wet spinning process, specifically, spinning by adopting a three-channel spinneret plate to obtain membrane filaments, wherein the spinning temperature is controlled at 65 ℃, the traction speed of the PET material woven tube is 9 m/min, the pump speed of the old PVDF resin spinning solution B is 15 Hz/min, the pump speed of the PVDF resin spinning solution A is 10 Hz/min, the temperature of a pure water gel bath is 60 ℃, the length of an air bath is 0.15m, and the temperature is 35 ℃.

104 Soaking the membrane filaments in pure water for 10 hours, then carrying out heat treatment on the membrane filaments in pure water at 60 ℃ for 45min, then soaking the membrane filaments in 12wt% of glycerol for 0.5 hour, taking out, hanging and airing to obtain the hollow fiber membrane with the double-layer structure.

Based on the method, the obtained hollow fiber membrane with the double-layer structure comprises a lining, wherein an old PVDF resin layer B is wrapped outside the lining, and a PVDF resin layer A is wrapped outside the old PVDF resin layer.

The preparation process of the old polyvinylidene fluoride comprises the following steps: cutting the waste film yarn into short yarns with the length of 5-10cm, placing the short yarns in a water tank, flushing with clear water for 2 hours, removing sludge on the surface of the waste film yarn, cleaning the waste film yarn with the sludge removed by using oxalic acid solution with the mass fraction of 1% and soaking the waste film yarn for 2.0 hours, and cleaning the waste film yarn with 10000mg/L sodium hypochlorite and soaking the waste film yarn for 2.0 hours.

Performing performance test on the obtained hollow fiber membrane with the double-layer structure:

(1) Membrane silk flux refers to the amount of water which is transmitted through a unit membrane area in unit time under certain temperature and pressure, and is one of the performance evaluations of membrane products, and the membrane silk flux is used for detecting the liquid permeability of the membrane products. Membrane filament flux testing method: 3-5 samples of 35cm each with an effective length of 30cm; pure water test at 25 ℃ under 0.1MPa, the calculation formula is as follows: flux (L/. Square.x h) = (flow L x 3600S/h)/(3.14 x outer diameter m x effective length m x time S).

(2) And testing the inner diameter and the outer diameter of the membrane wire by adopting an optical microscope, and representing the thickness of an effective membrane layer of the membrane wire.

(3) Initial bubble point: taking 50cm membrane filaments, sealing one end, introducing compressed air into one end, immersing the whole membrane filaments in water, continuously pressurizing, and recording the initial bubble point value of the membrane filaments.

Comparative example 1 a hollow fiber single-layer membrane was prepared using PVDF resin dope a, and the spinning process parameters were the same.

Comparative example 2 preparation of hollow fiber Single-layer Membrane Using old PVDF resin spinning solution B, spinning Process parameters were the same

The results of the above test are shown in Table 1.

The obtained hollow fiber membrane of a double-layered structure, comparative example 1 and comparative example 2 were simultaneously scanned using a scanning electron microscope, see fig. 2, 3 and 4.

And as the lining cannot be brittle broken under the liquid nitrogen condition, membrane wires are scratched in sample preparation, and the membrane wire samples are removed after the lining is removed to carry out liquid nitrogen brittle breaking sample preparation.

Fig. 2 is a cross section of a hollow fiber single-layer membrane prepared from the old PVDF resin dope B of comparative example 2, in which fig. 2 (a) is a surface of a hollow fiber single-layer membrane prepared from the old PVDF resin dope B, and fig. 2 (B) is a cross section of a hollow fiber single-layer membrane prepared from the old PVDF resin dope B. As can be seen from fig. 2, in comparative example 2, the surface of the hollow fiber single-layer membrane prepared from the old PVDF resin spinning solution B has a certain number of macropores, and the distribution is uneven; the section presents a large cavity structure, and a large number of small holes are formed in the inner wall of the cavity;

fig. 3 is a view showing a hollow fiber single-layer membrane prepared by PVDF resin dope a of comparative example 1, wherein fig. 3 (a) is a view showing a surface of the hollow fiber single-layer membrane prepared by PVDF resin dope a, and fig. 3 (b) is a cross section of the hollow fiber single-layer membrane prepared by PVDF resin dope a. As can be seen from fig. 3, the hollow fiber single-layer membrane prepared by PVDF resin spinning solution a of comparative example 1 has a smaller surface pore diameter and a gradient pore structure in cross section;

FIG. 4 is a double-layer hollow fiber membrane, wherein FIG. 4 (a) is a surface of the double-layer hollow fiber membrane, and FIG. 4 (b) is a cross section of the double-layer hollow fiber membrane; as can be seen from fig. 4, the membrane pores of the hollow fiber membrane with the double-layer structure are between the surface pores of the two single-layer membranes of comparative example 1 and comparative example 2, a large number of micropores are also present on the surface, the micropores are uniformly distributed, the inner layer and the outer layer structures are clearly visible in cross section, the inner layer cross section structure presents a glue loose honeycomb-shaped pore, and the outer layer cross section structure presents a relatively dense sponge-shaped pore; the enlargement of the junction position can see that the middle of the two layers of structures is not an air structure, but the upper layer and the lower layer of macropores and pores are mutually penetrated; the outer layer is thinner by about 20um, the inner layer is thicker by about 40um, and the purpose of the thin outer and thick inner section of the expected film wire film layer is achieved.

The single-layer hollow fiber membrane prepared in comparative example 1, the single-layer hollow fiber membrane prepared in comparative example 2 and the double-layer hollow fiber membrane were each prepared to have a module area of 0.023m ² Is put into sewage with the sludge concentration of 11.56g/LAnd (5) performing pollution-resistant long-term operation test, and recording pressure change in the operation process when the fixed operation flux is 30LMH, wherein the test result is shown in figure 5.

As can be seen from FIG. 5, the small module prepared by the single-layer hollow fiber membrane prepared in comparative example 2 was not resistant to contamination, and the operating pressure was increased rapidly, reaching approximately 15kpa after the end of one cycle, for 5 cycles; the double-layer hollow fiber membrane has stable running pressure and little difference with the single-layer membrane prepared in comparative example 1.

Example two

201 18 parts of new polyvinylidene fluoride (PVDF), 4 parts of polyethylene glycol 400 (PEG 400), 10 parts of polyethylene glycol 20000 (PEG 20000), 3 parts of polyvinylpyrrolidone (PVPK 60), 3 parts of ethylene glycol and 70 parts of azomethide (DMAC) are mixed, stirred uniformly, pumped and defoamed to obtain PVDF resin spinning solution A.

202 25 parts of recycled old polyvinylidene fluoride (old PVDF), 2 parts of polyethylene glycol 400 (PEG 400), 8 parts of polyethylene glycol 20000 (PEG 20000), 5 parts of polyvinylpyrrolidone (PVPK 60), 5 parts of ethylene glycol and 70 parts of azomethine formamide (DMAC), and after uniform stirring, pumping and defoaming, the old PVDF resin spinning solution B is obtained.

203 Taking the old PVDF resin spinning solution B as spinning inner layer solution, taking the PVDF resin spinning solution A as spinning outer layer solution, taking a PET material woven tube as a lining, and spinning by adopting a hollow fiber membrane wet spinning process to obtain membrane filaments;

204 Soaking the membrane filaments in pure water for 10 hours, then carrying out heat treatment on the membrane filaments in pure water at 60 ℃ for 45min, then soaking the membrane filaments in 20wt% of glycerol for 0.5 hour, taking out, hanging and airing to obtain the hollow fiber membrane with the double-layer structure.

In the process of the hollow fiber membrane wet spinning technology, the spinning temperature is 70 ℃, the pump speed of the PVDF resin spinning solution A is 30 Hz/min, and the pump speed of the old PVDF resin spinning solution B is 45 Hz/min.

The pulling speed of the inner lining of the woven tube is 25 m/min, the pure water gel bath is pure water at 70 ℃, the length of the air bath is 0.5m, and the temperature is 35 ℃.

The properties of the obtained hollow fiber membrane with the double-layer structure are shown in Table 2.

Comparative example 3 a single layer film was prepared using PVDF resin dope a of example two, and the other parameters and properties are shown in table 2, as in example.

Scanning the obtained hollow fiber membrane with the double-layer structure by adopting a scanning electron microscope, wherein the scanning is shown in fig. 6, wherein fig. 6 (a) is a surface view of the hollow fiber membrane with the double-layer structure, and fig. 6 (b) is a sectional view of the hollow fiber membrane with the double-layer structure.

As can be seen from FIG. 6, a large number of micropores are visible on the surface of the hollow fiber membrane with the double-layer structure, and the micropores are uniformly distributed; the section is clear, the inner layer structure and the outer layer structure are visible, the inner layer is loose in honeycomb holes, and the outer layer is a dense spongy hole; the mutual penetration of the middle position of the two layers of structures can be seen by enlarging the boundary position; the electron microscope picture can show that the upper layer is about 30um, and the lower layer is about 40um; the preparation of the composite film can control the thickness of the inner and outer film layers through the adjustment of spinning technological parameters.

Example III

301 15 parts of new polyvinylidene fluoride (PVDF), 8 parts of polyethylene glycol 400 (PEG 400), 10 parts of polyethylene glycol 20000 (PEG 20000), 10 parts of polyvinylpyrrolidone (PVPK 60), 10 parts of ethylene glycol and 70 parts of azomethide (DMAC) are mixed, stirred uniformly, pumped and defoamed to obtain PVDF resin spinning solution A.

302 25 parts of recycled old polyvinylidene fluoride (old PVDF), 8 parts of polyethylene glycol 400 (PEG 400), 10 parts of polyethylene glycol 20000 (PEG 20000), 10 parts of polyvinylpyrrolidone (PVPK 60), 10 parts of ethylene glycol and 70 parts of azomethine formamide (DMAC) are mixed, stirred uniformly, and then pumped and defoamed to obtain the old PVDF resin spinning solution B.

303 Taking the old PVDF resin spinning solution B as spinning inner layer solution, taking the PVDF resin spinning solution A as spinning outer layer solution, taking a PET material woven tube as a lining, and spinning by adopting a hollow fiber membrane wet spinning process to obtain membrane filaments;

304 Soaking the membrane filaments in pure water for 10 hours, then carrying out heat treatment on the membrane filaments in pure water at 60 ℃ for 45min, then soaking the membrane filaments in 17wt% of glycerol for 0.5 hour, taking out, hanging and airing to obtain the hollow fiber membrane with the double-layer structure.

In the process of the hollow fiber membrane wet spinning technology, the spinning temperature is 75 ℃, the pump speed of the PVDF resin spinning solution A is 22 Hz/min, and the pump speed of the old PVDF resin spinning solution B is 33 Hz/min;

the pulling speed of the inner lining of the woven tube is 15 m/min, the pure water gel bath is pure water at 70 ℃, the length of the air bath is 0.2m, and the temperature is 35 ℃.

The properties of the obtained double-layer structured hollow fiber membrane are shown in Table 2.

Scanning the obtained hollow fiber membrane with the double-layer structure by adopting a scanning electron microscope, wherein the scanning is shown in fig. 7, wherein fig. 7 (a) is a surface view of the hollow fiber membrane with the double-layer structure, and fig. 7 (b) is a sectional view of the hollow fiber membrane with the double-layer structure.

As can be seen from FIG. 7, the cross section of the prepared hollow fiber membrane with the double-layer structure presents a compact sponge pore structure, the boundary between the inner layer resin and the outer layer resin is not obvious, and the pore diameter of the boundary position of the two layers of resin is larger than that of the upper edge and the lower edge.

As shown in FIG. 8, the invention also provides a preparation device of the hollow fiber membrane with a double-layer structure, which comprises

The first liquid storage tank 1, the second liquid storage tank 2, the first metering pump 3 and the second metering pump 4) are connected with the spinneret plate 5 in a three-way manner, and the traction roller set 6, the water bath 7 and the filament collecting roller 8 are connected with each other;

as shown in fig. 9, the three-way spinneret 5 comprises a hollow inner sleeve 51, an intermediate sleeve 52 sleeved outside the inner sleeve 51, an outer sleeve 53 sleeved outside the intermediate sleeve 52, a first liquid circulation channel arranged between the inner sleeve 51 and the intermediate sleeve 52, and a second liquid circulation channel arranged between the intermediate sleeve 52 and the outer sleeve 53;

the first liquid storage tank 1 is communicated with the first metering pump 3 through a pipeline, the second liquid storage tank 2 is communicated with the second metering pump 4 through a pipeline, the first metering pump 3 is communicated with a first liquid circulation channel of the three-way spinneret 5 through a pipeline, and the second metering pump is communicated with a second liquid circulation channel through a pipeline.

TABLE 1 hollow fiber membrane inner and outer diameters, pure water flux and initial bubble point data

TABLE 2 hollow fiber membrane inner and outer diameters, pure water flux and initial bubble point data

Compared with comparative example 1, the double-layer hollow fiber membrane obtained in example 1 has the advantages that the pure water flux is similar, the initial bubble point pressure is similar and is remarkably higher than that of comparative example 2, and the double-layer hollow fiber membrane obtained in example 2 is similar to that of comparative example 3, so that the preparation of the old PVDF resin spinning solution is selected for preparing the inner layer of the double-layer hollow fiber membrane, the integral performance is not affected, and the double-layer membrane and the raw material new PVDF single-layer membrane have stable running pressure and are not greatly different in pollution resistance.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. A preparation method of a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning is characterized by comprising the following steps: the preparation method comprises the following preparation steps:

2. The method for preparing a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning according to claim 1, which is characterized in that:

in the process of the hollow fiber membrane wet spinning technology, spinning is carried out by adopting a three-way spinneret plate;

the spinning temperature is 60-80 ℃;

the traction speed of the PET material braided tube is 5-30m/min;

the temperature of the pure water gel bath is 50-70 ℃;

the length of the air bath is 0.1-1m.

3. The method for preparing a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning according to claim 1, which is characterized in that: the PVDF resin spinning solution A comprises, by weight, 15-25 parts of polyvinylidene fluoride (PVDF), 8-38 parts of a pore-forming agent and 70 parts of a solvent, wherein the viscosity of the PVDF resin spinning solution A is 50000-150000 mPa.s;

4. The method for preparing a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning according to claim 1, which is characterized in that:

the pore-forming agent is polyethylene glycol 400 (PEG 400), polyethylene glycol 20000 (PEG 20000), polyvinylpyrrolidone (PVPK 60) and ethylene glycol;

the solvent was azodicarbonamide (DMAC).

5. The method for preparing a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning according to claim 1, which is characterized in that:

in PVDF resin spinning solution A, according to the weight portion, the pore-forming agent comprises polyethylene glycol 400 (PEG 400) 2-8 portions, polyethylene glycol 20000 (PEG 20000) 1-10 portions, polyvinylpyrrolidone (PVPK 60) 3-10 portions and ethylene glycol 2-10 portions;

6. The method for preparing a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning according to claim 1, which is characterized in that:

the preparation process of the old polyvinylidene fluoride comprises the following steps: cutting the waste film yarn into short yarns with the length of 5-10cm, placing the short yarns in a water tank, flushing with clear water for 2 hours, removing sludge on the surface of the waste film yarn, cleaning the waste film yarn with the sludge removed by using oxalic acid solution with the mass fraction of 1% and soaking the waste film yarn for 2.0 hours, and cleaning the waste film yarn with 10000mg/L sodium chlorate and soaking the waste film yarn for 2.0 hours.

7. The method for preparing a hollow fiber membrane with a double-layer structure by using new and old PVDF resin spinning according to claim 1, which is characterized in that: after the membrane silk is obtained, soaking the membrane silk in pure water for 8-24 hours, then heat-treating the membrane silk in pure water at 60 ℃ for 45 minutes, soaking in 10-20wt% of glycerol for 0.5-1.0 hour, taking out, hanging and airing.

8. A double-layer hollow fiber membrane obtained based on the method for producing a double-layer hollow fiber membrane spun with a new and old PVDF resin according to any one of claims 1 to 7, characterized in that: the lining comprises a lining, an old PVDF resin layer B is wrapped outside the lining, and a PVDF resin layer A is wrapped outside the old PVDF resin layer.

9. The double-layer structured hollow fiber membrane according to claim 8, wherein: the total thickness of the old PVDF resin layer B and the PVDF resin layer A is 50-100um;

10. A production apparatus based on the double-layer structure hollow fiber membrane according to claim 8 or 9, characterized in that: the device comprises a first liquid storage tank, a second liquid storage tank, a first metering pump, a second metering pump, a three-way spinneret plate, a traction roller set, a water bath and a filament collecting roller;