NOVELTY - The device comprises a separating unit (14), a compressor (2) connected in upstream of the separating unit, and two filter units (5, 6) connected in parallel upstream of the separating unit. A permeate outlet of the separating unit is connected by lines to the respective input of the filter units. An outlet of the filter units is connected by the lines (9, 10) respectively to an offgas line (11). The device further comprises a control valve and control or regulating valves arranged in the lines. The offgas line is connected to a reheater.    USE - The device is useful for separating a gas mixture into product gas and offgas by gas permeation (claimed), where gas mixture includes biogas used for generation of electrical energy for a vehicle or a gas supply system, the product gas is methane and offgas is carbon dioxide.    ADVANTAGE - The device easily and rapidly separates the gas mixture into product gas and offgas.    DETAILED DESCRIPTION - The device comprises a separating unit (14), a compressor (2) connected in upstream of the separating unit, and two filter units (5, 6) connected in parallel upstream of the separating unit. A permeate outlet of the separating unit is connected by lines to the respective input of the filter units. An outlet of the filter units is connected by the lines (9, 10) respectively to an offgas line (11). The device further comprises a control valve and control or regulating valves arranged in the lines. The offgas line is connected to a reheater. The compressor with gas mixture is connected to the inputs of the filter units via lines. A heat exchanger is provided in a branch line and in the line of the reheater. The control or regulating valve is arranged in the line in upstream of the heat exchanger. The control valve is present in fluid communication with the off-gas line via the control or regulating valve. An INDEPENDENT CLAIM is included for a method for cleaning and regeneration of the filters.    DESCRIPTION OF DRAWING(S) - The figure shows a block diagram of a device for separating a gas mixture into product gas and offgas.    Compressor (2)    Filter units (5,6)    Lines (9, 10)    Offgas line (11)    Separating unit. (14)