Kinetics of Dry Neutralization of Dodecyl-Benzenesulfonic Acid with Respect to Detergent Granulation

Abstract

Sodium dodecyl-benzenesulfonate, a common anionic surfactant used in powder detergents, is a product of the so-called “dry neutralization” reaction between dodecyl-benzenesulfonic acid and sodium carbonate. The acid acts not only as a reactant but also as a binder in a granulation process; the carbonate particle wetting by the acid droplets and the neutralization reaction occur simultaneously. In this work the reaction and wetting kinetics have been investigated by a macroscopic method of observing the behavior of an acid drop on a substrate pellet made from sodium carbonate. Wetting kinetics at three temperatures (20, 40, and 60 °C) were measured and expressed as a relationship between the three-phase contact line velocity and the instantaneous contact angle. The reaction rates were evaluated from the volume of CO2 gas evolved during the reaction. The kinetic parameters (temperature-dependent reaction rate constant and apparent diffusion coefficients) have been evaluated using a numerical model of coupled reaction and diffusion processes in the passivation layer. The results indicate that because of diffusion limitations the neutralization reaction takes place predominantly in the “wet” product layer rather than at the solid–liquid interface.