Effects of Tetrabutyl-(ammonium/phosphonium) Salts on Clathrate Hydrate Capture of CO2 from Simulated Flue Gas

Quaternary salts can form semi-clathrate hydrates, caging gas molecules in the empty small cages, which have the potential for the separation of mixtures, such as the simulated flue gas [CO 2 (17 mol %)/N 2 mixtures]. To enhance the CO 2 separation from CO 2 /N 2 binary mixtures, three quaternary salts, tetra- n -butylammonium bromide (TBAB), tetra- n -butylphosphonium bromide (TBPB), and tetra- n -butylammonium nitrate (TBANO 3 ), are investigated at different operating conditions by a one-stage hydrate separation process. The results indicate that the induction time for each quaternary salt system can be shortened to less than 5 min under the optimal operating condition. Meanwhile, each quaternary salt can significantly promote the CO 2 separation under its optimal condition. TBANO 3 displays the strongest capability in terms of gas consumption and CO 2 separation with the pressure drop of 0.72 MPa and the highest split fraction of 67% and separation factor of 15.54 compared to the other two salts. Besides, CO 2 can be further removed from 17 to 7 mol % in the presence of TBANO 3 . TBPB also has a potential effect on CO 2 separation with the pressure drop of 0.57 MPa and the separation factor of 14.06. The result demonstrates that TBANO 3 and TBPB are two better additives for efficient hydrate capture of CO 2 .