ADSORPTION IN MICROPOROUS MATERIALS: ANALYTICAL EQUATIONS FOR TYPE I ISOTHERMS AT HIGH PRESSURE

摘要

Existing analytical equations for Type Ⅰ isotherms such as the Langmuir equation and its modifications fail to describe experimental adsorption isotherms at high pressure. All of these equations predict that the amount adsorbed increases monotonically with increasing pressure. Experimental adsorption isotherms attain a maximum value in the amount adsorbed and then fall to zero. At the critical temperature of the gas, the maximum in the isotherm occurs at a pressure of about 10 bars and the zero occurs at a much higher pressure of several hundred bars. For subcritical gases, the maximum occurs at lower pressure and for supercritical gases the maximum occurs at higher pressure. The observed behavior of high-pressure adsorption isotherms can be predicted from the low-pressure (sub-atmospheric) portion by separating the Type Ⅰ behavior expected for absolute adsorption from the experimental behavior observed for excess adsorption.