Iron-based ionic liquid ([BMIM][FeCl4]) as a promoter of CO2 hydrate nucleation and growth

Hydrate technology is a promising alternative method for carbon dioxide (CO2) capture and storage from flue gas. In order to promote the hydrate growth rate and increase gas storage capacity, CO2 hydrate nucleation and growth induced by iron-based ionic liquid ([BMIM][FeCl4]) was studied with 400 rpm rotation speed at a temperature of 274.15 K and initial pressure of 5.0 MPa in this work. The induction time of CO2 hydrate formation was decreased by 52.8% and the storage capacity of CO2 hydrate was increased by 13.7% in 25.0 g/L [BMIM][FeCl4] solution. The local hydrogen bonds are strengthened by the combination interaction between the complex anion ([FeCl4]−) and water (H2O) molecules, which is favorable to the ordered arrangement and the proton exchange rate of H2O molecules during the hydrate nucleation. Besides, large mass transfer channels are formed by the large molar volume and regular tetrahedral structure of [FeCl4]− during the hydrate growth, which improves the diffusion rate of CO2 and H2O molecules in the solution to promote the hydrate growth. Distribution of lipophilic cation and hydrophilic anion with a large molecular volume of [BMIM][FeCl4] at the gas-liquid interface hinders the formation of cage structure of H2O molecules.