Empirical evaluation of the Krichevskii parameter for aqueous solutes

The Krichevskii parameter, AKr, is the only solute-specific characteristic of an infinitely diluted species close to the critical point of a solvent, governing many properties of solutions, including the near-critical variations of Henry's constant and solubility of a solute. The knowledge of the Krichevskii parameter is important for non-empirical applications in the SCF extraction and other technological processes at near-critical conditions. The experimental determination of AKr typically requires accurate measurements at challenging conditions of the near-critical region and cannot be performed for all solutes of industrial interest. Here we present an empirical linear relation between the Krichevskii parameter of aqueous solutes and the Gibbs energy of hydration (or Henry's constant) of corresponding species at 298.15 K and 0.1 MPa. Even in the absence of thermodynamic information, the knowledge of the composition and chemical properties of solutes may be used to roughly predict the type of the near-critical behavior (repulsive, weakly attractive or attractive) and the approximate value of the Krichevskii parameter of aqueous neutral species.