posted on 2023-01-10, 16:04authored byHan K. Chau, Quy P. Nguyen, Ana Carolina Jerdy, Dai-Phat Bui, Lance L. Lobban, Bin Wang, Steven P. Crossley
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.