Near-infrared spectroscopic solubility measurement for thermodynamic analysis of melting point depressions of biphenyl and naphthalene under high-pressure CO2

作者：Takebayashi Yoshihiro^*; Sue Kiwamu; Furuya Takeshi; Hakuta Yukiya; Yoda Satoshi

来源：Journal of Supercritical Fluids, 2014, 86: 91-99.

DOI：10.1016/j.supflu.2013.12.007

• Vibrational spectroscopy
• Peng-Robinson equation of state
• Supercritical carbon dioxide
• CO2-expanded liquids
• Solid-liquid-gas phase equilibrium
• Activity coefficient

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 3 nu(C-H) absorption band, and that of CO2 from the 2 nu(1) + nu(3) 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 k(12). 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 degrees C at 20 MPa, whereas CO2 solubility effect reduces it by ca. 30 degrees 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 degrees C.

• 出版日期2014-2