Microstructured mixers

By the use of microstructured mixers, pigment and other particulate syntheses can be improved. In this way, finer particles with more uniform size distribution were yielded for the commercial azo pigment Yellow 12 (see Fig. 2) [11]. The particles formed in the microstructured mixer have better optical properties such as the glossiness or transparency at similar tinctorial power. Since the micro-mixer made pigments have more intense colour, lower contents of the costly raw material in the commercial dye products can now be employed which increases the profitability of the pigment manufacture. 

Production operation (1700 kg h" ) of a microstructured mixer-reactor for high-value polymer intermediate product (FZK works) [17]... 

Experts predict a trend from stirred-vessel mixing to the use of continuous mixing, e.g. by in-line mixers [1]. This again provides a chance for many microstructured mixers. 

Many passive microstructured mixers (see e.g. [2, 3]) follow design principles used at the macro-scale for static mixers with internal packings [4], It stands to reason that some of the advantages in processing claimed for conventional static mixer also apply or may be even more pronounced when using static mixers [4] ... 

In addition, the following specific chemical engineering drivers may govern the decision to use a micro or microstructured mixer ... 

These techniques are the most often used and simplest ways to characterize mixing in microstructured mixers. Certainly, many more were used in the past. Information on such specially techniques given in the next two chapters where the respective mixer is discussed. 

Micro mixer elements, micro mixers and micro structured mixers typically have flows in the ml h-1, 11 h-1 and 1000 1 tf1 ranges, respectively, thus covering the whole flow range up to the conventional static mixers and being amenable to analysis and chemical production as well (see Figure 1.4). When used at the upper flow limit, microstructured mixers can act as process-intensification (PI) equipment. 

M 39] [P 37] Using an azo-type competitive reaction, the selectivities were compared for the P- and V-type micro mixers having straight and oblique fluid injection, respectively [41]. In this way, laminar- and turbulent-flow mixing achieved by vertical interdigital microstructured mixers can be compared. The selectivities of the turbulent V-type mixer are better to some extent as compared with the P-type device however, neither approaches the characteristics of the ideal tubular reactor. The micro devices, however, are better than a conventional jet mixer. 

The difference between the microstructured mixers can be understood when considering the fact that the crossing of the streams yields additional shearing which provides new interfaces for mixing [41]. Concentration differences are reduced much faster in this way. 

This interdigital concentric consecutive microstructured mixer is composed of a housing with a cylindrical recess in which a platelet stack is inserted (see Figure 1.108) [130], The device can be operated up to 100 bar and at a temperature of600 °C. 

Figure 1.108 Interdigital concentric consecutive microstructured mixers have the potential for use as chemical production tools, as evidenced by their comparatively large outer dimensions and owing to an internal numbering-up of the micro-structured platelets. Left, front StarLam300 right, back StarLam3000 [130],...

This approaches the performance of conventional static mixers, closing the gap between this smallest class of industrially used apparatus and micro mixers for analytical purposes [130], Thus, a toolbox of microstructured mixers is available for the whole range of flow rates. This box comprises interdigital multi-laminating with a few ml h 1 capacity and split-and-recombine micro mixers (caterpillar type) up to 1001 h 1 as well as interdigital concentric microstructured mixers (StarLam type) series achieving 300, 1000 and up to 3000 1 h, dependent on the respective sub-version. 

Figure 1.111 Flow rate dependence of the Dushman mixing quality of the interdigital concentric consecutive microstructured mixers of the StarLam series and other micro mixers taken for benchmarking [130].

M 72] [M 73] [P 65] A linear dependence of the pressure drop on the volume flow rate was observed both for the intersecting and the helical microstructured mixers (see Figure 1.154) [2], The pressure drop of the helical device is lower than that of the intersecting mixer. A flow rate of about 11 h 1 was found for the helical mixer at a pressure of about 150 mbar, whereas the intersecting mixer gives 0.75 1 h 1 at about 250 mbar. 

Figure 5.32 StarLam 3000 microstructured mixer retrofitted to existing plant peripherals and tank reactor (by courtesy of Wiley-VCH Verlag GmbH) [67],...

The inlet pipes of the two starting reactants to the batch vessel were simply connected to the StarLam mixer [67]. The only difference to the previous feed lines was the installation of filter cartridges before the entries to the microstructured mixer, necessary to avoid blocking of the reactor. The pressure drop in the lines was lower than 3 bar so that it was possible to keep the pumps used before in the plant. At the outlet of the reactor, a tube reactor was installed. During optimization it was found that it is sufficient to insulate this tube to reach the temperature needed to finish the reaction. The pipe ended directly in the batch vessel where the second endothermic reaction step was carried out as before. 

The first start-up of the plant was in June 2005 [67]. A temperature diagram shows that most of the heat is released in the retention time tube (see Figure 5.33). The temperature measured directly at the outlet of the microstructured mixer-reactor StarLam 3000 was below 50 °C even at higher throughputs. During the retention time, tube temperatures up to about 130 °C were reached. The throughputs for this first test mn were increased in three steps to up to 3600 kg/h. 

P. Pfeifer, L. Bohn, O. Gorke, K. Haas-Santo, U. Schygulla, K. Schubert, Microstructured mixers for gas-phase processes - Manufacture, characterization and applications, Chem. Eng. Technol. 28 (2005) 439. 

Microstructured Mixer-reactors for Piiot and Production Range and Scaie-out issues... 

Caterpillar microstructured mixer-reactors owe their name to their total micro-channel shape, characterized by alternately up- and down-lifting ramps at the floor and ceiling of the fluid path, which as a whole resemble the fringes along the body... 

Microstructured Mixer-reactors for Pilot and Production Range and Scale-out Issues 89... 

StarLam microstructured mixers consist of disk-like platelets with a hollow starshaped feeding zone where the fluid is re-directed into an inner central circular mixing zone (Fig. 6.6) [21] (see also Refs. [1, 9]). Many such platelets form a complete, rod-shaped inner mixing channel into which the several streams are injected, virtually via small slit-like nozzles. For efficient mixing, injection in the turbulent range is advised. The flow properties at small Re are less well known. 

Fig. 6.9 StarLam300 (left) and StarLam3000 (right, back) microstructured mixers, with Swagelok connectors [29],...

For many reactions, the microstructured mixers are simply followed by tube reactors, e.g., double-mantled tubes or shell-in-tube heat exchangers. The benefit from mixing in combination with the benefits of the continuous-flow process through the tube give process intensihcation, while providing reliable operation, especially when for larger volume flow ranges. 

Fig. 6.17 A mixing test station for pilot-sized microstructured mixers up to the 5000-l/h range. Shown above are three StarLam microstructured mixers.

Micromixers have been developed for flows ranging from < 1 mL h up to 10 000 L h At the low flow range, only single elements of the micromixer are required. These are often used in integrated systems for credit card sized fluidic chips [65]. For flows > 1 L h microstructured mixers are used for process intensification in pilot- and conventional-scale applications [65]. 

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