Oxidation of ascorbic acid by air oxygen catalyzed by copper(II) ions in batch and continuous flow stirred tank reactors: bistability, oscillations and stochastic resonance

We report various nonlinear phenomena observed in the oxidation of ascorbic acid (H(2)Asc) by molecular oxygen in the presence of copper(II) ions in a continuous flow stirred tank reactor (CSTR) as well as in a batch reactor (closed system). Transient irregular oscillations were observed in a batch reactor by varying the initial concentrations of H(2)Asc and copper(II) ion s. The behavior of the system in a CSTR was studied by varying the flow rat e (k(f)) and the inflow concentrations of H(2)Asc and copper(II) ions. At l ow inflow concentrations of copper(II) ions the system exhibits bistability and small amplitude regular oscillations. In a two-dimensional parametric plot with coordinates k(f) and [Cu2+](0) the regions of bistability and osc illations form a cross-shaped diagram if the inflow concentration of H(2)As c is kept constant. For increasing values of k(f) oscillations emerge via a Hopf bifurcation and disappear due to a homoclinic orbit. Simultaneously a pplied small amplitude periodic and stochastic perturbations imposed onto t he flow rate close to the bistable region revealed the phenomenon of stocha stic resonance, which is confirmed by an analysis of probability distributi on functions, power spectra, and singular value decomposition.