Investigation of semi-clathrate formation kinetics for post-combustion CO 2 capture in the presence of amino acids

Semi-clathrates are a class of inclusion compounds in which a part of guest molecule involves in the formation of cage structure along with water and the other remaining part of guest molecule occupies and stabilizes the gas hydrate structure. Semi-clathrate based carbon capture encages carbon dioxide in hydrate cages which is an energy -efficient and economical pathway for carbon dioxide capture. This study examines the kinetics of tetrabutyl ammonium flouride (TBAF) based carbon dioxide capture at near ambient temperatures and the impact of amino acids on hydrate formation have been examined. The promotion effect of three selected amino acids - Lmethionine, L-tryptophan and L -leucine on TBAF mixed semi-clathrates has been documented in this work. Experiments were conducted with simulated flue gas mixture of 25.2% CO 2 /74.8% N 2 at 8 MPa pressure and temperatures of 293.2 K and 298.2 K. The morphology of hydrate growth and the composition of recovered CO 2 gas are also presented. Results indicate that lower TBAF concentration (10 - 20 wt%) experiments showcase an improved CO 2 selectivity of up to 70% in the hydrate phase and higher TBAF concentration improved the total amount of gas stored per mole of water with a maximum of about 10 mmol of gas/mol of water. The gas uptake was found to increase for higher concentrations (20 wt% and 33.7 wt%) of TBAF in the solution. The average gas uptake value increased from 2.43 mmol/mol (10 wt% TBAF) to 9.96 mmol/mol (33.7 wt% TBAF) during the hydrate formation at 298 K and 8 MPa. 20 wt% TBAF solution showed highest separation of CO 2 in hydrate phase. L methionine, L-tryptophan and L -Leucine amino acids in concentration range of 0.1 wt% - 2 wt% were used with 10 wt% TBAF solution amongst which 2 wt% L-methionine provided the best promotion.