Application of Microstructured Reactor Technology for the Photochemical Chlorination of Alkylaromatics

Abstract

The advantageous application of a falling-film microreactor for a photochemical gas/liquid reaction was demonstrated by the selective photochlorination of toluene-2,4-diisocyanate (TDI). In the microstructured reactor the selectivity to the side-chain chlorinated product 1-chloromethyl-2,4-diisocyanatobenzene (1Cl-TDI) achieved a value of 80% at 55% TDI conversion, whereas the side product toluene-5-chloro2,4-diisocyanate (5Cl-TDI) was formed with only 5% selectivity. The yield of 1Cl-TDI was enhanced by increasing the residence time from 24% after 5 s to 54% after 14 s. At the same time the formation of consecutive products increased and the selectivity to 1Cl-TDI decreased to 67% after 14 s residence time. The influence of the reactor material was shown. In presence of a Lewis acid such as FeCl3, formed by chlorination using a reaction plate made of iron, consecutive products were formed and the selectivity to 1Cl-TDI was lowered. The microstructured reactor led to remarkably higher selectivities than the conventional batch reactor, where the selectivity to 1Cl-TDI was only 45% at 65% TDI conversion and the side product 5Cl-TDI was formed with 50% selectivity. The space-time yield of 1Cl-TDI achieved in the microstructured reactor (400 mol l?1 h?1) clearly exceeded the performance of the batch reactor (space-time yield 1.3 mol l?1 h?1). Based on the microreactor data, a kinetic model for the TDI chlorination including by-product formation was suggested and used to predict product selectivity at full TDI conversion.

Process intensification in green synthesis

“…A higher selectivity for the formation of monofl uorinated toluene and space-time yields in a falling-fi lm microreactor is reported when compared to the conventional bubble column (Figure 12 ). Ehrich et al [78] used the falling-fi lm microreactor for the photochlorination of toluene-2,4-diisocyanate using both a nickel and an iron reaction plate. They compared the performance of the falling-fi lm reactor performance with the conventional batch reactor ( Figure 13 ).…”

Chemie in Mikrostrukturreaktoren

“…[196] Löwe et al entwickelten einen Mikrostrukturreaktor für elektrochemische organische Synthesen (Abbildung 21). [197] Schema [194] Schema 25. Die Reaktion von a-Terpinen mit Singulettsauerstoff ergibt Ascaridol.…”

Microstructured Reactors for Multiphase Reactions: State of the Art

“…Wehle et al 83 studied chlorination of acetic acid by chlorine in a MSR at a temperature over 140°C, and the byproduct (dichloroacetic acid) was reduced significantly meaning that there is no need for a costly and time-consuming separation process. Further, Ehrich et al 84 demonstrated photochemical gas-liquid reaction by the selective photochlorination of toluene-2,4-diisocyanate. The space-time yield of 1Cl-TDI, formed by side chain chlorination of TDI, achieved in the MSR significantly exceeded the one of the batch reactor.…”