Pyrolysis mechanism and recycling strategy of end-of-life photovoltaic modules based on the experiment and the density functional theory

Recent advancements in renewable energy have enabled a reduction of fossil fuel usage. However, the so-called energy waste, such as end-of-life (EoL) photovoltaic (PV) modules, has become a simultaneous emerging issue in the field of solid waste management. Debonding of ethylene-vinyl-acetate (EVA) copolymer is critical for recycling EoL PV modules. The separation of organic substances may be done effectively using pyrolysis technology. Therefore, in this work we investigated the pyrolysis characteristic and mechanism of EVA. Based on TG, TG-FTIR, and Py-GC/MS, the pyrolysis products and pyrolysis characteristics of EVA were examined. Activation energies and reaction mechanisms were determined through iso-conversional model-free and model-fitting methods. Combined with density functional theory (DFT) calculations, the pyrolysis mechanism of EVA was discussed. Our research shows that the pyrolysis technology can almost completely decompose EVA without residue and the EVA pyrolysis can be divided into two stages. Combined with DFT calculation, it was found that in the stage Ⅰ, acetoxy was removed to generate acetic acid, and in the stage Ⅱ, the main chain of EVA was broken to generate olefins. The recycling strategy based on two-step pyrolysis of Eol PV modules was accordingly proposed.