ir is used to remove butane from a heavy hydrocarbon oil in a countercurrent tower at $1$ bar and $300$ K$.$

The air flows at $50$ mol$/$hr and contains $1$ mol$\%$ butane. The oil stream is $100$ mol$/$hr and contains $40$ mol$\%$

butane. The vapor pressure of butane can be approximated using this equation: Psat $=0\mathrm{.}105$ T $29$; Psat

in bar, T in Kelvin. For the purpose of this problem, ignore the possibility of the oil boiling or the air

condensing. You may assume ideal gas and ideal solution.

a$)$ Determine the number of equilibrium stages required to remove $90\%$ of the feed butane from the oil.

b$)$ Suppose we use the same flow rates and the same inlet compositions, but we allow the use of a

different column and a different temperature. Determine the range of temperature that will still allow

$90\%$ recovery of butane.AA