Flow capillary microreactor

Kashid, M. N., Gerlach, 1., Goetz, S., Franzke, J., Acker, J., Platte, F., et al. (2005). Internal circulation within the liquid slugs of a liquid-liquid slug-flow capillary microreactor. Industrial... 

Ghaini, A., Kashid, M., Agar, D. (2010). Effective interfacial area for mass transfer in the liquid-liquid slug flow capillary microreactors. Chemical Engineering and Processing Process Intensification, 49, 358—366. 

Kashid, M. N., Agar, D. W. (2007). Hydrodynamics of liquid-liquid slug flow capillary microreactor flow regimes, slug size and pressure drop. Chemical Engineering Journal, 131, 1-13. 

Kashid, M.N. (2007) Experimental and Modelling Studies on Liquid-Liquid Slug Flow Capillary Microreactors, University of Dortmund, Dortmund. 

Figure 15.9 Stable flow patterns that can be achieved in the liquid-liquid flow capillary microreactor.

M. N. Kashid, Experimental and modelling studies on liquid-liquid slug flow capillary microreactors, PhD Thesis, Technical University of Dortmimd, 2007. 

Sulfonations are a further important type of electrophilic substitution reaction. However, only very few examples can be found in the literature describing the use of microstructured reactors for the strongly exothermic liquid-phase sulfonation of aromatics (sulfonation of toluene wdth gaseous SO3 was described by Jaehnisch et al. [34]). Burns and Ramshaw [25, 35] claimed that their concept of performing liquid/liquid nitration reactions in a slug-flow capillary-microreactor can be also... 

A thermophilic alcohol dehydrogenase (TADH) was applied in a segmented flow capillary microreactor to perform the enzyme-catalyzed reduction of racemic 3-methylcyclohexanone 5 to (lS,3S)-6 in a hquid-hquid two-phase system [76]. This study demonstrated the excellent mass transfer rates accomphshed by the enhanced surface area to volume ratio as the true benefit of microreactor systems in multiphase enzymatic catalysis. 

K. (2011) Miniaturizing biocatalysis enzyme-catalyzed reactions in an aqueous/organic segmented flow capillary microreactor. Adv. 

Continuous flow capillary microreactors with embedded monometallic (Pd) or bimetallic (Pd25Zn75) catalysts have been tested in the selective hydrogenation of alkyne reagents, among which was 2-methyl-3-butyne-2-ol [155]. Under conventional reaction conditions a number of side products can be formed. 

The capillary plasma reactor consists of a Pyrex glass body and mounted electrodes which are not in direct contact with the gas flow in order to eliminate the influence of the cathode and anode region on CO2 decomposition. Analysis of downscaling effects on the plasma chemistry and discharge characteristics showed that the carbon dioxide conversion rate is mainly determined by electron impact dissociation and gas-phase reverse reactions in the capillary microreactor. The extremely high CO2 conversion rate was attributed to an increased current density rather than to surface reactions or an increased electric field. 

The catalytic experiments were performed in a continuous flow tubular microreactor. The catalyst bed consisted of 0.8 cm of 0.3-0.5 mm pellets, prepared by compressing of the NH -T zeolite powder into flakes, crushing and sieving. The zeolite was activated in the reactor by deammoniation at 673 K. The vapors of the acids were diluted with helium. The reaction conditions are further specified in Table 1. The reaction products were analysed on-line with GC, using a capillary fused silica column, coated with CP Sil5 (Chrompack) and F.l.D. detector. CO2 and H2O were not analysed. 

Ahmed-Omer, B., Barrow, D., and Wirth, T. (2007) Effect of segmented fluid flow, sonication and phase transfer catalysis on biphasic reactions in capillary microreactors. Chem. Eng. J, 135 (Suppl. 1), S280-S283. 

Power input, a decisive parameter for benchmarking technical reactors, has been investigated using the experimental pressure drop and compared with conventional contactor as shown in Table 15.5. The comparison reveals that the liquid-liquid slug flow microreactor requires much less power than the alternatives to provide large interfacial area - as high as a = 5000 m m in a 0.5 mm capillary microreactor, which is way above the values in a mechanically agitated reactor (a 500 m m ). 

Weber and coworkers reported catalyst screening of the Stille coupling reaction using a capillary microreactor (75 pm i.d., 6.7 m length) [17]. Optimum palladium catalysts and ligands were screened effectively by the flow regime, where the reaction products were analyzed by on-line gas chromatography. 

Both reactor types R3 and R4 use the segmented flow (Taylor) principle. They are divided into two categories R3 has very small channels (<1 mm) and R4 are monolith reactors (honeycomb), well developed on the laboratory scale with at least one example of industrial application. Category R3 includes single-channel and multi-ple-channel reactors [10], etched in silicon [10] or glass [10,11], with wall-coated or immobilized catalysts in the case of gas-liquid-solid additions [12], and capillary microreactors for gas-liquid-liquid systems [13]. 

Figure 0.4 Observed flow regimes in the capillary microreactor (Y-junction ID = 1 mm, capillary ID = 1 mm), (a) Slug flow, (b) drop flow, and (c) deformed interface flow. (Adapted from Kashid, M.N. and Agar, D.W., Chem. Eng. J. 131, 1, 2007.)...

Figure 7 Overview of the strategy of immobilized salen-type catalysts by (a) on-column reaction GC, (b) on-column reaction capillary electrophoresis (CE)Zelectrokinetic chromatography (EKS), (c) flow-through microreactor, and (d) coated glassware.

Multiphase flow in a tubular, chip-based, or freestanding capillary microreactor may be controlled such that the sosegmented flow creates serial, contiguous packets of immiscible fluids (Figure 1.17). 

Ahmed-Omer et ol. [31] have shown that phase-transfer catalyzed segmented flow in a capillary microreactor can even be accelerated by sonication. The hydrolysis of p-nitrophenyl acetate in toluene with 0.5 M aqueous sodium hydroxide at different temperatures was used as a test reaction for this system (Scheme 8.5). Sonication and tetrabutylammonium hydrogen sulfate as phase-transfer catalyst were used to increase the rate of reaction showing an increase in the yields. It was also shown in a comparison of flow forms that segmented flow had an advantage over parallel flow because of the increased surface to volume ratio. The reaction in flow was also shown to be superior to batch conditions. A more in-depth investigation of the effect of sonication on the hydrolysis of p-nitrophenyl acetate has been performed by Janisch and Hiibner et al. [32]. They showed that sonication of the reaction was indeed beneficial showing increased yields compared to silent conditions. 

---