C. Hofmann

Visualization of Flow Patterns and Chemical Synthesis in Transparent Micromixers

The design of a glass made interdigital micromixer consisting of several functional layers is described. Its transparency allows the observation of the hydrodynamics directly in the mixing zone via optical imaging. By monitoring thin lamellae of dyed and pure water in the mixing zone, hydrodynamic and geometric lamellae focusing can be described. In the case of contacting immiscible fluids in the mixer, droplet formation is examined experimentally and compared to computational predictions. It is found that simulation data fit well with experimental results gained from the model system water / silicon oil. As a more realistic binary system of immiscible fluids, in the view of practical relevance in organic chemistry, concentrated sulfuric acid / toluene is investigated in a rectangular shaped glass micromixer. Droplet formation and quality of the emulsion are strongly influenced by the total flow rate. Subsequently, the hydrolysis of benzal chloride and one of its mono fluorinated derivates with concentrated sulfuric acid is examined in an interdigital micromixer. In comparison to results obtained from standard reaction tools like a stirred vessel and a mixing tee the dominance of the micro fluidic device can be demonstrated.

High Temperature HCN Generation in an Integrated Microreaction System

A high-temperature microreactor was designed for the performance of the Andrussov process. The microreactor enables isothermal processing and rapid cooling times of this ultrafast, highly exothermal reaction. An array of 20 channels, each 70 μm in diameter, forms the reaction zone in the centre of a catalyst structure which was heated to a reaction temperature of about 1050°C. Electrical connectors were realized from a metallic solder by micromilling allowing a reversible exchange of the catalyst structure. Gas tightness of the reactor was achieved using a new developed metal-ceramic joining technique and standard flat sealing by graphite foils.