Norbert Kockmann

Novel process windows for enabling, accelerating, and uplifting flow chemistry.

Novel Process Windows make use of process conditions that are far from conventional practices. This involves the use of high temperatures, high pressures, high concentrations (solvent-free), new chemical transformations, explosive conditions, and process simplification and integration to boost synthetic chemistry on both the laboratory and production scale. Such harsh reaction conditions can be safely reached in microstructured reactors due to their excellent transport intensification properties. This Review discusses the different routes towards Novel Process Windows and provides several examples for each route grouped into different classes of chemical and process-design intensification.

Enabling Continuous‐Flow Chemistry in Microstructured Devices for Pharmaceutical and Fine‐Chemical Production

Microstructured devices offer unique transport capabilities for rapid mixing, enhanced heat and mass transfer and can handle small amounts of dangerous or unstable materials. The integration of reaction kinetics into fluid dynamics and transport phenomena is essential for successful application from process design in laboratory to chemical production. Strategies to implement production campaigns up to tons of pharmaceutical chemicals are discussed, based on Lonza projects.

Micro Process Engineering

The fundamentals of chemical engineering are presented with the aim of applications in microsystem technology, microfluidics, and transport processes in microstructures. After a general overview about both disciplines and common areas the concept of unit operations is briefly introduced. The balance equations are derived from statistical mechanics and applied to other relevant systems of process engineering together with the kinetic description of main transfer processes. Engineering tools like dimensional analysis, order of magnitude estimations, or lumped element modeling are explained, which are very helpful for dealing with complex nonlinear systems. Concluding this chapter, the benefits and limits of miniaturization of various unit operations and typical issues are explained that might serve as a plentiful source for the future development.

Flow regimes and mass transfer characteristics in static micromixers

The design and calculation of micro mixers is done by conventional analytical and numerical calculations. Due to the small dimensions, laminar flow is expected and the mass transfer is supposed to be dominated by diffusion. A detailed CFD-study by CFDRC-ACE+ of simple static mixers shows a deviation from strictly laminar flow in a wide range of Re numbers and channel dimensions. The static mixers under test have a T-Profile with rectangular cross sections and characteristic dimensions of 50 to 400 μm. The mean flow velocity is varied from 0,01 m/s to 5 m/s, which are typical values for chemical and biological applications, chemical analysis, and microfluidics with acceptable pressure losses. With increasing flow velocity and increasing Re numbers the flow starts to develop a vortex at the entrance of the mixing channel. With further increasing velocity the flow tends to instabilities, which causes the break up of the flow symmetry. With the onset of the vortex formation and with the occurrence of the flow instabilities the mass transfer is enhanced by the exchange of fluid elements. The laminar diffusion model cannot describe this mixing effect. A simple analytical model for first calculations is proposed.

Fluid Dynamics and Transfer Processes in Bended Microchannels

Abstract The understanding of the flow processes in microchannels and micromixers is essential for the design of microfluidic devices like microreactors or analytical equipment. We have performed a systematic numerical CFD-study of mixing and mass transfer in sharp 90° bends and heat transfer in T-joints to obtain a detailed insight into the flow patterns and corresponding transfer processes in a wide range of Reynolds numbers. With increasing flow velocity, the straight laminar flow starts to form symmetrical vortices in the bend, at the entrance of the mixing channel, and in T-joints. The vortices enhance the transport processes like heat and mass transfer in the channels significantly. The influence of the geometry and the flow conditions is shown by an analytical estimation of the relevant forces. The appearance of convective transport processes is used for the definition of microflows, which are controlled by viscous forces and diffusive transfer processes.

Transitional Flow and Related Transport Phenomena in Curved Microchannels

In microchannels with typical dimensions from 10 μm to a few hundreds of micrometers, the flow is dominated by viscous forces, often leading to laminar flow conditions. At the entrance or in bends and curves, where the flow changes its velocity or direction, inertial forces generate transverse flow velocities. Due to continuity, vortex pairs, such as Dean flow in circular bends, are generated, which are still laminar, steady, and showing no statistically distributed fluctuations typical for turbulent flow. This deviation from straight laminar conditions is called transitional flow, often occurring in channels larger than 500 μm at higher flow rates. Transitional flow phenomena include the first occurrence of flow bifurcation, pulsating vortices, period doubling of vortex pairs, and regularly fluctuating wake flow or vortex shedding. Chaotic flow phenomena are the first evidence of turbulence. Transitional flow augments the transport characteristics in microchannels for enhanced heat and mass transfer and for performing chemical reactions in microreactors. The profound understanding of how to generate and control vortices in microchannels guides the design of advanced microstructured devices for various applications.

Safety assessment in development and operation of modular continuous-flow processes

Improved safety is one of the main drivers for microreactor application in chemical process development and small-scale production. Typical examples of hazardous chemistry are presented indicating potential risks also in miniaturized equipment. Energy balance and kinetic parameters describe the heat production potential and, together with heat transfer capability, the temperature development in a continuous flow reactor. Besides these calculation procedures, checklists for laboratory safety and risk assessment are the basis for improved laboratory work as well as for equipment-related safety discussions. For complete and larger chemical plants, hazard and operation (HAZOP) studies are the appropriate method of handling hazardous processes and their scale-up.

Novel Process Windows: Innovative Gates to Intensified and Sustainable Chemical Processes

This book introduces the concept of novel process windows, focusing on cost improvements, safety, energy and eco-efficiency throughout each step of the process. The first part presents the new reactor and process-related technologies, introducing the potential and benefit analysis. The core of the book details scenarios for unusual parameter sets and the new holistic and systemic approach to processing, while the final part analyses the implications for green and cost-efficient processing. With its practical approach, this is invaluable reading for those working in the pharmaceutical, fine chemicals, fuels and oils industries.

Liquid–Liquid Test Reactions to Characterize Two-Phase Mixing in Microchannels

Multiphase flow is often found in chemical engineering, food processing, or analytical devices. First contacting and droplet generation as well as coalescence and redispersion are important for the flow characteristics. In all processes, the channel geometry, fluid properties, and flow velocity determine the flow regime, droplet size, and interfacial area. The hydrolysis of alkyl acetates in organic phase with sodium hydroxide NaOH in the aqueous phase is investigated as flexible test reaction for mass transfer and interfacial area determination. The alkyl group is chosen from ethyl, isopropyl, or n-butyl, which differ in water solubility, diffusivity, and rate constant, for adequate design of the characteristic time for mass transfer. The consumption of NaOH is used for calculation of specific area and related mass transfer coefficient. Different channel geometries are characterized and design considerations are derived.

Microstructured In-Plane Thermoelectric Generators with Optimized Heat Path

This paper proposes a multipurpose platform with standard thin-film CMOS fabrication technology for thermocouples for many materials and a high integration density. The heat flow path is perpendicular to the chip surface (cross-plane) and guided by special thermal connectors. On the thermocouples, a grid structure with thermally insulating SU-8 and electrodeposited metal stripes connects one junction of the thermocouple with the environment. The substrate is structured with trenches to connect the other junction with the environment. About 95% of the total temperature difference is between the two thermocouple junctions. Test chips with up to 13 460 thermocouples (Al - n-poly-Si) produce an output power of up to 3.17.10-3muW/mm2K2 per chip.