Thermodynamic properties of n-hexane

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 constantvolume 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%, 15 mK, and 0.001 mole fraction, respectively. The Krichevskii parameter was estimated (124.4 ( 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 V h 2 ∞ 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 H 2 O + n-C 6 H 14 mixture along the critical isotherm-isochore of pure water were also used to estimate the critical exponent of partial molar volume V h 2 ∞ ∝ x -( ) 0.795 ( 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 H 2 O + n-C 6 H 14 mixture with an average absolute deviation (AAD) of about 0.50-0.65% in the temperature and density ranges 0.98T c (x) e T e 1.15T c (x) and 0.35F c (x) e F e 1.65F c (x), respectively, and concentrations up to 0.05 mole fractions of n-hexane. The accuracy and predictive capability of the crossover model was confirmed by comprehensive comparison of present crossover EOS for the pure n-hexane with the available experimental data in the critical and supercritical regions.

Section: Resultsmentioning

confidence: 59%

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

Abdulagatov

Базаев

Magee

et al. 2005

“…Isochoric and isobaric heat capacities of methane and n -hexane. Points, literature data. ,, Lines, predictions of the proposed approach.…”

Section: Resultsmentioning

confidence: 99%

Standardized Critical Point-Based Numerical Solution of Statistical Association Fluid Theory Parameters: The Perturbed Chain-Statistical Association Fluid Theory Equation of State Revisited

Polishuk

2014

109

125

The current study has aimed at developing an approach replacing the lists of the compound-specific molecular parameters attached to perturbed chain-statistical association fluid theory (PC-SAFT) by the entirely transparent and universal method for their derivation. The proposed approach requires limited data for the numerical solution of the PC-SAFT parameters, namely, the critical constants and the triple point liquid density. Its implementation has necessitated a careful re-evaluation of part of the PC-SAFT universal parameters matrix and some additional revisions. The resulting model appears to be virtually free of several undesired numerical pitfalls characteristic for PC-SAFT. The proposed equation of state (EoS) has been implemented for modeling data of nonpolar substances such as the light compounds, n-alkanes, and 1-alkenes and their mixtures. Using a large experimental database (more than 6000 points) it has been demonstrated that it exhibits remarkable precision in predicting the high-pressure liquid phase densities and sound velocities, with AAD hardly exceeding 3% even in the cases of complex asymmetric mixtures. However, a major drawback of the proposed model is a poor accuracy of predicting the vacuum vapor pressures of heavy compounds away from their critical points.

“…For n -hexane and n -decane all parameters v 00 , u 0 , Gi , d 1 , and v 1 in the crossover SAFT EOS were found from a fit to the experimental data. For the critical parameters T c and ρ c we adopted the values obtained by Grigoryev et al for n -hexane and by Ely for n -decane. Comparisons of the crossover SAFT equation of state with PVT experimental data in the one-phase region for n -hexane and n -decane are shown in Figures and and with the VLE data in Figures and .…”

Section: Comparison With Experimental Datamentioning

confidence: 99%

Crossover SAFT Equation of State: Application for Normal Alkanes

Kiselev

Ely

1999

126

In this paper we develop a crossover modification of the statistical associating fluid theory (SAFT) equation of state for macromolecular chain fluids which incorporates the scaling laws asymptotically close to the critical point and is transformed into the original classical SAFT equation of state far away from the critical point. A comparison is made with experimental data for pure methane, ethane, n-hexane, n-decane, and n-eicosane in the one- and two-phase regions. We also present comparisons with experimental single-phase data for n-triacontane and n-tetracontane. We show that, over a wide range of states, the crossover SAFT model yields a much better representation of the thermodynamic properties of pure fluids than the original SAFT equation of state. The crossover SAFT equation of state reproduces the saturated pressure data in the entire temperature range from the triple point to the critical temperature with an average absolute deviation (AAD) of about 3.8%, the saturated liquid densities with an AAD of about 1.5%, and the saturated vapor densities with an AAD of about 3.4%. In the one-phase region, the crossover SAFT equation represents the experimental values of pressure in the critical region with an AAD of about 2.9% in the region bounded by 0.05ρc ≤ ρ ≤ 2.5ρc and T c ≤ T ≤ 2T c, and the liquid density data with an AAD of about 3% at the pressures up to P = 2000 bar. For the n-alkanes C m H2 m +2 with the molecular weight M w > 142 (m > 10), the crossover SAFT model contains no adjustable parameters and can be used for the pure prediction of the fluid thermodynamic surface.