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Accurate Values of Some Thermodynamic Properties for Carbon Dioxide, Ethane, Propane, and Some Binary Mixtures

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journal contribution
posted on 2011-06-30, 00:00 authored by Inmaculada Velasco, Clara Rivas, José F. Martínez-López, Sofía T. Blanco, Santos Otín, Manuela Artal
Quasicontinuous PρT data of CO2, ethane, propane, and the [CO2 + ethane] mixture have been determined along subcritical, critical, and supercritical regions. These data have been used to develop the optimal experimental method and to determine the precision of the results obtained when using an Anton Paar DMA HPM vibrating-tube densimeter. A comparison with data from reference EoS and other authors confirm the quality of our experimental setup, its calibration, and testing. For pure compounds, the value of the mean relative deviation is MRD(ρ) = 0.05% for the liquid phase and for the extended critical and supercritical region. For binary mixtures the mean relative deviation is MRD(ρ) = 0.70% in the range up to 20 MPa and MRD(ρ) = 0.20% in the range up to 70 MPa. The number of experimental points measured and their just quality have enable us to determine some derivated properties with satisfactory precision; isothermal compressibilities, κT, have been calculated for CO2 and ethane (MRD(κT) = 1.5%), isobaric expasion coefficients, αP, and internal pressures, πi, for CO2 (MRD(αP) = 5% and MRD(πi) = 7%) and ethane (MRD(αP) = 7.5% and MRD(πi) = 8%). An in-depth discussion is presented on the behavior of the properties obtained along subcritical, critical, and supercritical regions. In addition, PuT values have been determined for water and compressed ethane from 273.19 to 463.26 K up to pressures of 190.0 MPa, using a device based on a 5 MHz pulsed ultrasonic system (MRD(u) = 0.1%). With these data we have calibrated the apparatus and have verified the adequacy of the operation with normal liquids as well as with some compressed gases. From density and speed of sound data of ethane, isentropic compressibilities, κs, have been obtained, and from these and our values for κT and αP, isobaric heat capacities, Cp, have been calculated with MRD(Cp) = 3%, wich is within that of the EoS.