Depolimerization of Pet Bottle Wastes to Produce High-value Bhet Monomer Using Ethylenglycol

The main topic of this paper is the recycling of plastic wastes, focused on the chemical recycling process of polyethylene terephthalate (PET) into bis-hydroxyethyl terephtalate monomer (BHET). Although the most commonly recycling process are in-plant and mechanical methods, the benefits and opportunities offered by chemical recycling make it as one of the most interesting process to develop. In addition, consume of bottle grade PET is reaching high levels, due to its increasing applications in many industrial sectors. PET chemical recycling includes the recovery of high-value raw materials, bottle-grade, feasible from a technical, economical and environmental point of view. Although chemical recycling offers several possibilities: (methanolysis, hydrolysis, ammonolysis, aminolysis, etc...) glycolysis was selected for the present study. The glycolysis reaction was carried out into a 1L three necked flask with reflux, a thermocouple and a N2 line, using ethylenglycol (EG) as solvent. The temperature was 197 oC at the beginning of the reaction, increasing after 2,5 hours up to 201 oC. Neither stirring nor external pressure were applied. PET:EG ratio was studied to get an overview of the reaction behaviour and yield results taking into account the solvent excess influence. Ratios EG:PET (w:w) from 1,5:1 to 5:1 were assayed. The presence of Zinc Acetate was varied to optimise the response of the system, with ZnAc2:PET ratios (w:w) from 0,1:100 to 1,5:100. Depending on the operational conditions and the reactive ratios selected, yields nearby 85 % of BHET were obtained. The process has been up-scale to a pilot plant. In this case, stirring and external pressure have been also taken into account, increasing the number of parameters to control and optimise, which allows a more complete control of the process. Monomer and oligomers were characterized using DSC, TGA, FTIR and GC-MS techniques.