CATALYTIC CRACKING OVER CRYSTALLINE ALUMINOSILICATES .2. APPLICATION OF MICROREACTOR TECHNIQUE TO INVESTIGATION OF STRUCTURAL EFFECTS OF HYDROCARBON REACTANTS

Reactions which occur over a crystalline aluminosilicate catalyst of the X zeolite type and over an amorphous silica-alumina catalyst have been examined using four types of hydrocarbons as reactant: paraffins, olefins, alkyl aromatics, and cydoparaffins. Olefins crack much faster than paraffins of the corresponding carbon number and also undergo an isomerization reaction which does not occur with paraffins. A suggested mechanism for this isomerization involves intramolecular cydization of an olefinic carbonium ion, not derivable from paraffins, which then produces highly branched and cyclic isomers. Evidence for this mechanism is presented from experiments with n-octene, n-dodecene, and n-hexadecene. Cydoparaffins form carbonium ions by the same mechanism as paraffins, but product distribution resembles that of olefin cracking because of similarities of cyclic intermediates. Alkyl aromatics involve dealkylation of the alkyl group if the chain length is short, but this reaction is not the main one with longchain alkyl aromatics. © 1969, American Chemical Society. All rights reserved.