Micro bubble column

For toluene fluorination, the impact of micro-reactor processing on the ratio of ortho-, meta- and para-isomers for monofluorinated toluene could be deduced and explained by a change in the type of reaction mechanism. The ortho-, meta- and para-isomer ratio was 5 1 3 for fluorination in a falling film micro reactor and a micro bubble column at a temperature of-16 °C [164,167]. This ratio is in accordance with an electrophilic substitution pathway. In contrast, radical mechanisms are strongly favored for conventional laboratory-scale processing, resulting in much more meta-substitution accompanied by imcontroUed multi-fluorination, addition and polymerization reactions. 

The micro bubble column uses dispersion of gas in a liquid stream (Figure 5.3)... 

Figure 5.3 Schematic of contacting liquid and gaseous reactants in a micro bubble column [3. ...

Reactor type Micro bubble column Mini heat exchange channel width depth length 3000 pm 500 pm 40 mm... 

The micro bubble column comprises internal cooling via heat conduction from the reaction zone to a mini channel heat exchanger [3, 9, 10], Either two such heat exchange plates can encompass the reaction plate, or only one. In the latter case, the free position is occupied by an inspection window which allows direct observation of the quality of the flow patterns. 

Meanwhile, a redesign of the micro bubble column has been made with improved flow distribution (Figure 5.4). 

Figure 5.17 Comparison of performance of a typical laboratory column (LBC) with those of micro-reactor devices falling film micro reactor (FFMR) micro bubble column (MBC I and MBC II) [38].

The laboratory and the micro bubble column show decreasing selectivity with increasing conversion. The falling film micro reactor shows a near-constant selectivity-conversion relationship [3, 38]. 

GL 1] [R 1] [R 3] [P le] The falling film micro reactor has a better selectivity-conversion performance than the two micro bubble columns tested (Figure 5.18) (3, 38]. The micro bubble column with narrow channels has a better behavior at large conversion than the version with wide channels. The behavior of the falling film micro reactor and the micro bubble column with narrow channels is characterized by a nearly constant selectivity with increasing conversion, while the bubble column with wide channels shows notably decreasing selectivity with conversion (similar to the laboratory bubble column). 

GL 1] [R 1] [R 3] [P la-d] Space-time yields higher by order of magnitude were found for the falling film micro reactor and the micro bubble column as compared with the laboratory bubble column [38], The space-time yields for the micro reactors ranged from about 20 000 to 110 000 mol monofluorinated product m h. The ratio with regard to this quantity between the falling film micro reactor and the micro bubble column was about 2. The performance of the laboratory bubble column was of the order of 40-60 mol monofluorinated product m" h. ... 

Figure 5.19 Conversion of the direct fluorination of toluene in different reactor types as a function of the molar ratio of fluorine to toluene (a) and efficiency of these reactors, defined as conversion normalized by the molar ratio of fluorine to toluene, as a function of the molar ratio of fluorine to toluene (b). Falling film micro reactor (FFMR) micro bubble column (MBC) laboratory bubble column (LBC) [38].

GL 22] [R 3] [R 9] [R 10] [P 23] The mass transfer efficiency of different gas/liquid contactors as a function of residence time was compared qualitatively (Figure 5.29), including an interdigital micro mixer, a caterpillar mini mixer, a mixing tee and three micro bubble columns using micro channels of varying diameter [5]. 

The two micro bubble columns comprising the smaller micro channels reached nearly 100% conversion [5], The micro bubble column with the largest hydraulic diameter reached at best 75% conversion. The curve obtained displays the typical shape, passing through a maximum due to the antagonistic interplay between residence time and specific interfacial area. 

Figure 5.29 Special-type multi-purpose micro devices and mixing tee used for investigation of CO2 absorption. Comparison of their reactor performance as a function of the residence time. Micro bubble columns ( ) 1100 pm x 170 pm, (A) 300 pm x 100 pm and (T) 50 pm x 50 pm Interdigital mixer ( ) (40 pm) caterpillar mixer (A) (850 pm ramp) mixing tee (0) (1 mm) [5],...

Reactor model of micro bubble column performance... 

GL 26] [R 3] [P 28] See the discussion of results in the section Reactor model of micro bubble column performance, above [10]. 

Figure 5.32 Calculated values for conversion of butyraldehyde as a function of specific interfacial area for a micro bubble column [10],...

GL 27] [R 3] [P 29] By means of sulfite oxidation, the specific interfacial areas of the fluid system nitrogen/2-propanol were determined for different flow regimes [5]. For two types of micro bubble columns differing in micro-channel diameter, interfaces of 9800 and 14 800 m m , respectively, were determined (gas and liquid flow rates 270 and 22 ml h in both cases). Here, the smaller channels yield the multi-phase system with the largest interface. 

Characterization of a gas/liquid microreactor, the micro bubble column Determination of specific interfacial area, in Matlosz, M., Ehreeld, W., Baselt,... 

Haverkamp, V., Emig, G., Hessel, V., Liauw, M.A. and Lowe, H. (2001) Characterization of a gas/liquid microreactor, the micro bubble column determination of specific interfadal area, in Microreaction Technology- IMRET 5 Proceedings of the 5th International Conference on Microreaction Technology (eds M. Matlosz, W. Ehrfeld and J.P. Baselt), Springer-Verlag, Berlin, pp. 202-214. 

Packed column Countercurrent flow Co-flow 10-350 10-1700 Micro bubble column (1100 x170 pm) Isopropanol (observation) 5100... 

Microstructured falling film and micro bubble column reactor Single micro channel operating in annular flow regime Microstructured falling film reactor Microstructured falling film reactor... 

Figure 7.23 Schematic presentation of (a) microstructured falling film reactor and (b) micro bubble column (b) [75]. (Adapted with permission from Elsevier.)...

Similar to the numbered up Taylor-flow reactor, the micro bubble column achieved dispersion by an interdigital mixing element with many miniaturized mixing tees (Figures 9.17 and 9.18) [4,26,66,67,71,74,75]. This was one of the very... 

Figure 9.29 Reduction of reaction times by as given in Ref. [119]) as compared to standard several orders of magnitude using a falling film organic laborato processing with a laboratory microreactor (FFMR) or micro bubble columns bubble column (LBC). x residence time. Source (MBC I and II, denoting different dimensions, By courtesy of I MM.

Figure 9.34 Special-type multipurpose (A), (300pm x 100pm) micro bubble column...

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