Transfer and adsorption steps affecting partial hydrogenation of triglyceride oils

The numerous transfer, adsorption and true hydrogenation steps which occur during the partial hydrogenation of triglyceride oils are reviewed and discussed. Transfer steps involve the transfer or diffusion of the reactants to the catalyst surface and possibly also into the pores of the catalyst. In addition, the reaction products must then also be transferred back to the main body of the triglyceride oil. Such reaction products include not only the saturated groups (formed by the hydrogenation of the unsaturated groups) but also the geometrical and positional isomers of the original unsaturated groups. Once an unsaturated group reaches the catalyst surface, it is generally assumed that it is adsorbed on the catalyst. Polyunsaturated fatty groups are however preferentially adsorbed relative to monounsaturated fatty groups. The overall kinetics of hydrogenation affects the relative ratio of the adsorption of the polyunsaturated to the monounsaturated groups at the catalyst surface. Transfer and adsorption steps frequently, if not always, are the critical steps in controlling the degree of isomerization and selectivity of reactions in the partial hydrogenation process. Additional information is still needed relative to these steps but the general trends which occur are discussed.