Deoxygenation of fatty acids to transport fuels over supported metal-organic framework membranes

Abstract

Biofuel production technologies have recently received considerable attention as CO2 emission of biofuels is lower compared to conventional fuels. Typical sources of biofuels are natural oils and fats (e.g., animal fats, plant and seed oils). They are complex mixtures of fatty acid esters. Removing oxygen from fatty acids (deoxygenation) leads to the formation of paraffinic hydrocarbons that can potentially serve as or be converted to direct replacements for traditional petroleum-derived liquid transportation fuels and paraffinic petrochemical feedstocks. Deoxygenation of unsaturated fatty acids can be accomplished via hydrogenation of double bonds and further removal of the carboxyl group by releasing carbon dioxide and producing a paraffinic hydrocarbon (decarboxylation) or by releasing carbon monoxide and producing an olefinic hydrocarbon (decarbonylation). Depending on the catalyst nature and reaction conditions, the hydrodeoxygenation of fatty acids can compete with decarboxylation and/or decarbonylation reaction pathway. The current catalysts for the production of diesel ranged hydrocarbons from triglycerides and fatty acids display limited selectivity towards main hydrocarbon products. In this work, we demonstrate the catalytic deoxygenation and further conversion of fatty acids to paraffins, branched and aromatic hydrocarbons over metal-organic frameworks (MOFs) membranes supported on porous beads. Three catalytic systems were used: Cu-, Al- and Ga-based MOF crystals, Pt/ZIF-67 membrane/zeolite 5A and Ni-MOF/zeolite 5A. The best catalytic performance was achieved by Pt/ZIF-67membrane/zeolite 5A bead catalysts and the selectivity to desired product was ~90%. The work aims at having fundamental understanding on the structure-catalytic relationship of supported MOF membranes catalyst for the deoxygenation of fatty acids into liquid fuels. This research may lead to the development of novel MOF membranes with tailored structural, compositional, and morphological properties to be used as catalysts in a single step process for the conversion of lipid biomass to ‘drop-in’ hydrocarbon transport fuels, like motor and aviation gasoline.