Sidestream is 15 kmolh of 20 mol methanol reflux

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Unformatted text preview: tions: Constant molar overflow. Raoult's law K-values. Find: Number of theoretical stages and optimal locations of feed and sidestream. Analysis: First compute the material balance. Overall total material balance: F = 100 = D + B + S = D + B + 15 (1) (2) Overall methanol material balance: 75 = 0.96D + 0.05B + 0.20(15) Solving Eqs. (1) and (2), D = 74.45 kmol/h and B = 10.55 kmol/h Now determine the equilibrium curve. At 1 atm (14.696 psia), methanol boils at 64.7oC and ethanol boils at 78.4oC. From Fig. 2.4, the vapor pressure of ethanol at 64.7oC = 8.2 psia. The vapor pressure of methanol at 78.4oC = 25 psia. For the Raoult's law K-value, Eq. (2-44) applies. Combining this equation with the definition of the relative volatility of Eq. (2-21), gives, for methanol with respect to the less volatile ethanol, , = (Ps)M/ (Ps)E . At 64.7oC, , = 14.696/8.2 = 1.79. At 78.4oC, , = 25/14.696 = 1.70. Since these values are close (within about 5%), use an equilibrium curve based on a constant = (1.70 + 1.79)/2 = 1.745. From Eq. (7-3), the curve is computed from, y = x/[1 + x(-1)] = 1.74...
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This note was uploaded on 09/08/2008 for the course CHE 244 taught by Professor Selebi during the Spring '06 term at Lehigh University .

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