Continuous stirred tank reactor hysteresis

Fig. 23. Hysteresis in an irreversible exothermic reaction in a continuous stirred tank reactor.

Example 14. /. Multiple steady states and hysteresis in a nonisothermal continuous stirred-tank reactor (CSTR) [1,2]. In a CSTR, the curve for the temperature dependence of heat loss to the cooling coil is linear (loss proportional to temperature difference) while that for heat generation by the reaction is S-shaped (Arrhenius ex-... 

A major breakthrough with regard to the understanding of this phenomenon in the field of chemical reaction engineering was achieved by Ray and co-workers (Uppal et ai, 1974, 1976) when in one stroke they uncovered a large variety of possible bifurcation behaviours in non-adiabatic continuous stirred tank reactors. In addition to the usual hysteresis type bifurcation, Uppal et al. (1976) uncovered different types of bifurcation diagrams, the most important of which is the isola which is a closed curve disconnected from the rest of the continuum of steady states. 

When this reaction is run in an open system—a so-called continuous-flow stirred tank reactor, or CSTR (fig. 4.4), with continuous influx of reactants and outflow products and unreacted reactants—then for certain influx conditions the system may be in one of two stationary states far from equilibrium one of high I2 concentration, made visibly blue by addition of some starch, and one of low I2 concentration, a colorless solution. Measurements of bistability and chemical hysteresis in this system are shown in fig. 4.5. Bistable reaction systems have some similarities with bistable electronic switches, as pointed out some years ago by Roessler (see cited references in [1-3]). With bistable electronic switches it is possible to build an electronic computer, and now... 

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