Unformatted text preview: 0 psi.
Number of stages = 7 plus a partial reboiler
Feed to stage 1
At the top, no condenser
At the bottom, bottoms flow rate = 99.33 lbmol/h
Estimated distillate rate = 450 lbmol/h (actual rate = 551.59 - 99.33 = 452.26 lbmol/h)
Estimated reflux rate = 550 lbmol/h
Estimated temperature of stage 1 = 50oF
Estimated temperature of bottom stage = 250oF
Estimated temperature of stage 2 = 80oF
Convergence was achieved in 4 iterations. The results are shown on the following two pages.
The column feed is 14.5 mol% vaporized. The heat duty of the reboiler is 4.4674 MMBtu/h.
The % stripping of each component in the feed is as follows: Component
nC6 % Stripped
8.03 Exercise 10.41 (continued)
Analysis: (continued) Analysis: (continued) Exercise 10.41 (continued) Exercise 10.42
Subject: Liquid-liquid extraction of a mixture of cyclohexane (1) and cyclopentane (2) with
Given: Feed of 700 lbmol/h of cyclohexane and 300 lbmol/h of cyclopentane. Methanol
solvent of 1,000 lbmol/h. Extractors with various numbers of equilibrium stages, operating at
Assumptions: Phase equilibria predicted by NRTL or UNIQUAC equations.
Find: Product rates and compositions, and interstage flow rates and compositions for 1, 2, 5,
and 10 equilibrium stages.
Analysis: Reference 55 in Chap. 2 presents L/L equilibria data for the ternary system at 25oC
(77oF). These data are fitted to the NRTL and UNIQUAC equations in "Liquid-Liquid
Equilibrium Data Collection - Ternary Systems", Vol. V, Part 2 of the Chemical Data Series, by
J. M. Sorenson and W. Arlt, DECHEMA (1980). Their fit to the simpler NRTL equation is
almost as good as the UNIQUAC fit. Therefore, the NRTL equation is used here, with the
following binary interaction parameters for use in the Chemcad program, where from Eq. (2-94),
τ ij = I
3 gij − g jj
RT = Bij BIJ
361.38 T , where T is in Kelvins BJI
0.2 Using the Binodal Plot feature of the Chemcad program, a predicted ternary liquid-liquid
equilibrium diagram is obtained, as shown on the next page, along with a corresponding table of
predicted tie lines. It is seen that at 25oC, cyclopentane is completely soluble in methanol, but
cyclohexane is only partially soluble in methanol. Is methanol a good solvent for the separation
of cyclopentane from cyclohexane? From the slope of the tie lines, the answer is no;
Cyclopentane distributes preferably to the cyclohexane-rich phase. For example, for one
equilibrium stage, using the LLVF model of Chemcad, the following two liquid phases (raffinate
and extract) are calculated when the given feed and solvent are mixed and brought to equilibrium
at 25oC and 30 psia, where the pressure exceeds the bubble-point pressures of the feed (2.69 psia)
and solvent (2.44 psia) so that a vapor phase does not form. Very little separation of (1) and (2)
occurs. Exercise 10.42 (continued)
Analysis: (continued) Analysis: (continued) Exercise 10.42 (continued) The Extract model of the Chemcad program was used to calcula...
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