Effect of n-dodecane on equilibrium dissociation conditions of carbon dioxide hydrate

•The effect of n-dodecane on CO2 hydrate phase equilibrium conditions is presented.•Less addition of n-dodecane improves hydrate formation at the higher pressures.•Excessive addition of n-dodecane inhibits carbon dioxide hydrate formation.•n-Dodecane has little effect on CO2 hydrate phase boundary at lower pressure. The effect of n-dodecane on the phase equilibrium conditions of carbon dioxide hydrate is investigated in this work. The phase equilibrium conditions for (carbon dioxide + n-dodecane + water) mixtures were measured under constant volume conditions using a stepwise heating method. This experiments were carried out in the different n-dodecane mass fractions of 0.3333, 0.4286, 0.5000 and 0.6000, respectively. The experimental results shows that the carbon dioxide hydrate phase equilibrium pressures with small amount addition of n-dodecane are lower than that of the system of pure carbon dioxide at higher temperatures. But as the addition mass fraction of n-dodecane increases, the hydrate formation temperature-pressure equilibrium curve shifts to the left at higher pressures. Moreover, excessive addition of n-dodecane inhibits carbon dioxide hydrate formation, rather than promoting it.