Continuous foam fractionation: The effect of operating variables on separation

Abstract

AbstractContinuous foam fractionation has a great deal of promise as a chemical engineering separation technique; however more information is needed concerning the effect of operating variables upon the separation which may be obtained. An experimental investigation is presented of the influence of temperature, of liquid residence time, and of the position of feed introduction upon the foam fractionation of the ethylhexadecyldimethylammonium bromide‐water system. The study involves three series of experiments and ninety foam separation runs. For a given air rate and feed stream concentration and rate, the drain stream concentration and rate increase linearly with temperature and the foam concentration and enrichment ratio are increasing functions of temperature. Equations derived from a multiple linear regression analysis enable the calculation of the drain stream concentration and rate from the feed concentration, air rate, and temperature.Based upon experiments involving the variation in liquid residence time by two methods, changes in solution height have no influence upon the separation, indicating the rapid achievement of equilibrium. Changes in feed rate and air rate show that the volume of air employed per unit volume of feed treated is a prime variable affecting the separation.Positioning the feed inlet at the solution‐foam interface, compared with feeding into the solution, provides a significant increase in drain rate and decrease in drain concentration. Moving the feeder higher into the column of foam results in a continued decrease in drain concentration, but in the passage of the drain rate and foam concentration through maximum values at a height corresponding to approximately the midpoint of the column of foam.