3.17b. Material balances in batch processes: drying of soap with air.
It is desired to dry 10 kg of soap from 20% moisture by weight to no more than 6% moisture by contact with hot air. The wet soap is placed in a vessel containing 8.06 m3 of air at 350 K, 1 atm, and a water-vapor partial pressure of 1.6 kPa. The system is allowed to reach equilibrium, and then the air in the vessel is entirely replaced by fresh air of the original moisture content and temperature. How many times must the process be repeated in order to reach the specified soap moisture content of no more than 6%? When this soap is exposed to air at 350 K and 1 atm, the equilibrium distribution of moisture between the air and the soap is as follows:
Wt % moisture in soap Partial pressure of water, kPa
2.40 1.29
3.76 2.56
4.76 3.79
6.10 4.96
7.83 6.19
9.90 7.33
12.63 8.42
15.40 9.58
19.02 10.60
Solution
Generate the XY diagram
From the XY diagram, at the exit of the fifth equilibrium stage, X = 0.06 and
3.18b. Material balances in batch processes: extraction of an aqueous nicotine solution with kerosene.
Nicotine in a water solution containing 2% nicotine is to be extracted with kerosene at 293 K. Water and kerosene are essentially insoluble. Determine the percentage extraction of nicotine if 100 kg of the feed solution is extracted in a sequence of four batch ideal extractions using 49.0 kg of fresh, pure kerosene each. The equilibrium data are as follows (Claffey et al., Ind. Eng. Chem., 42, 166, 1950):
X', ´ 103 kg nicotine/kg water Y', ´ 103 kg nicotine/kg kerosene
1.01 0.81
2.46 1.96
5.02 4.56
7.51 6.86
9.98 9.13
20.4 18.70
Solution
From the XY diagram, after 4 extractions, X = 0.00422