264674 Modeling of Alkane Hydrate Dissociation Conditions in the Presence of Electrolyte Solutions and Alcohols Using Ion-Based Statistical Associating Fluid Theory
Modeling of Alkane Hydrate Dissociation Conditions in the Presence of Electrolyte Solutions and Alcohols Using Ion-Based Statistical Associating Fluid Theory
Ion-based statistical associating fluid theory (SAFT2), coupled with van der Waals and Platteeuw model for hydrate phase, is applied to describe the hydrate dissociation conditions for methane, ethane, and propane in the presence of electrolyte solutions, alcohols, and mixed electrolyte - ethylene glycol solutions.
The ions are treated as nonassociating spherical segments, the parameters of which are obtained by fitting experimental activity coefficient and liquid density data of single aqueous salt solution. The binary interaction parameters for correcting the short-range interactions between ions and water, and between ions and alkanes are not needed. The model can be conveniently extended to mixed electrolytes solutions without introducing additional binary interaction parameters. The inhibition effects of NaCl, KCl, and CaCl2 solutions, including their mixtures, on alkane hydrate are found to be well predicted.
The alcohol parameters are obtained by fitting experimental saturation pressure and liquid density data of pure alcohol. The binary interaction parameters between alcohols and water are regressed from the vapor-liquid equilibrium data of binary water – alcohol mixtures. The binary interaction parameters between alkanes and alcohols are not needed. With this approach, the alkane hydrate dissociation conditions in the presence of ethanol, ethylene glycol (MEG), and glycerol are also well predicted.
Without additional fitted parameters, except for the constant binary interaction parameter between Ca2+ and ethylene glycol, the model is successfully applied to the prediction of alkane hydrate dissociation conditions in the presence of solutions containing both electrolytes (NaCl, KCl, CaCl2) and ethylene glycol (MEG). In contrast to the commonly used thermodynamic models for mixed electrolyte solutions, which in many cases require concentration-dependent parameters, we find that the proposed model, with a simple extension to mixtures, accurately predicts the alkane hydrate dissociation conditions and well-captures the effect of different compositions of mixed inhibitors.