Chaotic pH Oscillations in the Hydrogen Peroxide−Thiosulfate−Sulfite Flow System

Abstract

Detailed numerical studies and experiments have revealed that two types of limit cycle pH oscillations with very different frequencies, complex periodic behavior, and chaos are exhibited by a catalyst-free H2O2−S2O32-−SO32-−H+ aqueous reaction system in a continuous-flow stirred tank reactor at 20.0 °C. Chaos appears around pH 6 in the case of a small excess of H2O2 over the reducing agents in a narrow range of input concentrations and flow rates. The main features of the observed dynamical behavior have been reproduced by a simple chemical mechanism derived from an earlier proposed model of the Cu2+-catalyzed H2O2−S2O32- oscillatory reaction. Slow and reversible proton-assisted dehydration of HOS2O3- intermediate to S2O3 reactive species and its subsequent reaction with S2O32- to form S4O62- have been considered in addition to earlier proposed composite reactions.