PNNL

Abstract

In this study we investigated the conversion of aqueous methyl ethyl ketone (MEK) to olefin fuel precursors over ZnxZryOz mixed oxide catalysts. Experiments were carried out in aqueous media as MEK is intended to be produced from the dehydration of 2,3-butanediol in fermentation broth which is highly diluted in water. We demonstrated that ZnxZryOz catalysts are highly effective for converting aqueous MEK to C4-C5 olefins. High selectivity to olefins equal to 85% was reached at 92% per pass conversion when under H2 atmosphere. Catalyst stability in aqueous media was demonstrated for 60 hours’ time on stream, highlighting the potential for upgrading 2,3-butanediol contained in fermentation broth without the need for energy-intensive water separation. Increased concentration of MEK in the feed results in increased activity towards olefin production. However, water inhibits catalyst deactivation from coking. A mechanistic investigation revealed the impact of the reaction environment (inert or reducing atmosphere) on the reaction pathways. In an inert environment, the mechanism involves consecutive aldol condensation of MEK and 3-pentanone intermediate. Under reducing conditions two reaction pathways compete with each other as MEK hydrogenation to butenes occurs concurrently with the aldol condensation/decomposition.