Kinetic model of CO2 methanation in a microreactor under Power-to-Gas conditions

The kinetics of CO2 methanation using a 12%Ni/gamma-Al2O3 catalyst was modeled in a catalytic microreactor, considering the three-dimensional momentum, heat and species continuity balances in stationary state. The microreactor consisted of 80 microchannels with dimensions 0.45 x 0.15 x 50 mm(3) in each one with an average 0.04 mm catalytic thickness. Several experimental tests were carried out at various conditions of flow rate (110, 130 and 140 mL/min), temperature (275, 300, 325 and 350 degrees C) and reactants partial pressure. Kinetic parameters were modeled and fitted using COMSOL Multiphysics 6.0 and Matlab 2021 R. Using the corrected Akaike information criterion (AICc), it was determined that a power kinetic model with a low kinetic exponent, 0.12 <= n <= 0.18, is adequate to represent a wide range of experimental CO2 conversion and CH4 yield (up to 86%) data. An activation energy around 83-85 kJ/mol was estimated, as well as a correlation between the different parameters of the power rate law. The temperature raise significantly increases the CO2 conversion and methane yield under the operational conditions used, due to the distance from thermodynamic equilibrium. It was numerically verified that under the experimental conditions the microchannels operate isothermally. Using this model, it is possible to evaluate the effect of operational variables (temperature, volumetric flow and H-2/CO2 ratio) and reactor design (microchannel surface/volume ratio) on methane production, proving potential application in catalytic efficiency studies for Power-to-Gas applications. It is clear that processes intensification is useful to achieve higher CO2 conversions fostering sustainable development of closed-carbon production cycles.