Evaluated Data and New Computational Tools for Chemical Reaction Engineering
D.R. Burgess
Objective: To develop computational tools that utilize thermochemical and chemical kinetic data for the modeling of chemical mechanisms, and to validate these tools through comparison with evaluated data.
Problem: Many computational tools used in chemical reaction engineering have limited ability to assign rigorous quantitative uncertainties to the results of the calculations. In addition, the evaluated data for benchmarking the computational models are often not readily available.
Approach: Data are evaluated for developing robust chemical kinetic measurements. This evaluation involves a synthesis of experimental data and computational predictions as a means of verifying the quality of the data. The primary goals are to provide high quality thermochemical functions and rate expressions. A secondary focus is to determine procedures for providing quantitative uncertainties to values that are traceable to ab initio calculations (energetics) and solutions to the master equation (rate expressions). We are also developing tools for managing the thermochemical and chemical kinetic data necessary for reacting flows simulation and for reaction path analysis and mechanism generation/reduction.
Results and Future Plans: Current systems of interest are hydrocarbon combustion and halogenated hydrocarbon destruction chemistries. We have compiled, calculated, and evaluated thermochemical data for the C1 and C2 fluorinated hydrocarbons. We have compiled experimental rates of reactions and calculated ab initio transition states for HF elimination pathways from the fluoromethanes and fluoroethanes. The geometries and energies of the transition states are determined from high-level ab initio quantum chemistry calculations employing the G2 and CBS methods. The transition states are then used as inputs to master equation calculations, which yield temperature and pressure dependent rate expressions. We have had significant success in validating the calculated rate expressions against experimental data and have identified previously unrecognized decomposition channels. We have now begun ab initio transition state calculations for thermal decomposition of the C1 and C2 chlorinated hydrocarbons.
In a related effort, we are working with Reaction Design Corporation in (1) developing database tools for managing the thermochemical and chemical kinetic data needed in reacting flows simulations; (2) implementing Deterministic Equivalent Modeling Method (DEMM), a recently developed computational tool, which provides quantitative uncertainties for simulation results if uncertainties are input for the thermochemical and chemical kinetic data; (3) implementing computational tools for reaction path analysis and mechanism generation/reduction (e.g., Principal Component Analysis); and (4) assigning computationally useful uncertainties to recommended rate expressions for hydrocarbon combustion chemistries for use in DEMM-based calculations.
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Last modified: 21 February 2000