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

Abstract

Enzymatic depolymerization of poly(ethylene terephthalate) (PET) has received considerable attention for closed-loop polyester recycling. However, current approaches for enzymatic PET recycling face challenges to achieve commercial viability with lower environmental impacts compared with virgin polyester manufacturing. Here we present multiple process innovations for enzymatic PET recycling that enable economic and environmental feasibility. We show that substrate amorphization through extrusion and quenching is energy-efficient and enables near-quantitative enzymatic conversion in 50 h. Using ammonium hydroxide for pH control and thermolysis of the isolated diammonium terephthalate salt reduces the acid and base consumption by >99%, lowering annual operating expenses by 74%. Fed-batch processing increased ethylene glycol concentration, leading to a 65% reduction in energy consumption for ethylene glycol recovery. These improvements were modeled in an optimal process, with recycled PET estimated to be US$1.51 kg−1 relative to US domestic virgin PET at US$1.87 kg−1 and eliminating key life cycle obstacles to scale this technology. Enzymatic recycling is an emerging technology to circularize the ubiquitous polyester poly(ethylene terephthalate). Here the authors evaluate and implement multiple process changes to improve the scalability and viability of this recycling technology. Process modeling demonstrates that these changes could enable cost competitiveness and greatly reduce overall life cycle impacts.