Separation Processes

CHEG 4200 Separation Processes Exam 1 – February 25, 2009

The exam consists of three problems; the value of each problem is given next to the problem number. Read through the exam carefully before starting. Clearly state any assumptions and carefully, and clearly, define all variables.

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Problem 1: 25 points.

A system of propane and n-butane exists in two phase vapor / liquid equilibrium at 10 bar and 323 K. The mole fraction of propane in the vapor phase is 0.67 and 0.40 in the liquid phase. Additional pure propane is added to the system and the system is brought again to equilibrium at 10 bar and 323 K. What is the effect of the propane addition on the mole fractions of propane in the vapor and liquid phases? Explain your answer. (A qualitative, rather than a quantitative, answer with appropriate reasoning is acceptable.)

Problem 2: 35 points

A mixture containing 45.1 mole % propane, 18.3 mole % isobutane, and 36.6 mole % n-butane is flashed in a drum at 200 F and 350 psia. Estimate the mole fraction of the original mixture vaporized in the flash drum and the compositions of the liquid and vapor phases. You may assume ideal gas behavior. Figures 2.4, 2.6, and 2.9 may be helpful --- but then again, maybe not. CHEG 4200 Separation Processes Exam 1 – February 25, 2009

Problem 3. 40 points

Isopropyl ether (IE) is used to separate acetic acid (AA) from water (W). The liquid-liquid equilibrium data are given in the attached chart, constructed from the tie line data given below.

One hundred kilograms of a 30 wt% AA, 70 wt% W solution are contacted with pure ether in one equilibrium stage. It is desired to recover 95% of the acetic acid in the extract phase. How much ether is required?

Table I

Water / Acetic Acid / Isopropyl Ether Tie Line Data

Water Rich (Raffinate) Layer Ether Rich (Extract) Layer Wt% AA Wt% W Wt% IE Wt% AA Wt% W Wt% IE 1.41 97.1 1.49 0.37 0.73 98.9 2.80 95.5 1.61 0.79 0.81 98.4 6.42 91.7 1.88 1.93 0.97 97.1 13.3 84.4 2.30 4.82 1.88 93.3 25.5 71.1 3.40 11.4 3.9 84.7 36.7 58.9 4.40 21.6 6.9 71.5 45.3 45.1 9.60 31.1 10.8 58.1 46.4 37.1 16.5 36.2 15.1 48.7