Experimental determination and thermodynamic modeling of methane and nitrogen hydrates in the presence of THF, propylene oxide, 1,4-dioxane and acetone

Three-phase hydrate equilibria of the methane+water+cyclic ether and nitrogen+water+cyclic ether systems were measured by employing the temperature search method. Three cyclic ethers of THF, propylene oxide and 1,4-dioxane were chosen and their concentration was fixed at 3 mol% relative to water. The addition of cyclic ethers caused the hydrate equilibrium pressure to be drastically lowered at a specified temperature and equivalently the hydrate equilibrium temperature to be greatly raised at a specified pressure. This stabilization effect on hydrate formation was found to be the highest for THF solution and in the order of THF>propylene oxide>1,4-dioxane>acetone. A new thermodynamic model was developed to describe the phase equilibria of mixed hydrates containing two guest molecules. The Soave–Redlich–Kwong equation of state (SRK-EOS) was used with the modified Huron–Vidal (MHV2) mixing rule incorporated with the modified UNIFAC. Both the predicted and experimental equilibrium data agreed well over whole temperature and pressure ranges investigated in this study.