Fast hydrolysis for chemical recycling of polyethylene terephthalate (PET)

Abstract

Chemical recycling of post-consumer polyethylene terephthalate (PET) provides a path toward circular production and use of this material. This article reports the effect of reaction severity and PET/water mass ratio on fast hydrolysis of PET, which can lead to complete depolymerization to monomers in tens of seconds. Rapid heating (5-10 °C s−1) during fast hydrolysis can promote hydrolytic PET depolymerization. This non-isothermal, non-catalytic reaction provided recovery of terephthalic acid (TPA), one of PET's monomers, exceeding 90% for reaction times as short as 75-95 seconds. More severe conditions (higher temperature and longer time) increased TPA decomposition while lower severities reduced PET depolymerization. Initial PET/water mass ratios of 1/10 or 1/8 gave the highest TPA yields and lowest values for the environmental energy impact metric associated with the depolymerization reaction. We determined an environmental energy impact factor of 436 ± 66 °C min, which is the lowest to date and surpasses the performance of isothermal PET hydrolysis, whether performed in neutral water (as is done here) or under acid catalysis. Byproducts, including phthalic acid, isophthalic acid, bis(2-hydroxyethyl)terephthalate, and benzoic acid, were also observed during the process.