ALKYLATION OF ISOBUTANE BY ETHYLENE USING A SOLID FRIEDEL-CRAFTS CATALYST

Alkylation of isobutane with ethylene was investigated over a gamma-Al 2O3-Cl catalyst at temperatures below 380 K. Ethylene was fully conver ted over a period of 5-20 h, then conversion steadily decreased. The o nly products were alkanes, mainly C-6 and C-8. The composition of the alkylate varied with the isobutane/ethylene ratio and with time-on-str eam. Among the C-6, 2,3-dimethylbutane became predominant (> 95%) afte r a few hours. The composition of octanes appeared less selective. The kinetic distributions of isomers are interpreted by a new mechanism b ased on cyclopropane-carbonium ions. Upon catalyst ageing, alkane isom erization decays faster than alkylation, oligomerization being least a ffected.