New catalysts for the upgrading of ethanol to butanol biofuels

• Main Author: Lee, Jason
• Published: University of Bristol 2015
• Subjects: 662.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682364

We propose an alternative method for the sustainable transformation of ethanol to longer-chained alcohols, specifically n-butanol, for use as an advanced biofuel efficient enough to provide an alternative' drop-in' replacement for petrol fuels. Particular attention was made to discovering new catalysts to achieve this transformation, addressing the drawbacks suffered by the first generation catalyst devised within our research group. The first draw back of the first generation catalyst was identified as having intolerance to water build-up during the course of the reaction. This was addressed (chapters 2 and 3) firstly through the screening of water-soluble ruthenium catalysts based on dipyridyl-containing ligands. Optimisation experiments revealed that ruthenium(II) complexes in the presence of N-heterocyclic bidentate ligands and a hydroxide base co-catalyst can successfully couple ethanol to allow unprecedented yields and selectivity to n-butanol to be obtained. These complexes have also shown to remain catalytically active under aqueous conditions, making them ideal candidates for industrial applications. An extensive study into the homogeneity of the catalytic system is reported, indicating that, what may have been anticipated to be homogeneous may in fact possess characteristics of both homogeneous and heterogeneous catalysis. The instability of the first generation catalysts highlighted the second drawback whereby decomposition of the catalysts was often observed due to the harsh reaction conditions. Reported here (chapter 4) is the discovery of a more stable ruthenium-diphosphine catalyst which has shown to be the most active catalyst, to date, toward the coupling of ethanol to higher a1cohols, with unprecedented yields and selectivity to n-butanol achieved. Catalyst loading and catalyst recycling studies were investigated, indicating that catalysts of this type have the greatest potential for the creation of future biofuels. Ruthenium complexes in the presence of higher denticity ligands were studied, highlighting a switch in reaction product from n-butanol to ethyl acetate and 2-butanol.