Reaction kinetics of OH radicals with 1,3,5-trimethyl benzene: An experimental and theoretical study |
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| Affiliation: | 1. King Abdullah University of Science and Engineering (KAUST), Clean Combustion Research Center, Physical Sciences and Engineering Division, Thuwal 23955-6900, Saudi Arabia;2. Molecular Science and Nano-Materials Lab, Institute for Computational Science and Technology, SBI Building, Quang Trung Software City, Tan Chanh Hiep Ward, District 12, Ho Chi Minh City, Vietnam;3. University of Science, Vietnam National University – HCMC, 227 Nguyen Van Cu, Ward 4, District 5, Ho Chi Minh City, Vietnam;4. Vietnam National University – HCMC, Quarter 6, Linh Trung Ward, Thu Duc City, Ho Chi Minh City, Vietnam;5. International University, Quarter 6, Linh Trung Ward, Thu Duc City, Ho Chi Minh City, Vietnam;1. Institute of Combustion Technology, German Aerospace Center (DLR), Pfaffenwaldring 38-40, 70569 Stuttgart, Germany;2. Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland;3. Mass Spectrometry in Reactive Flows, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany;4. Division 9, State Health Office, Nordbahnhofstraße 135, 70191 Stuttgart, Germany;5. Technical Thermodynamics, Paderborn University, 33098 Paderborn, Germany;1. Chair of High Pressure Gas Dynamics, Shock Wave Laboratory, RWTH Aachen University, Aachen 52056, Germany;2. Institute of Technical Thermodynamics, RWTH Aachen University, Aachen 52056, Germany;3. DRIVE EA1859, Université de Bourgogne Franche-Comté, 49 Rue Mademoiselle Bourgeois, Nevers 58000, France;4. IRCER, UMR CNRS 7315, Université de Limoges, Limoges 87032, France;1. Key Laboratory for Power Machinery and Engineering of MOE, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China;2. CRECK Modeling Lab, Department of Chemistry, Materials, and Chemical Engineering “G. Natta”, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy;3. National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, PR China |
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| Abstract: | Alkylated aromatics are ubiquitous in transportation fuels. 1,3,5-Trimethyl benzene (135TMB) is a popular surrogate for the aromatic content of distillate fuels due to its symmetry (point group, C3h), which facilitates the construction of an accurate chemical kinetic model. The reaction of OH radicals with 135TMB plays a crucial role in the oxidation kinetics of 135TMB. In this work, the reaction kinetics of OH-initiated oxidation of 135TMB were investigated behind reflected shock waves over 975–1318 K and atmospheric pressure. The reaction was followed by monitoring OH radicals near 307 nm. The rate coefficients were extracted from detailed chemical kinetic modeling of OH concentration-time profiles. Our measured data clearly showed a positive temperature dependence, in contrast to the negative temperature dependence of the literature low-temperature data. At 1000 K, our measured rate coefficient is 1.3 × 10−11 cm3 molecule−1 s−1, which is roughly a factor of 5 lower than the room-temperature data reported in the literature. This observation reflects the complex nature of the OH + 135TMB reaction, similar to that observed for various aromatics + OH chemical systems. Our measurements did not show any discernible pressure dependence over the narrow pressure range of 870 – 1148 Torr. The title reaction has several possible channels in the reactive potential energy surface. The importance of each channel was characterized using ab initio/RRKM-ME calculations over T = 200–2000 K and P = 0.76 -7600 Torr. Our analyses revealed that addition channels and hydrogen abstraction from the methyl site have negative energy barriers. The reaction was found to undergo almost exclusively (∼93%) via the addition channel under ambient conditions. However, beyond 600 K, the abstraction channels take the lead, yielding the positive T-dependence of the overall rate coefficient. Although addition channels display a sharp fall-off behavior beyond 500 K, the general rate coefficients are pressure-independent. The title reaction shows a complex kinetic behavior due to competing channels whose contribution changes significantly with temperature. Our theoretical calculations nicely reproduced the complex T-dependence of the reaction. After adjusting the barrier height, our theory remarkably captured the positive T-dependence of our high-T kinetic data and the negative T-dependence of the low-T literature data. To our knowledge, this is the first detailed study on the reaction kinetics of 135TMB with OH radicals. The reported rate data will be helpful for the combustion modeling of alkylated aromatic species. |
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