Photochemical reactor falling film

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 7. Falling film tubular photochemical reactor, for reactions requiring excitation of a reactive gas [2,3].

Figure 18. Annular falling film photochemical reactor [2, 3, 71].

Experience with falling film photochemical reactors lead us to the... 

Figure 6,20 Examples of photochemical reactors (a) for batch production the lamp L is placed in the middle of the sample holder S, separated by a filter F and a thermostatted vessel T through which the coolant is circulated, (b) The falling film reactor uses a central lamp L surrounded by a filter F. The sample Sff) falls slowly as a thin film on the inner wall of the reactor, and the photoproducts are collected at the bottom...

The photochemical chlorination of toluene-2,4-diisocyanate has also been reported (Scheme 8.3). A falling-film microflow reactor is used with irradiation of gaseous chlorine, through a quartz window, enabling the in situ generation of chlorine radicals. The optimal residence time is 9 s at 130 °C, and benzyl chloride-2,4-diisocyanate is produced in 81.0% yield. 

The microstructured falling film reactor has also been used for chlorination reactions [77]. Chlorination of acetic acid at a temperature over 140 C was carried out and the by-product (dichloroacetic acid) was reduced significantly, meaning that there is no need for additional costly and time-consuming separation processes. Further, a photochemical gas-liquid reaction by the selective photochlorination of toluene-2,4-diisocyanate (TDl) was demonstrated [78]. 

DifTerent types of microreactors, ranging from single-channel to multi-channel designs, and even more complex falling film reactors, have been investigated for carrying out photochemical reactions. Reported channel dimensions of photomicroreactors range from 10 to 1000 pm. 

K. Jahnisch, U. Dingerdissen, Photochemical generation and [4 + 2)-cycloaddition of singlet oxygen in a falling-film micro reactor, Chem. Eng. Tech. 2005, 28, 426-427. 

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