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ch09 - Exercise 9.1 Subject Selection of type condenser and...

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Exercise 9.1 Subject: Selection of type condenser and operating pressure for distillation of propionic and n-butyric acids. Given: Distillate of 95 mol% propionic acid. Bottoms of 98 mol% n-butyric acid. Assumptions: Ideal solutions so that Raoult's K -values apply. Find: type condenser and operating pressure Analysis: From Perry's Handbook or other source, the normal boiling points are: Propionic acid 141.1 o C n-Butyric acid 163.5 o C Using Fig. 7.16, an operating pressure of 30 psia or less, with a total condenser , might be used. Could also consider using subcooled reflux with a top pressure of just above atmospheric pressure.

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Exercise 9.2 Subject: Selection of type condenser and operating pressure for distillation of a mixture of light paraffin hydrocarbons in two columns Given: Feed and product compositions as follows: kmol/h: Component Feed Product 1 Product 2 Product 3 C 1 160 160 0 0 C 2 370 365 5 0 C 3 240 5 230 5 nC 4 25 0 1 24 nC 5 5 0 0 5 Total: 800 530 236 34 Find: Type condensers and operating pressures for: (a) Direct sequence. (b) Indirect sequence. Analysis: Use Chemcad or other simulator to make the bubble-point and dew-point calculations, using the SRK equation of state. The results should be close to hand calculations using K -values from Figs. 2.8 and 2.9. Use Fig. 7.16 to determine pressure and type condenser. Column 1 of direct sequence: Distillate is Product 1. Can not condense at 120 o F because this temperature is above the critical temperatures of methane and ethane. At 415 psia , the dew point temperature is 16 o F. Therefore, use a partial condenser with a refrigerant boiling at a temperature of about 6 o F . One choice of refrigerant is propane. Bottoms temperature would not be in the decomposition range. Column 2 of direct sequence: Distillate is Product 2, which is mainly propane. Bubble-point pressure at 120 o F is 256 psia, which is greater than 215 psia. Dew-point pressure at 120 o F is 248 psia. Use partial condenser with about 250 psia pressure at the top. Use cooling water in the condenser . Bottoms conditions present no problems. Column 1 of indirect sequence: Distillate is a mixture of Products 1 and 2. At 120 o F, pressure is very high, even for a partial condenser. Dew-point temperature at 415 psia is 83 o F. Raise pressure a little and use cooling water in the condenser. Bottoms conditions present no problems. Column 2 of indirect sequence: Conditions at the top are the same as Column 1 of the direct sequence. Therefore, use a partial condenser with a refrigerant for removing heat at 16 o F .
Exercise 9.3 Subject: Selection of type condenser and operating pressure for the distillation of a mixture of methane, ethane, benzene, and toluene by the direct sequence in two columns. Given: Feed and product conditions as follows from Fig. 9.20: kmol/h: Component Feed Product 1 Product 2 Product 3 Methane 20 20.000 0.000 0.0 Ethane 5 4.995 0.005 0.0 Benzene 500 5.000 485.000 10.0 Toluene 100 0.000 0.500 99.5 Total: 625 29.995 485.505 109.5 Find: Type condenser and operating pressure in each column.

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ch09 - Exercise 9.1 Subject Selection of type condenser and...

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