Continuous separation of CO₂ from a H₂ + CO₂ gas mixture using clathrate hydrate

CO₂ capture using clathrate hydrates is an environmentally friendly separation technology. When considering operational efficiency, it is desirable to operate the separation process continuously. In this experimental study, the continuous separation of CO₂ from a model fuel gas was performed for H₂ + CO₂ + H₂O and H₂ + CO₂ + tetra-n-butylammonium bromide (TBAB) + H₂O systems with TBAB mass fractions of w_TBAB = 0, 0.05, 0.10, and 0.32. Measurements were taken to track the time evolution of compositions of the gas phase and hydrate slurry. After between 37 and 48 h from the start of the experiment, H₂ compositions in the gas phase reached steady state values of 0.87, 0.81, and 0.78 for w_TBAB values of 0, 0.05, and 0.10, respectively. For the same conditions, CO₂ compositions in the hydrate slurry reached steady state values of 1.00, 0.82, and 0.79, respectively. In carrying out this work we have shown that it is possible to successfully separate CO₂ using structure I hydrates and ionic semiclathrate hydrates, on a continuous basis. There is the caveat, however, that for w_TBAB = 0.32 a continuous separation process is not possible. The split fraction of CO₂ we attained were 0.76, 0.64, and 0.62 for w_TBAB values of 0, 0.05, and 0.10, respectively. The water system (w_TBAB = 0) exhibited the highest H₂ compositions in the gas phase, highest CO₂ compositions in the hydrate slurry, and highest split fraction of CO₂. Although short-term operation, specifically 18 h, is possible with w_TBAB = 0, continuous hydrate formation cannot be implemented. The concentration of captured CO₂ for w_TBAB = 0 was comparable to that obtained from hydrate-based gas separation in multistage processes or chemical absorption.