Photochemical flow reactor

A stereoselective Wolff rearrangement of a-diazo-A-methoxy-A-methyl-p-ketoamides (formed from enantiopure aminoacids) leads to enantiopure (k lactams (see Scheme 5). The reaction is conveniently carried out in a continuous-flow photochemical reactor made from inexpensive laboratory equipment and is amenable to scale-up." ... 

Photocatalytic decomposition of benzene over Ti02 in gas-phase at room temperature was studied with a flow-type photochemical reactor similar to that show in Fig. 8.4, at room temperature. The main objective of the study described here was to evaluate the dependence of the product distribution on reaction conditions and to elucidate the role of 02 and H20 in the photoreaction. 

The same flow-type photochemical reactor as shown in Fig. 8.4 was used here, although the reaction time was lunger and the reaction temperature was from 298-353 K. As shown in Fig. 8.17, MC was transformed to dichloroethene (CH2CC12) on Ti02 in the dark and under dry conditions. The MC consumption increased with the reaction temperature. The ratio of MC consumed to CH2CC12 produced was close to unity, indicating that the elimination of HC1 from MC predominantly occurred in this temperature range. 

Figure 3 shows a schematic view of a flow reactor. It is similar to the photochemical reactor previously described in [5] but the UV photolysis cell has been replaced by a 1 m. stainless steel coil in a heated oil bath. As before, FTIR is used to monitor the conversion and optimise the conversion of reactant to product. Using such a system (C5Me5)Mn(CO)2(C2H4) can be obtained in a high yield as in Scheme 1. We are now scaling up this miniature reactor to a technical scale, ultimately with the aim of carrying out solvent-free reactions on a kilogramme scale.

Many commercial photochemical reactor systems make use of the batch recirculation mode for the treatment of highly contaminated wastewaters of limited volume. On the other hand, cascades of photoreactor modules (in serial or parallel mode) allow the gradual treatment of contaminated water streams with a very high photon flow Op in total. Hence, there exist powerful photochemical waste-... 

Water flow must be very fast to avoid freezing, which could result in breakage of the photochemical reactor and generation of a hazardous situation. Water flow should be monitored continuously during the course of the reaction. 

The photochemically-initiated polymerization of vinyl fluoride has also been carried out in a continuous-flow, cylindrical reactor at pressures up to 30 atm (30 Pa). The polymers produced by this method had a higher proportion of a head-to-tail arrangement than commercial polymer [21]. 

Booker-Milburn and co-workers also explored a number of photochemical rearrangements utilizing their wrapped photochemical reactor. One example is the rearrangement of electron-deficient pyrroles to form tricyclic aziridines (Scheme 7C). In batch the reaction afforded a 34% yield of the desired product after one hour. In flow they observed only a slight acceleration with 51% of the desired product after one hour. While the overall acceleration of the reaction was low, the reaction throughput was markedly higher in the flow reactor, affording 21.9 g per day (83 mmol) compared to 0.1 g (0.029 mmol) per day in batch. 

Another example of the OBRs use with solid particles is as a photochemical reactor with solids suspension, in this case the vortical flow patterns being used to suspend catalytic titania particles to convert organics in wastewater. The tita-nia needs to be activated by ultraviolet, and the reaction requires the presence of oxygen, so air is bubbled through. The gas-liquid mass transfer is enhanced by the oscillation of the fluid, as it increases hold-up time (bubble residence time) and reduces bubble size (increasing surface area and further increasing hold-up time). The flow patterns simultaneously ensure good exposure of the titania particles to the radiation from an axially located ultraviolet lamp. 

The photochemically initiated polymerization and copolymerization of VF were also carried out in a continuous flow cylindrical reactor at room temperature and under pressures of up to 30x10 Pa in order to achieve higher yields and to control the polymerization conditions [483]. From F-NMR analysis it turned out that the homopolymers prepared with the help of UV light were of higher regularity and contained less head-to-head addition than commercial PVF prepared at high temperatures. 

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