Toward the Accurate Prediction of Liquid Phase Oxidation of Aromatics: A Detailed Kinetic Mechanism for Toluene Autoxidation

Abstract

Toluene is an important compound in the chemical industry as well as an often chosen simple surrogate compound for aromatic components in transport fuels. As a result, an improved understanding of the liquid phase oxidation of toluene is of interest to both the chemical industry and the transportation sector. In this work, a detailed autoxidation mechanism for the liquid phase oxidation of toluene is developed using an automated mechanism generation tool. The resultant mechanism is significantly improved using quantum chemistry calculations to update the thermodynamic parameters of key species in solution. Comparisons are made between the predicted and experimentally measured induction period and the obtained mechanism. The agreement between both is found to be within 1 order of magnitude. Rate of production analysis and sensitivity analysis are carried out to explain and understand the reactions paths present in the mechanism. The behavior of the mechanism is commented upon qualitatively; however, no quantitative data could be obtained with the selected test method.

Structure–Reactivity Relationships in Fuel Stability: Experimental and Kinetic Modeling Study of Isoparaffin Autoxidation

“…Thus, within the framework of the full comprehension of fuel stability, this work confirms and extends previous work performed on the autoxidation of normal parraffins 12,[15][16][17][18][19] to isoparaffins 17,20,21 . The present study is in-line with others autoxidation studies performed at IFPEn on aromatics 14,22 and naphthenes 22 . All these studies aim at improving the comprehension of the autoxidation of each chemical family present in fuels.…”

“…The generated mechanisms were coupled to a previously developed reactor model to reproduce experimental results 11,12,14 . This reactor model includes a constant-concentration option for species specified in the input file.…”

Molecule‐Induced Radical Formation (MIRF) Reactions—A Reappraisal

“…One additional challenge in kinetics studies of decomposition reactions of hydroperoxides, peroxides, and peresters is that their reaction can be “induced” by radicals formed in the decomposition steps. This is best established for hydroperoxides and includes reactions of chain‐carrying radicals, through abstraction of either hydrogen or a HO group from the terminal OOH unit . This implies that the decomposition kinetics of hydroperoxides can be especially complex and difficult to analyze in terms of the contributions of individual processes.…”

“…R18 + 202.0 [33,35] R19 + 181.3 [33] Angewandte Chemie this step is likely to fragment to tert-butyloxy radical (8)a nd phenylacetate (57), whose proton transfer reaction with radical cation 55 then yields acid 59,t ogether with the other products known from pathway A.A si ndicated in Scheme 5 (pathway C), acid 59 can also be generated directly through aClass CMIRF reaction between perester (50)and thiophenol via transition state TS5051.F urther MIRF variants of Class Ba re conceivable that involve attack of thiophenol at the carbonyl group of peresters 50, and we should also not overlook reaction pathways lacking open-shell intermediates that generate product 59 through, for example,aseries of nucleophilic substitution reactions.All of these variants have to eventually live up to the challenge of rationalizing the reaction rates for phenyl-substituted derivatives of 50 and its dependence on thiol concentrations.One additional challenge in kinetics studies of decomposition reactions of hydroperoxides,p eroxides,a nd peresters is that their reaction can be "induced" by radicals formed in the decomposition steps.This is best established for hydroperoxides and includes reactions of chain-carrying radicals,t hrough abstraction of either hydrogen or aH Og roup from the terminal OOH unit. [54][55][56] This implies that the decomposition kinetics of hydroperoxides can be especially complex and difficult to analyze in terms of the contributions of individual processes. As econd example,w here MIRF reactions may play arole,concerns the chemistry of lipid hydroperoxides (LHPs) and their potential to co-initiate the autoxidation of polyunsaturated fatty acids (PUFAs) and their esters.T his latter process has been studied in great detail because of its enormous role in aging as well as cardiovascular and neurodegenerative diseases.…”

Molekül‐induzierte Radikalbildung – eine Neubewertung

“…Eine zusätzliche Herausforderung bei der experimentellen Untersuchung der Reaktionskinetik von Peroxid‐Zerfallsreaktionen besteht in der Induzierbarkeit des Zerfalls durch bereits gebildete Radikale. Dies ist besonders für Hydroperoxide bekannt, wo kettentragende Radikale die Hydroperoxide entweder durch H‐Atom‐ oder HO‐Gruppen‐Abstraktion von der endständigen HOO‐Einheit aktivieren . Dies impliziert, dass besonders die Zerfallskinetik von Hydroperoxiden recht komplex und deren Analyse im Sinne einzelner Elementarschritte durchaus anspruchsvoll ist.…”