Development of an event oriented Monte Carlo simulation and applications to problems of diffusion and reaction
Description
This work presents the development of an event oriented simulation method. The thesis describes a new procedure to manage the set of pending events which is an integral part of an event oriented discrete simulation. As an application of the method, the problem of reaction and diffusion in a specific zeolite structure is treated in detail An event oriented model was developed, as this allows for greater flexibility and increases accuracy as compared to a fixed interval simulation method. As most future event set algorithms are not adequate to handle the large numbers of events generated by this simulation, a new event list algorithm, based on a B-tree, has been devised that offers superior insertion and retrieval capabilities The simulation method was applied to the cause of a reversible first order reaction occurring within a particle with a pore geometry conforming to a three dimensional rectangular grid. It was found that the product formation rate passes through a maximum as the pressure of surroundings is increased. This finding was substantiated by analytical solution of differential equations describing the reaction-diffusion model Two different modes of catalyst deactivation, site suppression and site blockage, were examined. Site suppression deactivates sites without affecting diffusional access to deactivated sites, while site blockage prevents further access to deactivated sites. For both modes, series and parallel deactivation mechanisms were considered. In the parallel site blockage mode, the edges of the particle are blocked first, thus deactivating the particle faster than the parallel site suppression mode. However, the series site blockage mode blocks the center of the particle, increasing the production as compared to the series site suppression A more complex system, the reaction of toluene and methanol to form xylene isomers was modeled. A plug flow heterogeneous reactor was simulated by using a series of single particle simulations. In these simulations, the interior diffusion was decoupled from the transport of molecules at the surface of the particle into the bulk phase. This model has produced results consistent with various reported effects. The simulation correctly predicts increased para-xylene selectivity with unmodified particles. Also, the approach to thermodynamic equilibrium follows the correct reaction path