Experimental investigations on cryogenic adsorption of nitrogen over activated charcoal

Three samples of activated charcoal were tested for nitrogen adsorption capacity at 77 K. Adsorption isotherms have been generated for the samples with equilibrium pressures ranging from pbar levels to the saturation pressure. The isotherms’ shape is of Type-I and has a linear p/V vs p relationship which is consistent with the behavior of microporous adsorbents. Adsorption capacities for Sample 1 are 11% w/w at pbar equilibrium pressure levels and around 34% w/w at near saturation pressure. Similarly, for Sample 2 and 3, the corresponding capacities are 6% w/w, 8% w/w and 30% w/w, 28% w/w. Based on the data, design of inline purifiers for Helium refrigerator/liquefier cold boxes and external Helium purifiers can be made more precise. Knowledge of capacity variation with impurity concentration will enable the designer to select a suitable average adsorption capacity over the range of concentration desired in the purifier.