Alkylation of isobutane with 2-butene over a HFAU zeolite. Composition of coke and deactivating effect

The transformation of an isobutane -2-butene mixture with a 40 weight ratio was carried out in liquid phase at 50 degrees C on an USHY zeolite with a framework Si/Al ratio of 4.5. The reaction products can be classified into seven families: (a) trirnethylpentanes resulting from isobutane alkylation with 2-butene or from isobutane self-alkylation, (b) dimethylhexanes, (c) C -8 alkenes, (d) heavy products (mainly C-9-C-12), (e) light products C-5-C- 7 alkanes, (f) n-butane, and (g) nondesorbed products (coke). These latter products, which are responsible for deactivation, were removed from samples coked for different times, after dissolution of the zeolite in a hydrofluo ric acid solution, and analyzed by GC, IR, HNMR, MS, and GC/MS coupling. Th e coke components were identified as alkyl bicyclic olefinic compounds with 12-28 carbon atoms. IR spectroscopy analysis of the coked zeolite samples shows that coke molecules interact with the protonic sites, this interactio n being mainly responsible for deactivation. Large differences can be obser ved in deactivation of the various reaction steps. The steps which are the more demanding in number (e.g., hydride transfer) or in strength (e.g., iso merization) of the acid sites are preferentially deactivated.