Experimental and kinetic modeling investigation on methyl decanoate pyrolysis at low and atmospheric pressures

Abstract

The pyrolysis of methyl decanoate (MD), an ideal surrogate of biodiesels, was investigated in a flow reactor at the pressures of 30 and 760 Torr and the temperature ranging from 773 to 1198 K. A great variety of pyrolysis products including free radicals, n-alkanes, 1-alkenes, alkynes, unsaturated esters and aromatics were comprehensively observed and identified by employing synchrotron vacuum ultraviolet photoionization mass spectrometry. A new kinetic model for MD pyrolysis was constructed and applied to validate the experimental data. Modeling analyses involving rate of production analysis and sensitivity analysis were performed to help explore the pyrolysis kinetics of MD and the formation mechanisms of key species. The analysis results show that the decomposition of MD is determined by the H-abstraction and unimolecular dissociation reactions during the whole pyrolysis process, whereas the contributions of H-abstraction reactions are enhanced as the pressure elevates. C4-C9 unsaturated esters are principally yielded from the β-scission of ester radicals; while the β-scission reactions of MD radicals are responsible for the formation of C5-C9 1-alkenes. In addition, 1-alkenes can be further decomposed to form small radicals and molecules. Through the combination reactions such as the reaction routes of C3 + C3, C4 + C2 and C5 + C2, these radicals and molecules can be transformed into benzene and benzyl radical, which are demonstrated as the crucial precursors of polycyclic aromatic hydrocarbons. In conclusion, the pyrolysis of MD would not only significantly enhance the cognitions of various pollutant formation mechanisms but also have a guiding significance for the combustion in the fuel-cooled engine.