Portable medical oxygen concentrator comprising an air separation system (15) adapted to recover oxygen from air a bottom platform (9) and a shell (1) having an outer wall, wherein the shell is detachably connected to the bottom platform, wherein the shell and bottom platform define an enclosed volume when the shell is connected to the bottom platform, and wherein the air separation system is disposed in the enclosed volume and one or more rechargeable batteries (11,13) detachably connected to the outer wall of the shell and adapted to provide power to drive the air separation system. The air separation system (15) may comprises a pressure swing adsorption system having two or more adsorbent columns and a rotary valve for directing gas flow sequentially to, from, and among the columns. A base assembly attached to the bottom platform may be adapted to support the two or more adsorbent columns and the rotary valve.
