Method for efficiently separating and recycling PET (Polyethylene Terephthalate) material in waste photovoltaic back plate

Abstract

The invention provides a method for efficiently separating and recycling a PET material in a waste photovoltaic backboard, and belongs to the technical field of waste photovoltaic panel recycling, the method comprises the following steps: S1, crushing and screening the waste photovoltaic backboard subjected to wet de-encapsulation treatment to obtain a crushed material; s2, the crushed material is placed in alkali liquor to be heated, soaked and cleaned, and a first material is obtained; s3, performing friction cleaning on the first material to obtain a second material; s4, the second material is sequentially subjected to countercurrent washing, ultrasonic cleaning, centrifugal dewatering separation and hot air separation, and a heavy material is obtained; and S5, screening the heavy material, and carrying out material sorting and color sorting to obtain the PET material. According to the method disclosed by the invention, the PET material adhered with the coating film is dissociated from the mixture by utilizing the processes of soaking cleaning and friction cleaning, and is purified by utilizing a series of sorting steps, and the obtained PET base film fragments are relatively high in purity and can be further utilized, so that the economic value is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of waste photovoltaic panel recycling, and in particular to a method for efficiently separating and recycling PET materials in waste photovoltaic backboards. Background Art

[0002] To achieve the "dual carbon" goals, China is vigorously developing clean photovoltaic energy. By 2023, grid-connected photovoltaic power generation capacity will reach 470 GW. Photovoltaic laminates, core components of photovoltaic equipment, have a lifecycle of 10-15 years. Complex operating environments are accelerating their aging and obsolescence, leading to explosive growth in the scrapping of crystalline silicon photovoltaic laminates, projected to reach 8-10 million tons per year by 2035. Therefore, the safe disposal and resource recycling of retired photovoltaic laminates is a key path to achieving the "dual carbon" goals.

[0003] Retired photovoltaic laminates feature an ultra-thin, multi-layered structure, high density, and durability. Furthermore, their numerous material components (photovoltaic glass, EVA, PET, silicon wafers, metals such as Ag, Al, and Cu) create a high degree of complexity, making them difficult to dissociate and cleanly regenerate. In retired crystalline silicon photovoltaic modules, the photovoltaic backsheet, as one of the encapsulation materials exposed to the external environment over a large area, can become powdered, cracked, bulged, and even delaminated under prolonged exposure to sunlight and heat. Furthermore, it adheres to EVA (ethylene-vinyl acetate copolymer), making recycling and reuse challenging. Initial disassembly of retired crystalline silicon photovoltaic cells, which have significant potential for recycling, directly produces waste PET backsheet material, accounting for approximately 1% of the total cell weight. Previously, these cells were treated only by landfill and incineration, resulting in significant environmental impacts at the end-of-life stage of crystalline silicon photovoltaic cell management. Invention patents CN117863273A, CN118165363A, CN118180121A, CN118604167A, and CN118663658A all mention technologies and devices for wet decapsulation of photovoltaic panels, but none mention how to effectively remove and separate surface attachments from PET to achieve the purpose of recycling high-quality PET materials.

[0004] Therefore, it is of great significance to develop a method that can effectively remove and separate the surface attachments of PET backboard materials. Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present invention provides a method for efficiently separating and recycling PET materials in waste photovoltaic backboards, aiming to solve the technical problems that the existing wet desealing photovoltaic panels cannot effectively separate PET surface attachments and the PET recovery purity is low.

[0006] In a first aspect, the present invention provides a method for efficiently separating and recycling PET materials from waste photovoltaic backsheets, comprising the following steps: S1. Crushing and screening the waste photovoltaic backsheets that have undergone wet decapsulation to obtain crushed materials; S2, placing the crushed material in an alkaline solution for heating, soaking and cleaning to obtain a first material; S3, friction-cleaning the first material to obtain a second material; S4, sequentially subjecting the second material to countercurrent washing, ultrasonic cleaning, centrifugal dehydration separation, and hot air separation to obtain a heavy material; S5. After screening the heavy materials, perform material sorting and color sorting to obtain PET materials.

[0007] Preferably, the waste photovoltaic backsheet that has undergone wet decapsulation treatment is a PET material with EVA glue, PVF film and silicone grease attached to the surface.

[0008] Preferably, the particle size of the crushed material is 2-16 mm.

[0009] Preferably, the conditions for heating, immersing and cleaning are: temperature of 95-100° C., immersing and cleaning time of 20-30 min; and conductivity of the alkali solution of 70-90 mS / cm.

[0010] Preferably, the alkali solution comprises sodium hydroxide solution.

[0011] Preferably, the friction cleaning treatment conditions are: the friction cleaning time is 300-600s, the friction shaft speed is 150-300rpm, and the grinding aid and water are added simultaneously during the friction cleaning feeding.

[0012] Preferably, the amount of the grinding aid added is 5% to 10% of the weight of the first material; and the amount of water added is 20% to 25% of the weight of the first material.

[0013] Preferably, the grinding aid includes at least one of No. 5 quartz sand, 30-50 mesh glass beads, and iron oxide particles.

[0014] Preferably, the ultrasonic cleaning time is 2 to 5 minutes, and the ultrasonic cleaning frequency is 50 to 100 kHz.

[0015] Preferably, the particle size of the heavy material after screening is ≥2mm; the material sorting is to exclude non-PET materials, and the color sorting is to exclude non-white materials.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The PET base film obtained by the traditional recycling process is mostly in a mixed state. The PET base film in this state can usually only be used for fuel processing or as a low-end filler. However, the method for efficiently separating and recycling PET materials in waste photovoltaic backboards provided by the present invention uses the soaking cleaning and friction cleaning processes to separate the adhered film-coated PET material from the mixture, and then uses a series of sorting steps to purify it to obtain PET base film fragments with high purity. The obtained high-purity PET base film fragments have broad application prospects. They can not only replace virgin materials in a certain proportion and be reused in the production of photovoltaic backboards, but also meet the uses of higher standards and higher quality requirements such as fiber grade and injection molding grade, bringing greater economic benefits.

[0017] The method provided by this invention for efficiently separating and recycling PET materials from waste photovoltaic backsheets is significantly environmentally friendly. It creates a viable recycling chain for PET materials, significantly reducing the large amount of waste generated by discarded PET materials. It effectively avoids the potential release of microplastic pollutants from PET materials used as fillers and the generation of various toxic and hazardous substances during the incineration of PET waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic structural diagram of a waste photovoltaic PET backsheet in Example 1 of the present invention; Figure 2 This is a physical picture of the waste photovoltaic PET backsheet in Example 1 of the present invention; Figure 3 The figure is a schematic flow chart of the method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to the present invention. DETAILED DESCRIPTION

[0019] The following embodiments of the technical solution of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention.

[0020] In order to solve the technical problem that the existing wet desealing of photovoltaic panels fails to effectively separate PET surface attachments and the PET recovery purity is low, the present invention provides a method for efficiently separating and recycling PET materials in waste photovoltaic backsheets, wherein the PET material with adhesion and coating is separated from the mixture through the use of immersion cleaning and friction cleaning processes, and then purified through a series of sorting steps to recover high-purity PET materials.

[0021] Please refer to Figure 3 In a first aspect, an embodiment of the present invention provides a method for efficiently separating and recycling PET materials from waste photovoltaic backsheets, comprising the following steps: S1. Crushing and screening the waste photovoltaic backsheets that have undergone wet decapsulation to obtain crushed materials; S2, placing the crushed material in an alkaline solution for heating, soaking and cleaning to obtain a first material; S3, friction-cleaning the first material to obtain a second material; S4, sequentially subjecting the second material to countercurrent washing, ultrasonic cleaning, centrifugal dehydration separation, and hot air separation to obtain a heavy material; S5. After screening the heavy materials, perform material sorting and color sorting to obtain PET materials.

[0022] In the technical solution of the embodiments of the present invention, the raw material to be processed is waste photovoltaic backsheet material obtained by wet decapsulation (solvent method, utilizing the dissolution / swelling principle to separate and encapsulate EVA material) and removal of materials such as glass, silicon, and metal. The material is composed of PET material with EVA glue, PVF film, and silicone grease attached to the surface. The purpose of crushing is to reduce large pieces of backsheet material to a size suitable for processing, thereby increasing the kinetics of dissociation during the soaking and cleaning process. The purpose of screening is to remove materials that are difficult to handle during subsequent color sorting and material separation. The alkaline solution heating soaking and cleaning utilizes the chemical activity of the alkaline solution and the energy provided by heating to accelerate the separation of impurities from the PET material, thereby removing most impurities. Friction cleaning removes residual tiny impurity particles through physical friction, further improving the purity of the PET material. This series of steps works in conjunction with each other to gradually remove surface deposits on the PET material from both chemical and physical levels, ultimately obtaining high-purity PET material that can be effectively dissociated from the mixed material. The mechanism of action of the alkaline solution heating soaking and cleaning is as follows: When EVA adhesive (ethylene-vinyl acetate copolymer) encounters a strong alkaline solution, its molecular chains are disrupted, causing the adhesive to lose its adhesiveness and eventually delaminate or dissolve. PVF film has excellent chemical stability, but in alkaline solutions, the alkali can penetrate the interface between the PVF film and the PET material. The hydroxide ions in the alkali react with the chemical bonds at the interface, changing the chemical properties of the interface and weakening the adhesion between the PVF film and the PET material. Silicone grease is an organic silicone material whose molecular structure contains silicon-oxygen (Si-O) and silicon-oxygen-carbon (Si-OC) bonds. Under alkaline conditions, these bonds undergo saponification reactions, forming soluble silicates and alcohols, which loosen the structure of the silicone grease and cause it to detach from the PET surface.

[0023] Furthermore, in some embodiments, the waste photovoltaic backsheet that has undergone wet decapsulation treatment is a PET material with EVA glue, PVF film and silicone grease attached to the surface.

[0024] In the technical solution of the embodiment of the present invention, further, in some embodiments, the particle size of the crushed material is 2-16 mm.

[0025] Furthermore, in some embodiments, the conditions for heating and immersing cleaning are: temperature of 95-100° C., immersion cleaning time of 20-30 min; and conductivity of the alkaline solution of 70-90 mS / cm.

[0026] In the technical solution of the embodiment of the present invention, in order to enhance the cleaning effect, it is necessary to further optimize the process parameters such as heating temperature, alkaline solution conductivity, and cleaning time. If the heating temperature, conductivity, and cleaning time are insufficient, the film cannot be effectively separated. If they are excessive, production costs will increase.

[0027] Furthermore, in some embodiments, the alkaline solution includes sodium hydroxide solution.

[0028] Furthermore, in some embodiments, the friction cleaning treatment conditions are: the friction cleaning time is 300-600s, the friction shaft speed is 150-300rpm, and the grinding aid and water are added simultaneously during the friction cleaning feeding.

[0029] Furthermore, in some embodiments, the amount of the grinding aid added is 5% to 10% of the weight of the first material; and the amount of water added is 20% to 25% of the weight of the first material.

[0030] Furthermore, in some embodiments, the grinding aid includes at least one of No. 5 quartz sand, 30-50 mesh glass beads, and iron oxide particles.

[0031] In the technical solution of the embodiment of the present invention, the friction cleaning treatment is to achieve the comprehensive effect of dissociating the coating. If the cleaning time, friction shaft speed, and amount of grinding aid added are insufficient, the effect of dissociating the material cannot be achieved. If the water ratio is too little or too much, the equipment operation will be affected.

[0032] Furthermore, in some embodiments, the ultrasonic cleaning time is 2 to 5 minutes, and the ultrasonic cleaning frequency is 50 to 100 kHz.

[0033] Furthermore, in some embodiments, the particle size of the heavy material after screening is ≥2 mm; the material sorting is to exclude non-PET materials; and the color sorting is to exclude non-white materials.

[0034] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product specifications were used. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased commercially.

[0035] Example 1 The raw materials to be processed are waste photovoltaic backsheet materials obtained by wet method (solvent method, using the dissolution / swelling principle to separate and encapsulate EVA materials) decapsulation and removal of glass, silicon, metal and other materials. The composition is PET material with EVA glue, PVF film and silicone grease attached to the surface (its structural diagram is shown in the figure). Figure 1 As shown in the actual picture Figure 2 As shown), the specific steps of the method for separating and recycling the PET material in the above-mentioned waste photovoltaic backsheet are as follows; S1. Crushing and screening: Use a shear crusher to crush the waste photovoltaic backsheets. The crusher screen is 16mm. After crushing, the screen is screened. The aperture of the screening equipment is set to 2mm. S2, soaking and cleaning: the material with a sieve size of ≥2 mm obtained in step S1 is heated and soaked for cleaning, the soaking water temperature is 95° C., sodium hydroxide is added during the soaking until the conductivity of the alkali solution is 70 mS / cm, and the soaking time is 30 min; S3, friction cleaning: the mixed material after soaking and cleaning in step S2 is placed in a friction cleaning device, wherein the friction cleaning device adopts a closed friction tank, and No. 5 quartz sand is added as a grinding aid during friction. The friction cleaning time is 600s, the friction shaft speed is 300rpm, the amount of grinding aid added is 10% of the material weight, and 20% of the material weight of water is added simultaneously during feeding; S4, countercurrent flushing: Place the material obtained by friction cleaning in step S3 in a countercurrent flushing tank, and use a plate chain conveyor to drive the material transportation. Use water to flush the material in the direction opposite to the material transportation direction. The flushing distance is not less than 6m; S5, ultrasonic cleaning: placing the material obtained in step S4 in an ultrasonic cleaning tank and performing 100kHz ultrasonic cleaning for 200s; S6, dehydration and separation: centrifugation and dehydration of the material obtained in step S5; S7, hot air separation: Use the heat exchanger to heat the exhaust heat from the hot water used for soaking and cleaning to heat the fan outlet, and adjust the air volume at the outlet to effectively separate the lighter materials and obtain the heavier materials; S8. Sorting: Pass the heavy material through a 2 mm sieve, take the material on the sieve, and sort it by material and color respectively, remove non-PET material and non-white material, and obtain PET material.

[0036] Example 2 The difference between this embodiment and embodiment 1 is that in step S2, sodium hydroxide is added during soaking and cleaning until the conductivity of the alkaline solution reaches 80 mS / cm.

[0037] Example 3 The difference between this embodiment and embodiment 1 is that in step S2, sodium hydroxide is added during soaking and cleaning until the conductivity of the alkaline solution reaches 90 mS / cm.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S2, the temperature of the hot water for soaking and cleaning is 80°C.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that in step S2, sodium hydroxide is added during the soaking and cleaning process until the conductivity of the alkali solution reaches 50 mS / cm.

[0040] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S2, the soaking and cleaning time is 10 minutes.

[0041] The PET materials obtained using the methods described in Examples 1-3 and Comparative Examples 1-3 were tested for impurity content. The specific testing method is as follows: PVF, silicone grease, and PET materials undergo visually distinguishable changes in color and morphology at a certain temperature, thereby separating materials that have not been effectively removed or dissociated. A 2000g sample was weighed and evenly spread on a dry, clean sample tray of known mass. The tray was pre-heated to 220°C (±5°C) in a drying oven with airflow. Once the oven temperature reached 220°C, the timer began. Dry the tray under continuous airflow for 1 hour. Remove the tray from the drying oven and immediately weigh it until the difference in the two sample masses did not exceed 1g. The smallest sample mass was used as the dried sample mass (m0). Samples with blackened, yellowed, or opaque surfaces were removed from the tray and weighed (m1) to an accuracy of 0.001g. The impurity content (in ppm) was calculated as m1 / m0.

[0042] The test results are shown in Table 1.

[0043] Table 1

[0044] The test results above demonstrate that the PET material recovered using the method described herein is highly pure, effectively separating and removing coatings such as silicone grease from the PET surface of waste photovoltaic backsheets. Data from Comparative Examples 1-3 indicate that insufficient temperature, conductivity, and duration during the immersion cleaning process prevent effective film separation.

[0045] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the present invention, other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A method for efficiently separating and recycling PET materials from waste photovoltaic backsheets, characterized in that: The following steps are involved: S1. Crushing and screening the waste photovoltaic backsheets that have undergone wet decapsulation to obtain crushed materials; S2, placing the crushed material in an alkaline solution for heating, soaking and cleaning to obtain a first material; S3, friction-cleaning the first material to obtain a second material; S4, sequentially subjecting the second material to countercurrent washing, ultrasonic cleaning, centrifugal dehydration separation, and hot air separation to obtain a heavy material; S5. After screening the heavy material, perform material sorting and color sorting to obtain PET material.

2. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 1, characterized in that: The waste photovoltaic backboard that has undergone wet decapsulation treatment is a PET material with EVA glue, PVF film and silicone grease attached to the surface.

3. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 1, characterized in that: The particle size of the crushed material is 2-16 mm.

4. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 1, characterized in that: The conditions for the heating immersion cleaning are: a temperature of 95-100° C., a immersion cleaning time of 20-30 minutes, and an electrical conductivity of the alkali solution of 70-90 mS / cm.

5. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 4, characterized in that: The alkali solution includes sodium hydroxide solution.

6. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 1, characterized in that: The friction cleaning treatment conditions are as follows: the friction cleaning time is 300-600s, the friction axis speed is 150-300rpm, and the grinding aid and water are added simultaneously during the friction cleaning feeding.

7. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 6, characterized in that: The amount of the grinding aid added is 5% to 10% of the weight of the first material; the amount of water added is 20% to 25% of the weight of the first material.

8. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 6, characterized in that: The grinding aid includes at least one of No. 5 quartz sand, 30-50 mesh glass beads, and iron oxide particles.

9. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 1, characterized in that: The ultrasonic cleaning time is 2-5 min, and the ultrasonic cleaning frequency is 50-100 kHz.

10. The method for efficiently separating and recycling PET materials from waste photovoltaic backsheets according to claim 1, characterized in that: The particle size of the heavy material after screening is ≥2mm; the material sorting is to exclude non-PET materials; and the color sorting is to exclude non-white materials.

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