Iron-Catalyzed Hydrodecarboxylation of Fatty Acids from Vegetable Oils for Drop-in Biofuel Production
hydrodecarboxylation, fatty acids, iron, drop-in biofuels.
The use of drop-in biofuels represents a promising alternative to conventional fuels, since they are obtained from renewable sources and exhibit physicochemical properties
similar to those of fossil-based fuels. In other words, these biofuels can be applied without major changes to existing infrastructure and may contribute to the reduction of
greenhouse gas emissions. In this context, hydrotreatment is the main process employed for the production of these materials through biomass deoxygenation. However, the
use of high temperatures and the consumption of hydrogen gas make the search for alternative methods desirable. Thus, the present work aimed to develop a
hydrodecarboxylation methodology to promote the deoxygenation of fatty acids under mild conditions, using an iron complex as catalyst and a silane as an alternative
hydrogen source. To achieve this, the fatty acids were converted into redox-active esters, and an optimization study was carried out using lauric acid ester as the model
compound. Different reaction parameters were investigated, and after 75 reactions it was possible to identify the optimal set of reaction conditions, which enabled the
hydrodecarboxylation of the lauric ester at room temperature, under open-air atmosphere, and without specialized reactors. Furthermore, the reaction scope of the method
was extended to convert esters derived from other fatty acids, including a synthetic mixture of these compounds, and the results obtained by GC-FID indicated the
production of renewable hydrocarbons with high selectivity and yields ranging from 32% to 89%. Subsequently, the study of the method in one-pot reactions also proved
satisfactory for the direct conversion of the tested fatty acids, yielding overall conversions comparable to those obtained using isolated starting materials — indicating that
an ester isolation step may be unnecessary. Finally, the developed protocol was applied to fatty acids obtained directly from hydrolyzed vegetable oils, and significant
results were also achieved, with high selectivity and hydrocarbon yields ranging from 15% to 94%.