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Unformatted text preview: LD/VB = 0.8. Combining this with Eq. (3), VB = 125 moles/100 moles of feed, which is close to the analytical value. Exercise 7.24 (continued) Exercise 7.25
Rectification of a mixture of benzene and chlorobenzene at total reflux. Given: Feed of 100 kmol of 20 mol% benzene and 80 mol% chlorobenzene. Column has 4 theoretical plates, a total condenser, a reflux drum, and a still to vaporize the feed. At an operating pressure of 1 atm, relative volatility of benzene with respect to chlorobenzene = = 4.13. Operate at total reflux with holdups only in the reflux drum and the still. Want liquid in the still with 0.1 mol% benzene. Assumptions: Perfect mixing to give uniform compositions in the reflux drum and the still. Find: Moles of liquid in the still at steady state. Analysis: This exercise can be solved analytically or graphically. Since benzene is the more volatile component, Eq. (7-3) gives the equilibrium relation at the still or any of the 4 plates, n, as,
yn = xn 4.13xn = 1 + xn ( - 1) 1 + 313xn . (1) At total reflux, numbering stages up from the bottom,...
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