Systematic design of chemical oscillators. 63. Large amplitude pH oscillation in the oxidation of hydroxylamine by iodate in a continuous-flow stirred tank reactor

Abstract

Large amplitude pH oscillation occurs in the iodate oxidation of hydroxylamine in a continuous-flow stirred tank reactor (CSTR) in a narrow range of flow rates and input concentrations. In addition to pH, the redox potential, the iodide ion concentration, the rate of gas (N20) formation, and the color of the solution (1,) change periodically. The oscillatory period is extremely long, 2-6 h. The dynamical behavior of the reaction was modeled by a scheme that takes into account the following component processes: the protonation equilibrium of NHzOH, the dissociation of water, the direct redox reaction between IO3and NH30H+, the Dushman reaction between IO; and I-, the autoinhibitory reaction between I2 and NH30H+, the fast dimerization of NOH to N20, the reaction of NOH with NH,OH, and the volatility of iodine. Empirical rate laws of the component reactions were used successfully to calculate the kinetic behavior in a closed system, as well as in the CSTR.