Kinetic analysis of CO2 hydrate formation in the aqueous solutions of transition metal chlorides

Abstract

CO₂ hydrate technology can be applied to seawater desalination. However, the kinetics of CO₂ hydrate formation were inhibited in the aqueous solution with inorganic salts, and the kinetic mechanism of CO₂ hydrate formation for inorganic salts with different metal cations and anions was still unclear. In this work, CO₂ hydrate nucleation and growth were studied in aqueous solutions of metal chlorides. Instead of Na⁺ and K⁺ ions, CO₂ hydrate nucleation was promoted in the presence of Ni²⁺, Mn²⁺, Zn²⁺ and Fe³⁺ ions due to the co-ordination bonds between transition metal ions and water molecules to enhance the formation of the critical crystal nuclei. The induction time was increased by 61.1% in aqueous solution with 0.32 mol/L NaCl, while it was shortened by 55.6% in FeCl₃ aqueous solution at the same concentration of Cl⁻ anions. In the process of CO₂ hydrate growth, Cl⁻ ions played a more important role than the metal ions in affecting the stability of CO₂ hydrate cages. The gas storage capacity was reduced by 10.3% in the presence of NaCl, and was lower than that of other metal chlorides. Cl⁻ anions were absorbed on the hydrate surface and involved in hydrate cages to inhibit the hydrate growth due to the hydrogen bonds between the Cl⁻ ions and water molecules of the hydrate cages. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.