Near-infrared spectroscopic solubility measurement for thermodynamic analysis of melting point depressions of biphenyl and naphthalene under high-pressure CO2 |
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Affiliation: | 1. Mary Kay O’Connor Process Safety Center, Artie McFerrin Department of Chemical Engineering, Texas A&M University System, College Station, TX 77843-3122, USA;2. Professor of Environmental Chemistry & Processes, Department of Environmental & Natural Resources Management, School of Engineering, University of Patras, SEFERI 2, Agrinio, Greece, Greece |
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Abstract: | Melting temperatures of organic solids are often depressed by high-pressure CO2 due to a dissolution of CO2 in the molten organic compounds. For thermodynamic analysis of the melting point depression, solubilities of CO2 in molten biphenyl and naphthalene were measured by near-infrared spectroscopy at various temperatures and pressures up to 20 MPa. Molarity of the organic component was determined from the 3νCH absorption band, and that of CO2 from the 2ν1 + ν3 band. Mole fraction of CO2 in the liquid phase was found to be an increasing function of the pressure up to 0.6 at 20 MPa and a weakly decreasing function of the temperature. The solubility data were used for modeling of the mixtures by the Peng–Robinson equation of state with a binary interaction parameter k12. Calculation of the solid–liquid–gas phase equilibrium for the model fluid qualitatively described a large decrease in the melting temperature with increasing pressure up to 10 MPa followed by a small change at higher pressures. The melting point change was interpreted by the two competing effects: hydrostatic pressure effect increases the melting point by ca. 8 °C at 20 MPa, whereas CO2 solubility effect reduces it by ca. 30 °C. Decomposition of the solubility effect into ideal and non-ideal mixing parts revealed that the non-ideality increases the melting point by more than 10 °C. |
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Keywords: | Vibrational spectroscopy Peng–Robinson equation of state Supercritical carbon dioxide Solid–liquid–gas phase equilibrium Activity coefficient |
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