Systematic evaluation of semiclathrate-based pre-combustion CO2 capture in presence of tetra-n-butylammonium fluoride (TBAF): effect of TBAF concentration and kinetic additives

In this study, tetra-n-butylammonium fluoride (TBAF) is investigated as a promoter for pre-combustion CO2 capture via hydrate formation process. Hydrate phase equilibrium data for fuel gas mixture at 6.0 MPa with TBAF of various concentrations (0.80, 1.50, 2.00, 2.50, 2.96 and 3.38 mol%) were first determined. The kinetic performance with different TBAF concentrations was studied at 6.0 MPa given the same temperature driving force (ΔT = 4.1 K) in a stirred tank reactor. 3.38 mol% TBAF performed the best in terms of normalized gas uptake based on unit amount of water, while 1.50 mol% TBAF solution could capture the most amount of gas in terms of unit volume of solution. Solution with a higher TBAF concentration resulted in a higher CO2 composition in the non-gaseous phase after hydrate formation, and 97.7 mol% CO2 composition was achieved by 0.80 mol% TBAF solution. The effect of three kinetic additives, namely sodium dodecyl sulfate (SDS), leucine and tryptophan, were also evaluated. All kinetic additives studied were able to significantly reduce the induction time. However, the short induction time and block of stirring caused by drastic hydrate formation leaded to low gas uptakes.