Method for treating EVA (Ethylene Vinyl Acetate) adhesive film of retired photovoltaic module by using low-temperature chemical method

Abstract

The invention belongs to the field of photovoltaic module recovery, and discloses a method for treating an EVA (Ethylene Vinyl Acetate) adhesive film of a decommissioned photovoltaic module by a low-temperature chemical method. The method comprises the following steps of: disassembling the decommissioned photovoltaic module and cutting the decommissioned photovoltaic module into small samples; pretreating the sample; and putting the pretreated sample into a mixed solution of gamma-valerolactone, D-limonene, polyethylene glycol, absolute ethyl alcohol, 2-methylimidazole and polydimethylsiloxane, and soaking at low temperature, so that the EVA adhesive film is swelled, the adhesive force between the EVA adhesive film and the battery piece is reduced, and the separation of the EVA adhesive film and the battery piece is realized. Treatment can be carried out at low temperature, energy consumption is remarkably reduced, and the environment-friendly requirement is met; the operation process is simple, and the treatment period is short.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic module recycling technology, and particularly relates to a method for treating EVA film of retired photovoltaic modules using a low-temperature chemical method. Background Technology

[0002] Retired photovoltaic (PV) modules are rich in materials such as glass, Al, Si, and Ag, possessing enormous recycling potential. Achieving efficient recycling and resource utilization of retired PV modules holds broad market prospects. EVA film, the material connecting PV glass and solar cells, is a crucial step in PV module recycling. Currently, EVA film disposal technologies mainly revolve around physical, chemical, and pyrolysis methods, each differing in separation efficiency, environmental friendliness, and economic viability.

[0003] The physical method involves four stages: pretreatment, embrittlement, crushing, and sorting. First, the frame and junction box of the photovoltaic module are mechanically removed. Then, the module is cut, and specific physical methods are used to induce embrittlement of the EVA film. The material is then crushed through methods such as compression or high-pressure pulses to generate shock waves. Finally, screening and sorting are used to classify and recycle the photovoltaic glass, silicon wafers, backsheets, and EVA according to particle size. Granata et al. used a dual-blade rotor crusher and hammer crushing, finding that EVA film and backsheet fragments were mainly concentrated in the portion with d > 5 mm, and more than 80% of the glass could be directly recycled or graded for recycling. The physical separation method is simple and has low energy consumption, but mechanical crushing leaves EVA and metal impurities on the silicon wafer surface, resulting in low purity of the recovered silicon, silver, and other materials.

[0004] Chemical methods utilize the polarity matching mechanism between solvent molecules in solution and EVA to achieve film dissolution and swelling. Their core advantage lies in precise interface dissociation without damaging the silicon wafer's crystal structure. Generally, they do not require high-pressure equipment, aligning with current green and low-carbon development trends and becoming an important method in the field of photovoltaic module recycling. Different types of organic solvents have varying dissolving abilities and mechanisms for EVA, providing diverse options for EVA separation. The Doi team at the University of Tokyo compared various solvents such as acetone and toluene, finding that non-crosslinked EVA is readily soluble in most organic solvents, while crosslinked EVA is only effectively dissolved in trichloroethylene at 80°C. However, the processing time is relatively long, requiring 7-10 days to complete the separation, resulting in lower efficiency. Chemical methods also have drawbacks, such as environmental pollution from the generated waste liquid and the potential for silicon wafer breakage under stress. Furthermore, the high reaction temperature and long reaction time can lead to poor separation results.

[0005] Pyrolysis utilizes high temperatures to disrupt the structure of the EVA film, accelerating its softening and decomposition, reducing its adhesiveness, and achieving separation. When the temperature exceeds the glass transition temperature of EVA, the material transitions from a glassy state to a highly elastic state. With further increases in temperature, the chemical bonds in the polymer backbone break, triggering chain degradation. Studies by Dias et al. found that pyrolysis of broken photovoltaic modules at 500℃ under a nitrogen atmosphere for 0.5-3 hours successfully removed >99% of the polymer. While pyrolysis offers high EVA separation rates and significant economic benefits, it involves high pyrolysis temperatures and long pyrolysis times, resulting in high energy consumption and potentially damaging the integrity of silicon solar cells. During thermal decomposition, EVA releases gases and expands, applying uneven thermal stress to the silicon wafers, easily causing wafer breakage, and the resulting waste gas leads to secondary pollution. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects in the above-mentioned background technology and provide a method for treating EVA film of decommissioned photovoltaic modules by low-temperature chemical method.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for treating EVA film of decommissioned photovoltaic modules using a low-temperature chemical process includes the following steps: (1) Disassemble the retired photovoltaic modules and cut them into small samples; (2) Pre-treat the sample after step (1); (3) Place the sample after pretreatment in step (2) in a mixed solution of γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol, 2-methylimidazolium and polydimethylsiloxane, and immerse it at low temperature to make the EVA film swell, reduce the adhesion between the EVA film and the battery cell, and achieve the separation of the EVA film and the battery cell.

[0008] In the above-mentioned method for treating the EVA film of decommissioned photovoltaic modules by low-temperature chemical treatment, preferably, in step (3), the amount of γ-valerol is 12-20 mL, the amount of D-limonene is 8-15 mL, the amount of polyethylene glycol is 5-12 mL, the amount of anhydrous ethanol is 8-15 mL, the amount of polydimethylsiloxane is 0.5-1.5 mL, and the amount of 2-methylimidazole is 0.5-1.0 g.

[0009] In the above-mentioned method of treating the EVA film of decommissioned photovoltaic modules by low-temperature chemical treatment, preferably, in step (3), the temperature of the low-temperature soaking is 25-75℃ and the soaking time is 0.5-1.5h.

[0010] In the above-mentioned method of treating the EVA film of retired photovoltaic modules by low temperature chemical method, preferably, in step (3), the mixed solution is magnetically stirred during the soaking process, and the stirring speed is 500-1000 rpm.

[0011] In the above-mentioned method of treating the EVA film of retired photovoltaic modules by low-temperature chemical treatment, preferably, in step (2), the pretreatment refers to soaking the sample in citric acid solution.

[0012] In the above-mentioned low-temperature chemical treatment method for EVA film of decommissioned photovoltaic modules, preferably, the concentration of the citric acid solution is 1-2 mol / L, the soaking temperature is 25-75℃, and the soaking time is 10-30 min.

[0013] The main inventive mechanisms of this application include: the carboxyl group of citric acid forms a stable complex with aluminum ions, reducing metal contamination and weakening the EVA-metal interface binding energy, creating favorable conditions for subsequent swelling and separation; the strong polar functional group of γ-valerolactone, the cyclic ester group, matches the polarity of the EVA ester group, and through dipole interaction, the cyclic ester group inserts into the EVA molecular chain, reducing the interchain forces of EVA; the C=O (carbonyl oxygen) contained in the ester group region of the EVA molecular chain has strong electronegativity and can act as a hydrogen bond acceptor; the CH bond adjacent to the ester group has a partially positive charge due to the electron-withdrawing effect of the carbonyl group, and can act as a hydrogen bond donor. EVA molecular chains can form a weak hydrogen bond network, enhancing intermolecular forces. The C=O group of γ-valerolactone is also a hydrogen bond acceptor, while the CH group of EVA can act as a donor. Therefore, γ-valerolactone can compete for the original hydrogen bond sites of EVA, disrupting its hydrogen bond network and weakening the interactions between EVA molecular chains, thus promoting swelling. The nonpolar alkyl chain of D-limonene is compatible with the ethylene segment (nonpolar) of EVA. Due to the solubilizing effect (nonpolar molecules or groups tend to aggregate or adsorb onto other nonpolar surfaces in polar solvents), D-limonene preferentially adsorbs and penetrates into the interior of EVA. After entering EVA, the bulk of D-limonene... The accumulation effect expands its cross-linked network, increasing free volume and lowering the glass transition temperature of EVA, making it more prone to swelling. Simultaneously, the low viscosity of D-limonene reduces the overall viscosity of the mixed solvent, thereby increasing the diffusion coefficient of solvent molecules. This allows polar solvents such as γ-valerol to diffuse more easily into the ester group region (polar region) of EVA, forming a synergistic "polar-nonpolar" mechanism with γ-valerol during EVA swelling. The ether bonds of polyethylene glycol insert into EVA segments, and their lone pair electrons can form dipole interactions with the C=O groups of the EVA ester groups, weakening the polar attraction between EVA molecular chains. The methylene groups of polyethylene glycol interact with the E... The ethylene segments of VA are bound by van der Waals forces, promoting solvent penetration. Anhydrous ethanol can regulate polarity balance, and its short-chain structure can adsorb onto the interface between EVA and D-limonene, reducing interfacial tension and promoting the penetration of D-limonene into the non-polar region of EVA. 2-Methylimidazole binds to the carbonyl carbon of the EVA ester bond through the lone pair electrons of the nitrogen atom in the imidazole ring, forming a tetrahedral intermediate. Water molecules provide protons, causing the intermediate to decompose into carboxylic acid and methanol, thus efficiently catalyzing the hydrolysis of ester bonds in the swollen EVA network. In addition, polydimethylsiloxane migrates to the silicon wafer interface to form a molecular lubricating layer, reducing interfacial energy and sharply decreasing adhesion. The solvents work synergistically, through the combined effects of "polar swelling-network expansion-catalytic chain scission-interfacial viscosity reduction," to complete the dissociation of the EVA film in a short time at 25-75℃, which is beneficial for the separation and recycling of solar cells and photovoltaic glass.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, retired photovoltaic modules are first pretreated in citric acid solution, and then soaked in a mixed solution of γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol, 2-methylimidazolium and polydimethylsiloxane. By utilizing the synergistic effect of each solvent, through the synergistic effect of "polar swelling-network expansion-catalytic chain breaking-interfacial viscosity reduction", the EVA film is dissociated in a short time at 25-75℃, which is conducive to the separation and recycling of battery cells and photovoltaic glass.

[0015] (2) In the process of processing the EVA film of retired photovoltaic modules, the present invention uses a lower soaking temperature, which is only 25-75℃, compared with the traditional method of 80-120℃. Compared with the thermal decomposition method (generally 300-700℃), the temperature is significantly reduced, energy consumption is reduced, and environmental protection requirements are met. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram of the low-temperature chemical treatment method for EVA film of decommissioned photovoltaic modules provided in Embodiment 1 of the present invention.

[0018] Figure 2 This is the front view of the photovoltaic module sample obtained after removing the aluminum frame and wiring board, peeling off the photovoltaic glass and back sheet, and cutting it into 2cm×2cm pieces in Embodiment 1 of the present invention. Figure 3 This is the reverse side of the photovoltaic module sample obtained after removing the aluminum frame and wiring board, peeling off the photovoltaic glass and back sheet, and cutting it into 2cm×2cm pieces in Embodiment 1 of the present invention.

[0019] Figure 4 This is a sample image obtained after processing in Example 1 of the present invention.

[0020] Figure 5 This is a sample image obtained after processing in Example 2 of the present invention.

[0021] Figure 6 This is a sample image obtained after processing in Example 3 of the present invention.

[0022] Figure 7 This is a sample image obtained after processing Comparative Example 1 of the present invention.

[0023] Figure 8 This is a sample image obtained after processing in Comparative Example 2 of this invention.

[0024] Figure 9 This is a sample image obtained after processing in Comparative Example 3 of this invention. Detailed Implementation

[0025] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0026] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0027] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0028] The decommissioned photovoltaic modules processed in the following examples and comparative examples are from the same batch of decommissioned photovoltaic modules, provided by Changsha Research Institute of Mining and Metallurgy.

[0029] Example 1: A method for treating EVA film of decommissioned photovoltaic modules using a low-temperature chemical process according to the present invention is shown in the process flow diagram below. Figure 1 As shown, it includes the following steps: (1) Remove the aluminum frame and junction box from the retired photovoltaic module, peel off the photovoltaic glass and backsheet, and cut it into samples with a size of 2cm×2cm; the front photo of the sample is as follows. Figure 1 As shown, the white transparent solid on the surface is residual photovoltaic glass; the reverse side of the sample is shown in the image. Figure 3 As shown, the gray part is the EVA film contaminated with aluminum; (2) Immerse the sample after step (1) in a citric acid solution with a concentration of 1 mol / L and soak at 25°C for 20 min; (3) The sample after step (2) was immersed in a mixed solution containing γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol and 2-methylimidazole for water bath soaking. The water bath temperature was 25℃, the magnetic rotor stirring speed was 500 rpm, and the soaking time was 1.5h. The mixed solution containing γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol, 2-methylimidazole and polydimethylsiloxane was prepared by the following method: 20 mL of γ-valerol, 15 mL of D-limonene, 12 mL of polyethylene glycol, 15 mL of anhydrous ethanol and 1.5 mL of polydimethylsiloxane were weighed, mixed and stirred evenly, and finally 0.8 g of 2-methylimidazole was weighed and stirred to dissolve. (4) After the soaking treatment, the solution was filtered to obtain the separated silicon solar cells and EVA film. The separation results are as follows: Figure 4 As shown.

[0030] Example 2: A method for treating EVA film of decommissioned photovoltaic modules using a low-temperature chemical process according to the present invention includes the following steps: (1) Remove the aluminum frame and junction box from the retired photovoltaic module, peel off the photovoltaic glass and back sheet, and cut it into samples with a size of 2cm×2cm; (2) Immerse the sample after step (1) in a citric acid solution with a concentration of 1 mol / L and pretreat it at 50°C for 20 min; (3) The sample after step (2) was immersed in a mixed solution containing γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol, 2-methylimidazole and polydimethylsiloxane for water bath soaking. The water bath temperature was 30℃, the magnetic rotor stirring speed was 500 rpm, and the soaking time was 1 h. The mixed solution containing γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol and 2-methylimidazole was prepared by the following method: 20 mL of γ-valerol, 15 mL of D-limonene, 12 mL of polyethylene glycol, 15 mL of anhydrous ethanol and 1.5 mL of polydimethylsiloxane were weighed, mixed and stirred evenly, and finally 1.0 g of 2-methylimidazole was weighed and stirred to dissolve. (4) After the soaking treatment, the solution was filtered to obtain the separated silicon solar cells and EVA film. The separation results are as follows: Figure 5 As shown, the EVA film is basically separated from the silicon solar cell.

[0031] Example 3: A method for treating EVA film of decommissioned photovoltaic modules using a low-temperature chemical process according to the present invention includes the following steps: (1) Remove the aluminum frame and junction box from the retired photovoltaic module, peel off the photovoltaic glass and back sheet, and cut it into samples with a size of 2cm×2cm; (2) Immerse the sample after step (1) in a citric acid solution with a concentration of 1 mol / L and pretreat it at 75°C for 20 min; (3) The sample after step (2) was immersed in a mixed solution containing γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol, 2-methylimidazole and polydimethylsiloxane for water bath soaking. The water bath temperature was 75℃, the magnetic rotor stirring speed was 500 rpm, and the soaking time was 0.5 h. The mixed solution containing γ-valerol, D-limonene, polyethylene glycol, anhydrous ethanol and 2-methylimidazole was prepared by the following method: 20 mL of γ-valerol, 15 mL of D-limonene, 12 mL of polyethylene glycol, 15 mL of anhydrous ethanol and 1.5 mL of polydimethylsiloxane were weighed, mixed and stirred evenly, and finally 1.0 g of 2-methylimidazole was weighed and stirred to dissolve. (4) After the soaking treatment, the solution was filtered to obtain the separated silicon solar cells and EVA film. The separation results are as follows: Figure 6 As shown, the EVA film is completely separated from the silicon solar cell.

[0032] Comparative Example 1: The only difference between this comparative example and Example 1 is the choice of mixed solution in step (3). The difference between the mixed solution in this comparative example and Example 1 is the absence of D-limonene in the mixed solvent. The separation effect is as follows: Figure 7 As shown, the sample only swelled slightly, and the EVA film did not separate.

[0033] Comparative Example 2: The only difference between this comparative example and Example 1 is the choice of the mixed solution in step (3). The difference between the mixed solution in this comparative example and Example 1 is the absence of γ-valerolactone in the mixed solvent. The separation effect is as follows: Figure 8 As shown, the sample only swelled slightly, and the EVA film did not separate.

[0034] Comparative Example 3: The only difference between this comparative example and Example 1 is the choice of the mixed solution in step (3). The difference between the mixed solution in this comparative example and Example 1 is the absence of polydimethylsiloxane in the mixed solvent. The separation effect is as follows: Figure 9 As shown, the sample only swelled slightly, and the EVA film did not separate.

[0035] As can be seen from the comparison of the above examples and comparative examples, when the mixed solution of γ-valerolactone, D-limonene, polyethylene glycol, anhydrous ethanol, 2-methylimidazole and polydimethylsiloxane of the present invention is used to treat retired photovoltaic module samples, the solvents work together to achieve the separation of EVA film in a short time at 25-75°C.

Claims

1. A method for treating EVA adhesive film of decommissioned photovoltaic modules by low-temperature chemical method, characterized in that, The method comprises the following steps: (1) disassembling and cutting the retired photovoltaic module into small samples; (2) pretreating the sample after step (1); (3) placing the sample after the pretreatment in step (2) in a mixed solution of gamma-valerolactone, D-limonene, polyethylene glycol, anhydrous ethanol, 2-methylimidazole and polydimethylsiloxane, and soaking at low temperature to make the EVA adhesive film swell, reduce the adhesion between the EVA adhesive film and the battery piece, and realize the separation of the EVA adhesive film and the battery piece.

2. The method for treating EVA film of decommissioned photovoltaic module by low-temperature chemical method according to claim 1, characterized in that, In step (3), the amount of gamma-valerolactone is 12-20 mL, the amount of D-limonene is 8-15 mL, the amount of polyethylene glycol is 5-12 mL, the amount of anhydrous ethanol is 8-15 mL, the amount of polydimethylsiloxane is 0.5-1.5 mL, and the amount of 2-methylimidazole is 0.5-1.0 g.

3. The method for treating EVA film of decommissioned photovoltaic module by low-temperature chemical method according to claim 1, characterized in that, In step (3), the temperature of the low-temperature soaking is 25-75℃, and the soaking time is 0.5-1.5 h.

4. The method for treating EVA film of decommissioned photovoltaic module by low-temperature chemical method according to claim 1, characterized in that, In step (3), the mixed solution is subjected to magnetic stirring during the soaking process, and the stirring speed is 500-1000 rpm.

5. The method for treating EVA film of decommissioned photovoltaic module by low-temperature chemical method according to claim 1, characterized in that, In step (2), the pretreatment refers to soaking treatment of the sample with a citric acid solution.

6. The method for treating EVA film of decommissioned photovoltaic module by low-temperature chemical method according to claim 5, characterized in that, The concentration of the citric acid solution is 1-2 mol / L, the soaking temperature is 25-75℃, and the soaking time is 10-30 min.

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