Investigating Reforming Kinetics of a Synthetic Biogas Mixture on Ni: Model Development and Experimental Validation

A thermodynamically consistent mechanistic rate modelfor steamreforming (SRM) and catalytic partial oxidation (CPOx) of a syntheticbiogas mixture on a Ni catalyst is derived in this work. A microkineticmodel (MKM) consisting of 42 irreversible reactions served as thestarting point for the development of the model equations presentedin this study. A global sensitivity analysis based on ANOVA usingSobol sampling is conducted on the MKM to identify important reactionsthat describe SRM, CPOx, and water-gas shift reaction (WGSR),which occur alongside CH4 reforming. The unimportant reactionsare eliminated to obtain a reduced elementary reaction model, whichis subjected to validation by reproducing the predictions of 42 reactionsof the MKM. The rate-determining steps (rds) are identified for SRM,WGSR, and CPOx, from the reduced mechanism by using a net reactionrate and partial equilibrium analysis. Mechanistic rate expressionsare derived from the identified rds by adopting the Langmuir-Hinshelwood-Hougen-Watsonapproach. The parameters of these mechanistic rate models for SRM,WGSR, and CPOx are estimated by using a real coded genetic algorithm.The rate models with the estimated parameters could reproduce theexperimental observations with good accuracy. The predictive capabilityof the derived rate models is established by comparing the model predictionswith the experimental measurements of SRM, combined steam and dryreforming, and trireforming. The reforming experiments were performedfor a synthetic biogas mixture containing CH4/CO2 = 2, in a packed bed reactor using 10 wt % Ni/& gamma;-Al2O3. Overall the mechanistic models were able to predictthe experimental measurements with good accuracy.