Thermodynamic Relationship to Estimate the Effects of High CO2 Concentration on the CO2 Equilibrium and Solubility in Seawater

Abstract

The effects of high CO2 concentrations on carbonate equilibrium are important in studies related to the disposal of liquid CO2 into the oceans. Using available thermodynamic data of liquid CO2 and CO2 solubility in seawater, an equation of solubility of liquid CO2 in seawater was developed as a function of temperature, pressure, and salinity. It is shown that the non-ideal behavior of acid-base species subjected to high CO2 conditions can be accounted for by Pitzer's parameters. The solubility of liquid CO2 in seawater between values from calculation using thermodynamic equations and those from literature was presented. The pH of seawater equilibrated with liquid CO2 was calculated to be elevated by approximately 0.20 pH unit due to the non-ideal effects of dissolved CO2 on acid-base equilibrium. Effects of high CO2 on seawater alkalinity are discussed. The interaction of liquid CO2 with seawater results in high CO2 concentrations. Technical assessment of environmental condition for a pool of liquid CO2 has to include measurements of two parameters of the carbonate system as a minimum, to calculate the others. The commonly accepted procedure for the calculation of the carbonate system of seawater includes equilibrium constants that were determined at trace concentrations of dissolved free CO2 in seawater. This chapter uses a theoretical approach, which permits one to take into account the effects of high CO2 concentrations on acid-base equilibrium using the ionic interaction approach or Pitzer method.