Understanding the important variables to optimize glycolysis of polyethylene terephthalate with lanthanide-containing ionic liquids

Abstract

Glycolysis is a widely studied method for chemical recycling of polyethylene terephthalate (PET). Metal-containing ionic liquids (MILs) are attractive catalysts for the glycolysis of PET, as they have been shown to have high stability and can be easily recycled. While a range of MILs have been studied with varying cations and metal containing anions, there are no conclusive trends for the different variables in MIL catalyst design and how they affect glycolysis of PET. We report the use of lanthanide MILs to identify which catalyst design variables and reaction conditions can be tuned to make the biggest difference in the deconstruction of PET. Mixtures of ionic liquids (ILs) with lanthanide metal salts were found to lead to homogeneous MIL catalysts that are active for the glycolysis of PET. These studies identified that finding a metal salt and IL combination that leads to a cooperative MIL catalyst was more important than the basicity of the IL or metal salt anion itself. Finally, the high performance of MILs with a high ratio of IL to metal salt lowers the loading of metal salts with supply risk, while maintaining the value of MIL over metal-free IL catalysts.