The Depolymerization And Catalytic Depolymerization Of Polyethylene Terephthalate In Supercritical And Subcritical Methanol And Cosolvent

Depolymerizing polymers into monomers, dimers, and useful hydrocarbon materials or liquid fuels in supercritical fluids has become a new approach for polymer recycling. The paper introduced the basic characteristics of supercritical fluids and its application on chemical recycling of waste plastics. Recent studies on recycling of polyethylene terephthalate (PET), especially on chemical recycling, were summarized.Depolymerization of Polyethylene terephthalate(PET) in supercritical and subcritical methanol and cosolvent was carried out in a stirred batch autoclave at different conditions such as the weight ratio of methanol to PET, reaction temperature, reaction time and the dosage of water and so on. The depolymerization products were examined by gas chromatography mass spectrometry(GC-MS), gas chromatography(GC), FT-IR spectrometry, respectively. The main reaction products were dimethyl terephthalate (DMT) and ethylene glycol(EG). The yield of DMT in the products ascended with the increase of reaction temperature and the reaction time. It was found that the optimized conditions of the reaction were the weight ratio of methanol to PET of 8, temperature of 280℃, reaction time of 30 min and the water of dosage of 25%. By kinetic analysis, the activation energy of the PET depolymerizaion in supercritical and subcritical methanol and cosolvent was 101.61 kJ·mol^-1.Catalytic Depolymerization of PET in supercritical and subcritical methanol and cosolvent was also carried out at different temperature range and at reaction time respectively. The main reaction products were examined by GC-MS, GC, and FT-IR respectively. The main reaction products were DMT and EG The yield of DMT in the products ascended with the increase of reaction temperature and the reaction time. It was found that the optimized conditions of the reaction were the weight ratio of methanol to PET of 8, temperature of 260℃, reaction time of 15 min and the weight of catalyst of 1 g/160 mL. By kinetic analysis, the activation energy of the PET catalytic depolymerizaion in supercritical and subcritical methanol and cosolvent was 85.07 kJ·mol^-1. Obviously, it meaned that the addition of catalyst was beneficial to the catalytic depolymerization of PET in supercritical and subcritical methanol and cosolvent.