Magnetic ionic liquid catalyst functionalized with antimony (III) bromide for effective glycolysis of polyethylene terephthalate

Abstract

In a previous study, we demonstrated the efficient depolymerization of polyethylene terephthalate (PET) through glycolysis using antimony (III) oxide, a commonly used catalyst in PET synthesis. In the present research, we introduce a novel approach involving the synthesis of a magnetic bifunctional ionic liquid, Fe3O4@PMIM.SbBr4, containing only 2.2 wt% of antimony. The aim is to reduce the required antimony dosage for the reaction and enable its facile recovery and reuse. By employing this catalyst in PET chemical recycling through glycolysis to generate bis (2-hydroxyethyl) terephthalate (BHET) monomer, we achieved 100% PET conversion with a 96.4% yield and selectivity for BHET. This outcome was obtained using a catalyst loading of 6.0 wt% at 200 °C and 0.6 bar in a high-pressure reactor. We explored the impact of catalyst loading on BHET yield and conducted a comparative assessment of the Fe3O4@PMIM.SbBr4 catalyst against antimony (III) bromide, and another synthesized unsupported antimony-containing ionic liquid. Our results revealed the superior catalytic activity of the magnetic ionic liquid catalyst in PET glycolysis. The utilization of this catalyst offers promising potential for PET glycolysis due to its effortless separation using an external magnet, ability to produce highly pure BHET, and recyclability for repetitive use.