A stream of 5.00 wt% oleic acid in cottonseed oil enters an extraction unit at a rate of 100.0 kg/h. The unit operates as an equilibrium stage (the streams leaving the unit are in equilibrium) at 85°C. At this temperature, propane and cottonseed oil are essentially immiscible, and the distribution coefficient (oleic acid mass fraction in propane/oleic acid mass fraction in cottonseed oil) is 0.15.

(a) Calculate the rate at which liquid propane must be fed to the unit to extract 90% of the oleic acid.

(b) Estimate the minimum operating pressure of the extraction Unit (i.e., the pressure required to keep the propane liquid at 85°C).

(c) High-pressure operation is costly and introduces potential safety hazards. Suggest two possible reasons for using propane as the solvent when other less volatile hydrocarbons are equally good solvents for oleic acid.