(227b) Process Advances and Kinetics Models for Hydrolytic Depolymerization of Post-Consumer Polyethylene Terephthalate (PET)

Chemical recycling of waste plastics provides a conceptual path to recover and reuse small molecules via depolymerization or decomposition of the plastics. Polyethylene terephthalate (PET) is used in large volume to make single-use packages for the consumer market (e.g., bottled water). PET is synthesized via condensation reactions, so it can be depolymerized via hydrolysis. This presentation explores advanced process concepts for the hydrothermal chemical recycling of PET waste into one of its monomers, terephthalic acid (TPA), by using microwave reactors and fast hydrolysis.

Microwave methods can reduce reaction times compared with conventional thermal heating processes. We compared TPA yields from microwave-assisted PET hydrolysis with conventional thermal heating with and without potential catalysts (zeolite HY, acetic acid, zinc iodide, and TPA). TPA yields with microwave hydrolysis (70%) with added TPA exceeded that from conventional thermal heating (41%) at 200 ËšC for 1 h. The TPA yield from hydrolysis with zeolite HY was negligible at 200 ËšC for 1 h with conventional thermal heating, but with microwave heating, it was 25%.

Fast hydrolysis involves rapid non-isothermal heating (e.g., 10 °C/sec) for a short time (e.g., 60 sec), which promotes plastic depolymerization while limiting byproduct formation. We optimized fast hydrolysis by measuring TPA and oligomer yields at different heating rates (3 to 12 ˚C/sec), reaction times (15 sec to 3 min), and PET/water mass ratios (1/4-1/10). TPA yields above 80% were obtained in less than one minute, with 100% PET conversion.

Finally, we developed a reaction network and kinetic model to describe the catalytic and non-catalytic hydrolysis of PET. The model can describe isothermal and fast hydrolysis and provides predictions for PET disappearance and formation of the various reaction products.