Gas solubility and Henry's law near the solvent's critical point

Abstract

Abstract It has been experimentally observed, for water and nonaqueous solvents alike, that Henry's constant passes through a maximum and then declines as the temperature is raised from the triple point to the critical point. From classical and nonclassical models, we derive exact relations for the value of Henry's constant and its temperature dependence at the solvent's critical point, showing that the decline of this constant is a universal phenomenon. We demonstrate that the limiting temperature dependence of Henry's constant can be predicted from the thermodynamic properties of the pure solvent and the initial slope of the critical line. The validity of our prediction is tested by comparing it with experimental solubility data for several gases in high‐temperature water and benzene. Our predictive model appears valid over a temperature range of at least 15% in temperature below the critical point of the solvent.