Experimental and numerical study on the kinetics of CO₂–N₂ clathrate hydrates formation in silica gel column with dodecyltrimethylammonium chloride for effective carbon capture

The kinetics of carbon dioxide (CO₂) and nitrogen (N₂) gas mixtures hydrates formation in silica gel (SG) columns of varied pore sizes are studied both experimentally and numerically. Dodecyltrimethylammonium chloride (DTAC) solution with concentrations of 0–0.6 wt% was used to speed up the hydrate formation and improve the CO₂ separation performance. A comprehensive shrinking-core model was established to reveal the roles of CO₂ and N₂ molecules diffusion and reaction in hydrate formation, and to investigate the effects of DTAC on kinetics. The experimental results show that the induction time is much shorter in larger pores of SGs, and is reduced remarkably with the addition of DTAC. The CO₂ gas uptakes increase remarkably in the initial 200–270 min but change little later. The final CO₂ concentration in gas phase decreased from 70 mol% to 32.6 mol% in the presence of DTAC, showing the CO₂ separation factor raised by 36.6%–77.5%. However, N₂ is also involved in the hydrate phase. The simulation results show that the combined reaction rate constants of both CO₂ and N₂ increase with the addition of DTAC. The lower combined rate constant in smaller pores indicates that the diffusion rate constant changes with pore size more strongly than the “reaction” rate constant. The dramatic decreasing trend of the effective diffusion coefficient reflects the higher porosity of the hydrate shell with more DTAC added.