Enhancement of production rates in a bistable chemical reaction

We present experiments and calculations which show that a dramatic enhancem ent of the production rate may be achieved by external periodic forcing of chemical reactions with threshold properties if the product yield of the re action decreases with an increase in the Bow rate through a continuous flow stirred tank reactor (CSTR) at constant temperature. Since the production rate (PR) is represented by the (mathematical) product of the flow rate and the reaction yield, the optimal PR enhancement is achieved at high flow ra tes with short but large periodic pulses to lower flow rates where the yiel d is high. Here we investigate a bistability as a threshold at constant tem perature in the Minimal-Bromate reaction and we reach experimental PR enhan cements of up to 31% over the maximum PR in the unperturbed system. NFT mod el calculations are in agreement with the high enhancements observed in the experiments. In contrast, only a small PR enhancement(less than or similar to l%) is encountered for a first order thermokinetic reaction in which an existing bistability or subcritical Hopf bifurcation is crossed by an exte rnal periodic flow perturbation. Here the nonlinearity resides in the expon ential Arrhenius dependence of the rate constant on temperature. As a conse quence, narrow PR pulses occur which lead to only small enhancements in the averaged production rate. This is demonstrated by employing the Sal'nikov model with CSTR boundary conditions.