Effect of chloride salts and microwave 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), but 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 also in mild conditions. In particular, we recently contributed using Lewis/Brønsted acidic DESs (LBDESs), obtaining good results with iron(III) chloride and sulfonic acids. However, the choice of weaker acids such as acetic acid is more cost-effective and sustainable, with 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, reaching quantitative conversion and high yield in TA in 10 minutes and 180 °C.