Micro reactors, flow-through

Akay, G. Erhan, E. Keskinler, B. Bioprocess intensification in flow through micro-reactors with immobilized bacteria. Bioeng. Biotech. 2005, 90, 180-190. 

Simple flow through micro-reactor cells for operation in two-electrode mode have been proposed based on low pressure [39, 40] and high pressure [41] designs. Recently Birkin and coworkers proposed a versatile design based on a Viton microchannel foil [42] (see Fig. 3) for acetoxylation and TEMPO-mediated oxidations [43]. 

The EM Modular Reaction System can also be used to perform multi-step syntheses [83], For the production of pharmaceuticals, in this case for the synthesis of vitamin A, an ylid is formed from a phosphonium salt and a base in the first stage at 2 °C. In a second stage, the ylid reacts with an aldehyde at 60 °C in a flow-through capillary reactor. In a third stage the crude product is hydrolyzed at 20 °C in an additional micro mixer to form the target product vitamin A acetate, as illustrated. For the claimed reaction, no further experimental details were given. 

The figure indicates the transport of gas bubbles through the reaction channel. In contrast to the standard process, which is of batch type, the micro reactor allows the fluids to be proceeded in a continuous-flow manner. 

Better chemistry through confinement economy of scale limits and expenditure of scale-up micro reactors origin from microfabrication expert opinions general advantages of micro flow hybrid construction industry s efforts chip micro reactors numbering-up vision of computer-like chemical workstation [205]. 

In chemical micro process technology with porous catalyst layers attached to the channel walls, convection through the porous medium can often be neglected. When the reactor geometry allows the flow to bypass the porous medium it will follow the path of smaller hydrodynamic resistance and will not penetrate the pore space. Thus, in micro reactors with channels coated with a catalyst medium, the flow velocity inside the medium is usually zero and heat and mass transfer occur by diffusion alone. 

This class of hybrid components comprises chip micro-reactor devices, as described in Section 4.1.3, connected to conventional tubing. This may be H PLC tubing which sometimes has as small internals as micro channels themselves. The main function of the tubing is to provide longer residence times. Sometimes, flow through the tube produces characteristic flow patterns such as in slug-flow tube reactors. Chip-tube micro reactors are typical examples of multi-scale architecture (assembly of components of hybrid origin). 

For the application referred to, the interdgital micro mixers were used on their own, without tubing attached, as reactors. Especially at low flow rates, the internal flow-through chamber acts as delay loop for providing a sufficient residence time. 

P 38] Ethanol solutions of ethyl propiolate and diisopropylethylamine were pumped via electroosmotic flow through the micro channels of the reactor [8], By mixing thereof the enolate was obtained. By subsequent contacting with the 1,3-dicarbonyl compound, the product was obtained. The temperature was set to room temperature. In a period of 20 min a volume sufficiently large for analysis was sampled. The reaction product spectra was analyzed by GC/MS via comparison with synthetic standards. The remaining amount of diketone was used for calculating conversions. 

Following the above-mentioned motivation, precise control over temperatare can be exerted in micro reactors [9,10]. Also, parallel or fast serial screening, handling small volumes distributed over compactly arranged reaction flow-through chambers, can be achieved in micro reactors. 

P 53] Before operation, a start-up time of about 10 min was applied to stabilize pressure in the chip micro reactor ([R 6]) [20]. As a result, a stable flow pattern was achieved. The reactant solutions were filled into vials. Slugs from the reactant solutions were introduced sequentially into the micro chip reactor with the autosampler and propelled through the chip with methanol as driving solvent. The flow rates were set to 1 pi min The slug volume was reduced to 2.5 pi. 

To study the effects of molecular diffusion and formation/destabilization of reaction fronts it is advised to rely on small flow-through chambers such as capillaries or cells of sheet-type cross-section [68]. These micro reactors simply provide the small-scale environment needed for such laboratory investigations. 

A coolant channel is guided through the metal block in a serpentine fashion [15], Hence reactant and coolant flows are orthogonal. A thermocouple measures the temperature at the product outlet of the single-channel thin-film micro reactor. 

Fukuyama, Ryu and coworkers reported intermolecular [2 + 2]-type cycloaddition of various cyclohexenone derivatives and alkenes using a micro reactor made entirely of glass, which was supplied by Mikroglas (Scheme 4.26) [39]. The device was equipped with a heat exchanger channel system through which water flowed to maintain isothermal reaction conditions. The remarkable photochemical efficiency of this device was manifested in rapid cycloaddition of vinyl acetate to cyclohex-2-enone. With this device, the desired product was obtained in 88% yield after 2 h, whereas the same reaction carried out in a Pyrex flask was very sluggish (only 8%... 

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