Determination of P–V–T–x properties of the CO2–H2O system up to 573.15 K and 120 MPa—Experiments and model

• A new method was developed to measure P–V–T–x properties of the CO2–H2O system up to 513.15 K and 120 MPa.
• The data partially fill the current density/molar volume data gap.
• The apparent molar volume of CO2 in water (VΦ,CO2) shows obvious negative dependence on pressure beyond 298.15 K.
• The pivoting temperature (where ρCO2–H2O = ρH2O) monotonously increases from 489 K at 30 MPa to 575 K at 120 MPa.
• A revised VΦ,CO2 model for dilute CO2–H2O systems was proposed.

A new method is being developed as part of this study to measure the Pressure–Volume–Temperature–composition (P–V–T–x) properties of the CO2–H2O system at temperatures from 273.15 to 513.15 K and pressures from 30 to 120 MPa. The density of a CO2–H2O solution is determined by measuring the volumetric change of the solution sealed in a capillary High-Pressure Optical Cell (HPOC), through a systematic correction. This study partially fills the current density/molar volume data gap for dilute CO2–H2O systems. Data show that the density of CO2–H2O mixture (ρCO2–H2O) changes little below 298.15 K, then decreases more rapidly than ρH2O with increasing temperature at constant pressure, and eventually becomes lower than ρH2O in high temperature range (for example, above 489 K at 30 MPa). This pivoting temperature (Tp, above which ρCO2–H2O becomes lower than ρH2O) monotonously increases with increasing pressure (to 575 K as the pressure reaches 120 MPa). The calculated apparent molar volume of CO2 in water (VΦ,CO2) is independent of CO2 concentration, but is negatively correlated to pressure when the temperature is above 298.15 K. A revised VΦ,CO2 model for dilute CO2–H2O systems is proposed based on this study. This revised model can reproduce both the current and previous density data with an acceptable error range at temperatures up to 573.15 K and pressures up to 120 MPa. It can be used reliably to simulate geological sequestration of CO2 into water aquifers, and in the study of P–V–T–x evolution of geo-fluids (e.g., CO2-bearing aqueous ore forming fluids).

Figure optionsDownload as PowerPoint slide