Application of feedback-induced bifurcation for evaluating steady-state and transient heterogeneous catalysis kinetic models
✍ Scribed by Michael R. Prairie; James E. Bailey
- Publisher
- Elsevier Science
- Year
- 1986
- Tongue
- English
- Weight
- 849 KB
- Volume
- 41
- Category
- Article
- ISSN
- 0009-2509
No coin nor oath required. For personal study only.
✦ Synopsis
Experimental study of bifurcations to steady-state multiplicity and oscillatory dynamics provides a systematic and sensitive data base for evaluating kinetic models. Previously limited to exotic reaction systems which exhibit such behavior naturally. bifurcations can be induced in tame systems using an external feedback loop to manipulate reaction conditions. This strategy has been applied to ethylene hydrogenation over Pt/AlsOs in a catalytic CSTR by manipulating the ethylene and hydrogen feed rates as functions of the ethylene concentration in the reactor effluent. Pitchfork bifurcations to steadystate multiplicity have been experimentally observed for 9.5% Pt/AlsOs (30 OC. latm) as functions of ethylene feedback gain. given several different hydrogen gains. The data demonstrate the general result that small discrepencies between the actual and the chosen reference steady state give rise to imperfect, cusp-like bifurcations. These phenomena are well described by a kinetic model proposed by Mullins and Saltsburg. Steady-state rate data were used to And two parameter sets for the model; however, only one of these sets adequately approximates the bifurcation data. Examples of Hopf bifurcation to limit cycles are also presented and compared with results for Hopf bifurcation on 0.05% Pt/ Alsos. Hopf and step-response transient experiments for the 0.5% Pt/AlsOs catalyst are well described by the model containing only two surface time constants while three or more are required for the low-loaded catalyst.
Hydrogen spillover is suggested as the source of this difference.