(400at) Efficient Separation Processes for Styrene Monomer Recovery from Waste Polystyrene Pyrolysis Oil

This study addresses the energy-efficient purification of styrene monomer (SM) from waste polystyrene (PS) pyrolysis oil, which contains toluene (TOL), ethylbenzene (EB), SM, cumene (CM), alpha-methyl styrene (AMS) in ascending order of boiling point, using vacuum distillation, emphasizing the avoidance of azeotrope formation and polymerization risks at high temperatures. We proposed separation processes using three distillation columns to purify TOL, EB, SM, and CM/AMS. Three main configurations were examined: (1) a direct-direct sequence that removes lighter components sequentially, (2) a direct-indirect sequence that separates light and heavy components first before separating EB and SM, and (3) a dividing wall column (DWC) design that integrates two columns into one. Simulation results in Aspen Plus showed that the direct-indirect sequence reduced total utility consumption by 30% and the dividing wall column further lowered energy requirements by 40% compared to the direct-direct baseline. However, the capital cost of DWC was higher due to the large column vessel, making the total annual cost (TAC) similar to that of the direct-indirect sequence at small capacities. At higher feed capacities (over 2,000 kg/h), the DWC’s superior operating cost savings became more pronounced, leading to a greater economic advantage. A corresponding decrease in CO₂ emissions was also observed in energy-efficient designs, particularly in the DWC configuration. These findings suggest that the direct-indirect sequence is more economical at lower scales, whereas a DWC is favored in larger-scale processes where reduced operating costs can offset the higher capital investment. Overall, this work provides practical separation processes to recover high-purity SM from pyrolysis oil derived from waste PS, offering substantial energy savings, reduced carbon footprint, and enhanced circular-economy potential for PS recycling.