Olefin skeletal isomerization of n–butene, n–hexene and n–octene using alumina–based catalysts

Abstract

Stringent standards to improve air quality and to protect human health are continuously implemented due to the environmental impact of auto emissions. As a result, researching options for alternative components or alternative processes are very important to continuously improve the octane number in the fuel pool. Therefore, by exploiting the high olefin (butene, hexene and octene) content part of the feedstocks, the overall aim of this study was to obtain olefin skeletal isomerization for the improvement of the RON in the refinery fuel pool. The influence of temperature variation (350 °C, 400 °C and 450 °C) on the performance of the different alumina catalysts (eta (η)-alumina, H-ZSM-5 and silicated alumina) was investigated. All experiments were performed using a fixed bed reactor at atmospheric pressure and a constant weight hourly space velocity of 5 h-1. The effect of the different conditions and additions on conversion and selectivity was determined. Eta alumina and the silicated alumina (Siralox 40) were proved to be the catalysts that were most prone to cause skeletal isomerization when in contact with longer carbon chains. Butene did not isomerize to a significant extent when contacted over either Eta alumina or Siralox 40. In the case of the zeolite catalyst (ZSM-5), none of the feeds isomerized and it was speculated that it could have been due to the high activity of ZSM-5 which made this catalyst more likely to cause side reactions rather than the preferred skeletal isomerization reaction.