Kinetics of PET alcoholysis using deep eutectic solvents for DOTP production

Polyethylene terephthalate (PET) is a common plastic found in everyday items such as clothing and beverage bottles. Unfortunately, PET contributes to plastic pollution due to its limited recyclability through mechanical means. Valuable chemicals can be recovered from waste PET through chemical recycling, which involves reacting PET with suitable chemicals. One notable reaction is between PET and 2-ethyl-1-hexanol (2-EH), resulting in the production of dioctyl terephthalate (DOTP). This compound has gained attention as a green plasticiser in the plastics industry.

Researchers have previously studied the use of deep eutectic solvents (DESs) as sustainable catalysts for the formation of DOTP from PET. However, the kinetics of this reaction have not been thoroughly documented. In this work, the temperature-dependent kinetics of the reaction between PET and 2-EH, catalysed by choline chloride (ChCl)-Zn acetate (ZnAc) DES, to produce DOTP are presented.

The reactions involved PET in powder form (5 g), as well as 2-EH (17 g, 99%), ChCl (≥99%) and anhydrous ZnAc (99.9%). The experiments took place in a 100 mL glass reactor with continuous stirring at atmospheric pressure, and heating was provided by an oil bath. Reaction temperatures ranged from 150 °C to 190 °C. The yield of DOTP was determined by gas chromatography, while PET conversion was determined gravimetrically. The kinetic model developed from this study can predict the maximum yield observed at specific temperatures, aligning with findings from this and previous research.