State Conditions Transferability Problem
Objective:
The objective of this section of the IFPSC is to test the ability of computer modeling (any method) to predict the change in bubble point pressure of a binary mixture when temperature is changed.
Background:
The ability of computer modeling to predict properties for state points that are challenging, inaccessible to experiment, or simply missing is often used as a justification for its development. We want to test/promote/validate this capability.
Thermophysical properties, phase equilibria, and solution chemistries are the underlying physical and chemical phenomena of industrial chemical processes. Rigorous thermodynamic modeling of such phenomena establishes a sound and scientific foundation for simulation of chemical processes and subsequent process development, optimization and control.
There are three main aspects of applied thermodynamics and phase equilibria of interest:
1) How to obtain data experimentally?
2) How to predict data from properties of pure components or pairs of components?
3) How to correlate limited data so they can be interpolated or extrapolated or combined into a representation of multicomponent behavior?
In the 1st and 2nd contest we have tested aspect number 2 with varying results. For example, one task was to predict pure component vapor pressures. Another was to predict vapor-liquid equilibria of binary mixtures at varying conditions.
In this 3rd contest we want to focus on parts of aspect number 3. It is a common task in chemical and related industries to use mixture phase equilibria information obtained at one isotherm or isobar and extrapolate to state conditions at other temperatures, pressures, and/or compositions. This is sometimes done with or without the knowledge of exprimental pure component properties.
Challenge:
For a binary mixture of
ethanol (CAS# 64-17-5)
and
1,1,1,2,3,3,3-heptafluoropropane or HFC-227ea (CAS# 431-89-0)
compute the bubble point (or total pressure) at constant temperature T = 343.13 K (69.98 oC) for the following seven (7) liquid phase mole fractions x:
x(ethanol) x(HFC-227ea)
0.0604 0.9396
0.1228 0.8772
0.3314 0.6686
0.5219 0.4781
0.7260 0.2740
0.8547 0.1453
0.9440 0.0560
Rules of the challenge:
- The force field employed must be capable of describing the interactions of each of the molecules in a consistent manner. The same force field must be used in all calculations.
- Any force field previously published in the open literature prior to the announcement of this challenge is acceptable, as long as its development adheres to the condition above.
- There is no limitation on the experimental data for the individual components that can be used to parameterize a model.
- No mixture data (binary and/or higher order) for the specified system can be used other than the experimental data provided as part of the problem description (see data below.)
- Estimates of uncertainty for computed bubble point pressure must be included.
- Any theory/modeling/simulation method, e.g. group contribution methods, can be used provided that the above rules are followed with respect to parameterization and application.
Experimental data for the system ethanol and HFC-227ea:
The following data may be used for solving the challenge:
Isotherm (I) at temperature = 283.17 K (10.02 °C)
Mole fraction Bubble Point Pressure
Ethanol N/m2 psia
0. 2.801E+05 40.63
0.0545 2.698E+05 39.13
0.1123 2.639E+05 38.28
0.2152 2.561E+05 37.15
0.3173 2.487E+05 36.07
0.4137 2.404E+05 34.87
0.5097 2.297E+05 33.32
0.6066 2.099E+05 30.45
0.7328 1.756E+05 25.466
0.7893 1.485E+05 21.538
0.8553 1.078E+05 15.632
0.9001 7.633E+04 11.071
0.9392 4.784E+04 6.939
0.9670 2.757E+04 3.999
1. 3.075E+03 0.446
Isotherm (II) at temperature = 343.13 K (69.98 °C)
Mole fraction Bubble Point Pressure
Ethanol N/m2 psia
0. 1.487E+06 215.72
0.0604 TBD
0.1228 TBD
0.3314 TBD
0.5219 TBD
0.7260 TBD
0.8547 TBD
0.9440 TBD
1. 7.274E+04 10.55
Contest Scoring:
Scoring will be done by using the following simple formula:
where Pi,exp and Pi,calc are experimental and calculated bubble point pressures respectively for the mixture of composition i. The pure component vapor pressures do not count for the scoring, since they are provided as input for model development.
The entry with the lowest score F wins the competition. The entry with the 2nd lowest score F earns 2nd place and so on.
Other entry guidelines:
- A submission for this challenge problem is to be in the form of a manuscript suitable for submission to a refereed, archival, scientific journal. The manuscript must contain sufficient detail about the simulation method and about the force field so that an experienced simulator could reproduce the results without requiring access to proprietary information. In particular, all potential parameters and molecule geometry parameters must be explicitly specified in the manuscript. The results are to be reported in SI units. A randomly selected subset of the submitted predictions will be validated by the judges by reproducing the reported calculations.
- An analysis of the uncertainty in the calculated results is required and must be included in the manuscript.
- Entries are expected to present results that are statistically significant and to present sufficient supporting evidence to establish this quality. Also, the scientific reasoning behind any new (unpublished) force field parameterizations must be clearly spelled out in the entry. If there is a consensus among the judges that an entry is of poor quality (uses a method commonly accepted to be fundamentally flawed, presents results that are not statistically significant, fails to provide sufficient supporting data and details, violates the various rules and guidelines established for the competition, or for any other reason would be unlikely to be accepted by any peer-reviewed scientific journal in the field), that entry will be rejected and will not be considered in the judging.
- Entries that represent collaborations between multiple research groups are welcomed.
