Pure and Applied Chemistry

Abstract: Capturing CO₂ emissions from energy production and storing it under the ground is a potential CO₂ mitigation strategy that currently receives much attention. Both CO₂ capture and CO₂ storage are solubility problems. This paper reviews some important solubility aspects of CO₂ capture and storage that are often overlooked. Until very recently, there was not a single CO₂ solubility relationship that was both applicable in a wide temperature range and thermodynamically consistent with the enthalpy of solution of CO₂. Furthermore, very often the relationship used for the first acidity constant of carbonic acid as a function of temperature is inconsistent with the relationship used for the solubility constant (or Henry constant) of CO₂. The removal of CO₂ from a gas stream with amine solutions is usually viewed as a chemical reaction, which leads to the practice of heating to remove the CO₂ from the solvent. However, viewing this process as a solubility phenomenon suggests the practice of using vacuum to remove the CO₂ from the solvent, a potentially more efficient approach.