Glycolysis optimisation of different complex PET waste with recovery and reuse of ethylene glycol

The poly(ethylene terephthalate) is a thermoplastic polyester, non-degradable in the environment that due to the huge amount of waste generated and accumulated in landfills, chemical recycling through glycolysis is considered the most successful method for polymer recycling. In this work, glycolysis of virgin PET and different PET waste (highly coloured PET, multilayer PET and municipal sorting waste PET) is carried out using excess ethylene glycol in the presence of zinc acetate as catalyst. Glycolysis temperature, glycolysis time, amount of catalyst and amount of solvent are important factors affecting the glycolysis of PET waste. A Taguchi orthogonal array L9, 34, is applied to study the main interactions between these factors to optimise the yield. The process results in a good yield (79–88%) to the monomer, bis(2-hydroxyethyl) terephthalate (BHET), with optimum conditions. One of the inconvenient of the glycolysis process is the excessive use of EG, so the recovery and reuse of the remaining EG from the process are studied in order to optimise the glycolysis of PET waste making it economical and environmentally friendly. BHET is characterised by FTIR and DSC techniques confirming that is a valid and pure monomer.