Micromixer multilamination mixers

Cha et al. [68] presented a novel micromixer design relying on a concept not far from that of the multilamination mixer, named a chessboard mixer. The mixer was able to complete the mixing in only 1.400 mm and the author claimed that the flow rate can be increased easily by using different arrays without affecting the performance (Fig. 3c). 

The reason behind such a low energetic efficiency is the mismatch of flow fields and concentration fields. The mechanical energy provided to the mixer is used to achieve the flow in device, but in zones of pure component with no interface with another component, this energy does not contribute in mixing. In the case of micromixers, multilamination improves mixing by reducing the striation thickness, but it requires additional mechanical power to create fine multilamellae before contacting. 

Sprogies et al. compared micromixers for use in extractions based on emulsions [32]. They revealed that a multilamination mixer is more efficient than a simple T-junction, whereas a nozzle-type mixer and a split-and-recombine mixer show the best results for emulsification and thus for extraction. 

As industrial relevant Friedel-Crafts reaction, the synthesis of Bisphenol-F, a material for epoxy resin, from phenol and formaldehyde was chosen [57]. This reaction involves formation of higher order condensates such as tris-phenols. To minimize the latter, the molar ratio of phenol to formaldehyde is set to a very high value (30-40), which is more than 15 times larger than the amount theoretically necessary. Three types of micromixers were used. These are a T-shaped mixer with 500 pm inner diameter, a multilaminating interdigital micromixer with 40 pm channels and a so-called self-made K-M micromixer with center collision mixing. 

When a T-shaped mixer is used, the product selectivity is essentially the same as for the macrobatch reactor (Scheme 6.4). The use of the YM-1 mixer, a splitting-and-recombination-type micromixer (see Chapter 7), increases the selectivity, however, a significant amount of dialkylation product is still produced. The use of the IMM multilamination-type micromixer results in excellent selectivity of the monoalkylation product. The amount of dialkylation product is very small. Therefore, the product selectivity strongly depends on the manner of mixing. 

In interdigital multilamination micromixers, the small thickness of the lamellae leads to short diffusion paths, resulting in fast mixing. Further thinning of the liquid lamellae should lead to shorter diffusion paths and faster mixing. The IMM single mixer applied this concept by shrinking the channel width in the slit. A further extension of this concept leads to the... 

The effects of mixing in radical polymerization of MMA are interesting [168]. The use of a 5 mm static mixer leads to fouling in the reactor. In contrast, the use of an interdigital multilamination micromixer with 36 lamellae of 25 pm thickness results in a reduction in fouling. This numbering-up approach enables production of 2,000 tons per year without the fouling problem [169]. 

Yoshida et al. also demonstrated the effect of mixing on alkylation yields and selectivity by using an efficient multilamination micromixer (supplied by IMM channel width = 25 pm) and a T-mixer (500 pm). 

Figure 22.13 Micromixers employed in the experimental setups for surfactant dispersion. The V-type mixer of FZK (a) is a parallel multilamination micromixer whereas the caterpillar mixer of IMM (b) is a split-and-recombine micromixer (serial multilamination) [3].

The Friedel-Crafts alkylation of aromatic and heteroaromatic compounds often suffers from a polyalkylation problem owing to competitive, consecutive alkylation reactions. Owing to the large exothermicity of the reaction, the product distribution has proved difficult to control on the macroscale, resulting in synthesis of a large proportion of dialkylated products (the monoalkylated dialkylated ratio may be 1 1). Yoshida et al. carried out an alkylation reaction in a microchannel at —78 °C as per Fig. 5 [3]. Yoshida et al. also demonstrated the effect of mixing on alkylation yields and selectivity by using an efficient multilamination micromixer (supplied by IMM channel width = 25 xm) and a T-mixer (500 xm). 

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