A detailed kinetic model for biogas steam reforming on Ni and catalyst deactivation due to sulfur poisoning

Abstract

This paper deals with the development and validation of a detailed kinetic model for steam reforming of biogas with and without H2S. The model has 68 reactions among 8 gasphase species and 18 surface adsorbed species including the catalytic surface. The activation energies for various reactions are calculated based on unity bond index-quadratic exponential potential (UBI-QEP) method. The whole mechanism is made thermodynamically consistent by using a previously published algorithm. Sensitivity analysis is carried out to understand the influence of reaction parameters on surface coverage of sulfur. The parameters describing sticking and desorption reactions of H2S are the most sensitive ones for the formation of adsorbed sulfur. The mechanism is validated in the temperature range of 873–1200 K for biogas free from H2S and 973–1173 K for biogas containing 20–108 ppm H2S. The model predicts that during the initial stages of poisoning sulfur coverages are high near the reactor inlet; however, as the reaction proceeds further sulfur coverages increase towards the reactor exit. In the absence of sulfur, CO and elemental hydrogen are the dominant surface adsorbed species. High temperature operation can significantly mitigate sulfur adsorption and hence the saturation sulfur coverages are lower compared to low temperature operation. Low temperature operation can lead to full deactivation of the catalyst. The model predicts saturation coverages that are comparable to experimental observation.