This contribution explores the influence of curved unstable distillation boundaries. on the performance of batch distillations in ternary mixtures and its incorporation into a conceptual modeling framework under the assumption of a batch rectifier with an infinite number of stages. First, the concept of preferred separation in batch distillation is presented. Calculation of "pitchfork" distillation boundaries is then determined using a robust predictor-corrector algorithm based on improved memory method with the purpose of estimating the maximum feasible distillate composition, in the preferred separation line: Four highly nonideal systems are studied. Finally, the model is extended to allow simulation of the operation at different reflux policies. Results of a complete simulation performed with the enhanced conceptual model are shown for the system octane/2-ethoxyethanol/ethylbenzene.