Vapor–Liquid Equilibria Study of the Aqueous Systems Containing {Choline Chloride + Glucose or Urea} and Their Deep Eutectic Solvents at 298.15 K and 85 kPa

Abstract

In this work, to study the vapor–liquid equilibria (VLE) for the aqueous systems containing {choline chloride + glucose} and {choline chloride + urea} at 298.15 K and atmospheric pressure, water activity was measured using the improved isopiestic method. The obtained water activity lines showed that these systems have negative deviation from the semi-ideal solution, and therefore solute–solute interactions are favorable. From the measured water activity data, osmotic coefficient values were calculated and the polynomial method is used to fit these data from which activity coefficients of urea or glucose in ternary and binary solutions were determined. The transfer Gibbs energy values calculated from these activity coefficients were negative for the transfer of urea or glucose from binary to ternary aqueous solutions containing choline chloride, indicating again favorable interaction between choline chloride and urea or glucose. In addition, a comparative isopiestic study was made on the two synthesized deep eutectic solvents (DESs) containing choline chloride + glucose or urea and corresponding mixtures with the same molar ratios, with the addition of different amounts of water to investigate the effect of dilution on the existing hydrogen bonding interactions in these DESs at 298.15 K. The measured water activity and water mass fraction values were used to study the weakening of these interactions by dilution, and it was found that the H-bonding interaction between two components of both DESs disappears at around 75% (g/g) of water.