Synthesis of 1,3-Diethylimidazolium Acetate Ionic Liquid by Silver Salt Metathesis and Its Application in the Glycolysis of Waste Polyethylene Terephthalate (PET) to Produce Bis(hydroxyethyl) Terephthalate (BHET)

Abstract

A silver salt metathesis route for the synthesis of 1,3-diethylimidazolium acetate ionic liquid, [Deim][OAc], is presented and compared with the traditional method. The metathesis reaction between [Deim]Br and silver acetate produces a colorless [Deim][OAc] ionic liquid with improved purity compared to the traditional method, which yields a brown product containing organic impurities. Although the silver salt metathesis route provided a pure ionic liquid with the absence of organic impurity, it contains residual bromide and silver. The presence of trace amounts of Ag+ and Br– ions in the ionic liquid can be a potent catalyst poison and could lower catalytic activity. The structure of the synthesized ionic liquid was confirmed by FTIR, 1H NMR, and 13C NMR spectroscopy. The catalytic activity of [Deim][OAc] ionic liquid and its aluminum and iron acetate complexes was evaluated in the glycolysis of waste polyethylene terephthalate (PET) to produce bis(hydroxyethyl) terephthalate (BHET). The ionic liquid synthesized by the silver salt metathesis route achieved 95% PET conversion and 24% BHET yield, whereas the conventionally synthesized ionic liquid provided 73% PET conversion and 10% BHET yield under identical conditions. The improved catalytic performance is attributed to the higher purity of the ionic liquid and the absence of colored organic impurities produced during the conventional synthesis route. The iron complex, [Deim][Fe(OAc)3] exhibited enhanced catalytic activity, yielding 20% BHET, outperforming the aluminum complex, [Deim][Al(CH3CO2)2(OH)2] which provided 10% BHET.