The existing infrastructure for natural gas storage and transport made the Sabatier process an attractive step within the power‐to‐gas process chain for intermittent renewable energy storage. A model‐based optimal design for the methanation of carbon dioxide with hydrogen to methane under process‐wide constraints is presented. After inclusion of the downstream units into the analysis, the product methane fulfils the specifications for the natural gas grid. The optimization goal was to maximize the space–time yield by applying the systematic flux‐oriented elementary process function methodology. The optimum temperature and concentration profiles along the reaction coordinate were first determined, after which they were approximated using two reaction configurations: 1) a hydrophilic membrane reactor and 2) a cascade of polytropic reactors with interstage condensation. The results show that an optimized cascade of three polytropic fixed bed reactors (e.g., optimum temperature profile) and two intermediate condensation steps is the best technical approximation for maximizing the space–time yield.

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In the present contribution, the operation of a low temperature polymer electrolyte membrane fuel cell (PEMFC) with H2/CO and N2/CO mixtures is studied. The aim of the work is to clarify a discrepancy between earlier experiments with conventional electrochemical arrangements and experiments carried out with PEMFCs: Investigations of CO oxidation with rotating disk electrode (RDE) setups in acidic electrolytes revealed a hysteresis in the polarization curve around the onset overpotential of CO oxidation, which was not found in PEMFCs so far. The proof of a hysteresis in the PEMFC polarization curve could be interesting in terms of fuel cell performance, because it was argued that its presence also influences the oxidation of H2/CO mixtures. Indeed, in the present work, this hysteresis during operation with a N2/CO mixture is found, but it is seen that it disappears once H2 is added. To understand the background of these studies, a spatially lumped model is derived.