IDENTIFICATION OF COKE PRECURSORS IN HEPTANE REFORMING WITH A MULTIOUTLET FIXED-BED REACTOR AND A NOVEL VIBRATIONAL MICROBALANCE

This work aims to determine the major coke precursors in n-heptane ref orming over a commercial Pt-Re/Al2O3 catalyst. We employ both a multio utlet fixed-bed reactor and a new microbalance that measures coke-on-c atalyst by monitoring the natural vibrational frequency of a tapered e lement that is pinned at one end and has catalyst at its free end. Thi s microbalance does not have the gas bypass problem common to conventi onal gravimetric microbalances. We show that five-carbon ringed naphth enes (C5N) are the only reforming reaction participant species lump wh ose concentration rises whenever the rate of catalyst activity loss in creases in response to changes in temperature, pressure, or space velo city. A more quantitative treatment shows that the C5N concentration p rofile along the fixed-bed reactor tracks both the coke profile and th e profile of a measure of the local catalyst deactivation rate. Furthe r detailed microbalance studies with different hydrocarbon feeds show that the coking rate is first order in C5N and is almost independent o f toluene concentration. The C5N formed in n-heptane reforming quantit atively accounts for most of the coke produced. All experiments pointe d to C5N as the major coke precursor in n-heptane reforming. (C) 1997 Academic Press.