Thermodynamic transfer functions at infinite dilution and clathrate formation of ethanolamines in water

The ultrasonic velocities and densities of solutions of water in various binary aqueous solutions of ethanolamines were measured over the full range of compositions at 298, 308 and 318 K. The experimental data in the dilute region with mole fraction of water <0.1 was analyzed to determine the partial molar volume and adiabatic compressibilities at infinite dilution. Compressibility isotherms intersect approximately at a common point for triethanolamine (TEA), methyldiethanolamine (MDEA), dimethylethanolamine (DMEA) and diethylethanolamine (DEEA) and this is attributed to the formation of quasi-clathrate-like structures in the liquid solutions. The standard thermodynamic transfer functions were calculated to evaluate the environment of water at infinite dilution in these systems. The transfer functions of water between the various ethanolamines are considerably larger for ethanolamines that differ in their degree of hydrophobicity.