Adsorption of nitrogen on alumina at high pressure

A method is described for determining adsorption isotherms of gases on solids under elevated pressures. Results are given for nitrogen as adsorbate and alumina as adsorbent. The range covered extends to 3000 atm at temperatures between ‐ 7.6° and 100°. The volume in which the experimentally determined equation of state is valid is defined as the total volume v minus a volume v0 of the adsorbent sample inaccessible to the gas as determined with helium at low pressures. A quantity ΔG is taken as a measure of the amount of gas adsorbed. It is defined as the difference between the total amount of gas exposed to the adsorbent and the quantity which would be present in the volume v ‐ v0 at the experimental temperature and pressure if no adsorption occurred. With increase of pressure ΔG increases till a gas density ρg of about 175 amagat is reached, then it falls off (practically linearly with ρg), but rises again steeply at densities above 500 amagat. No hysteresis has been found; the alumina showed no permanent change after completion of the experiments. In the first and second range δΔG/δT is negative but in the third section it changes sign. Apparently the adsorption then changes from an exothermic to an endothermic process. An attempt is made to interpret the linear section in terms of a simple two‐phase model.