Modeling in Microreactors

This reaction serves as literature-known model reaction to characterize mass transfer efficiency in microreactors [318]. As it is a very fast reaction, solely mass transfer can be analyzed. The analysis can be done simply by titration the reactants are inexpensive and not toxic. 

Another enzyme that was studied extensively in microreactors to determine kinetic parameters is the model enzyme alkaline phosphatase. Many reports have appeared that differ mainly on the types of enzyme immobilization, such as on glass [413], PDMS [393], beads [414] and in hydrogels [415]. Kerby et al. [414], for example, evaluated the difference between mass-transfer effects and reduced effidendes of the immobilized enzyme in a packed bead glass microreactor. In the absence of mass-transfer resistance, the Michaelis-Menten kinetic parameters were shown to be flow-independent and could be appropriately predicted using low substrate conversion data. 

This chapter is devoted to chemical reactivity, so structures of association colloids are taken as givens. The properties of solvent, surfactant, and cosurfactant that control aggregate structure are discussed in terms of theoretical models in Refs. 1--6, 18, and 23-27. Current interpretations of the effects of association colloids on chemical reactivity view aggregates as microreactors, i.e., reaction regions distinct from bulk solvent, but distributed throughout the solution (Fig. 1). In normal and cosurfactant-modified micelles and in O/W microemulsions, ionic or polar groups that are in contact with the bulk aqueous medium... 

Microreactors are developed for a variety of different purposes, specifically for applications that require high heat- and mass-transfer coefficients and well-defined flow patterns. The spectrum of applications includes gas and liquid flow as well as gas/liquid or liquid/liquid multiphase flow. The variety and complexity of flow phenomena clearly poses major challenges to the modeling approaches, especially when additional effects such as mass transfer and chemical kinetics have to be taken into account. However, there is one aspect that makes the modeling of microreactors in some sense much simpler than that of macroscopic equipment the laminarity of the flow. Typically, in macroscopic reactors the conditions are such that a turbulent flow pattern develops, thus making the use of turbulence models [1] necessary. With turbulence models the stochastic velocity fluctuations below the scale of grid resolution are accounted for in an effective manner, without the need to explicitly model the time evolution of these fine details of the flow field. Heat- and mass-transfer processes strongly depend on the turbulent velocity fluctuations, for this reason the accuracy of the turbulence model is of paramount importance for a reliable prediction of reactor performance. However, to the... 

The type of kinetic model to be used depends on the type of reaction considered. For a homogeneous reaction occurring in the bulk of the fluid, a power-law kinetic model is often appropriate (see, e.g., [79]). In such models the rate of a certain reaction depends on a product of powers of the species concentration. On the other hand, heterogeneously catalyzed reactions are often conducted in microreactors. In a strict sense, power-law kinetics does not capture the dynamics of such processes over the full range of pressure, temperature and concentrations. Rather, a more complicated kinetic model of, e.g., Langmuir-Hinshelwood type [80] would have to be used. Nevertheless, power-law kinetics is frequently applied to heterogeneously catalyzed processes in a limited parameter range to simplify the description. 

Schwarz, S., Borovinskaya, E.S., and Reschetilowski, W. (2013) Base catalyzed ethanolysis of soybean oil in microreactors experiments and kinetic modeling. 

O. Tonomura, Simulation and analytical modeling for microreactor design, in Micro Process Engineering, ed. N. 

Figure 6.6 Schematic procedure of a multivariate calibration. Data are taken from the NIR spectroscopic monitoring of the nitration of toluene conducted in microreactors using pure nitric acid as nitrating agent [10]. Note that model optimization is an iterative approach that requires the multiple application of steps (c) and (d). (a) Definition of an experimental design within the investigated parameter space. Here, a central composite plan is presented, (b) Experiments in accordance with the design spectrum generation in a flow-through cell and...

Nanoparticle Synthesis in Microreactors, Figure 8 Particle growth kinetics analysis of CdSe nanoparticles (a) average particle size development (b) fitting result to diffusion growth model... 

Moore, J.S. (2012) Kinetic Modeling and Automated Optimization in Microreactor Systems. Ph.D. thesis, Massachusetts Institute of Technology. 

Lipase catalyzed synthesis of isoamyl acetate in n-heptane/buffer using acetic acid as acyl donor enhanced reaction rates in microreactor compared to batch model simulations achieved by numerical solution of nonlinear systems provided a good fit to experimental data Technique relies on segmented-flow biphasic system crude cell lysate allowed for enatio-selective synthesis of cyanohydrins in microchannels. The reaction rate and selectivity only achieved in larger batch mode with intense shaking (stable emulsion formed). 

The efficiency of solution-phase (two aqueous phase) enzymatic reaction in microreactor was demonstrated by laccase-catalyzed l-DOPA oxidation in an oxygen-saturated water solution, and analyzed in a Y-shaped microreactor at different residence times (Figure 10.24) [142]. Up to 87% conversions of l-DOPA were achieved at residence times below 2 min. A two-dimensional mathematical model composed of convection, diffusion, and enzyme reaction terms was developed. Enzyme kinetics was described with the double substrate Michaelis-Menten equation, where kinetic parameters from previously performed batch experiments were used. Model simulations, obtained by a nonequidistant finite differences numerical solution of a complex equation system, were proved and verified in a set of experiments performed in a microreactor. Based on the developed model, further microreactor design and process optimization are feasible. 

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