Effect of Salts, Impurities, and Low Water Contents in the Formation of Gas Hydrates in CO₂-Rich Streams

Abstract

Carbon capture utilization and storage (CCUS) together with natural gas production from high CO 2 -containing reservoirs has raised attention to the formation of CO 2 -rich gas hydrates. These gas mixtures can contain impurities such as Ar, O 2 , N 2 , H 2 , NxOy, CO, H 2 S, SO 2 , or mercury, some of which are also hydrate formers or potential corrosion enhancers. This paper addresses the use of thermodynamic models to predict the phase behavior of CO 2 -rich streams. It starts from the overall binary phase equilibria of CO 2 with water. Then, gas hydrates and the effect of different impurities on the hydrate phase behavior are observed. Furthermore, the effect of salts on CO 2 solubility and the influence of inhibitors such as salts on CO 2 hydrate suppression are analyzed. For modeling hydrates, the solid solution theory of van der Waals and Platteeuw, as implemented by Parrish and Prausnitz, is used coupled with the Cubic-Plus-Association equation of state (CPA EoS) for representing the fluid phases. The influence of electrolytes on hydrate formation and CO 2 solubility in brines is modeled with an add-on electrolyte term based on the Debye−Huckel theory. The main objective of this Perspective is to consider all possible phase equilibria simultaneously, as in CCUS applications we cannot detach the different phase equilibria conditions. The results demonstrate that the selected models can accurately represent the phase behavior of CO 2 -rich streams and the effect of salts and impurities on gas hydrate formation.