Solid-liquid reaction kinetics – experimental aspects and model development

Abstract

Solid-liquid reactions are commonly encountered in industry as well as every day life. Vast amounts of the applied bulk and specialty chemicals are produced employing solid-liquid reactions. The knowledge of the kinetics is crucial for the design and development of these processes. Quantitative modeling of reactive solids behavior in liquids is a big challenge. The reaction mechanism can be a very complex one, often comprising several unknown elementary steps. The structure and structural changes of the solid material are also often difficult to determine. Kinetics and mass transfer effects are coupled; to determine the intrinsic kinetics, the experiments should be free from mass transfer limitations. External mass transfer resistance can be suppressed by creating strong enough turbulent effects around the solid particles, but internal mass transfer effects can be present for porous particles. Due to these facts, modeling of dissolution reactions is often simplified. Even though such simplifications are necessary, a more in-depth investigation of the related phenomena combined with quantitative studies and more thorough modeling brings new understanding and precision to process development and optimization. Several example cases of solid-liquid reactions were chosen for this work, based on their industrial relevance and varying nature. Moreover, different experimental cases were studied to illustrate a basis for the theoretical development. Two of the cases are organic reactions, while the rest are inorganic ones. The objective of the current review is to exemplify challenges related to studying solid-liquid reactions and how these challenges can be overcome. This is done through the nine example cases, which serve as good examples of the various difficulties often encountered. The published articles serve as a convenient route for finding more detailed information on the topic. Based on the literature evaluation and the experience gained in the present work, theoretical development was made based on physico-chemical fundamentals. The main advances of the current work are in the quantitative modeling of a solid phase during its reaction with a liquid. This includes the dynamic and flexible implementation of the surface morphology and particle size distribution, as well as the reaction mechanism into an overall kinetic model, in which the internal and external mass transfer phenomena are taken into account. This helps in model development and discrimination between rival models, as well as in the interpretation of curiosities in kinetic models which can be found in literature.