Solubility of NaCl in CO 2 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 H 2O–CO 2–NaCl system by Duan, Moeller and Weare [Duan, Z., Moller, N., and Weare, J. H. (1995) Equation of state for the NaCl–H 2O–CO 2 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 a NaCl,v = RT ln x NaCl,v - 2 W NaCl – CO 2 G · x NaCl,v + B NaCl – CO 2 G , where, x NaCl,v is mole the fraction of NaCl in the vapor phase, W NaCl – CO 2 G = ( 1936.3 - 43.669 · P ) × 10 6 , B NaCl – CO 2 G = 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.