Isobaric heat capacity measurements of liquid methane + propane, methane + butane, and a mixed refrigerant by differential scanning calorimetry at high pressures and low temperatures

Tauqir H. Syed, Thomas J. Hughes, Kenneth N. Marsh, Eric F. May

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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·c p 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 CH 4 + 0.333 C2H6 + 0.258 C3H 8 + 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·c p 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.

Original languageEnglish
Pages (from-to)968-974
Number of pages7
JournalJournal of Chemical and Engineering Data
Issue number4
Publication statusPublished - 10 Apr 2014
Externally publishedYes

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