KOH-Etched Nozzles for Monodisperse Bubble Generation in Microreactors

Monodisperse micro bubbles are a great benefit for the direct fluorination of organic compounds, which is done via a direct injection of gaseous fluorine into the liquid reaction partner. In this two-phase system the fluorination process is improved by the large interfacial area of a chain of micro bubbles compared to slug or jet flow. A predictable generation of micro bubbles with high frequencies will lead to a higher yield and improved selectivity. Moreover, perfluorination is achievable. Here we describe the design and characterisation of a novel potassium hydroxide (KOH) etched nozzle concept for the generation of monodisperse microbubbles in a silicon microreactor. The gas is injected through the KOH-nozzle apex into a perpendicular liquid flow shearing off the gas bubbles. This concept enables a controlled variation of the bubble formation frequency and the gas-liquid interface. The control factors are the aspect ratio and the orientation of the nozzle with respect to the cross flowing liquid.