Dissolution Study of Salt of Long Chain Fatty Acids (Soap Scum) in Surfactant Solutions. Part II: Kinetics of Dissolution

摘要

A study of the dissolution kinetics of soap scum, calcium octadecanoate (Ca(C_(18))2), by aqueous solutions was carried out by measuring the rate of dissolution of Ca(_(18)8)2 using a flow cell apparatus. These solutions contained three different types of surfactants: dimethyldodecylamine oxide (DDAO), sodium dodecyl sulfate (SDS), or octyl polyglycoside (C8APG), in the presence of a chelating agent, disodium ethylenediamine-tetraacetate (Na2EDTA). The resulting rate of dissolution corresponds well with the equilibrium solubility obtained in the part I of this series even though the dissolution is rate limited (far from equilibrium). High rates of Ca(C_(18))2 dissolution are achieved in solutions of zwitterionic DDAO or nonionic C8APG with Na2EDTA at high pH. From rate analysis, the Ca(C_(18))2 dissolution was found to be surface-reaction limited rather than limited by solution processes or wettability.