Assessing PET chemical recycling via neutral hydrolysis

Abstract

Chemical recycling of PET waste is a promising approach for the recovery of high-quality monomers that aims at improving the circularity of plastic production. Solvolysis technologies are being developed and include hydrolysis with acid/base catalysts or enzymes to promote depolymerization reactions into PET constituent monomers, terephthalic acid (TPA) and ethylene glycol (EG). However, the use of electricity, steam and organic solvents/chemicals has been identified as main factor affecting the economic and environmental performance of these technologies. This paper studies an alternative neutral hydrothermal process (nHTP), which involves hydrolysis at high temperatures and pressures without the use of catalysts, looking into the impact of water recycling and EG recovery in terms of costs and GHG emissions. The results reveal that recovering EG pays off the higher CAPEX and OPEX and yields a significant reduction in wastewater treatment costs, resulting in a TPA production cost of 1–1.4 EUR/kg and a carbon footprint of 1–1.7 kg CO₂e/kg TPA. Although the process demands less electricity and steam compared to other hydrolysis technologies, fuel requirements for high temperature heat might limit its potential in the absence of sustainable heat options. Future studies are recommended to assess the utilization of lower-cost feedstocks (mixed waste and textiles), valorization of the solid by-product, and system integration possibilities to identify synergies between technologies in a broader chemical recycling context.