Recycling methods and systems for waste photovoltaic backsheets

Abstract

This invention relates to the field of waste photovoltaic backsheet recycling technology, specifically to a method and system for recycling waste photovoltaic backsheets. (1) The waste photovoltaic backsheet is contacted with solvent I for a first dissolution to obtain liquid phase component I and solid phase component I; (2) Liquid phase component I is finely filtered to obtain liquid phase component I' and filter residue; (3) Liquid phase component I' is contacted with solvent II for a first back-exchange to obtain liquid phase component II and solid phase component II; (4) Solid phase component I is contacted with solvent III for a second dissolution to obtain liquid phase component III and solid phase component III; (5) Liquid phase component III is contacted with solvent IV for a second back-exchange to obtain liquid phase component IV and solid phase component IV. The waste photovoltaic backsheet recycling method provided in this invention can not only significantly improve the separation efficiency and recovery rate of PVDF and PET, but also recover titanium dioxide, avoiding the waste of titanium dioxide.

Description

Technical Field

[0001] This invention relates to the field of waste photovoltaic backsheet recycling technology, specifically to a method and system for recycling waste photovoltaic backsheets. Background Technology

[0002] A photovoltaic backsheet is a photovoltaic encapsulation material located on the back of a solar cell module. In outdoor environments, it primarily protects the solar cell module, resisting the erosion of the encapsulation film and solar cells by environmental factors such as light, humidity, and heat, thus providing weather-resistant insulation protection. The extensive use, iteration, and replacement of solar cells generate a large amount of waste photovoltaic backsheets, which can have adverse environmental impacts. The main components of waste photovoltaic backsheets include PVDF (polyvinyl chloride), PET (polyethylene terephthalate), titanium dioxide, and polymer films. Recovering these components from waste photovoltaic backsheets is of great significance for achieving efficient recycling of photovoltaic backsheets.

[0003] Currently, several technical approaches have been developed for the recycling and reuse of waste photovoltaic backsheets. CN115945497A discloses a method for peeling off the backsheet of a photovoltaic module. CN103752190A discloses a method for recycling and reusing waste polyvinylidene fluoride (PVDF) flat sheet film, which achieves the dissolution and recycling of PVDF by immersing the PVDF flat sheet film in NMP at 40°C for 10 hours.

[0004] Although these methods can separate and recycle PVDF and PET from waste photovoltaic backsheets, the above-mentioned separation and recycling methods and systems generally suffer from low separation efficiency and long dissolution time. Moreover, they do not recycle titanium dioxide, resulting in resource waste. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of long recycling process, low separation efficiency, long dissolution time, high energy consumption, and inability to effectively separate titanium dioxide in the existing technology for waste photovoltaic backsheets, and to provide a recycling method and system for waste photovoltaic backsheets.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for recycling waste photovoltaic backsheets, wherein the method includes the following steps:

[0007] (1) The waste photovoltaic backsheet is contacted with solvent I to perform a first dissolution, resulting in liquid phase component I and solid phase component I; wherein, the waste photovoltaic backsheet includes PVDF, PET, TiO2 and a polymer film; the solvent I is selected from at least two of dimethyl sulfoxide, N-methylpyrrolidone and N-formylmorpholine; wherein, the liquid phase component I includes PVDF, solvent I and TiO2;

[0008] (2) The liquid phase component I is finely filtered to obtain liquid phase component I' and filter residue, wherein the filter residue is TiO2;

[0009] (3) The liquid phase component I' is contacted with solvent II to perform a first back-evolution to obtain liquid phase component II and solid phase component II; wherein, solvent II is selected from one or more of water, ethanol, and toluene; and solid phase component II is PVDF;

[0010] (4) The solid phase component I is contacted with solvent III to perform a second dissolution to obtain liquid phase component III and solid phase component III; wherein, solvent III is selected from one or more of trifluoroacetic acid, hexafluoroisopropanol, o-chlorophenol, and chloroform, and solid phase component III is a polymer membrane;

[0011] (5) Contact the liquid phase component III with solvent IV and perform a second back-diffusion to obtain liquid phase component IV and solid phase component IV; wherein, solvent IV is selected from one or more of water, ethanol and toluene, and solid phase component IV is PET.

[0012] A second aspect of the present invention provides a recycling system for waste photovoltaic backsheets, wherein the recycling system includes a PVDF dissolving device 1, a fine filtration device 2, a PVDF back-extraction device 3, a PET dissolving device 4, and a PET back-extraction device 5; wherein the PVDF dissolving device 1 is connected to the fine filtration device 2 and the PET dissolving device 5 respectively, the fine filtration device 2 is connected to the PVDF back-extraction device 3, and the PET dissolving device 4 is connected to the PET back-extraction device 5.

[0013] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0014] 1) The waste photovoltaic backsheet recycling method provided in this invention utilizes solvent I to selectively dissolve PVDF, solvent II to back-extract PVDF, solvent III to dissolve PET, and solvent IV to back-extract PET, which can significantly improve the separation efficiency and recovery rate of PVDF and PET.

[0015] 2) The recycling method for waste photovoltaic backsheets provided in this invention uses solvents I, II, III and IV, which are all green solvents with good environmental performance;

[0016] 3) The waste photovoltaic backsheet recycling method provided in this invention utilizes freeze drying to effectively recover solvent I and solvent II encapsulated in PVDF, resulting in PVDF purity ≥ 95%; and utilizes vacuum drying to effectively recover solvent III and solvent IV encapsulated in PET, resulting in PET purity ≥ 95%.

[0017] 4) The recycling method for waste photovoltaic backsheets provided in this invention can achieve efficient recycling of titanium dioxide and avoid waste of titanium dioxide;

[0018] 5) The recycling method for waste photovoltaic backsheets provided in this invention solves the problems of long separation process, high energy consumption, low separation efficiency and incomplete product recycling in the existing technology, and fills the technical gap of using organic solvents to efficiently recycle waste photovoltaic backsheets. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of a recycling system for waste photovoltaic backsheets provided in this invention.

[0020] Explanation of reference numerals in the attached figures

[0021] 1. PVDF dissolution device; 2. Fine filtration device; 3. PVDF reverse separation device.

[0022] 4. PET melting device; 5. PET backwashing device; 6. First solid-liquid separation device.

[0023] 7, Second solid-liquid separation device; 8, Third solid-liquid separation device; 9, Fourth solid-liquid separation device

[0024] 10. Calcination apparatus; 11. Freeze-drying apparatus; 12. Vacuum drying apparatus

[0025] 13. Distillation Column I 14. Distillation Column II Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] A first aspect of the present invention provides a method for recycling waste photovoltaic backsheets, wherein the method includes the following steps:

[0028] (1) The waste photovoltaic backsheet is contacted with solvent I to perform a first dissolution, resulting in liquid phase component I and solid phase component I; wherein, the waste photovoltaic backsheet includes PVDF, PET, TiO2 and a polymer film; the solvent I is selected from at least two of dimethyl sulfoxide, N-methylpyrrolidone and N-formylmorpholine; the liquid phase component I includes PVDF, solvent I and TiO2;

[0029] (2) The liquid phase component I is finely filtered to obtain liquid phase component I' and filter residue, wherein the filter residue is TiO2;

[0030] (3) The liquid phase component I' is contacted with solvent II to perform a first back-evolution to obtain liquid phase component II and solid phase component II; wherein, solvent II is selected from one or more of water, ethanol, and toluene; and solid phase component II is PVDF;

[0031] (4) The solid phase component I is contacted with solvent III to perform a second dissolution to obtain liquid phase component III and solid phase component III; wherein, solvent III is selected from one or more of trifluoroacetic acid, hexafluoroisopropanol, o-chlorophenol, and chloroform, and solid phase component III is a polymer membrane;

[0032] (5) Contact the liquid phase component III with solvent IV and perform a second back-diffusion to obtain liquid phase component IV and solid phase component IV; wherein, solvent IV is selected from one or more of water, ethanol and toluene, and solid phase component IV is PET.

[0033] In this invention, the inventors discovered through research that PVDF can be separated from waste photovoltaic backsheets by utilizing the selective solubility of solvent I, and PVDF dissolved in solvent I can be slowly precipitated by utilizing solvent II; PET can be separated from waste photovoltaic backsheets by utilizing the selective solubility of solvent III, and PET dissolved in solvent IV can be slowly precipitated by utilizing solvent IV; and TiO2 and polymer film can be separated from waste photovoltaic backsheets by utilizing the insolubility of TiO2 and polymer film and the difference in particle size between them.

[0034] In step (1):

[0035] In one embodiment of the present invention, based on the total mass of the waste photovoltaic backsheet, the waste photovoltaic backsheet contains 60-85 wt% PET, 5-15 wt% PVDF, 2-10 wt% TiO2, and 10-30 wt% polymer film.

[0036] In this invention, the main components of the waste photovoltaic backsheet are PVDF, PET and nano-level TiO2, in addition to some polymer films that act as adhesives.

[0037] In one embodiment of the present invention, the particle size of the waste photovoltaic backsheet is 0.5-3cm, preferably 0.8-2.5cm.

[0038] In this invention, the polymer film can be broken into small flakes along with the waste photovoltaic backsheet. Breaking the waste photovoltaic backsheet can accelerate the dissolution rate and control the particle size of the polymer film, so as to achieve the separation of TiO2 and polymer film through the particle size difference.

[0039] In one embodiment of the present invention, solvent I is dimethyl sulfoxide and N-methylpyrrolidone. The mass ratio of dimethyl sulfoxide to N-methylpyrrolidone is 1:0.01-1.5, preferably 1:0.6-1.2.

[0040] In this invention, solvent I selectively dissolves PVDF but not PET. Contacting waste photovoltaic backsheets with solvent I separates PVDF from the waste photovoltaic backsheets, yielding a liquid phase component I containing PVDF. The inventors of this invention have discovered that, compared to using dimethyl sulfoxide, N-methylpyrrolidone, and N-formylmorpholine individually, using a mixture of at least two of these compounds to dissolve waste photovoltaic backsheets significantly increases the dissolution rate and shortens the dissolution time.

[0041] In one embodiment of the present invention, the mass ratio of the waste photovoltaic backsheet to solvent I is 1:5-20, preferably 1:1:7-12.

[0042] In one embodiment of the present invention, the operating conditions for the first dissolution include: a first dissolution temperature of 70-120°C, preferably 85-95°C; a first dissolution pressure of 0.05-0.5 MPa, preferably 0.1-0.3 MPa; and a first dissolution time of 10-100 min, preferably 30-60 min.

[0043] In one embodiment of the present invention, after the first dissolution is completed, a first solid-liquid separation is performed to obtain liquid phase component I and solid phase component I; wherein, the liquid phase component I includes PVDF, solvent I and TiO2.

[0044] In this invention, the TiO2 in the waste photovoltaic backsheet is in the form of nanoparticles, and the polymer film is in the form of fine sheets. During the first solid-liquid separation, PVDF dissolves in solvent I, and most of solvent I and nano-sized TiO2 enter the liquid phase to form liquid phase component I. PET and the polymer film carry some solvent I into the solid phase to form solid phase component I.

[0045] In step (2):

[0046] In one embodiment of the present invention, the fine filtration is performed in a filter with a mesh size ≤100nm, preferably ≤50nm.

[0047] In this invention, through fine filtration, nano-sized TiO2 can be almost completely separated from liquid phase component I, thereby realizing the recovery of TiO2.

[0048] In one embodiment of the present invention, step (2) further includes: roasting the filter residue to obtain recovered TiO2.

[0049] In this invention, the filter residue obtained through fine filtration still retains some solvent I on its surface. Calcining this residue removes solvent I, yielding high-purity recovered TiO2. The calcination temperature can be 500-1000℃, and the calcination time can be 2-6 hours.

[0050] In step (3):

[0051] In one embodiment of the present invention, solvent II is water, preferably deionized water. In this invention, solvent II is added to liquid phase component I', and under the action of solvent II, PVDF can precipitate from liquid phase component I', thereby separating PVDF.

[0052] In one embodiment of the present invention, the mass ratio of liquid phase component I' to solvent II is 1:1-5, preferably 1:2-3.

[0053] In one embodiment of the present invention, the operating conditions of the first back-density reaction include: a first back-density reaction temperature of 50-90°C, preferably 60-80°C; a first back-density reaction pressure of 0.05-0.5 MPa, preferably 0.1-0.3 MPa; and a first back-density reaction time of 20-80 min, preferably 40-60 min.

[0054] In one embodiment of the present invention, after the first back-diffusion is completed, a second solid-liquid separation is performed to obtain liquid phase component II and wet solid phase component II'; wherein, the liquid phase component II includes solvent I and solvent II.

[0055] In one embodiment of the present invention, the wet solid phase component II' is freeze-dried to obtain solid phase component II and freeze-dried liquid.

[0056] In this invention, by freeze-drying, solvent I and solvent II coated on PVDF particles can be separated to obtain PVDF particles with a purity of ≥95%.

[0057] In one embodiment of the present invention, the freeze-drying operating conditions include: a freeze-drying temperature of -115°C to -90°C, preferably -105°C to -100°C; a freeze-drying pressure of 0.2-0.8 MPa, preferably 0.4-0.6 MPa; and a freeze-drying time of 12-14 h, preferably 24-36 h.

[0058] In one embodiment of the present invention, the liquid phase component II and / or the freeze-dried liquid are distilled to recover solvent I and solvent II. In this invention, the recovered solvent I can be returned to step (1), and the recovered solvent II can be returned to step (2) for reuse.

[0059] In step (4):

[0060] In one embodiment of the present invention, solvent III is trifluoroacetic acid and / or hexafluoroisopropanol, preferably trifluoroacetic acid and hexafluoroisopropanol; wherein the mass ratio of trifluoroacetic acid and hexafluoroisopropanol is 1:0.1-2, preferably 1:0.5-1.5.

[0061] In this invention, solvent III can dissolve PET in solid phase component I, thereby separating PET from solid phase component I to obtain liquid phase component III containing PET and solvent III, and solid phase component III containing a polymer membrane. Compared with a single solvent, solvent III, when using a mixed solvent, has a better dissolving effect on PET, which can further improve the PET recovery rate.

[0062] In one embodiment of the present invention, the mass ratio of solid component I to solvent III is 1:5-25, preferably 1:10-15.

[0063] In one embodiment of the present invention, the operating conditions for the second dissolution include: a second dissolution temperature of 25-120°C, preferably 30-55°C; a second dissolution pressure of 0.05-0.5 MPa, preferably 0.1-0.3 MPa; and a second dissolution time of 10-100 min, preferably 30-60 min.

[0064] In one embodiment of the present invention, after the second dissolution is completed, a third solid-liquid separation is performed to obtain liquid phase component III and solid phase component III.

[0065] In this invention, after the third solid-liquid separation, the separated solid component III contains a small amount of liquid, and the solid component III can be dried according to actual needs.

[0066] In step (5):

[0067] In one embodiment of the present invention, solvent IV is water, preferably deionized water. In this invention, solvent IV is added to liquid phase component III, and under the action of solvent IV, PET can precipitate from liquid phase component III, thereby separating PET particles.

[0068] In one embodiment of the present invention, the mass ratio of liquid phase component III to solvent IV is 1:1-5, preferably 1:2-3.

[0069] In one embodiment of the present invention, the operating conditions for the second back-density reaction include: a second back-density reaction temperature of 25-90°C, preferably 30-55°C; a second back-density reaction pressure of 0.05-0.5 MPa, preferably 0.1-0.3 MPa; and a second back-density reaction time of 20-80 min, preferably 40-60 min.

[0070] In one embodiment of the present invention, after the second back-diffusion is completed, a fourth solid-liquid separation is performed to obtain a liquid phase component IV and a wet solid phase component IV'. The liquid phase component IV comprises solvent III and solvent IV'.

[0071] In one embodiment of the present invention, the wet solid phase component IV' is subjected to vacuum drying to obtain solid phase component IV and vacuum-dried liquid.

[0072] In this invention, solvent III and solvent IV wrapped on wet PET particles can be separated by vacuum drying to obtain PET particles with a purity of ≥95%.

[0073] In one embodiment of the present invention, the liquid phase component IV and / or the vacuum-dried liquid are distilled to recover solvent III and solvent IV. In this invention, the recovered solvent III can be returned to step (3), and the recovered solvent IV can be returned to step (4) for reuse.

[0074] A second aspect of the present invention provides a recycling system for waste photovoltaic backsheets, wherein the recycling system includes a PVDF dissolving device 1, a fine filtration device 2, a PVDF back-extraction device 3, a PET dissolving device 4, and a PET back-extraction device 5; wherein the PVDF dissolving device 1 is connected to the fine filtration device 2 and the PET dissolving device 4 respectively, the fine filtration device 2 is connected to the PVDF back-extraction device 3, and the PET dissolving device 4 is connected to the PET back-extraction device 5.

[0075] In a preferred embodiment of the present invention, the recycling system further includes a first solid-liquid separation device 6, a second solid-liquid separation device 7, a third solid-liquid separation device 8, and a fourth solid-liquid separation device 9; wherein, the first solid-liquid separation device 6 is connected to the PVDF dissolving device 1, the fine filtration device 2, and the PET dissolving device 4 respectively; the second solid-liquid separation device 7 is connected to the PVDF back-extraction device 3; the third solid-liquid separation device 8 is connected to the PET dissolving device 4 and the PET back-extraction device 5; and the fourth solid-liquid separation device 9 is connected to the PET back-extraction device 5.

[0076] In a preferred embodiment of the present invention, the recycling system further includes a roasting device 10, wherein the roasting device 10 is connected to the fine filtration device 3.

[0077] In a preferred embodiment of the present invention, the recovery system further includes a freeze-drying device 11, a vacuum drying device 12, a distillation column I13, and a distillation column II14; wherein, the freeze-drying device 11 is connected to the second solid-liquid separation device 7 and the distillation column I13 respectively, and the distillation column I13 is also connected to the PVDF dissolving device 1 and the PVDF back-extraction device 3 respectively; the vacuum drying device 12 is connected to the fourth solid-liquid separation device 9 and the distillation column II14, and the distillation column II14 is also connected to the PET dissolving device 4 and the PET back-extraction device 5 respectively.

[0078] In this invention, waste photovoltaic backsheets and solvent I are brought into contact in a PVDF dissolving device for a first dissolution. Solvent I selectively dissolves the PVDF in the waste photovoltaic backsheets. The solution is then transported to a first solid-liquid separation device for a first solid-liquid separation to obtain a liquid phase component I containing PVDF, solvent I, and TiO2, and a solid phase component I containing PET, a small amount of solvent I, and an insoluble polymer membrane.

[0079] The obtained liquid phase component I is fed into a fine filtration device for fine filtration, which yields a filter residue containing TiO2 and a liquid phase component I' containing PVDF and solvent I. The obtained filter residue is then fed into a calcination device for calcination, which yields recovered TiO2.

[0080] The obtained liquid phase component I' is fed into a PVDF back-drying unit. Liquid phase component I' and solvent II are contacted in the PVDF back-drying unit for the first back-drying. PVDF is precipitated from liquid phase component I under the action of solvent II. Then, it is fed into a second solid-liquid separation unit for the second solid-liquid separation to obtain liquid phase component II and wet solid phase component II'. The obtained wet solid phase component II' is fed into a freeze-drying unit for freeze-drying to obtain solid phase component II and freeze-dried liquid.

[0081] The obtained liquid phase component II and the freeze-dried liquid are fed to distillation column I for distillation to recover solvent I and solvent II. The recovered solvent I is condensed by condenser I and returned to the PVDF dissolution unit for recycling, and the recovered solvent II is condensed by condenser I and returned to the PVDF back-diffusion unit for recycling.

[0082] The obtained solid phase component I is contacted with solvent III in a PET dissolving device for a second dissolution, in which the PET in solid phase component I is dissolved in solvent III. Then it is transported to a third solid-liquid separation device for a third solid-liquid separation to obtain liquid phase component III and solid phase component III.

[0083] The obtained liquid phase component III and solvent IV are contacted in a PVDF back-diffusion apparatus for a second back-diffusion. Under the action of solvent IV, PET is precipitated from liquid phase component III. Then it is transported to a fourth solid-liquid separation apparatus for a fourth solid-liquid separation to obtain liquid phase component IV and wet solid phase component IV'.

[0084] The obtained wet solid phase component IV' is sent to a vacuum drying device for vacuum drying to obtain solid phase component IV and vacuum dried liquid; the obtained liquid phase component IV and vacuum dried liquid are sent to distillation column II for distillation to recover solvent III and solvent IV; the recovered solvent III is condensed by condenser II and returned to the PET dissolving unit for recycling, and the recovered solvent IV is condensed by condenser II and returned to the PET back-extraction unit for recycling.

[0085] In a preferred embodiment of the present invention, the system further includes a pretreatment unit, wherein the pretreatment unit includes a cleaning device, a drying device, and a crushing device.

[0086] In a preferred embodiment of the present invention, the present invention does not impose special limitations on the PVDF dissolving device, fine filtration device, PVDF back-drying device, PET dissolving device and PET back-drying device, first solid-liquid separation device, second solid-liquid separation device, third solid-liquid separation device, fourth solid-liquid separation device, calcination device, freeze-drying device, vacuum drying device, distillation column I, distillation column II, cleaning device, drying device and crushing device, and can be specifically selected according to actual needs.

[0087] A key feature of this invention is that the first, second, third, and fourth solid-liquid separation devices can be the same intermittently used device or multiple different devices. Similarly, distillation column I and distillation column II can be the same intermittently used device or multiple different devices.

[0088] The present invention will be described in detail below through examples. Waste photovoltaic backsheets are cleaned, dried, and crushed to a particle size of 1-2 cm. Elemental analysis and subtraction methods determine that the waste photovoltaic backsheets contain 80 wt% PET, 5 wt% PVDF, 2 wt% TiO2, and 13 wt% polymer film.

[0089] The PVDF dissolving device and the PET dissolving device are countercurrent leaching devices with stirring and heating functions. The PVDF back-extraction device and the PET back-extraction device are stirrers with heating functions. The first solid-liquid separation device, the second solid-liquid separation device, the third solid-liquid separation device and the fourth solid-liquid separation device are the same, all of which are filters with a screen pore size of less than 1 mm. The fine filtration device is a filter with a screen pore size of less than 50 nm.

[0090] Example 1

[0091] (1) 500g of waste photovoltaic backsheets are contacted with 5000g of solvent I (a mixture of dimethyl sulfoxide and N-methylpyrrolidone in a mass ratio of 1:1) in a PVDF dissolution device. The first dissolution is carried out at 90℃ and 0.1MPa. After stirring for 50min, the mixture is transferred to a first solid-liquid separation device for the first solid-liquid separation to obtain liquid phase component I and solid phase component I.

[0092] (2) The obtained liquid phase component I is fed into a fine filtration device for fine filtration to obtain filter residue and liquid phase component I'; the obtained filter residue is calcined at 800℃ for 4h to obtain recovered TiO2; wherein, the mass of recovered TiO2 is 9.9g and the purity is 99.7%;

[0093] (3) The obtained liquid phase component I' is contacted with deionized water in a PVDF back-diffusion device and subjected to the first back-diffusion at 70°C and 0.1 MPa. After 50 min, it is transferred to the second solid-liquid separation device for the second solid-liquid separation to obtain liquid phase component II and wet solid phase component II'; wherein, the mass ratio of liquid phase component I' to deionized water is 1:3.

[0094] The obtained wet solid component II' was fed into a freeze dryer and dried at -104℃ and 0.5MPa for 24h to obtain solid component II and freeze-dried liquid; wherein, solid component II is white PVDF particles with a mass of 24.8g and a purity of 99.6%;

[0095] The obtained liquid phase component II and the freeze-dried liquid are fed into continuous distillation column I for distillation to recover dimethyl sulfoxide, N-methylpyrrolidone and water; the recovered dimethyl sulfoxide and N-methylpyrrolidone are condensed by a condenser and returned to step (1) for recycling, and the recovered water is condensed by a condenser and returned to step (2) for recycling.

[0096] (4) The obtained solid phase component I and solvent III (a mixture of trifluoroacetic acid and hexafluoroisopropanol in a mass ratio of 1:1) are contacted in a PET dissolving device and a second dissolution is carried out at 40°C and 0.1 MPa. After stirring for 50 min, the mixture is transferred to a third solid-liquid separator for a third solid-liquid separation to obtain liquid phase component III and solid phase component III. The mass ratio of solid phase component I to solvent III is 1:10, and solid phase component III is a white polymer membrane with a mass of 65.7 g.

[0097] (5) The obtained liquid phase component III was contacted with deionized water in a PET back-diffusion apparatus and subjected to a second back-diffusion at 40°C and 0.1 MPa. After 50 min, it was transferred to a fourth solid-liquid separation apparatus for a fourth solid-liquid separation to obtain liquid phase component IV and wet solid phase component IV'. The mass ratio of liquid phase component III to deionized water was 1:3.

[0098] The obtained wet solid phase component IV' was transferred to a vacuum drying oven and vacuum dried at 80°C and 200 mbar for 24 h to obtain solid phase component IV and vacuum dried liquid; solid phase component IV was white PET granules with a mass of 398.5 g and a purity of 99.5%;

[0099] The obtained liquid phase component IV and the vacuum dried liquid are fed into continuous distillation column II for distillation to recover trifluoroacetic acid, hexafluoroisopropanol and water. The recovered trifluoroacetic acid and hexafluoroisopropanol are condensed by a condenser and returned to step (3) for recycling, and the recovered water is condensed by a condenser and returned to step (4) for recycling.

[0100] Example 2

[0101] Same as in Example 1, except that: in step (1), solvent I is a mixed liquid of dimethyl sulfoxide and N-formylmorpholine, with a mass ratio of dimethyl sulfoxide to N-formylmorpholine of 1:0.2; the first dissolution is carried out at 95°C and 0.1 MPa, and after stirring for 80 min, it is transported to the first solid-liquid separation device for the first solid-liquid separation.

[0102] The separated recovered TiO2 weighed 9.7g with a purity of 99.3%; the separated PVDF was white granules weighing 24.2g with a purity of 98.9%; the separated polymer membrane was white with a mass of 66.6g; and the separated PET was white granules weighing 397.9g with a purity of 99.3%.

[0103] Example 3

[0104] Similar to Example 1, except that in step (3), the mixture of trifluoroacetic acid and hexafluoroisopropanol is replaced with an equal amount of trifluoroacetic acid.

[0105] The separated recovered TiO2 weighed 9.9g with a purity of 99.5%; the separated PVDF was white granules weighing 24.5g with a purity of 99.6%; the separated polymer membrane was white with a mass of 83.8g; and the separated PET was white granules weighing 383.5g with a purity of 99.4%.

[0106] Comparing Examples 1 and 3, it is evident that the mixture of trifluoroacetic acid and hexafluoroisopropanol exhibits better solubility for PET than trifluoroacetic acid alone. When trifluoroacetic acid was used alone to dissolve solid component I, under the same operating conditions, some PET was not fully dissolved. In the third solid-liquid separation, the undissolved PET entered solid component III along with the polymer membrane, resulting in a slightly higher polymer membrane yield and a slightly lower PET yield.

[0107] Comparative Example 1

[0108] Similar to Example 1, except that in step (1), the mixture of dimethyl sulfoxide and N-methylpyrrolidone is replaced with an equal amount of N-methylpyrrolidone, and the mixture is dissolved at 90°C and 0.1 MPa. After stirring for 3 hours, the mixture is transported to the first solid-liquid separation device for the first solid-liquid separation to obtain liquid phase component I and solid phase component I.

[0109] The separated recovered TiO2 weighed 9.9g with a purity of 99.6%; the separated PVDF was white granules weighing 21.2g with a purity of 99.6%; the separated polymer membrane was white with a mass of 66.1g; and the separated PET was white granules weighing 397.5g with a purity of 99.5%.

[0110] By comparing Example 1 and Comparative Example 1, it can be seen that, under the same conditions, the PVDF recovery rate when using N-methylpyrrolidone alone as solvent I is slightly lower than that when using a mixture of dimethyl sulfoxide and N-methylpyrrolidone as solvent I, the recovery effects of the two are basically equivalent. However, the dissolution time required in Comparative Example 1 is significantly longer, more than three times that in Example 1. Therefore, the combined use of dimethyl sulfoxide and N-methylpyrrolidone can not only significantly improve the dissolution rate of PVDF and shorten the dissolution time, but also improve the dissolution effect of PVDF and increase the PVDF recovery rate.

[0111] Comparative Example 2

[0112] Similar to Example 1, except that in step (2), the obtained wet solid phase component II' is transported to a vacuum drying oven and vacuum dried at 100°C and 200 mbar for 24 hours to obtain solid phase component II and vacuum dried liquid; the obtained liquid phase component II and the vacuum dried liquid obtained in step (2) are sent to a continuous distillation column for distillation.

[0113] The separated recovered TiO2 weighed 9.9g with a purity of 99.6%; the separated PVDF was pink porous particles weighing 26.9g with a purity of 92.4%; the separated polymer membrane was white with a mass of 66.3g; and the separated PET was white particles weighing 397.3g with a purity of 99.5%.

[0114] In Comparative Example 3, the recovered PVDF mass was too large, indicating that vacuum drying is not effective in removing the highly viscous and high-boiling-point dimethyl sulfoxide (DMSO) and N-methylpyrrolidone (N-MPP) particles encapsulated within the PVDF particles. The recovered PVDF was pink, indicating that decomposition had occurred. This is because DMSO and N-MPP have high boiling points, requiring a longer vacuum drying time to achieve better results. Furthermore, DMSO and N-MPP are acidic; during prolonged vacuum drying, they slowly react with the PVDF, causing discoloration.

[0115] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recycling waste photovoltaic backsheets, characterized in that, The method includes the following steps: (1) The waste photovoltaic backsheet is brought into contact with solvent I for a first dissolution to obtain liquid phase component I and solid phase component I; wherein, the waste photovoltaic backsheet includes PVDF, PET, TiO2 and polymer film; the solvent I is selected from at least two of dimethyl sulfoxide, N-methylpyrrolidone and N-formylmorpholine; wherein, the liquid phase component I includes PVDF, solvent I and TiO2; (2) The liquid phase component I is finely filtered to obtain liquid phase component I' and filter residue, wherein the filter residue is TiO2; (3) The liquid phase component I' is contacted with solvent II to perform a first back-exchange to obtain liquid phase component II and solid phase component II; wherein, solvent II is selected from one or more of water, ethanol, and toluene; and solid phase component II is PVDF; (4) The solid phase component I is contacted with solvent III to perform a second dissolution, thereby obtaining liquid phase component III and solid phase component III; wherein, solvent III is selected from one or more of trifluoroacetic acid, hexafluoroisopropanol, o-chlorophenol, and chloroform; and solid phase component III is a polymer membrane; (5) Contact the liquid phase component III with solvent IV and perform a second back-diffusion to obtain liquid phase component IV and solid phase component IV; wherein, solvent IV is selected from one or more of water, ethanol and toluene, and solid phase component IV is PET.

2. The recycling method according to claim 1, wherein, Based on the total mass of the waste photovoltaic backsheet, the waste photovoltaic backsheet contains 60-85 wt% PET, 5-15 wt% PVDF, 2-10 wt% TiO2, and 10-30 wt% polymer film.

3. The recycling method according to claim 1, wherein, Solvent I is dimethyl sulfoxide and N-methylpyrrolidone.

4. The recycling method according to claim 3, wherein, The mass ratio of dimethyl sulfoxide to N-methylpyrrolidone is 1:0.01-1.

5.

5. The recycling method according to claim 4, wherein, The mass ratio of dimethyl sulfoxide to N-methylpyrrolidone is 1:0.6-1.

2.

6. The recycling method according to claim 1, wherein, The mass ratio of the waste photovoltaic backsheet to solvent I is 1:5-20.

7. The recycling method according to claim 6, wherein, The mass ratio of the waste photovoltaic backsheet to solvent I is 1:7-12.

8. The recycling method according to claim 1, wherein, The first dissolution operating conditions include: a first dissolution temperature of 70-120℃, a first dissolution pressure of 0.05-0.5MPa, and a first dissolution time of 10-100min.

9. The recycling method according to claim 8, wherein, The first dissolution operating conditions include: a first dissolution temperature of 85-95℃, a first dissolution pressure of 0.1-0.3MPa, and a first dissolution time of 30-60min.

10. The recycling method according to claim 1, wherein, After the first dissolution is completed, a first solid-liquid separation is performed to obtain liquid phase component I and solid phase component I.

11. The recycling method according to any one of claims 1-10, wherein, The fine filtration is performed in a filter with a mesh size of ≤100nm.

12. The recycling method according to claim 11, wherein, The fine filtration is performed in a filter with a mesh size of ≤50nm.

13. The recycling method according to any one of claims 1-10, wherein, Step (2) further includes: roasting the filter residue to obtain recovered TiO2.

14. The recycling method according to any one of claims 1-10, wherein, Solvent II is water.

15. The recycling method according to any one of claims 1-10, wherein, The mass ratio of liquid phase component I' to solvent II is 1:1-5.

16. The recycling method according to claim 15, wherein, The mass ratio of liquid phase component I' to solvent II is 1:2-3.

17. The recycling method according to any one of claims 1-10, wherein, The operating conditions for the first back-density reaction include: a first back-density reaction temperature of 50-90℃, a first back-density reaction pressure of 0.05-0.5MPa, and a first back-density reaction time of 20-80min.

18. The recycling method according to claim 17, wherein, The operating conditions for the first back-density reaction include: a first back-density reaction temperature of 60-80℃, a first back-density reaction pressure of 0.1-0.3MPa, and a first back-density reaction time of 40-60min.

19. The recycling method according to any one of claims 1-10, wherein, After the first back-diffusion is completed, a second solid-liquid separation is performed to obtain liquid phase component II and wet solid phase component II'; wherein, the liquid phase component II includes solvent I and solvent II; The wet solid phase component II' was freeze-dried to obtain solid phase component II and freeze-dried liquid; The liquid phase component II and / or the freeze-dried liquid are subjected to distillation to recover solvent I and solvent II.

20. The recycling method according to claim 19, wherein, The freeze-drying operating conditions include: a freeze-drying temperature of -115℃ to -90℃, a freeze-drying pressure of 0.2-0.8MPa, and a freeze-drying time of 12-14h.

21. The recycling method according to claim 20, wherein, The freeze-drying operating conditions include: a freeze-drying temperature of -105℃ to -100℃, a freeze-drying pressure of 0.4-0.6MPa, and a freeze-drying time of 24-36h.

22. The recycling method according to any one of claims 1-10, wherein, Solvent III is trifluoroacetic acid and / or hexafluoroisopropanol.

23. The recycling method according to claim 22, wherein, Solvent III is trifluoroacetic acid and hexafluoroisopropanol.

24. The recycling method according to claim 23, wherein, The mass ratio of trifluoroacetic acid to hexafluoroisopropanol is 1:0.1-2.

25. The recycling method according to claim 24, wherein, The mass ratio of trifluoroacetic acid to hexafluoroisopropanol is 1:0.5-1.

5.

26. The recycling method according to any one of claims 1-10, wherein, The mass ratio of solid component I to solvent III is 1:5-25.

27. The recycling method according to claim 26, wherein, The mass ratio of solid component I to solvent III is 1:10-15.

28. The recycling method according to any one of claims 1-10, wherein, The operating conditions for the second dissolution include: a second dissolution temperature of 25-120℃, a second dissolution pressure of 0.05-0.5MPa, and a second dissolution time of 10-100min.

29. The recycling method according to claim 28, wherein, The operating conditions for the second dissolution include: a second dissolution temperature of 30-55℃, a second dissolution pressure of 0.1-0.3MPa, and a second dissolution time of 30-60min.

30. The recycling method according to any one of claims 1-10, wherein, After the second dissolution is completed, a third solid-liquid separation is performed to obtain liquid phase component III and solid phase component III.

31. The recycling method according to any one of claims 1-10, wherein, Solvent IV is water.

32. The recycling method according to any one of claims 1-10, wherein, The mass ratio of liquid phase component III to solvent IV is 1:1-5.

33. The recycling method according to claim 32, wherein, The mass ratio of liquid phase component III to solvent IV is 1:2-3.

34. The recycling method according to any one of claims 1-10, wherein, The operating conditions for the second back-density reaction include: a second back-density reaction temperature of 25-90℃, a second back-density reaction pressure of 0.05-0.5MPa, and a second back-density reaction time of 20-80min.

35. The recycling method according to claim 34, wherein, The operating conditions for the second back-density reaction include: a second back-density reaction temperature of 30-55℃, a second back-density reaction pressure of 0.1-0.3MPa, and a second back-density reaction time of 40-60min.

36. The recycling method according to any one of claims 1-10, wherein, After the second back-diffusion is completed, a fourth solid-liquid separation is performed to obtain liquid phase component IV and wet solid phase component IV'. The wet solid phase component IV' was subjected to vacuum drying to obtain solid phase component IV and vacuum-dried liquid; The liquid phase component IV and / or the vacuum-dried liquid are distilled to recover solvent III and solvent IV.

37. A recycling system applicable to the recycling method of any one of claims 1-36 for waste photovoltaic backsheets, characterized in that, The recycling system includes a PVDF dissolving device (1), a fine filtration device (2), a PVDF back-extraction device (3), a PET dissolving device (4), and a PET back-extraction device (5). The PVDF dissolving device (1) is connected to the fine filtration device (2) and the PET dissolving device (4) respectively. The fine filtration device (2) is connected to the PVDF back-extraction device (3), and the PET dissolving device (4) is connected to the PET back-extraction device (5).

38. The recycling system according to claim 37, wherein, The system also includes a first solid-liquid separation device (6), a second solid-liquid separation device (7), a third solid-liquid separation device (8), and a fourth solid-liquid separation device (9). The first solid-liquid separation device (6) is connected to the PVDF dissolving device (1), the fine filtration device (2) and the PET dissolving device (4) respectively; the second solid-liquid separation device (7) is connected to the PVDF back-extraction device (3); the third solid-liquid separation device (8) is connected to the PET dissolving device (4) and the PET back-extraction device (5); and the fourth solid-liquid separation device (9) is connected to the PET back-extraction device (5).

39. The recycling system according to claim 37, wherein, The system also includes a roasting device (10), wherein the roasting device (10) is connected to the fine filtration device (2).

40. The recycling system according to claim 38, wherein, The recovery system also includes a freeze-drying device (11), a vacuum drying device (12), a distillation column I (13), and a distillation column II (14); wherein the freeze-drying device (11) is connected to the second solid-liquid separation device (7) and the distillation column I (13) respectively, and the distillation column I (13) is also connected to the PVDF dissolution device (1) and the PVDF back-extraction device (3) respectively; the vacuum drying device (12) is connected to the fourth solid-liquid separation device (9) and the distillation column II (14), and the distillation column II (14) is also connected to the PET dissolution device (4) and the PET back-extraction device (5) respectively.

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