With research, I found my idea of using Dewar’s findings to separate air has been widely used in industry. of course. In fact, it is still used for volumes of less than several tons of oxygen or nitrogen production per day. (at rates greater than that, oxygen and nitrogen are first liquefied cryogenically and then distilled).
The process is not a chromatography process as i suggested, but is called pressure swing adsorption (not absorption), or temperature swing adsorption. At high pressure and/or low temperature gas is adsorbed onto the surface are of a highly porus material, and at low pressure and/or high temperature the gas is desorbed, oxygen first followed by nitrogen. On an industrial scale, PSA requires only a couple atmospheres, achievable in a single stage air compressor. Oxygen purities of 90-95% result. the other 5% or so is mostly argon. Nitrogen can also be purified in this way.
The temperature at which the charcoal is formed is crucial in making an effective adsorber. not only the surface area per volume is important, but also the charge structure of the charcoal.
I am very happy to learn about this process, because it is easily achievable on a small scale (bicycle powered?), and has been proven for about one hundred years. Also, the flue gasses of combustion processes using this oxygen would be mostly polar oxides and inert argon. I think argon could be realistically extracted, as carbon, hydrogen and sulfer dioxides have radically divergent solubilities and sizes from argon.