A column with a partial reboiler and a total condenser is distilling hydrocarbons at 7.0 bar. The saturated liquid feed is \(25.0 \mathrm{~mol} \%\) ethane, 35.0 \(\mathrm{mol} \% \mathrm{n}\)-butane, and \(40.0 \mathrm{~mol} \% \mathrm{n}\)-pentane, and \(\mathrm{F}=100.0 \mathrm{kmol} / \mathrm{h}\). Recover \(99.2 \%\) of the \(\mathrm{n}\)-butane in distillate and \(98.3 \%\) of the n-pentane in bottoms. Reflux is a saturated liquid and \(\mathrm{L}_{0} / \mathrm{D}=3.0\). Find the optimum feed stage and the total number of equilibrium contacts required. Assume CMO, and use DePriester charts or Eq. (2-28). Use of a spreadsheet to do dew-point calculations is highly recommended.

Equation 2-28

In K = a/T + a/T + a + a In p+ a2/p + : T2' T6 pl ap3/p