Dissolution kinetics or pure mass transfer? A mechanistic study of dissolution



In many cases, classic in vitro tests are used to investigate dissolution from powders and solids. A problem with these kinds of tests is the frequent use of agitation, leading to a lumped description of the properties at the solid–liquid interface. The hydrodynamic forces arising from agitation might have a nontrivial impact on the dissolution properties, thus calling for a comparison of results with those stemming from stagnant dissolution with the aim to increase the understanding of the dissolution process. Stagnant dissolution of compressed solid benzoic acid was examined using the noninvasive electronic speckle pattern interferometry technique in this study. The diffusion coefficient for benzoic acid in 37°C water was measured using the same technique, and, by combining the results, the surface kinetics at the solid–liquid interface were calculated. A comparison with previous dissolution data from a rotating disk suggests that the presence of convection can increase the observed surface kinetics. © 2010 American Institute of Chemical Engineers AIChE J, 2011