(230e) New Insight in the NaCl-H2O Phase Diagram Under Pressure and Temperature

The phase diagram of NaCl-H₂O is known for a long time exhibiting a diphasic domain L-V up to 450°C (at 25MPa) and a V-S diphasic domain above. We have developed an experimental set-up to measure the salt solubility under near- and supercritical conditions. It is based on the precipitation of salts in a continuous tubular reactor with a filter to avoid the transport of solid particles ; the experimental set-up is equipped with an online conductivity cell to follow the evolution of salt concentration as a function of pressure and temperature. This experimental set-up has been validated with the determination of the solubility of Na₂SO₄ as a function of pressure and temperature. We obtained solubility values in good agreement with the values of the state of the art. We have after used this new set-up for investigating the precipitation of NaCl in near- and supercritical water. The first interesting result concerns the impact of the diphasic domain on the solubility of NaCl. While the NaCl-H₂O binary diagram predicts the end of the L-V domain at a temperature of 450°C as aforementioned, experimentally an abrupt decrease in NaCl concentration is observed at about 415°C, indicating its precipitation. This presentation aims to introduce the new developed set-up for the solubility measurement of salts in near- and supercritical water, to discuss our new insights in the NaCl-H₂O phase diagram thanks to this new set-up and to investigate the influence of this new zone of the NaCl-H₂O phase diagram on the behaviour of a more complex system, the NaCl-Na₂SO₄-H₂O one.