Multiple-Phase Hydrate Equilibria of the Ternary Carbon Dioxide, Methane, and Water Mixtures

Three-phase equilibria consisting of vapor, water-rich liquid, and solid hydrate were measured for the aqueous solutions containing two guest molecules of carbon dioxide and methane in the temperature range of 272−284 K and at pressures of 15, 20, 26, 35, and 50 bar. At the specified isobaric condition the three-phase equilibrium temperatures become higher as the relative concentrations of carbon dioxide to methane increase. The upper quadruple points at which the four phases of vapor, water-rich liquid, CO 2 -rich liquid, and solid hydrate coexist were also measured to examine the phase boundary of the hydrate stability region. At five different temperatures the concentrations of vapor, water-rich liquid, and carbon dioxide-rich liquid were measured and examined through five triangular diagrams. For the prediction of hydrate phase equilibria, the vapor and liquid phases were treated with the Soave−Redlich−Kwong equation of state (SRK-EOS) incorporated with the second-order modified Huron−Vidal (MHV2) mixing rule and the hydrate phase with the van der Waals−Platteeuw model.