Water coadsorption effect on the physical adsorption of N-2 and O-2 at room temperature on carbon molecular sieve fibers

The effect of water vapours on the physical adsorption of nitrogen and oxyg en from air, on the surface of an activated carbon molecular sieve fibre, w as studied by temperature-programmed desorption mass spectrometry with a su personic molecular beam inlet system. During exposure of the carbon surface at room temperature to moist air, the adsorption kinetics for oxygen and n itrogen are fast, with oxygen being slightly faster, however, the water ads orption kinetics are much slower. When water starts to fill the pore volume , the adsorbed nitrogen and oxygen are removed, with oxygen being more easi ly removed. At high relative humidity, hydrogen bonding between neighbourin g water molecules leads to the formation of clusters of adsorbed water, whi ch trap the nitrogen molecules and form new sites for nitrogen adsorption. The effect of surface modification of carbon molecular sieves, by evacuatio n at high temperatures, on the adsorption sites of nitrogen and oxygen was also explored.