Evaluation of amino acid L-leucine as a kinetic promoter for CO2 sequestration as hydrate: A kinetic and morphological study

Carbon capture and sequestration (CCS) are widely recognized as the most effective technology for reducing CO2 emissions and mitigating global climate change. Hydrate-based CO2 sequestration (HBCS) has emerged as a promising technology for long-term and stable CO2 storage. There are growing interests in employing hydro-phobic amino acids to enhance CO2 hydrate formation kinetics recently. However, there is still a lack of understanding of how amino acids promote CO2 hydrate effectively. In this study, we systematically investigate an environmental-benign kinetic promoter (L-leucine, L-Leu) varying from 0.05 to 2.00 wt% to enhance CO2 hydrate formation at an initial pressure of 5.5 MPa and temperature of 275.2 K. The results show that varying L-Leu concentration has limited effect on tind. The kickoff concentration of L-Leu in promoting CO2 hydrate kinetics is 0.30 wt%. 2.00 wt% L-Leu yields the optimal CO2 gas uptake of 62.17 +/- 0.78 mmol/mol with CO2 partition in the hydrate phase of 66 %. CO2 hydrate forms a layer at the gas-liquid interface and turns to be porous at CL-Leu above 0.30 wt% followed by a significant wall-climbing growth with rapid CO2 gas uptake. L-Leu precipitation occurs at CL-Leu above 1.00 wt% and leads to a decrease in final CO2 gas uptake in repeated experiments at CL-Leu = 2.00 wt%. A mechanism of L-Leu in promoting CO2 hydrate kinetics by adsorption on the surface at CL-Leu above 1.00 wt% is proposed. L-Leu is evaluated to be effective in improving CO2 hydrate kinetics. These findings provide insights for a novel environmental-benign CO2 hydrate kinetic promoter in HBCS application, which requires rapid CO2 hydrate formation and high CO2 gas uptake.