KINETICS OF FATTY-ACIDS POLYETHOXYLATION

Fatty acids (C-12-C18) ethoxylation in the presence of alkaline catalysts is normally performed in industry for the production of nonionic surfactants. The reaction takes place in two steps. In the first one, monoethoxylation occurs with a decelerative behavior. When all the acid has reacted, reaction rates strongly increase as consequence of the alcoholate anion formation. In this paper we will show that the first step reaction mainly occurs with a noncatalytic mechanism and that the observed behavior can be described with a first-order kinetic law with respect to the free fatty acid. In the second step of the reaction, that is during propagation reactions, reaction rates are affected from the catalyst concentration. Together with ethoxylation, a transesterification reaction occurs, producing diesters and polyglycols. This reaction is promoted by the alkaline medium; therefore, it mainly occurs during the second reaction step. In this work, a kinetic model able to satisfactorily reproduce all the experimental observations has been developed and discussed.