Role of Water on Zeolite-Catalyzed Dehydration of Polyalcohols and EVOH Polymer

Selective dehydration of polyalcohols over zeolites containing Brønsted acids is a promising approach to purify and recycle multilayer polymer films consisting of non-polar polymers such as polyethylene and polar polymers like ethylene–vinyl alcohol copolymer. In addition, polar aprotic solvents can be utilized to improve the diffusion of polymer molecules to access the active sites in solid catalysts. Here, we reveal the positive role of water on dehydration of ethylene–vinyl alcohol polymer over a solid acid catalyst in the presence of γ-valerolactone as the solvent. Through vapor-phase experiments with 2,5-hexanediol as a model compound and theoretical calculations, we reveal that water facilitates dehydration reactions by delocalizing surface-bound protons and allowing dehydration rates to occur even in the presence of solvents that would otherwise inhibit reaction rates. The hydronium ion clusters act as delocalized acid sites, leading to improved surface coverage of the reactant, and consequently enhance dehydration activity in the presence of solvent molecules. This example of co-solvent-induced modulation of environments around active sites could open doors for polymer recycling and upcycling.