Phase equilibria of mixtures of hydrogen, propane and fatty oil derivatives at supercritical conditions

L.J. ROVETTO; S. PEREDA; S.B. BOTTINI; C.J. PETERS

Versailles, France

Simposio; 6th International Symposium on Supercritical Fluids; 2003

The phase behavior of supercritical hydrogenation mixtures can be quite complex. Drastic changes in density and solubility with temperature, pressure and composition can be expected, due to the presence of a near-critical or supercritical solvent in a mix

The most common industrial process to obtain margarines and natural fatty alcohols is by catalytic hydrogenation of vegetable oils and fatty acid methyl esters, respectively. The addition of supercritical propane to the reactive mixture can bring the organic substrate and hydrogen into a homogeneous phase, increasing reaction rate and selectivity. Knowledge of the phase behavior of these mixtures is a prerequisite in order to explore adequate process conditions. In the present work experimental phase equilibrium data on selected binary and ternary mixtures, typical of the supercritical hydrogenation of vegetable oils and fatty acid methyl esters, are reported. A group contribution equation of state GCA-EOS (Gros et al., Fluid Phase Equilibria, 116, 535, 1996) is applied to correlate and predict the fluid phase behavior of mixtures of hydrogen, propane, reactants and reaction products at different degrees of conversion, temperatures and pressures. Depending on its concentration, hydrogen may have an anti-solvent effect, reducing the solubility of reactants and products in the supercritical fluid. The solubility of hydrogen in fatty alcohols is lower than that in the corresponding methyl esters; hence, in the hydrogenolysis process the limits of the one-phase region depend on the extent of reaction. Regions of partial liquid miscibility have been predicted by the GCA-EOS model and experimentally corroborated. From the results of this study it can be concluded that the composition of the reaction mixture and the operating process conditions have to be carefully selected in order to ensure single-phase supercritical hydrogenation processes.