Selective CO₂ Capture from CO₂/N₂ Gas Mixtures Utilizing Tetrabutylammonium Fluoride Hydrates

Gas hydrates, a type of inclusion compound capable of trapping gas molecules within a lattice structure composed of water molecules, are gaining attention as an environmentally benign gas storage or separation platform. In general, the formation of gas hydrates from water requires high-pressure and low-temperature conditions, resulting in significant energy consumption. In this study, tetrabutylammonium fluoride (TBAF) was utilized as a thermodynamic promoter forming a semi-clathrate-type hydrate, enabling gas capture or separation at room temperature. Those TBAF hydrate systems were explored to check their capability of CO₂ separation from flue gas, the mixture of CO₂ and N₂ gases. The formation rates and gas storage capacities of TBAF hydrates were systematically investigated under various concentrations of CO₂, and they presented selective CO₂ capture behavior during the hydrate formation process. The maximum gas storage capacities were achieved at 2.36 and 2.38 mmol/mol for TBAF·29.7 H₂O and TBAF·32.8 H₂O hydrate, respectively, after the complete enclathration of the feed gas of CO₂ (80%) + N₂ (20%). This study provides sufficient data to support the feasibility of TBAF hydrate systems to be applied to CO₂ separation from CO₂/N₂ gas mixtures based on their CO₂ selectivity.