Study of drop coalescence behavior for liquid-liquid extraction operation

Using a video camera, a time course of coalescence was observed for toluene droplets formed at the top of adjacent nozzles in water. Several parameters which may control the coalescence have been investigated, such as concentration of acetone added to toluene, direction of mass transfer, time for attaining contact of the droplets, and flow rate of the continuous phase. The average coalescence times decrease with acetone concentration when acetone is transferred from the dispersed phase towards the continuous phase, and they increase with the time required for attaining contact. At high acetone concentration, oscillation of droplets appears, which restrains the coalescence. The average coalescence time increases when the acetone is transferred from the continuous phase towards the dispersed phase. An attempt has been made to predict coalescence times at low solute concentration (no oscillation) by assuming that the difference of interfacial tension causes the film drainage and leads to the drop coalescence. The agreement between the calculated and experimental values is not sufficiently quantitative but reasonable. For lower solute concentration, calculated coalescence times depend strongly on the time for attaining contact, which is in agreement with our experimental observation. (C) 2000 Elsevier Science Ltd. All rights reserved.