Enhanced selective glycerol oxidation in multiphase structured reactors

Gold catalysis has potential for multiphase oxidation using molecular oxygen but hitherto has been evaluated only in batch autoclaves. The use of continuous flow structured reactors for the oxidation of glycerol under mild conditions using a gold/carbon catalyst is demonstrated. Both monolith and meso-scale structured downflow slurry bubble column designs lead to a significant enhancement in the reaction rate over autoclave studies which is an order of magnitude greater for the gold/carbon coated monolith, and two orders of magnitude for the meso-scale structured downflow slurry bubble column reactor. A change in the reaction products is observed between structured monolith reactor and meso-structured slurry bubble column reactor. The monolith and autoclave data show very high selectivity to glyceric acid, whereas the thin channel slurry bubble column yields approximately equal quantities of dihydroxyacetone and glyceric acid under similar conditions. Since the same batch of catalyst is used for both the autoclave and the meso-scale structured downflow slurry bubble column reactor, the difference in selectivity cannot be attributed to a particle size effect. The difference in selectivity is attributed to enhanced interaction between bubbles and particles from structuring gas–liquid–solid reacting flows in thin channels or capillaries.