A Low-Cost, Metal-Free Choline Chloride–Acetamide Deep Eutectic Solvent for Sustainable and Recyclable PET Aminolysis to BHETA

Abstract

Poly(ethylene terephthalate) (PET) waste remains a major challenge in polymer recycling, demanding green and economical upcycling routes. In the present work, a biocompatible and metal-free deep eutectic solvent (DES) based on choline chloride and acetamide (1:2 mol ratio) was developed as an efficient medium for PET aminolysis using ethanolamine. Under mild conditions (140 °C, 1 h), the optimized system achieved 87% yield of bis(2-hydroxyethyl) terephthalamide (BHETA) with excellent selectivity and reproducibility. Kinetic analysis followed the Arrhenius relationship with an apparent activation energy of 57 kJ mol −1 , consistent with literature values for catalytic aminolysis. DES was recycled for five consecutive runs with negligible loss of activity and minimal viscosity or spectral change, highlighting its operational stability. Comprehensive characterization of the product by FTIR, ¹H NMR, XRD, TGA/DSC, and HPLC confirmed high purity. Compared with conventional catalysts and other DES systems (ChCl:urea, ChCl:ZnCl 2 ), the present formulation offers superior yield, simplicity, and safety while eliminating metal residues. Preliminary green-metric evaluation indicates a lower E-factor and energy footprint relative to glycolysis or hydrolysis routes. This current research demonstrated a practical and sustainable method for PET valorization through aminolysis using a low-cost choline chloride–acetamide DES.