Selection of Hydrogen Donors for the Production of Renewable Diesel by in Situ Catalytic Deoxygenation of Palm Oil

Abstract

Recently, advanced biofuels have gained interest and importance; as a result, the world production of renewable diesel has quadrupled in the last 5 years. Renewable diesel is a type of biodiesel whose functional properties are similar, or even superior, to those of fossil diesel. It also looks more attractive than conventional biodiesel (FAME), as an option for the partial or complete replacement of liquid fossil fuels in the effort to reduce GHG emissions generated in the transport sector of diesel engines. However, when obtained by hydrotreating, the use of gaseous hydrogen makes the process lose sustainability due to its petrochemical origin (at least 90% comes from the reforming of naphtha) and high risk in its safe handling, besides increasing the costs due to its intensive operating conditions (temperature and pressure). A possible solution to this remarkable disadvantage is the generation of hydrogen in situ, which can be carried out by hydrogenation by catalytic transfer, using a donor, usually a solvent that transfers hydrogen. This is an interesting alternative for the hydrogenation of organic compounds, with substantial advantages over processes that use molecular hydrogen, in addition to moderate process conditions and reduction of the intensive energy consumption. In this sense, it is necessary to evaluate potential donors as renewable sources of hydrogen to obtain renewable diesel from palm oil. To carry out the previous analysis, in this study, a multicriteria decision method (MACBETH) is applied, using criteria such as renewable origin, decomposition products, cost, availability and toxicity, which are considered to select the most appropriate family of organic compounds that act as hydrogen donor: alcohols, polyols, aldehydes, ketones, carboxylic acids, condensed aromatic homologs, amines and alkanes. Results show that alcohols, polyols and carboxylic acids are the most suitable organic families for the generation of hydrogen in situ during hydroprocessing. According to sustainability and taking into account the atomic economy, the availability and biorefinery origin, it was found that the most promising compounds to use as donors in each of these families are the ethanol, glycerine and formic acid, which are then evaluated using thermodynamic analysis.