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

ABSTRACT

This paper presents measurements of the enthalpy of vaporization of pure and binary hydrocarbon fluid mixtures using a commercial differential scanning calorimeter (DSC). The DSC was modified to allow the direct measurement of enthalpies of vaporization, vapH, at temperatures as low as 80 K and pressures as high as 10 MPa and was tested by measuring enthalpies of vaporization, both under vaporization and under condensation, for pure methane at T = (118, 123, 128, and 133) K and pure ethane at T = (208 and 213) K. The measured values had relative deviations of less than 3% from recommended literature values. Then vapH was measured for mixtures of methane + ethane, methane + propane, and ethane + propane at various temperatures by both condensing and vaporizing samples. In contrast to the pure fluid measurements, the measurement pathway affected the value of vapH obtained because the condensation occurred along a constant composition pathway whereas the composition varied during vaporization as a result of distillation. To facilitate comparison of the vapH measured for mixtures along the vaporization pathway, samples of the vapor phase produced at different temperatures were captured and their composition analyzed. For the mixture with a cricondentherm temperature below 235 K, the vapH values measured during both condensation and vaporization had relative deviations from the values predicted using the GERG EOS of less than 2%. However, for the other mixtures with higher temperature cricondentherms relative deviations between 5% and 40% were observed because of limitations with the fill stem s temperature control. This analysis of the limitations of the mixture measurements could enable more successful efforts in the future.