Glycolytic depolymerization of PET waste in a microwave reactor

Abstract

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.

Polymer Degradation Under Microwave Irradiation

“…Degradation of PET in a microwave reactor was also examined by the group of Achilias and collaborators using four different chemical reagents [29][30][31][32]. Initially, hydrolytic depolymerization in an alkaline solution was investigated [29].…”

“…Subsequently, glycolysis of PET with DEG was investigated in a microwave reactor [30]. The main degradation product, analyzed and identified by Fourier transform infrared (FTIR) spectroscopy, was an oligoester diol.…”

Recycling of poly(ethylene terephthalate) waste through methanolic pyrolysis in a microwave reactor

“…Research efforts have thus lead to numerous applications in material processing techniques that have resulted in shorter reaction times and greater convenience. Microwave assisted recycling of PET has been also the subject of some investigations [26][27][28][29][30][31][32][33][34][35] reviewed in Ref. [34].…”

“…In this study, continuing our previous work on microwave assisted recycling of PET [33][34][35], depolymerization of PET waste, taken from common soft drink bottles, was subjected to methanolysis with methanol and zinc acetate catalyst in a lab-scale microwave reactor in order to study the effect of microwave irradiation on the reaction kinetics. The reaction was carried out in a sealed microwave reactor in which temperature was controlled and continuously recorded together with pressure.…”

Kinetics of the hydrolytic depolymerization of poly(ethylene terephthalate) under microwave irradiation

“…The facts that the polymer depolymerizations could be accelerated by microwave irradiation, and that the depolymerization mechanism was a combination of regular and random chain scissioning have generally been accepted. [7][8][9][10][11] In terms of the applications of microwave irradiation, some of the kinetic processes of PET depolymerization have been studied, such as glycolytic and aminolytic depolymerizations of PET in a microwave reactor, which were conducted by Achilias et al 12,13 The activation energy (E a ) of the depolymerization reactions was evaluated by a simple kinetic model. Moreover, Achilias et al 14 reported the hydrolytic depolymerization of PET in an alkaline solution with a phase-transfer catalyst under microwave irradiation, and the E a was also evaluated.…”