Gas-Agitated Liquid-Liquid Extraction in a Spray Column

Abstract

The hydrodynamic characteristics of the air-water-toluene three-phase system in a spray extraction column at 20 °C were examined. The average and local hold-up data of the dispersed phase were determined in dependence on the flow rates of the continuous, dispersed and gaseous phases. The average gas phase hold-up was also measured and analyzed. A comparison was made of the hydrodynamic characteristics of the two-phase (water-toluene) and three-phase (air-water-toluene) systems.With respect to the dispersed phase hold-up, a spray extraction column can operate in three modes of packing of the dispersed phase drops 1,2 : dispersed, restrained, and dense. The efficiency is relatively low when the column is operated in the dispersed or restrained drop packing mode, mainly due to a high axial mixing in the continuous phase. An increased efficiency of the spray extraction column is attained with the dense packing of the dispersed phase drops, where the axial mixing in the two phases is significantly decreased.The efficiency of non-mechanically agitated extraction columns with different packings can be considerably increased by introducing an inert gas as a mixing agent in the two-phase system 3-5 . The energy thus introduced increases the turbulence within the now three-phase, gas-liquid-liquid (G-L-L) system, which brings about improved dispersion of the droplets and, consequently, a higher hold-up and a larger mass transfer area 3 . Priestley and Ellis 5 observed that the dispersed phase droplets were smaller and there was more backmixing in the continuous phase when a gas was introduced into the packed extraction column. Galkin et al. 6 found the largest reduction of the height equivalent to a theoretical stage (HETS) in plate extraction columns with superficial gas velocities of 0.02 -0.03 m s −1 . The authors concluded that this way of energy introduction was more efficient than by stirring or pulsation of the column.Gas-Agitated Liquid-Liquid Extraction

Hydrogen Peroxide Synthesis: An Outlook beyond the Anthraquinone Process

“…When the oxidation of AHQ with oxygen and the extraction of hydrogen peroxide from the anthraquinone working solution are carried out in a sieve plate column, both the conversion of AHQ and the extraction efficiency increase with the superficial velocity of the gaseous phase. [60] This increase may be caused by an increase in the contact time of oxygen (reactive gas) and the dispersed phase (reactive liquid phase) owing to their oscillatory motion and/or an increase in the containment volumes of dispersed and gaseous phases. [61] Alternatively, the mass-transfer coefficient at the gas-liquid interface increases with increasing flow rate of the reactive gas, [62,63] and thus the rate of oxidation increases and the conversion of AHQ is improved.…”

Hydrodynamics of gas-agitated liquid-liquid extraction columns

“…At the same time, figure 4. in the paper (29) shows the data for gas-phase holdup in the three-phase system air-water-kerosene obtained from empirical relationship of Bandiotphayay et al (28), whose form is: where: u g -superficial velocity of the gaseous phase,  M ,  M -density and dinamic viscosity of the liquid mixture, respectively. [14] correlates their data for the air-kerosene-water system worse than those for the air-water systems, but still it gives rise to larger values than for the experimental data of Asai and Yoshizawa (29) for both systems. This is not in line with the findings of Hatate et al (23), Kato et al (24) and Bandyopadhyay et al (28), who found lower average gas holdups for the air-kerosene-water system.…”

“…On the basis of the amount of experimental data simple empirical equations for the estimation of the slip velocity and dispersed phase holdup in the two-phase L-L columns were derived by several authors (11)(12)(13)(14)(15). The equation presented by Kumar et al (11) predicts the slip velocity for the dispersed phase holdup (0.01 to 0.75) and Reynolds number (7 to 2450).…”

“…The Experimental procedure applied in the paper (14) was as follows: at the beggining of each run, the cylindrical part of the spray extraction column was filled to about half its volume with water (continuous phase) throuh a water distributor at the top of the column, and the level of continuous phase (H c ) was recorded. At that moment, the dispersed phase (toluene) was introduced at the bottom of the column with a chosen flow rate, and two-phase dispersion occurred.…”

Wasserstoffperoxid‐Synthese: Perspektiven jenseits des Anthrachinon‐Verfahrens

“…Die Technologie der reaktiven Trennung führt damit zu wesentlichen Einsparungen an Investitions‐ und Betriebskosten. Wenn die Sauerstoffoxidation von AHC und die Extraktion des Wasserstoffperoxids aus der AC‐Arbeitslösung in einer Siebbodenkolonne durchgeführt werden, erhöhen sich Umsatz von AHC und die Effizienz der Extraktion mit der Leerrohrgeschwindigkeit des Gases 60. Ursache könnte die verlängerte Kontaktzeit zwischen dem Sauerstoff (Reaktivgas) und der dispergierten Phase (reaktive flüssige Phase) aufgrund ihrer oszillierenden Bewegung und/oder eines größeren Haftinhalts der beiden Phasen sein 61.…”