Exercise 2
How to chose the best
property prediction
method for simulation ?
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Importance of Selecting the Appropriate
Prediction Method
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Correct predictions of the physical
properties of the mixture as a function of
temperature and pressure.
Each method is suitable only for particular
types of components and limited to certain
operating conditions.
Choosing the wrong method may lead to
incorrect simulation results.
Particularly important for reliable
computations associated with separation
operations (distillation, LL extraction, etc.).
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Principle Steps in Selecting the
Appropriate Thermodynamics Package
1.
Choosing the most suitable
model/thermo method.
2. Comparing the obtained predictions
with data from the literature.
3. Adding estimates for components
that not available in the chosen
thermo package. Can they be
neglected?
4. Generation of lab data if necessary
to check the thermo model.
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Sources of Information
1.
Publications and professional
literature that deal with the process
in question or with the components
that participate in the process.
2. Simulator reference manual (HELP).
3. DATABANKS
4. Rules of thumb.
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Issues in Selection of the Appropriate
Thermodynamics Package
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Nature of mixture (e.g.,
hydrocarbon, polar,
electrolyte, etc.)
Pressure and temperature
range
Availability of data.
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Recommendations for the Selection of
the Appropriate Thermodynamics Package
Eric Carlson,
“Don’t gamble with physical
properties for simulations,” Chem. Eng. Prog.
October 1996, 35-46
Prof J.D. (Bob) Seader,
University of Utah
Hyprotech Recommendations
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Eric Carlson’s Recommendations
Figure 1
Polar
Non-electrolyte
E?
Electrolyte NRTL
Or Pizer
Electrolyte
Real
All
Non-polar
Peng-Robinson,
Redlich-Kwong-Soave
Lee-Kesler-Plocker
R?
Polarity
R?
Real or
pseudocomponents
P?
Pressure
E?
Electrolytes
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See Figure 2
Pseudo & Real
P?
Vacuum
054402 Design & Analysis II
Chao-Seader,
Grayson-Streed or
Braun K-10
Braun K-10 or ideal
7
Yes
Figure 2
Yes
LL?
P < 10 bar
ij?
(See also
Figure 3)
P?
No
Yes
No
No
Yes
LL? Liquid/Liquid
P > 10 bar
P?
Pressure
ij?
Interaction Parameters
Available
WILSON, NRTL,
UNIQUAC and
their variances
UNIFAC LLE
LL?
Polar
Non-electrolytes
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NRTL, UNIQUAC
and their variances
ij?
UNIFAC and its
extensions
Schwartentruber-Renon
PR or SRK with WS
PR or SRK with MHV2
No
054402 Design & Analysis II
PSRK
PR or SRK with MHV2
8
Hexamers
Figure 3
Yes
DP?
Dimers
Wilson
NRTL
UNIQUAC
UNIFAC
VAP?
DP?
Wilson, NRTL, UNIQUAC,
or UNIFAC with special EOS
for Hexamers
VAP?
No
Wilson, NRTL, UNIQUAC,
UNIFAC with Hayden O’Connell
or Northnagel EOS
Wilson, NRTL,
UNIQUAC, or UNIFAC*
with ideal Gas or RK EOS
Vapor Phase Association
Degrees of Polymerizatiom
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UNIFAC* and its Extensions
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Bob Seader’s Recommendations
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Bob Seader’s Recommendations
Yes
Figure 4
Yes
Yes
Yes
No
HC?
No
LG?
Light gases
See Figure 5
E?
Electrolyte
See Figure 6
PC?
Organic Polar
Compound
See Figure 5
Modified NRTL
E?
No
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Hydrocarbons
PC?
No
Yes
HC?
PC?
No
LG?
PSRK
Special: e.g., Sour Water (NH3, CO2, H2S, H2O)
Aqueous amine solution with CO2 and H2S
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Figure 5
Critical
Cryogenic
Narrow or
wide
HC and/
or LG
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P?
Non-Critical
T?
Non- Cryogenic
BP?
Very wide
PR
PR, BWRS
SRK, PR
T?
Boiling point range
of compound
Temperature region
P?
Pressure region
BP?
LKP
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Figure 6
Yes
Available
PC with HC
PPS?
BIP?
Not Available
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NRTL, UNIQUAC
No
Wilson
UNIFAC
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BIP?
Binary Interaction
Parameters
PPS?
Possible Phase
Splitting
13
Hyprotech Recommendations
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Example

Find the best thermodynamic package
for 1-Propanol , H2O mixture.
Eric Carlson,
“Don’t gamble with physical
properties for simulations,” Chem. Eng. Prog.
October 1996, 35-46
Prof J.D. (Bob) Seader,
University of Utah
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Eric Carlson’s Recommendations
Figure 1
for 1-Propanol ,H2O mixture
Non-electrolyte
Polar
See Figure 2
E?
Polarity
R?
Real or
pseudocomponents
P?
Pressure
E?
Electrolytes
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Figure 2
Yes
P < 10 bar
ij?
(See also
Figure 3)
P?
Polar
Non-electrolytes
LL?
WILSON, NRTL,
UNIQUAC and
their variances
No
No
LL?
No
UNIFAC and its
extensions
LL? Liquid/Liquid
P?
Pressure
ij?
Interaction Parameters
Available
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Bob Seader’s Recommendations
for 1-Propanol ,H2O mixture
Figure 4
Yes
HC?
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LG?
Yes
No
See Figure 6
HC?
Hydrocarbons
LG?
Light gases
E?
Electrolyte
PC?
Organic Polar
Compound
PC?
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Figure 6
Yes
Available
PC with HC
PPS?
BIP?
Not Available
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NRTL, UNIQUAC
UNIFAC
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BIP?
Binary Interaction
Parameters
PPS?
Possible Phase
Splitting
19
1-Propanol, H2O
TXY diagram for 1-Propanol, H 2O
100
Perry
NRTL
PRSV
UNIQUAC
Van-Laar (Built-in
Van-Laar(Perry)
98
96
T [oC]
94
92
90
88
86
84
82
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1-Propanol mol. frac.
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TXY macro for HYSYS
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