(173e) Functionalized TiO2 Nanotubes for Selective Dehydration and Hydrogenation of Polyols

Selective catalytic conversion of polar polymers, such as EVOH, in multicomponent polymer resins is an appealing strategy for processing of mixed plastics waste streams and multilayered films. However, the dehydration of polyols is often subject to rapid sequential reactions such as C-C bond formation of resulting olefins and ketones, decreasing catalyst lifetimes and reaction efficiency. This work focuses on studying the selective dehydration and hydrogenation of 2,5-hexanediol (a small surrogate for polyols), and functionally similar real polymer stream ethylene vinyl alcohol (EVOH) over Pd-TiO₂ nanotubes. The primary focus of the proposed work is on accessing fundamental understanding necessary to tailor the balance between the metal and acid functional groups to enable selective deoxygenation while maintaining catalyst activity.

The conversion for 2,5-hexanediol was carried out in three different solvents as a function of temperature reactant concentration. The products and their concentrations for the 2,5-hexanediol conversion were determined by GC-MS and GC-FID, respectively. In comparison, the conversion of ethylene vinyl alcohol was conducted in pure melts as well as in the presence of solvents described above at varying catalyst ratios, temperatures, and polymer pellet sizes. The products of reactions in the crucible and lab-scale extruder were monitored by TGA, MS, FTIR, SEM, and EDX. The use of γ-valerolactone at 150 °C was shown to be sufficient to promote selective conversion while minimizing reactions of the solvent itself. For the pure EVOH, we utilized these results to identify conditions that maximize EVOH decomposition rate without substantial formation of new C-C bonds. We summarize the intrinsic rate constants in both the model compound blends and real polymers, which are used to identify conditions (temperature and hydrogen pressure) necessary for the selective conversion of polyols to deoxygenated products in multicomponent blends.