Reaction micro falling-film reactor

The high heat-transfer rate of micro heat exchangers raised the possibility of preparing microreactors for highly exothermic chemical reactions. Examples are oxidation reactions with molecular oxygen [11] or direct fluorination in micro falling-film reactors [12]. These appHcations impressively demonstrated that microreactors are tools for the performance of chemical reactions in reaction regimes not accessible even in state-of-the-art conventional reactors. 

The control of contact of the organic and SO3 gas is the most critical part of the process. It is important that it should be controlled on both an overall (macro) and a point-by-point (micro) scale. Sulfonation equipment suppliers have devoted decades and tens of thousands of effort hours to the perfection of falling-film reactor design with the goal of controlling the ratio of organic to SO3 gas and the temperature of the reaction. 

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. 

Internal heat exchange is realized by heat conduction from the microstructured reaction zone to a mini channel heat exchanger, positioned in the rear of the reaction zone [1,3,4], The falling film micro reactor can be equipped, additionally, with an inspection window. This allows a visually check of the quality of film formation and identification of flow misdistribution. Furthermore, photochemical gas/liquid contacting can be carried out, given transparency of the window material for the band range of interest [6], In some cases an inspection window made of silicon was used to allow observation of temperature changes caused by chemical reactions or physical interactions by an IR camera [4, 5]. 

Figure 5.18 Comparison of space-time yields of direct fluorination of toluene for the falling film micro reactor (FFMR), micro bubble column (MBC) and laboratory bubble column (LBC) referred to the reaction volume (a) and referred to an idealized reactor geometry (b) [38],...

GL 1[ [R 1[ [P la[ The residence time distribution between the individual flows in the various micro channels on one reaction plate of a falling film micro reactor was estimated by analysing the starting wetting behavior of an acetonitrile falling film [3]. For a flow of 20 ml h it was found that 90% of all streams were within a 0.5 s interval for an average residence time of 17.5 s. 

GL 1[ [R 1[[P la[ By autofocus laser imaging, the average position of the liquid surface in all micro channels of a reaction plate of a falling film micro reactor was determined [3]. It was found that very thin films of the order of 20-25 pm were formed for total volume flows of 20-80 ml h The thickness of the films in the various channels differed, but by no more than 30% on average. At high flows, e.g. > 180 ml hr, flooding of the channels occurs. 

P 12] A falling film micro reactor was applied for generating thin liquid films [6]. A reaction plate with 32 micro channels of channel width, depth and length of 600 pm, 300 pm and 66 mm, respectively, was used. Reaction plates made of pure nickel and iron were employed. The micro device was equipped with a quartz window transparent for the wavelength desired. A 1000 W xenon lamp was located in front of the window. The spectrum provided ranges from 190 to 2500 nm the maximum intensity of the lamp is given at about 800 nm. 

GL 13] [R 1] [P 12] By using a nickel plate, space-time yields up to 401 mol 1 h were achieved in the falling film micro reactor [6]. Control experiments in a batch reactor at a 30 min reaction time resulted in a space-time yield of only 1.3 mol 1 h , hence orders of magnitude smaller. By using an iron plate, space-time yields up to 346 mol h were achieved in the falling film micro reactor. 

Acetic acid and 10, 15, or 20% acetyl chloride were fed as a mixture into a modified falling film micro reactor (also termed micro capillary reactor in [57]) at a massflow rate of 45 g min and a temperature of 180 or 190 °C [57]. Chlorine gas was fed at 5 or 6 bar in co-flow mode so that a residual content of only 0.1% resulted after reaction. The liquid product was separated from gaseous contents in a settler and collected. By exposure to water, acetyl chloride and acetic anhydride were converted to the acid. The hydrogen chloride released was removed. 

Catalyst coatings on the reaction plate of a falling film micro reactor were prepared by four routes and tested [60]. 

It is remarkable that the falling film micro reactor achieved complete conversion for all process variations applied [5]. This is unlike conventional reactor operation reported for this reaction, displaying pronounced mass transfer resistance. 

To reduce the decomposition, H202 is evaporated in a micro structured falling film evaporator at the bottom of the plant The gaseous H202 flows upwards to the micro structured mixer where it is mixed with propylene. This mixture is guided through the likewise micro structured catalytic reactor. The mixture of the reaction, mainly propylene oxide, unreacted propylene and water is carried off at the top of the plant [100],... 

Owing to the complex and often dedicated equipment required to perform gas-liquid phase reactions within research laboratories, this area of synthetic chemistry is somewhat underutilized. Over the past decade, however, numerous research groups have developed an array of continuous flow reactors capable of conducting such reactions in a safe and efficient manner, including microchannel contactors, falling film micro reactors, and packed-bed reactors [68, 69]. 

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