†Speaker; ^*Corresponding Author (sandler@che.udel.edu)

Introduction

In our research on this project, we have used ab initio molecular orbital calculations to compute the degree and strength of hydrogen-bonding for a number of small, organic molecules. The calculations were performed using the computationally inexpensive Hartree-Fock Theory and the more rigorous density functional theory using the Becke3LYP functional.

Results and Discussion

We first applied the results of these calculations to an engineering equation of state: Statistical Associating Fluid Theory (SAFT). We have shown that by relating the results of our molecular orbital calculations to the association parameters in SAFT it is possible to reduce the number of adjustable parameters in this equation of state for pure associating fluids, without a loss of accuracy. We have also treated binary mixtures of an associating compound and a non-associating compound with accuracy equal to or exceeding that of the original SAFT, while requiring fewer total adjustable parameters.

For mixtures of two self-associating compounds, we have used the results of our molecular orbital calculations to derive a mixing rule that allows the SAFT parameters describing the cross-association reaction to be determined from the values of the SAFT parameters for self-association. Using this mixing rule, we were able to correlate binary mixture data to a high degree of accuracy.

The final class of mixtures we considered was binary mixtures of a self-associating compound and non-associating compound which can cross-associate. An example of this type of system is methanol + acetone. In this type of system the SAFT parameters for cross-association can not be determined from a mixing rule, as one of the compounds does not self-associate. We have used the results of our molecular orbital calculations to determine the values of these SAFT parameters for cross-association. The resulting correlations of mixture data are superior to the correlations using the original SAFT model and a single adjustable parameter.

Wolbach, J. P., and Sandler, S. I., "Thermodynamics of Hydrogen Bonding from Molecular Orbital Theory. 1. Water", AIChE J., 43(6), 1589 (1997).

Wolbach, J. P., and Sandler, S. I., "Thermodynamics of Hydrogen Bonding from Molecular Orbital Theory. 2. Organics", AIChE J., 43(6), 1597 (1997).

Wolbach, J. P., and Sandler, S. I., "Using Molecular Orbital Calculations to Describe the Phase Behavior of Hydrogen-Bonding Fluids", Ind. Eng. Chem. Res., 36(10), 4041 (1997).

Wolbach, J. P., and Sandler, S. I., "The Use of Molecular Orbital Calculations to Describe the Phase Behavior of Hydrogen-Bonding Fluids", Int. J. of Thermophys., 18(4), 1001 (1997).

Wolbach, J. P., and Sandler, S. I., "The Use of Molecular Orbital Calculations to Describe the Phase Behavior of Cross-Associating Mixtures", Manuscript submitted to Ind. Eng. Chem. Res.

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e-mail: Sandler@che.udel.edu