KINETICS OF ETHOXYLATION AND PROPOXYLATION OF 1-OCTANOL AND 2-OCTANOLCATALYZED BY KOH

Ethoxylation and propoxylation reactions are often performed together or in alternation to obtain surfactants with particular properties or random and block copolymers. Both reactions are normally performed in the same reactor, in the presence of an alkaline catalyst, at relative ly low temperature, 120-130 degrees C, to avoid the intervention of th e side reactions that are typical of the propoxylation. The propoxylat ion of a primary fatty alcohol is slower than the corresponding ethoxy lation and gives place to a secondary hydroxyl terminal group that is still less reactive. On the contrary, ethoxylation restores more react ive primary hydroxyl terminal groups. Therefore, it is important for o ptimizing the described industrial operations to know the reactivity o f ethylene and propylene oxide with, respectively, primary and seconda ry hydroxyls, in the presence of the most used KOH catalyst. In this p aper, the kinetics of both the ethoxylation and propoxylation of 1- an d 2-octanol catalysed by KOH have been studied for this purpose. We wi ll show, first of all, that propylene oxide ring opening occurs select ively giving only secondary hydroxyls as terminal groups. The ratio of addition rate of ethylene oxide to primary and secondary alcohol with respect to that of propylene oxide is always greater than 1. Kinetic data collected have been interpreted by using a kinetic model able to simulate during the time the consumption of both the octanol and the a lkoxide and the evolution of the oligomer distributions. The kinetic m odel and related parameters can be easily extrapolated to different in dustrial situations in which ethoxylation and propoxylation occur toge ther or in alternation.