The continuous increase of electricity production from renewable energy sources (RES) introduces the intrinsic fluctuating characteristic of RES in the electric power grid, causing non-trivial grid management issues (e.g. grid congestion). In this work, an innovative power to liquefied methane concept was developed and process simulations for a 200 kWel demonstration plant were carried out. The proposed concept is based on water electrolysis to produce hydrogen, CO2 capture from air using solid adsorption materials, catalytic CO2 methanation, gas separation and a single mixed refrigerant (SMR) liquefaction process. The gas separation unit produces an exhaust stream, rich in hydrogen and carbon dioxide but also in methane, that is recycled to the methanation unit inlet. A thermodynamic analysis excluded the possibility of carbon deposition formation in the methanation reactor due to methane recirculation. The gas separation system was designed using a combination of temperature swing adsorption techniques (stream dehumidification) and membrane separation (CO2 separation). After a screening of different polyimide type membranes, a two-stage layout was selected and dimensioned. Subsequently the liquefaction unit was developed optimizing the SMR composition and pressures to minimize the total work required. Hence, the minimum work required for the liquefaction resulted being 0.57 kWhel/kgLNG. Finally, the thermal integration was performed to minimize the external heat requirement. The heat produced by the electrolyser and methanation unit is greater than the thermal energy requirement by the CO2 capturing unit during desorption. A process efficiency up to 46.3% (electric to chemical) resulted from the study. The process modelling results also evidenced that the impact of the gas pre-treatment and liquefaction process on the plant energetics is 4% of the total power input.

Power to gas systems is one of the most interesting long-term energy storage solutions. As a result of the high exothermicity of the CO₂ methanation reaction, the catalyst in the methanation subsystem is subjected to thermal stress. Therefore, the performance of a commercial Ni/Al₂O₃ catalyst was investigated over a series of 100 hour-long tests and in-process relevant conditions, i.e. 5 bar from 270 to 500 °C. Different characterization techniques were employed to determine the mechanism of the observed performance loss (N₂ physisorption, XRD, TPO). The TPO analysis excluded carbon deposition as a possible cause of catalyst aging. The BET analysis evidenced a severe reduction in the total surface area for the catalyst samples tested at higher temperatures. Furthermore, a direct correlation was found between the catalyst activity decline and the drop of the catalyst specific surface. In order to correctly design a reliable methanation reactor, it is essential to have a kinetic model that includes also the aging kinetics. For this purpose, the second set of experiments was carried out, in order to determine the intrinsic kinetics of the catalyst. The kinetic parameters were identified by using nonlinear regression analysis. Finally, a power-law aging model was proposed to consider the performance loss in time.

Solar-driven CO2 reduction technologies face unique challenges when transitioning from laboratory to prototype scale. In the European Union-funded SunCoChem project, efforts focused on designing and validating a reactor for CO2 conversion to syngas with a suitable ratio, with an area up to 2,400 cm2, for subsequent upgrading into a hydroformylation unit. In addition to selectivity, ensuring process durability remains critical for economic viability. Yet practical implementation at the lab scale remains difficult. To address this, we combined operando electrochemical impedance spectroscopy (EIS) with stress testing, enabling early identification of degradation pathways based on productivity-related parameters. Importantly, we overcame the intrinsic limitations of conventional EIS analysis based on equivalent-circuit modelling by using relaxation-time distribution analysis. We present an integrated approach that successfully couples in-operando EIS with a 120 cm2 prototype, providing a diagnostic framework for real-time monitoring and quantification of failure modes. We discuss practical approaches to addressing current technological bottlenecks and give a perspective on future optimization strategies.