(431c) Rapid Hydrothermal Hydrogenation and Decarboxylation of Oleic Acid over Activated Carbon Using Formic Acid As in Situ Source of Hydrogen

We developed and studied a novel approach to rapid converting of fatty acids into n-alkanes in a continuous flow process. Heptadecane and other fuel range hydrocarbons were produced from oleic acid under sub- and supercritical water conditions in a tubular reactor packed with granulated activated charcoal (the weight hourly space velocity was 4 h^-1) at the temperatures from 350 to 400 °C and pressure of 3500 psi (24 MPa). 1% v/v formic acid was added to the reaction medium as an in situ source of hydrogen. The oleic acid and formic acid solution were delivered into the reactor at the ratio 1:5 by volume. Hydrogenation of oleic acid and decarboxylation of the resulting stearic acid with production of heptadecane were the main reaction pathways observed in the studied process. The use of formic acid as a donor of hydrogen made it possible to produce straight-chain alkanes with good yield and selectivity to heptadecane. The yield of heptadecane ca. 70% with the selectivity greater than 80% was observed in the range of temperatures from 370 to 380 °C within 21 min of residence time. Kinetics study showed that the rates of oleic acid conversion displayed Arrhenius behavior with the activation energy of 120 kJ/mol. The proposed rapid continuous flow process can be readily scaled up and used for renewable fuel production from various lipid-based feedstocks.