CATALYST DEACTIVATION KINETICS FROM VARIABLE SPACE-VELOCITY EXPERIMENTS

Reliable estimates of catalyst deactivation parameters are difficult t o get from conventional experiments at constant space velocity where c onversion declines with time on stream, or when temperature is adjuste d to compensate for the loss of catalyst activity. An alternate techni que, where space velocity is adjusted to maintain constant conversion, is shown here to give reliable rate information for both the catalyst deactivation and the primary catalytic reactions. This technique, at constant temperature, provides kinetics data on a deactivating catalys t in which the catalyst is exposed to reactant and product concentrati ons that are relatively constant. In principle, the kinetics of deacti vation are obtained directly as the kinetic regime remains unchanged. This technique is used quite successfully for many catalytic processes of industrial significance. In this paper, the variable-space-velocit y experimental technique is demonstrated for the methanol to hydro car bons process on a ZSM-5 catalyst. The deactivation kinetic parameters were determined at several temperatures in a fixed-bed reactor. This r ate information was then used to determine the temperature-time policy for maintaining constant reactor outlet conversion at a fixed space-v elocity. The predicted temperature-time policies are in good agreement with experimental data on fixed-bed and fluid-bed reactors. Mathemati cal analysis of interpreting experimental data. as well as predicted t emperature-time policies for practical applications, is illustrated. ( C) 1997 Elsevier Science Ltd.