Belousow-Zhabotinski Reaction in a Closed Reactor

One of the most interesting results of the thermod5mamics of irreversible processes (thermod5mamics far from equilibrium) is the realization that reaction systems in open or closed reactors tmder special premises are able to oscillate. One of the early discovered, popular and intensively investigated reactions is the Belousow-Zhabotinski reaction. The overall process is the oxidation of malonic acid by means of bromate in sulphuric aqueous solution in the presence of the catalyst cerium  

During the discontinuous conversion in a closed reactor under conditions of oscillation, the reactants and the products do not perform damped oscillations, but the catalyst alternates in the time after an inducing and a finishing phase of the overall reaction rhythmically between two degrees of oxidation via certain intermediate reactions. Detailed detective work revealed that all in aU 20 intermediate reactions run [12]. 

The course of conversion has already been photometrically, polarographically and barometrically recorded. The polarographic measurement, almost free of inertia, has revealed a sawtooth-shaped oscillation. Calorimetric investigation has been carried out until now only in micro calorimeters by differential thermal analysis DTA (non-isothermal) and by differential-scanning-calorimetry DSC (quasi-isothermal). The calorimetric inertia of the control systems is too large to enable the system to record correctly sawtooth-shaped oscillations, i.e. relatively abmpt changes in reaction power. The characteristic course can only be distortedly recorded. 

The author has therefore tried to measure the thermal reaction power as well as the change in pressure due to CO2 produced in the bench scale calorimeter TKR under virtually isothermal conditions. The level of the pH-value, prerequisite for the start of oscillations, is produced by an injection of strong concentrated sulphuric acid into the batch, which is already brought to the set temperature of the reaction. The unavoidable stroke of heat due to the abruptly released large amount of heat of dilution cannot be compensated completely, even despite having pre-chilled sulphuric acid and electric heating power p2 temporarily reduced to zero (Fig. 5.15). The result is a large jump in temperature within the reaction mixture, so that the set temperature respectively the equilibrium of control is achieved relatively late. 

During this time the induction phase of the oscillation has already finished, i.e. the oscillation is already started. 

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Fig. 5.15 Temporal course of thermal reaction power of Belousow-Zhabotinski reaction in a closed reactor under virtually isothermal conditions...

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