Microreactor laboratory-scale

Microreactor Laboratory-scale Process Developments for Future Industrial Use... 

Microreactor Laboratory-scale Process Developmentsfor Future Industrial Use I 111... 

Due to short residence times inside the micromixer almost no heat was released there. In the residence time tube, temperatures up to 150 °C have been observed. In these experiments, we were able to show that it is possible to finish the first reaction step on the continuous microreactor laboratory-scale plant in less than 60 s. The same reaction step in the cooled batch vessel of the production plant took about 4 h. With these results, we came to the conclusion that it should be possible to realize the first exothermic step of the process in a microreactor. After finishing this step continuously in a closed system, the reaction solution could be transferred into the existing batch vessel and be heated there to finish the second reaction step. As the time for the first step is reduced from several hours to a few minutes for the same amount of product, it should be possible nearly to double the capacity just by installing a microreactor right before the existing batch vessel to mix the first two educts. 

Microwave technology has now matured into an established technique in laboratory-scale organic synthesis. In addition, the application of microwave heating in microreactors is currently being investigated in organic synthesis reactions [9-11] and heterogeneous catalysis [12, 13]. However, most examples of microwave-assisted chemistry published until now have been performed on a... 

In this way, the operational range of the Kolbe-Schmitt synthesis using resorcinol with water as solvent to give 2,4-dihydroxy benzoic acid was extended by about 120°C to 220°C, as compared to a standard batch protocol under reflux conditions (100°C) [18], The yields were at best close to 40% (160°C 40 bar 500 ml h 56 s) at full conversion, which approaches good practice in a laboratory-scale flask. Compared to the latter, the 120°C-higher microreactor operation results in a 130-fold decrease in reaction time and a 440-fold increase in space-time yield. The use of still higher temperatures, however, is limited by the increasing decarboxylation of the product, which was monitored at various residence times (t). 

The modern methods of three dimensional microfabrication have lead to the development of extremely miniaturized chemical and biotechnological systems. These so called microreactors represent novel approaches in respect of production flexibility and chemical reactions not yet applied in chemical processing. This has stimulated world-wide research in this field so that the technical feasibility of such devices has been demonstrated in the laboratory scale. 

The exploration of new process regimes is tightly correlated to the task of chemical production [3, 8, 25]. Microreactors will then not only serve to investigate processes of macroreactors under ideal or otherwise not feasible conditions, but are expected to partially replace macroreactors for different applications. An example for a reaction which can hardly be achieved even on a laboratory scale is the direct fluorination of aromatics. 

A laboratory-scale microprocess plant was built using a falling-film microreactor for the first step and an interdigital mixer-microchannel reactor for the second one (see Figure 5.14) [50]. 

In particular, two main streams of PI applications have been identified (i) PI innovations for reactors (e.g., microreactors, monolith reactors, spinning disc reactors, reactive separations) and (ii) PI technologies for more efficient energy transfer (e.g., ultrasound, pulse, plasma, microwave). Several PI technologies offer important potential, but require important fundamental/strategic research to reach proof-ofconcept on the laboratory scale. These PI technologies are ... 

Microreactor technology is a tool used by most large chemical and pharmaceutical companies and also by some SMEs. Various examples are discussed by Hessel et al. [176], based on the collaboration of the Institute for Micro-Technology at Mainz (Germany) with various companies. We recall here some relevant cases to further evidence how microreactors are not more only at a laboratory-scale stage of development, even though most of the applications are stUl on a small-size scale. 

Additionally, in a microreactor the intrinsic kinetics and deactivation behavior of SCR catalysts is studied with flows up to 1.5m h . In both test facilities it is possible to vary all process parameters temperature, the ammonia to nitric oxide feed ratio, the nitric oxide and sulfur dioxide concentrations, the space velocity, and the catalyst geometry. These techniques provide information for somewhat small areas and therefore should always be performed to complement bench- or laboratory-scale activity and selectivity measurements. 

The titration method, based on rapidly varying the injection speed of reagent stock solutions into the mass spectrometer via a microreactor, offers a valuable alternative to more conventional laboratory-scale methodologies, provided that the selected supramolecular system is suitable to be studied by ESI-MS.60 The most important advantages of this approach are the limited sample... 

The specific nature of microreactors at the laboratory scale, e.g., due to their small size, continuous way of operation, and their interconnectors, raises the need for compact tailored platforms, and indeed suppliers have provided such complete systems, i.e., as bench-scale microreactor plants [2]. Meanwhile, a choice of modular multi-purpose or dedicated microreactor laboratory plants is available on the market, approaching the pilot-scale level [2]. Still, suitable tools for dovmstream processing are missing to satisfy all customers needs. 

Fig. 6.18 Flow sheet of the laboratory-scale microreactor configuration of the phenyl boronic acid microreactor process, equipped with an interdigital micromixer. (Courtesy of the American Chemical Society [30].)...

An industrial batch reactor has neither an inflow nor an outflow of reactants or products while the reaction is being carried out. Batch reactions can be carried out in droplet microreactors, where nanoliters of fluid are individually manipulated using techniques such as electrowetting on dielectric (EWOD) and surface tension control. Semibatch reactors are used in cases where a by-product needs to be removed continuously and to cany out exothermic batch reactions where a reactant has to be added slowly. Microfluidics allows precise control of concentration and temperature, which allows batch and semibatch reactions to be carried out in a continuous manner. Figure 1 shows the general components of a simple industrial-reactor semp, compared with a laboratory-scale setup to carry out a reaction with microfluidic chips. 

Both reactor types R3 and R4 use the segmented flow (Taylor) principle. They are divided into two categories R3 has very small channels (<1 mm) and R4 are monolith reactors (honeycomb), well developed on the laboratory scale with at least one example of industrial application. Category R3 includes single-channel and multi-ple-channel reactors [10], etched in silicon [10] or glass [10,11], with wall-coated or immobilized catalysts in the case of gas-liquid-solid additions [12], and capillary microreactors for gas-liquid-liquid systems [13]. 

Figure 103 Product selectivity versus propane conversion at (a) 695 K and (b) 734 K and (c) propane conversion versus inlet temperature for laboratory-scale reactor and SS/Ti microreactors [17]. Laboratory-scale reactor, closed symbols Ti microreactor, open symbols SS microreactor, open symbols with dot.

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