Low Energy Pyrolysis Of Scrapped Photovoltaic Modules Catalyzed By CeO₂ Based On Controllable Swelling Of EVA

The large-scale installation of lifespan-limited photovoltaic（PV）modules means that the wave of scrapped PV modules will come in the near future.As the last step of PV industry,the recycling of PV modules is the ultimate guarantee for realizing the original intention of PV"green"energy.The purpose of recycling PV modules is to reuse valuable resources in the modules to alleviate resource depletion,and recycle heavy metals and organic packaging materials in the modules to avoid environmental pollution.However,the difficulty of recovering resources from PV modules is how to separate the tightly packed PV lamination to expose various resources.（1）In this study,different layers were characterized to understand their characteristics before the lamination separation experiment.The main component of photovoltaic glass is Si O₂,the main component of packaging material EVA is ethylene vinyl acetate copolymer,silver wires and aluminum layers lie on the front and back surfaces of solar cells,respectively,and the backsheet is a blend of PVF and PET.（2）Aiming to the high toxicity of traditional reagents,low efficiency of layer separation In,and over-swelling of EVA in the traditional chemical method,this study screened green,high boiling point and mild swelling agents from the perspective of EVA molecular structure.According to the linear structure of the main chain of EVA,the new swelling agent DMPU(C₆H₁₂N₂O,N,N′-dimethylpropenylurea)was screened based on the principle of"low steric hindrance".According to the ester group in the side chain of EVA molecule,the new swelling agent DBE(C₂₁H₃₆O₁₂,dibasic ester)was selected based on the principle of"similarity of molecular polarity".The effects of the size of PV piece,reaction temperature,solid-liquid ratio,and ultrasonic power on the separation of PV lamination with the two reagents were discussed.The results show that the separation ratio of PV lamination is negatively correlated with the size of PV piece,and positively correlated with the reaction temperature and ultrasonic power during the same period of time.Under the conditions of 140℃and 900 W ultrasonic power,a 2×2 cm PV piece can be separated by new swelling agents within 30 min.At the same time,the effects of the two swelling agents and traditional swelling agents on the separation of different layers were compared.The results show that the two swelling agents will not cause the over-swelling of EVA,which can keep the initial size of solar cells bonded with EVA,and facilitate the subsequent resource recovery.In addition,the mechanism of layer separation with new swelling agents was discussed.The results show that DMPU can destroy the structure of EVA molecule to separate different layers,while DBE can penetrate into the PV lamination gap to reduce the adhesion between different layers to separate the PV lamination.Finally,green,sufficient and reagent-recyclable resource recovery routes were proposed based on the separation of PV lamination using new swelling agents.（3）Aiming to the high energy consumption of direct pyrolysis of PV modules,a method to reduce the energy consumption of PV module pyrolysis was preliminarily explored:CeO₂colloid was prepared with（DMSO+toluene）mixed solvent,in which the PV piece was placed to achieve the adhesion of CeO₂on EVA surface.On the one hand,this method can realize the pre-separation of glass and backsheet in the PV lamination to indirectly reduce the energy consumption of pyrolysis.On the other hand,the catalysis of CeO₂can directly reduce the energy consumption of pyrolysis:EVA attached by CeO₂can achieve 95%weight loss at 440℃,and the temperature for complete decomposition of EVA in oxygen atmosphere decreases from 530℃to510℃.This study innovatively screened new green swelling agents from the perspective of EVA molecular structure,and proposed feasible ways to reduce the energy consumption of direct pyrolysis of PV modules,and initially explored the method to reduce the energy consumption of PV module pyrolysis.This study has important guiding significance on how to separate the lamination of PV modules in an environmentally friendly,efficient,and sufficient way.