Multiple steady states in binary distillation—Theoretical and experimental results

Abstract

Steady-state multiplicity and instability in distillation is studied theoretically and experimentally for columns with volumetric reflux. Using nonlinear wave propagation theory for distillation processes, we derive simple expressions for the prediction of multiplicity regions in parameter space with paper and pencil. This method also gives further insight into qualitative column dynamics in the region of multiple steady states. The results are illustrated for ideal binary mixtures and further conclusions are drawn for nonideal binary mixtures and ideal or nonideal multicomponent mixtures. With regard to experimental work, a rigorous, numerical bifurcation analysis of more detailed models is presented for the separation of methanol-1-propanol. The interaction between the boundary set of feasible operation and the bifurcation set is shown to be of great importance for the understanding of multiplicity and stability features for this type of column configuration. Finally, these multiple steady states are confirmed experimentally.