NOVELTY - Separating a first gas mixture comprising carbon dioxide and methane into a second gas mixture with a relatively high methane content and a third gas mixture with a relatively high carbon dioxide content, comprises (i) providing the first gas mixture, (ii) admitting the first gas mixture into at least one vessel (1-4) in which an adsorption mass (5) to adsorb carbon dioxide is received, (iii) discharging the separated second gas mixture from the vessel, and (iv) discharging the third gas mixture, where the method is performed in accordance with a vacuum swing adsorption process (VSA process).    USE - The method is useful for separating a first gas mixture comprising carbon dioxide and methane into a second gas mixture with a relatively high methane content and a third gas mixture with a relatively high carbon dioxide content (claimed). The methane is useful as renewable energy carrier.    ADVANTAGE - The method economically separates the carbon dioxide and methane without performing compression or thermal regeneration steps and with high yields of 90-99%, purity of at least 97 vol.%, and reduced energy consumption.    DETAILED DESCRIPTION - Separating a first gas mixture comprising carbon dioxide and methane into a second gas mixture with a relatively high methane content and a third gas mixture with a relatively high carbon dioxide content, comprises (i) providing the first gas mixture, (ii) admitting the first gas mixture into at least one vessel (1-4) in which an adsorption mass (5) for adsorbing carbon dioxide is received, (iii) discharging the separated second gas mixture from the vessel, and (iv) discharging the third gas mixture from the vessel, where the method is performed in accordance with a vacuum swing adsorption process (VSA process), and admitting the first gas mixture during step (ii) takes place under an absolute pressure of a maximum of 1.5 bar, and discharging the third gas mixture during step (iv) takes place under an absolute pressure of a maximum of 0.5 bar, and the adsorption mass comprises carbon molecular sieve (CMS) material. An INDEPENDENT CLAIM is included for a device (10) for separating a first gas mixture comprising carbon dioxide and methane into a second gas mixture with a relatively high methane content and a third gas mixture with a relatively high carbon dioxide content, comprising a number of vessels, where each vessel has at least one inlet (6) and one outlet (7), and an adsorption mass for absorbing carbon dioxide is provided in each of the vessels.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a device for separating a first gas mixture.    Vessel (1, 2, 3, 4)    Adsorption mass (5)    Inlet (6)    Outlet (7)    Device for separating a first gas mixture. (10)