Perfectly mixed flow reactors polymerization

Polymerization in Perfectly Mixed Flow Reactors Stability of Operation and Transient Behavior... 

Performing polymerization reactions in perfectly mixed flow reactors leads to quite different results from those obtained in batch or plug flow reactors, as discussed in 1951 already by Denbigh [1951]. The key point concerns the relative lifetimes of the active propagating polymer species. If this is long relative to the mean holding time of the fluid in the reactor, the rules in Section... 

Polymerization reactions require stringent operating conditions for continuous production of quality resins. In this paper the chain-growth polymerization of styrene initiated with n-butyllithium in the presence of a solvent is described. A perfectly mixed isothermal, constant volume reactor is employed. Coupled kinetic relationships descriptive of the initiator, monomer, polystyryl anion and polymer mass concentration are simulated. Trommsdorff effects (1) are incorporated. Controlled variables include number average molecular weight and production rate of total polymer. Manipulated variables are flow rate, input monomer concentration, and input initiator concentration. The... 

Depending upon the particular polymer system, a CSTR or a series of CSTRs may offer several advantages over batch and tubular flow reactors both with respect to polymer production rate and polymer quality. With a perfectly mixed CSTR it is often possible to achieve a molecular weight distribution considerably narrower than can be obtained with a batch (or tubular) reactor with the same holdup time. This is true with any polymerization where molecular weights are controlled by termination. By running CSTRs in series or in parallel it is possible to produce tailor-made polymers with a broader MWD simply by operating each CSTR at a different temperature and/or with different residence times. Another feature of CSTRs is that the CCD can be very narrow in comparison with batch (or tubular) reactors, where the CCD is broadened due to the drift in monomer composition. 

The commercially used emulsion polymerization reactors (stirred-tank and continuous-loop) are designed to achieve perfect mixing. As will be discussed in Section 6.4.5, perfect mixing is not always achieved. Nevertheless, this flow model allows a good prediction of the emulsion polymerization reactor performance with a moderate mathematical effort, and it will be used here. Macroscopic balances (i.e., considering the reactor as a whole) are used. For the sake of generality, inlet and outlet streams are included in the balances. Both terms should be removed for batch operation, the outlet term should be eliminated in semibatch and both maintained in continuous processes. 

There are several product quality reasons for favoring flow reactors. If the life of a growing chain is small, as in free-radical polymerizations, a perfectly mixed CSTR will give the lowest polydispersity and the narrowest composition distribution for copolymers. Heat and mass transfer are best accomplished in flow systems. Thus the continuous mode is preferred for vinyl addition polymers where there is a large exotherm. It is also preferred for condensation polymers where the by-product must be removed to overcome an equilibrium limitation and for situations in general where a small molecule, typically solvent or unreacted monomer, must be removed as part of a clean-up operation. 

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