Hydrogenation of fatty acid methyl ester to fatty alcohol at supercritical conditions

Hydrogenation of various types of oleochemicals is a major unit operation in industry. Natural fatty alcohols are important raw materials for surfactants and lubricants and can be produced by catalytic hydrogenation of fatty acid methyl esters (FAME). Commercial multiphase processes are necessarily operated at high pressures and high hydrogen-to-ester mole ration owing to low solubility of hydrogen in liquid phase. Using the supercritical fluid, a substantially homogeneous supercritical phase could be created, whereby hydrogen could completely access to the active site of the solid catalyst. In this paper, the supercritical hydrogenation was studied in a batch, stirred reactor. The results showed that adding of the propane prompt the mass transfer of hydrogen to the catalyst and increase the concentration of hydrogen on the catalyst surface. It was found that the reaction time and the hydrogen-to-ester mole ratio were two key factors affecting the conversion. The conversion increased from 14% to 96% as the reaction time prolonged from 15min to 240min at the hydrogen-to-ester mole ratio of 11, and the conversion increased from 54% to 97% as the hydrogen-to-ester mole ratio increased from 8.8 to 21.6 at the reaction time of 150min. Compared with traditional batch hydrogenation, the concentration of reactants on the catalyst surface could be controlled effectively in supercritical condition, which could promote the selectivity of lauryl alcohol from 80% to 95% above and reduce the hydrogen-to-ester mole ratio from about 100 to 20 below.