Phase behaviour of gas hydrates of carbon dioxide in the presence of tetrahydropyran, cyclobutanone, cyclohexane and methylcyclohexane

This paper presents experimental data on gas hydrate phase behaviour of ternary systems containing water+carbon dioxide+additive. The four additives studied are tetrahydropyran, cyclobutanone, cyclohexane and methylcyclohexane. Since all organic additives are very poorly soluble in water, they will be referred to as insoluble. Compared to the additive-free binary carbon dioxide system, reduction of the gas hydrate equilibrium pressure was observed in all systems. The pressure reducing effect of the additives on the hydrate equilibrium was similar for ternary systems with water+methane+additive and water+carbon dioxide+additive. However, the phase behaviour of the latter type of systems is more complex, due to the occurrence of a liquid carbon dioxide phase. Quintuple points (H–Lw–La–Lhc–V) are reported for these systems. In the presence of tetrahydropyran, cyclobutanone and cyclohexane sII hydrates are assumed to be formed, while the hydrate phase with methylcyclohexane may be either sI or sH hydrate.