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Fatty acids and their derivatives can be converted to renewable and carbon‐neutral fuel‐like hydrocarbons that are entirely fungible with fossil fuels. Typically, these hydrocarbon‐based biofuels are obtained through hydrotreating, a method which has the significant disadvantages of requiring problematic sulfided catalysts and high pressures of hydrogen. In recent years, decarboxylation/decarbonylation has been proposed as an alternative method, as this approach has the advantages of permitting the use of simpler catalysts and requiring less hydrogen than hydrotreating. In this contribution, the deoxygenation of fatty acids and their derivatives to fuel‐like hydrocarbons via decarboxylation/decarbonylation is critically reviewed. The main aspects discussed include the influence of the feed, catalyst, reactor system and reaction conditions on the decarboxylation/decarbonylation reaction, as well as the reaction mechanism and catalyst deactivation/regeneration. Copyright © 2012 Society of Chemical Industry

The deoxygenation of triglycerides (tristearin, triolein and soybean oil) under nitrogen atmosphere was investigated over 20 wt% Ni/C, 5 wt% Pd/C and 1 wt% Pt/C catalysts. Use of the Ni catalyst resulted in near quantitative conversion of the triglyceride in each case, high yields of linear C5 to C17 alkanes and alkenes being obtained. Oxygen was rejected as CO and CO 2 , while small amounts of light alkanes (C1-C4) and H 2 were also formed. 13 C NMR spectroscopic analysis of the liquid product from soybean oil deoxygenation at intermediate reaction times suggested that one pathway for triglyceride deoxygenation involves liberation of fatty acids via C-O bond scission and concomitant H transfer, followed by elimination of CO 2 from the acids in a later step. Compared to Ni, catalysts containing Pd or Pt supported on activated carbon showed lower activity for both triglyceride deoxygenation and for cracking of the fatty acid chains.

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The ability of Cu and Sn to promote the performance of a 20% Ni/Al 2 O 3 catalyst in the deoxygenation of lipids to fuel-like hydrocarbons was investigated using model triglyceride and fatty acid feeds, as well as algal lipids. In the semi-batch deoxygenation of tristearin at 260 °C a pronounced promotional effect was observed, a 20% Ni-5% Cu/Al 2 O 3 catalyst affording both higher conversion (97%) and selectivity to C10-C17 alkanes (99%) in comparison with unpromoted 20% Ni/Al 2 O 3 (27% conversion and 87% selectivity to C10-C17). In the same reaction at 350 °C, a 20% Ni-1% Sn/Al 2 O 3 catalyst afforded the best results, giving yields of C10-C17 and C17 of 97% and 55%, respectively, which contrasts with the corresponding values of 87 and 21% obtained over 20% Ni/Al 2 O 3. Equally encouraging results were obtained in the semi-batch deoxygenation of stearic acid at 300 °C, in which the 20% Ni-5% Cu/Al 2 O 3 catalyst afforded the highest yields of C10-C17 and C17. Experiments were also conducted at 260 °C in a fixed bed reactor using trioleina model unsaturated triglycerideas the feed. While both 20% Ni/Al 2 O 3 and 20% Ni-5% Cu/Al 2 O 3 achieved quantitative yields of diesel-like hydrocarbons at all reaction times sampled, the Cu-promoted catalyst exhibited higher selectivity to longer chain hydrocarbons, a phenomenon which was also observed in experiments involving algal lipids as the feed. Characterization of fresh and spent catalysts indicates that Cu enhances the reducibility of Ni and suppresses both cracking reactions and coke-induced deactivation.

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