Deactivation of ZSM-5 additives in laboratory for realistic testing

Abstract

ZSM-5 deactivates differently from Y zeolite. Dealumination of Y zeolite during deactivation causes UCS shrinkage and thereby decline in activity and changes in selectivity. For ZSM-5 instead deactivation removes alumina from the zeolite structure, but in spite of that the zeolite structure does not collapse. Therefore, deactivation causes activity decline due to loss of active alumina sites, but no significant changes in the strength and separation between acid sites. Unlike with FCC catalyst, physical properties of ZSM-5 additive do not change significantly with deactivation and surface area and pore volume measurements cannot be used as indications of additive performance. Yet, since both Y and ZSM-5 are used simultaneously in practice, the information on the relative rates of deactivation between the two zeolites is very important. Therefore, the question remains, what is the best way to deactivate and test ZSM-5 additives in the laboratory to obtain realistic performance, e.g. propylene yield and to obtain proper ranking of various additives. This paper discusses the effect of deactivation conditions as well as performance testing aspects of ZSM-5 additives. It is shown that choice of deactivation conditions has an effect on additive ranking and performance. By choosing the deactivation conditions properly ranking can be made clearer and more realistic additive performance is obtained.