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

•Cobalt(II) was extracted with an undiluted ionic liquid in a microfluidic reactor.•The system is subject to several non-idealities (e.g., non-linear equilibrium).•The effect of said non-idealities on the mass transfer coefficient are estimated.•Gas–liquid like behavior occurs depending on the continuous phase viscosity.