Reactor micro-scale

Fig. 2. Properties of model and biological particle systems Micro scale related particle diameter dp/riL versus maximum energy dissipation e , in stirred reactors explanations see Table 3 and Table 4...

Today s Shape of Micro-reactor Bench-scale Plants ... 

It has been shown, particularly for the latter reaction and for the ethylene oxide process, that micro reactors allow safe processing of otherwise hazardous oxidations [4, 26, 40, 42, 43, 84]. This is first due to the fact that the inner volume of micro reactors is small so that explosions also happen only on a micro scale . The... 

Studies at Mobil Research have shown that light olefins instead of gasoline can be made from methanol by modifying both the ZSM-5-type MTG (Methanol-to-Gasoline) catalyst and the operating conditions. Work carried out in micro-scale fluidized-bed reactors show that methanol can be completely converted to a mixture of hydrocarbons containing about 76 wt% C2-C5 olefins. The remaining hydrocarbons are 9% C1-C5 paraffins, of which the major component is isobutane, and 15% C6+, half of which is aromatic. 

For multiphase flow that is normally encountered in fluidized bed reactors, there are two kinds of definitions of the micro-scale first, it is the scale with respect to the smaller one between Kolmogorov eddies and particles second, it is the scale with respect to the smallest space required for two-phase continuum. If the first definition is adopted, the... 

Reactor up-scaling during the screening process, for example from primary leads to secondary process parameter screening, is facilitated if a flexible combination of meso- and micro-scale reactors could be used in the same experimental set-up. 

The above-mentioned integrated process development combines simulation tools with miniplant equipment to bypass the set-up of a pilot-scale plant Similar to this combined approach, a micro structured reactor plant can bridge laboratory-scale and micro-scale development. One could think of a future micro-integrated process... 

The Fraunhofer Alliance Modular Microreaction System (FAMOS) is currently working on a micro reaction simulation toolkit (Figure 4.82) with special attention to micro-scale phenomena [124], The virtual toolkit comes with a physical micro reaction toolkit. The MicroSim software reflects the process by considering reaction conditions and reactor geometries. Of course, this approach on the other hand limits the software to the dimensions and geometries of the reactors supplied with the physical toolkit. 

As a more critical example concerning the transfer of macroscopic modeling to micro-scale applications, the following example of a simulation of a homogeneous catalytic reaction is described [133], This example also represents a typical approach in process simulation if a new reactor model or a model for a new unit operation... 

The heterogeneous reactors with supported porous catalysts are one of the driving forces of experimental research and simulations of chemically reactive systems in porous media. It is believed that the combination of theoretical methods and surface science approaches can shorten the time required for the development of a new catalyst and optimization of reaction conditions (Keil, 1996). The multiscale picture of heterogeneous catalytic processes has to be considered, with hydrodynamics and heat transfer playing an important role on the reactor (macro-)scale, significant mass transport resistances on the catalyst particle (meso-)scale and with reaction events restricted within the (micro-)scale on nanometer and sub-nanometer level (Lakatos, 2001 Mann, 1993 Tian et al., 2004). 

In all of the above cases, a strong non-linear coupling exists between reaction and transport at micro- and mesoscales, and the reactor performance at the macroscale. As a result, the physics at small scales influences the reactor and hence the process performance significantly. As stated in the introduction, such small-scale effects could be quantified by numerically solving the full CDR equation from the macro down to the microscale. However, the solution of the CDR equation from the reactor (macro) scale down to the local diffusional (micro) scale using CFD is prohibitive in terms of numerical effort, and impractical for the purpose of reactor control and optimization. Our focus here is how to obtain accurate low-dimensional models of these multi-scale systems in terms of average (and measurable) variables. 

The ratio of the rms velocity fluctuation to the average velocity in the impeller zone is about 50 percent with many open impellers. If the rms velocity fluctuation is divided by the average velocity in the rest of the vessel, however, the ratio is on the order of 5 percent. This is also the level of rms velocity fluctuation to the mean velocity in pipeline flow. There are phenomena in micro-scale mixing that can occur in mixing tanks that do not occur in pipeline reactors. Whether this is good or bad depends upon the process requirements. 

For the experiments in this study, three types of reactor system were used. One had some separate micro-scale reactors, and it was used to measure HDS and HDM activity at constant operational conditions. The volume of each micro-reactor was 70 cc. 

A starting point for reaction engineers is the formulation of a reactor model for which the basis is the micro-scale species mass - and enthalpy balances. For practical applications the direct solution of these equations is too costly and simplifications or average representations are usually introduced. 

---