Modelling diffusion and reaction accompanied by capillary condensation using three-demensional pore networks. 2. Dusty gas model and general reaction kinetics

A pore network model incorporating a rigorous model of diffusion/reaction and an analysis of pore filling by capillary condensation has been developed. This paper presents an extension of the algorithm described in part I to cover multicomponent diffusion and reaction represented by any type of kinetic expression. The novel aspects of the model reported here are that reactions of interest to industry can be simulated since realistic rate equations, such as Langmuir-Hinshelwood expressions, are represented and the possibility of capillary condensation in the pores is also accounted for. Bulk diffusion, Knudsen diffusion and convection of multicomponent vapours are analysed using the dusty gas model, representing a more comprehensive approach to modelling transport in a pore than the Fickian model applied in part 1. The model is used to simulate thiophene hydrogenation over a Co-Mo/Al2O3 catalyst. At temperatures and pressures close to the dew point, capillary condensation occurs in the network. For example at 553 K and 21.5 bar, 55% of the pores are liquid filled. Capillary condensation in the network leads to a decrease in thiophene conversion at the network centre. This effect is particularly pronounced when the percolation threshold of the network is approached. The reduction of thiophene conversion in networks containing condensate is thought to result from loss of surface area available for vapour phase reaction and an increased fraction of dead-end pores, which contribute less to the flux of reactants than open pores. The effect of the size of the network used in the simulations upon the range of pressures over which capillary condensation and percolation phenomena occur is considered. (C) 2002 Elsevier Science Ltd. All rights reserved.