Advanced Sustainable Process Integration and Comprehensive Techno-Economic Evaluation of Polystyrene Waste Upcycling into Methanol as a Clean Alternative Fuel

This study presents an integrated and sustainable approach for the valorization of polystyrene (PS) plastic waste into methanol, contributing to circular carbon utilization and waste-to-fuel strategies. Two simulation models were developed in Aspen plus. In Case 1, PS is converted to syngas through steam gasification, followed by its conversion into methanol. In Case 2, a steam methane reforming (SMR) unit is integrated with the gasification unit, using the heat from the gasifier-derived syngas to boost hydrogen production and overall methanol yield. This integration boosts the hydrogen-to-carbon ratio, doubling methanol production in Case 2 compared to Case 1. In terms of energy performance, Case 2 exhibits a process efficiency of 81% and exergy efficiency of 73%, both significantly higher than 48% and 60%, compared to Case 1. From an economic standpoint, Case 2 requires greater capital investment and annual operational expenditure, yet it proves to be more cost-effective in the long run compared to Case 1 due to the higher methanol production. The methanol production cost is reduced by 50%, from $1.001/kg in Case 1 to $0.505/kg in Case 2. These improvements are driven by increased throughput and process integration that supports sustainable and circular carbon management.