Continuous microflow processing

S. Liu, T. Fukuyama, M. Sato, I. Ryu, Continuous microflow synthesis of butyl cinnamate by a Mizoroki—Heck reaction using a low-viscosity ionic liquid as the recycling reaction medium, Org. Process Res. Dev. 2004, 8, 477- 81. 

Because liquid-liquid nitration reactions are described in another chapter [15-19], this section deals with nitration reactions involving the gas phase. The nitration of naphthalene using N2O5 in both the gas phase (in situ production from N2O4 and O3) and the liquid phase has been carried out in microflow reactors under continuous flow conditions at 30 C (Scheme 8.10) [20,21]. The residence time is 3 s. The same reactions in conventional macrobatch operation require temperatures from —50 to —20°C to avoid undesired side-reactions. The isomer ratio of the dinitration products (C D) in a macrobatch process (1 3.6) is different from that for the microflow process (1 2.8). The isomer ratio of mononitration products (A B) can also be changed it is 20 1 for the macrobatch process and 32 1 for the microflow process. 

More recently, Lowe and coworkers reported a detailed study on the addition of secondary amines to ethyl acrylate and acrylonitrile using a continuous microreaction process based on an IMM micromixer and tabular reactor [16]. In the best case, space-time yields (g/ml h) for the microflow system were much higher than those for the batch system, by a factor of 650. 

In a detailed process optimization study, the impact of the type of micromixers and process parameters was determined [56]. As a result, a pilot with a Toray Hi-mixer connected to a shell and tube microheat exchanger was constructed. Continuous operation for 24 h was carried out to obtain pentafluorobenzene (PFB) after protonation (92% yield). In this time, 14.7 kg of the product was produced, that is, about 5 t/a. Thus, the industrial-scale production carried out using a batch reactor (10 m3) can be replaced by adding only four microflow systems of the scale investigated. The pilot plant produces 0.5 kg in 6h continuous operation, thus about 730kg/a (see Figure 5.19). The name of the industrial company was not disclosed. 

J. (2006) Radical polymerization using microflow system numbering-up of microreactois and continuous operation. Org. Process Res. Dev., 10 (6), 1126-1131. 

The [2 + 2] qrcloaddition reaction of maleimide and 1-hexyne in a photochemical microflow reactor has also been reported. The development of flow reactors for continuous processes can allow large-scale reactions [18]. This reaction can be achieved with 83% conversion on a large scale (0.7 kg) (Scheme 5.8). 

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