Problem 11.6:

a) A stream contains a mixture of 40% normal heptane (by mol) and 60% toluene. Calculate the bubble and dew pressure of the mixture at 120 °C.

b) You are requested to adjust the volatility of the mixture so that the bubble pressure at 120 °C is 4 bar. You may add either normal pentane or normal octane. Which component will you add and in what amount? Report the amount as mol of additive per mole of the original solution.

c) Regardless of your answer in part (b), your supervisor instructs you to add 0.2 moles of normal octane per mol of solution. This new stream is flashed and the vapor and liquid streams are separated. The available information for the streams in the separator are shown below. Fill out the missing entries and determine the pressure:

Additional information: The saturation pressures at 120 °C are: Ppentane = 9.2 bar, Pheptane = 1.8 bar, Poctane = 1.1 bar, Ptoluene = 1.0 bar.