Chemical recycling of polyethylene terephthalate (PET) to monomers: Mathematical modeling of the transesterification reaction of bis(2-hydroxyethyl) terephthalate to dimethyl terephthalate

The accumulation of plastic waste in the environment is making recycling a compelling issue, particularly for polyethylene terephthalate (PET), used in products with a short shelf-life. An appealing route to chemical recycling of PET is glycolysis, leading to bis(2-hydroxyethyl) terephthalate (BHET). Its subsequent transesterification with methanol to dimethyl terephthalate (DMT) is crucial for the recovery of polymer-grade monomers. To favor the industrial applicability of this process, this work investigates the influence of three main parameters, i.e. the methanol to ethylene glycol molar ratio, the solvent to oligomers molar ratio and the mass fraction of the catalyst, on the transesterification of BHET to DMT. A kinetic model has been proposed, and the reaction rates evaluated by comparison with the experimental data. The model was used to predict the performances of the process in a wide range of operating conditions, in order to establish the optimal ones for high yield to DMT.