(376a) Model Generation and Evaluation for the Oxidation of Ketones

Several classes of endophytic fungi have been recently identified that convert cellulosic biomass to a range of oxygenated molecules which are potentially viable as biofuels [1,2]. These oxygenated molecules include a variety of ketones, for which the oxidation chemistry is not yet well understood. To evaluate the viability of these ketones as alternative fuels, predictive detailed kinetics models are needed. These models will provide a mechanistic understanding of the chemistry involved in ketone oxidation, which will aid in recommending particular ketones for further study.

In this work, detailed kinetics models for several ketones -- including diisopropyl ketone (DIPK), isopropyl tert-butyl ketone (IBTPK), di-tert-butyl ketone (DTBK), cyclopentanone (CP), and 2-methylcyclopentanone (MCP) -- have been generated using the automatic mechanism generation software package RMG [3]. RMG generates a set of possibly important species and reactions from a database of reaction families and libraries, and then uses a flux-based heuristic for determining which of the species and reactions are actually important to the mechanism. This process iterates until all important species and reactions are identified. Estimates of the thermodynamic and kinetic parameters needed for detailed kinetics models are made by querying a database of rules and heuristics for similar species and reactions. Several new and improved rate rules have been added to the RMG database in order to improve the performance of the generated ketone models when compared with experimental data.

The ketone models have been evaluated using experimental measurements from a variety of sources. The products of pulsed-laser chlorine-initiated oxidation of DIPK, IBTPK, and DTBK have been monitored as a function of reaction time, mass, and photoionization energy by using Multiplexed Photoionization Mass Spectrometry (MPIMS) with tunable ionizing radiation provided by the Chemical Dynamics Beamline at the Advanced Light Source. At 550 K and 8 torr, the primary products are the cyclic ethers, as predicted by the RMG models. A minor product is observed at a mass-charge ratio consistent with HO₂ elimination; however, preliminary calculations suggest that the molecule may not be the expected HO₂ elimination product from the standard peroxy chemistry included in the RMG models. The DIPK model has also been compared against experimental ignition delay time measurements for a rapid compression machine. The experimental measurements show a significant region of negative-temperature correlation over the range of 650 to 750 K at 10 bar. This negative-temperature correlation is also predicted by the RMG model, but at a higher temperature than in the experimental data.