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

Sodium dodecyl-benzensulfonate (NaLAS) is one of the most common anionic surfactant that is being used in powder detergents. It is a product of dry neutralization, which is a chemical reaction where one of the reagents (in this case the base, sodium carbonate) is in the solid state. Dry neutralization usually takes place in a reactive granulator where drops of dodecyl-benzensulfonic acid (HLAS) are mixed with primary particles of sodium carbonate to form the final granules. The acid therefore acts not only as a reactant but also as a particle binder, and the particle wetting and simultaneous chemical reaction influence each other. In this work the reaction and wetting kinetics of dry neutralization are being investigated with a macroscopic method of observing the behavior of a HLAS drop on a substrate pellet made from sodium carbonate. The reaction rate at different temperatures was evaluated from the increasing volume of the drop with rising amount of carbon dioxide bubbles that are a side product of dry neutralization. Wetting kinetics is represented as a relationship between the velocity of a three-phase contact line and dynamic contact angle. From experiments carried out to date, it seems that the chemical reaction rate is limited by a passivation layer made from liquid crystals of NaLAS and water. The relevant kinetic parameters (reaction rate constant and apparent diffusion coefficients) have been evaluated using a numerical model of coupled reaction and diffusion processes in the passivation layer.