Gradient-free recycle reactors

Figure 4.15. Differential reactors concentration profiles for a differential reactor and for a gradient-free (recycle) reactor.

CA, the conversion per cycle CAc approaches zero if the recycle ratio Rr is increased more and more. Thus, at sufficiently high recycle flow rates, the concentration and temperature gradients along the catalyst bed can be kept small in the same way as in the differential reactor. The overall conversion in the reactor can be set at any desirable, easily measurable level by regulating the net flow rate < . A further benefit of high recycle flow rates lies in the fact that, due to the high fluid velocities past the catalyst particles, any possible interface transport effects can be eliminated. The recycle reactors, therefore, are called gradient-free reactors. 

The conversion per reaction cycle is a differential amount, but it is at the high level of conversion typical of an integral reactor. The loop reactor is therefore referred to as a pseudo-differential reactor or gradient-free reactor. The identity indicated in Equ. 4.16 can be more easily recognized when the two parts that result from the mass equivalence of a recycling reactor (left side) and set equal to that of an ideal stirred vessel (right side), and the resulting equation is then solved for ... 

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