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 benefitting 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 reactors characterization and serves as an aid for reaction selection dependent on the kinetics of the studied reaction. The suitability of a reactor for very fast reactions (reaction halflife < 1 s) or fast reactions (reaction time 1 s to 10 min) is discussed.

This paper investigates, for the first time, the breaking mechanism of particles exposed to implosions of stable and transient cavitation bubbles via Kapur function analysis. The effect of ultrasonic frequencies of 30−1140 kHz and powers of 4−200 W on particle breakage of paracetamol crystals was studied. The dominant cavitation bubble type was defined via sonoluminescence measurements. The breakage rate of seed crystals with a median size of 75 μm was found to be independent of the applied power when ultrasonically generated stable cavitation bubbles were generated. Furthermore, a particle size threshold of ca. 35 μm was observed. The particle size could not be reduced below this size regardless of the applied power or frequency. For transient bubbles, in contrast, higher powers lead to considerably smaller particles, with no threshold size within the investigated power range. The Kapur function analysis suggests that stable bubbles are more efficient than transient bubbles to break coarse particles with sizes above 40 μm. Finally, cumulative breakage functions were calculated, and it was observed that transient bubbles generate more abrasion than stable bubbles.

Membrane fouling by natural organic matter is one of the main problems that slow down the application of membrane technology in water treatment. O(3) is able to efficiently change the physico-chemical characteristics of natural organic matter in order to reduce membrane fouling. This paper presents the state-of-the-art knowledge of the reaction mechanisms between natural organic matter and molecular O(3) or *OH radicals, together with an in-depth discussion of the interactions between natural organic matter and membranes that govern membrane fouling, inclusive the effect of O(3) oxidation on it.