Process innovations to enable viable enzymatic poly(ethylene terephthalate) recycling

Enzymatic depolymerization of poly(ethylene terephthalate) (PET) has received considerable attention for closed-loop polyester recycling. Despite significant progress, current approaches for enzymatic PET recycling face challenges to achieve commercial viability with lower environmental impacts compared to virgin polyester manufacturing.. Here we present multiple process innovations for enzymatic PET recycling that, taken together, enable both economic and environmental feasibility. We show that substrate amorphization through extrusion and quenching is energy-efficient and enables complete PET hydrolysis, with quantitative conversion in 50 hours. Using ammonium hydroxide for pH control and thermolysis of the isolated diammonium terephthalate product enables base recycling, eliminates process salt waste, and reduces the acid and base consumption by >99%, leading to a 74% annual operating expense reduction. Fed-batch enzymatic hydrolysis enables increased ethylene glycol (EG) concentration and a 65% reduction in the energy input required for EG recovery via distillation with mechanical vapor recompression. Together, these improvements were modeled in an optimal process that is less expensive than U.S. domestic virgin PET ($1.51/kg vs. $1.87/kg), provides substantial life-cycle impact reductions relative to virgin PET production and previously reported methods, and eliminates key obstacles to the scale-up of this technology.