Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Isobaric heat capacity cp measurements are reported at temperatures between (108 and 168) K for liquid mixtures of CH4 (1) + C3H8 (3) at x1 0.8 and p 5 MPa; CH4 (1) + C4H10 (4) at x1 = 0.96, 0.88, and 0.60 and p 5 MPa; and a five-component mixture that is similar in composition to a commercial mixed refrigerant at p = (1.0 and 5.0) MPa. Measurements were made, with an estimated uncertainty of about 0.02*cp, using a specialized calorimeter further modified to prevent preferential condensation of the less volatile component and minimize possible stratification of the mixture during sample loading. Our results for CH4 + C3H8 agreed within 0.02*cp of the values predicted using the GERG 2008 equation of state (EOS), whereas literature cp data over the same temperature range agree within 0.03*cp. In contrast the cp predicted for this mixture with the Peng Robinson EOS (PR-HYSYS) shows an offset of about 0.02*cp from the average of the literature data at 165 K, which increases to 0.045*cp at 120 K. For CH4 (1) + C4H10 (4) our data for x1 = 0.96 and 0.88 are within 0.05*cp of the GERG 2008 predictions; however, at x1 = 0.6, the deviations increase from 0.02*cp at 168 K to nearly 1.1*cp at 118 K. The PR-HYSYS predictions for this binary mixture deviate from the measured cp data by 0.11*cp at 168 K, which increases to 0.21*cp at 118 K. For the mixed refrigerant (mole fraction composition 0.247 CH4 + 0.333 C2H6 + 0.258 C3H8 + 0.076 C4H10 + 0.059 N2), the deviations of the measured cp from GERG 2008 are less than 0.02*cp in the range (168 to 148) K, increasing to 0.19*cp at 108 K. The deviations from the predictions of PR-HYSYS range from 0.07*cp at 168 K to 0.15*cp at 108 K. Similar differences from the various EOS are observed for the data of Furtado, who measured the cp of a mixture with a mole fraction composition of 0.359 CH4 + 0.314 C2H6 + 0.327 C3H8 at similar temperatures.