CO₂Methanation in a Slurry Bubble Column Reactor - Influence of the Liquid Phase on the Reaction Kinetics and Reactor Design

The Power-to-Gas process, which enables the transformation of electric energy to chemical energy via water electrolysis and subsequent methanation, is a promising way to store surplus electricity from renewable sources in form of chemical energy carriers. In this process, electric energy can be provided by fluctuating and intermittent solar and wind energy, while biogas can be used as CO2 source for the methanation. Because of the fluctuating nature of renewable electricity, the CO2 methanation has to be operated under dynamic conditions. The CO2 methanation reaction is highly exothermic, which makes reactor temperature control under dynamic operation conditions challenging. To tackle this issue, a slurry bubble column reactor is an attractive reactor concept: the high heat capacity of the heat transfer liquid allows for isothermal process conditions and a more efficient cooling compared to state-of-the-art two-phase reactors. For the design of a slurry bubble column reactor for CO2 methanation purposes, some pieces of information are required. The CO2 methanation reaction kinetics in a three-phase system is needed and the effect of the liquid phase on the reaction kinetics of the CO2 methanation has to be clarified. The experimental results related to CO2 methanation kinetics measured in a three-phase system and a kinetic rate equation for the CO2 methanation will be shown. Additionally, to clarify the influence of a liquid phase on the methanation kinetics, experimental measurements on CO2 methanation kinetics carried out in a two-phase system will be provided and compared to results from three-phase system. Based on this information, the influence of the liquid phase on the methanation reaction and on the overall Power-to-Gas process design will be shown.