Detailed mass transfer studies of a ternary system in the presence of unidirectional ejections coupled with unconfined density convection in both phases

Abstract

Experiments were carried out to transfer acetic acid from toluene to water under static conditions (inside a 50 cm³ buret) for a fixed initial concentration of 1 mol dm⁻³ of acid in toluene. The phase volumes (i.e., 5 and 10 cm³) were equal for the separate sets of runs at different extraction times. The extraction experiments were carried out for up to 60 min. Complete concentration profiles of the solute in both phases were developed, leading to variable solute concentrations on both sides of the interface at different extraction times. In the ternary system, intermittent ejection phenomena were only visible from the organic to the aqueous phase, over a fraction of the total interfacial area. Two theories of energy instability were verified experimentally through numerical calculations of the instability criteria at different extraction times. The molecular energy of acetic acid in toluene was estimated to be 3000 J mol⁻¹. In both the phases, the Rayleigh number ranged from 10⁸ to 10⁹ due to the unstable density gradients. The interfacial mass transfer coefficient, calculated under static conditions, was one-fifth of that under stirred conditions, where the Marangoni instability was superimposed on the energy instability. The interfacial mass transfer coefficient was higher than the bulk phase transfer coefficient in the raffinate phase, even in the presence of density convection. The dynamic interfacial energy barrier was found to be higher than the static energy barrier, i.e., the free energy of the interface.

Keywords:

• Acetic acid
• density gradient
• ejection
• extraction
• molecular theory
• toluene
• water