This paper deals with the development and validation of a detailed kinetic model for steam reforming of biogas with and without H 2 S. 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 H 2 S 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 H 2 S and 973-1173 K for biogas containing 20-108 ppm H 2 S. 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 H atoms 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.

This paper presents detailed study of biogas reforming. Model biogas with different levels of H 2 S is subjected to reforming reaction over supported Ni catalyst in a fixed bed reactor at 700 o C and 800 o C. In order to understand the poisoning effects of H 2 S the reactions have been initially carried out without H 2 S in the feed stream. Three different H 2 S concentrations (20, 50 and 100 ppm) have been considered in the study. The H 2 O to CH 4 ratio is maintained in such as way that CO 2 also participates in the reforming reaction. After performing the poisoning studies, regeneration of the catalyst has been studied using three different techniques i) removal of H 2 S from the feed stream ii) temperature enhancement and iii) steam treatment. Poisoning at low temperature is not recoverable just by removal of H 2 S from the feed stream. However, poisoning at high temperature is easily reversed just by removal of H 2 S from the feed stream. Unlike some previous reports [1,2], catalyst regeneration is achieved in shorter time frames for all the regeneration techniques attempted.

The vapor-phase reactions of nascent volatiles derived from the fast pyrolysis of lignin were investigated both experimentally and numerically. Lignin residue after enzymatic hydrolysis was pyrolyzed in a two-stage tubular reactor at 773− 1223 K. The nascent volatiles formed in the first stage underwent vapor-phase reactions in situ in the second stage. A detailed chemical kinetic model that consists of more than 500 species and 8000 elementary reactions was used to simulate the vaporphase reactions of volatiles derived from fast pyrolysis of lignin. The contribution of tar in the vapor-phase reactions was considered in global reactions, which improves the predictive capability of the kinetic model. The experimental data and numerical predictions of 31 products were compared and analyzed to understand the mechanism of vapor-phase reactions of lignin. The model predictions were in good agreement with the experimental observations. Reaction pathway analysis for the formation of aromatic hydrocarbons was performed. Cyclopentadienyl radicals produced from phenol decomposition were suggested as important intermediates in the formation of aromatic hydrocarbons during lignin pyrolysis.

The reaction pathways leading to aromatic hydrocarbons such as benzene and naphthalene in gas phase reactions of multi-component mixtures derived from cellulose fast pyrolysis were studied both experimentally and numerically. A two-stage tubular reactor was used for evaluating the reaction kinetics of secondary vapor phase cracking of the nascent pyrolysates at temperature

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