Robust downstream technologies in polystyrene waste pyrolysis:Design and prospective life-cycle assessment of pyrolysis oil reintegration pathways

Chemical recycling of polystyrene waste to virgin styrene by fluidized bed pyrolysis and purification of pyrolysis oil in a distillation sequence is investigated. It is shown experimentally that pre-treatment of expanded polystyrene (EPS) waste by hot washing does not improve styrene yields and thus styrene content in the pyrolysis oil, suggesting that no elaborate waste pre-treatment is necessary for polystyrene chemical recycling. Based on experimental results, pyrolysis oils with styrene content from 30 wt.-% to 80 wt.-% are considered in an Aspen Plus® downstream simulation. Process robustness is evaluated in terms of operating parameter sensitivity such as reflux and distillate-to-feed ratio. It is shown that for the purification of highly variable feed compositions trade-offs such as more columns or higher RR must be made. Prospective LCA reveals that chemical recycling is preferable to incineration of polystyrene waste, although to varying degrees depending on critical impurities present in the pyrolysis oil.