A fluorine-restrained pyrolysis process for sustainable photovoltaic modules recycling: two-stage decomposition of EVA and fluorine-containing backsheets

Annually accumulating decommissioned Photovoltaic modules pose severe environmental risks. Pyrolysis is key for resource recovery via disassembly, but conventional 500 °C pyrolysis produces hazardous fluorinated pollution. This study analyzed pyrolysis mechanisms for EVA encapsulant and fluorinated KPK backsheets (PVDF/PET/PVDF) using thermal, IR, and MS techniques. Key findings: (1) EVA pyrolyzes in two stages: dominant deacetylation (300–400 °C), then chain scission (400–500 °C); (2) PVDF decomposition (300–600 °C) releases most fluorine as gaseous pollutants (e.g., 1,2,4-trifluorobenzene, SiF₄), leaving fluoride-containing solid residues; (3) The major KPK weight loss peak (350–500 °C) stems primarily from PET. Exploiting these thermal properties, a novel two-stage, fluorine-controlled process is proposed: First, heat to 350 °C to trigger intense EVA deacetylation and adhesion loss before significant PVDF cracking, allowing non-polluting backsheet removal. Then, raise temperature to 500 °C to fully pyrolyze residual EVA. This clarifies fluoride pathways and offers a practical emission-mitigation solution for thermal dismantling.