Hydrodynamics of a Liquid‐Liquid Countercurrent Extraction Column with Upflow Gas Agitation

Abstract

The advent of new processes involving new materials and the need for lowering energy consumption are promoting the development of new liquid-liquid extraction equipment. In this work, energy is used to blow a gas (air) through the column to create a sufficient area of contact between the liquids. We have a three-phase L-L-G system which has the advantages of hollow columns for working with suspended solids and has no moving parts. The column can also function as a gas-liquid reactor, and the second liquid phase can be utilized as an extracting agent to shift the reaction towards the desired product or to remove chemicals which impede the principal reaction [l]. Moreover, a large quantity of experimental data has been published on the hydrodynamics of one three-phase system, viz. the solid-liquid-gas system [2], but no data on L-L-G systems are available in the literature. The aim of this work is to study empirically the operational capacity of this three-phase column, and to determine the operating limits and various design parameters. ExperimentalThe experimental equipment consists of three parts: liquid and gas supply systems and the contact column. Water and countercurrent kerosene mutually saturated were continuously introduced into the column by means of a dosimeter pump and a damping tank. The air was saturated in both liquids and introduced into the column base through a hole 3 mm in diameter. The cylindrical Pyrex glass column has a length of 3.05111 and a diameter of 5.2cm; bell-shaped reservoirs at its extremes make up the total volume to 12dm3. Sampling and tape pressure points were distributed along the column. The hydrodynamic characteristics of the flow depend mainly on the magnitude of gas flow. Flow of gas in the slug regime and of kerosene in the drop regime result at high gas flow rates; the bubble and swarm regimes are obtained for the respective media at lower gas flow rates, and the corresponding gas flow rate limit increases with the water/ kerosene liquid flow ratio. Furthermore, at intermediate gas flow rates, the gas is in the bubble and kerosene in the drop flow regime for low kerosene flow ratcs, and the gas in the slug and kerosene in the swarm regime at very high kerosene flow rates. Apart from the existence of these four possible regimes, the column is heterogeneous and we will preferentially have gas in bubbles and kerosene in swarms in the bottom part of the column. The operating limits of this countercurrent column are thus the insufficient efficiency (or excessively large droplets) at the lower gas flow rates, and the high gas upflow rate which entrains the descending water flow. Over this upper gas flow limit, the entrainment percentage could be adjusted to the power of 1.15 and 1.40 of the two rising flow rates of kerosene and air, respectively. ResultsThe droplet size was investigated by photographic techniques with less than lo-' exposure time in duplicate tests. Most of the drops were between 0.1 and 5mm in diameter. The Sauter mean diameters and variances of the size distri...

Hydrodynamics of gas-agitated liquid-liquid extraction columns

“…Hatate et al (23) also measured the mean droplet size for several systems using two columns and correlated it as a function of the superficial gas velocity, interfacial tension, and column diameter. Diaz et al (25) examined the dependence of the mean droplet size on the superficial gas and liquid velocities, and measured the dispersion coefficients of both liquids, for the air-kerosene-water system. with a perforated plate as a gas sparger.…”

Gas-Agitated Liquid-Liquid Extraction in a Spray Column

“…Water and countercurrent toluene, saturated with each other, were continuously introduced into the column by means of two piston pumps (4,5). Air saturated with the two liquids was introduced at the column base by using a compressor (19).…”

“…Experimental hydrodynamic characteristics and mass transfer data have been reported for packed columns [3][4][5]7 , for a spray column 8 and for bubble columns [9][10][11] . Ziebland and Hackl 8 made first attempts to describe the phenomena associated with the introduction of an inert gas into the spray column.…”

“…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][4][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 .…”

Experimental Investigation and Simulation of a Gas‐agitated Sieve Plate Column

“…Classical methods a for liquidliquid extractor design involve graphical techniques, which combine material and energy balances with liquid-liquid equilibrium relations on the assumption that the liquid phases leaving the extractor are in equilibrium [7,8]. In the gas-liquid-liquid gas-agitated extractors, the main function of the gas agitation is to increase the interfacial area and extraction efficiency [9].…”