Effect of chloride salts and microwaves on polyethylene terephthalate (PET) hydrolysis by iron chloride/acetic acid Lewis/Brønsted acidic deep eutectic solvent

Abstract

Chemical recycling offers a convenient solution for the disposal of plastic items made of polyethylene terephthalate (PET); however, there is still much room for improvement in terms of integration into the current waste treatment cycles. Recently, deep eutectic solvents (DESs) have exhibited interesting properties in PET glycolysis and hydrolysis, in some cases under mild conditions. In particular, we recently reported good results with Lewis/Brønsted acidic DESs (LBDESs) containing iron(III) chloride and sulfonic acids. However, the choice of weaker acids, such as acetic acid, is more cost effective and sustainable, with an associated reduced risk of corrosion and improved safety. In this study, we demonstrate that a simple post-reaction procedure significantly enhances the yield of terephthalic acid (TA) using FeCl₃·6H₂O/acetic acid (molar ratio 1 : 1) LBDES from 4% (literature value) to 54% under the same experimental conditions. Furthermore, we investigate the effect of chloride salts as additives and microwave irradiation on the reaction, achieving quantitative conversion and a high yield of TA in 10 minutes at 180 °C.