Reaction and coking kinetics of n-heptane catalytic reforming

In order to gain an understanding of the coking processes of a reforming catalyst and of how the reforming reactions interact with coking, this thesis reports experiments on the model system of n-heptane reforming over a Pt-Re/Al{dollar}sb2Osb3{dollar} catalyst in a temperature range of {dollar}rm 733 K < T < 799 K{dollar} and pressure range of {dollar}rm 207 kPa < P < 1034 kPa{dollar} in a multi-outlet fixed bed reactor and a novel vibrational microbalance reactor.; We have found that the bulk of catalyst coke in n-heptane reforming derives from C5 naphthene intermediates (alkyl-cyclopentanes). This motivated the development of a simple, five-lump kinetic model for the reforming reactions that includes one lump for the potent coke-forming C5 naphthenes, to provide a precursor profile along the bed. Armed with knowledge af the precursor and how its concentration varies in space, we use methyl- and ethyl-cyclopentane as model C5 naphthenes, focused on determining the kinetics of coke formation: {dollar}{lcub}dCsb{lcub}k{rcub}over dt{rcub} = esp{lcub}-alpha Csb{lcub}k{rcub}{rcub}Psb{lcub}C5N{rcub}({lcub}kappasb1 over Psb{lcub}Hsb2{rcub}{rcub} + {lcub}kappasb2over Psbsp{lcub}Hsb2{rcub}{lcub}2{rcub}{rcub}){dollar} where {dollar}Csb{lcub}k{rcub}{dollar} is the catalyst coke content, {dollar}alpha, kappasb1 and kappasb2{dollar} are the parameters. This work proposes a new multi-layer coking model and a coking mechanism to explain the data measured. The multilayer model, together with the site-coverage concept, strongly suggests a catalyst deactivation mechanism.; This work then unifies the newly proposed reforming and coking mechanisms. First, the deactivation mechanism deriving from the coking study predicts the decay of the reforming model's rate constants. Second, the measured (or predicted) C5 naphthene profile predicts the coke profile. These results form a rather complete, consistent picture of reforming reaction and coking for n-heptane reforming system.; In addition we found that in the absence of hydrocarbon feed, flowing hydrogen can strip a portion of the coke even in our temperature/pressure range. The kinetics of this process suggests the identification of removable with new, low molecular weight coke, and we construct a mechanism based on this identification.; Finally, it has been possible to carry out these sensitive experiments only because we, together with R&P Company, developed a novel microbalance system. This system accurately measures the time evolution of both the coke amount and the composition of the gas phase in contact with the catalyst simultaneously, under realistic conditions. This microbalance works by sensing how a change in mass affects the balances natural vibrational frequency. It alleviates the problem of severe feed gas by-passing that conventional gravimetric microbalances encounter by virtue of a new flow-through design.