Vapor−Liquid Equilibria Measurements of the Methane + Pentane and Methane + Hexane Systems at Temperatures from (173 to 330) K and Pressures to 14 MPa

Abstract

New pTxy data are reported for methane + pentane and methane + hexane at pressures up to 14 MPa over the temperature range (173 to 333) K using a custom-built vapor−liquid equilibria apparatus. For methane (1) + pentane (2), a mixture with overall mole fraction z 2 ≈ 0.02 was prepared gravimetrically, and measurements were performed along an isochoric pathway. For the methane (1) + hexane (3) mixture, liquid hexane was pumped into the evacuated cell using an HPLC pump, and then after the addition of methane, isothermal measurements were made at 11 temperatures. Two liquid phases were observed close to the bubble point in the methane + hexane mixture at (183.15 and 233.15) K at pressures of (3.31 and 12.99) MPa, respectively. Our data are compared with previous literature data and with the predictions of the Groupe European de Recherche Gaziere (GERG-2004 XT08) multiparameter equation of state (EOS) and the Peng−Robinson and Advanced Peng−Robinson cubic equations of state implemented in commercial process simulation software. The differences from the GERG-2004 EOS in the liquid phase mole fraction x 1 were up to 0.1 for methane + pentane and up to 0.3 for methane + hexane. The systematic increase in the deviations with pressure, at constant temperature, is clear evidence of the need for tuning of the EOS parameters, especially at high pressure. The differences are smaller for the Peng−Robinson and the Advanced Peng−Robinson EOS; however, all three EOS failed to predict the second liquid phase in methane + hexane. Our data agree with the x 1 values reported by Chen et al. (J. Chem. Eng. Data 1976, 21, 213−219) for the appearance of a second liquid phase.

Characterisation of a microwave re-entrant cavity resonator for phase-equilibrium measurements and new dew-point data for a (0.25 argon + 0.75 carbon dioxide) mixture

“…Phase equilibrium (vapour-liquid) measurements of fluid mixtures are often carried out via the analytic method, which involves taking samples from the coexisting phases to analyse the composition (e.g., by gas chromatography, GC) [4]. The uncertainty achievable in the measured composition via the analytic method is, however, limited by both the challenges of sampling repeatability and the accuracy of the GC's detector calibration [5]. In contrast, the synthetic method, where the phase boundary of a fluid with known composition is measured, does not suffer the disadvantages associated with sampling but it does require a means of detecting the onset of a phase transition.…”

Simulating the capture of CO2 from natural gas: New data and improved models for methane + carbon dioxide + methanol

“…The apparatus used for VLE measurements in this work has been described in detail previously; (Kandil et al, 2010(Kandil et al, , 2011 and improvements described by Kandil et al (2011) for the methane + hexane measurements were implemented in this work. For the methane (1) + methanol (2) binary, one measurement was made at a T = 200.10 K and p = 3.07 MPa and five measurements were made at T = 193.15 K and p between 0.55 and 2.88 MPa.…”

“…The liquid mole fractions predicted with the simulator using the default values of the EOS's binary interaction parameters (BIPs) are shown to be poor, as has been found elsewhere, e.g. (Kandil et al, 2010(Kandil et al, , 2011. To improve the calculated VLE, the BIPs for each cross-binary were optimized (the optimization method is described below) using the standard mixing rule, but the need for further improvement was still evident.…”

“…As described in our previous works (Kandil et al, 2010(Kandil et al, , 2011, to rigorously quantify the uncertainty in composition measurements by GC it is essential to perform a calibration of the GC's detectors. The GC was equipped with both thermal conductivity detectors (TCDs) and flame ionization detectors (FIDs).…”

“…The area measured using the FID was compared to the areas measured with the gas sample loops and the volume of the liquid sampling valve was determined to be 0.43 ± 0.01 L. The methanol FID response factor was then obtained by passing pure methanol and two gravimetrically prepared solutions of methanol in 2-propanol (x 2 = 0.1 and 0.5) from the sample valve to the GC. Finally, relative response coefficients were determined for methanol relative to methane (FID) and carbon dioxide relative to methane (TCD) (Kandil et al, 2010(Kandil et al, , 2011.…”