Modelling of the overall volumetric mass transfer coefficient measured by the dynamic method in gas-liquid-liquid systems

Abstract

Liquid-liquid emulsions encountered in aerobic bioprocesses consist of an immiscible dispersed oil phase that that acts as a solute gas vector or the bioprocess substrate. Mass transfer of solute gases into such systems has been a topic of continual research. It has been established that the oil phase is responsible for the higher solubility of the solute gas, but its presence also affects the overall volumetric mass transfer coefficient. Enhanced, depressed and constant values of the latter have been reported in literature, and such varied behaviour has long posed a difficulty in its modelling. However, recent studies on the equivalent absorption concept have illustrated that varied behaviour of the overall volumetric mass transfer coefficient can be linked to how changes in the emulsion’s solubility are accounted for in the formulations describing the system. These findings suggest that current reports in literature can be reconciled by reviewing how different formulations account for the emulsion’s solubility. This study re-examines formulations used to study mass transfer by the frequently employed dynamic method. The overall volumetric mass transfer coefficient, as measured by this method, is modelled in terms of modified enhancement factor models. These models are able to simulate enhanced, depressed and constant values of the overall volumetric mass transfer coefficient. Furthermore, the models are validated against two experimental case studies that considered oxygen absorption into perfluorocarbon/water and n-alkanes/water emulsions. It is concluded that these models can be used in future empirical and predictive studies on mass transfer by the dynamic method in gas-liquid-liquid and gas-liquid-liquid solid systems.