Aqueous phase recirculation as a water management strategy and its effect on chemical recycling of poly(ethylene terephthalate) (PET) by neutral hydrothermal processing

Neutral hydrothermal processing is a promising chemical recycling pathway for polyethylene terephthalate waste into its monomers. The process yields a solid and an aqueous product: the solid phase retains about 80 % of the carbon as terephthalic acid, while the aqueous phase contains the remaining 20 %, primarily as ethylene glycol (EG). If untreated, this dilute aqueous stream increases the process water footprint and limits recovery of valuable products. This study explores aqueous phase recirculation as a water management strategy at 250 °C, 280 °C, and 310 °C. Results show that EG and other soluble compounds accumulate during successive recirculation cycles, eventually stabilizing as makeup water dilutes the stream. Importantly, such accumulation does not affect reaction chemistry. Batch experiments extrapolated to continuous operation indicate a 67 % reduction in water consumption and an increase in EG concentration from 1.6 wt% to 4.8 wt%. Thus, aqueous recirculation reduces water use while enhancing EG recovery potential.