(206b) Closing the Loop on Polystyrene Using Chemical Recycling: Thermodynamic, Economic, and Emissions Analysis

Polystyrene is used in food packaging and shipping where its mechanical and thermal properties are difficult to replicate in cost effective competitive materials. Unfortunately, less than 5% of polystyrene is currently recycled due to the many challenges associated with collecting, sorting, and especially processing the end-of-life material. Interestingly and unlike other major polymers, polystyrene unzips during pyrolysis to produce roughly 60% yield of the styrene monomer. This monomer is contaminated with other 1-ring side products, including toluene, ethyl benzene, and a-methyl styrene. Removing these impurities provides an opportunity to recover monomer-grade styrene that can be repolymerized to close the loop on polystyrene use. In this study, we analyzed a reaction-separation process to determine the thermodynamic, economic, and emissions performance. Figure 1 is a schematic. Thermodynamically, the process can produce monomer-grade styrene (>99% purity) with less than 10 MJ/kg energy input for many relevant scenarios, as shown in Figure 2. Economically, we find that realistic prices of waste polystyrene, ranging from -60 to +60 USD per ton result in positive investment opportunities, as measured by the net present value (NPV) and as summarized in Figure 3. Combining the thermodynamic analysis with the economic analysis permits estimation of a CO2 abatement cost. Using capital expenses as the resource input and comparing with pyrolysis to fuels as competing approach to avoid landfilling results in an abatement cost of about $1.50 per ton of averted CO₂.