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Research Produced by Use of Grommet

"A Novel Approach to Phase Equilibria Predictions Using Ab Initio Methods"

Amadeu K. Sum and Stanley I. Sandler*
Center for Molecular and Engineering Thermodynamics
Department of Chemical Engineering

submitted to the Industrial and Engineering Chemistry Journal

Molecular orbital ab initio calculations have been used to compute interaction energies between pairs of molecules in a large molecular cluster. These energies are then used as the interaction energy parameters in the widely-used Wilson and UNIQUAC activitiy coefficient models. Low-pressure vapor-liquid equilibria predictions based on the calculated parameters have been computed for binary systems of water with methanol, ethanol, 1-propanol, 2-propanol, formic acid, acetic acid, acetone, acetonitrile, acetaldehyde, and m-methylformamide. Excellent predictions are obtained with the UNIQUAC model, whereas poor results are found with the Wilson model. In several cases, our predictions are also superior to those obtained from UNIFAC. In addition, using the same parameters and the UNIQUAC model, high-pressure vapor-liquid equilibria predictions were made using the Peng-Robinson Stryjek-Vera equation of state and the Wong-Sandler mixing rule for methanol, ethanol, 2-propanol, and acetone separately with water. The low- and high-pressure results demonstrate that this unique approach can lead to accurate vapor-liquid equilibrium predictions for hydrogen-bonding mixtures based only on pure component properties and the structure of the molecules.

"On Initiation Reactions of Acetylene Oxidation in Shock Tubes. A Quantum Mechanical and Kinetic Modeling Study"

A. Laskin and H. Wang

Chemical Physics Letters, in press

Reaction between acetylene and molecular oxygen was analyzed using quantum mechanical calculations and kinetic modeling of acetylene oxidation in shock tubes. Calculations at the G2(B3LYP) level of theory show that the direct attack of molecular oxygen on the pi-bond in acetylene has a larger energy barrier than acetylene - vinylidene isomerization, such that this isomerization followed by the reaction of vinylidene with molecular oxygen is the energetically favorable initiation reactions of acetylene oxidation. It is further shown that detailed kinetic models of acetylene oxidation including this initiation process predict well the experimental shock tube ignition delay data.

"Propyne Pyrolysis in a Flow Reactor: An Experimental, RRKM, and Detailed Kinetic Modeling Study"

S.G. Davis, C. K. Law, and H. Wang

Journal of Physical Chemistry, submitted 1998

Propyne pyrolysis was experimentally studied in a flow reactor at 1208 K and 1 atm. At these conditions, the decomposition of propyne was found to be highly sensitive to the initiation reactions, namely, propyne-to-allene isomerization and propyne CH fission. The pressure-dependent rate coefficients for several reactions relevant to propyne pyrolysis were determined with ab initio quantum mechanical calculations and Rice-Ramsperger-Kassel-Marcus (RRKM) analyses. These include the mutual isomerization of propyne and allene, the chemically activated reactions of propyne and allene with the H atom and of acetylene with methyl on the C3H5 potential energy surfaces. A detailed reaction mechanism, employing the current RRKM rate coefficients and the CH fission rate coefficients of propyne and allene also examined in this study, is shown to accurately predict the experimental species profiles determined in the flow reactor and literature shock-tube data of propyne and allene pyrolysis up to 1500 K.

"Binary CF3Br- and CHF3-Inert Flame Suppressors: Effect of Temperature on the Flame Inhibition Effectiveness of CF3Br and CHF3"

Y. Saso, Y. Ogawa, N. Saito, and H. Wang

Combustion and Flame, in press

A numerical investigation with detailed chemistry and transport has been conducted on the inhibition effectiveness of binary halogenated suppressant and inert gas mixtures. Computational results demonstrate that while positive synergism persists between CF3Br and inert gases, little or negative synergism exists between CHF3 and inert gases. These synergistic effects are attributed to the sensitivity of flame inhibition effectiveness of the chemical suppressant, in that while the inhibition effectiveness of CF3Br is enhanced at lower flame temperatures, it remains relatively unchanged with CHF3 over the examined temperature range. The temperature sensitivity of CF3Br inhibition effectiveness is a result of enhanced catalytic inhibition cycles at lower flame temperatures. It is also demonstrated that water vapor tends to diminish the flame inhibition effectiveness of CHF3.

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