(293f) Screening Catalysts for Hydrothermal Recycling of Post-Consumer PET Waste

Polyethylene Terephthalate (PET) is a commodity polyester produced in fiber- (85%) and bottle-grades, which mainly differ in the average molecular weight. While mechanical recycling is a well-established process, the US recycles only 28% of its post-consumer PET. To increase the recycling rate for PET and improve upcycling processes, we explore the hydrothermal chemical recycling of PET waste into its monomers or oligomers. Our study focusses on the hydrolysis of post-consumer PET waste to terephthalic acid (TPA). We examined hydrolysis over a wide range of temperatures (190-270 ºC), pressures (1-35 MPa), acidity (0.67-5.6 pH), shear stress and with different potential homogeneous and heterogeneous catalysts (e.g., sulfuric acid, acetic acid, ionic liquids, zeolites, and CO₂). We obtained PET conversions up to 100% and TPA yields up to 80% from hydrolysis at 200 ºC for 2 h. At these conditions, the effect of water as vapor, saturated liquid, and compressed liquid was studied, along with the effect of added CO₂. Experimental results revealed that PET conversion is improved with CO₂ addition, which is consistent with the added CO₂ increasing the acidity of the hydrothermal medium and altering the morphology of the polymer swelling particle. This presentation will outline the results from this experimental study and offer insights into the catalysts and conditions that are best for hydrothermal recycling of post-consumer PET.