This article considers high-purity distillation columns with large recycle (and thus internal) flow rates. A singular perturbation analysis is employed to document a well-known observation for such columns, namely, the existence of fast and slow dynamics associated with internal and external flows, respectively. A nonlinear low-order model of the slow column dynamics, suitable for analysis and nonlinear feedback controller synthesis, is also derived. A two-tiered controller design procedure, which incorporates such a nonlinear controller, is finally proposed, and its performance and robustness characteristics are evaluated through simulations.