CERE seminar by Omofolasewa Hillary Jayeola

Mixtures of CO₂+ brine: density measurements

The geological storage of CO₂requires a comprehensive understanding of theintricate phase behaviour of CO₂ + X, where "X" denotes impurities, such as nitrogen, argon, methane, SO_x, NO_x, etc., in the injected CO₂stream, or the in-situ fluids that interact with CO₂like brine and hydrocarbon phases. To store CO₂with minimal to no additional purification after capture to meet the current rigorous standards for storage[1,2], quality experimentally measured phase equilibria and transport properties data are crucial. These data can then be used to develop thermodynamic models that can accurately predict the phase behaviour of the relevant mixtures. However, such data pertinent to this field are still sparse in literature.

To that end, we measured the single-phase densities of CO₂in [()NaCl +CaCl₂](aq) brine at 1 and 2.5 mol·kg^-1molality, where= 0.089 mol·mol^-1, using the vibrating tube densimeter illustrated in Figure 1. Measurements were taken at temperatures ranging from 278.15 to 463.15 K and at pressures up to 140 MPa. These conditions were selected to extensively investigate the influence of temperature, pressure, composition and salt salinity on the mixture density for CO₂storage.

The density results show that the partial molar volume is independent of the composition of CO2 for all the systems. The apparent molar density () modelling approach in conjunction with the model proposed by Al Ghafri et al.[2]for pure salt mixtures has been found to be reliable for modelling CO₂+ brine systems. As illustrated in Figure 1, the data collected show thatincreases with temperature, with a stronger dependency than pressure, particularly at higher temperatures.

[1]         [1] Northern Lights, Liquid CO₂(LCO₂) Quality Specifications, 2024.https://norlights.com/wp-content/uploads/2024/06/NorthernLights-GS-co2-spec2024.pdf.

[2]         [2] Porthos CO₂Transport and Storage, CO₂Specifications, 2021.https://www.porthosco2.nl/wp-content/uploads/2021/09/CO2-specifications.pdf.

[3]         [3] S. Al Ghafri, G.C. Maitland, J.P.M. Trusler, Densities of aqueous MgCl₂(aq), CaCl₂(aq), KI(aq), NaCl(aq), KCl(aq), AlCl₃(aq), and (0.964 NaCl + 0.136 KCl)(aq) at temperatures between (283 and 472) K, pressures up to 68.5 MPa, and molalities up to 6 mol·kg^-1, J Chem Eng Data 57 (2012) 1288–1304.https://doi.org/10.1021/je2013704.