Hydrate phase equilibrium of binary guest-mixtures containing CO2 and N2 in various systems

• TBAB/THF obviously alleviates the formation condition of (CO2 + N2) hydrate.
• TBAB affects hydrate equilibrium more obvious than THF in low concentration range.
• Phase equilibrium of (CO2 + N2) hydrate has no change in natural seasand.
• Seawater inhibits (CO2 + N2) hydrate formation due to the depressed activity of water.
• (CO2 + N2) hydrate formation is inhibited by ion rather than sand in (seasand + seawater).

For sequestration or separation of CO2 from flue gas, hydrate phase equilibrium of (CO2 + N2) binary guest-mixtures (xCO2xCO2 = 0.101, 0.180, 0.251 M fraction) was investigated using isochoric multi-step heating dissociation method in various systems, i.e., pure water, Tetrahydrofuran (THF, yTHF = 0.004, 0.012, 0.042 M fraction) aqueous solution, Tetrabutyl ammonium bromide (TBAB, yTBAB = 0.004, 0.012, 0.042 M fraction) aqueous solution, natural seawater, seasand and (seawater + seasand) mixture. All measurements were carried out in a temperature and pressure region of (271.5 to 289.6) K and (0.62 to 18.27) MPa, respectively. The results show that the formation pressure of (CO2 + N2) hydrate is still too high in pure water, but it can be obviously decreased in TBAB and THF aqueous solution and the pressure drop caused by TBAB is greater than THF only at the lower concentration of solution (in the concentration ranges investigated in this work). In seawater, hydrate formation pressure is raised while the seasand sample has no impact on it. Besides, hydrate equilibrium is mainly influenced by the ions in the (seasand + seawater) mixture while the effect of seasand particles is not obvious.