(379b) In Situ Product-Removal for the Enzymatic Biodegradation of Poly(ethylene terephthalate) (PET) Via a Membrane Reactor

Increasing plastic production rates continue to vastly outpace recycling and recovery efforts, making plastic waste pollution a pressing issue. Enzyme-depolymerization of PET has drawn significant attention due to its low energy cost and being an environmentally friendly alternative to other recycling methods. Researchers have strived to improve the enzymes used in enzymatic depolymerization, but few studies have examined the possibility of improving depolymerization by using in-situ biodegradation techniques that will limit enzyme inhibition while maintaining a favorable pH for the enzymes.

In this work, post-consumer recycled PET (RPET) flakes, that were pretreated via reactive extrusion, are enzymatically depolymerized with leaf branch compost cutinase (LCC) in a control and a membrane experimental setup at 55 °C. Both reactions are carried out with 10 mg/ml of RPET, 3 ml of potassium phosphate buffer pH 8 (PP8), and LCC. Tubes are used for the control reactions while the Slide-A-Lyzer G2 Dialysis Cassettes of 7000 MWCO, are used as membrane reactors and placed in a beaker containing PP8 for in-situ product removal.

HPLC analyzes depicted the production of terephthalic acid (TPA), mono(2-hydroxyethyl) terephthalic acid, and bis(2-hydroxyethyl)-TPA. The membrane reactions depicted twice the product yields obtained in the control reactions. The pH in the control experiments dropped from 8 to 6.48 after 5 days while that of the membrane experiments with a dilution ratio (DR) of 67 remained relatively stable, with no base addition. Our analysis suggest that high amounts of acid and base would be required for subsequent TPA crystallization and solution neutralization, respectively.

The results suggest the production of higher quantities of TPA to enable the production of PET of the same mechanical qualities, compared to the existing thermochemical recycling methods. Our analysis also depicts optimal DR of 1 to 4 to guarantee the usage of small amounts of acid/base when recovering TPA.