Safa Kutup Kurt

Separation units and equipment for lab-scale process development

For complete chemical processes, downstream operation steps are essential, but on a miniaturized scale, they are not so far developed as the microreactors. This contribution presents three different unit operations for phase and component separation. Liquid-liquid extraction is often performed in columns, which were miniaturized for higher separation efficiency and flow rates suitable for processes in flow chemistry. Two-phase mass transfer processes in capillaries benefit from rapid final phase separation, which can be performed in an in-line phase splitter based on different surface wetting behavior. Crystallization is often a final purification step, which is performed in a continuously operated helical tube setup with narrow residence time distribution. For all unit operations, design criteria are shown with typical applications. The methodology of downscaling of known equipment and employing typical microscale phenomena such as good flow control, laminar flow, or dominant surface forces leads to successful equipment design.

Mixing and Heat Transfer in Helical Capillary Flow Reactors With Alternating Bends

Capillary flow is often occurring in natural and technical systems. Due to small diameter channels, laminar flow is established, while heat transfer is high from large specific surface area. For chemical reactions, good mixing and a narrow residence time distribution are important for high selectivity and yield. To improve mixing and residence time distribution, several measures of bend flow, helical arrangements and curved capillaries are proposed in literature. This contribution describes the flow, residence time distribution, and its influence on chemical reactions in short helical, alternating reactor capillaries (SHARC). The influence of the number of bends between alternating coils on the residence time distribution is described for different capillary and coil diameter, coil length and flow rate in laminar regime. The residence time distribution is a good measure for axial mixing and dispersion, while the heat transfer is mainly affected by the flow rate. The SHARC device was built from polymer capillaries of fluorinated ethylene propylene (FEP, inner diameter of 0.38 and 0.75 mm) with high mechanical flexibility for bending and good chemical resistance. Despite of low heat conductivity of the wall material, volumetric heat transfer coefficients of more than 5 MW/m3K were measured in a water bath. A highly exothermic reaction with adiabatic temperature increase of more than 100 K could be operated without detecting reaction runaway.Copyright

Two-Phase Flow and Mass Transfer in Helical Capillary Flow Reactors With Alternating Bends

Microstructured devices have gained much attention in R&D and industry as they offer large specific surface area with enhanced mass and heat transfer. Helically coiled tubular devices in micro-scale can further increase the performance in terms of transport phenomena, as secondary flow (Dean vortices) enhances the radial mixing along the tube. In the content of this work liquid-liquid mass transfer of different helical capillary flow reactors was investigated and compared with straight capillaries by using water/acetone/butyl acetate test systems for liquid extraction. Helically flow capillary reactors with alternating bends and straight capillaries were fabricated by using FEP tubes (fluorinated ethylene propylene) with inner diameter of 1 mm. Slug flow was introduced within the reactors by utilizing T-shaped mixing elements at the inlet. In order to obtain robust and precise downstream analyses, a continuously working, in-line phase splitter was fabricated and connected to the outlets of the reactors. It instantaneously splits the organic and aqueous phases depending on their wettability characteristics. Total volumetric flow rate was varied in the range of 1–8 mL min−1 and volumetric flow ratios (aq/org) in the range of 0.5–2.0. Effects of contact time, volumetric flow ratio, and the reactor geometry on extraction efficiency were investigated for the experiments at ambient temperature by generating slug flow patterns. Experimental results revealed that the helical capillary flow reactors offer higher extraction efficiency up to 20 % compared to straight capillaries at constant contact times. Hence, these types of reactors can be applied for liquid-liquid mass transfer processes, which require longer residence time due to slow mass transfer rates.Copyright