Choosing Property Models
CHEN 4460 – Process Synthesis,
Simulation and Optimization
Dr. Mario Richard Eden
Department of Chemical Engineering
Auburn University
Lab Lecture No. 4 – Selection of Property Models
October 2, 2012
Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel
Importance of Selection
•
Correct predictions of physical properties of the
mixture as 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.).
Principal Selection Steps
 Choosing
method.
the
most
suitable
model/thermo
 Comparing the obtained predictions with data
from the literature.
 Adding estimates for components not available in
the chosen thermo package. Can they be
neglected?
 Generation of lab data if necessary to check the
thermo model.
Sources of Information
•
Publications and professional literature that deal
with the process in question or with the
components that participate in the process.
•
Simulator reference manual (HELP).
•
DATABANKS
•
Rules of thumb.
Types of Models
EOS Models
Activity Coefficient Models
Limited ability to represent non-ideal liquids
Can represent highly non-ideal liquids
Consistent in critical region
Inconsistent in critical region
Can represent both vapor and liquid phases
Can represent liquid phase only. Gas phase
must still be described by an EOS model
Parameters extrapolate well with temperature
Binary parameters are highly dependent on
temperature
NO
Do you have any POLAR
components in your system?
YES
Use EOS Model
YES
Are the operating conditions
near the CRITICAL region of the
mixture?
NO
NO
Do you have LIGHT gases or
SUPERCRITICAL components
in your system?
Use Activity Coefficient
Model
YES
Use Activity Coefficient
Model with Henry’s law
Recommendations
•
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
•
Aspentech Recommendations
Eric Carlson
Non-electrolyte
Figure 1
Polar
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
See Figure 2
Pseudo & Real
P?
Vacuum
Chao-Seader,
Grayson-Streed or
Braun K-10
Braun K-10 or ideal
Eric Carlson
Yes
Figure 2
Yes
LL?
P < 10 bar
ij?
(See also
Figure 3)
P?
NRTL, UNIQUAC
and their variances
No
Yes
No
No
Yes
P > 10 bar
P?
Pressure
ij?
Interaction Parameters
Available
UNIFAC LLE
LL?
Polar
Non-electrolytes
LL? Liquid/Liquid
WILSON, NRTL,
UNIQUAC and
their variances
ij?
No
UNIFAC and its
extensions
Schwartentruber-Renon
PR or SRK with WS
PR or SRK with MHV2
PSRK
PR or SRK with MHV2
Eric Carlson
Figure 3
Hexamers
Yes
DP?
Dimers
Wilson
NRTL
UNIQUAC
UNIFAC
VAP?
DP?
VAP?
No
Wilson, NRTL, UNIQUAC,
or UNIFAC with special EOS
for Hexamers
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
UNIFAC* and its Extensions
Bob Seader
Bob Seader
Figure 4
Yes
Yes
Yes
Yes
No
HC?
No
Hydrocarbons
LG?
Light gases
See Figure 5
E?
Electrolyte
See Figure 6
PC?
Organic Polar
Compound
PC?
No
Yes
HC?
PC?
No
LG?
PSRK
See Figure 5
Modified NRTL
E?
No
Special: e.g., Sour Water (NH3, CO2, H2S, H2O)
Aqueous amine solution with CO2 and H2S
Bob Seader
Critical
Figure 5
Cryogenic
Narrow or
wide
HC and/
or LG
P?
Non-Critical
T?
Non- Cryogenic
BP?
Very wide
PR
LKP
PR, BWRS
SRK, PR
T?
Boiling point range
of compound
Temperature region
P?
Pressure region
BP?
Bob Seader
Figure 6
Yes
Available
PC with HC
NRTL, UNIQUAC
PPS?
BIP?
Not Available
No
Wilson
UNIFAC
BIP?
Binary Interaction
Parameters
PPS?
Possible Phase
Splitting
Aspentech
Example: 1-Propanol/Water
•
Find the best thermodynamic package for 1Propanol , 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
Carlson: 1-Propanol/Water
Non-electrolyte
Figure 1
Polar
Polarity
R?
Real or
pseudocomponents
P?
Pressure
E?
Electrolytes
E?
See Figure 2
Carlson: 1-Propanol/Water
Figure 2
Yes
P < 10 bar
ij?
(See also
Figure 3)
P?
LL?
WILSON, NRTL,
UNIQUAC and
their variances
No
No
Polar
Non-electrolytes
LL? Liquid/Liquid
P?
Pressure
ij?
Interaction Parameters Available
LL?
No
UNIFAC and
its extensions
Seader: 1-Propanol/Water
Figure 4
Yes
HC?
LG?
Yes
No
PC?
See Figure 6
HC?
Hydrocarbons
LG?
Light gases
E?
Electrolyte
PC?
Organic Polar
Compound
Seader: 1-Propanol/Water
Figure 6
Yes
Available
PC with HC
NRTL, UNIQUAC
PPS?
BIP?
Not Available
UNIFAC
BIP?
Binary Interaction
Parameters
PPS?
Possible Phase
Splitting
Solution: 1-Propanol/Water
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
1-Propanol mol. frac.
0.7
0.8
0.9
1