Influence of Amino Acid Compound Additives on Hydrate Formation Kinetics, CO₂/N₂ Gas Separation, and CO₂ Capture

The increasing global carbon emissions necessitate efficient CO2 separation and capture technologies. The hydrate-based CO2 separation and capture technology has recently gained increasing attention and application due to its advantages. In this study, flue gas (CO2/N2 = 0.2/0.8) hydrate formation was investigated at 7.0 MPa using tetra-n-butyl ammonium bromide (TBAB) as a thermodynamic promoter and l-methionine (l-Met) as a kinetic promoter. The results revealed that hydrate formation occurred instantaneously upon initiating stirring regardless of whether TBAB or a combination of TBAB and l-Met was used as the additive. Increasing the concentration of TBAB or decreasing the reaction temperature accelerated the formation of the hydrates. When both the TBAB and l-Met were used concurrently, the maximum CO2 gas consumption was 0.101 mol at a temperature of 277.1 K, with a TBAB mass fraction of 0.1. Compared to the pure l-Met additive system, the addition of TBAB causes the hydrate structure to transition from pure structure I to a mixture of structure I and semiclathrate. Furthermore, the hydrate crystals were larger and exhibited stacked growth with pure TBAB as an additive, whereas distinct pore channels were observed in the system with both l-Met and TBAB.