Conventional and MW assisted PET glycolysis promoted by titanium based catalyst

Polyethylene terephthalate (PET) flakes from postconsumer bottles were depolymerized in the presence of ethylene glycol (EG) and titanium (IV) phosphate (TiP) as catalyst. Glycolysis was carried out both as conventional heated and under microwave (MW) irradiation. For the former method the reaction conditions were: molar ratio PET repeating unit to EG-1:2.77, without catalyst and with different amounts of TiP at 200 °C. The MW assisted process was performed under similar experimental conditions applying a power range 400–600 W. It was optimizated with respect to the catalyst concentration and yeild of bis(2-hydroxyethyl) terephthalate (BHET). The experiments showed that the optimal result was achieved in a MW reactor using 0.2 wt% TiP (based on PET weight) at 450 W for 45 min reaction time. The degradation product contained the monomer BHET (61.7%), dimers, trimers and low amounts oligomers and EG. The yield of BHET achieved was 87%. The glycolysis products were characterized by a combination of analytical techniques – chromatographic, spectroscopic and thermal methods. The comparison of both approaches showed the advantages of MW assisted degradation in view of efficiency and time saving.