Carbon dioxide methanation kinetic model on a commercial Ni/Al2O3 catalyst

Intrinsic kinetic characterization of the carbon dioxide methanation was determined over a commercial 14–17 wt.% Ni/Al2O3 between 623 K and 723 K at atmospheric pressure in the absence of heat and mass transfer limitations. Following a Hougen-Watson formalism, both direct path (CO2 methanation rate equation) and indirect path (Reverse Water Gas Shift rate equation +CO methanation rate equation) were described. As a first step, kinetic tests were performed operating in differential mode to evaluate the reaction rate dependence on reactants and products partial pressure at different temperatures in order to select the form of each reaction rate equation. Kinetic models available in the literature were evaluated and compared with the experimental results and model adaptations were proposed to identify the kinetic laws that fit the best the experimental values. Kinetic and adsorption parameters were calculated from these laws. Then, the identified parameters were adjusted simultaneously on experimental tests from 5% to 75% CO2 conversion using an isothermal plug-flow reactor. The three reaction rates and their reverse reactions were identified in order to minimize the error on CO2 conversion and CH4 and CO selectivities at 623 K, 673 K and 723 K. The final identified kinetic model was able to reflect the kinetics from differential conversion to thermodynamic equilibrium with an accuracy of 20% on the CH4 formation rate for the three temperatures.