Metal deactivation, cyclic propylene

Contaminant-Metal Deactivation and Metal-Dehydrogenation Effects During Cyclic Propylene Steaming of Fluid Catalytic Cracking Catalysts... 

Recent work on laboratory catalyst deactivation in the presence of Ni and V by cyclic propylene steaming (CPS) has shown that a number of conditions affect the dehydrogenation activity and zeolite destruction activity of the individual metals. These conditions include find metal oxidation state, overall exposure of the metal to oxidation, the catalyst composition, the total metal concentration and the NiA ratio. Microactivity data, which show dramatic changes in coke and hydrogen production, and surface area results, which show changes in zeolite stability, are presented that illustrate the effect each of these conditions has on the laboratory deactivation of metals. The CPS conditions which are adjustable, namely final metal oxidation state and overall exposure of the metal to oxidation are used as variables which can control the metal deactivation procedure and improve the simulation of commercial catalyst deactivation. In particular, the CPS procedure can be modified to simulate both full combustion and partial combustion regeneration. 

There is only a limited amount of information on the deactivation mechanisms and rates of vanadium and nickel migration. The formation of metal silicates and/or aluminates has been proposed, as they seem to form more easily by reduction and oxidation cycles. Rajagopalan et al. [8] confirm that methods involving cyclic redox aging of metals in the presence of sulfiir are needed for screening metals-tolerant catalyst. They propose a cyclic test (the cyclic propylene steam method), which addresses the redox aging of the metal, but not the nonuniform laydown and age distribution of metals on the catalyst. 

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