Residence time control

Hquid residence time control scrap iaput no no Material input yes yes yes... 

Continuous-flow reactors with residence time control for larger-scale preparation. 

During the pyrolysis process, the final conversion mainly depends on three phenomena the heat transfer from the reactor to the feedstock, the feedstock movement in the reactor and the kinetics of pyrolysis reactions. The heat transfer rate determines the rate of temperature increase of the feedstock. The feedstock movement behaviour determines the residence time of the feedstock particles in the reactor. In turn the heating rate and the residence time control the quantity of energy transferred and thus the ten Jerature distribution throughout the feedstock in the reactor. Once the tenqserature distribution is known, the kinetic behaviour of the feedstock determines the final conversion at the reactor outlet. 

In the following sections, we will focus on o-bromophenyllithium (Figure 6.22) as an example of a highly reactive, unstable intermediate, and on the control of its generation and reactions based on residence time control. 

As demonstrated in this chapter, a number of microfluidic devices of various structures and sizes for extremely fast mixing, heat exchanging and residence time control have been developed based on conventional and modern fabrication technologies. Microflow systems composed of such microfluidic devices are expected to serve as powerful tools for conducting extremely fast, highly exothermic reactions in a highly controlled manner to effect flash chemistry, where desired products are formed within milliseconds to seconds. 

As shown in Figure 8.13, the reaction of an acid fluoride and an amine, which are derived from the corresponding amino acids, in the presence of N-methylmorpholine has been carried out at several temperatures. The reaction was complete in 3 min at 90 °C, and the yield of the dipeptide was excellent. Reaction at higher temperatures and/or for a prolonged period leads to a decrease in the yield of the dipeptide and an increase in the yield of the tripeptide. Residence-time control in a microflow system is quite effective in reducing the amount of undesired tripeptide byproducts. Some other examples, which are combined with fluorous tag technology, " are shown in Scheme 8.12. In the first case, the reaction was complete in 3 min at 90 °C, whereas the corresponding conventional... 

The fact that the molecular weight increased linearly with the increase of monomer/initiator ratio, as shown in Figure 9.3, suggests that the chain-transfer reaction does not play a significant role in this system. Extremely fast mixing, effective temperature control, and residence time control by virtue of the microsystem seem to be responsible for the excellent molecular-weight distribution control. 

In summary, microflow systems are quite effective for molecular-weight distribution control of very fast, highly exothermic free-radical polymerizations. The superior heat transfer ability of the microflow system in comparison with conventional macrobatch systems seems to be responsible for the high molecular-weight distribution controllability. It should be noted that the controllability is much lower than is achieved by conventional living free-radical polymerization, because residence time control does not work for controlling radical intermediates. The lifetime of a radical intermediate is usually much shorter than the residence time in a microflow system. It is also noteworthy that the more rapid and exothermic the polymerization is, the more effective the microflow system is. These facts speak well for the potentiality of microflow systems in the control of highly exothermic free-radical polymerization without deceleration by reversible termination. 

The rotors may be one of several zero-clearance designs, a rigid fixed clearance type, or in the case of tapered rotors, an adjustable clearance construction type (Fig. 16). One vertical design includes an optional residence time control ring at the end of the thermal surface to hold back product and thus build up the film thickness. The majority of thin-film evaporators in operation are the vertical design with a cylindrical fixed-clearance rotor shown in Fig. 14. 

Widmer, F. and Giger, A., Residence Time Control in Thin-Film Evaporators, Chem. and Process Eng., London (Nov. 1970)... 

The mechanical system used for this evaluation consisted of several automated components feed control, reactants preparation, synchronized injected reactant pulses, reactor temperature and pressure and residence time control, on-line analytical, fraction collector for product sample collection, as well as programming for multi-system coordination. 

Microreactors have also been used for ionic polymerization or polycondensation processes. Nagaki et al. [136] have synthesized polystyrene-poly(alkyl methacrylate) block copolymers by butyllithium initiated anionic polymerization in an integrated flow microreactor system. A high level of control of molecular weight was achieved at temperatures between -28 and +24 °C due to fast mixing, fast heat transfer, and residence time control. Santos and Metzger... 

Vortex dryers can be configured vertically or horizontally (Figure 21.42). The vertical configuration is widely known as a convex dryer. The horizontal vortex dryers are less popular, but they can easily be used in a multistage arrangement that allows for extended residence times, controlled temperature regimes, and intermittent operation, if necessary. 

Residence time control The length of time that the solution remains inside the reactor is called the residence time. In flow reactors, the residence time increases with the length of the channel and decreases with the flow speed. In flow microreactors, the residence time can be greatly reduced by shortening the length of the microchannels. This feature of flow microreactors is extremely... 

Nagaki A, Matsuo C, Kim S et al (2012) Lithiation of 1,2-dichloroethene in flow microreactors versatile synthesis of alkenes and alkynes by precise residence-time control. Angew Chem Int Ed 51 3245-3248... 

Compounding Extruders Davis-Standard Kombiplast Variations in screw design can control heat/shear history. Residence time control led by L/D. Twin screw types produce excellent blends/alloys. 

Three characteristic features of microreactors that have been found to be effective for the enhancement of chemical selectivity and yield are fast mixing, efficient heat exchange, and precise residence time control. However, it is rather difficult to completely separate the effects of these three factors on the outcome of chemical reactions. 

Fixed Clearance with Residence Time Control Ring... 

Under these conditions the drying process is so called residence time controlled . 

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