Chemical recycling of monolayer PET tray waste by alkaline hydrolysis

Abstract

The high demand for recycled polyethylene terephthalate (rPET) driven by an increase in environmental awareness, the application of more restrictive environmental legislations, together with the large increase in the generation of post-consumer PET plastic waste, has resulted in an urgent need for efficient recycling processes. In this work, alkaline hydrolysis is presented as a promising chemical recycling alternative for PET tray waste. PET depolymerization reactions were carried out under mild conditions (80–100 ºC and atmospheric pressure) using tributylhexadecylphosphonium bromide quaternary salt (TBHDPB) as catalyst. Several operating variables were studied based on PET conversion and terephthalic acid (TPA) yield criteria: (i) catalyst mass ratio of TBHDPB to PET (0–0.2); (ii) particle size (0.5–10 mm); (iii) stirring rate (350–700 rpm); and, (iv) temperature (80–100 °C). A good compromise between PET conversion (99.9%) and TPA yield (93.5%) was established after 4 h of reaction, under the following operating conditions: TBHDPB:PET catalyst ratio, 0.2; 100 °C; particle size, 1–1.4 mm; and, stirring rate, 525 rpm. In addition, the experimental kinetic data correctly fits to the proposed shrinking core model. Activation energy values of 60 and 57.4 kJ mol-1 were established for the non-catalyzed and catalyzed reactions, respectively, which implies that TBHDPB catalyst does not apparently modify the reaction mechanism.