Hydrotalcite-type catalysts for narrow-range oxyethylation of 1-dodecanol using ethyleneoxide

Abstract

Hydrotalcite-type catalysts were studied for the oxyethylation of 1-dodecanol. Hydrotalcite-type catalysts treated with dodecanoic acid are very active for the narrow-range oxyethylation of 1-dodecanol. The narrow distribution of oxyethylene units in the dodecylethoxylates is elucidated by the constrained reaction on the surface of hydrotalcite-type catalysts. In the proposed surface reaction scheme, the following points are presented. (1) The relatively basic reactants, ethylene oxide and dodecylalcohol or dodecylethoxylates, are adsorbed on the relatively acidic Al 3+ sites of the surface. (2) The adsorption of ethylene oxide is increasingly interfered with due to the occupation of dodecylethoxylates of higher number of oxyethylene units on the isolated acidic sites of the catalyst. (3) The interference results in the decrease of oxyethylation rate in each additional ethylene oxide insertion step, due to a smaller number of the ethylene oxide molecules adsorbed near the growing point of alcohol ethoxylates. (4) The difference in ethylene oxide insertion rates with the numbers of oxyethylene units in the dodecylethoxylate products causes peaking of the distribution. The large difference of oxyethylation activity over hydrotalcite-type catalysts of distinct Mg and Al composition ratios may be correlated with the numbers of Al 3+ sites at the closest distance from an Al 3+ site, which can be deduced from the ideal hexagonal or orthorhombic super lattice of Al 3+ sites on the hydrotalcite surface layer.