Recycling method of solar back plate

Abstract

The invention relates to the technical field of recycling and reusing of solar back plates of photovoltaic modules, and discloses a recycling method of a solar back plate. The recovery method of the solar back panel is characterized by comprising the following steps: (1) in the presence of a protective gas and a catalyst, carrying out alcoholysis reaction on the solar back panel and alcohol to obtain a depolymerized mixed solution; and (2) carrying out purification treatment on the depolymerized mixed solution obtained in the step (1) to obtain bis (2-hydroxyethyl) terephthalate (BHET), polyvinylidene fluoride and polyolefin. According to the method, the PET middle layer in the solar panel can be completely depolymerized into the BHET monomer, the yield is greater than or equal to 78%, and the purity is greater than or equal to 98%; pVDF and PP (or PE) products can be respectively obtained after the PVDF and PP (or PE) materials which do not participate in depolymerization are separated and purified; the whole chemical recovery process is simple in operation method and high in efficiency, and has good economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and reuse of photovoltaic module solar backsheets, and particularly to a method for recycling solar backsheets. Background Art

[0002] Due to the renewable and pollution-free characteristics of solar energy, the photovoltaic industry has developed rapidly. A solar cell is a photoelectric semiconductor device that converts solar energy into electrical energy. The backsheet film is an important material for encapsulating the back of the solar cell and plays a role in supporting and protecting other components. As a photovoltaic encapsulation material, the backsheet film is directly in contact with the external environment and needs to have good electrical insulation, heat and humidity resistance, corrosion resistance, water resistance, aging resistance and other properties. Generally, solar backsheets are mostly three-layer composite structures. The outermost film is directly in contact with the outside world to protect the intermediate layer from external environmental erosion. Generally, a polymer film with chemical inertness and low surface energy is used, such as a fluorine-containing polymer material, and commonly used ones are polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF); the intermediate layer plays a role in support, water resistance and electrical insulation, and a material with excellent mechanical strength, insulation, water resistance, dimensional stability, tear resistance and easy processing is used, such as polyethylene terephthalate (PET); the lamination adhesive layer generally uses films with strong adhesiveness such as EVA and PE (as Figure 1 shown). At present, the recycling of solar backsheets mainly adopts physical recycling methods such as landfilling or incineration, which not only causes environmental pollution but also wastes resources to a certain extent.

[0003] Due to the chemical corrosion resistance and low surface energy of fluorine-containing solar backsheet materials, it is difficult to recycle and reuse backsheet materials by traditional waste plastic recycling technologies. CN114248369A puts the solar backsheet into a mixed solution containing water, alkali, penetrant and organic solvent and stirs it to separate the outer layer, intermediate layer and lamination adhesive layer of the solar backsheet material and recycle them separately, but this method uses a physical method to separate the layers of the solar backsheet film and will cause a decline in the performance of the material itself. Therefore, it is necessary to develop a method that can effectively recycle solar backsheets. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem in the prior art that it is difficult to recycle and reuse fluorine-containing solar backsheet materials with chemical corrosion resistance and low surface energy by traditional waste plastic recycling technologies, and to provide a method for recycling solar backsheets.

[0005] To achieve the above purpose, the first aspect of the present invention provides a method for recycling solar backsheets, which is characterized in that the method includes:

[0006] (1) In the presence of a protective gas and a catalyst, carry out an alcoholysis reaction on the solar backsheet with an alcohol to obtain a depolymerization mixed solution;

[0007] (2) Purify the depolymerized mixture solution described in step (1) to obtain bis(2-hydroxyethyl) terephthalate, polyvinylidene fluoride, and polyolefin respectively.

[0008] Through the above technical solution, the present invention can obtain at least the following beneficial effects:

[0009] 1) The present invention chemically recycles the solar backsheet material, and can completely depolymerize the PET intermediate layer into bis(2-hydroxyethyl) terephthalate (BHET) monomers. For the PVDF and PP (or PE) materials that do not participate in the depolymerization, after separation and purification, PVDF and PP (or PE) products can be obtained respectively;

[0010] 2) After the PET depolymerization solution is purified, bis(2-hydroxyethyl) terephthalate (BHET) with a yield ≥ 78% and a purity ≥ 98% can be obtained. BHET can be directly polymerized into PET or other high-value-added polyester products to realize the chemical recycling and reuse of PET;

[0011] 3) The operation method of the chemical recycling process is simple and efficient. The PP (or PE) and PVDF products that do not participate in the depolymerization can be recycled respectively, with good economic benefits. Description of the Drawings

[0012] Figure 1 is a schematic diagram of the solar backsheet structure;

[0013] Figure 2 is the infrared spectrum of BHET prepared and purified in Example 1;

[0014] Figure 3 is the 1 HNMR spectrum of BHET prepared and purified in Example 1;

[0015] Figure 4 is the ultra-high performance liquid chromatography spectrum (UPLC) of BHET prepared and purified in Example 1;

[0016] Figure 5 is the infrared spectrum of PVDF separated and purified in Example 1;

[0017] Figure 6 is the DSC curve of r-PET prepared in Example 10;

[0018] Figure 7 is the TGA curve of r-PET prepared in Example 10;

[0019] Figure 8 is the UPLC spectrum of BHET prepared and purified in Example 11;

[0020] Figure 9 It is the infrared spectrum of PP prepared and purified in Example 11. Detailed implementation manners

[0021] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0022] As described above, the first aspect of the present invention provides a method for recycling a solar backsheet, characterized in that the method includes:

[0023] (1) In the presence of a protective gas and a catalyst, subject the solar backsheet to alcoholysis reaction with an alcohol to obtain a depolymerization mixture;

[0024] (2) Purify the depolymerization mixture obtained in step (1) to obtain bis(2-hydroxyethyl) terephthalate, polyvinylidene fluoride, and polyolefin.

[0025] In the present invention, the solar backsheet generally contains 78-80% by weight of ethylene glycol terephthalate (PET), 8-10% by weight of polyvinylidene fluoride, and 10-14% by weight of polyolefin.

[0026] In some embodiments of the present invention, preferably, in step (1), the catalyst is selected from titanium-containing compounds and / or titanium-containing compositions, preferably at least one of alkyl titanates, titanium glycolates, titanium phosphates, and organic-inorganic hybrid titaniums, more preferably at least one of tetraethyl titanate, tetrabutyl titanate, tetraisopropyl titanate, tetraisobutyl titanate, titanium glycolate, titanium phosphate, titanium-silicon composite catalyst, and titanium-rare earth composite catalyst.

[0027] In some embodiments of the present invention, preferably, the alcohol is ethylene glycol.

[0028] In some embodiments of the present invention, preferably, in step (1), the dosage of the catalyst is 0.05-0.5 wt% of the solar backsheet, preferably 0.08-0.2 wt%. This catalyst dosage range can achieve the effect that the PET layer in the solar backsheet has a depolymerization rate > 99%.

[0029] In some embodiments of the present invention, preferably, the titanium-silicon composite catalyst is prepared by compounding an organic titanium compound and an orthosilicate compound; more preferably, the organic titanium compound is selected from at least one of tetrabutyl titanate, isopropyl titanate, tetraethyl titanate, titanium glycolate, titanium acetylacetonate, and diisopropyl bis(acetylacetonato)titanate, and the orthosilicate compound is selected from at least one of tetrabutyl orthosilicate, tetraethyl orthosilicate, and tetramethyl orthosilicate.

[0030] In some embodiments of the present invention, preferably, the molar ratio of the organic titanium compound to the orthosilicate compound is 95:5 - 70:30. According to a preferred embodiment of the present invention, the titanium-silicon composite catalyst of the present invention and its components and mass ratio correspond to and are the same as those defined in Patent Application No. 202310836415.1, which is hereby incorporated herein in its entirety by reference.

[0031] In some embodiments of the present invention, preferably, the titanium-rare earth composite catalyst comprises a titanium compound and a rare earth compound; more preferably, the titanium compound is selected from at least one of tetraethyl titanate, tetrabutyl titanate, isopropyl titanate, tetraisobutyl titanate, titanium acetylacetonate, diisopropyl bis(acetylacetonato)titanate, titanium glycolate, and titanium phosphate, and the rare earth compound is selected from at least one of yttrium acetylacetonate, neodymium acetylacetonate, dysprosium acetylacetonate, terbium acetylacetonate, and lanthanum acetylacetonate.

[0032] In some embodiments of the present invention, preferably, the mass ratio of the titanium compound to the rare earth compound is 0.1 - 20:1, more preferably 0.5 - 10:1. According to a preferred embodiment of the present invention, the titanium-rare earth composite catalyst of the present invention and its components and mass ratio correspond to and are the same as those defined in Patent Application No. 202310841232.9, which is hereby incorporated herein in its entirety by reference.

[0033] Using the above-preferred titanium-rare earth composite catalyst and titanium-silicon composite catalyst can further improve the yield and purity of the depolymerization product BHET.

[0034] In some embodiments of the present invention, preferably, the mass ratio of the alcohol to the solar backsheet is 2 - 8:1, preferably 3 - 5:1. This mass ratio range can achieve the effect that the PET layer in the solar backsheet has a depolymerization rate > 99%.

[0035] In some embodiments of the present invention, preferably, the temperature of the alcoholysis reaction is 190 - 250 °C; the pressure is 0.2 - 0.6 MPa; the time is 1 - 10 h, preferably 2 - 5 h. This temperature range can achieve the effect that the PET layer in the solar backplane has a depolymerization rate > 99%. This time range can achieve the effect that the PET layer in the solar backplane has a depolymerization rate > 99%. At the same time, the polyolefin layer and the PVDF layer can be completely separated from the PET layer. When the temperature and time are controlled within the above preferred ranges, the depolymerization is more complete and the energy consumption is lower.

[0036] In some embodiments of the present invention, preferably, in step (2), the purification process is successively the first purification treatment, the second purification treatment, the third purification treatment, the fourth purification treatment, and the fifth purification treatment.

[0037] In some embodiments of the present invention, preferably, the purification method includes at least one of solid-liquid separation, dilution, cooling, precipitation, and drying.

[0038] In some embodiments of the present invention, preferably, in step (2), the depolymerization mixture is successively subjected to the first purification treatment, the first dilution treatment, and the second purification treatment to obtain bis(2-hydroxyethyl) terephthalate.

[0039] In some embodiments of the present invention, preferably, the polyolefin is polypropylene (PP) and / or polyethylene (PE).

[0040] In some embodiments of the present invention, preferably, the diluent A for the first dilution treatment is deionized water.

[0041] In some embodiments of the present invention, preferably, the mass ratio of the depolymerization solution to the deionized water is 1:1 - 10, more preferably 1:2 - 5. This mass ratio range can enable the depolymerization product bis(2-hydroxyethyl) terephthalate (BHET) of the PET layer to be fully dissolved in deionized water, while the solubility of the oligomer is very low, thereby achieving the effect that BHET has higher purity and higher yield.

[0042] In some embodiments of the present invention, preferably, the process of the first purification treatment includes solid-liquid separation to obtain a depolymerization solution.

[0043] In some embodiments of the present invention, preferably, the process of the first dilution treatment includes adding deionized water to the depolymerization solution and stirring.

[0044] In some embodiments of the present invention, preferably, the temperature of the solid-liquid separation is 90 - 130 °C.

[0045] In some embodiments of the present invention, preferably, the temperature of the stirring is 60 - 100 °C, more preferably 70 - 90 °C; the time is 0.5 - 3 h, more preferably 1 - 2 h. This temperature range can make the depolymerization product of the PET layer, bis(2-hydroxyethyl) terephthalate (BHET), completely dissolve in deionized water, while the oligomers hardly dissolve, so as to achieve the effect that the final product BHET has higher purity and higher yield. This time range can allow sufficient time for all of the BHET to dissolve into the deionized water, achieving the effect that BHET has higher purity and higher yield.

[0046] In some embodiments of the present invention, preferably, the process of the second purification treatment includes solid-liquid separation, cooling crystallization, and drying; wherein, filtrate A and filter cake A are obtained after the solid-liquid separation.

[0047] In some embodiments of the present invention, preferably, in step (2), the method for obtaining the polyolefin includes:

[0048] (i) The filter cake A is subjected to a second dilution treatment and a third purification treatment to obtain a mixture of polyolefin and polyvinylidene fluoride;

[0049] (ii) The mixture in step (i) is subjected to a fourth purification treatment to obtain a polyolefin product;

[0050] Wherein, the definition of the filter cake A is the same as the definition of the aforementioned filter cake A.

[0051] In some embodiments of the present invention, preferably, in step (i), the diluent A for the second dilution treatment is deionized water.

[0052] In some embodiments of the present invention, preferably, the mass ratio of the depolymerization solution to the deionized water is 1:1 - 10, more preferably 1:2 - 5. This mass ratio range is more conducive to removing trace amounts of BHET to achieve the effect that the mixture is only a mixture of polyolefin and polyvinylidene fluoride.

[0053] In some embodiments of the present invention, preferably, the process of the second dilution treatment includes adding deionized water to the depolymerization solution and stirring.

[0054] In some embodiments of the present invention, preferably, the process of the third purification treatment includes solid-liquid separation.

[0055] In some embodiments of the present invention, preferably, the temperature of the stirring is 60 - 100 °C, more preferably 70 - 90 °C; the time is 0.5 - 3 h, more preferably 1 - 2 h. This temperature range is more conducive to removing trace amounts of BHET to achieve the effect that the mixture is only a mixture of polyolefin and polyvinylidene fluoride. This time range is more conducive to fully dissolving trace amounts of BHET in deionized water to achieve the effect of removing trace amounts of BHET.

[0056] In some embodiments of the present invention, preferably, in step (ii), the process of the fourth purification treatment includes adding the mixture to a solvent and stirring, followed by solid-liquid separation to obtain filtrate B containing polyolefin and cake B, and adding precipitant A to the filtrate containing polyolefin, followed by solid-liquid separation.

[0057] In some embodiments of the present invention, preferably, the mass ratio of the mixture to the solvent is 1:2 - 500, more preferably 1:10 - 100. This mass ratio range is more conducive to fully dissolving the polyolefin in the solvent to achieve the effect of maximizing the recovery of polyolefin.

[0058] In some embodiments of the present invention, preferably, the volume ratio of precipitant A to the solvent is 1:5 - 100, more preferably 1:10 - 50.

[0059] In some embodiments of the present invention, preferably, the solvent is selected from at least one of xylene, mesitylene, dichlorobenzene, trichlorobenzene, decalin, tetralin, and cyclohexanone.

[0060] In some embodiments of the present invention, preferably, precipitant A is selected from at least one of methanol, ethanol, propanol, acetone, and ether.

[0061] In some embodiments of the present invention, preferably, the temperature of the stirring is 90 - 140 °C; the time is 0.5 - 4 h, more preferably 1 - 2 h. This temperature range is more conducive to fully dissolving the polyolefin in the solvent to achieve the effect of maximizing the recovery of polyolefin. This time range is more conducive to fully dissolving the polyolefin in the solvent to achieve the effect of maximizing the recovery of polyolefin.

[0062] In some embodiments of the present invention, preferably, in step (2), the method for obtaining polyvinylidene fluoride includes:

[0063] (a) Performing a third dilution treatment on cake B and a fifth purification treatment to obtain a crude polyvinylidene fluoride product;

[0064] (b) Performing a sixth purification treatment on the crude product in step (a) to obtain a polyvinylidene fluoride product;

[0065] Wherein, the definition of cake B is the same as the definition of cake B described above.

[0066] In some embodiments of the present invention, preferably, in step (a), the diluent B for the third dilution treatment is selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide (DMAc).

[0067] In some embodiments of the present invention, preferably, the mass ratio of the filter cake 2 to the diluent B is 1:2 - 500, more preferably 1:10 - 100. This mass ratio range is more conducive to fully dissolving polyvinylidene fluoride in the solvent to achieve the effect of maximizing the recovery of polyvinylidene fluoride.

[0068] In some embodiments of the present invention, preferably, the process of the third dilution treatment includes adding the diluent to the filter cake B and stirring.

[0069] In some embodiments of the present invention, preferably, the process of the fifth purification treatment includes solid-liquid separation.

[0070] In some embodiments of the present invention, preferably, the temperature of the stirring is 60 - 100 °C, preferably 70 - 90 °C; the time is 0.5 - 3 h, preferably 1 - 2 h. This temperature range is more conducive to fully dissolving polyvinylidene fluoride in the solvent to achieve the effect of maximizing the recovery of polyvinylidene fluoride. This time range is more conducive to fully dissolving polyvinylidene fluoride in the solvent to achieve the effect of maximizing the recovery of polyvinylidene fluoride.

[0071] In some embodiments of the present invention, preferably, in step (b), the process of the sixth purification treatment includes adding a precipitant B to the filtrate containing polyvinylidene fluoride, performing solid-liquid separation, and drying.

[0072] In some embodiments of the present invention, preferably, the volume ratio of the precipitant to the diluent is 1:5 - 100, preferably 1:10 - 50. This volume ratio range is more conducive to completely precipitating polyvinylidene fluoride from the solvent to achieve the effect of maximizing the recovery of polyvinylidene fluoride.

[0073] In some embodiments of the present invention, preferably, the precipitant B is selected from at least one of methanol, ethanol, propanol, toluene, n-hexane, n-heptane, diethyl ether, water, and tetrahydrofuran.

[0074] The present invention will be described in detail below by way of examples. In the following examples, the purity of BHET was measured by ultra-high performance liquid chromatography (UPLC) method (the elution time of BHET was determined by UPLC, and the purity was calculated based on the peak area of BHET on UPLC); PP and PVDF were characterized by infrared spectroscopy, and the thermal properties of recycled PET were measured by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) methods. The solar backsheet was recycled material, containing about 79 wt% of ethylene terephthalate (PET), about 9 wt% of polyvinylidene fluoride, and about 12 wt% of polyolefin.

[0075] Example 1

[0076] Recovery of solar backsheet:

[0077] In the presence of nitrogen (protective gas) and 0.12 wt% (based on the mass of the solar backsheet) of tetrabutyl titanate (catalyst), the solar backsheet and ethylene glycol (mass ratio of the two is 1:3) were subjected to alcoholysis reaction at 210 °C and 0.35 MPa for 2.5 h to obtain a depolymerization mixture;

[0078] Purification of bis(2-hydroxyethyl) terephthalate (BHET):

[0079] The depolymerization mixture was filtered at 120 °C (first purification treatment). Deionized water (mass ratio of the two is 1:2) was added to the obtained depolymerization solution and stirred at 80 °C for 2 h (first dilution treatment), and then filtered to obtain filtrate A and cake A. The filtrate A was cooled and crystallized at 4 °C for 12 h to obtain bis(2-hydroxyethyl) terephthalate (BHET), which was dried in a vacuum oven at 60 °C for 2 h and then weighed (second purification treatment). The purity was 98.4% and the yield was 81.3%. The infrared spectrum of BHET prepared and purified in this example is as Figure 2 shown; the 1 HNMR spectrum of the BHET is as Figure 3 shown; the ultra-high performance liquid chromatography (UPLC) spectrum of the BHET is as Figure 4 shown.

[0080] Purification of polyolefin:

[0081] Add deionized water to filter cake A at a mass ratio of filter cake A:deionized water (diluent A) = 1:2. After stirring at 70 °C for 1 h (second dilution treatment), filter to obtain a solid mixture of polyolefin and polyvinylidene fluoride (third purification treatment). Add xylene to the mixture of polyolefin and polyvinylidene fluoride at a ratio of 1:50, stir at 130 °C for 2 h, filter, and add methanol (precipitant A) to the obtained liquid at a volume ratio of xylene:methanol = 1:50. After standing for 5 minutes, filter (fourth purification treatment) to obtain a polypropylene (PP) product with a yield of 70.3%. The infrared spectrum of the PP separated and purified in this example is as Figure 9 shown.

[0082] Purification of polyvinylidene fluoride:

[0083] Add deionized water to filter cake B at a mass ratio of filter cake B:deionized water (diluent A) = 1:2. After stirring at 80 °C for 0.5 h (third dilution treatment), filter to obtain a PVDF crude product (fifth purification treatment); add DMF (diluent B) to the PVDF crude product at a ratio of 1:30, stir at 60 °C for 1 h, filter, and add methanol (precipitant B) to the obtained liquid at a volume ratio of DMF:methanol = 1:10. After standing for 5 minutes, filter (sixth purification treatment) to obtain a PVDF product with a yield of 71.6%. The infrared spectrum of the PVDF separated and purified in this example is as Figure 5 shown.

[0084] Example 2

[0085] Recycling of solar backplane:

[0086] In the presence of nitrogen (protective gas) and 0.1 wt% (based on the mass of the solar backplane) isopropyl titanate (catalyst), carry out alcoholysis reaction of the solar backplane and ethylene glycol (mass ratio of the two is 1:4) at 200 °C and 0.4 MPa for 3 h to obtain a depolymerization mixture;

[0087] Purification of bis(2-hydroxyethyl) terephthalate (BHET):

[0088] Filter the depolymerization mixture at 110 °C (first purification treatment), add deionized water (mass ratio of the two is 1:3) to the obtained depolymerization solution, stir at 80 °C for 2 h (first dilution treatment), filter to obtain filtrate A and filter cake A. Cool and crystallize the filtrate A at 4 °C for 12 h to obtain bis(2-hydroxyethyl) terephthalate (BHET), dry it in a vacuum oven at 60 °C for 2 h and then weigh it (second purification treatment), with a purity of 98.0% and a yield of 80.2%.

[0089] Purification of polyolefin:

[0090] Add deionized water to filter cake A at a mass ratio of filter cake A:deionized water (diluent A) = 1:3. After stirring at 75 °C for 1 h (second dilution treatment), filter to obtain a mixture of polyolefin and polyvinylidene fluoride (third purification treatment). Add trimethylbenzene to the mixture of polyolefin and polyvinylidene fluoride at a ratio of 1:100, stir at 140 °C for 2 h, filter, and add ethanol (precipitant A) to the obtained liquid at a volume ratio of trimethylbenzene:ethanol = 1:50. After standing for 5 minutes, filter (fourth purification treatment) to obtain a polypropylene (PP) product with a yield of 68.9%. The infrared spectrum of the PP obtained by separation and purification in this example is as Figure 9 shown.

[0091] Purification of polyvinylidene fluoride:

[0092] Add deionized water to filter cake B at a mass ratio of filter cake B:deionized water = 1:5. After stirring at 80 °C for 1 h (third dilution treatment), filter to obtain a PVDF crude product (fifth purification treatment); add DMAc (diluent B) to the PVDF crude product at a ratio of 1:20, stir at 70 °C for 1 h, filter, and add methanol (precipitant B) to the obtained liquid at a volume ratio of DMAc:ethanol = 1:5. After standing for 5 minutes, filter (sixth purification treatment) to obtain a PVDF product with a yield of 70.2%.

[0093] Example 3

[0094] Recycling of solar backsheet:

[0095] In the presence of nitrogen (protective gas) and 0.1 wt% (based on the mass of the solar backsheet) isopropyl titanate (catalyst), carry out alcoholysis reaction of the solar backsheet and ethylene glycol (mass ratio of the two is 1:5) at 200 °C and 0.4 MPa for 3 h to obtain a depolymerization mixture;

[0096] Purification of bis(2-hydroxyethyl) terephthalate (BHET):

[0097] Filter the depolymerization mixture at 110 °C (first purification treatment), add deionized water (mass ratio of the two is 1:5) to the obtained depolymerization liquid, stir at 70 °C for 2.5 h (first dilution treatment), filter to obtain filtrate A and filter cake A. After cooling and crystallizing the filtrate A at 4 °C for 12 h, obtain bis(2-hydroxyethyl) terephthalate (BHET), dry it in a vacuum oven at 60 °C for 2 h and then weigh it (second purification treatment). The purity is 98.4% and the yield is 79.6%.

[0098] Purification of polyolefin:

[0099] Add deionized water to filter cake A at a mass ratio of filter cake A:deionized water (diluent A) = 1:4. After stirring at 80 °C for 1 h (second dilution treatment), filter to obtain a solid mixture of polyolefin and polyvinylidene fluoride (third purification treatment). Add dichlorobenzene to the mixture of polyolefin and polyvinylidene fluoride at a ratio of 1:80, stir at 140 °C for 2 h, filter, and add propanol (precipitant A) to the obtained liquid at a volume ratio of dichlorobenzene:propanol = 1:80. After standing for 5 minutes, filter (fourth purification treatment) to obtain a polypropylene (PP) product with a yield of 69.6%. The infrared spectrum of the PP separated and purified in this example is as Figure 9 shown.

[0100] Purification of polyvinylidene fluoride:

[0101] Add deionized water to filter cake B at a mass ratio of filter cake B:deionized water = 1:10. After stirring at 70 °C for 0.5 h (third dilution treatment), filter to obtain a PVDF crude product (fifth purification treatment); add NMP (diluent B) to the PVDF crude product at a ratio of 1:50, stir at 100 °C for 0.5 h, filter, and add methanol (precipitant B) to the obtained liquid at a volume ratio of NMP:ethanol = 1:20. After standing for 5 minutes, filter (sixth purification treatment) to obtain a PVDF product with a yield of 68.9%.

[0102] Example 4

[0103] Recycling of solar backsheets:

[0104] In the presence of nitrogen (protective gas) and 0.3 wt% (based on the mass of the solar backsheet) isopropyl titanate (catalyst), carry out an alcoholysis reaction between the solar backsheet and ethylene glycol (mass ratio of the two is 1:5) at 220 °C and 0.3 MPa for 2 h to obtain a depolymerization mixture;

[0105] Purification of bis(2-hydroxyethyl) terephthalate (BHET):

[0106] Filter the depolymerization mixture at 100 °C (first purification treatment), add deionized water to the obtained depolymerization liquid (mass ratio of the two is 1:10), stir at 75 °C for 1.5 h (first dilution treatment), filter to obtain filtrate A and filter cake A. Cool and crystallize the filtrate A at 4 °C for 12 h to obtain bis(2-hydroxyethyl) terephthalate (BHET). After drying in a vacuum oven at 60 °C for 2 h and weighing (second purification treatment), the purity is 98.0% and the yield is 78.9%.

[0107] Purification of polyolefin:

[0108] Add deionized water to filter cake A at a mass ratio of filter cake A:deionized water (diluent A) = 1:5. After stirring at 85 °C for 1 h (second dilution treatment), filter to obtain a mixture of polyolefin and polyvinylidene fluoride as the solid (third purification treatment). Add trichlorobenzene to the mixture at a ratio of the mixture:trichlorobenzene (solvent) = 1:80, stir at 120 °C for 2 h, filter, and add acetone (precipitant A) to the obtained liquid at a volume ratio of trichlorobenzene:acetone = 1:80. After standing for 5 minutes, filter (fourth purification treatment) to obtain a polypropylene (PP) product with a yield of 70.1%. The infrared spectrum of the PP separated and purified in this example is as Figure 9 shown.

[0109] Purification of polyvinylidene fluoride:

[0110] Add deionized water to filter cake B at a mass ratio of filter cake B:deionized water = 1:4. After stirring at 70 °C for 0.5 h (third dilution treatment), filter to obtain a PVDF crude product as the solid (fifth purification treatment); add DMSO (diluent B) to the PVDF crude product at a ratio of the PVDF crude product:DMSO = 1:100, stir at 90 °C for 0.5 h, filter, and add methanol (precipitant B) to the obtained liquid at a volume ratio of DMSO:n-hexane = 1:50. After standing for 5 minutes, filter (sixth purification treatment) to obtain a PVDF product with a yield of 68.8%.

[0111] Example 5

[0112] Operate according to the method of Example 3, except that chemical depolymerization is carried out in the presence of nitrogen (protective gas) and 0.1 wt% (based on the mass of the solar backsheet) of a titanium-silicon composite catalyst (wherein, the titanium-silicon composite catalyst is prepared by mixing isopropyl titanate and tetrabutyl orthosilicate, and the mass ratio of isopropyl titanate to tetrabutyl orthosilicate is 4:1, and the preparation method of the titanium-silicon composite catalyst is the same as that in Example 1 of Patent Application 202310836415.1) to obtain a depolymerization mixture; the purity of BHET is 98.5% and the yield is 84.3%.

[0113] Example 6

[0114] Operate according to the method of Example 3, except that chemical depolymerization is carried out in the presence of nitrogen (protective gas) and 0.1 wt% (based on the mass of the solar backsheet) of a titanium-rare earth composite catalyst (wherein, the titanium-rare earth composite catalyst includes titanium glycolate and lanthanum acetylacetonate, and the mass ratio of titanium glycolate to lanthanum acetylacetonate is 4:1) to obtain a depolymerization mixture; the purity of BHET is 98.5% and the yield is 85.1%.

[0115] Example 7

[0116] Operate according to the method of Example 4, except that the diluent B is DMF, and DMF is added in a ratio of PVDF crude product:DMF = 1:100, stirred at 100 °C for 0.5 hours, the precipitant is ethanol, and the PVDF yield is 69.0%.

[0117] Example 8

[0118] Operate according to the method of Example 4, except that DMF is added in a ratio of PVDF crude product:DMF = 1:360, stirred at 50 °C for 0.5 hours, the precipitant B is n-hexane, and the PVDF yield is 68.9%.

[0119] Example 9

[0120] Operate according to the method of Example 4, except that DMF is added in a ratio of PVDF crude product:DMF = 1:2, stirred at 100 °C for 1 hour, the precipitant B is n-heptane, and the PVDF yield is 69.4%.

[0121] Example 10

[0122] Operate according to the method of Example 4, except that DMF is added in a ratio of PVDF crude product:DMF = 1:500, stirred at 50 °C for 0.5 hours, the precipitant B is water, and the PVDF yield is 70.6%.

[0123] Example 11

[0124] Operate according to the method of Example 4, except that the precipitant is B toluene, and the PVDF yield is 70.3%.

[0125] Example 12

[0126] This example is used to illustrate that the BHET recovered according to the method described in Example 6 can be reused to synthesize r-PET with a high weight-average molecular weight, a narrow molecular weight distribution, and thermal properties equivalent to those of native PET:

[0127] Add 83 g of self-made BHET monomer and 0.52 g of tetrabutyl titanate into a three-necked flask, gradually heat up to 190 °C under a nitrogen atmosphere, react for 1 hour, replace with a vacuum distillation device, heat up to 270 °C, gradually adjust the vacuum degree of the system to less than 300 Pa, and after reacting for 1 hour, obtain an r-PET product with a number-average molecular weight of 23,000 g / mol, a weight-average molecular weight of 58,000 g / mol, a molecular weight distribution of 2.5, and an r-PET melting point Tm = 250 °C (as Figure 6 shown), and an r-PET Td (5% weight loss) = 394 °C ( Figure 7 shown).

[0128] Example 13

[0129] Recycling of solar backsheet:

[0130] In the presence of nitrogen (protective gas) and 0.12 wt% (based on the mass of the solar backsheet) of titanium glycolate (catalyst), the solar backsheet and ethylene glycol (mass ratio of the two is 1:5) are subjected to alcoholysis reaction at 210 °C and 0.35 MPa for 2.5 h to obtain a depolymerized mixture;

[0131] Purification of bis(2-hydroxyethyl) terephthalate (BHET):

[0132] The depolymerized mixture is filtered at 100 °C (first purification treatment). Deionized water (mass ratio of the two is 1:2) is added to the obtained depolymerized solution and stirred at 80 °C for 2 h (first dilution treatment), and then filtered to obtain filtrate A and filter cake A. The filtrate A is cooled and crystallized at 4 °C for 12 h to obtain bis(2-hydroxyethyl) terephthalate (BHET). After drying in a vacuum oven at 60 °C for 2 h and weighing (second purification treatment), the purity is 98.1% and the yield is 79.8%. The ultra-high performance liquid chromatography (UPLC) spectrum of BHET prepared and purified in this example is as Figure 8 shown.

[0133] Purification of polyolefin:

[0134] Deionized water (diluent A) is added to the filter cake A according to the ratio of filter cake A: water = 1:2, and stirred at 80 °C for 0.5 h (second dilution treatment), and then filtered (third purification treatment) to obtain a mixture of PVDF and PP; the mixture and xylene (solvent) are stirred at 130 °C for 3 h according to the ratio of mixture: xylene = 1:30, and then filtered to obtain filtrate B and filter cake B.

[0135] Methanol (precipitant A) is added to the second filtrate according to the volume ratio of xylene: methanol = 1:20, and after standing for 5 min, it is filtered (fourth purification treatment) to obtain a PP product with a yield of 70.0%. The infrared spectrum of PP separated and purified in this example is as Figure 9 shown.

[0136] Purification of polyvinylidene fluoride:

[0137] The method of Example 1 is followed, except that DMF (diluent B) is added according to the ratio of the PVDF crude product: DMF = 1:10, stirred at 90 °C for 0.5 h, filtered, and ethanol (precipitant B) is added to the obtained liquid according to the volume ratio of DMF: ethanol = 1:30. After standing for 5 minutes, it is filtered (sixth purification treatment) to obtain a PVDF product with a yield of 69.4%.

[0138] Example 14

[0139] Recycling of solar backsheet:

[0140] In the presence of nitrogen (protective gas) and 0.1 wt% (based on the mass of the solar backsheet) of isopropyl titanate (catalyst), the solar backsheet and ethylene glycol (mass ratio of the two is 1:4) are subjected to alcoholysis reaction at 200 °C and 0.4 MPa for 3 h to obtain a depolymerization mixture;

[0141] Purification of polyethylene terephthalate:

[0142] The depolymerization mixture is filtered at 110 °C (first purification treatment). Deionized water (mass ratio of the two is 1:3) is added to the obtained depolymerization solution and stirred at 80 °C for 2 h (first dilution treatment), and then filtered to obtain filtrate A and filter cake A. The filtrate A is cooled and crystallized at 4 °C for 12 h to obtain bis(2-hydroxyethyl) terephthalate (BHET), which is dried in a vacuum oven at 60 °C for 2 h and then weighed (second purification treatment). The purity is 98.0% and the yield is 80.5%.

[0143] Purification of polyolefin:

[0144] Deionized water (diluent A) is added to filter cake A in a ratio of filter cake A: water = 1:3, and stirred at 80 °C for 0.5 h (second dilution treatment), and then filtered (third purification treatment) to obtain a mixture of PVDF and PP (or PE); the mixture and mesitylene (solvent) are stirred at 130 °C for 3 h in a ratio of mixture: mesitylene = 1:50, and then filtered to obtain filtrate B and filter cake B.

[0145] Methanol (precipitant A) is added to the second filtrate in a volume ratio of mesitylene: methanol = 1:30, and after standing for 5 min, it is filtered (fourth purification treatment) to obtain PP product, and the yield is 67.9%.

[0146] Purification of polyvinylidene fluoride:

[0147] The method of Example 1 is followed, except that NMP (diluent B) is added to the PVDF crude product in a ratio of PVDF crude product: NMP = 1:10, stirred at 80 °C for 1 h, and filtered. Methanol (precipitant B) is added to the obtained liquid in a volume ratio of NMP: methanol = 1:30, and after standing for 5 minutes, it is filtered (sixth purification treatment) to obtain PVDF product, and the yield is 68.5%.

[0148] Example 15

[0149] Recycling of solar backsheet:

[0150] In the presence of nitrogen (protective gas) and 0.2 wt% (based on the mass of the solar backsheet) of isopropyl titanate (catalyst), the solar backsheet and ethylene glycol (mass ratio of the two is 1:6) are subjected to alcoholysis reaction at 205 °C and 0.3 MPa for 5 h to obtain a depolymerization mixture;

[0151] Purification of polyethylene terephthalate:

[0152] The depolymerization mixture is filtered at 100 °C (first purification treatment). Deionized water is added to the obtained depolymerization solution (mass ratio of the two is 1:4), and after stirring at 70 °C for 1.5 h (first dilution treatment), it is filtered to obtain filtrate A and filter cake A. The filtrate A is cooled and crystallized at 4 °C for 12 h to obtain bis(2-hydroxyethyl) terephthalate (BHET). After drying in a vacuum oven at 60 °C for 2 h and weighing (second purification treatment), the purity is 98.0% and the yield is 80.4%.

[0153] Purification of polyolefin:

[0154] Deionized water (diluent A) is added to filter cake A according to the ratio of filter cake A:water = 1:4, and after stirring at 80 °C for 0.5 h (second dilution treatment), it is filtered (third purification treatment) to obtain a mixture of PVDF and PP (or PE); the mixture and dichlorobenzene (solvent) are stirred at 130 °C for 3 h according to the ratio of mixture:dichlorobenzene = 1:50, and then filtered to obtain filtrate B and filter cake B.

[0155] Methanol (precipitant A) is added to the second filtrate according to the volume ratio of dichlorobenzene:acetone = 1:20, and after standing for 5 min, it is filtered (fourth purification treatment) to obtain PP product with a yield of 69.7%.

[0156] Purification of polyvinylidene fluoride:

[0157] It is carried out according to the method of Example 1, except that DMAc (diluent B) is added to the PVDF crude product according to the ratio of PVDF crude product:DMAc = 1:10, and after stirring at 80 °C for 1 h and filtering, n-hexane (precipitant B) is added to the obtained liquid according to the volume ratio of DMAc:n-hexane = 1:30, and after standing for 5 minutes, it is filtered (sixth purification treatment) to obtain PVDF product with a yield of 70.3%.

[0158] Example 16

[0159] Recovery of solar backsheet:

[0160] In the presence of nitrogen (protective gas) and 0.3 wt% (based on the mass of the solar backsheet) of isopropyl titanate (catalyst), the solar backsheet and ethylene glycol (mass ratio of the two is 1:5) are subjected to alcoholysis reaction at 220 °C and 0.3 MPa for 2 h to obtain a depolymerization mixture;

[0161] Purification of polyethylene terephthalate:

[0162] Filter the depolymerization mixture at 100 °C (first purification treatment). Add deionized water to the obtained depolymerized solution (mass ratio of the two is 1:4), stir at 70 °C for 1.5 h (first dilution treatment), then filter to obtain filtrate A and filter cake A. Cool the filtrate A at 4 °C for 12 h to obtain bis(2-hydroxyethyl) terephthalate (BHET). Dry it in a vacuum oven at 60 °C for 2 h and then weigh it (second purification treatment). The purity is 98.0% and the yield is 80.8%.

[0163] Purification of polyolefin:

[0164] Add deionized water (diluent A) to filter cake A in a ratio of filter cake A: water = 1:4, stir at 80 °C for 0.5 h (second dilution treatment), then filter (third purification treatment) to obtain a mixture of PVDF and PP (or PE); stir the mixture with trichlorobenzene (solvent) in a ratio of 1:50 at 130 °C for 3 h, then filter to obtain filtrate B and filter cake B.

[0165] Add methanol (precipitant A) to the second filtrate in a volume ratio of trichlorobenzene: acetone = 1:20, let it stand for 5 min, then filter (fourth purification treatment) to obtain PP product with a yield of 70.2%.

[0166] Purification of polyvinylidene fluoride:

[0167] Carry out according to the method of Example 1, except that add DMAc (diluent B) to the PVDF crude product in a ratio of 1:10, stir at 80 °C for 1 h, then filter. Add n-hexane (precipitant B) to the obtained liquid in a volume ratio of DMAc: n-hexane = 1:30, let it stand for 5 minutes, then filter (sixth purification treatment) to obtain PVDF product with a yield of 70.3%.

[0168] Example 17

[0169] Operate according to the method of Example 16, except that the solvent is decalin, the diluent B is DMF, add DMF to the PVDF crude product in a ratio of 1:50, stir at 100 °C for 0.5 h, the precipitant B is ethanol, the yield of PP is 71.2%, and the yield of PVDF is 70.5%.

[0170] Example 18

[0171] Operate according to the method of Example 16, except that the solvent is tetralin, the diluent B is DMAc, DMAc is added in a ratio of PVDF crude product:DMAc = 1:360, stirred at 50 °C for 0.5 hours, the precipitant B is n-hexane, the PP yield is 69.2%, and the PVDF yield is 69.7%.

[0172] Example 19

[0173] Operate according to the method of Example 16, except that the solvent is cyclohexanone, the diluent B is DMF, DMF is added in a ratio of PVDF crude product:DMF = 1:2, stirred at 100 °C for 1 hour, the precipitant B is n-heptane, the PP yield is 68.7%, and the PVDF yield is 69.3%.

[0174] Example 20

[0175] Operate according to the method of Example 16, except that DMF is added in a ratio of PVDF crude product:DMF = 1:500, stirred at 50 °C for 0.5 hours, the precipitant B is water, and the PVDF yield is 70.3%.

[0176] Example 21

[0177] Operate according to the method of Example 16, except that the precipitant B is toluene, and the PVDF yield is 68.9%.

[0178] From the experimental results of Examples 1-21 and Figure 2 - 9 It can be seen that by adopting the technical solution of the present invention, the PET intermediate layer in the solar panel can be efficiently depolymerized into BHET monomers; while the PVDF and PP (or PE) materials that do not participate in the depolymerization can also obtain PVDF and PP (or PE) products respectively after separation and purification. Compared with the prior art (CN114248369A), the BHET monomer prepared by the present invention has a high yield, reaching ≥78%; and a high purity, reaching ≥98%. At the same time, the infrared spectra of the separated PVDF and polyolefin are consistent with the standard products, which cannot be achieved by the prior art. Moreover, the operation method of the entire chemical recycling process is simple, efficient, and has good economic benefits.

[0179] 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 technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for recycling a solar backsheet, characterized in that, The method includes: (1) In the presence of a protective gas and a catalyst, subjecting a solar backsheet to alcoholysis reaction with an alcohol to obtain a depolymerization mixture; (2) Purifying the depolymerization mixture obtained in step (1) to obtain bis(2-hydroxyethyl) terephthalate, polyvinylidene fluoride, and polyolefin.

2. The method according to claim 1, wherein, In step (1), the catalyst is selected from titanium-containing compounds and / or titanium-containing compositions, preferably at least one of alkyl titanates, titanium glycolates, titanium phosphates, and organic-inorganic hybrid titaniums, more preferably at least one of tetraethyl titanate, tetrabutyl titanate, tetraisopropyl titanate, tetraisobutyl titanate, titanium glycolate, titanium phosphate, titanium-silicon composite catalyst, and titanium-rare earth composite catalyst; and / or, the alcohol is ethylene glycol.

3. The method according to claim 1 or 2, wherein In step (1), the dosage of the catalyst is 0.05-0.5 wt% of the solar backsheet, preferably 0.08-0.2 wt%.

4. The method according to any one of claims 1 to 3, wherein, The mass ratio of the alcohol to the solar backsheet is 2-8:1, preferably 3-5:

1.

5. The method according to any one of claims 1-4, wherein The temperature of the alcoholysis reaction is 190-250 °C; the pressure is 0.2-0.6 MPa; the time is 1-10 h, preferably 2-5 h.

6. The method according to any one of claims 1-5, wherein, In step (2), the process of the purification treatment sequentially includes a first purification treatment, a second purification treatment, a third purification treatment, a fourth purification treatment, and a fifth purification treatment; Preferably, the method of the purification treatment includes at least one of solid-liquid separation, dilution, cooling, precipitation, and drying.

7. The method according to claim 1, wherein, In step (2), subject the depolymerization mixture to a first purification treatment, a first dilution treatment, and a second purification treatment in sequence to obtain bis(2-hydroxyethyl) terephthalate.

8. The method according to claim 7, wherein, The diluent A used in the first dilution treatment is deionized water; Preferably, the mass ratio of the depolymerization solution to the deionized water is 1:1-10, more preferably 1:2-5; Preferably, the process of the first purification treatment includes solid-liquid separation to obtain a depolymerization solution; Preferably, the process of the first dilution treatment includes adding deionized water to the depolymerization solution and stirring; Among them, the temperature of the solid-liquid separation is 90-130 °C; Among them, the temperature of the stirring is 60-100 °C, preferably 70-90 °C; the time is 0.5-3 h, preferably 1-2 h.

9. The method according to claim 7 or 8, wherein the process of the second purification treatment includes solid-liquid separation, cooling crystallization, and drying; wherein, After the solid-liquid separation, a filtrate A and a filter cake A are obtained.

10. The method according to claim 1, wherein, In step (2), the method for obtaining polyolefin includes: (i) Subject the filter cake A to a second dilution treatment and a third purification treatment to obtain a mixture of polyolefin and polyvinylidene fluoride; (ii) Subject the mixture in step (i) to a fourth purification treatment to obtain a polyolefin product; Among them, the definition of the filter cake A is the same as that defined in claim 9.

11. The method according to claim 10, wherein, In step (i), the diluent B used in the second dilution treatment is deionized water; Preferably, the mass ratio of the depolymerization solution to the deionized water is 1:1-10, more preferably 1:2-5; Preferably, the process of the second dilution treatment includes adding deionized water to the depolymerization solution and stirring; Preferably, the process of the third purification treatment includes solid-liquid separation; Among them, the temperature of the stirring is 60-100 °C, preferably 70-90 °C; the time is 0.5-3 h, preferably 1-2 h.

12. According to the method described in claim 10 or 11, in step (ii), the process of the fourth purification treatment includes adding the mixture to a solvent and stirring, followed by solid-liquid separation to obtain filtrate B containing polyolefin and cake B, adding precipitant A to the filtrate containing polyolefin, and then performing solid-liquid separation; Preferably, the mass ratio of the mixture to the solvent is 1:2 - 500, preferably 1:10 - 100; Preferably, the volume ratio of precipitant A to the solvent is 1:5 - 100, preferably 1:10 - 50; Among them, The solvent is selected from at least one of xylene, trimethylbenzene, dichlorobenzene, trichlorobenzene, decalin, tetralin, and cyclohexanone; Among them, precipitant A is selected from at least one of methanol, ethanol, propanol, acetone, and ether; Among them, the temperature of the stirring is 90 - 140 °C; the time is 0.5 - 4 h, preferably 1 - 2 h.

13. The method according to claim 1, wherein, In step (2), the method for obtaining polyvinylidene fluoride includes: (a) Performing a third dilution treatment on cake B and a fifth purification treatment to obtain a crude polyvinylidene fluoride product; (b) Performing a sixth purification treatment on the crude product in step (a) to obtain a polyvinylidene fluoride product; Among them, the definition of cake B is the same as that described in claim 12.

14. The method according to claim 13, wherein, In step (a), the diluent C for the third dilution treatment is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and N,N-dimethylacetamide; Preferably, the mass ratio of cake B to diluent C is 1:2 - 500, more preferably 1:10 - 100; Preferably, the process of the third dilution treatment includes adding diluent C to cake B and stirring; Preferably, the process of the fifth purification treatment includes solid-liquid separation; Among them, the temperature of the stirring is 60 - 100 °C, preferably 70 - 90 °C; the time is 0.5 - 3 h, preferably 1 - 2 h.

15. According to the method described in claim 13 or 14, in step (b), the process of the sixth purification treatment includes adding precipitant B to the filtrate containing polyvinylidene fluoride, performing solid-liquid separation, and drying; Preferably, the volume ratio of precipitant B to diluent C is 1:5 - 100, preferably 1:10 - 50; Among them, Precipitant B is selected from at least one of methanol, ethanol, propanol, toluene, n-hexane, n-heptane, ether, water, and tetrahydrofuran.

16. The method according to claim 1, wherein, In step (2), the process of the purification treatment includes: filtering the depolymerization mixture in step (1) to obtain filtrate A and cake A containing the same; adding deionized water to filtrate A, stirring, filtering, and cooling crystallization to obtain bis(2-hydroxyethyl) terephthalate; adding deionized water to cake A, stirring and filtering to obtain a mixture of polyolefin and polyvinylidene fluoride, then adding a solvent, stirring and filtering to obtain filtrate B and cake B, adding precipitant A to filtrate B and then filtering to obtain polyolefin; adding a solvent to cake B, stirring and filtering, adding precipitant B to the obtained filtrate and then filtering and drying to obtain polyvinylidene fluoride.

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