PVTx Measurements and Crossover Equation of State of Pure n-Hexane and Dilute Aqueous n-Hexane Solutions in the Critical and Supercritical Regions

Published

February 2, 2005

Author(s)

Ilmutdin Abdulagatov, Emil Bazaev, Joe W. Magee, Sergei B. Kiselev, James F. Ely

Abstract

The PVTx relationship of aqueous n-hexane solutions (0.0201, 0.082 and 0.8500 mole fraction of n-hexane) has been measured in the near-critical and supercritical regions with a constant-volume piezometer. Measurements were made on the critical isotherm of pure water 647.1 K with pressures ranging from 8 to 33 MPa. The total uncertainties of density, pressure, temperature, and composition measurements are estimated to be less than 0.16%, 0.05%, 15mK, and 0.001 mole fraction, respectively. The Krichevskii parameter was estimated (124.4 plus or minus} 20 MPa) from direct measurements of the P–x dependence along the critical isotherm-isochore of pure water. The measured PVTx data were used to calculate partial molar volumes at infinite dilution for n-hexane in near-critical water. The asymptotic behavior of the partial molar volume along the solvent's (pure water) critical isotherm-isobar was studied. The molar volume values for the dilute H₂O + n-C₆H₁₄ mixture along the critical isotherm-isochore of pure water were also used to estimate the critical exponent of the partial molar volume at infinite dilution for n-hexane proportional to x^-ε(ε = 0.795 plus or minus} 0.001). Using our new PVTx data together with data obtained in other studies, we developed a crossover Helmholtz free-energy model (CREOS) for dilute aqueous n-hexane solutions in wide temperature and pressure ranges around the vapor-liquid critical points. The CREOS model requires only the critical locus as an input and represents all available experimental PVTx data for a dilute H₂O = n-C₆H₁₄ mixture with an average absolute deviation (AAD) of about 0.50-0.65% in the temperature and density ranges 0.98T_c(x) less than or equal to} T less than or equal to} 1.15T_c(x) and 0.35pc(x) less than or equal to} ρ less than or equal to} 1.65 ρc(x) respectively, and concentrations up to 0.05 mole fractions of n-hexane. The accuracy of present crossover EOS for the pure n-hexane with the available experimental data in the critical and supercritical regions.

Citation

Industrial and Engineering Chemistry Research

Issue

44

Pub Type

Journals

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Citation

Abdulagatov, I. , Bazaev, E. , Magee, J. , Kiselev, S. and Ely, J. (2005), PVTx Measurements and Crossover Equation of State of Pure n-Hexane and Dilute Aqueous n-Hexane Solutions in the Critical and Supercritical Regions, Industrial and Engineering Chemistry Research, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50128 (Accessed November 7, 2025)