Measurement of mass transfer coefficients in liquid‐liquid mixing

Abstract

Most of the work reported in the literature on liquidliquid mass transfer is for steady state conditions in extraction columns and spray towers (1, 3, 5, 10, 12, 14, 17, 2 0 ) . The reports have correlated the volumetric mass transfer coefficients with the flow rates of the continuous and dispersed phases. These results are useful for specifying the values of liquid flow rates for column operation, but more information is needed for complete elucidation of the basic mechanisms of liquid-liquid mass transfer in such systems. Of particular importance are data which will relate size of equipment to the rate of mass transfer, and no data on continuous flow liquid-liquid mass transfer systems are available for equipment of different size to provide such data.The use of continuous flow equipment allows the experimenter to reach a steady state and to make sufficient measurements to determine accurate material balances and rate coefficients. However in two-phase liquid-liquid mass transfer operations the equipment size itself is a very significant variable and interacts not only with fluid motion conditions but also with the physical properties of the fluids. Accordingly data are required for engineering design on a large scale. To evaluate the effect of size large scale continuous types of experiments would be highly desirable, but the amount of material to be handled and the size of auxiliary equipment necessary makes the cost of such studies much too high for practical consideration. Therefore a batch type of experiment is desired which will minimize the bulk of the equipment and material to be handled and still provide for sufficient accuracy so that the data may be translated to the performance of a continuouq flow operation. Then large size batch experiments can be made at far less cost than for large scale continuous operations and data obtained to elucidate the effects of size for continuous flow systems.Single-drop studies (4, 7, 18) have been used to develop both theoretical and empirical models to describe the relationship of mass transfer rates to the variables such as the fluid flow conditions, the physical properties of the liquids, etc. Such models describe the experimental results to a fair degree of accuracy, but their main weakness is that they are for single drops. When masses of drops are present, there is considerable coalescence and breakup of them causing the formation of new surface area as well as redistribution of the solute in the dispersed phase, hence the significant difference in overall rate transfer data between single and multiple drops in a turbulent field.In studies made with masses of drops the physical properties of the liquids and the flow motion of the system should be changed as independent variables because there is interaction between fluid motion and physical properties (16). Few such studies (6, 9, 1 1 ) have heretofore been made, perhaps because of the large number of interrelated variables which make an independent study of the variables difficult. Lewis (6) worked with an ap...

Drop size and continuous‐phase mass transfer in agitated vessels

“…It was highly soluble in all three organic solvents, but its solubility in water is only 0.25 parts per 100 parts of water at 15°C. Octanoic acid was also a good solute, as recommended by Rushton et al (1964), in view of its distribution ratio and rate of transfer, but it made the mixture of two phases too cloudy to measure droplet size.…”

“…Thr changc. of solute concentration was mcasured by inonitoring electrical conductivity as recoininended by Rushton et al (1964). The inethod of smipling the continuous phase through a tul~ular, fritted glass filtpr, followed b y titration, \vas tried and found to be unsuitable for batch operation, because of rapidly changing solutc concentrations.…”

Enhancement of mass transfer using colloidal liquid aphrons: Measurement of mass transfer coefficients in liquid-liquid extraction

“…The concentration of heptanoic acid in the aqueous phase was measured by electrical conductivity, as recommended by Rushton et al (1964). A YSI 3417 (K ‫ס‬ 1.0/cm) conductivity probe (YSI Inc., Yellow Springs, OH), with a 0.5-in.…”

Using maximum entropy approach for prediction of drop size distribution in a pilot plant multi-impeller extraction contactor

“…The motion of droplets between compartments in these columns is therefore dependent upon the droplet size, the physical properties of the phases, the phase ow rates and the agitator speed. 3,4 The power input to multi-impeller column extractors is thus transferred to the kinetic, surface, potential and heat energy of the droplets.…”