Chapter 6, Problem 6.97P

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 a single equilibrium stage (the streams leaving the unit are in equilibrium) at 85°C. At this temperature, propane and cottonseed oil are essentially immiscible, the vapor pressure of propane is 34 atm, and the distribution coef?cient (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. Explain your answer.

(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.