A gas separation unit for the separation of carbon dioxide from air is proposed for use in a cyclic adsorption/desorption process and using a loose particulate sorbent material. The loose particulate sorbent material is disposed within an internal volume of an external support structure and supported by the external support structure, the external support structure comprising a plurality of base portions, deflected portions, and openings. The sheets are arranged parallel defining an inlet face and an outlet face, are arranged with a distance in the range of 0.1-2.5 cm (preferably 0.1-0.5 cm), and the inflow passes through the inlet face, subsequently through the particular sorbent material located in the cavity of the respective layer, subsequently to exit the layer through the outlet face to form the gas outflow. Directionality of the inflow and the outflow through the external support structure is controlled by the deflected portions of the external support structure.