An air stream flowing at 1500 kmol/h containing benzene vapor is to be scrubbed using 25 kmol/h of hexadecane (C16H34) as the solvent. The mole fraction of benzene in the inlet gas is 0.010, and the required outlet mole fraction is 0.00050. The hexadecane is being returned to the scrubber from a stripper, so the mole fraction of benzene in the feed hexadecane is 0.00010. The column may be assumed to operate at 150 kPa and 35°C. Raoult’s law may be assumed to define the benzene equilibrium. Dilute solutions may be assumed.

1. How many equilibrium stages are needed? Keep the decimal places.

2. What is the outlet mole fraction of benzene in the hexadecane? What do you conclude about the assumptions made?

3. The column is operational, and the outlet mole fraction of benzene in the air is measured to be 0.0010. You send an operator to check the conditions in the column, and the temperature, pressure, air flowrate, and hexadecane flowrate are all as per design specifications. Suggest two possible causes for the process upset, and provide exact values for the offspec conditions, assuming that only one condition at a time is off-spec.

4. Determine the diameter of a sieve tray column for an 18-in tray spacing for operation at 75% of flooding. The fraction of active tray area is 0.88.

5. Determine the diameter of a packed column at 75% of flooding with 2-in, ceramic Raschig rings.

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log10 P (mm Hg) = 6.90565 SGhexadecane liquid SGbenzene liquid = 0.88 hexadecane liquid 3.474 CP = 0.77 = 1211.033 T(°C)+220.79