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Power-to-Methane as one part of Power-to-Gas has been recognized globally as one of the key elements for the transition towards a sustainable energy system. While plants that produce methane catalytically have been in operation for a long time, biological methanation has just reached industrial pilot scale and near-term commercial application. The growing importance of the biological method is reflected by an increasing number of scientific articles describing novel approaches to improve this technology. However, these studies are difficult to compare because they lack a coherent nomenclature. In this article, we present a comprehensive set of parameters allowing the characterization and comparison of various biological methanation processes. To identify relevant parameters needed for a proper description of this technology, we summarized existing literature and defined system boundaries for Power-to-Methane process steps. On this basis, we derive system parameters providing information on the methanation system, its performance, the biology and cost aspects. As a result, three different standards are provided as a blueprint matrix for use in academia and industry applicable to both, biological and catalytic methanation. Hence, this review attempts to set the standards for a comprehensive description of biological and chemical methanation processes.

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Three ionic liquids {butyl-trimethyl-ammonium bis(trifluoromethylsulfonyl)imide [N 1114 ][BTA], 1-methyl-1propyl-piperidinium bis(trifluoromethylsulfonyl)imide [PMPip][BTA], and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][Tf]} and two heat-transfer oils [dibenzyltoluene (DBT) and polydimethylsiloxane (trade name X-BF)] were evaluated for use in the three-phase methanation and the biogas purification processes. The density, viscosity, and surface tension of these liquids were measured and modeled as a function of the temperature. The solubilities of H 2 , CO, CO 2 , and CH 4 in these five liquids were also obtained under different pressures and temperatures. Additionally, the criteria required for each of the two processes considered were identified: the three-phase methanation process requires a thermally stable liquid with a low vapor pressure and a high H 2 , CO 2 and CO solubility, while the biogas purification process requires a highly selective CO 2 solubility liquid at ambient temperature. From the evaluation of both the experimental data and the process requirements, the most suitable liquid for each of the aforementioned processes was identified. For the three-phase methanation process, the two ionic liquids [N 1114 ][BTA] and [PMPip][BTA] and the two heat-transfer oils DBT and X-BF met the minimum requirements, while [EMIM][Tf] showed promising potential for the biogas purification process.

This work focuses on the deactivation and in-situ regeneration effects of a commercial PdO/Al 2 O 3 catalyst for removal of oxygen by oxidation of CH 4 at low O 2 :CH 4 ratios when hydrogen sulfide and sulfur dioxide are applied. The experimental work is carried out at an operating temperature range of 200 °C < T < 300 °C, atmospheric pressures and H 2 S contents of < 50 ppmv. SO 2 and H 2 S show a different behavior in the examined range of operating conditions. Due to the low operating temperatures and low oxygen contents applied in this work, it was possible to identify an intermediate species, presumably PdSO 3 , with an increased activity for the oxidation of methane. This stands in contrast to the literature, where SO 2 typically causes catalyst deactivation. Based on the experimental results, a reaction scheme was derived and kinetic measurements for each of the participating reactions were carried out separately.