EVALUATION OF COMMERCIAL FCC CATALYSTS FOR HYDROCARBON CONVERSION - II - TIME-ON-STREAM BEHAVIOR OF N-HEXANE CONVERSION AND COMPARISON OF N-HEXANE CONVERSION TO MAT

n-Hexane conversion over commercial FCC catalysts was investigated in a plug-flow reactor system allowing analysis of products with a high t ime resolution. The different decays of protolytic cracking, dehydroge nation and hydride transfer with time-on-stream suggests different and /or additional sites for the different reaction pathways. In particula r, dehydrogenation proceeds via two pathways, of which one is only imp ortant at short times-on-stream (TOS). This reaction pathway is specul ated to be affiliated with the extra-lattice aluminum in the zeolite. The variation of methane with TOS is correlated to the dehydrogenation , and a part of methane is produced by active sites also dehydrogenati ng n-hexane. Addition of water decreased the rates of all reaction pat hways due to competitive adsorption. Under the reaction conditions use d, the carbonaceous species responsible for deactivation seem to be ra ther small in molecular weight (e.g. cyclic alkenes or single-ring aro matics). The rate of n-hexane conversion is directly proportional to t he activity evaluated by the microactivity test. The octane numbers an d the amount of coke formed derived from this latter test can be well correlated to the isoparaffin-to-n-paraffin ratio and the rate of hydr ide transfer in n-hexane cracking, respectively. (C) 1998 Elsevier Sci ence B.V.