The influence of aqueous phase pH on the rate of liquid−liquid extraction was investigated, using single
drop experiments for a range of drop size and in either of the mass transfer directions. The chemical system
of toluene−acetone−water was employed with the advantage of high accuracy and repeatability when analyzed
with gas chromatography. The pH of continuous aqueous phase was adjusted within 5.5−8, a range in which
most industrial waters are lain. An extraction column was used to introduce the drops into the aqueous phase.
Results have demonstrated the impact of pH on the mass transfer performance giving a significant reduction
in mass transfer with increasing pH and nearly independent of the kind of accompanied cation for two utilized
bases. This matter can be attributed to the adsorption of hydroxyl ions from the aqueous phase which causes
small drops to be more prone to this effect. The rate of mass transfer is greater for the dispersed to continuous
phase direction under similar conditions.
Temperature can alter the performance of conventional
liquid–liquid extraction columns in which one phase is dispersed
inside another phase. In this research, the influence of temperature
on the extraction process was investigated using a toluene–acetic
acid–water chemical system with dominant mass transfer resistance
in the organic phase. Single drop experiments with a range of drop
size within 2.49–3.77 mm and temperature within 15–40
°C were performed. Results demonstrate significant impact of
temperature on the rate of mass transfer with an average enhancement
of 93.6% in overall mass transfer coefficient while small drops are
benefited more. Having lower contributions by drop size and terminal
velocity, the extraction efficiency is the most effective term in
this regard which itself is increased by increasing molecular diffusivity
in the organic dispersed phase. For the aim of modeling, effective
diffusivity was substituted for molecular diffusivity in Newman’s
equation and consequently, a reliable empirical equation was derived
for the enhancement factor of diffusivity as a function of dimensionless
variables.
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