Investigation of multicomponent mass transfer in liquid–liquid extraction systems at microscale

A theoretical study of multicomponent mass transfer in liquid–liquid extraction systems at microscale is carried out using the standard extraction system water/toluene/acetone/MIPK. We focus on the diffusional interactions between the transferred components, the so-called cross effects, and investigate the conditions at which these effects can significantly influence multicomponent mass transfer behaviour at microscale. For this purpose, a rigorous mathematical model is developed based on the Stefan–Maxwell equations. Another, less rigorous model that does not consider cross effects is built up using effective diffusion coefficients. The latter model is used as a reference, because such models are widely used for the description of multicomponent mass transfer in conventional macroscopic devices. Both models are implemented into a commercial CFD software. The comparison of the simulation results obtained by both approaches permits the impact of cross-effects to be estimated. Microchannel dimensions and the contact time of the two immiscible phases, which flow countercurrently, are varied over a large range. Furthermore, different mass transfer directions are examined. It is found that the cross effects can considerably influence mass transfer behaviour and hence extraction performance at small-scale microchannel dimensions and sufficiently large contact times. The intensity of this influence largely depends on the component transfer direction.