Circular economy of expanded polystyrene waste: Techno-economic and life cycle assessments of chemical recycling processes

Abstract

The global plastic waste crisis demands urgent attention due to its harmful impact on ecosystems. Chemical recycling of plastic waste offers a perspective aligned with circular economy principles and carbon neutrality, utilizing plastic waste as a carbon source to replace fossil-based feedstock. This study conducts techno-economic and life cycle assessments, based on experimental data, to demonstrate the chemical recycling of expanded polystyrene (EPS) waste through depolymerization to produce recycled styrene monomer (r-SM). Process simulations were carried out to obtain mass and energy balances and equipment sizes. The simulation outcomes served as inputs for economic and life cycle assessments. Three cases were evaluated: Case 1) low-grade r-SM (>95 % purity) without using a solvent for dissolution, Case 2) low-grade r-SM (>95 % purity) by using THF as a solvent for dissolution, and Case 3) a high-grade r-SM (>99 % purity) without using a solvent. Case 3 offers the most economically viable option, with a minimum product selling price (MPSP) of $1.06/kg, comparable to virgin styrene monomer (v-SM). Sensitivity analysis identified EPS waste costs as the biggest influence on MPSP. The life cycle assessment (LCA) showed that all cases have a lower Global Warming Potential (GWP) than the production of v-SM, with Case 1 achieving an 89 % GWP reduction. Energy consumption is identified as the primary contributor to GWP results. These findings reveal further research prospects to explore in the pursuit of implementing EPS waste recycling.