Microflow tools

Precise control of concentration and residence time can increase the selectivity of the sulfonation of toluene, as this allows to optimally set the interplay between the readions 4.4.1-4.4.4 [315,316], The highly exothermic nature of the reaction demands for good temperature control. A single microreador is not suited to condud the various readion steps with all their different needs on temperature and residence time. Thus, a continuously operated plant with many microflow tools was developed. The plant design was based on a fluidic backbone providing unitized ports and plant unit sites to facilitate the connection of microstructured components from different suppliers (see Figure 4.49). 

Concerns about an industrial use of microprocess technology are still existing [62]. Process chemists need to be familiarized with the new tool. Often it seems that these soft factors are even more relevant than the hard factors. Nonetheless, the performance of microprocess technology must show up a clear driver in the interplay of operating and capital costs of existing equipments and respective costs on the microflow processing side. 

Based on these arguments, it is reasonable to conclude that microflow systems are essential tools for performing flash chemistry. In the following chapter, we will discuss the details of microflow systems consisting of microfluidic devices. 

As demonstrated in this chapter, a number of microfluidic devices of various structures and sizes for extremely fast mixing, heat exchanging and residence time control have been developed based on conventional and modern fabrication technologies. Microflow systems composed of such microfluidic devices are expected to serve as powerful tools for conducting extremely fast, highly exothermic reactions in a highly controlled manner to effect flash chemistry, where desired products are formed within milliseconds to seconds. 

Online analysis Online sample processing techniques such as flow injection provide advantages such as reliability, sample economy, ease of automation, measurement standardization, high speed, optional sample dilution, and the ability to derivatize the analyte so as to suit the analyzer/detector. These procedures facilitate the online monitoring of fermentation substrate materials, respiratory gases, and biomass. The modifications to flow injection analysis for accurate discontinuous flow operation include sequential injection analysis and bead injection spectroscopy. The most recent invention in online techniques is the introduction of the Lab-on-a-Valve, which opens the way to development of a novel type of microflow analytical system monitored by UV-visible spectrophotometry using fiber optics. This system is an ideal tool for fermentation monitoring. 

Addition and elimination reactions are one of the most important classes of reactions in organic synthesis because they serve as powerful tools for the construction of a variety of organic structures. This chapter provides an overview of elimination and addition reactions using microflow reactors. 

Addition reactions of Grignard reagents to carbonyl compounds are also performed in microflow reactors. For example, the reaction of cyclohex-2-enone with isopropylmagnesium bromide leads to the formation of both 1,4-adduct A and 1,2-adduct B (Scheme 5.4). It is noteworthy that the microflow reactor serves a beneficial tool for optimization of the reactions conditions. By testing 14 different reaction conditions, the yield was increased from 49% to 78% and the ratio of the regioisomers was improved from 65 35 to 95 5 [12, 13]. 

Oxidation and reduction are fundamental processes in the synthesis of organic and inorganic compounds. Some oxidation and reduction reactions are difficult to control in macro-scale batch reactors and in such cases microflow reactors serve as powerful tools for accomplishing the reactions in a highly controlled manner. This is especially true for many oxidation reactions because of their exothermic nature. It should also be noted that the danger of unexpected explosions can be avoided by the use of microflow reactors because of the small volume and highly efficient heat transfer ability of microflow systems. This chapter provides an overview of oxidation and reduction reactions using chemical, electrochemical and biochemical methods in microflow reactors. 

Enzymatic reactions have attracted significant research interest because of their environmentally friendly nature. Microflow systems can serve as eflScient tools for the development of enzyme processes [67]. 

Microflow reactors serve as powerful tools for accomplishing gas-Uquid-phase reactions in addition to liquid- and liquid-liquid-phase reactions. This chapter provides an overview of electrophilic and free-radical substitution under gas-liquid-phase conditions using microfiow reactors. 

Electro-organic processes offer versatile and powerful tools which are often classed as green [27, 28] or sustainable chemistry [29]. Millimeter-spaced electrodes in flow reactors have been employed for many years with major applications in industry [30], but recently, more interest in sub-millimeter or microflow systems has arisen due to further potential benefits such as (i) lower flow volume, (ii) a faster conversion with better control over flow and diffusion layer, (iii) better heat exchange, (iv) the use of co-flow and rapid mixing, (v) better control over... 

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