Liquid-liquid mass transfer in microfluidic reactors: Assumptions and realities of non-ideal systems

The mass transfer coefficient, k L α , is often used to benchmark the liquid–liquid mass transfer performance in a microfluidic reactors. Cobalt(II) was extracted with an undiluted, highly viscous, ionic liquid from an aqueous phase in a microfluidic reactor (1 mm ID) and k L α values were determined (0.0002–0.033 s−1). It is concluded that the high viscosity of the ionic liquid causes two-phase slip, greatly reducing the efficiency of the microfluidic reactor. Furthermore, deviations (or non-idealities) from the assumptions related to mass transfer calculations (e.g., no reaction effects) can have a drastic impact on the measured k L α values. This work reports deviations between −25 and +40%. In general, it is shown how several non-idealities (i.e., a high continuous phase viscosity, non-linear equilibrium behavior and concentration effects) can affect the calculated mass transfer coefficient.