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of 99.9 mol% MEK for recycle. The two columns were designed with the SCDS (simultaneous
correction) model of Chemcad leading to the following final material balance, which satisfies the
product purity specifications:
Component
Acetone
Methanol
MEK
Total:
Temp, oC Mol/s:
Feed Solvent
30
10
40
144.9 60
60
145 Column 1
distillate
0.016
8.526
0.158
8.700
144.6 Column 1
bottoms
29.984
1.474
59.842
91.300
169.5 Column 2
distillate
29.924
1.474
0.101
31.499
55.8 Column 2
bottoms
0.060
0.000
59.741
59.801
79.1 The pressure of the extractive distillation column (Column 1) was set at 12 atm, with a solvent
rate of 60 mol/s at 145oC. The following Chemcad SCDS results, for the listed conditions, was
obtained after 11 iterations. The resulting product compositions are those in the above table.
Other combinations of stages, reflux, and solvent rate could also give satisfactory results:
Number of stages = 60 (includes total condenser and partial reboiler)
Solvent enters stage 20 from the top
Feed enters stage 40 from the top
Acetone mole fraction in distillate = 0.98
Bottoms flow rate = 91.3 mol/s
Solvent flow rate = 60 mol/s at 145oC
Initial guesses: Distillate rate = 8 mol/s
Reflux rate = 80 mol/s
Temperatures: Stage 1, 145oC
Stage 60, 170oC
Stage 2, 145oC
Stage 59, 160oC Exercise 11.10
Analysis: (Extractive Distillation Column continued)
The reflux ratio was computed to be 8.083.
The liquid phase composition profile is shown below. The extractive distillation column was
sized with Chemcad for sieve trays, with:
24inch tray spacing
12% downcomer area
10% hole area
1/4inch holes
80% of flooding
The resulting column inside diameter was determined to be 5 feet. For a final design, the
computations should be repeated taking into account tray pressure drop, tray efficiency, and
impurity in the MEK solvent. Exercise 11.10 (continued)
Analysis: (continued)
Ordinary Distillation Column: This column, at a pressure of 1 atm, separates the bottoms from
the extractive distillation column to obtain 95 mol% acetone and 99.9 mol% MEK. A starting
point for this separation is obtained by using the ShortCut Column (FUG) model of Chemcad
with an operating reflux ratio of 1.3 times the minimum ratio. The feed is assumed to be at the
bubble point. Thus, the bottoms from Column 1 at 169.5oC and 12 atm is cooled and
decompressed to 68.7oC and 1 atm. Using the above material balance table, the specifications for
the ShortCut Column model are 29.924/29.984 = 0.998 for the recovery of the LK (methanol) to
the distillate and 0.101/59.842 = 0.0169 for the recovery of the HK (MEK). The results are:
Minimum number of equilibrium stages = 17.7
Minimum reflux ratio = 2.52
Reflux ratio = 1.3(2.52) = 3.28
Number of equilibrium stages = 34.1
Feed stage location (Kirkbride equation) = 18 from the top
The SCDS Column model of the Chemcad program was then used to make a rigorous calculation
based on the following input data:
Pressure constant at 1 atm
Number of stages = 35 (includes the total condenser and the partial reboiler)
Feed stage = 20 from the top
Acetone purity in the distillate = 95 mol%
MEK purity in the bottoms = 99.9 mol%
Estimated distillate rate = 31.4 mol/s
Estimated reflux rate = 109.9 mol/s (reflux ratio of 3.5)
Estimated temperatures: Stage 1, 64oC Stage 35, 78oC Stage 2, 65oC
Stage 34, 75oC
A converged result was obtained in 5 iterations, with a computed reflux rati...
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 Spring '11
 Levicky
 The Land

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