Characterization of Milli- and Microflow Reactors: Mixing Efficiency and Residence Time Distribution

The increasing academic and industrial interest in flow chemistry resulted in the development of various micro- and milliflow reactors for a wide range of reactions. Owing to this variety in flow reactors, it is vital to select the correct type benefiting the considered chemical reaction. This decision can be based on two fundamental reactor characterization techniques, namely, the residence time distribution (RTD) and the Villermaux–Dushman protocol. The first technique highlights deviations from ideal plug flow, while the latter is a reaction based characterization technique to quantify the efficiency of micromixing. This paper compares the performance of classical tube reactors with internal diameters ranging from 0.4 to 4.8 mm and commercial chip reactors from Little Things Factory and Chemtrix (KiloFlow and Labtrix). The reactor characterization serves as an aid for the reaction selection, dependent on the kinetics of the studied reaction. The suitability of a reactor for very fast reactions (reaction half-life <1 s) or fast reactions (reaction time 1 s to 10 min) is discussed.