Energy-Efficient Design Sequences for the Purification of Styrene Monomer from the Pyrolysis Oil of Waste Polystyrene

This study focuses on the energy-efficient separation process of styrene monomer, avoiding the formation of an azeotrope by using a vacuum distillation, derived from the pyrolysis of waste polystyrene (PS). The direct-indirect sequence, which positions the separation column of ethylbenzene and styrene monomer as the last step, exhibited a 30% reduction in the total utility consumption and a 37% reduction in the total annual cost compared to that of the direct-direct sequence that separates lighter components sequentially. A dividing wall column (DWC) configuration derived from the direct-indirect sequence showed the most significant reduction of 40% in utility consumption. However, when the feed capacity was low, the increased capital cost of DWC resulted in a total annual cost similar to that of the direct-indirect sequence. As the capacity of the entire distillation system increased, the reduction in the total operating cost of the DWC was amplified, indicating the advantages of using the DWC in high product throughputs from both energy and economic perspectives. Therefore, implementing the DWC in large-scale PS recycling processes demonstrates superior performance compared to the conventional distillation process, resulting in a more streamlined process with substantial energy savings and CO2 emissions.