Decontamination of industrial alumina catalyst for skeletal isomerization of n-butenes

Abstract

Causes of alumina catalyst deactivation in a process of skeletal n-butene isomerization, which leads to decreasing of the conversion from 31 to 26 % were examined. It is shown that contamination of Fe, Mg metal combination microimpurities reduces the conversion of n-butenes of about 2,5 %. The catalyst activity can be restored by cleaning from metallic impurities. Steam piping and feed are the source of metallic impurities. The accumulation of δ-modification of aluminum oxide in the catalyst occurs during the operation that leads to a decrease in the conversion of n-butenes of about 3 abs.%; this kind of deactivation is irreversible. Probable cause of the partial phase transition at a temperature below 600 °C is the reducing of the phase transition temperature under the influence of trace Fe and Mg. It is shown that the accumulation of trace and δ-phase alumina decreases the amount of acid sites of alumina catalyst and the resulting decrease in conversion. Recommendation to extend the life of the catalyst is to capture metal impurities from steam feed flow by installing a protective layer the inert to butene fraction macroporous material with a developed surface in front of the catalyst bed.