Correlation strategy for determining the parameters of the revised Helgeson-Kirkham-Flowers model for aqueous nonelectrolytes

Isothermal compressibilities and isobaric expansibilities of pentane, hexane, heptane and their binary and ternary mixtures from density measurements

The apparent molar volumes Vφ of aqueous α-alanine, β-alanine, and proline have been determined with platinum vibrating tube densitometers at temperatures from 298 to 523 K and at pressures in excess of steam saturation. Values of the standard partial molar volumes V° for the aqueous amino acids increase with temperature then deviate toward negative values at temperatures above 398 K, consistent with a lowering of the critical temperature in the solutions relative to water. This is opposite to the behavior predicted by the correlations developed by Shock and Helgeson (Geochim. Cosmochim. Acta. 1990 54, 915−945) and Amend and Helgeson (J. Chem. Soc., Faraday Trans. 1997 93, 1927−1941). The contribution to V° from the solvent polarization by the large dipole moment of the zwitterions deviates toward negative infinity as Tc is approached, in a manner similar to the V° values for each of the aqueous amino acids. While this agreement is qualitatively consistent, it is not quantitatively consistent, which sugge...

Amino Acids under Hydrothermal Conditions: Apparent Molar Volumes of Aqueous α-Alanine, β-Alanine, and Proline at Temperatures from 298 to 523 K and Pressures up to 20.0 MPa

The apparent molar heat capacities Cp° of aqueous α-alanine, β-alanine, glycine, and proline have been determined using a differential flow calorimeter and a Picker flow microcalorimeter at temperatures of 298 K ≤ T ≤ 500 K and at pressures from steam saturation to 30 MPa. Comprehensive equations to describe the standard-state properties over this range are reported. Values of the standard partial molar heat capacities Cp° for the aqueous amino acids increase with temperature and then deviate toward negative values at temperatures above about 390 K, consistent with increasing the critical temperature in the solutions relative to water, i.e., negative Krichevskii parameters. This is opposite to the behavior predicted by correlations reported in the geochemical and chemical literature. The temperature dependence of Cp° predicted using the very recent functional group additivity model of Yezdimer et al. (Chem. Geol. 2000, 164, 259−280) is only in qualitative agreement with the experimental results. The resul...

Amino acids under hydrothermal conditions: Apparent molar heat capacities of aqueous α-Alanine, β-Alanine, glycine, and proline at temperatures from 298 to 500 K and pressures up to 30.0 MPa

Luis Delgado

Papers

Volumetric properties of glycine in water at elevated temperatures and pressures measured with a new optically driven vibrating-tube densimeter