METAL/METAL OXIDE CATALYSTS FOR UPCYCLING MULTISTREAM PLASTICS

Abstract

Multilayered plastic films, for example, containing polyethylene (PE) and either poly(vinyl alcohol-co-ethylene) (EVOH) or polyvinyl chloride (PVC), are of great importance for packaging applications due to the excellent environmental barrier properties of EVOH and PVC. However, their presence creates significant challenges for subsequent recycling because traditional recycling processes of melting and thermal degradation leave behind small domains of immiscible phases that reduce material value and divert waste to landfills. To address these challenges, this work develops catalytic strategies for selective deoxygenation, dechlorination, and upcycling of multilayered films with lower energy and material demands. This research uses functionalized TiO2 nanotubes owing to their low cost, high surface area, and tunable surface properties. Functionalization with Pd generated catalysts exhibiting excellent activity and selectivity for C–O and C-Cl bond scissions and hydrogenation. Studies reveal that Lewis-acid sites generated on the TiO2 surface, coupled with hydrogen dissociation on the metal particles and unique sites at the metal support interface, enhanced hydrodeoxygenation and hydrodechlorination rates at atmospheric pressure. Then, a biphasic solvent system with the interfacially active Pd/TiO2 catalysts was introduced to facilitate the continuous recovery of the product into the non-polar phase by washing it from the catalyst surface to yield a stream compatible with PE. This approach offers great potential for selective reactions and separation of plastic waste. In addition, the results also highlight the influence of surface defects and interfacial sites on hydrodeoxygenation and hydrodechlorination mechanisms supported by kinetic studies. A techno-economic evaluation simulates an industrial-scale recycling process for the PE product with the minimum selling price below the market price, indicating promise for the economical recycling of multilayered films. The mechanistic insights and process-level innovations enable selective removal of heteroatoms while preserving the polymer's hydrocarbon backbone. These complementary catalytic strategies establish a foundation for multifunctional catalysts and present a pathway toward scalable and economical recycling of multilayer plastics.