Application of film theory on the reactions of solid particles with liquids: Shrinking particles with changing liquid films

- Reactive solid particles with shrinking films were modelled.
- A new general model was developed for shrinking particles and films.
- The shift of the reaction domain is predicted.
- The theory was illustrated with numerical simulations.

The reactivity of soluble solid particles with liquids was described with extended film theory: the solid material dissolves in the liquid phase and diffuses through the liquid film surrounding the particle. In both the liquid film and bulk liquid, chemical reactions take place. The solid particle shrinks due to the dissolution and consequent reactions and the film becomes thinner and thinner due to the decreasing particle size. A general mathematical model was developed for the solid particle, the liquid film and the liquid bulk phase. The dynamic models were based on mass balances for the solid, film and bulk liquid. The models consisting of coupled parabolic partial differential equations and ordinary differential equations were solved numerically by applying the method of lines. The gPROMS ModelBuilder was used in the computations of generic cases. The models predict the shift of the reaction domain being predominantly located in the liquid film towards the liquid bulk during the progress of the solid-liquid process. The roles of the liquid film and the liquid bulk phases were illustrated with contribution analysis.

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