A process used to selectively adsorb one or more components in a gas mixture under pressure onto a porous solid surface and then to release them again under reduced pressure. It is used in the separation of gases from mixtures such as the absorption of nitrogen from air onto a zeolite. The air leaving the process is therefore richer in oxygen. The zeolite is regenerated by reducing the pressure. Other commonly used absorbents include activated carbon, silica gel, and alumina.