Semiclathrate based CO2 capture from fuel gas mixture at ambient temperature: Effect of concentrations of tetra-n-butylammonium fluoride (TBAF) and kinetic additives

Hydrate-based gas separation (HBGS) for pre-combustion CO2 capture from fuel gas is one of the attractive methods to reduce carbon emission. To further advance the HBGS technology, there is a need to identify promoters that can moderate the operating conditions and enhance the kinetics and separation efficiency. Tetra-n-butylammonium fluoride (TBAF) is a semiclathrate former that can enable the HBGS process to be operated at ambient temperatures. In this study, the kinetic performance of CO2/H2/TBAF semiclathrate formation was evaluated under various TBAF concentrations in a stirred tank reactor at 6.0 MPa with a temperature driving force of 4.1 K. Compared with other concentrations, 0.8 and 1.5 mol% solutions exhibited higher gas uptake (normalized by the solution volume), hydrate formation rate, and CO2 composition in the captured gas. In addition, the effects of three kinetic additives on hydrate formation were tested, including sodium dodecyl sulfate (SDS), leucine, and tryptophan. All additives could reduce the induction time and increase the hydrate formation rate. The visual images of hydrate formation indicated two morphology styles, with the occurrence of style II identified to be highly related to the long induction time and the presence of leucine or tryptophan.