Influence of mixing on the performance of periodic chemical reactors

The interaction between imperfect mixing and cyclic operation is examined for several continuous polymerizations in stirred‐tank reactors. The reactor is represented by a mixed model involving two interconnected ideal stirred vessels. Cyclic fluctuations in the concentration of a chain transfer agent during Ziegler‐catalyzed olefin polymerization can yield molecular weight distributions significantly different from those of a conventional steady state reactor. This result is consistent with the available experimental data. It is especially interesting that the cyclic reactor effluent with a modified molecular weight distribution is of approximately time‐invariant composition when the period of cycling is on the order of the reactor holding time. Imperfect mixing has a lesser effect on cycled reactors for free‐radical and polycondensation polymerization than it has on cycled olefin polymerization reactors.