Process optimization and techno-economic analysis of polyethylene terephthalate (PET) depolymerization in a non-aqueous alkaline environment for monomer recovery and reuse

This study presents a comprehensive investigation into optimizing polyethylene terephthalate (PET) depolymerization under alkaline conditions using response surface methodology (RSM). The critical process parameters studied were temperature, NaOH concentration, and reaction time. In the first phase, the combined effect of ozone pretreatment and ultrasound assistance on depolymerization efficiency was examined, revealing a positive direct correlation. In the second phase, RSM optimization with ozone pretreatment with ultrasonication conditions achieved 83.58% terephthalic acid (TPA) recovery and a total monomer recovery of 92.14%. Notably, applying the RSM-optimized conditions to virgin PET samples without pretreatment yielded comparable results thus highlighting the importance of statistical optimization tools. Techno-economic analysis using RSM optimized conditions for plant capacities ranging from 2.4 to 72 MT/day identified a minimum selling price of $1,533 USD/MT for TPA at the largest making it competitive with virgin TPA and other depolymerization methods. Sensitivity analysis highlighted feedstock and equipment costs as primary economic drivers, revealing opportunities for cost optimization.