Clathrate hydrate equilibria in mixed monoethylene glycol and electrolyte aqueous solutions

Monoethylene glycol (MEG) is commonly added in the formulation of hydraulic and drilling fluids and injected into pipelines to prevent the formation of gas hydrates. It is therefore necessary to establish the effect of a combination of salts and thermodynamic inhibitors on gas hydrate equilibria. In this communication, water activity of five ternary solutions (MEG-H2O-NaCl, MEG-H2O-CaCl2, MEG-H2O-MgCl2, MEG-H2O-KCl and MEG-H2O-NaBr) and four multicomponent solutions have been measured by a reliable resistive electrolytic humidity sensor. We also report new experimental measurements of the locus of incipient hydrate-liquid water-vapour curve for systems containing methane or natural gas with aqueous solution of ethylene glycol and NaCl over a wide range of concentrations, pressures and temperatures. A thermodynamic approach in which the Cubic-Plus-Association equation of state is combined with a modified Debye Huckel electrostatic term is employed to model the phase equilibria. These new data have been used to optimise binary interaction parameters between salts and MEG implemented in the modified Debye Huckel electrostatic term. The model developed has been evaluated using the new generated hydrate data and literature data. Good agreement between predictions of the modified model and experimental data is observed, supporting the reliability of the developed model. (C) 2012 Elsevier Ltd. All rights reserved.