Molecular Insights into Water Solubility in Fluid Carbon Dioxide for CCS Applications

Abstract

Abstract We estimate the solubility of water as an impurity in fluid CO2 by calculating the chemical potential from intermolecular interactions. The evaluation is conducted across a broad range of temperatures and pressures relevant to CO2 transport and storage. The formation of hydrate from impurity of water reduces the solubility relative to the value expected for fluid CO2 coexisting with the metastable aqueous solution without hydrate formation. The solubility of water obtained shows good agreement with experimental measurements and model calculations. Compression leads to a lower solubility in a range of the gaseous state when the solubility is expressed in the conventionally used mole fraction. We show that this is merely an apparently strange behavior and disappears by changing the unit to molarity. The molarity-based solubility is beneficial not only for the present study to understand temperature and pressure dependence of solubility in terms of intermolecular interactions but also for correlating it with the driving force for water-induced corrosion. These fundamental insights into the phase equilibria of fluid CO2 and water are valuable for technological development to prevent pipeline blockages caused by hydrate formation and to mitigate water-induced corrosion in CO2 transport and storage.