A saturated liquid feed of 500 kmol/h consists of 10 mol% propane, 35 mol% n-butane and 55 mol% n-hexane. A distillate recovery of 99.5 mol% n-butane and bottoms recovery of

97.5 mol% n-hexane is desired. \text { The average relative volatility is } \alpha_{\text {propane-butane }}=2.04 ; \alpha_{\text {butane }-\text { butanc }}=1.00 ; \text { and } \alpha_{\text {hexane }-\text { butane }}=0.2 constant molar overflow (CMO) is valid. Reflux is returned as a saturated liquid. Thelumn has a partial reboiler and a total condenser. Using the Fenske equation, determine the number of staĝes required at total reflux (Nmin)-