Bifurcation behavior of an exothermic CST

Previous research on the steady-state multiplicity behavior of exothermic continuous-flow stirred tank reactors (CSTRs) neglected the coolant temperature dynamics. However, we demonstrate in this thesis that this assumption is tantamount to assuming the presence of a stabilizing inner-loop cascade controller in the two-state CSTR model, since a three-state CSTR model incorporating cooling jacket dynamics may be open-loop unstable when the two-state model is stable. An analysis of the bifurcation behavior of exothermic CSTRs is presented in this thesis. The focus of this work is on the more pragmatic issue of characterizing operating regions with "undesirable" behavior in order to remove or minimize their occurrence. We show that output multiplicities can be removed in the two-state CSTR model by increasing the heat transfer coefficient or the area for heat transfer, yet one can not remove output multiplicities in the three-state CSTR model in this manner. The effect of process design and operation parameters on the steady-state multiplicity is studied. We demonstrate that infeasible reactor operation regions may occur when the CSTR is "scaled-up". The influence of more general kinetics, recirculating and lumped cooling jacket models, and a variable heat transfer coefficient on the bifurcation behavior is characterized. The steady-state bifurcation conditions are related to energy generated and energy removed rate curves. The steady-state multiplicity analysis is extended to study the behavior of a jacketed styrene polymerization CSTR. Conditions on the monomer, initiator, and solvent flowrate are developed to guarantee monotonic steady-state input-output behavior. A new cascade control system design procedure that incorporates the "inner-loop" controller in the "outer-loop" controller design procedure is developed. The bifurcation behavior of cascade controlled nonlinear systems is analyzed.