Fresh synthetic catalyst added daily to the inventory of a commercial F. C.-C. unit suffers a rapid loss of activity. In an attempt to assess the relative contribution to this loss from thP major known deactivating agencies, the separate effects of heat, steam, trace metals and carbon were studied. in relation to catalyst activity, selectivity and surface properties. The extent of thermal deactivation is dependent on both time and temperature, and is always accompanied by pronounced changes in the surface properties of the catalyst and by a small loss of water. In laboratory tests only a severe thermal treatment deactivated fresh catalyst to a level comparable with equilibrium catalyst. Steam accelerated thermal ageing but at plant temperatures it did not cause the deterioration of test samples to a level comparable with that of equilabrium catalyst. Laboratory exppriments showed that trace metals had an appreciable effect on the performance but no very considerable effect on the surface properties of partially deactivated catalyst. A loss of activity and of selectivity in the presence of heavy metals were indicated by reduction in gasoline yield and by a large deposition of carbon and an increase in the gas-gasoline ratio.
Sodium caused a deterioration in activity withoutiaffecting selectivity, and the results obtained were consistent with the carbonium-ion theory of catalytic cracking. The deposition of carbon was found to increase with catalyst activity. The removal of carbon improved the activity of equilibrium catalyst by a few units.
It was concluded that high temperatures were mainly responsible for the final state of equilibrium catalyst. On this basis a mechanism is proposed in which unrecorded high temperatures may occur on the surface of particles during the removal of large quantities of carbon. As a result of these high temperatures, trace metals may become trapped in the body of the catalyst, and their effect on catalyst selectivity is then appreciably reduced.
Le catalyseur synthétique frais quotidiennement ajouté dans une installation P. C. c. perd rapidement une grande partie de son activité. Rn vue de déterminer la contribution respective des principaux agents de désactivation ù cette perte, les effets de la chaleur, de la vapeur, des traces dP métaux, du carbone ont été étudiés séparément par rapport d l'action catalytique, ù la sélectivité, aux caractéristiques de surface. L'importance de la désactivation provoquée par la chaleur dépend du temps comme de la température: elle est toujours accompagnée par des variations sensibles des propriétés de surface du cataly-SeUr et par une petite perte d'eau. Au cours des essais de laboratoire, on a constaté que seul un traitement thermique sévère parvenait ù dés
