Speed of sound measurements conducted at high pressures on aqueous alcohol and aqueous diol systems at T = 298.15 K

Abstract

The pulse echo overlap technique has been used in conjunction with three unique high-pressure cells to measure ultrasonic speeds of sound in dilute aqueous solutions of the alcohols 2-propanol, 2-butanol, 2-propanol and 2-hexanol and the diols 1,4-butanediol, 1-5-pentanediol and 1,6-hexanediol at p = 0.1, 20.0, 40.0, 60.0, 80.0 and 120.0 MPa and T = 298.15 K. A procedure is described by which the sound velocity measurements may be utilised to calculate precise densities and apparent molar volumes. The concentration and pressure dependences of the calculated apparent molar volumes have been modelled using empirical equations which in turn have been used to obtain values for apparent molar volumes at infinite dilution. In addition, measured speeds of sound have been used to calculate isentropic and isothermal compressibilities, and their associated apparent molar properties, for the investigated aqueous alcohol and diol systems. The latter properties have also been modelled as functions of concentration and pressure using empirical equations to obtain the pressure dependences of the apparent molar properties at infinite dilution. A group additivity approach has been used to model the pressure dependences of apparent molar volumes at infinite dilution. This analysis has provided estimates of the pressure dependences of the contributions of methylene and hydroxyl groups to apparent molar volumes at infinite dilution.