pH-oscillations in the bromate–sulfite reaction in semibatch and in gel-fed batch reactors
The simplest bromate oxidation based pH-oscillator, the two component BrO 3 À -SO 3 2flow system was transformed to operate under semibatch and closed arrangements. The experimental preconditions of the pH-oscillations in semibatch configuration were predicted by model calculations. Using this information as guideline large amplitude (DpH$3), long lasting (11-24 h) pH-oscillations accompanied with only a 20% increase of the volume in the reactor were measured when a mixture of Na 2 SO 3 and H 2
... f Na 2 SO 3 and H 2 SO 4 was pumped into the solution of BrO 3 À with a very low rate. Batch-like pH-oscillations, similar in amplitude and period time appeared when the sulfite supply was substituted by its dissolution from a gel layer prepared previously in the reactor in presence of high concentration of Na 2 SO 3 . The dissolution vs time curve and the pH-oscillations in the semibatch and closed systems were successfully simulated. Due to the simplicity in composition and in experimental technique, the semibatch and batch-like BrO 3 À -SO 3 2-pH-oscillators may become superior to their CSTR (continuous flow stirred tank reactor) version in some present and future applications. V C 2015 AIP Publishing LLC. All pH-oscillators known so far have been discovered in continuous flow stirred tank reactor. There is an increasing interest in developing batch and semibatch pHoscillators, because in some suggested applications of the pH-oscillators, the use of flow reactor arrangement is not feasible. With our recently proposed method, we were successful with converting the bromate-sulfite-ferrocyanide and the bromateÀsulfite-manganese(II) two-substrate pHoscillators to function under both semibatch and closed conditions. In this work, we report on transforming the simplest bromate-based pH-oscillator, the bromateÀsulfite core system to the form that operates in closed and halfclosed versions. In the semibatch system, the high amplitude pH-oscillations can be maintained for 24 h. In the batch-like system, the number of oscillations is less but due to the high amplitude and long period time, this one may also be capable of inducing periodic changes not only in the fast chemical equilibria but in the much slower pHgoverned physical processes or properties as well, for example, in shrinking and swelling of hydrogels or in the permeability of a membrane. These responses may constitute the basis of some applications of pH-oscillators. The use of closed, even half-closed pH-oscillators instead of their flow equivalents would surely facilitate the fabrication of utilizable devices, such as molecular motor or pulsating drug delivery system.