KINETICS OF FATTY-ACIDS POLYETHOXYLATION

Fatty acids (C-12-C18) ethoxylation in the presence of alkaline cataly sts is normally performed in industry for the production of nonionic s urfactants. The reaction takes place in two steps. In the first one, m onoethoxylation occurs with a decelerative behavior. When all the acid has reacted, reaction rates strongly increase as consequence of the a lcoholate anion formation. In this paper we will show that the first s tep 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, t hat is during propagation reactions, reaction rates are affected from the catalyst concentration. Together with ethoxylation, a transesterif ication reaction occurs, producing diesters and polyglycols. This reac tion is promoted by the alkaline medium; therefore, it mainly occurs d uring the second reaction step. In this work, a kinetic model able to satisfactorily reproduce all the experimental observations has been de veloped and discussed.