CN115612169A - Method and application for recycling PVDF (polyvinylidene fluoride) in membrane wire material, freezing separation device and application - Google Patents

Abstract

The invention provides a method for recovering PVDF (polyvinylidene fluoride) in membrane filament materials and application thereof, a freezing separation device and application thereof, and relates to the technical field of high polymer material recovery. Specifically, the method comprises the following steps: 1) Spraying liquid nitrogen to the pretreated membrane silk material; 2) Performing a surface treatment to separate a low temperature surface layer; 3) Repeating the steps 1) and 2) at least 3 times in a circulating manner to obtain a mixture; and screening and separating the mixture to obtain the recycled PVDF. Aiming at the technical problems that membrane filaments are not easy to recycle, the recycling cost of a dissolving method is high, the using amount of an organic solvent is large, and the environment is not friendly, the recycling process provided by the invention quickly cools a PVDF layer by low-temperature freezing, then crushes the brittle PVDF surface layer by external physical action and falls off from a PET supporting layer, and finally realizes the separation of the PVDF layer and the PET supporting layer; the method avoids the use of organic solvent, has low cost and environmental protection, and has wide application prospect in the aspect of membrane filament recovery treatment.

Description

Method and application for recycling PVDF (polyvinylidene fluoride) in membrane wire material, freezing separation device and application

Technical Field

The invention relates to the technical field of polymer material recovery, in particular to a method for recovering PVDF in a membrane silk material and application thereof, a freezing separation device and application thereof.

Background

The PVDF (polyvinylidene fluoride) resin has the advantages of good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance and ray radiation resistance, has special performances such as piezoelectricity, dielectricity, pyroelectricity and the like, and is mainly applied to the fields of coating, injection molding, lithium batteries, water treatment films, solar backboard films and the like. With the rapid development of new energy industries such as lithium batteries and photovoltaics in recent years, the demand for PVDF (polyvinylidene fluoride) is rapidly increased, and the proportion of lithium batteries and photovoltaics in a downstream demand structure is also improved. The PVDF membrane silk material is a composite membrane silk material which takes a PET (polyethylene terephthalate) braided tube as a supporting layer and PVDF as a filtering layer; in the actual production and application process, the material is easy to produce leftover materials and engineering waste filaments, the waste of PVDF raw materials is generated to a large extent, the production cost of enterprises is indirectly increased, and how to recycle the waste products of the PVDF membrane filaments with linings is a big problem which needs to be overcome in the current production link.

At present, the industry mainly adopts a dissolution method to realize the recovery and the reutilization of PVDF film silk waste silk with lining, firstly, the waste silk is cleaned by acid or alkali liquor to obtain clean film silk, then, good solvent is adopted to soak and dissolve the film silk, after the PVDF layer is completely dissolved, the processes of centrifugation and the like are adopted to separate, pore-forming agent and small molecular weight additive are added into the recovered PVDF to prepare casting film liquid, and finally, the wet spinning is carried out by utilizing the phase inversion principle, thereby realizing the recovery and the reutilization of the waste silk.

The invention patent 201410374894.0 discloses a method for recovering and purifying PVDF resin on the surface of a waste filtering membrane, which comprises the steps of firstly removing pollutants on the surface of the waste filtering membrane by cleaning, drying, immersing the waste filtering membrane in an organic solvent to dissolve and recover PVDF on the surface of the filtering membrane, and removing a filtering membrane supporting material by centrifugal solid-liquid separation to obtain a PVDF extracting solution; then pouring the extracting solution into water, precipitating to separate out a white solid, and drying to obtain PVDF resin; and obtaining the high-purity PVDF resin solid through multiple dissolving, high-speed centrifugal impurity removal and precipitation separation treatments. The method can effectively realize the recovery and purification of the PVDF resin on the surface of the waste filtering membrane, but has the disadvantages of large organic solvent consumption, environmental friendliness and higher cost.

The invention patent 201910512362.1 discloses a PVDF membrane silk waste silk recovery processing system, which consists of a spinning device, a pouring device, a cutting device, a first soaking pool, a second soaking pool, a spraying and cleaning device, a dryer, a separator, a PET braided tube sorting device, a PET braided tube dryer, a melting device, a granulating device, a membrane liquid drying device, a gel solidifying device, a membrane liquid solidifying dryer and a crushing device; the PVDF is recycled mainly through sealed sodium hypochlorite in a first soaking pool and sealed ethanol solution in a second soaking pool, repeated cyclic washing and drying are carried out after soaking treatment, and then PVDF resin and PET braided tubes are completely separated through a good solvent in a dissolving device at the lower part of a dryer. The system also uses a large amount of organic solvent, and the process is complicated and the soaking time is long.

In addition, the two soluble recovery processes have many disadvantages in the practical application process: (1) when the lined PVDF waste membrane filaments are dissolved and recovered, the PET braided tube can absorb a certain amount of solvent, so the dosage of the solvent is large, and the used solvents are all organic solvents such as DMAC, DMF, NMP, TEP or DMSO and the like, and are expensive, so that the recovery cost of the dissolving method is high. (2) In recent years, relevant departments actively implement a 'zero emission' policy, part of organic solvents are volatile, pollutants are easily generated in the production and use process, the organic solvents are harmful to human bodies and the environment, and the organic solvents do not conform to the green production concept advocated by the relevant departments. (3) The PET braided tube used as the lining in the process of recovering PVDF by a solvent method can absorb a large amount of solvent, and cannot be completely separated in the centrifugal process, so that the recovery difficulty and cost are directly improved in the subsequent PET recovery process while the solvent is wasted.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention provides a method for recovering PVDF (polyvinylidene fluoride) in a membrane wire material, and the method is used for solving the technical problems that waste membrane wire is not easy to recover and reuse, PVDF recovered by a dissolution method is high in cost, large in organic solvent consumption and not friendly to environment and human bodies, and the like; spraying liquid nitrogen on the pretreated membrane wires to quickly freeze the PVDF layer, crushing the brittle PVDF surface layer by external physical action, and dropping the brittle PVDF surface layer from the PET support layer, so as to finally realize the separation of the PVDF layer and the PET layer; the method avoids the use of organic solvent, has low cost and environmental protection, and has wide application prospect in the aspect of membrane silk recovery treatment.

The second purpose of the invention is to provide the PVDF material obtained by the method for recovering PVDF in the membrane silk material.

A third object of the present invention is to provide a freeze separation apparatus adapted to the method of recovering PVDF in membrane filament material as described above.

A fourth object of the present invention is to provide a spinning film-forming apparatus including the above-described freeze separation apparatus.

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

a method for recycling PVDF in membrane silk materials mainly comprises the following steps:

(1) Spraying liquid nitrogen to the pretreated membrane silk material;

(2) Performing a surface treatment to separate a low temperature surface layer;

(3) Repeating the step (1) and the step (2) at least 3 times in a circulating manner to obtain a mixture; sieving and separating the mixture to obtain recovered PVDF;

wherein the membrane silk material comprises a PET braided tube and a PVDF filter layer; the membrane silk material can be the recycled waste membrane silk, and can also be leftover materials or other waste raw material membrane silks in the processing process.

The difference of the embrittlement temperatures of PVDF polymer materials and PET polymer materials in the membrane silk materials is large, and the embrittlement temperature of the PET braided tube is lower than that of the PVDF filter layer; therefore, the surface of the membrane wire is sprayed by low-temperature liquid nitrogen to realize the quick freezing of the PVDF as the membrane material, while the PET as the lining layer basically keeps the original toughness unchanged due to the low catalytic temperature, so that the PET and the lining layer are hard and brittle, then the fragile PVDF filter layer is crushed and falls off from the PET braided tube by a mechanical surface treatment mode, and finally the separation of the PET and the PVDF is realized.

Preferably, the pre-treatment is performed before performing step (1); the pretreatment includes at least one of the following features (a) to (d):

(a) Cutting the membrane silk material to a length of 5-10 cm;

(b) Spraying and/or soaking the membrane silk material with water;

(c) Rinsing the membrane silk material by using a sodium hypochlorite solution;

(d) Pickling the membrane wire material;

it is noted that all references to (a), (b), (c), and (d) in the present invention are for descriptive purposes only and are not to be construed as indicating or implying a relative importance, and that (a) - (d) are not intended to be limiting as to the order of operation or chronological order; for the specific selection and processing order of features (a) - (d), one skilled in the art can adopt any permutation and combination, such as (b) → (d), such as (a) → (d) → (c), and further such as (c) → (d) → (b) → (a) and the like;

more preferably, when the cleaning condition of the membrane thread material is relatively good, only step (b) is performed;

more preferably, after the pretreatment and before the step (1), drying the membrane silk material until no moisture exists on the surface of the membrane silk material, so as to facilitate subsequent low-temperature treatment;

more preferably, in the step (b), the soaking time is 12-24 h;

more preferably, in step (c), the concentration of the sodium hypochlorite solution is 5000ppm to 6000ppm, and the rinsing time is 1h to 10h;

more preferably, in step (d), the acid used for the acid washing comprises at least one of hydrochloric acid, oxalic acid, nitric acid and sulfuric acid;

further preferably, in the step (d), the mass fraction of the acid is 3% to 5%, and the acid washing time is 1h to 10h.

Preferably, in the step (2), the surface treatment includes at least one of kneading, shaking, sanding, polishing and ultrasonication; the surface treatment includes, but is not limited to, the above-described operation mode, and any technical means for separating the low-temperature surface layer by physical action can be used as the surface treatment of the present invention;

preferably, in the step (2), the time for the surface treatment is 1min to 10min;

preferably, in the step (2), the usage amount of the liquid nitrogen is adaptively adjusted according to the mass and the volume of the membrane silk material; only one reference parameter is given in the present invention as follows: when the mass of the membrane wire material is 60 kg-80 kg and the length of the membrane wire material is 5 cm-10 cm, the flow rate of the liquid nitrogen is 2L/min-3L/min, the surface treatment is carried out after the spraying is carried out for 3 min-5 min, and then the operation is continued to be circulated;

preferably, in the step (3), the steps (1) and (2) are repeated 3 to 5 times; it should be noted that the operation of the pre-treatment need not be repeated when step (1) is repeated;

preferably, in the step (3), the sieve is selected to have a mesh size of 10-14 meshes.

The PVDF material obtained by the method for recycling the PVDF in the membrane silk material as described above;

preferably, the PVDF material is adopted for spinning and recycling, and the method mainly comprises the following steps: dissolving the PVDF material by DMAC (dimethylacetamide) to obtain a membrane casting solution, adding a proper amount of pore-forming agent into the membrane casting solution to obtain a spinning solution, and spinning by a phase inversion method to obtain the PVDF membrane material;

more preferably, the mass fraction of PVDF in the casting solution is 10-25%;

more preferably, the method further comprises the following steps: solid-liquid separating the membrane casting solution to filter impurities; optionally, a 300-500 mesh screen is used for filtration.

A freeze separation apparatus adapted to the method of recovering PVDF in membrane filament material as described above; the freezing separation device comprises the following structural units which are connected in sequence:

the device comprises a liquid nitrogen storage unit, a freezing separation unit, a discharging unit and a collecting unit.

Specifically, the structural units and the components thereof have the following functions and structural relationships:

one) liquid nitrogen storage unit: for storing liquid nitrogen required by the freeze separation unit; the structure and the storage condition of the liquid nitrogen storage unit are not limited, and only national regulations such as chemical dangerous article safety management conditions, implementation rules, and regulations on safe use of chemicals in workplaces are required.

II) a freezing and separating unit: a main operation unit for separating the PET woven tube and the PVDF filter layer in the membrane silk material; in particular, the freeze separation unit comprises at least the following functional components: cold source shower nozzle, vertical pressure subassembly, horizontal pressure subassembly, compressed sheet, interception net and shell body.

2.1 Cold source shower head: the liquid nitrogen storage unit is used for storing liquid nitrogen; the liquid nitrogen storage unit is connected with the liquid nitrogen storage unit through a pipeline, and components such as a pressure pump, a valve, a flowmeter and the like can be arranged on the connecting pipeline in a conventional way; in addition, the cold source spray head is connected with the outer shell;

preferably, the number of the cold source spray heads is at least 1; optionally, the number of the cold source spray heads is adaptively adjusted according to the volume of a space formed by the compression plate and the interception net and/or according to the mass or the volume of the membrane wire material;

preferably, the cold source spray head is fixedly connected with the outer shell;

preferably, the cold source nozzle adopts a telescopic structure, covers the space formed by the compression plate and the interception net when spraying operation is performed, and contracts after the spraying operation is finished.

2.2 Pressure receiving plate and intercepting net: for building up and forming one or more spaces for accommodating the membrane thread material; the pressed plate realizes mechanical action on the membrane silk material through parallel movement, and the interception net is used for preventing the membrane silk material from leaving a stressed area;

preferably, two pressure receiving plates and two intercepting nets are arranged in the freezing and separating unit; the plate surfaces of the two compression plates are parallel to each other, and each compression plate is connected with the two interception nets;

preferably, the freezing and separating unit is provided with more than two pressure receiving plates and more than two intercepting nets; the membrane silk material is used for building a plurality of accommodating spaces and enabling the membrane silk material to be stressed more fully;

preferably, the plate surface of the pressed plate is independently provided with a convex structure for increasing the stress area of the membrane silk material;

preferably, the mesh number of the interception net is more than 10 meshes.

2.3 Longitudinal pressure assembly: for applying longitudinal pressure (i.e., the pressure of the pressure receiving plate in the vertical direction) to the membrane thread material;

preferably, the longitudinal pressure assembly is fixedly connected with the outer shell, and the longitudinal pressure assembly is movably connected with the pressure receiving plate;

preferably, the number of longitudinal pressure assemblies is at least 2;

more preferably, when the number of the pressure receiving plates is larger than or equal to 2, each pressure receiving plate is movably connected with at least one longitudinal pressure assembly.

2.4 Transverse pressure assembly: for applying a transverse pressure (i.e., a pressure in a parallel direction of the pressure receiving plate) to the membrane wire material;

preferably, the transverse pressure assembly comprises a transverse pressure main element, a bearing beam and a transverse pressure sub-element which are connected in sequence; the transverse pressure main element is connected with the outer shell, and the transverse pressure sub-element is movably connected with the pressure receiving plate; specifically, the transverse pressure general element is used for providing transverse pressure, the transverse pressure subelement is used for uniformly distributing the transverse pressure to the plate surface of the pressure plate, and the bearing beam is used as an intermediate connecting element between the transverse pressure general element and the transverse pressure subelement;

more preferably, when the number of the pressure receiving plates is more than or equal to 2, the number of the transverse pressure total elements is at least 2; the number of the transverse pressing sub-elements is at least 4, and each pressed plate is movably connected with at least two transverse pressing sub-elements;

preferably, the transverse pressure general element is fixedly connected with the outer shell, and/or a sliding rail is further arranged between the transverse pressure general element and the outer shell; when the sliding rail is arranged, the transverse pressure assembly can be ensured to integrally move together with the pressed plate;

preferably, when the transverse pressure assembly is started, the acting force between the transverse pressure assembly and the pressure receiving plate is 500N-1000N.

Thirdly), a discharging unit: for controlling the discharge of the freeze separation unit; a discharge pipeline is arranged in the discharge unit and is connected with the collection unit;

preferably, the lower part of the space formed by the compression plate and the interception net is provided with an inserting plate and a gate valve matched with the inserting plate;

preferably, a funnel-shaped collecting pipe or a funnel-shaped groove is arranged at the lower part of the freezing and separating device.

Four) a collection unit: for collecting and storing the separated PVDF; in the invention, no additional limitation is imposed on the structure and storage condition of the collection unit, and the collection unit can play the role of a container.

A spinning film-making device, comprising the freezing separation device;

the freezing treatment device can be used as a leftover material treatment device in a production workshop for lining type composite film silk materials; the device can also be used for a waste material and used material processing device; the PVDF raw material is obtained in the collecting means of the freezing processing apparatus, and is put into production of a spinning film.

Compared with the prior art, the invention has the beneficial effects that:

(1) The freezing separation method adopted by the invention is more environment-friendly, and the lined PVDF membrane silk material is recycled in a freezing separation mode, so that the use of an organic solvent which is easy to pollute the environment is avoided; the only consumable in the invention is liquid nitrogen, but the content of nitrogen in the atmosphere is known to be about 78%, so that the gasified liquid nitrogen in the recovery process has little influence on the environment and completely meets the currently advocated green production standard.

(2) Compared with the prior art, the method has lower recovery cost; according to investigation, when the PVDF membrane yarn material is recovered by adopting a dissolution method, the estimated cost of recovering the PVDF is at least 100 yuan/kg due to large solvent dosage and expensive organic solvent price; when the PVDF membrane yarn is recovered by adopting a freezing separation method, the investment on equipment in the early stage is removed, the cost is only about 40 yuan/kg, and the recovery cost of the PVDF is greatly reduced.

(3) In the invention, after PVDF is recycled, the PET supporting layer is also easier to recycle; compared with the dissolution method, after the PVDF is recovered, because a large amount of organic solvent is adsorbed by the residual PET supporting layer, the solvent is required to be separated when the PET is recovered subsequently, the recovery cost is greatly increased, and if the PET is not treated properly, pollutants are also easily generated; the freezing separation method can completely separate PVDF from PET, and the PET braided tube obtained by separation can be directly dissolved and granulated.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 provides a schematic diagram of a freeze separation apparatus;

FIG. 2 provides a schematic diagram of a freeze separation unit;

FIG. 3 provides a schematic perspective view of the freeze separation unit shown in FIG. 2;

FIG. 4 provides a pictorial representation of the embodiment 1;

FIG. 5 provides a pictorial representation of the embodiment 2;

FIG. 6 provides a pictorial representation of the embodiment 3.

Reference numerals are as follows:

100-liquid nitrogen storage tank; 200-a freeze separation unit;

300-a feed unit; 400-a discharge unit;

500-collecting tank;

201-longitudinal pressure assembly; 202-cold source spray head;

203-transverse pressure subelement; 204-a pressure receiving plate;

205-an interception net; 206-bearing beam;

207-transverse pressure summation element; 208-a slide rail;

209-outer shell;

401-plug board; 402-a gate valve;

403-sink.

Detailed Description

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and the detailed description, but those skilled in the art will understand that the following described embodiments are some, not all, of the embodiments of the present invention, and are only used for illustrating the present invention, and should not be construed as limiting the scope of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "parallel", "longitudinal", "transverse", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless explicitly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in a specific case to those of ordinary skill in the art.

Test example freeze separation device

According to the technical scheme recorded in the invention, the experimental example provides a feasible refrigeration separation device. Fig. 1 is a schematic structural diagram of the freeze separation apparatus, which includes a liquid nitrogen storage tank 100, a freeze separation unit 200, a feeding unit 300, a discharging unit 400 and a collecting tank 500, wherein the discharging unit 400 includes an insert plate 401, a gate valve 402 and a leakage groove 403; fig. 2 and 3 specifically provide a schematic structural diagram of the freezing and separating unit 200, which includes a longitudinal pressure assembly 201, a cold source spray head 202, a transverse pressure sub-element 203, a pressure receiving plate 204, a blocking net 205, a bearing beam 206, a transverse pressure total element 207, a sliding rail 208 and an outer shell 209. Specifically, the following functional components are present in the freeze separation unit 200 in the present test example:

(1) Longitudinal pressure assemblies 201 (4 total): two compression plates 204 are arranged at the edge of each compression plate 204 and are fixed with the compression plates 204 and the outer shell 209 through screws respectively; during operation, the longitudinal pressure assembly 201 pushes and pulls the pressure receiving plate 204 and carries out longitudinal kneading movement;

(2) Cold source spray head 202 (4 in total): the two sides of the telescopic design are respectively arranged at the left side and the right side, are distributed in a crossed manner and are fixed on the outer shell 209 through screws; after the membrane wire material is added, stretching out, spraying liquid nitrogen to the membrane wire, and retracting after spraying is finished;

(3) Transverse pressure subelements 203 (8 in total): the compression joint is fixed with the compression plate 204 and the bearing beam 206, 4 compression joints are respectively arranged on two sides of the compression plate 204, and the compression joint and the transverse compression joint 207 apply transverse compression to the compression plate 204;

(4) Pressure receiving plate 204 (2 in total): the device can be longitudinally movably designed, the surface is of a convex structure, and the two compression plates 204 rub the internal membrane silk material through the anti-parallel motion, and the size is 2000mm multiplied by 800mm;

(5) Interceptor net 205 (2 in total): the raw material is steel, is connected with the two pressure-receiving plates 204, is respectively provided with 1 in the front and the back, has the average mesh number of 100 meshes (the range limit is 90-120 meshes), has the function of intercepting the membrane thread material, prevents the membrane thread material from leaving the washboard action area in the separation process, and has the size of 400mm multiplied by 800mm;

(6) Bearer beam 206 (2 in total): connecting the transverse pressure sub-element 203 with the transverse pressure overall element 207;

(7) Transverse pressure summation element 207 (2 total): the transverse pressure sources and the bearing beams 206 are respectively positioned at two sides of the pressure receiving plate 204 and fixed on the sliding rails 208 on the inner wall of the outer shell 209;

(8) Slide rail 208 (2 in total): the left side and the right side are respectively provided with one and fixed on the outer shell 209, so that the transverse pressure system can move together with the pressure receiving plate 204;

(9) Outer shell 209 (total 1): cubic structure without bottom plate; the outer wall is internally provided with a heat insulation interlayer, and a power circuit of the longitudinal pressure assembly 201 and the transverse pressure total element 207 is embedded.

The operation method of the freezing separation device provided in this test example is as follows:

(1) Feeding the film filament material through a feeding unit 300; closing the gate valve 402 so that the gate 401 closes the bottom of the freeze separation unit;

(2) After the feeding is finished, starting the spraying system, extending the cold source spray head 202 out, spraying liquid nitrogen on the material, and recovering the cold source spray head 202 after the spraying is finished;

(3) The transverse pressing system and the longitudinal pressing system are started simultaneously, so that the materials and the materials are fully extruded, the materials and the compression plate 204 are fully extruded, after the materials are subjected to sufficient external force and crushed and separated, the transverse pressing system and the longitudinal pressing system are stopped, and the compression plate 204 is restored to the initial position;

(4) Optionally repeating the step (2) and the step (3) according to the separation condition;

(5) The gate valve 402 is opened to allow the separated material to pass through the chute 403 and obtain a mixed material in the collection unit.

Example 1

(1) Preparing and pretreating materials: cutting recovered 80kg of engineering waste silk into small sections with the length of 5cm by using a cutting machine, then carrying out hydraulic flushing, washing off visible attachments such as surface sludge and the like, then putting the small sections into NaClO solution with the concentration of 5000ppm for soaking for 8 hours, then taking out the small sections, putting the small sections into oxalic acid solution with the mass fraction of 3% for soaking for 8 hours, then taking out the small sections, soaking the small sections in clear water for 24 hours, and finally putting the small sections into an oven for complete drying.

(2) Freezing and separating: the separation and recovery were carried out by using the freeze separation apparatus as in the above test examples, and the freeze separation apparatus was used in accordance with the operation method described above;

after feeding, controlling the flow rate of a single cold source spray head 202 to be 2L/min, controlling the first-round spraying time to be 5min, then stopping spraying, starting a transverse pressure application system and a longitudinal pressure application system to rub the frozen membrane filaments at the same time, stopping rubbing for 3min, and performing second-round spraying; spraying and pressing and kneading for 5 times in total; after the freeze separation is finished, the gate valve 402 is opened to enable the mixed material to fall into the collecting tank 500, and after the mixed material is heated to the room temperature, the mixed material is sieved by a 10-mesh sieve to obtain the recycled PVDF.

FIG. 4 is a schematic diagram of the present example, in which FIG. 4 (A) is a schematic diagram of the original engineering waste filaments after being processed in step (1), FIG. 4 (B) is a PET support layer obtained after freeze separation, and FIG. 4 (C) is a PVDF powder obtained after freeze separation.

(3) PVDF recycling spinning: 1. preparing a spinning solution: dissolving the recovered PVDF into a casting solution with the mass fraction of 25% by using a solvent DMAC, and adding a pore-forming agent (PVP K30), wherein the using amount of the pore-forming agent is 30% of the mass of the PVDF; 2. sieving: filtering with 400 mesh screen cloth manufactured by Shanghai Haihong screen cloth manufacturing company Limited; 3. spinning: the hollow fiber spinning machine is adopted for spinning, the dry spinning process is 3 cm, the temperature of the spinning solution is 60 ℃, and the temperature of the coagulating bath is 35 ℃.

(4) And (3) testing spinning performance: testing the diameter, the average pore diameter, the tensile strength and the pure water flux performance of the spun new silk; the specific test method is as follows: (1) the average pore diameter of the fresh yarn was measured using a model 9310 microanalyzer (mercury porosimeter) manufactured by Michkok corporation, USA; (2) measuring the diameter of the new silk by adopting an XTT zoom stereomicroscope produced by an electro-optic instrument factory in Beijing; (3) testing the tensile strength of the new wire by using a WDT-5 electronic tension tester sold by the practical testing equipment Limited in the Shijiazhu development area; all the tests are carried out at the temperature of 20 ℃ according to the standard of the China's republic of China ocean industry test method for hollow fiber microporous filter membranes HY/T051-1999; (4) one end of an ultra-micro filtration fiber membrane with the length of 30cm is sealed, pure water is connected to the other end of the ultra-micro filtration fiber membrane, and the pure water flux of the hollow fiber membrane is measured by an internal pressure method under the pressure of 0.1 mPa.

Example 2

(1) Preparing and pretreating materials: cutting the recovered 60kg of engineering waste silk into small sections with the length of 10cm by using a cutting machine, soaking the small sections in clear water for 18 hours, and then putting the small sections in a drying oven until the small sections are completely dried.

(2) Freezing and separating: the freezing separation device in the above test example was used for separation and recovery, and the freezing separation device was used according to the above-described operation method;

after feeding, controlling the flow of a single cold source spray head 202 to be 3L/min, controlling the first-round spraying time to be 3min, then stopping spraying, starting a transverse pressure application system and a longitudinal pressure application system to rub the frozen membrane filaments at the same time, stopping rubbing for 3min, and performing second-round spraying; spraying and pressing and kneading for 4 rounds in total; after the freeze separation is finished, the gate valve 402 is opened, the mixed material falls into the collection tank 500, and after the mixed material is heated to the room temperature, the mixed material is sieved by a 12-mesh sieve, so that the recovered PVDF is obtained.

FIG. 5 is a schematic diagram of the present example, wherein FIG. 5 (A) is a schematic diagram of the original engineering waste filaments after being processed in step (1), FIG. 5 (B) is a PET support layer obtained after freeze separation, and FIG. 5 (C) is a PVDF powder obtained after freeze separation.

(3) And (4): the same as in steps (3) and (4) of example 1.

Example 3

(1) Material preparation and pretreatment: cutting recovered 80kg of engineering waste silk into small sections with the length of 8cm by using a cutting machine, then carrying out hydraulic flushing, washing off visible attachments such as surface sludge, and the like, then putting the small sections into NaClO solution with the concentration of 6000ppm for soaking for 6h, then taking out and putting the small sections into oxalic acid solution with the mass fraction of 5% for soaking for 6h, then taking out and soaking in clear water for 24h, and finally putting the small sections into an oven for complete drying.

(2) Freezing and separating: the freezing separation device in the above test example was used for separation and recovery, and the freezing separation device was used according to the above-described operation method;

after feeding, controlling the flow rate of a single cold source spray head 202 to be 2.5L/min, controlling the spraying time of the first round to be 4min, then stopping spraying, starting a transverse pressure application system and a longitudinal pressure application system to rub the frozen membrane filaments at the same time, stopping rubbing for 5min, and performing the second round of spraying; spraying and pressing and kneading for 5 times; after the freeze separation is finished, the gate valve 402 is opened, the mixed material falls into the collection tank 500, and after the mixed material is heated to the room temperature, the mixed material is sieved by a 10-mesh sieve, so that the recovered PVDF is obtained.

FIG. 6 is a schematic diagram of the present example, in which FIG. 6 (A) is a schematic diagram of the original engineering waste filaments after being processed in step (1), FIG. 6 (B) is a PET support layer obtained after freeze separation, and FIG. 6 (C) is a PVDF powder obtained after freeze separation.

Comparative example

A commercially available PVDF (manufactured by Shanghai Sanai Fuji, model FR-905) was spun and tested in the same manner as in steps (3) and (4) of example 1.

Table 1 summary of test results of examples and comparative examples

While particular embodiments of the present invention have been illustrated and described, it will be appreciated that the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit it; those of ordinary skill in the art will understand that: modifications may be made to the above-described embodiments, or equivalents may be substituted for some or all of the features thereof without departing from the spirit and scope of the present invention; the modifications or the substitutions do not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present invention; it is therefore intended to cover in the appended claims all such alternatives and modifications that are within the scope of the invention.

Claims (10)

1. A method for recycling PVDF in membrane silk materials is characterized by comprising the following steps:

(1) Spraying liquid nitrogen to the pretreated membrane silk material;

(2) Performing a surface treatment to separate a low temperature surface layer;

(3) Repeating the step (1) and the step (2) at least 3 times in a circulating manner to obtain a mixture; sieving and separating the mixture to obtain recovered PVDF;

wherein, the membrane silk material includes PET braided tube and PVDF filter layer.

2. The method for recycling PVDF in membrane filament materials according to claim 1, wherein the pretreatment comprises at least one of the following features (a) to (d):

(a) Cutting the membrane silk material to a length of 5-10 cm;

(b) Spraying and/or soaking the membrane silk material with water;

(c) Rinsing the membrane silk material by using a sodium hypochlorite solution;

(d) Pickling the membrane wire material;

preferably, in the step (c), the concentration of the sodium hypochlorite solution is 5000ppm to 6000ppm, and the rinsing time is 1h to 10h;

preferably, in step (d), the acid used for acid washing includes at least one of hydrochloric acid, oxalic acid, nitric acid and sulfuric acid;

more preferably, in the step (d), the mass fraction of the acid is 3% to 5%, and the acid washing time is 1 to 10 hours.

3. The method for recycling PVDF in membrane silk material as claimed in claim 1, wherein in step (2), the surface treatment comprises at least one of kneading, shaking, grinding, polishing and ultrasound;

preferably, in step (3), step (1) and step (2) are repeated 3 to 5 times.

4. PVDF material obtained by the method for recovering PVDF from membrane filament materials as claimed in any one of claims 1 to 3.

5. A freeze separation apparatus adapted to the method for recovering PVDF from a membrane filament material according to any one of claims 1 to 3; the freezing and separating device comprises the following structural units which are connected in sequence:

the device comprises a liquid nitrogen storage unit, a freezing separation unit, a discharging unit and a collecting unit;

wherein the freeze separation unit comprises the following components:

cold source shower nozzle, vertical pressure subassembly, horizontal pressure subassembly, compressed sheet, interception net and shell body.

6. A freeze separator device according to claim 5, wherein two pressure receiving plates and two intercepting screens are provided in the freeze separator unit;

the plate surfaces of the two compression plates are parallel to each other, and each compression plate is connected with the two interception nets;

preferably, the plate surface of the pressure receiving plate is independently provided with a convex structure.

7. A freeze separation device according to claim 6 wherein the longitudinal pressure assembly is fixedly connected to the outer housing and the longitudinal pressure assembly is movably connected to the pressure receiving plate;

preferably, the number of the longitudinal pressure assemblies is at least 2, and each pressure receiving plate is movably connected with at least one longitudinal pressure assembly.

8. A freeze separation device according to claim 6 wherein the lateral pressure assembly comprises a lateral pressure main element, a bolster and a lateral pressure subelement connected in series;

the transverse pressure main element is connected with the outer shell, and the transverse pressure sub-element is movably connected with the pressure receiving plate;

preferably, the number of said transverse pressure summation elements is at least 2; the number of the transverse pressing sub-elements is at least 4, and each pressed plate is movably connected with at least two transverse pressing sub-elements.

9. The freeze separation device of claim 8, wherein the lateral pressure assembly is fixedly connected to the outer housing, and/or a slide rail is further disposed between the lateral pressure assembly and the outer housing;

preferably, when the transverse pressure assembly is started, the acting force between the transverse pressure assembly and the pressure receiving plate is 500N-1000N.

10. A spinning film-forming apparatus comprising the freeze separator according to any one of claims 5 to 9.

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