Enhanced CO2 capture from flue gas using TBAF semi-clathrate hydrates: A comprehensive thermodynamic and kinetic study

The rapid increase in atmospheric CO₂ concentrations has exacerbated the greenhouse effect, posing a significant threat to ecological balance. Conventional CO₂ capture methods suffer from high energy consumption and poor selectivity. Hydrate-based CO₂ separation technology has garnered significant attention due to its high energy efficiency and environmental friendliness. In this study, the thermodynamic and kinetic properties of CO₂ + N₂ hydrate formation were explored using TBAF as a thermodynamic promoter at room temperature with the aim of improving hydrate formation and reducing energy costs. At the same degree of subcooling, 5 wt% TBAF showed the shortest semi-completion time (T₉₀), while 20 wt% TBAF resulted in the highest gas consumption, indicating that the optimal additive concentration requires a balanced consideration of multiple factors. The synergistic effect of additive blends containing 10 wt% TBAF and L-methionine, L-tryptophan or graphite particles on hydrate formation was evaluated. Specifically, the addition of 0.4 wt% 35 nm graphite particles resulted in a 62.4 % reduction in the time to T₉₀, while the use of 0.6 wt% L-tryptophan led to a 14.4 % increase in gas consumption. Notably, the promotion efficacy followed the order: graphite particles > L-methionine > L-tryptophan, which can be attributed to the superior specific surface area and thermal conductivity of graphite. Additionally, 35 nm graphite particles demonstrated higher solubility compared to 500 nm and 1000 nm counterparts. Interestingly, TBAF semi-clathrate hydrates showed two different crystallization pathways depending on the degree of subcooling. This study offers valuable insights into the development of HBGS technology and the mechanisms of semi-clathrate hydrate formation.