Pyrolysis behavior of multi-component photovoltaic modules waste: A coupled STA-FTIR-MCC and modeling approach

Abstract

With the first million tons of photovoltaics (PV) modules approaching decommissioning, efficient recycling is crucial. Pyrolysis has proven to be an effective method for PV modules recycling. This work details a methodology to characterize the pyrolysis behavior of multi-component PV modules. The mass loss, heat flow, and gaseous products evolution of pyrolyzing PV modules were systematically investigated through simultaneous thermal analysis (STA) and Fourier transform infrared spectroscopy. It was found that the pyrolysis process of PV modules proceeded through four stages, including the melting of polyethylene terephthalate (PET) component, initial thermal decomposition of ethylene-vinyl acetate (EVA) component, progressive pyrolysis of EVA coupled with PET chain scission, and pyrolysis of residual organic matter. The gaseous products were primarily composed of CO₂, H₂O, and carboxylic acids along with their derivatives. The heat released from the combustion of volatile products was measured using microscale combustion calorimetry (MCC). Through the inverse modeling of STA-MCC results using coupled ThermaKin2Ds modeling framework and Hill-climbing optimization method, the pyrolysis reaction kinetics, heat of reactions, heat capacities of condensed-phase components, and heat of combustion of gaseous products were determined. Subsequently, the pyrolysis model of PV modules was developed, accurately reproducing the experimental pyrolysis reaction rate, heat flow, and heat release rate, with total mass loss deviations < 3 %, total integral heat flow deviations < 10 %, and total heat released deviations < 10 %. This model was further testified against experimental data acquired under varied heating conditions. This work can provide guidance for optimizing pyrolysis recycling of PV modules waste.