Reactor modelling for fluid-solid systems

The aim of the present doctoral thesis is the development of reliable mathematical models for the simulation of fluid-solid reactors. The main idea was to elaborate a rigorous general non-isothermal three-phase tubular reactor model. The evolution of both concentration and temperature profiles was along all the four coordinates constituting the reactor itself, i.e.: (i) reactor length, (ii) reactor radius, (iii) radius of each particle located inside each position of the reactor, (iv) time. The model was developed to be switchable, giving the possibility to derive submodels by setting some parameters at zero. Different sub-models were tested on real case studies, and good results in terms of data interpretation were obtained. Each chapter of this thesis is dedicated to the presentation of a model/sub-model with a related application to a practical case study. The general model was applied to an exothermic three-phase reaction performed in a laboratory-scale trickle bed reactor. The simultaneous solution of both mass and heat balances was described in detail. The tested sub-models were either twophase or single-phase models. In particular, two microreactor models were developed for the partial oxidation of ethylene, and a two-phase packed bed reactor for the partial oxidation of ethanol. The final chapter describes the results of a special liquid-solid system, where the solid acts as a reactant and diminishes in size as the reaction progresses. The reaction was considered to proceed simultaneously both in the stagnant film surrounding the solid particle and in the bulk phase of the liquid. As the reaction proceeds, the particle radius shrinks and the stagnant film becomes thinner. An approach was presented for a development of a shrinking particle model, where the problem of the moving boundary was successfully solved. The model was applied to a real case, that is the limestone dissolution, obtaining good results. The developed models will be the basis for future application on both laboratory and industrial scale reactors.