Definition of the Catalyst Family for the Production of Green Diesel by Hydrotreatment in Situ of Triglycerides

Abstract

As an alternative to the use of conventional biodiesel, a good number of researches have been carried out searching for a more similar green diesel to fossil diesel. The most promising route at the commercial level to produce it is by hydrotreatment of oleaginous biomass, which breaks large molecules (such as triglycerides) through the catalytic action of hydrogen and removes oxygen atoms (deoxygenation) and other elements that are not carbon and hydrogen. However, using hydrogen gas at high pressure to solubilise it in the liquid phase makes the process lose sustainability, since at least 90 % of the hydrogen comes from non-renewable sources. One of the possible solutions to this issue is the use of a biodonor that generates the hydrogen required in the process and transfers it catalytically to the substrate that is aimed to be hydrotreated. As additional advantages, a reduction in the operating pressure and improved catalyst stability can be achieved. The following work aims to find the most appropriate catalyst for the process of deoxygenation of oleaginous biomass with hydrogen generation in situ, considering that it must promote the generation of hydrogen by catalytic transfer and at the same time it should favour the deoxygenation of triglycerides (it must be bifunctional). By means of a multicriteria decision algorithm (Macbeth method), a group of catalysts is selected from five families (transition metal sulphides, metal carbides, nitrides and phosphides, reduced noble metals, and reduced transition metals) with five criteria (preparation-acquisition, bifunctionality-selectivity, cost-availability, hydrogen dissociation and stability-useful life). Then, within the selected family, possible catalysts are chosen according to the review carried out considering physicochemical aspects of the interaction of the molecules with the surface. For this process, the most promising catalysts are noble metals, mainly Pd/C.