Power-to-fuel applications represent a relevant option among energy storage technologies to overcome grid issues, such as overgeneration due to renewable energy sources exploitation. The production of raw hydromethane mixture, through water electrolysis and, downstream, methanation, can be integrated in power to liquefied natural gas systems allowing the exploitation of liquefied natural gas as energy carrier. It enables multiple uses linking multiple sectors (e.g. transport, industry, electric power production). Cryogenic separation techniques could be implemented aiming to an enhanced overall conversion efficiency. Key of this systematic review is the identification and analysis of the gas upgrade technologies that, moving from the raw hydromethane mixture, guarantee a final liquefied natural gas composition meeting the requirements imposed by: (i) grid injection and use in conventional endothermal engines after regasification (2 vol% H2); (ii) particular sensitivity of the natural gas liquefaction process to the presence of water (< 0.1 ppm) and CO2 (< 50 ppm). A critical review for hydromethane upgrade which faces the issues of real utilization is not available in literature, thus it is provided in this work. The paper is structured in two main parts: in the first gas dehydration techniques are described, while the second focuses on CO2 separation, highlighting advantages and application limits of low temperature techniques to the case of study. In the conclusions, a process optimal configuration is discussed for the production of liquefied natural gas from renewable electricity, as energy carrier suitable for multisectoral applications and compliant with scenarios of high renewable energy penetration.
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