NOVELTY - Device for separating gases comprises: three membrane separating units comprising a feed stream separating unit, a retentate separating unit and a permeate separating unit; at least one compressor; and/or at least one, preferably one or two vacuum pumps. The feed stream separating unit separates feed stream comprising at least two components into a first permeate stream and a first retentate stream. The retentate separating unit separates the first retentate stream into a second permeate stream, which is fed to the feed stream, and a second retentate stream, which is removed as a product.    USE - The device is useful for separating gases.    ADVANTAGE - The device: separates the gas mixtures into components with high purity; requires less investment- and operational costs; and carries out the separation in simple process.    DETAILED DESCRIPTION - Device for separating gases comprises: three membrane separating units comprising a feed stream separating unit, a retentate separating unit and a permeate separating unit; at least one compressor; and/or at least one, preferably one or two vacuum pumps. The feed stream separating unit separates feed stream comprising at least two components into a first permeate stream and a first retentate stream. The retentate separating unit separates the first retentate stream into a second permeate stream, which is fed to the feed stream, and a second retentate stream, which is removed as a product. The permeate separating unit separates the first permeate stream into a third retentate stream, which is fed to the feed stream, and a third permeate stream which is removed as a product. The first permeate stream is not subjected to recompression. A gas separation membrane module with a mixed gas selectivity of at least 30 is used at least in one feed stream separating unit, preferably in all three membrane separating units. The device is designed such that the total recirculated gas volumes in the second permeate stream and the third retentate stream, is less than 60 vol.% of the volume of crude gas stream. The concentration of at least one permeate gas of the feed stream separating unit, after returning the second permeate stream and the third retentate stream into the feed stream, is increased by at least 2%, preferably 3-40%, respectively in comparison to the concentration in the crude gas stream. An INDEPENDENT CLAIM is also included for separating the gas mixtures, comprising using the above device.