Four phase hydrate equilibria of methane and carbon dioxide with heavy hydrate former compounds: Experimental measurements and thermodynamic modeling

We experimentally investigated the hydrate dissociation condition for four phase hydrate (H)-aqueous liquid (LAq)-hydrocarbon rich liquid (LHC)-vapor (V) for the ternary systems of help gas-heavy hydrate former-water. Methane and carbon dioxide are known as help gases and benzene and cyclohexane are considered as heavy hydrate formers. The experimental data were generated using an isochoric pressure-search method. Two different equations of state (EOS) were employed to study the equilibrium phase behavior of ternary four phase systems. The EOSs considered are Valderama-Patel-Teja EOS combined with non-density dependent mixing rule (VPT+NDD) and Statistical Associating Fluid Theory EOS proposed by Huang and Radosz (SAFT-HR). The required binary interaction parameters (BIP) were obtained using vapor-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE) data. The hydrate phase was modeled by the modification of the solid solution theory of van der Waals and Platteeuw. To obtain reliable results, distortion of cages due to occupation of large molecules was considered. The Kihara parameters of cyclohexane were adjusted to hydrate dissociation data. Model calculations for hydrate forming conditions were found to be in satisfactory agreement with the newly reported data in this work and literature data.