A comparative study of mechanical crushing and pyrolysis techniques for separation and recovery of discarded polycrystalline silicon photovoltaic modules

Abstract

With the rapid growth of the photovoltaic (PV) industry, efficient recovery and utilization of discarded polycrystalline silicon PV modules have attracted increasing attention. This study compares the application of mechanical crushing and pyrolysis techniques in the recovery of PV modules. The results indicate that while mechanical crushing can preliminarily disintegrate materials, its effectiveness in separating valuable materials such as silver and aluminum is limited, particularly for particles larger than 1 mm. In contrast, pyrolysis techniques demonstrate outstanding performance in removing organic matter and separating silicon wafers and glass, notably enhancing the recovery rate of large glass particles. However, the brittleness of silicon wafers presents a challenge during pyrolysis. Furthermore, the pyrolysis mechanisms of ethylene-vinyl acetate (EVA) film and backsheet materials are thoroughly discussed. The pyrolysis process of EVA film involves two stages: firstly, the preferential decomposition of acetyl oxygens on ester side chains, followed by further pyrolysis decomposition of the main chain and side chains to generate alkanes. Pyrolysis of polyethylene terephthalate (PET) begins with the generation of methyl and benzoyl radicals, while polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF) pyrolysis initiates with the detachment of head-group units, followed by sequential detachment of chain units. Given the advantages of pyrolysis techniques, this study recommends them as the preferred method for PV module recovery.