Performance of a Co-Ni catalyst for propane reforming under low steam-to-carbon ratios

Although the catalytic steam reforming of hydrocarbon for synthesis gas production is often carried out with excess steam-to-carbon ratio (S:C > 3), on-line catalyst deactivation due to coking invariably affects reformer performance. It is therefore necessary to obtain quantitative relation on the coupling between carbon deposition and pure steam reforming activity in order to develop optimal reformer-regenerator policy. Since kinetic information on steam reforming is often collected under carbon-free conditions, the effect of coke on the rate parameters is not fully understood. This investigation addresses the procurement of both steam reforming and deactivation kinetic constants simultaneously from transient reaction data under conditions of low steam-to-carbon ratio in a fluidised bed reactor fed with propane and employing an alumina-supported Co-Ni catalyst. Two-way ANOVA statistical treatment confirmed strong interaction between temperature and S:C ratio on the coking dynamics. Although the steam reforming kinetic constant exhibited Arrhenius dependency on temperature, the deactivation rate coefficient is characterised by a negative activation energy since carbon deposition increased with decreasing temperature in the range examined (773-873 K). This was corroborated by total organic carbon (TOC) analysis, XRD data and temperature-programmed oxidation (TPO) results of the used catalysts. The TPO spectra evidenced the formation of two types of carbonaceous pools with different C:H ratios of 1 and 6-an indication that coke formation proceeded via dehydropolymerisation of surface CHx species to naphthalenic compounds. (C) 2004 Elsevier B.V. All rights reserved.