A distillation column with \(6.0 \mathrm{ft}\) of packing can be operated as a stripper with liquid feed, as an enricher with vapor feed, or at total reflux. We are separating methanol from isopropanol at \(101.3 \mathrm{kPa}\). Equilibrium can be represented by constant relative volatility, \(\alpha=2.26\).

a. At total reflux vapor mole fraction methanol entering column \(\mathrm{y}_{\text {in }}=\) 0.650 , and vapor mole fraction methanol leaving \(\mathrm{y}_{\text {out }}=0.956\). Determine \(\mathrm{n}_{\mathrm{OG}}\) and the average value of \(\mathrm{H}_{\mathrm{OG}}\).

b. We operate the system as an enricher with \(L / D=2.0\). The vapor mole fraction methanol entering the column \(\mathrm{y}_{\text {in }}=0.783\) (this is feed), and vapor mole fraction methanol leaving \(\mathrm{y}_{\text {out }}=0.940\). Determine \(\mathrm{n}_{\mathrm{OG}}\) and the average value of \(\mathrm{H}_{\mathrm{OG}}\).

c. This problem was generated with a constant HETP. Why do estimates in parts a and \(b\) differ?