Limit Cycles in Homogeneous Azeotropic Distillation

In spite of significant nonlinearities even in the simplest model, the distillation literature generally takes for granted that distillation columns display relatively simple dynamic behavior. For example, although widely observed in chemical reactors, any instances of periodic oscillations have not yet been associated with models of distillation columns. In this paper we study the steady-state and dynamic behavior of the azeotropic distillation of the ternary homogeneous system methanol-methyl butyrate-toluene. Our simulations reveal nonlinear behavior not reported in earlier studies. Under certain conditions, the open-loop distillation system shows a sustained oscillation (limit cycle). The limit cycles are accompanied by traveling waves inside the column. Significant underdamped oscillations are also observed over a wide range of product rates. To our knowledge, this is the first simulation result reporting the presence of Hopf bifurcation points in open-loop distillation models.