Microscale reactors

The use of microscale reactors is not confined to single-phase systems. Both striated and droplet flows of two-phase liquid mixtures have been studied, as have suspensions of solid particles. It seems that almost any chemistry can be used at the microscale. Effectiveness factors in heterogeneous catalysis will be nearly 1.0 since diffusion distances are so small. As pointed out below, rapid molecular diffusion gives nearly instantaneous cross-channel mixing and may cause significant axial mixing. 

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The ability to use just-in-time chemical manufacturing because of ultra-short residence times in microscale reactors. 

Gil S, Lavilla I, Bendicho C (2008) Mercury removal from contaminated water by ultrasound-promoted reduction/vaporization in a microscale reactor. Ultrason Sonochem... 

The shallow depth of the channels (125 pm in the PDMS-E microreactors and 100 pm in the silicon wafer microreactor) provides for very short reactant diffusion lengths. This is one of the great advantages of microscale reactors. Small cross-channel dimensions also induce laminar flow. All experimental flows in this study had Reynolds numbers below 1.0. 

Many existing chemistries can be studied over very wide variable ranges efficiently, safely and rapidly in microreactor equipment, especially when the reactor is interfaced to on-line analysis equipment. Unfortunately, a significant number of reactions are still difficult to study in this equipment. However, notably, since microreactors can also be numbered up to provide commercial scale production, new chemical routes to product production may be possible. Thus, reactions that would not have been deemed reasonable for large volume production in traditional processing equipment due to problems with heat and mass transfer issues may now be possible in microscale reactors. The good news is that it should be possible to explore these new chemistries much more rapidly. 

Reference is made to Example 9.2 and Figure 9.9. The microscale reactor shown in Figure 16.6 is an open system although the velocity profile is no longer fiat. The solution theoretically requires integration from—oo < z < -boo, but practical results... 

As a result of high temperature and pressure, the high concentration of various chemically active radicals is generated. The chemical reactions requiring above critical conditions can be performed in an ultrasonic cavity, which can be regarded as a microscale reactor. The results of theoretical calculation of the cavitation intensity are reported in Fig. 5.11. 

Nielsen et al. described an automated system for the characterization of liquid-phase ethylene polymerizations [10]. The system had control of residence times, concentration of catalysts, temperature and pressure. In real time with in-line sensors, it was possible to determine the heat evolved from the reaction and to determine catalyst performance. Thus, by using a carefully controlled microscale reactor with in-line analysis capabilities, a complex polymerization reaction could be characterized in the laboratory setting. 

As a typical multiphase and multiscale process, the research of MTO process spanning molecules, zeohtes, catalyst particles, microscale reactors, and pilot-scale reacton to industrial equipments, cross a wide time and length scales. The development of efficient mesoscale methods are expected for further optimizing the DMTO process and improving fluidized bed reactor design and operation. 

The last method [3,33,34] is expected to be promising in nanoscale and microscale reactors since surface forces predominate in such situations. This method relies on the fact that gas is likely to attach to a poorly wetted solid body [35-39]. An example will be briefly reviewed below. 

A. de Mello, J. de Mello, Microscale reactors nanoscale products. Lab Chip 4, IIN (2004)... 

The novelty in the aforementioned studies is the use of a comprehensive numerical model for the investigation of catalytic microscale reactors which includes, for the first time in the literature, detailed heterogeneous and homogeneous chemical reaction mechanisms, two-dimensional treatment for both the gas and solid wall phases and surface radiation heat transfer, under both steady and transient (quasisteady) conditions. Moreover, a validated chemical kinetics model for the coupled catalytic and gas-phase combustion of propane (a fuel of particular interest for portable applications) is presented for the first time. 

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