Process development and techno-economic analysis for mechanochemical recycling of poly(ethylene terephthalate)

Chemical recycling of consumer plastics has garnered great attention recently towards achieving circular economy goals. Particularly in the case of PET waste, mechanochemical depolymerization in ball mill reactors has been identified as a very promising technology due to the high conversion rates achieved under mild conditions. While the absence of solvents in the reaction mixture reduces significant separation costs, mechanochemical depolymerization still presents challenges with respect to the efficient separation and purification of monomers. Thus, meticulous experiments, process modeling, and simulations are essential for demonstrating the separation and purification of monomers. In this study, we present the lab-scale separation process flow for the recovery of terephthalic acid (TPA) and ethylene glycol (EG) from mechanochemically depolymerized polyethylene terephthalate (PET). We additionally examine the use recycling of ideal PET powder and commercial samples (e.g., PET fibers, bottles, and food containers) as feedstocks. The process parameters are optimized to achieve 97 %+ of monomer recovery with 99 %+ purity. The complete recovery of EG, and recycling of process water enables a 'zero-liquid discharge' process design. Subsequently, we conduct a techno-economic analysis (TEA) to evaluate the economic potential of the proposed sequence, which resulted in a positive net present value (NPV) for the different scenarios and a minimum selling price (MSP) of $0.99/kg. Finally, we compare the economic potential of mechanochemical recycling of PET to fossil-based production and other recycling methodologies based on economic metrics.