Mass transfer-controlled reactions with substantially no flow communication between adjacent flowthrough paths

Mass transfer-controlled reactions are those reactions which are controlled by the velocity of the reactants passing through the catalyst body and by the type of flow of the reactants, namely degree of turbulence, through the catalyst body. These reactions take place essentially at a catalytic rate equal to the rate of mass transfer of reactants to the catalyst surface. Thus, the reaction rate is controlled or limited primarily by the extent of reactant-catalytic surface contact. By increasing the velocity of the reactants, the period of contact of a turbulent flow of fluid with the catalytically-active metal component on the walls of the honeycomb structure is reduced, but the rate of mass transfer is increased since the distance for diffusion of the reactants in the gas phase to contact the catalyst is less. Hence the degree of completion of the reaction is not lessened in proportion to the reduction in catalytic time. On the other hand, if the velocity of the reactant gases through the flowthrough paths of the catalyst is such that the flow is laminar in nature, there is no offsetting compensation for the reduction in contact time due to an increase in velocity since the distance required for the reactants to diffuse through the vapor phase reactant stream and contact the catalytically-active surface is essentially unchanged. In practice, when employing gas velocities which provide laminar flow, the pattern of flow of the entering gases at the initial portion of the flowthrough paths will resemble turbulent flow until the flow pattern becomes settled. Velocities of the reactants which fall between laminar and turbulent flow, for example, transitional flow, may also be employed. However, due to the generally unpredictable nature of transitional flow and the possibility of significant variations in the pattern of flow with small variations in velocity, velocities in this range may not find as convenient an application to provide stable conversion rates in mass transfer-controlled reactions as velocities which provide laminar or turbulent flow.