Residence time unit

The microreactor system used was the commercial CYTOS College System [18]. The reactor is made of stainless steel, has 100 ptm channels and 2 ml volume. It has two inlets operated by two piston pumps. An additional 45 ml residence time unit (RTU) is coimected to the system after the reactor itself to increase the reaction time. The parts of the device are comiected by polytetrafluoroethylene (PTFE) tubings. 

CPC developed a series of table-top micro reaction systems called CYTOS (Figure 4.22), SEQUOS and OPTIMOS based on a standardized platform. CYTOS is the basic laboratory system with internal and external modularity for high flexibility by running different chemical reactions. The internal modularity offers the realization of variable reaction times up to 45 min by using several residence time units. The external modularity provides a system configuration for a multi-step synthesis. CPC Systems individual connecting principle minimizes the dead volume in the system and provides the reaction with isothermal conditions through the whole system [74, 75]. 

Because of the expected better workup and disposal procedures, nitration in acetic acid was tried first. Stock solutions of4-(phenyl)morpholin-3-one in glacial acetic acid (2 m) and nitric acid (65%) in concentrated sulfuric acid (4.8 m) were used. For the reaction optimization, two disposable polypropylene syringes (3 mL capacity) were hlled with the different stock solutions and mounted on a syringe pump. The syringes were connected with the silicon micromixer that was connected with a residence time unit, a Teflon tube of known inner diameter and length. The flow of the syringe pump was adjusted according to the residence time required, the only variable. For simplicity, nitrations were carried out at room temperature. 

For chemical reactions, micromixers are mounted in front of a residence time unit that provides the required residence time for the reaction to complete. The choice of the micromixer to be used depends on the characteristic reaction time. 

Another successful application of [BMIMJIPFe] ionic liquid supported catalytic microflow reactions for Pd-catalyzed carbonylative Sonogasnira coupling of aryl iodides and phenylacetylene was reported by Rahman et al. (2006). Ionic liquid containing Pd catalysts, CO and the substrates were mixed successively, in different micromixers (channel diameter = 1 and 0.40 mm), and then pumped as a multiphase (ionic liquid-substrate-CO) into heated capillary tube reactor acting as a residence time unit (V=14.1 mL). It was found that Pd-catalyzed production of solely the acetylenic ketones in ionic liquids, when conducted in conjunction with a microreactor, preceded efficiently with superior selectivity and higher yields compared to the conventional batch system, even at low CO pressures. Authors suggested that this improvement in selectivity and yield was the result of a large interfacial... 

An example of a microflow continuous palladium-catalyzed Mizoroki-Heck coupling between iodobenzene with butyl acrylate, in combination with continuous microextraction/ catalyst recyclation was reported by Liu and coworkers (Liu et al., 2004). Their reaction was catalyzed by a [Pd(PPh3)Cl2(BMIM)] carbene complex, which was immobilized in the low-viscosity ionic liquid l-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][(CF3S02)2N]). Using automated microflow apparatus (Figure 7), iodobenzene, butyl acrylate, and tripropylamine were introduced from one inlet of the micromixer (channel width 0.1 mm, inner volume 2 mL), and the ionic liquid containing the Pd catalyst was introduced from the other inlet. Two solutions were mixed in the microreactor and were pnimped into the temperature controlled residence time unit. 

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