Constant-coke arrhenius plots: A diagnostic tool

Abstract

The presence in coke of highly unsaturated hydrocarbons produced by unneeded side reactions and strongly adsorbed on the catalyst, is known to decrease the activity of the catalyst. If the coke molecule is adsorbed on a site hitherto active in the desired reaction, the catalyst loses activity because the site has been taken out of circulation. The presence of coke molecules adsorbed on pore walls increases the resistance to mass transfer inside the catalyst pellet, decreases the concentration of reactant in the fluid phase above an active site, and thereby decreases the rate of reaction. It is important to know which phenomenon is the predominant one in causing deactivation by coking. If both are important, it is important to know the time on stream and/or coke level at which the transition may be considered to occur. How modification of a technique recently reported can be used to evaluate separately (pseudo-) first-order intrinsic rate constants and effective diffusivities of the reactant under actual reaction conditions is shown.