Residence-time distributions summary

A consequent dimensional-analytical treatment of the homogenization process, residence time distribution and heat transfer behavior in single-screw machines was performed by Pawlowski and was published in a sequence of scientific papers. A summary of this work is printed as a monograph [65],... 

A summary of the possible limiting combinations of macro- and micromixing, and the result in terms of a residence-time distribution result for the step-function experiment that we have described, is given in Figure 4.5. 

In summary, the sizing of the reactors should be based on the rate of polymerization data from pilot-scale investigations or (preferably) previous plant experience, while the choice of reactor type should be made based on kinetic as well as economic considerations. The effect of the CSTR residence time distribution on each of the three common types of polymerization kinetics will now be discussed. 

In summary, since the lifetime of a growing polymer chain is equal to its residence time in the reactor, the effect of the residence time distribution causes extreme broadening of the molecular weight distribution during step-growth polymerization in a CSTR. The constancy of the polymerization environment, which acted to narrow the distribution in free radical polymerization, has an insignificant effect in step-growth polymerization. 

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. 

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