Experimental and kinetic modeling study of n-pentane oxidation at 10 atm, Detection of complex low-temperature products by Q-Exactive Orbitrap

Renewable feedstock such as biomass derivatives (hemicellulose, furfural) can be used to produce synthetic fuels, e.g., n-pentane, of interest for enhancing performance of diesel and gasoline engines. Whereas numerous studies of n-pentane have been published, its low temperature oxidation is not fully characterized and even recent kinetic models do not incorporate extended oxidation pathways which still need to be observed for n-pentane. In this context, a continuous flow fused-silica jet-stirred reactor (JSR) was used for studying the oxidation of 2500 ppm of n-pentane at 520-800 K, 10 atm (representative of piston engines operating conditions), an equivalence ratio of 0.5, and a residence time of 1.5 s. Oxidation products were analyzed in the gas phase using gas chromatography (thermal conductivity, TCD and flame ionization, FID), Fourier-transform infrared spectrometry (FTIR), and electron impact ionization-quadrupole mass spectrometry (EI-qMS). Gaseous products were also dissolved in acetonitrile for characterization using flow injection analysis (FIA), high-pressure and ultra-high-pressure liquid chromatography (HPLC and UHPLC) coupled to atmospheric pressure chemical ionization (APCI) and Q-Exactive (R)-Orbitrap high resolution mass spectrometry (HRMS). This allowed detecting lower and higher mass oxygenated molecules such as methyl vinyl ketone (MVK) and 2,5-dihydrofuran (C4H6O), 2-butanone (C4H8O), 3-pentene-2-one (C5H8O), pentanediones (C5H8O2), cyclic ethers and pentanones (C5H10O), C-3-C-5 alkylhydroperoxides (C3H8O2, C4H10O2, C5H12O2), C-2-C-5 alkenylhydroperoxides (C2H4O2, C3H6O2, C4H8O2, C5H10O2), C-3-C-5 keto-hydroperoxides (C3H6O3, C4H8O3, C5H10O3), and highly oxygenated molecules (C5H8O4, C5H12O4, C5H10O4, C5H10O5, C5H10O7) produced through multiply O 2 addition on fuel's radicals and internal H-shifts. Among these products 15 had not been reported before. Simulation of the present experiments showed discrepancies between experimental results and predictions. (C) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigated the low temperature oxidation of n-pentane using experimental and simulation methods, revealing new oxidation products. Discrepancies were found between experimental results and predictions, suggesting the need for further research.