Kinetics of Fat Hydrogenation

Abstract

Substrates containing electronegative groups have a strong trend to reduce hydrogenation activity of catalysts owing to self-poisoning, and fat hydrogenation is not exceptional. Paid due cautions on self-poisoning zero order with respect to substrates is readily confirmed. Discussions, putting aside the problem of poisoning, are concentrated on the behaviors of reactants on catalysts in connection with ethylene hydrogenation. Fat hydrogenation is considered as a specific instance of ethylene hydrogenation, where partial pressure of ethylene is enormously excess. A theory of local mobilization respecting reactants is advanced to meet the ethylene hydrogenation kinetics of independency on partial pressure of major species at low temperatures and of dependency on partial pressures of both species at high temperatures. Only for the latter case the Langmuir-Hinshelwood theory is applicable. Discrimination between active and inactive sites is thereby necessary. Interpretation for the preferential hydrogenation of linoleic acid to oleic acid on nickel catalyst is made in terms of equilibrium shift between two assumed quasi-complex compounds involving all the components concerned, one with linoleic acid and the other with oleic acid as a component, which also accounts for the failure of selectivity under high hydrogen pressures.