Semiclathrate-based CO2 capture from pre-combustion fuel gas using tetra-n-butylammonium chloride: A thermodynamic, kinetic, and spectroscopic study

The primary objective of this study was to investigate the feasibility of pre-combustion CO2 capture using tetra-n-butylammonium chloride (TBAC) semiclathrate in a fuel gas mixture comprising CO2 (40%) + H2 (60%), with a primary focus on examining the thermodynamic, kinetic, and spectroscopic aspects of this process. Phase equilibria measured at various TBAC concentrations revealed that the CO2 + H2 + TBAC semiclathrates exhibited maximum thermodynamic stability at a stoichiometric concentration (3.3 mol%). CO2 concentrations in both the vapor and semiclathrate phases, along with gas consumption during and after semiclathrate formation, were measured to assess CO2 selectivity and gas uptake in the semiclathrate phase. Notably, CO2 enrichment was approximately 90% in the semiclathrate phase. In-situ Raman spectroscopy provided clear confirmation of the enclathration of both CO2 and H2 in the semiclathrate lattices, while powder X-ray diffraction analysis revealed the tetragonal (P42/m) structure of the CO2 + H2 + TBAC (3.3 mol%) semiclathrate. Furthermore, a high-pressure micro-differential scanning calorimeter was used to measure the dissociation enthalpies of the CO2 + H2 + TBAC (3.3 mol%) semiclathrate at various pressures. The comprehensive results obtained in this study strongly support the potential use of TBAC semiclathrate as a material for pre-combustion CO2 capture.