Integrated neutral-hydrolysis recycling of mixed poly(ethylene terephthalate) and poly(butylene terephthalate) waste: System-level design, techno-economic, and environmental evaluation

Abstract

Mixed poly(ethylene terephthalate)/poly(butylene terephthalate) (PET/PBT) waste represents an increasing fraction of heterogeneous polyester streams with limited compatibility with mechanical recycling within municipal material recovery facilities. This study evaluates a continuous neutral-hydrolysis process for a nominal 70/30 PET/PBT feed using Aspen Plus simulation, techno-economic analysis, and cradle-to-gate life-cycle assessment (LCA). The framework integrates literature-based reaction kinetics with simulated separation, economic, and environmental inventories to assess the system-level implications of mixed PET/PBT neutral hydrolysis. At 270 °C, 60 bar, and 30 min residence time, the simulation predicted 80.75 kg/h terephthalic acid (TPA) in the recovered solid cake from 100 kg/h mixed PET/PBT feed, corresponding to 97.1 % of the stoichiometric maximum. The recovered cake contained 96.45 wt% TPA prior to product polishing. Thermal demand is concentrated in hydrolysis and downstream separation, with the base-case simulation used to quantify external utility requirements. A separate pinch-based utility-displacement analysis indicates that recovering roughly 40 % of the available hot-cold overlap could reduce external utility demand; this value represents a thermodynamic integration target, not demonstrated heat-exchanger-network performance. With glycol coproduct credits included, the estimated minimum selling price was $3.66/kg TPA, while LCA estimated a greenhouse-gas intensity of 2.68 kg CO 2 -eq/kg TPA. Within the modeled system boundary, neutral hydrolysis may complement mechanical recycling for PET/PBT-rich waste streams. Pilot-scale validation with representative mixed PET/PBT feedstocks and assessment of contaminant partitioning, solids handling, and recycle-water stability remain essential next steps.