Gas absorption in an agitated gas–liquid–liquid system

Abstract

Gas–liquid–liquid systems have gained interest in the past decade and are encountered in several important industrial applications. In these systems an immiscible liquid phase may affect the gas absorption rate significantly. This phenomenon, however, is not completely understood and underlying mechanisms need further study. In this work the well-known Danckwerts-plot technique is used to determine the liquid side mass transfer coefficient k L and the gas–liquid interfacial area a simultaneously in this type of systems. As absorption/reaction system CO 2 absorption in a 0.5 M K 2 CO 3 0.5 M KHCO 3 buffer solution catalysed by sodium hypochlorite was chosen. Toluene, n-dodecane, n-heptane and 1-octanol were applied as dispersed liquid phases. The Danckwerts-plot could be well used in gas–liquid–liquid systems and from the results it appeared that two types of systems exist; systems that enhance mass transfer and systems that do not enhance mass transfer. Effects at low dispersed phase hold-up were observed to be very strong and are thus important, but were not taken into account in further analysis of the effect of dispersed phase hold-up on mass transfer. In systems where dodecane and heptane were added to the buffer solutions no enhancement of mass transfer was observed. However, the addition of toluene and 1-octanol caused an enhancement of mass transfer that could be well described using a homogeneous model of the shuttle mechanism.