Heterogeneous reaction with solid catalyst in droplet-flow millifluidic device

The purpose of the work was to develop a miniaturized reactor based on digital millifluidics dedicated to the quantification of heterogeneous catalysis, especially liquid/solid reactions. By using concentric injection tubes, we generate drops of small volume (μL) that bring into contact the reactants and an homogenized suspension of the catalyst at a well defined time, and which are then carried downstream by inert oil in a 2.2 mm inner diameter tubing. We characterize experimentally how the solid catalyst (mean size 9–10 μm) is dispersed inside the drops and identify three main regimes: total and partial segregation, and good homogenization; we provide a basic criterion which compares sedimentation and wall-forced convection and which permits to choose the conditions in which the catalyst can be fully homogenized. We then quantify in our millidevice an industrially relevant reaction, the acylation of anisole, performed at a temperature variable in the range 90–120 °C. Thanks to a set collection ports positioned along the millidevice, we sample the reaction at tunable times and characterize it using infra-red spectroscopy. It is compared favourably to data acquired in classical batch conditions. We illustrate the device at work by screening of several types of zeolites and we recover their typical efficiencies with the use of a minute amount of solid.

► Set-up of a millifluidic reactor with continuous injection of solid particles up to 20 μm.
► Liquid–liquid–solid flow with suspension of the solid in one of the dispersed liquid phase.
► Diagram phase realisation: particle suspension regimes versus catalyst concentration and flow rates.
► Monitoring of the kinetics of a Friedel–Crafts catalytic reaction for several catalysts.
► Good agreement of the data with classical batch reactor data.