Separation Process Principles- 2n - Seader & Henley - Solutions Manual

At the top have almost pure benzene at 130 kpa 19

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Unformatted text preview: denser with a refrigerant for removing heat at 16oF. 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 Methane 20 20.000 0.000 Ethane 5 4.995 0.005 Benzene 500 5.000 485.000 Toluene 100 0.000 0.500 Total: 625 29.995 485.505 Product 3 0.0 0.0 10.0 99.5 109.5 Find: Type condenser and operating pressure in each column. Analysis: Use Chemcad or other simulator to make the bubble-point and dew-point calculations, with the SRK equation of state. Use Fig. 7.16 to determine pressure and type condenser. Column 1: Distillate is Product 1. Bubble point on Product 1 at 120oF gives an impossible very high pressure because the critical temperatures of methane and ethane are less than 120oF. A dew point on Product 1 at 120oF gives 31.4 psia because of the presence of benzene. Therefore, can use a partial condenser with cooling water. No problems occur at the bottom. Column 2: Distillate is Product 2. Bubble point on Product at 120oF gives 5.1 psia. No need to operate at a vacuum. Raise condenser pressure to 30 psia or just above atmospheric pressure and use a total condenser, possibly with subcooled reflux. No problems at the column bottom. Subject: Exercise 9.4 Number of equilibrium stages for a deethanizer. Given: Deethanizer with feed and average relative volatilities as follows from Fig. 9.21: Component C1 C2 C3 nC 4 nC 5 Feed, kmol/h Avg. Relative volatility 160 8.22 370 2.42 240 1.00 25 0.378 5 0.150 Distillate is to contain 2 kmol/h of C3. Bottoms is to contain 2 kmol/h of C2. Therefore, LK is C2 and HK is C3. Assumptions: Relative volatilities are relative to C3. Find: Number of equilibrium stages for 2.5 times minimum number of stages. Analysis: To compute the minimum number of stages, use component flow rate form of the Fenske equation given by (9-12): log N min = d C2 bC3 dC3 bC 2 log α C 2 ,C3 log = 370 − 2 240 − 2 2 2 log 2.42 N = 2.5Nmin = 2.5(11.3) = 28.3 = 11.3 Exercise 9.5 Subject: Determination of the minimum number of stages by the Fenske equation for each of three sections in a distillation column with a vapor sidestream Given: The following feed and product compositions for a distillation column: kmol/h: Component Feed Distillate Vapor sidestream Bottoms Benzene, B 260 257.0 3.0 0.0 Toluene, T 80 0.1 79.4 0.5 Biphenyl, BP 5 0.0 0.2 4.8 Pressure, kPa 165 130 180 200 Assumptions: Raoult's law for K-values. Find: Using the Fenske equation, the minimum number of stages for sections between: (a) Distillate and feed. (b) Feed and vapor sidestream. (c) Sidestream and bottoms. Analysis: (a) For this section, take the LK as benzene and the HK as toluene. At the top, have almost pure benzene at 130 kPa = 19 psia. Therefore, from Fig. 2.4, the distillate temperature = boiling point of benzene at 19 psia = 195oF. At the feed po...
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