Chlorinated alumina as an alkylation catalyst: influence of acidity moderators

Chlorinated alumina catalysts obtained by reacting a gamma-alumina with hyd rogen chloride show high initial activity in isobutane-butene alkylation. A fter a few hours on stream however, the conversion decays due to self poiso ning. This work attempts at improving the catalyst lifetime by modifying th e Al2O3-Cl catalyst. Best results were obtained by adding small amounts of alkaline cations to the alumina before chlorination. For a particular catio n, lithium or sodium, the improvement in catalyst lifetime depends on the c hlorination procedure (pre-treatment with CCl4, final temperature). Additio n of cations also enhances the selectivity for octanes, mainly by decreasin g the amount of cracked products. Degradation of 2,2,4-trimethylpentane was found to occur over the Al2O3-Cl catalysts at 273 K. The influence of cati on addition on this process was examined. Thus, the occurrence of dimethylh exanes and cracked or heavier alkanes among alkylation products may be expl ained by the degradation of 2,2,4-TMP. (C) 2000 Elsevier Science B.V. All r ights reserved.