Problem

A Benzene$-$Toluene mixture containing $42$mol$\%$ Benzene is to be separated in multiple steps. In the first step a distillation column with a reboiler and a partial condenser is to be used to separate the flow into one holding $70$mol$\%$ Benzene and another holding $10$ mol$\%$ Benzene.

a$)$ How many physical trays are needed in the column if the feed consist of $75\%$ saturated vapour and $25\%$ saturated liquid, the reflux ratio is $1\mathrm{.}5$ and the overall tray efficiency $40\%?(7$ p$)$

b$)$ What is the minimum reflux ratio?

Hint:

Draw upper operating line

Draw the $q-$ line $($or feed line$).$ Locate the operating point.

Draw the operating line for the stripping line.

Draw the steps and number them.

Locate the optimal feed stage $($or feed location$).$