Dissolution of a benzoic acid wall into aqueous alkaline solutions flowing laminarly in a parallel-plate duct

Mass transfer accompanied by dissolution of benzoic acid from the wall of a parallel-plate duct into aqueous alkaline solutions was studied, using a theoretical model based on diffusion equations. Chemical and ionic interactions of each species, together with diffusion and convection, are considered in this analysis. The theoretical equations were solved as an initial-value problem by using a finite-difference technique. Simultaneously, experiments were conducted under laminar-flow conditions to check the predicted overall rates of dissolution. The rate of dissolution of benzoic acid into KOH solutions was shown to be faster than that into LiOH solutions of equal concentration because of the larger mobility of the K⁺ ions. Under the conditions analyzed here, the agreement between theoretical and experimental overall rates of dissolution was excellent. This showed that the present theoretical analysis can be valid and useful in predicting rates of mass transfer in this kind of complex solid-liquid dissolution systems.