CO₂ Capture from Flue Gas Based on Tetra-n-butylammonium Fluoride Hydrates at Near Ambient Temperature

Semiclathrate hydrates of tetra-n-butylammonium fluoride (TBAF) are potential CO₂ capture media because they can capture CO₂ at near ambient temperature under moderate pressure such as below 1 MPa. In addition to other semiclathrate hydrates, CO₂ capture properties of TBAF hydrates may vary with formation conditions such as aqueous composition and pressure because of their complex hydrate structures. In this study, we investigated CO₂ capture properties of TBAF hydrates for simulated flue gas, that is, CO₂ + N₂ gas, by the gas separation test with three different parameters for each pressure and aqueous composition of TBAF in mass fraction (w _TBAF). The CO₂ capture amount in TBAF hydrates with w _TBAF = 0.10 was smaller than that obtained with w _TBAF = 0.20 and 0.30. The results found that gas pressure greatly changed the CO₂ capture amount in TBAF hydrates, and the aqueous composition highly affected CO₂ selectivity. The crystal morphology and single-crystal structure analyses suggested that polymorphism of TBAF hydrates with congruent aqueous solution may lower both the CO₂ capture amount and selectivity. Our present results proposed that an aqueous solution with w _TBAF = 0.20 is advantageous for the CO₂ capture from flue gas compared to near congruent solutions of TBAF hydrates (w _TBAF = 0.30) and dilute solution (w _TBAF = 0.10).