Frequency Response Analysis of the Unsteady-State CO/CO₂ Methanation Reaction: An Experimental Study
2022
Meyer, Dominik | Schumacher, Jannik | Friedland, Jens | Güttel, Robert
The utilization of renewable electricity for power-to-gas (PtG) applications induces fluctuations in H₂ availability from water electrolysis. For subsequent methanation of CO or CO₂, the unsteady-state operation of the respective reactor allows to minimize H₂ storage capacities. However, the impact of temporal fluctuations in feed gas composition on the methanation reaction and the respective transient kinetics has not yet been fully understood. We investigated the methanation of various CO/CO₂ (COₓ) feed gas mixtures under periodically changing gas compositions with an emphasis on the effect of frequency on the reactor response. We show that the frequency response of CH₄ exhibits a characteristic hysteresis, which depends on the switching direction between COₓ-lean and COₓ-rich feeds and their composition. From the shape of the hysteresis, we are able to conclude on the preferred COₓ species being hydrogenated to CH₄ under respective conditions, which also provides mechanistic insights. By applying high cycling frequencies, the highly reactive species present under CO methanation conditions can even be selectively activated, which explains the higher reactivity compared to steady-state conditions reported frequently.
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