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

Abstract

A thermodynamically consistent mechanistic rate model for steam reforming (SRM) and catalytic partial oxidation (CPOx) of a synthetic biogas mixture on a Ni catalyst is derived in this work. A microkinetic model (MKM) consisting of 42 irreversible reactions served as the starting point for the development of the model equations presented in this study. A global sensitivity analysis based on ANOVA using Sobol sampling is conducted on the MKM to identify important reactions that describe SRM, CPOx, and water–gas shift reaction (WGSR), which occur alongside CH4 reforming. The unimportant reactions are eliminated to obtain a reduced elementary reaction model, which is subjected to validation by reproducing the predictions of 42 reactions of the MKM. The rate-determining steps (rds) are identified for SRM, WGSR, and CPOx, from the reduced mechanism by using a net reaction rate and partial equilibrium analysis. Mechanistic rate expressions are derived from the identified rds by adopting the Langmuir–Hinshelwood–Hougen–Watson approach. 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 the experimental observations with good accuracy. The predictive capability of the derived rate models is established by comparing the model predictions with the experimental measurements of SRM, combined steam and dry reforming, and trireforming. The reforming experiments were performed for a synthetic biogas mixture containing CH4/CO2 = 2, in a packed bed reactor using 10 wt % Ni/γ-Al2O3. Overall the mechanistic models were able to predict the experimental measurements with good accuracy.