Other projects:
P-Dependence & Model Construction
Model Reduction and Numerical Toolkit
Adaptive Chemistry for Reacting-Flow Simulations
Sumathy Raman, C.D. Wijaya, W.H. Green
Supported by NSF, EPA, Alstom Power, Dow Chemical
Traditionally reaction mechanisms are generated manually, and are thus limited by the experience of the researcher, since their reliability depends heavily on the completeness and accuracy of the reactions considered. The increasing demand for more complete reaction mechanisms has led to the development of computer modeling techniques, which use algorithms to generate reaction mechanisms automatically. These kinetic model construction programs require accurate estimates for rate constants of the generated reactions in order to determine which reactions need to be included into the mechanism and which are unimportant with respect to the application. Existing approaches to predict reaction rates are based on known thermodynamic properties of reactants and/or products such as the Evans-Polanyi relationship (a linear relationship between activation energy and heat of the reaction), the bond energy bond order (BEBO) relationship or the correlation between bond energy and the energy to bring the reactants together. Though simple to use, the parameters involved in such relationships depend strongly on the nature and type of reaction. Also, these methods focus mainly on the activation energy of reaction types but provide no means of estimating Arrhenius pre-exponential rate factors. The success of Group Additivity approaches in predicting the relative stability (enthalpy), entropy (S298) and heat capacity (Cp(T)) of stable molecules as well as radicals has encouraged us to attempt an extension of this treatment to transition state structures. Knowledge of the thermochemical properties of the reactants and transition structures enables us to derive the rate coefficients for both the forward and backward reactions in association with the equilibrium constants.