Phase Stability of Semiclathrate Hydrates of Carbon Dioxide in Synthetic Sea Water

Experimental studies are carried out on semiclathrate hydrate of carbon dioxide (CO2) in tetra-n-butylammonium bromide (TBAB) for varying concentrations of TBAB (0.05, 0.10, and 0.20 mass fraction) + sodium chloride (NaCl) (0.035 and 0.10 mass fraction) in an aqueous system. The three-phase equilibrium (H-L-w-V) data are generated for quaternary system of CO2 + TBAB + H2O + NaCl and are not available in the open literature. The competing effect of TBAB and NaCl at different concentrations on phase behavior of semiclathrate hydrate equilibrium is studied. It is found that the inhibition effect of salt is much more pronounced at higher pressures compared to lower pressure conditions. It is observed that the inhibiting effect of the NaCl is suppressed by the promoting effect of semiclathrate hydrates of CO2 in TBAB. Although there is a shift in hydrate equilibrium curve toward inhibition zone compared to that of the same system in the absence of salt, this system is more stable than the hydrate of pure CO2 in a similar environment. The study, in general, shows that the semiclathrate hydrates of CO2 are more stable than the hydrates of pure CO2 in the real environments containing salts, thus promising their use for safe carbon capture and sequestration (CCS) application.