Automated and Continuous Production of Microstructured Metallic Plates via Cold Embossing

Many critical issues need to be addressed when microstructured reactors are manufactured in large unit volumes. The most crucial of these are cost, ease of production, and reliability. The lack of breakthrough manufacturing technology to provide high‐efficiency, low‐cost, high‐precision plates is a hindrance to the early market implementation of systems requiring metallic microstructured plates. This contribution focuses on the development and optimization of a combined embossing and bending tool for the quick and continuous manufacture of easily machined plates.     

Microchemical Engineering: Components,Plant Concepts User Acceptance – Part I

Over the last five years, many activities have focused on the unexploited field of carrying out reactions on small scales. Due to the rapid development of new components, this paper deals with recent developments only in a compressed form. An important point is the analysis of possible plant concepts for microreactors and whether these are a sensible option. Due to the enormous difference in size between the microchannels and the fluid periphera of possible components this is not just a technical question. It touches on the microtechnology concept as a whole. The direction in which the field should be developed and which measures can be taken to influence its development are questions that are addressed here with respect to the big industrial interest in microreactors.     

Versuchsplanerische Untersuchung der Umesterung von Sojaöl mit Ethanol im Mikroreaktor

Base‐catalyzed transesterification of fats and oils with primary alcohols in discontinuous operation is an established batch process for the biodiesel production. However, the application of microreaction technology and continuous flow process lead to an increase of process intensification. The ethanol/soy bean oil ratio at low flow rates as well as the reactor geometry have the most evident effects on the fatty acid ethyl ester yield of KOH‐catalyzed ethanolysis of soy bean oil in microreactors. The influence of the catalyst concentration is of a lower importance.     

Autothermal hydrogen generation from methanol in a ceramic microchannel network

In this paper, the authors present the first demonstration of a new class of integrated ceramic microchannel reactors for all-in-one reforming of hydrocarbon fuels. The reactor concept employs precision-machined metal distributors capable of realizing complex flow distribution patterns with extruded ceramic microchannel networks for cost-effective thermal integration of multiple chemical processes. The presently reported reactor is comprised of five methanol steam reforming channels packed with CuO/γ-Al₂O₃, interspersed with four methanol combustion channels washcoated with Pt/γ-Al₂O₃, for autothermal hydrogen production (i.e., without external heating). Results demonstrate the capability of this new device for integrating combustion and steam reforming of methanol for autothermal production of hydrogen, owing to the axially self-insulating nature of distributor-packaged ceramic microchannels. In the absence of any external insulation, stable reforming of methanol to hydrogen at conversions >90% and hydrogen yields >70% was achieved at a maximum reactor temperature of 400 °C, while simultaneously maintaining a packaging temperature <50 °C.     

STRATEGIES FOR SIZE REDUCTION OF MICROREACTORS BY HEAT TRANSFER ENHANCEMENT EFFECTS

One of the likely aims of reactor miniaturization in the field of chemical production and energy generation is to increase the conversion to the desired product and the selectivity of the process through better control of heat and mass transfer. In addition to the effects related to miniaturization, a further increase of the transfer coefficients is achieved by applying microstructuring techniques. In this context, three different approaches for heat transfer enhancement in miniaturized reaction systems are presented. The ideas put forward rely on entrance flow effects, inertial flows in meandering channels, and suppression of axial heat conduction. Among these ideas the entrance flow effect, realized by an arrangement of microfins with a typical dimension of a few hundred micrometers, provides the most efficient heat transfer. It is found that a heat transfer enhancement of at least one order of magnitude can be achieved compared to unstructured channels. On this basis, a miniaturized heat-exchanger reaction system is investigated, where a kinetic model of an endothermic, heterogeneously catalyzed gas-phase reaction is used. The miniaturized heat-exchanger reactor, both with and without heat transfer enhancement, is subsequently benchmarked against conventional fixed-bed technology. It is shown that, for the reaction system under study, a substantial reduction of the required amount of catalyst can be achieved in microsystems.     

Dynamic methods and new reactors for liquid phase molecular catalysis

Kinetic data acquisition and screening of transition metal complexes for homogeneous liquid phase catalysis calls for numerous testing in multiphase G/L, L/L and G/L/L systems. It is shown first, with an example in asymmetric hydrogenation, why detailed kinetics must be performed. Then, new reactors leading to fast experimental techniques are proposed. A liquid–liquid centrifugal partition chromatography is evaluated for determining rate constants and partition isotherms by combining frontal analysis and elution chromatography, the catalyst being maintained in a stationary aqueous phase. Two microreactors offering short residence time have also been tested and compared with a fast test reaction (t_R ca. 5–20 s). The combination of reacting pulses, carrier liquids and micromixer is proposed as a general high throughput tool for the investigation of G/L, L/L and G/L/L catalytic systems in a fast sequential way.     

Microchemical Engineering: Components,Plant Concepts,User Acceptance – Part III

Over the last five years, many activities have focused on the unexploited field of carrying out reactions on small scales. Due to the rapid development of new components, this paper deals with recent developments only in a compressed form. An important point is the analysis of possible plant concepts for microreactors and whether these are a sensible option. Due to the enormous difference in size between the microchannels and the fluid periphery of possible components this is not just a technical question. It touches on the microtechnology concept as a whole. The direction in which the field should be developed and which measures can be taken to influence its development are questions that are addressed here with respect to the big industrial interest in microreactors.     

Effect of Alternating Pumping of Two Reactants into a Microchannel on a Phase Transfer Reaction

Alternating pumping of two reactants into a microchannel was found to provide, in comparison with batch processes, a more effective mixing and an increased yield for a particular organic reaction which uses a phase transfer catalyst. The superiority of the microreactor method increased with the frequency of alternation of the pumping of the two liquids.     

Self‐Immobilizing Oxidoreductases for Flow Biocatalysis in Miniaturized Packed‐Bed Reactors

The industrial implementation of enzymes in flow biocatalysis microreactors is expected to be essential for the emergence of a bio‐based circular economy. Major challenges concern the efficient immobilization of delicate enzymes inside miniaturized reactors without compromising their catalytic activity. We describe the exploitation of the widely used His‐tag system in a microfluidic packed‐bed reactor that contains ketoreductase‐functionalized magnetic beads. In a continuous process, these reactors produced highly stereoselective (R)‐configured alcohols (d.r. 99:1) with an average conversion of > 90 % for more than 4 days. We believe that such miniaturized flow reactors can be of great utility for future sustainable production processes.