Mass Transfer Coefficient in Liquid−Liquid Extraction and the Influence of Aqueous Phase pH

Abstract

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.

Modelling mass transfer coefficient for liquid-liquid extraction with the interface adsorption of hydroxyl ions

“…The experimental work is as reported in our previous article [12]. The chemical system of toluene-acetone-water, a recommended system for liquid-liquid extraction studies [2], was chosen.…”

“…Drops were spaced more than 60 mm apart, typically with a range of flow-rate between 20.54-120.23 mL/h. Acetone concentration in the collected samples was measured with a GC (Shimadzu, 14B) with FID detector, calibrated with reference substances of toluene and acetone (Merck) for gas chromatography [12,21,28]. The concentration of acetone in the known samples was within the range of 1.5-44.7 g/L with 14 samples in calibration.…”

“…Like contaminants, the hydroxyl ion may therefore act in several ways, such as by reducing interfacial tension and so changing any balance of drop formation leading to a change in average drop size and hence mass transfer coefficient by making the interface more structured. The hydroxyl ions can also exert an interfacial barrier layer due to their adsorption, leading to hydrodynamic revolutions in lowering interfacial mobilization [11,12].…”

Effect of aqueous phase pH on liquid–liquid extraction with impinging-jets contacting technique

“…In the continuity of our previous works [6,7], concerning the influence of aqueous phase pH on the extraction process with drop dispersion method, an attempt is made here to investigate the influence of aqueous phase pH on the extraction efficiency and the rate of mass transfer, using an efficient impinging jets contactor instead of conventional devices. In a number of previously published articles by Berman and Tamir [8], and Dehkordi [9][10][11][12]; in addition to our recent work [13], the great potential of impinging jets technique for the liquid-liquid extraction process has been demonstrated.…”

Evaluation of the Suitability of Analytical Methods in Trichothecene A and B Degradation

“…According to Saien and Daliri,38 in an investigation of the influence of aqueous phase pH on mass transfer rate, it was possible to notice a significant reduction of the aqueous phase with pH increment, which was attributed to hydroxyl ion adsorption. During the partition step, the salt addition to the aqueous phase has a direct effect on the polarity range covered by the method, thus increasing its polarity and leading to higher recoveries of polar analytes.…”