We address liquid-liquid mass transfer between immiscible liquids using the system 1-butanol and water, with succinic acid as the mass transfer component. Using this system we evaluate the influence of two-phase flow transitions from Taylor flow to stratified flow and further to dispersed flow at elevated flow rates. In addition, we address the scale-up behavior of mass transfer coefficients and the extraction efficiency by using reactors on the micro- and the milli-scale. Flow imaging enables us to identify the different flow regimes and to connect them to the trends observed in mass transfer, and the obtained results highlight the dependence of mass transfer on flow patterns. Furthermore, the results show that on the milli-scale fluid-structure interactions are driving the phase dispersion and interfacial mass transfer, and such a reactor design ensures straightforward scalability from the micro- to the milli-scale. (C) 2014 The Authors. Published by Elsevier Ltd.