Microreactors liquids phase

Floyd, T. M., Losey, M. W., Fieebaugh, S. L, Jensen, K. E., Schmidt, M.A., Novel liquid phase microreactors for safe production of hazardous specialty chemicals, in Ehrfeld, W. (Ed.), Microreaction Technology 3rd International Conference on Microreaction Technology, Proc. of IMRET 3, pp. 171-180, Springer-Verlag, Berlin (2000). 

Quite new ideas for the reactor design of aqueous multiphase fluid/fluid reactions have been reported by researchers from Oxeno. In packed tubular reactors and under unconventional reaction conditions they observed very high space-time yields which increased the rate compared with conventional operation by a factor of 10 due to a combination of mass transfer area and kinetics [29]. Thus the old question of aqueous-biphase hydroformylation "Where does the reaction takes place " - i.e., at the interphase or the bulk of the liquid phase [23,56h] - is again questionable, at least under the conditions (packed tubular reactors, other hydrodynamic conditions, in mini plants, and in the unusual,and costly presence of ethylene glycol) and not in harsh industrial operation. The considerable reduction of the laminar boundary layer in highly loaded packed tubular reactors increases the mass transfer coefficients, thus Oxeno claim the successful hydroformylation of 1-octene [25a,26,29c,49a,49e,58d,58f], The search for a new reactor design may also include operation in microreactors [59]. 

Schneider, M.-A., Ryser, T., Maeder, P. and Stoessel, F. (2004) A microreactor-based system for the study of fast exothermic reactions in liquid phase characterization of the system. Chemical Engineering Journal, 101 (1-3), 241-50. 

The third chapter by Charlotte Wiles and Paul Watts addresses high-throughput organic synthesis in microreactors. They explain that one of the main drivers for the pharmaceutical industry to move to continuous production is the need for techniques which have the potential to reduce the lead time taken to generate prospective lead compounds and translate protocols into production. The rapid translation of reaction methodology from microreactors employed within R D to production, achieved by scale-out and numbering-up, also has the potential to reduce the time needed to take a compound to market. The authors discuss many examples of liquid phase, catalytic, and photochemical reactions and they conclude the chapter with a selection of current examples into the synthesis of industrially relevant molecules using microreactors. 

The industrially important nitration of aromatic compounds in a microreactor using two immiscible liquid phases was demonstrated in different studies using either parallel [220] or segmented flow [221]. In all studies, a PTFE capillary microchannel, connected to an inlet junction, was used in which either segmented or parallel flow can be created. The use of PTFE tubing is desirable as it is commercially available and no complicated microfabrication methods are involved. 

As mentioned, from the reaction kinetics viewpoint the behavior of zeolite catalysts shows large variability. In addition, the apparent kinetics can be affected by pore diffusion. The compilation of literature revealed some kinetic equations, but their applicability in a realistic design was questionable. In this section we illustrate an approach that combines purely chemical reaction data with the evaluation of mass-transfer resistances. The source of kinetic data is a paper published by Corma et al. [7] dealing with MCM-22 and beta-zeolites. The alkylation takes place in a down-flow liquid-phase microreactor charged with catalyst diluted with carborundum. The particles are small (0.25-0.40 mm) and as a result there are no diffusion and mass-transfer limitations. 

According to another scenario, the pressure of water vapor within microreactors is not high enough to break the walls. With an increase in pressure, the internal vapor pressure exceeds the critical limit and formation of the liquid phase occurs. The softer walls of the salt framework are found in the frozen diluted solutions, while harder walls of the salt framework could be observed at higher salt concentrations. 

Hessel et al. [33] centered their book on the analysis of a series of specific examples, from gas- and liquid-phase, to gas/liquid-phase and liquid/liquid-phase reactions, where the use of a microreactor (or more generally microprocess technology) allows significantly enhance in performance. It is a very valuable source of examples taken from over 1500 publications analyzed. The recent book ofWirth [34] focuses instead on the analysis of the opportunities for organic synthesis and catalysis in the use of microreactor technology. 

Microreactors can be used for either gas-phase or liquid-phase reactions, whether catalyzed or uncatalyzed. Heterogeneous catalysts (or immobilized enzymes) can be coated onto the channel wall, although on occasion the metal wall itself can act as the catalyst. Gas-liquid contacting can be effected in the microchannels by either bubbly or slug flow of gas, an annular flow of liquid, or falling liquid films along the vertical channel walls. Contact between two immiscible liquids is also possible. The use of microreactor systems in the area of biotechnology shows much promise, not only for analytical purposes but also for small-scale production systems. 

While microreactors tend to offer advantages for reaction control, which facilitates careful study, not all reactions are equally easy to perform in the systems. General purpose equipment exists to study gas phase reactions as well as gas phase heterogeneous catalyst reactions. However, while liquid phase reactions are also easily studied, specialized microreactor systems are usually built to study liquid phase heterogeneous catalyst reactions. Consequently, these systems are much more specialized and are often tuned to the specific chemistry rmder study. 

Microreactors allow, by simple means, the operational range to be broadened of liquid-phase reachons that are typically limited from cryogenic temperatrues... 

Polymerizations as part of liquid-phase organic reactions are also influenced by mass and heat transfer and residence time distribuhon [37, 48]. This was first shown with largely heat-releasing radical polymerizations such as for butyl acrylate (evident already at dilute concentration) [49]. Here, a clear influence of microreactor operation on the polydispersity index was determined. Issues of mass transfer and residence time distribution in particular come into play when the soluhon becomes much more viscous during the reachon. Polymerizahons change viscosities by orders of magnitude when carried out at high concentration or even in the bulk. The heat released is then even more of an issue, since tremendous hot spots may arise locally and lead to thermal runaway, known in polymer science as the Norrish-Tromsdorff effect. 

Gas-solid batch microreactor, initial outgassing of the catalyst for 2 h at 5(X) °C under vacuum (2) gas-liquid-solid slurry reactor, n-heptane liquid phase, 6 °C, 100 % conversion of ethylene, run time 34 h... 

Evaluation studies in industry have shown that microreactors can significantly contribute to improved chemical production. In principle, a variety of chemical reactions in the liquid phase or the gas phase can be carried out readily for the production of fine and specialty chemicals and active pharmaceutical ingredients. Nevertheless, it has to be said that so far no widespread use of microreactors has occurred. The main reasons for this is the lack of microstructured unit operations that can be connected easily with the reactor modules. In only a few examples has purification been implemented directly in the microreactor, as mentioned earlier... 

A wide range of liquid phase reactions have been performed in microreactor devices, such as Grignard reactions (Taghavi-Moghadam et al. 

Reactor Concepts for Aerobic Liquid phase Oxidation Microreactors and Tube Reactors... 

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