Towards a lumped approach for solid plastic waste gasification: Polystyrene pyrolysis

Abstract

In a circular economy perspective, solid plastic wastes (SPW) are a valuable source of chemicals, energy vectors and fuels. Chemical recycling through pyrolysis, gasification, and partial oxidation are promising alternatives to incineration and landfill disposal, allowing efficient exploitation of SPW. Modelling the combustion and gasification both at the particle and reactor scale requires first the definition of a suitable condensed phase pyrolysis mechanisms for each constituent. This work proposes a semi-detailed kinetic model for polystyrene (PS) pyrolysis. Following our recent work on polyethylene (PE) and polypropylene (PP), the model is based on the functional group approach firstly developed for polyvinylchloride (PVC) and biomass pyrolysis aiming at a consistent description of a wide palette of SPW components. The proposed approach retains an accurate description of low molecular weight species while representing high molecular weight species through their chemical functionalities only. The resulting liquid-phase model accounts for 34 species and 440 reactions and is attached to this paper together with the complementary gas-phase model. Model validation by a comprehensive comparison with experimental data proves its capability of predicting both mass loss and product distribution profiles with comparable accuracy to more expensive detailed models from the literature. The proposed model, together with other available subsets in the CRECK kinetic framework (i.e., biomass, PVC, PE, PP), offers a powerful tool for investigating key aspects in thermochemical recycling technologies thus supporting optimal reactor design. These aspects include mixture interactions (SPW and SPW/biomass mixtures), secondary cracking, catalytic, and gasification reactions.