About the Fractional Distillation Calculator

Fractional distillation separates a liquid mixture by exploiting differences in boiling point. Vapor rising through a column condenses and re-evaporates at each plate, each cycle enriching the vapor in the more volatile component. The relative volatility α quantifies how easily two components separate — it grows exponentially with the boiling-point gap, which is why a 22 °C difference (ethanol/water, α ≈ 2.2) needs a tall column while a 44 °C difference separates easily.

The Fenske equation

For a target distillate purity of 95% and bottoms of 5%, the minimum number of theoretical plates is N_min = ln(361) / ln(α) ≈ 5.89 / ln(α). Real columns run at 1.5–2× the minimum because each plate only achieves a fraction of ideal equilibrium. This calculator applies that standard shortcut to give a quick feasibility read on any two-component mixture from just its boiling points.