The 8th Industrial Fluid Properties Simulation Challenge will focus on predicting adsorption isotherms of n-perfluorohexane (n-C6F14) in the certified reference material BAM-P109 activated carbon.
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Activated carbons are among the most widely used industrial materials. Due to their low cost of production and high adsorption capacity, they have found use in applications including: gas and electrolyte storage; gas and fluid purification; and catalysts and catalyst supports. Activated carbons are typically synthesized from organic carbonaceous precursors such as woods, coconut shells and coals. By judicious choice of the precursor materials and synthesis conditions, they can be synthesized with a wide range of features such as pore size distribution, specific surface area and chemical composition
With increasing numbers of applications, the ability to predict the performance of activated carbon adsorbents for a wide range of sorbent compounds would be very valuable in pre-optimizing systems and reducing product development time. Molecular simulation techniques in principle could be ideal to predict the adsorption isotherms of activated carbon sorbents for sorbates of varied chemistry as well as for various chemically-modified activated carbon adsorbents.
Although adsorption in porous media has been an area of extensive and vigorous activity in the field of molecular simulation (e.g. in zeolites [1,2], metal-organic frameworks [3,4], nanotubes , and other porous carbons [6,7]), it was not the focus of the IFPSC until the recent 7th Simulation Challenge to predict adsorption of C6F14 in BCR-704 Faujasite zeolite. The 8th Simulation Challenge continues the theme to assess the capability of molecular simulation methods and force fields to accurately predict adsorption in porous media for practically relevant and moderately complex chemical systems in order to benchmark the state-of-the-art capability in this important application area.
Studies of adsorption equilibria by molecular simulation employing both Monte Carlo [8-10] and molecular dynamics [11,12] techniques have become relatively common. However, applying these methods to study adsorption equilibria using force fields (potential energy models) developed for bulk phase conditions remains an open issue. General, transferable force fields that are reasonably accurate over a wide range of state conditions in the bulk are not necessarily transferable to the adsorbed phase. Moreover, active sites on the surface of the adsorbent can dramatically affect the adsorption behavior.
The focus of the current challenge will be to assess the potential to use molecular simulation methods to predict adsorption isotherms for organic compounds. Specifically, the challenge will focus on predicting the adsorption isotherm of n-perfluorohexane on the certified reference material BAM-P109.
Ar, H2O, N2, and CO2 adsorption isotherm studies on the BAM-P109 activated carbon will be carried out by the leading industry expert company Quantachrome and provided to Challenge entrants to aid in validating simulation models. Elemental analysis, XPS studies, and X-ray diffraction studies will also be carried out and provided to Challenge entrants. The Ar, H2O, N2, and CO2 adsorption studies, elemental analysis, XPS and X-ray diffraction studies will be posted on the IFPSC web-site no-later then end of January 2014.
The experimental benchmark adsorption studies for n-perfluorohexane (n-C6F14) on the BAM-P109 activated carbon will also be carried out by Quantachrome. n-perfluorohexane (n-C6F14) is a high performance material produced by 3M Company.
Predict the adsorption isotherm of n-perfluorohexane (n-C6F14) on the Certified Reference Material BAM-P109 Carbon at a temperature of 273K and at relative pressures of 0.1, 0.3, and 0.6. The relative pressure is defined as that relative to the bulk saturation pressure predicted by the model for the given temperature. At these relative pressures, the micropores of BAM-P109 are expected to be filled with adsorbate, and an accurate simulation model for adsorption in the carbon micropores will be necessary for successful predictions. Evaluating this capability is the primary goal for the 8th Simulation Challenge.
The lowest relative pressure was chosen because it represents the approximate lowest pressure accessible for reliable, reproducible adsorption data for the experimental method and apparatus that is being used to measure the benchmark data. Additional adsorption over the range of 0.1 to 0.6 relative pressure (i.e. in the pseudo-plateau region of the adsorption isotherm) is expected to occur in the mesoporous regions of BAM-P109. Molecular simulation methods used to model adsorption in the micropores may not be directly applicable to predict adsorption in the mesopore regions. However, challenge entrants are encouraged to develop additional approaches to account for mesoporous adsorption (for example, via correlations to the provided experimental benchmark adsorption data) as a secondary aspect of this challenge.
Rules of the Game
Challenge champions along with 1st, 2nd, and 3rd runners-up will be awarded. Entries will be scored by comparing the predicted adsorption isotherm data to experimentally measured data. For adsorption isotherms, the amount of perfluorohexane experimentally adsorbed at the defined set of pressures will be compared to the amounts predicted at the same pressures. Full credit will be awarded for a prediction that falls within the experimental uncertainty.
The units for comparing between experiment and simulation will be volume [cm3 g-1] at STP. The scoring will be computed as a mean percent error, M%E, between the computed value and the experimental value at the specified relative pressures. Where the M%E will be computed for n points using
where Vab,exp and Vab,sim are the experimental and simulated volumes of absorbed gas, respectively. Vab,exp is the experimental volume of adsorbed gas ± the experimental uncertainty.
The M%E will be weighted such that the prediction of adsorption at 0.1 relative pressure will account for 60% of the score, while the predictions for adsorption at 0.3 and 0.6 relative pressures will account for 20% of the score each. The weighting reflects the adsorption filling of the microporous region below 0.1 relative pressure followed by further adsorption in the mesoporous region above 0.1 relative pressure.
Other Entry Guidelines
 G.E. Norman and V.S. Filinov, High Temp. (USSR), 7, 216 (1969).
 D. Frenkel and B. Smit, Understanding Molecular Simulation, Academic Press, San Diego (2002).
 NIST Web Book (webbook.nist.gov/cgi/cbook.cgi?ID=C355420&Mask=4)