A 50 mol% mixture of propane(1) and n-butane(2) enters an isothermal flash drum at 37°C. If the flash drum is maintained at 0.6 MPa, what fraction of the feed exits as liquid? What are the compositions of the phases exiting the flash drum? Work the problem in the following two ways.

(a) Use Raoult’s law (use the Peng-Robinson equation to calculate pure component vapor pressures).

(b) Assume ideal mixtures of vapor and liquid. (Use the Peng-Robinson equation to obtain f^sat for each component.)