Temperature Oscillations, Complex Oscillations, and Elimination of Extraordinary Temperature Sensitivity in the Iodate-Sulfite-Thiosulfate Flow System

Temperature oscillations and complex pH oscillations in the IO3--SO32--S2O32- system were observed in a continuously flow stirred tank reactor. During one period of oscillation, the temperature increases rapidly while the pH shows an extremely sharp change. High-amplitude pH oscillations undergo 1(1) complex oscillations (L-S oscillations with L large peaks and S small peaks per period) to another kind of higher-amplitude regular oscillations upon increasing the concentration of sulfite step by step. Importantly, the longstanding experimental phenomena, the extraordinary temperature sensitivity of oscillatory behavior reported 20 years ago by Rabai and Beck, can be eliminated by premixing of sulfite and sulfuric acid before entering into the reactor, avoiding local acidification, which brings out fluctuation and temperature sensitivity. The temperature oscillations can be understood by taking into account the interaction between thermal effect of various reactions and heat transfer. Experimental observations, both temperature oscillations and 1(1)-type pH oscillations, are reproduced with a four-step Horvath model by addition of an energy-balance equation. This new detailed dynamical behavior would have potential applications in designing complex chemical waves and pH responsive gels with rhythmical motion.