Ethylene Glycol-Guided Enhancement of Bis(2-Hydroxyethyl) Terephthalic Acid as a Primary Product of Enzymatic Poly(Ethylene Terephthalate) Depolymerization.

Recycling of enzymatically depolymerized poly(ethylene terephthalate) (PET) involves polycondensation of bis(2-hydroxy-ethyl) terephthalic acid (BHET)-a degradation product of enzymatic PET hydrolysis. The recycling process is simplified when more BHET is generated by the enzymatic reaction. Here, we report how ethylene glycol (EG) addition can maximize BHET formation using leading PET hydrolases, LCCICCG, and PHL7. EG at any level above 2-5% vol/vol was found to decrease the steady-state enzymatic degradation rates while enhancing the relative production of BHET. For LCCICCG, the highest measured BHET levels (product fraction approaching 0.5) were attained at EG levels of ∼27-29% and reaction temperature ∼62.5°C. EG shortened the enzymatic reaction lag-phase and lowered the lag-phase increase with PET crystallinity. EG works by perturbing the adsorption, including nonproductive adsorption, of the enzymes to the PET surface, which manifests as an apparent change in substrate affinity (increases the invKm in interfacial kinetics modeling) and directs the enzyme more to the liquid phase.