Alcoholysis of polyethylene terephthalate to produce dioctyl terephthalate using choline chloride-based deep eutectic solvents as efficient catalysts

Abstract

Dioctyl terephthalate (DOTP) is a new kind of green and non-toxic plasticizer. The traditional process to prepare DOTP is costly and complicated, thus it is very necessary to find an efficient and environmentally-friendly way to obtain DOTP. In this study, we prepared DOTP from the alcoholysis of polyethylene terephthalate (PET) by using 2-ethyl-1-hexanol (2-EH) as the solvent, and used choline chloride-based deep eutectic solvents (ChCl-based DESs) as the catalysts due to their cheapness, low toxicity and ease of preparation. Under the optimized conditions (ChCl/Zn(Ac)₂ 1 : 1, 5 wt%, 180 °C, 60 min, PET : 2-EH 1 : 5 molar ratio), the conversion of PET and the yield of DOTP were 100% and 84.7%, respectively. Furthermore, the possible mechanism was proposed through density functional theory (DFT) calculations and experimental results. It revealed that the hydrogen bonds (H-bonds) formed between 2-EH and DESs played a key role in accelerating the degradation process. Furthermore, the kinetics of the reaction was also investigated, and the results indicated that the alcoholysis of PET is a first-order reaction with an activation energy of 95.05 kJ mol⁻¹. This work confirmed that ChCl-based DESs are favorable for the degradation of PET to prepare DOTP under mild conditions, which can also be used for other polymer degradation strategies.