463542 A Novel Approach of Modeling Orientational Hydrogen Bonding Interactions in Associating Fluids with the COSMO-SAC Activity Coefficient Model

Tuesday, November 15, 2016: 2:04 PM
Yosemite B (Hilton San Francisco Union Square)
Wei-Lin Chen and Shiang-Tai Lin, Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan

Based on solid theoretical background in statistical thermodynamics and quantum mechanics, the COSMO-SAC model is a powerful predictive thermodynamic model which can provide reliable thermodynamic properties and phase behavior of mixture fluids. The model has been applied in many problems such as vapor-liquid equilibrium, liquid-liquid equilibrium, drug solubility, partition coefficient ionic liquid screening, etc over the last decades. The core knowledge in COSMO-SAC model is how to evaluate the interaction between molecules on the basis of surface segments whose properties such as position and charge density can be determined from quantum mechanical calculation. In recent years, some refinements such as including the temperature dependence on electronic interactions and differentiating the different types of hydrogen bonding interactions are introduced to improve the accuracy of COSMO-SAC model (Mu, Rarey et al. 2007). In this work, we propose a new approach which allows for consideration of spatial orientation of hydrogen bonds in the COSMO-SAC model. Instead of using a cutoff charge or a predefined hydrogen bonding atoms, we adopt the concept of molecular orbital, Valence Shell Electron Pair Repulsion theory (PETRUCCI, R.H 2002), to identify the hydrogen bonding surfaces (Fig. 1). The inclusion of molecular orbital information allows for specific the hydrogen bond interactions within certain spatial orientations and results in a more accurate description regarding the vapor-liquid equilibrium (VLE) of mixtures containing different hydrogen bonding specie. We examined 35 associating fluids (whose include water, alcohols, amines and amides) in total 598 mixtures (7583 data points, temperature range from 263.15K to 548.15 K). The prediction accuracy is found to be 6.75% (AARD-P%) and 2.67% (AAD-y%) in pressure and vapor composition, respectively. The results are more accurate than the original model (7.16% and 2.83%) (Hsieh, Sandler et al. 2010), while the number of universal parameters used are reduced from 10 to 9.

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(b)

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Water

water-cosmo-2nd

water-2016-2nd

Figure 1. (a) The structure of water molecule and its lone pair describing by VSEPR theory. (b) The screening charge distribution on water surface. (c) The spatial allowance in hydrogen bond restricted by the lone pair within a cut-off radius.

References

1.     Hsieh, C.-M., S. I. Sandler and S.-T. Lin (2010). "Improvements of COSMO-SAC for vapor¡Vliquid and liquid¡Vliquid equilibrium predictions." Fluid Phase Equilibria 297(1): 90-97.

2.     Mu, T. C., J. Rarey and J. Gmehling (2007). "Performance of COSMO-RS with sigma profiles from different model chemistries." Industrial & Engineering Chemistry Research 46(20): 6612-6629.

3.     PETRUCCI, R.H., HARWOOD, W.S. and HERRING, F.G. (2002). General ChemistryPrinciples and Modern Applications, 8th edn. Prentice Hall, Upeer Saddle River, NJ.


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