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

Abstract

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-nbutylphosphonium 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 .

Recent advances in gas hydrate-based CO2 capture

“…Increasing TBAB concentration not only reduces the equilibrium hydrate formation pressure but also increases the equilibrium hydrate forming temperature, which advances other clathrate hydrate promoters such as THF and CP (Meysel et al, 2011;Mohammadi et al, 2012). TBAB also has been found to reduce the induction time and increase the hydrate formation rate for the CO 2 /N 2 mixture Li et al, 2012b).…”

Experimental measurements of carbon dioxide solubility in aqueous tetra-n-butylammonium bromide solutions

“…To understand such a complicated system and develop a more precise thermodynamic model, reliable equilibrium data, such as gas solubility, hydrate formation conditions, and cage occupancy, are required. The solubility data of CO 2 in aqueous TBAB solutions can be found in the literature [15][16][17]. It is of interest that these studies report salting-in and -out effects, which depend on the aqueous TBAB concentration.…”

High‐efficiency CO2 capture and separation based on hydrate technology: A review

“…The results show that most of the promoters could reduce the induction time and shift phase equilibrium conditions. The pressure drop for the TBANO 3 systems is over 1.5 times higher than that for the TBAB system under the same operating conditions . Yi et al .…”