A study on three-phase CO₂ methanation reaction kinetics in a continuous stirred-tank slurry reactor

The reaction kinetics of the three-phase CO₂ methanation for a commercial Ni/SiO₂ catalyst suspended in a liquid phase is studied in a continuous stirred-tank slurry reactor at a CO₂ partial pressure of 1 bar and temperatures from 220 °C to 320 °C. By applying different liquids, namely squalane, octadecane, and dibenzyltoluene, showing different gas solubilities, it is found that the gas concentration in the liquid phase and not the partial pressure in the gas phase is the driving force for the CO₂ methanation reaction kinetics. The liquid phase does not influence the reaction kinetics but reduces the available gas concentrations and H₂/CO₂ ratio on the catalyst surface. Based on these findings, a kinetic rate equation for the three-phase CO₂ methanation is developed additionally incorporating the chemical equilibrium limitations relevant in the temperature regime.