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

Published

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 = 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 0.98Tc(x) less than or equal to} T less than or equal to} 1.15Tc(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

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 April 24, 2024)
Created February 1, 2005, Updated October 12, 2021