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Proposal for the 5th Simulation Challenge

Submitted by site admin on Fri, 2008-02-01 16:25.

This is a proposal for the 5th Industrial Fluid Properties Simulation Challenge problem. Please send you feedback and sugestions to ifpsc@fluidproperties.org by February 15, 2008.

Prediction of 1-Octanol-Water Partition and Infinite-Dilution Activity Coefficients

Objective:

The objective of this Challenge of the IFPSC is to test the ability of computer modeling (any method) to predict 1-Octanol-Water Partition (ko/w) and Infinite-Dilution Activity Coefficients (gam-inf).

Background:

The ability of computer modeling to predict properties 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 properties of pure components or mixtures 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 first 4 challenges we have tested these aspects with varying results. For example, one task was to predict pure component vapor pressures. Another was to predict vapor-liquid equilibria (VLE) of binary mixtures at varying conditions.

In this 5th challenge we want to refocus on aspect number 2. It is a common task in chemical and related industries to use octanol-water partition coefficients to aid in the design of product formulations with desired hydrophobicity or hydrophilicity character. ko/w is also used to estimate environmental bio-accumulation factors because it provides a crude model of partitioning between blood (water) and body tissue (1-octanol). Infinite-dilution activity coefficients are used to calculate air-water partition coefficients (Henry's Law constants) for environmental engineering applications. In addition, VLE of binary mixtures can be predicted (interpolated) over the entire binary composition using a two-parameter activity-coefficient model if the two infinite-dilution activity coefficients are known (Prausnitz, et.al, Molecular Thermodynamics of Fluid-Phase Equilibria, Third Edition, Appendix F, pps 804-807).

Challenge:

For each of the following molecules:

(i) an amine [exact chemical formula censored]

(ii) an alcohol [exact chemical formula censored]

Compute the:

(a) 1-octanol-water partition coefficient (mole-fraction units) at 300 K and 101.325 kPa.

(b) Infinite-dilution activity coefficient (mole fraction units, Lewis and Randall reference state) for the organic molecule dilute in water at 325 K and 13.5 kPa.

 

Rules of the game:

  • Any theory/modeling/simulation method, e.g. group contribution methods, can be used.
  • Any force field (or other model parameterization) previously published in the open literature prior to the announcement of this challenge is acceptable.
  • Force fields (or other models) that have not been published previously may not be parameterized for this challenge using octanol/water partition coefficient, infinite dilution activity coefficient or solubility in water data corresponding to the 2 challenge molecules. Force fields (or other models) may be parameterized using any other published physical property data.
  • Estimates of the uncertainty for computed water-octanol partition coefficients and the infinite-dilution activity coefficients must be included.


Challenge Scoring:

Quantitative Accuracy Metrics (60%)

  1. For each property, full credit will be awarded for predictions within the uncertainty limit of 5% of the experimental value.
  2. A linear interpolation of partial credit will be awarded for predictions with an absolute deviation above the minimum threshold and a maximum of 40%. No points will be awarded for prediction above the maximum deviation.

Relative Accuracy Metrics - Relative Ranking (40%):

The computed octanol-water partition coefficient and the infinite-dilution activity coefficient of each molecule will be compared to the respective experimental values. The molecule that is in best agreement to experiment will be used as a normalization to determine relative coefficients (ie: (coefficient worst predicted)/(coefficient best)). The relative ratios will be compared to the corresponding normalized ratios using the experimental data. The quantity (coefficient/coefficient-ref)predicted will receive full credit if it is within 5% of the corresponding quantity (coefficient/coefficient-ref)expt . As in the quantitative accuracy section, similar partial credit will be awarded on a sliding scale.

Click on the link below to see the 5th Challenge Problem scoring sheet.

Molecule Problem Scoring Spreadsheet (MS Excel file)

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 or other method and about the force field (if simulation) 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.
  • 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.
FAQ
Q: Based on the results of the 4th challenge, why not focus on vapor phase viscosity (which would represent a major methodological advance)?
A: While it does present some issues from a computation standpoint, it is not a property that had great industrial importance. When needed, other methods are available that give reasonably good estimates for vapor viscosity.
Q: Why not have a bigger scope by including a larger list of molecules covering a range of functionalities?
A: to be added
Q: Partitioning between octanol and water is complicated by the fact that water is soluble in octanol at a level of 0.2 to 0.3 in terms of mole fractions. Must entrants take this into account explicitly? Do they have to calculate the water saturation? Can they just ignore this complication?
A: to be added