Experimental study of the PVTx relationship, L–L–V and L–V phase boundary of n-hexane + water mixtures near the upper and lower critical lines

Abstract

PVTx relationship, three- (L–L–V) and two- (L–V) phase boundary properties (,) of n-hexane + water mixtures near the upper and lower critical lines, including UCEP, have been measured with a constant-volume piezometer technique. The lower and upper critical temperatures, , the critical pressures, and the critical densities, for binary n-hexane + water mixtures were determined from the measured PVTx and phase boundary data near the critical points. The values of the Krichevskii parameter were determined from the directly measured P-x data along the critical isotherm-isochore of pure components (n-hexane and water) at the infinite dilution (x→0). The thermodynamic and structural properties of dilute n-hexane + water mixture near the critical point of pure solvents (water and n-hexane) were calculated using the Krichevskii parameter principle. The critical behaviour of the strongly singular properties (,), in terms of the principle of isomorphism of critical phenomena in binary mixtures, was studied.

Keywords:

• coexistence curve
• critical lines
• Krichevskii parameter
• isomorphism
• upper critical endpoint

Acknowledgement

I.M. Abdulagatov thanks the Applied Chemicals and Materials Division at the National Institute of Standards and Technology for the opportunity to work as a Guest Researcher at NIST during the course of this research.