Solid–liquid equilibrium, density and electrical conductivity data for water + monoethylene glycol + calcium chloride mixtures

Abstract

Monoethylene glycol (MEG) is used as hydrate inhibitor in natural gas exploitation. During the process, MEG mixed with produced water and salts must be regenerated. Therefore, salt solubility and physicochemical properties of MEG aqueous mixture with electrolytes are useful to operate the regeneration unit. This work determines density and electrical conductivity data at 298.15 K for water+MEG+CaCl2 systems. The density data were correlated applying the excess volume approach and Redlich Kister expansion, resulting absolute and relative mean deviations of 3 × 10–4 g‧cm–3 and 0.028%. For electrical conductivity correlation a semiempirical model was applied resulting absolute and relative mean deviations of 1.27 mS‧cm–1 and 3.53%. CaCl2 solubilities in water-MEG mixtures at 298.15 and 323.15 K were also measured. The proposed analytical method used precise density measurements to determine salt solubility. Moreover, the solid phase composition was determined by thermogravimetry analysis. Four different solid phases were identified as function of the solvent composition. At 298.15 K the addition of MEG changed the solid phase from CaCl2•4H2O to CaCl2•3H2O•MEG for w’MEG ≥0.36. Regarding 323.15 K, solid phase changed from CaCl2•2H2O to CaCl2•H2O•MEG for w’MEG≥0.30. Density, electrical conductivities and CaCl2 solubilities were accurately determined and are of interest to the natural gas industry.