The multiplicity patterns of olefin oxidation, catalyzed by a Pt wire controlled to maintain a preset average temperature, are traced by varying the reactant concentrations and are mapped in the concentration plane. The similar bifurcation maps of ethylene and propylene oxidations exhibit regions of tristability and isolated branches in the directions of olefin and oxygen concentrations.Isobutylene oxidation exhibits mushroom-shaped bistability. Several features indicate the occurrence of symmetry breaking to form a partially ignited wire. Comparison of these results with the characteristic bifurcation maps of inhomogeneous solutions, drawn in part 1 of this work, shows that these complex patterns are induced by coupling of reactant inhibition with strong exothermicity. This work also develops an efficient methodology for fast tracing of all the multiplicity features of reacting systems. Bifurcation diagrams are traced automatically with a microcomputer-governed experimental system, and the continuity of features in the second and third dimensions is studied off-line to decide on further experimentation.In the first part of this work (Sheintuch, 1989), we demonstrated that surprisingly complex multiplicity patterns can be induced by relatively simple kinetics in systems that attain stable inhomogeneous solutions. We reviewed previous observations of bistability in reactions catalyzed by an "isothermal" wire, i.e., controlled to maintain a preset (average) temperature, and showed that the patterns with counterclockwise hysteresis or with isolated branches can be accounted for by stationary thermal fronts in systems with simple kinetics or with reactant inhibition. The analysis was also extended to systems that show tristability in order to account for the observations reported in this part.This work presents a comparative study of multiplicity patterns and bifurcation maps in olefin oxidation on a Pt wire, using a thermochemic method. Regions of uniqueness, bistability, and tristability are mapped in the oxygen versus olefin concentration plane at several temperatures.
A method is presented for using an adiabatic reactor to study the kinetics of reactions of gases on solid catalysts. The method is based on measurement of the steady state axial profile of temperature or composition in a specially designed adiabatic packed bed reactor. Reaction rates are calculated from these measured profiles by graphical differentiation. The method is applicable for multireaction systems and for any type of kinetic behavior.
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