Glycolytic depolymerization of PET waste in a microwave reactor

摘要

Recycling of waste PET bottles was examined using glycolytic depolymerization with diethylene glycol, under microwave irradiation. The objective was to investigate if depolymerization using microwave energy could provide the same product distribution, while carried out in milder experimental conditions and/or shorter reaction times, resulting, thus besides to polymer recycling, in substantial energy saving. The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled. Experiments under constant temperature or microwave power were carried out at several time intervals. The main glycolysis product was analyzed and identified by FTIR measurements. The average molecular weight of the PET residues was found to decrease with the percentage of PET degradation. In the experiments carried out under constant microwave power, complete depolymerization was observed at irradiation powers greater than 150 W for 2 min, or 100 W for 5 min. In the constant temperature experiments, it was clear that at temperatures below 150°C no degradation occurs, whereas complete depolymerization takes place at temperatures greater than or equal to 180°C for 5 min. These results when compared to the conventional heating, where more than 4 h are needed for complete with PET degradation, confirm the importance of the microwave power technique and the substantial energy saving achieved. Finally, from a simple kinetic model the activation energy of the reaction was evaluated.