ADSORPTION OF GASES AND VAPORS ON CARBON MOLECULAR-SIEVES

The adsorption phenomena of oxygen and nitrogen on a carbon molecular sieve were studied above the critical temperature of the adsorptives a s a function of pressure in order to understand further the mechanism of air separation. The uptake of both gases studied was virtually line ar at low equilibrium pressures, in agreement with Henry's law, but de viation occurred at higher pressures. The adsorption kinetics were stu died with different amounts of preadsorbed gas for changes in pressure of 11 kPa and partial pressure in helium of similar to 10 kPa. The ga s adsorption kinetics obey a linear driving force mass transfer model. The ratios of the rate constants (kO(2)/kN(2)) for each pressure incr ement were 35-43 for pure gases and 21-27 for gas/helium mixtures, and these ratios clearly demonstrate the molecular sieving characteristic s. The presence of water vapor is detrimental to the operation of carb on molecular sieves. The adsorption and desorption characteristics of water vapor with different amounts of preadsorbed water were studied f or comparison with oxygen and nitrogen adsorption over the pressure ra nge 0-1.8 kPa for pressure steps of 0.1 kPa. The results are discussed in terms of the mechanism of gas separation using carbon molecular si eves.