Annular-flow microreactor

Direct Fluorination of Aliphatics and Non-C Moieties The basic limitations of direct fluorinations are similar for aliphatic compounds as discussed already using the example of aromatic derivatives and so is the potential of microreactors. The fluorination of ethyl acetoacetate was carried out in an annular-flow microreactor. 

Ibashi, W., Groppi, G., and Forzatti, P. (2003) Kinetic measurements of CHj, combustion over a 10% PdO/Zr02 catalyst using an annular flow microreactor. Catal. Today, 83 (1-4), 115-129. 

Burkle-Vitzthum, V., Moulis, F., Zhang, J., Commenge, J.-M., Schaer, E., and Marquaire, P.-M. (2014) Annular flow microreactor an efficient tool for kinetic studies in gas phase at very short residence times. Chem. Eng. Res. Des. doi 10.1016/j. cherd.2014.10.003. 

Figure 4.35 Flow pattern map for the nitrogen/ acetonitrile flow in the dual-channel microreactor. Annular flow wavy annular flow (WA) wavy annular-dry flow, (WAD) slug flow bubbly flow annular-dry flow (AD). Transition lines for nitrogen-acetonitrile flows in a triangular channel (224 pm) (solid line). Transition lines for air-water flows in triangular...

The microreactor contained a single channel with two feeds for gas and liquid [309,273]. The gas flows were set so high that an annular-flow regime was reached with a central gas core surrounded by a liquid film wetting the channel. This flow pattern has a very high interface and low liquid-side resistance due to the thin film. Formic acid was used as a solvent. 

The oxidation of cyclohexanol to cyclohexanone with fluorine and aqueous acetonitrile was performed in a single-channel microreactor operated under annular flow at room temperature. A conversion of 84% and a selectivity of 74% were observed [313], In a similar way, diols such as 1,2-cyclohexanediol were partly or fully oxidized. A 53% selectivity to the monooxidation product was obtained at a conversion of 87% the dioxidation product was obtained with 30% yield. 

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. 

Interdigital mixers and micromixer with the split-recombine technique Single microchannel operating in annular flow regime Microstructured falling film reactor Mesh microreactor... 

This chapter provides an overview of the mass transfer characteristics of multiphase microreactors. Basic concepts are explained and related to mass transfer in sequented (drop/bubble) flow, annular flow, and to multiphase flow through packed microchannels. In multiphase microreactors, a chemical reaction can either involve two immiscible fluid phases (e.g. for gas-liquid reactions) or two fluid phases in the presence of a solid catalyst or the reaction is exclusively confined to one of the fluid phases that are present in the system. 

In many multiphase microreactor applications, stable fluid interfaces have been particularly important for performing gas-liquid reactions in the annular flow... 

At given gas and liquid superficial velocities Jg and ji that are defined by the volumetric flow rate of the respective phase divided by the cross-sectional area of the microchannel, de Mas et cd. [30] solved the force balance for the two co-flowing fluid phases. A capillary with a diameter equal to the hydraulic diameter of the microreactor was considered (Figure 11.2). The annular flow was assumed to be axisym-metric, laminar and fully developed. Using a constant pressure gradient in the gas and liquid phases along the streamwise direction, the flow satisfies the equations... 

A flow-pattern map was derived for nitrogen-acetonitrile flows in the dualchannel microreactor [65]. Bubbly, slug, churn, and annular flows were found as well as wavy annular and wavy annular-dry flows with smaller region of stability (Figure 9.11). 

Two classes of gas-liquid microchannel reactors were developed in the past years -continuous-phase contacting falling film, overlapping charmel, mesh, and annular flow approaches, and dispersed-phase contacting by Taylor flow reactors, micromixers for bubble and foam formation, and miniaturized packed bed microreactors, which follow classical trickle-bed operation at smaller scale. Recently integration of operations inside a microdevice has been studied and led to the development of membrane microreactors. 

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