The nonlinear behavior of reactor-separator-recycle systems is studied. The dimensionless mole-balance equations are parameterized by the plant Damkohler number (Da) and the separation specifications. Reactant accumulation does not occur if Da > Da(cr). Da(cr) corresponds to a bifurcation point of the mole-balance equations and depends on separation performance. For one reactant recycle and high purity separation, Da(cr) = 1. When two reactants are recycled, multiple steady states are possible. In this case, Da(cr) depends also on the control structure. Close to Da(cr), control structures must change the reaction volume or temperature in order to reject effectively the disturbances.