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 BrO3(-)-SO3(2-) flow 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 (ΔpH∼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 Na2SO3 and H2SO4 was pumped into the solution of BrO3(-) 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 Na2SO3. 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 BrO3(-)-SO3(2-) pH-oscillators may become superior to their CSTR (continuous flow stirred tank reactor) version in some present and future applications.