SOLUBILITY OF NaCl IN CO2 AT HIGH PRESSURE AND TEMPERATURE: FIRST EXPERIMENTAL MEASUREMENTS

Abstract

NaCl solubility in gaseous carbon dioxide has been measured in the pressure range from 30 to 70 MPa at 623 and 673 K. Our originally-designed high pressure apparatus allows in situ sampling of a portion of the fluid phase for chemical analysis. The results indicate that the solubility of NaCl increases with both temperature and pressure, and is about 4-5 orders of magnitude higher than saturated NaCl pressure values at the same temperature conditions (6.02 × 10-12 at 623 K and 1.51 × 10-10 at 673 K). It is also 1-2 orders of magnitude greater than predictions according to the Equation of State of the ternary H2O-CO2-NaCl system by Duan, Moeller and Weare [Duan, Z., Moller, N., and Weare, J. H. (1995) Equation of state for the NaCl-H2O-CO2 system: prediction of phase equilibria and volumetric properties. Geochim. Cosmochim. Acta 59, 2869] and has the opposite pressure dependence. The activity values of NaCl in the vapor phase, calculated from the experiments (with pure molten NaCl as a standard state in the vapor), have been fitted to the Darken Quadratic Formalism: RT ln aNaCl,v = RT ln xNaCl,v - 2 WNaCl s(-) CO2G · xNaCl,v + BNaCl s(-) CO2G, where, xNaCl,v is mole the fraction of NaCl in the vapor phase, WNaCl s(-) CO2G = (1936.3 - 43.669 · P) × 106, BNaCl s(-) CO2G = 83, 754 - 420.1 · P, where P is the pressure in MPa and T the absolute temperature. Caution should be exerted while extrapolating this empirical equation far beyond the experimental P-T-compositional range. © 2007 Elsevier Ltd. All rights reserved.