Quantitative Raman spectroscopic investigation of geo-fluids high-pressure phase equilibria: Part I. Accurate calibration and determination of CO2 solubility in water from 273.15 to 573.15 K and from 10 to 120 MPa

We developed an accurate method to calibrate Raman system for measuring the concentrations of dissolved gases in aqueous geo-fluids at high pressure, and determined CO2 solubility in water at temperatures from 273.15 to 573.15 K and pressures from 10 to 120 MPa. The Raman peak area ratio (PAR) and peak intensity ratio (peak height ratio, HR) of the upper band (at ∼1390 cm−1) of CO2 Fermi dyad to the OH stretching band of water in homogeneous CO2 solutions were obtained over wide temperature, pressure, and concentration ranges. Pressure and concentration (mCO2) show little effects on PAR/mCO2 and HR/mCO2, while PAR/mCO2 increases linearly with temperature from 273.15 to 573.15 K, and HR/mCO2 decreases linearly with temperature at a different rate at temperatures below and above 404.45 K. The solubility data obtained from 298 to 523.15 K are consistent with previous experimental and thermodynamic studies. However, predictions from commonly-used thermodynamic models for temperatures below 298.15 K and above 523.15 K substantially deviate from the new measurements, suggesting that new or refined parameters are needed to improve these models.