A theoretical investigation, based on mathematical modelling, of some important phenomena relating to porous catalysts has been undertaken. Two representative complex reaction schemes, concurrent and consecutive, are chosen for the purpose. The work is based on the numerical solution of ordinary/partial differential equations and also optimization techniques. The work can be subdivided into three parts. First, various theoretical models are presented as a representation of porous structure. The calculation of effective diffusivities and a comparison with experimental results of other researchers indicate that both the two and three dimensional models developed are more than satisfactory. Secondly (chapters 2 and 3 of the thesis), the effect of surface migration of reactant species and of adsorption of an independent poison on the selectivity of reaction is considered. The results indicate that these phenomena can either enhance or reduce the selectivity depending upon the reaction scheme, the thermicity of reaction and the kinetic parameters chosen. For concurrent reactions, the effects are critically dependent on whether the parameter delta (the difference between the energy of activation of a reaction and the heat of adsorption of the reactant) corresponding to the desired preduct is greater or less than that for the wasteful product. For consecutive reactions the dependence is less marked. Thirdly, attention is paid to the optimization of pore structure, size and shape of catalyst pellets. It is observed that for consecutive reactions, maximum selectivity is realized when the reaction is determined or controlled by the chemical reaction kinetics. However, for concurrent reactions in which delta for the desired reaction exceeds that for the wasteful reaction, the maximum selectivity is obtained when the reaction rate is limited by intraparticle diffusion.
|Date of Award||1977|