Two kinds of different mechanistic oscillations can be displayed in the H_2O_2-KSCN-CuSO_4-NaOH system. One discovered by this study is the pH oscillation in a continuous flow stirred tank reactor(CSTR) resulting from the oxidation of KSCN. The other is the oscillation of H_2O_2 decomposition in both CSTR and batch reactors(reported by Orbáin in 1986). Under appropriate experimental conditions, the system exhibits a birhythmicity in a CSTR. Two different pH oscillations are reported here. The pH oscillations which accompany the decomposition of H_2O_2 exist in the batch reactor and the CSTR at a high flowrate, but the pH oscillations in a CSTR at a low flowrate originates from proton positive and negative feedback in the oxidation of KSCN. The oscillation of non-catalyzed oxidation of KSCN by hydrogen peroxide in a CSTR can be found. Also we have observed whether Cu^(2+) exists or not in the batch system, the pH increases to near neutral ultimately after pH drops twice.
GAO Qing-yu, SUN Kang and MENG Fan-yong (College of Chemical Engineering, China University of Mining and Technology, Xuzhou 221008, P. R. China) CAI Zun-sheng and ZHAO Xue-zhuang (Department of Chemistry, Nankai University, Tianjin 300071, P. R. China) To whom correspondence should be addressed.
The reaction between chlorite and thiourea could display batch oligooscillation and CSTR oscillation of pH.Batch pH peak has the same character with pH oscillation in a CSTR.The oxidation of thiourea produced intermediates such as HOSC(NH)NH2,HO2SC(NH)NH2,HO3S(NH)NH2 and bisulfite.The valence change of sulfur has close relation with pH dynamics.Through the mechanistic analysis,a general model of sulfur(－ II) oxidation,which consists of negative hydrogen ion feedback(S(－ II) to S(0)),a transition process of S(0) to S(IV) and positive proton feedback from S(IV) to S(VI),could simulate batch oligooscillation and CSTR oscillation.This result is setting up a new channel to uncover the reaction mechanism and simulate the nonlinear phenomena in the reactions between chlorite and Sulfur(－ II).
A new method of controlling chemical chaos to attain the stabilized unstable periodic orbit (UPO) is proposed. It is an extension of the occasional proportional feedback (OPF) control strategy which spans the limitations of OPF, i.e. the linear region of the control rule, and extends to the whole chaotic region. It also expresses the nonlinear control rule with the back propogation-artificial neural network (BP-ANN) in order to increase the robustness of the control. Its effectiveness is examined through controlling an autocatalytic chaotic reaction model numerically.
