Advances in the circular economy of polystyrene: A critical review of pyrolysis in pilot-scale systems, distillation, and re-polymerization

The widespread use of plastics in many sectors has resulted in the generation of a significant amount of waste, causing major environmental issues. Polystyrene (PS) is one of the most demanded polymers nowadays. Therefore, a consistent recycling pathway must be established to transition to a circular economy strategy. Pyrolysis of PS can recover styrene monomer (SM) in a liquid fraction that can be used to make new plastics. This replaces the need for fossil-based styrene and creates a circular economy. Although literature on this technology exists at the laboratory scale, advancing it to the pilot scale and beyond is crucial for its near-term deployment. Thus, this review compiles pilot-scale pyrolysis studies of PS and provides the industrial potential of each examined technology. It also emphasizes the need to implement a pyro-oil purification process via distillation, which has been demonstrated to achieve a purity level of over 99 wt% for SM. The potential for producing new PS products with comparable properties to conventional ones using the recovered styrene (r-styrene) in the so-called re-polymerization process is also addressed. Some research gaps, challenges and future perspectives are also outlined. Among others, distillation and re-polimerization on pilot-scales are necessary to be demonstrated to endorse the potential benefits of PS pyrolysis-based recycling. In-depth life cycle assessments (LCAs) using industrially relevant data are also expected in the future. This comprehensive analysis of the PS circular economy cycle through pyrolysis, distillation and re-polymerization is expected to boost the deployment of industrial-scale plants.