Redesign Analysis of a
Distillation Column
Presented By: Michael Hoepfner
University of Utah 2006
Introduction
 Why
care about redesign?
Outline
 Objective
 Theory
 Experiment
 Results
 Aspen Analysis
 Recommendations
 Conclusion
/ Summary
Objective
 Scope

Isopropyl Alcohol (IPA) and Water to Ethanol
(EtOH) and Water
 Purpose


Is the switch possible?
What are the limitations?
Outline
 Objective
 Theory
 Experiment
 Results
 Aspen Analysis
 Recommendations
 Conclusion / Summary
Theory
 Distillation



Is among the most common of separations
Separates compounds based on volatility
Utilizes multiple equilibrium separations
Theory (cont.)
T-x-y Diagram
x-y Diagram
0.7
0.65
210
0.6
Bubble Line
205
0.55
Vapor r Fraction IPA
Temerature (ºF)
Dew Line
200
195
190
185
0.5
0.45
0.4
0.35
0.3
0.25
0.2
Equilibrium Line
0.15
45 Degree Line
180
0.1
0.05
175
0
0.1
0.2
0.3
0.4
0.5
0.6
Mole Fraction IPA
0.7
0.8
0.9
1
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Liquid Fraction IPA
0.5
0.55
0.6
Source: Perry’s Chemical Engineering Handbook, 7th Ed.
0.65
0.7
Theory (cont.)

McCabe-Thiele


Simple and useful
tool for defining a
distillation column
Three lines can
characterize the
conditions
Source: Seader, 2006
Theory (cont.)
Source: Seader, 2006
Theory (cont.)
 Efficiency

Liquid samples, therefore, liquid efficiency
E ML 
xi ,n 1  xi ,n
xi ,n 1  x *i ,n
Source: King, 1971
Theory (cont.)

1.38
1.375
1.37
Refractive Index
1.365
1.36
Refractive Index (RI)
was used to
measure the
concentration
1.355
1.35
1.345
1.34
1.335
1.33
0
5
10 15 20
25 30 35
40 45
50 55 60
65 70 75
80 85 90
95 100
Mole Percent IPA
Source: CRC Handbook of Chemistry and Physics, 64th Edition
Outline
 Objective
 Theory
 Experiment
 Results
 Aspen Analysis
 Recommendations
 Conclusion / Summary
Experiment

Apparatus




12 Trays with 3
inch bubble
caps
Total Condenser
Partial Reboiler
Thermal couple
at every tray
Source: Ong, 1952
Experiment (cont.)
 Operate

Collect samples for efficiency determination
 Operate

at total reflux
at 2 times the minimum reflux
Collect samples for efficiency determination
 Model
water
results in Aspen for ethanol and
Outline
 Objective
 Theory
 Experiment
 Results
 Aspen Analysis
 Recommendations
 Conclusion / Summary
Results

Obtained samples on three separate occasions
 Samples are numbered by the date collected

10/30/2006
• First run of total reflux

11/01/2006
• Second run of total reflux

11/06/2006
• Only run of partial reflux
Results (cont.)
Concentration of Samples
70.0
Mole Percent IPA
60.0
Total Reflux 10/30/2006
50.0
Total Reflux 11/01/2006
Partial Reflux 11/06/2006
40.0
30.0
20.0
10.0
0.0
0
1
2
3
4
5
6
7
8
Tray Number
9
10
11
12
Results (cont.)

Efficiency


Two
reasonably
reliable data
sets
All error is at a
95%
confidence
interval
Total Reflux
10/30/2006
Partial Reflux
11/06/2006
Tray
ML
Error
ML
ML Fixed
Error
Distillate
-
-
-
-
-
2
15.7
6.5
109.8
0
3
20.2
4.1
94.9
94.9
4
32.4
3.1
480.3
0
-
5
18.6
2.5
-93.2
0
-
6
27.0
2.0
-7.4
0
-
7
97.8
0*
4885.2
0
-
8
91.5
0*
-84.2
0
-
9
0
-
82.5
82.5
10
0
-
492.5
0
-
11
0
-
132.6
0
-
12
0
-
20.2
20.2
Bottoms
0
-
-113.8
0
Average
25.3
3.7
18.0
156.3
125.9
26.0
102.8
Outline
 Objective
 Theory
 Experiment
 Results
 Aspen Analysis
 Recommendations
 Conclusion / Summary
Aspen Analysis

Aspen



Used average stage
efficiency for every
stage
It is possible to do
separation
Limited by total
condenser load
• Max condenser load:
278±11 kW
• Max reboiler load:
2410±20 kW
TOPSC
F EED C
C OMPLEX
BOTTC
Aspen Analysis (cont.)
Feed
Flow
(gpm)
Condenser
Duty (kW)
Distillate
Flow
(kmol/hr)
Bottoms
Flow
(kmol/hr)
Upper
Reboiler Steam
Duty
Flow
(kW)
(kg/min)
7.85
289.19
20.68
53.93
401.09
10.58
Average
7.55
278.29
19.90
51.89
385.96
10.18
Lower
7.26
267.27
19.11
49.84
370.70
9.78
Outline
 Objective
 Theory
 Experiment
 Results
 Aspen Analysis
 Recommendations
 Conclusion / Summary
Recommendations
 Ethanol



separation is possible
Max feed 7.55±0.30 GPM of 15 mole %
ethanol
Reboiler steam required 10.18±0.40 kg/min
By redesigning the condenser, capacity can
be greatly increased
• Reboiler only at ~1/6th of capacity
 Allow
more time for partial reflux efficiency
Outline
 Objective
 Theory
 Experiment
 Results
 Aspen Analysis
 Recommendations
 Conclusion
/ Summary
Conclusion / Summary
 Redesign
analysis is an important part of
chemical processing
 Distillation column in senior lab is about
25.3 ± 3.7 % efficient
 Ethanol and water separation is possible

Limited by the total condenser
Sources






Weast, Robert C, Editor. CRC Handbook of Chemistry and Physics,
64th Edition. CRC Press, Inc. Boca Raton, 1983. p. D-253.
King, C. Judsen. Separation Processes. McGraw-Hill, New
York,1971. p 603.
Ong, John N. Jr, Jack M. Whitney. “The Operation of a Laboratory
Bubble-Plate Distillation Column”. University of Utah, June,
1952.
Perry, Robert H., Editor. Perry’s Chemical Engineering Handbook.
7th Edition. McGraw-Hill. New York, 1999. p. 115.
Seader, J. D., Ernest J. Henley. Separation Process Principles, 2nd
Edition. John Wiley and Sons. Hoboken, 2006. p. 193-294.
Silcox, Geoff. “Basic Analysis of Data”. Unpublished student aid.
University of Utah, 1999.
Questions?