Critical and supercritical properties for 0.3 to 3.0 mol · kg −1 CaCl 2(aq)

Abstract

Critical temperatures ( T c ) and densities ( ρ c ) for aqueous CaCl 2 solutions were measured using two different optical techniques. Fluid inclusions with compositions of 0.5 to 4.0 mol · kg −1 were synthesized from 600 to 820°C and at 1500 and 2500 bars in both the single and two-fluid phase fields. Critical temperatures were determined from measured homogenization temperatures and the observed mode of homogenization (i.e., to the liquid or vapor phase or by fading of the meniscus between apparent equal volumes of liquid and vapor). Critical temperatures determined by this method for 0.5, 1.0, 2.0, and 3.0 molal CaCl 2(aq) solutions are 395, 406, 466, and 565°C, respectively, T c for 4.0 molal CaCl 2(aq) was found to be in excess of 662°C. Critical pressures ( P c ) could not be accurately determined from these measurements but were estimated from another source. Measurements of T c were also made using sealed silica capillaries containing 0.3, 0.5, 1.0, and 2.0 molal CaCl 2(aq) solutions. T c values from these measurements are 388, 393, 405, and 465°C, respectively. Our data are in fair agreement with previously published data at and below 1.0 mol · kg −1. Above 1 mol · kg −1, data from the two published sources of CaCl 2(aq) T c measurements show substantially different trends, with the data from this study agreeing with the more recent of the two reports. Estimated values of ρ c are given for the solutions examined in the capillary tube experiments. These measurements are based on estimated tube volumes, measured liquid volumes, and solution densities at ambient temperature. Critical isochores are presented with new synthetic fluid inclusion derived isochores for 1.0 and 2.0 mol · kg −1 CaCl 2(aq) liquids to form a complete arrays of isochores for temperatures from ~ 100°C to those along the critical isochore and pressures to 5000 bars.