Understanding the Behavior of Reactive Solid Materials in Chemical Processes

Not all chemical processes occur completely in liquid or gas phases. Recently there has been a huge increase in the utilization of solid natural resources, for instance biomass such as cellulose, hemicelluloses and starch which are at least in the beginning of the processing in solid form. Another type of process having this feature are the reactions of minerals and ores. In the production of fine chemicals and pharmaceuticals, reactive solid phases are in many cases involved. In many cases, the solid structure is also desired for the product, hence the reactions and modifications need to be performed in solid state.

Reactions on solids possess a more advanced reactivity in the sense that the reaction might only occur on the surface of the particles, or, the gas or liquid reactant diffuses into the solid particle. It is also possible that the surface is reactive and the product layer is growing or dissolving, leading to a shrinking core or to a shrinking particle. How does the kinetics need to be treated in such a scenario? Solid particles can additionally be physically treated with some kind of external force, leading to larger pore sizes, cracks, or craters, increasing the available reaction surface. For instance, irradiation of solid materials such as cellulose with ultrasound or microwaves could lead to an increase of the specific surface areas of solid particles. The recent advancement of microscopic and spectroscopic surface characterization techniques has open a new window to the morphology and chemical composition of reactive solid surfaces. New theories for reactive solid surfaces have been developed based on experimental discoveries: surfaces which in the past were described like perfect spheres have in reality turned out to be a moon landscape with craters and cracks. This is a challenge for theoreticians to develop new models, which in best case can be used for process intensification and design of new processes.

This Research Topic invites contributions in all fields from the reaction engineering point, dealing with the phenomenon of coupled kinetic and diffusion effects and how to take into account these when doing mathematical modelling or conducting kinetic experiments.

Keywords: Reactive solids, kinetics, mass transfer, surface chemistry, non-ideal surface

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