Pre-hydrogenation stage as a strategy to improve the continuous production of a diesel-like biofuel from palm oil

The continuous production of a diesel-like biofuel from palm oil was evaluated by coupling two reactions stages in series, pre-hydrogenation with a Ni/Al2O3 catalyst at 250 °C and LHSV of 2 h−1, followed by deoxygenation with a sulfided Ni–Mo/Al2O3 at 350–380 °C and LHSV of 1.6–3.3 h-1. The purpose of this process configuration was to improve the selectivity because side reactions on the double bonds, such as polymerization, ring formation and aromatization could be avoided. Both reactions were studied at 3 MPa. In the Ni catalyst, all the metal was in its reduced state and in three different types of cluster. The sulfided Ni–Mo catalyst had mainly sulfided MoSx and Ni-MoSx, but also appreciable amounts of reduced metal species, and the sulfided species were stable up to 500 °C. The pre-hydrogenation enabled the use of higher LHSV without losing conversion nor yield and this means that for a fix throughput, less deoxygenation catalyst can be used. The yield was decreased, at all experimental conditions evaluated, when pre-hydrogenation was not done, due to side reactions on the double bonds. The decarboxylation route was predominant (69.3%) followed by the decarbonylation (11.5%) and the hydrodeoxygenation routes (19.2%). The product had properties similar or superior to those of fossil diesel and biodiesel, with the exception of cold flow properties that were worse than those of fossil diesel but very similar to those of biodiesel.