Microreactors, oxidation reactions

M., Zengerle, R., a modular microreactor design for high-temperature catalytic oxidation reactions, in Ehreeld,... 

The experiment in Fig. 36 has been analyzed according to the usual plug-flow model of the test microreactor. In this case, the ammonia mass balance equations were modified in order to include the oxidation reaction R5 in Table V, which was considered to proceed via adsorbed ammonia NH3. Moreover, the mass balance for gaseous nitrogen was introduced... 

Several examples of oxidation reactions, both in the liquid and in the gas phase, have been investigated in microreactors. Often the use of the microstructured device allows a better selectivity to the product of partial oxidation, because of a better temperature control on the catalyst surface (see, for instance, several examples in reviews [61a,b]). Indeed, several gas-phase oxidations can be completed in milliseconds, at significantly high temperatures. 

A related effort is FORSiM (Fast Oxidation Reaction in Si-technology-based Microreactors) which is funded by the Dutch Technology Foundation and is a cooperative venture between the University of Twente and the Technical University of Eindhoven. The objective of this work is to build and operate the first microreactor for catalytic partial oxidation for small-scale and on-demand hydrogen production61. 

For some oxidations, toxic heavy metal oxidants are used [313], This can be circumvented by the use of microreactor technology due to safe handling of elemental fluorine that can be used to mediate oxidation reactions [313], This is possible in a direct way via fluorine introduction into the substrate and subsequent replacement by an oxygen moiety. In an indirect manner, intermediate oxygen transfer reagents such as HOF MeCN can be generated by the reaction of aqueous acetonitrile with elemental fluorine that then attacks the substrate. The only byproduct is hydrogen fluoride that could be recycled by electrolysis. 

The toluene oxidation reaction was used as a probe to study the catalytic properties of the Mo-Ce complex oxides. The as-prepared oxides were introduced into a U-type quartz fixed bed microreactor and their catalytic properties for selective oxidation of toluene to benzaldehyde were evaluated under the reaction conditions of O.lMPa, 400 C, air/toluene = 9 (vol/vol), F/W =1900 ml/h g cat. The reaction products were analyzed by an on-line gas chromatography. Under the above reaction conditions, the main products were CO, CO2, H2O and benzaldehyde. 

Fig. 12.19 Methane oxidation reaction data for microreactor ACT-G2-4 channel B with a feed gas flow rate of 10.1 ml min". The feed composition was 14.9% methane, 10.3% oxygen, 39.8% nitrogen, and balance helium. This microreactor was placed in Reactor Board 2. Error bars represent the 95% confidence interval of each value.

Fig. 12.22 Ammonia oxidation reaction data versus temperature for microreactor ACT-G3-7 channel A with a feed gas flow rate of 4.0 mL min (Closed-loop temperature control was used for this experiment, and each heater was given the same set point temperature.)...

The high heat-transfer rate of micro heat exchangers raised the possibility of preparing microreactors for highly exothermic chemical reactions. Examples are oxidation reactions with molecular oxygen [11] or direct fluorination in micro falling-film reactors [12]. These appHcations impressively demonstrated that microreactors are tools for the performance of chemical reactions in reaction regimes not accessible even in state-of-the-art conventional reactors. 

In order to control highly exothermic catalytic partial oxidation reactions, small time constants for heating and cooling of gases are required. Microreactors equipped with a reaction chaimel that is capped on one side with a flat, thin, non-permeable membrane ( 1 pm thick) are very suitable for gas-phase reactions at temperatures... 

Scheme 7.8 Oxidative reaction of xanthine using microreactors with immobiiized xanthine oxidase.

In Pfeifer et al. (2011) this comparison was extended for the packed bed microreactor approach, showing that, with different catalyst systems for the oxidation reaction of SO2 to SC, both approaches can be competitive with conventional tubular reactors (Table 2). 

Endothermic and exothermic reactions can be successfully combined in microreactors because of the fast heat removal that reduces the required heat for the endothermic reaction. Tadbir and Akbari [63] numerically simulated methanol steam reforming in combination with methanol oxidation reaction in the neighboring chaimels of the microreactor. The authors used the mechanism of Peppley et al. [64] for the methanol steam reforming reactions, while the reaction rate for the methanol oxidation reaction was adopted from Ref [65], Thus, the following reactions were considered to be main reactions ... 

Basheer, C., Vetrichelvan, M., Suresh, V., Lee, H. K. (2006). Ionic-liquid supported oxidation reactions in a silicon-based microreactor. Tetrah. Lett, 47, 6, (February 2006) 957-961, ISSN 0040-4039... 

Reproducible measurements of absolute activity for sulfur dioxide oxidation catalysts are very difficult to obtain for a number of reasons, including the fact that the reaction is extremely fast. In addition, there are differences in techniques and reporting methods used by the various workers. Pulse microreactors have been used to study quantities of these catalysts as small as 500 mg (83). 

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