Micromixing microreactors

Comparative study of the synthesis of silica nanoparticles in micromixer-microreactor and batch reactor systems. Chem. Eng. J., 171,674-683. 

A microreactor was also applied to this reaction. The slit interdigital micromixer was purchased from IMM (Mainz, Germany). The width of the interdigital channels is 25 pm. HPLC pumps were used to feed the two reaction solutions. One is a mixture of Boc-AMP and 1.2 molar equivalents of r-BocaO. The other is a 50% aqueous KOH solution. The microreactor was immersed in a temperature controlled cooling bath at 15 °C. The product was quenched with an acid, and samples were taken for HPLC analysis. 

Stainless steel is the material of choice for process chemistry. Consequently, stainless steel microreactors have been developed that include complete reactor process plants and modular systems. Reactor configurations have been tailored from a set of micromixers, heat exchangers, and tube reactors. The dimensions of these reactor systems are generally larger than those of glass and silicon reactors. These meso-scale reactors are primarily of interest for pilot-plant and fine-chemical applications, but are rather large for synthetic laboratories interested in reaction screening. The commercially available CYTOS Lab system (CPC 2007), offers reactor sizes with an internal volume of 1.1 ml and 0.1 ml, and modular microreactor systems (internal reactor volumes 0.5 ml to... 

Ruy et al. have performed a similar reaction under microreactor conditions in a multiphase solvent system containing an ionic liquid as the catalyst carrier and reaction promoter [35]. Their system consisted of two T-shaped micromixers (i.d. 1,000 and 400 pm) and a capillary stainless steel tube as an RTU (1,000 pm i.d. and 18 m length, giving a 14.1 ml volume), equipped with pumps and control valves. Under the optimized conditions, Pd-catalysed carbonylation of aromatic iodides in the presence of a secondary amine provided only the double carbonylated product, ot-ketoamide, while the amide obtained by the single carbonylation was observed in high quantities only when the reaction was performed in batch (Scheme 13). 

Following similar trials with the formation of diarylbenzenes [63-65], the same research group has reported a multistep synthesis of photochromic diarylethenes using a microflow system that contained two linked micromixers and microreactors (MRi 2) [66]. Similarly to the previously reported linked microreactors, the reactors used in this setup were made of stainless steel tubes and T-shaped micromixers. Initial experiments were conducted in two steps in a continuous sequence to afford symmetrical octasubstitued diaryUiexafluoro cyclopentene (Scheme 29). 

Micromixing technologies have only recently been applied to the design of miniaturized devices for chemical applications, so called microreactors. The main components of such microreactors are mixers and heat exchangers. 

Figure 6 Schematic of an integrated microreactor for the continuous synthesis of CdSe/ZnS and CdS/ZnS nanoparticles (Sl-syringe pump with Se precursor, S2-syringe pump with S precursor, S3-syringe pump with Cd-OA-OLA, S4-syringe pump with Cd-OA-OLA-TOPO, Y—Y conjunction, M-micromixer, V-stop valve, C-channel images reproduced, with permission, from Yang et al., 2009).

Most examples describe catalyzed biphasic reactions taking the extra advantage of product isolation and catalyst recycling. De Bellefon et al. [211] published one of the first examples of biphasic reactions performed in a microreactor. The isomerization of allylic alcohols to carbonyl compounds was conducted in a liquid-liquid system using a micromixer combined with a microchannel tube. As there are limited examples of biphasic isomerization reactions, the authors were interested on... 

The Taylor-flow microreactor comprised a micromixer for mixing of the precursors for the particle synthesis followed by a gas inlet for separating this continuous mixed liquid stream into segments separated by gas bubbles [328,329]. 

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