Theoretical study of steady state multiplicity and stability in gas-liquid continuous stirred tank reactors



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This work investigates the multiplicity of steady states for exothermic, gas-liquid reactions carried out in a continuous stirred tank reactor (CSTR). Several approximating techniques based on film theory are employed in computing the enhancement of the physical mass transfer rate due to the chemical reactions. Single and consecutive reaction schemes in which the reactions are second-order and irreversible are investigated to analyze the effects of various physical and chemical parameters on the steady-state operation of the CSTR. The model predicts that under certain conditions multiple steady state solutions exist. The steady state multiplicity may be sensitive to the value of some physical and chemical parameters. Simulation studies of the chlorination of n-decane were performed to demonstrate the utility of the model. The steady-state temperature, conversion, and selectivity predicted by this model were in good agreement with experimental results obtained during the chlorination of n-decane. A rather simple transient model was developed for examining the stability of steady states. It was found that the analysis of van Heerden was sufficient in determining the criterion of stability, since the model involved several pseudo steady-state assumptions. In addition the model was used to investigate the effect of controlled-cyclic operation on the yield of the intermediate product. The numerical results show that a slight improvement in the yield is obtained by cycling around a naturally unstable steady state.