Rate-based distillation (Maxwell-Stefan, ChemSep-style)

A depentanizer split (n-pentane overhead from an n-pentane/n-hexane/n-heptane feed) solved with a rigorous rate-based (nonequilibrium) stage model rather than the usual equilibrium-stage assumption. Every stage carries separate bulk vapor and liquid compositions with a vapor-liquid interface in equilibrium and finite Maxwell-Stefan mass-transfer fluxes across each film, and the per-stage transfer coefficients come from the real Chan-Fair (1984) tray-efficiency correlations off estimated tray geometry -- the exact physics ChemSep and Aspen RateSep are built on. The result: real trays lag equilibrium, so the finite-transfer distillate is measurably less pure (~98.7% C5) than an equilibrium-stage model predicts (~99.8%) on the identical column -- roughly 5x more hexane slips overhead. Open the equivalent equilibrium column ('ethanol-water-distillation' or any 'distillation' node) to see the gap the equilibrium-stage assumption hides. As the mass-transfer coefficients grow the model collapses back onto the equilibrium column (the built-in validation limit).