Equilibrium conditions for methane hydrate formation in aqueous mixed electrolyte solutions

Equilibrium data on the formation of methane hydrate in six mixtures of NaCl and KCl, six mixtures of NaCl and CaCl₂ and a mixture of eight electrolytes found in sea water were experimentally obtained. The ionic strength (in molality units) of the NaCl and KCl mixtures ranged from 0.97 to 4.72 and that of the NaCl and CaCl₂ mixtures from 1.27 to 3.90. The experimental temperatures ranged from 264 to 284 K and the pressures from 2.5 to 9.7 MPa. Equilibrium pressures predicted using a recently proposed method (Englezos and Bishnoi, 1988) have been compared with the data obtained and it was found that the predictions match the data very well. The standard errors for the mixtures of NaCl and KCl, NaCl and CaCl₂ and the synthetic sea water were 5.54, 3.5 and 1.4%, respectively. The largest prediction error for an experimental data point was 10.1%.