(265g) Understanding Deoxygenation Reactions to Produce Fungible Transportation Fuels On An Optimized Supported Pt Catalyst

The removal of oxygen from biomass derived molecules is of fundamental interest for the production of fungible transportation fuels. Vegetable oils conversion to ?green diesel? by catalytic deoxygenation using a solid catalyst produces a fungible fuel that has a higher energy density than fatty acid methyl esters produced through transesterification. This work focuses on the deoxygenation of model esters, triglycerides and of natural lauric oils over supported platinum catalysts. A series of catalysts containing Pt, Sn and K supported on SiO2, in combination or separately, were used in liquid phase or gas phase reactions. For liquid phase tests a 300 ml Parr reactor was used at 300 - 350 psi and 300 - 330 oC in batch mode without hydrogen, or in semi-batch mode with hydrogen flow. In the gas phase, methyl hexanoate was converted in a fixed bed tubular reactor in He flow at atmospheric pressure and 380 oC. Products were analyzed by GC, GCMS and GCxGC MS. The catalysts were characterized using CO chemisorption, TPR, TPO, and XPS. For the reactions of triglycerides, the concentration profiles for the batch conversion of dilute solutions of the individual triglycerides, trilaurin and trimyristin, without hydrogen, were similar. A power law fit to the data resulted in the rate equation: . Products include primarily hydrocarbons, C11 or C13, as well as oxygenated intermediates and condensation reaction products. The conversion of mixtures of individual triglycerides or of pure palm kernel oil (PKO) was complicated by transesterification reactions. The conversion of triglycerides in pure PKO, in the presence of hydrogen, was found to fit the equation: . The products included hydrocarbons formed through both decarbonylation/decarboxylation and hydrodeoxygenation as well as fatty acids, ketones and esters. For the conversion of methyl hexanoate, the primary products are mainly hexanoic acid and condensation products (C11 symmetric ketones). The main secondary products are C5 unsaturated hydrocarbons, indicating that in the absence of hydrogen in the feed the main reactions are decarbonylation/decarboxylation of condensation products. The reactions of methyl hexanoate help to elucidate the bifunctional nature of the Pt-Sn-K/SiO2 catalyst. The oxide surface of the catalyst functions to form coupling products that then undergo decarbonylation/decarboxylation reactions to form alkenes on the metal surface. The addition of K to the Pt-Sn catalyst plays a key roll in the distribution and nature of the Sn in the reduced catalyst. In the absence of co-fed hydrogen, the optimal catalyst has a balance of a Pt metal function stabilized by the addition of Sn and an oxide surface with enhanced activity associated with the addition of Sn and K.