Process modeling and assessment of waste polystyrene pyrolysis: Comparing catalytic and thermal methods

The increasing use of plastics and growing societal demand for climate change mitigation have intensified efforts to recover monomers from polymers, such as polystyrene (PS). However, significant research gaps persist in the development of scalable processes and their commercial viability. This study suggests an optimal process design and operating conditions for PS depolymerization through a comprehensive design and assessment framework. A standardized process model was developed, integrating simulations and assessments performed using Aspen Plus, coupled with MATLAB, to assess economic and environmental feasibility. This evaluation was conducted by varying styrene monomer (SM) selectivity (40-80%) and light impurity ratio among total impurities (1-99%). Results revealed that catalytic pyrolysis, particularly using a base catalyst, demonstrates superior economic performance over thermal pyrolysis and other catalyst types. These findings were experimentally validated. The optimal process conditions, identified through techno-economic and life cycle assessment, were achieved with a K2O/SiO2 catalyst, which yielded 80.2% SM selectivity and 45% light impurity ratio. Furthermore, a comparison between thermal and catalytic pyrolysis under identical conditions demonstrated that the base catalytic pyrolysis proved more economical, with production costs of $1,437/ton SM compared to $2,431/ton SM for thermal pyrolysis. Environmentally, base catalytic pyrolysis showed a low global warming potential of 1.34 tonCO2eq/ ton SM, compared to 2.15 tonCO2eq/ton SM for thermal pyrolysis. This research provides a critical foundation for the industrial feasibility of PS depolymerization by identifying optimal catalyst conditions and operating parameters.