Surface carbon formation on reforming catalysts

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University of Dar es Salaam
The deactivation of platinum on alumina (PtA1203) reforming catalyst by carbonaceous materials called coke, is a significant industrial economic problem. In this work the kinetics of surface carbon formation of these carbonaceous materials has been studied, from C3 and C4 hydrocarbons feed stocks, at atmospheric pressure and in the temperature range of 450- 600 OC. The carbon formation process was monitored using a microbalance capable of detecting up to 10-6 g by weight of the carbon uptake. The effluent gases from the reactor were analysed on line with a gas chromatograph to detect possible intermediates in the cooking process. Surface area, metal area, pore size distribution, scanning and transmission electron microscopies, X-ray fluorescence analysis and energy dispersive analysis of X-rays were techniques employed to characterize the catalyst. The kinetic results have been interpreted using both Froment and Langmuir- Hinshelwood models. The rate of carbon deposition increased with increase in the hydrocarbon partial pressure and also temperature. The rate decreased with increase in the hydrogen partial pressure. The orders for carbon formation reaction seemed to be slightly temperature sensitive, in spite of the apparent linear relationship between the rate of carbon formation and the reciprocal of the absolute temperature from which activation energies were evaluated. Thus, the orders with respect to hydrocarbons increased as the temperature increased, while the orders with respect to hydrogen varied from one temperature to another. Similarly, the deactivation function orders obtained according to Froment model, increased as the temperature increased. This has been explained in terms of changes in mechanism due to the observed structural changes of the catalyst and extent of carbon deposition. The rates of carbon formation were also retarded by increasing the partial pressure of a paraffin while keeping the partial pressure of the olefin counterpart and of hydrogen, constant. A survey of the literature on catalytic carbon formation has been included in the introduction and the results of the present work have been compared with results in other systems.
Available in print form, East Africana Collection, Dr.WilbertChagula Library, (THS EAF QD 181.C1M45)
Mkayula, L. L (1980) Surface carbon formation on reforming catalysts, Masters dissertation, University of Dar es Salaam, Dar es Salaam.