Abstract
An oscillating baffle column (O. B. C.) is described for the extraction of acetic acid. Mass transfer of this solute has been examined in both cases, from carbon tetrachloride to water, and vice-versa. The studies were carried out in a pilot plant incorporating two sizes of O. B. C. The use of this liquid system was partly dictated by the need for safety within the existing laboratory. A limited number of experiments are available for the small column from previous studies in O. B. C. with methyl-isobutyl-ketone which can be used for comparison purposes. Equilibrium data were obtained for the liquid systems. Sampling of the continuous phase, and titration, gave the acetic acid concentration (y) along the column length. The disperse phase was not sampled and titrated with sufficient confidence for the results to be meaningful. The concentration of the disperse phase (x) was obtained therefore from a mass balance at each sampling level using the measured values of (y) and the flow conditions. The latter were varied, to assess the effect of liquid loading on the column performance up to the point of flooding. Concentration profiles were established along the column for different flow conditions. The longitudinal dispersion (axial mixing) which occurs in both phases was studied using a dye injection technique. Values of the variance (sigma2) and the Peclet numbers (Pe) were obtained and their significance discussed. An equation for predicting axial mixing coefficient (E) from the speed of oscillation (N) and the rate of liquid flow (V) is proposed. The relationship between piston flow, measured and the values of NTU and HTU have been established. Equations based on a modification of Rod's method give values for true concentration profiles of the disperse phase corresponding to the measured continuous phase (y) values. Drop size studies are reported based on photographic techniques. From the photographs, by the tedious process of observation and counting, values for the drop interfacial area and Sauter mean drop sizes were obtained. While no claim can be made for great accuracy, the magnitude of the interfacial areas are meaningful and enable the effect of flow conditions as the drop size and distribution to be demonstrated. An important contribution of the present studies was the successful measurement of the power requirements of the system. The power actually consumed to produce the stirring effect has been shown to be a small part of the total power by virtue of power losses due to mechanical friction and lost movement. An even smaller amount of power is actually taken from the stirring power which applies to the bulk fluid, in order to produce dispersion. This power is related to the HTU and extraction performance. Dimensional equations are derived for HTU and Power relative to the operating parameters.