Hydrogenation of CO/CO2 mixtures under unsteady-state conditions: Effect of the carbon oxides on the dynamic methanation process

The Power-to-Gas (PtG) process offers the opportunity to store fluctuating renewable energy in form of chemical energy by hydrogenating carbon oxides into methane. In addition, potential carbon point sources often consist of CO/CO2 (COx) mixtures. Hence, reactor design requires kinetic models valid for unsteady-state operation and a broad spectrum of feed gas compositions. In order to provide the required experimental data basis for derivation of kinetic expressions valid under transient conditions, the dynamic response of a continuously operated fixed-bed methanation reactor is studied by applying periodic step-changes in the feed composition. The obtained results are evaluated based on a simple reactor model, providing the molar flow rate exchanged between the gas bulk and the solid surface for CO, CO2, CH4, and H2O. The results further reveal that the transient kinetic processes at the catalyst surface strongly affect the reactor response under reaction conditions of technical relevance.