Micro-reaction device

One of the most far reaching analyzes along these lines of thought was given by Commenge [114] in the context of gas-phase reactions in continuous-flow processes. Specifically, he analyzed four different aspects of micro reaction devices, namely the expenditure in mechanical energy, the residence-time distribution, safety in operation, and the potential for size reduction when the efficiency is kept fixed. 

Micro-reaction technology can be one of the tools that process intensification may use [5]. Hence chemical micro processing and process intensification have a share, where the former supplies devices for the latter concept or purpose. However, both chemical micro processing and process intensification also cover imique aspects that the other field does not comprise. 

Separation layer mixers use either a miscible or non-miscible layer between the reacting solutions, in the first case most often identical with the solvent used [48]. By this measure, mixing is postponed to a further stage of process equipment. Accordingly, reactants are only fed to the reaction device, but in a defined, e.g. multi-lamination-pattem like, fluid-compartment architecture. A separation layer technique inevitably demands micro mixers, as it is only feasible in a laminar flow regime, otherwise turbulent convective flow will result in plugging close to the entrance of the mixer chamber. 

The Menschutkin reaction was carried out as a test reaction to show the feasibility of such novel micro flow concepts that allow to process fouling-sensitive reactions (see also Section 4.2.6 here another test reaction is decribed for the same purpose) [78]. The reaction of alkyl bromide with ternary bases such as pyridine or triethylamine gives quaternary salts insoluble in most solvents. Often, fairly rapid precipitation of this salt occurs, hence ideally serving as a test reaction for fouling sensitivity of micro-channel devices. The reaction of 4,4 -bipyridyl and ethyl bromoacetate [78] belongs to the category of fast-predpitating Menschutkin reactions, as the halide function is activated by the carbonyl fimction. 

For another investigation, amide formation was used as a model reaction to demonstrate the performance of parallel processing in micro-channel devices [23]. The target of such processing is combinatorial synthesis, the provision of multiple substances within one run. 

Given the feasibility of micro-channel devices for en2yme-based oligosaccharide synthesis, enhancement of mass transfer therein conld speed up this reaction. Also, it may be hoped that en2yme degradation may be reduced, for reasons that are not so straightforward. 

As micro devices, mixers from various suppliers (]R 19], [R 17]) were used [37]. These devices were each connected to a PTFE tube of length up to 150 cm. In addition, a tailor-made micro reaction system with parallel channels and integrated cooling was used (]R 26]). 

The precise definition of residence times for various stages of reactions by introducing reactants in a spatially confined manner in micro flow devices allows new ways... 

The LCA methodology has been used by Krahsch and Kreisel to investigate the pros and cons of micro-reaction technology at the stage of process development. The motivation for this study was the question whether ecological improvements can be expected for the chosen model reaction performed in the micro-structured device Cytos produced by CPC Systems GmbH, Germany. Such improvements were the premise for the construction of a continuously operated pilot plant based on Cytos micro-reactors. 

Additionally, the influence of the life time of the micro-structured devices as well as the expenditure of the peripheral equipment was estimated in order to obtain insight into the ecological hot-spots of the system. A conventional macro-scaled semi-continuously operated batch process was chosen as a reference process. The comparison of both technological systems was performed by means of the two-step synthesis of m-anisaldehyde serving as model reaction. 

Figure 7.2 Variation of environmental impact potentials as a consequence of the change from macro-scaled batch (0%) to micro-reaction mode Vbatch = 60%, Vdonti = 88% four scenarios regarding the lifetime of the micro-structured devices (Conti wc 1 week, Conti Set 3 months, Conti Sc2 3 years, Conti Sc3 10 years).

The results within the impact category GWP illustrate the great influence of both, the supply of chemicals (33% batch and 37% Conti wc, resp.) and the energy demand during synthesis (42% batch and 28% Conti wc, resp.) along the whole process chain. The disposal of the chemical refuse as well has a significant impact (23% both, batch and Conti wc). In the case of the worst-case scenario, the influence of the supply of the reaction device amoimts to 10% (assumed hfe time of the micro-structured devices 1 week) decreasing to 3% in Conti Scl (assumed life time of the micro-structured devices 3 month). 

Nistorica, C. Liu, J.-F. Gory, I. Skidmore, G. D. Mantiziba, F. M. Gnade, B. E. Kim, J. 2005. Tribological and wear studies of coatings fabricated by atomic layer deposition and by successive ionic layer adsorption and reaction for micro-electromechanical devices. J. Vacuum Sci. Technol. A. 23 836-840. 

Fig. 7. Illustration of an automated reagent introduction, reaction and analysis set-up based on the incorporation of a micro-fluidic device into a conventional HPLC system...

As illustrated in Scheme 1, on a small scale under reflux in ace-tone/water, 5% of starting material remained after 12 h reaction time and approximately 20% of the by-product was formed (entry 1). When performing the reaction at the same concentration in a lab-scale micro-wave device (Emrys Optimizer, entry 2) at 120°C, the reaction was complete after 5 min and gave a product of significantly higher purity and in higher yield. In the next step, 400 ml of reaction mixture was reacted in an 8 vessel rotor batch microwave (entry 3) at the same temperature... 

Building up expertise in this field, EMBL with its data library is well positioned to play an important European role in estabfishing a reference DNA array and SAGE database. In the future, the micro-array technology will be developed also for proteins, applying miniaturization, nanotechnology, micro-fabricated devices and reaction chambers. 

For the determination of reaction parameters, as well as for the assessment of thermal safety, several thermokinetic methods have been developed such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), accelerating rate calorimetry (ARC) and reaction calorimetry. Here, the discussion will be restricted to reaction calorimeters which resemble the later production-scale reactors of the corresponding industrial processes (batch or semi-batch reactors). We shall not discuss thermal analysis devices such as DSC or other micro-calorimetric devices which differ significantly from the production-scale reactor. 

However, most fuel cell systems can tolerate methane concentrations up to at least 1% in the reformate, no special purification reactions are required. In contrast, hence, removing small residual amounts of carbon monoxide from pre-purifled reformate applying the methanation reaction may be considered as an alternative to the preferential oxidation of carbon monoxide, provided that the CO concentration is low enough to have no significant impact on the hydrogen yield. However, no applications of methanation for CO clean-up in micro structured devices appear to have been reported, hence the issue is not discussed in depth. Finally, during hydrocarbon reforming all hydrocarbon species (saturated and unsaturated) smaller than the feed molecule may be formed. 

K., Liauw, M., Emig, G., A new micro-structured device for fast temperature cycling for chemical reactions, in Matlosz, M., Ehrfeld, W., Baselt, J. P. (Eds.), Microreaction Technology -IMRET 5 Proc. of the 5th International Conference on Microreaction Technology, Springer-Verlag, Berlin, 2001, 164-174. 

The economic benefit is one of the dominant problems if a micro structured reactor plant is used for chemical production. Without any doubt, an overall flow rate through a micro structured device can be achieved that is comparable to that with a conventional batch process. However, the residence time is very short because of the dimensions of a microstructured device. If the reaction kinetics are slow, an additional device is necessary to increase a dwell time. Hence, much effort should be devoted to increasing the reaction rate instead of transferring the standard protocol to a micro structured reactor [13]. 

Similar to computer technologies, so-called plug and play micro fluidic devices were developed. These devices are composed of a fluid driving unit and a polymer chip containing micro fluidic channels and reservoirs. The one and only connection is an electrical bus system which connects the chip with the external control unit. By filling the reservoirs with reagents, the chip can be used for performing chemical reactions or biochemical analysis [72],... 

Modularity is only needed where micro reaction technology is really demanded i.e. for micro fluidic modules. The motto of the developers is thus in analogy with the credo of the authors of this book, not to make microstructured devices as small as possible as many tools as necessary, not as many as possible . 

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