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 parameter s which may control the coalescence have been investigated, such as concent ration of acetone added to toluene, direction of mass transfer, time for at taining 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 coales cence. The average coalescence time increases when the acetone is transferr ed from the continuous phase towards the dispersed phase. An attempt has be en made to predict coalescence times at low solute concentration (no oscill ation) by assuming that the difference of interfacial tension causes the fi lm drainage and leads to the drop coalescence. The agreement between the ca lculated and experimental values is not sufficiently quantitative but reaso nable. 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 reserve d.