Microwave assisted glycolysis of poly(ethylene terephthalate) catalyzed by 1-butyl-3-methylimidazolium bromide ionic liquid

The combination of ionic liquid (IL) associated with microwave energy may have some potential application in the chemical recycling of poly (ethylene terephthalate). In this processes, glycolysis of waste poly (ethylene terephthalate) recovered from bottled water containers were thermally depolymerized with solvent ethylene glycol (EG) in the presence of 1-butyl-3-methyl imidazolium bromide ([bmim]Br) as catalyst (IL) under microwave condition. It was found that the glycolysis products consist of bis (2-hydroxyethyl) terephthalate (BHET) monomer that separated from the catalyst IL in pure crystalline form. The conversion of PET reach up to 100% and the yield of BHET reached 64% (wt %). The optimum performance was achieved by the use of 1-butyl-3-methyl imidazolium bromide as a catalyst, microwave irradiations temperature (170-175°C) and reaction time 1.75-2 h. The main glycolysis products were analyzed by ¹H NMR, ¹³C NMR, LC-MS, FTIR, DSC, and TGA. When compared to conventional heating methods, microwave irradiation during glycolysis of PET resulted in short reaction time and more control over the temperature. This has allowed substantial saving in energy and processing cost. In addition, a more efficient, environmental-friendly, and economically feasible chemical recycling of waste PET was achieved in a significantly reduced reaction time.