Packed reactors miniaturized

The principle of the FIA preconcentration technique is illustrated in Fig. 4.38, which demonstrates how reduced dispersion of the injected sample (i.e., D < 1) might be achieved by introducing a relatively large volume of sample solution, the analyte content of which is retained on an incorporated miniaturized packed reactor within the FIA channel, from which column the analyte subsequently is released and passed to a detector. The method was originally proposed to enhance the sensitivity of measurement of cationic trace elements in very diluted aqueous samples using... 

Using a packed bed of Hg-coated Ag particles approximately the size of a precolumn, Eggli and Asper (1978) developed a novel scheme for the detection of thiols and disulfides. The packed reactor was inserted between the column and an amperometric Hg pool electrode detector. Incoming disulfides were effectively reduced in the reactor to the parent thiol, followed by the latter s downstream detection at the Hg pool, llie approach was considerably miniaturized using a dual Hg/Au thin-layer cell, with concomitant improvement in SNR (Allison and Shoup, 1983). 

Regular flow patterns are provided by the segmented flow in a single capillary or in multi-channel microreactors. Miniaturized packed-bed microreactors follow the paths of classical engineering by enabling tridde-bed or packed bubble column operation. M ost of the microstructured multiphase reactors are at the research stage. Due to the small reaction volumes th will find their appHcation mainly in small-scale production in the fine chemical and pharmaceutical industries. 

Online sorptive preconcentration exploiting renewable solid surfaces, the so-called bead injection (Bl), in the miniaturized LOV platform has been hyphenated to GC separation with electron-capture detection for automated determination of trace levels of PCBs in solid-waste leachates. To this end, the MSFIA system presented in Chapter 3, Figure 3.19, has been implemented. It comprises a mul-tisyringe burette, an extra solenoid valve, an LOV, and an injection valve (IV) as well as reversed-phase copolymeric beads with hydroxylated surface (Bond Elut Plexa) included into the channels of a poly(ether imide) LOV microconduit, thus serving as a transient microcolumn-packed reactor for preconcentration of organic species [194]. 

Modeling and analysis of miniaturized packed-bed reactors for mobile devices powered by fuel cells... 

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. 

Marquez N, Castano P, Moulijn JA, Makkee M, Kreutzer MT. Transient behavior and stability in miniaturized multiphase packed bed reactors. Ind. Eng. Chem. Res. 2010 49(3) 1033-1040. 

These reactors are literally the new kids in town. The heat transfer problem that is so inhibitory in packed bed systems becomes a nuisance in the small sizes of the microfluidic reactors. The mass transfer problem can also be relinquished in the microdomains. The microdomains provide excellent flow control, as well as bring in the surface tension as an additional force field to inertial and viscous forces that we are used to dealing with so far. The surface and interface forces at this level of miniaturization become driving forces for better mixing domains. 

Unfortunately, the widely used flow reactors (for example, microreactors, multi-cell flow reactors, and disk reactors) do not tolerate solid particulates and precipitates, which would clog the miniaturized flow devices. Therefore, immobilization of the reagents/catalysts by a solid support is of significant importance in this field. Hence, a broad range of solid supports have been employed to incorporate the reagent/ catalyst into the reactors, including packed-beds, monoliths, and other systems that exploit the high surface-to-volume areas obtained in microchannel devices. 

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