New experimental evidences about the formation and consumption of ketohydroperoxides

doi:10.1016/j.proci.2010.05.001

Proceedings of the Combustion Institute

Volume 33, Issue 1, 2011, Pages 325-331

https://doi.org/10.1016/j.proci.2010.05.001 Get rights and content

Abstract

The formation of hydroperoxides postulated in all the kinetic models for the low temperature oxidation of alkanes have been experimentally proved thanks to a new type of apparatus associating a quartz jet-stirred reactor through a molecular-beam sampling system to a reflectron time-of-flight mass spectrometer combined with tunable synchrotron vacuum ultraviolet photoionization. This apparatus has been used to investigate the low-temperature oxidation of n-butane and has allowed demonstrating the formation of different types of alkylhydroperoxides, namely methylhydroperoxide, ethylhydroperoxide and butylhydroperoxide, and of C₄ alkylhydroperoxides including a carbonyl function (ketohydroperoxides). In addition, the formation of products deriving from these ketohydroperoxides, such as C₄ molecules including either two carbonyl groups or one carbonyl and one alcohol functions, has been observed. Simulations using a detailed kinetic model have been performed to support some of the assumptions made in this work.

Introduction

Tunable synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry combined with molecular-beam sampling has been proved to be a successful method to probe in many types of laboratory combustion systems [1]. While this system has been often coupled to laminar premixed (e.g. to demonstrate the presence of enols in flames [2]) and co-flow flames, flow reactors used to study pyrolysis, plasmas discharge and low-pressure catalytic oxidation apparatuses [1], it has never been used to investigate the low-temperature oxidation of organic compounds. As jet-stirred reactors (JSR) have already been used with success to study the formation of a wide range of products during the low-temperature oxidation of organic compounds (e.g. [3], [4]), the purpose of this paper is to investigate if interesting new results on the low-temperature oxidation of n-butane can arise from the coupling of a JSR through a molecular-beam sampling system to a reflectron time-of-flight (RTOF) mass spectrometer combined with SVUV photoionization. n-Butane has been chosen because it is the smallest alkane which has a low-temperature oxidation chemistry representative of that of the larger ones present in gasoline and diesel fuels. Apart from work performed in static reactors in the 70’s [5] and in a rapid compression machine [6] to follow ignition and cool flame delay times, the low-temperature oxidation of n-butane has not been much investigated.

Section snippets

Experimental facility

As shown in Fig. 1, the apparatus associated a JSR through a molecular-beam sampling system to a RTOF mass spectrometer combined with SVUV photoionization. The experiments were performed at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. This part describes in more detail the jet-stirred reactor, the molecular-beam sampling and photoionization mass spectrometry. The gases used in this study were provided by Dalian Guangming Special Gas Products (purity of +99%). Gas flows

Experimental and simulation results

This apparatus described above was used to study of the oxidation of n-butane between 580 and 720 K, under quasi-atmospheric pressure (1.05 atm), at a mean residence time of 6s and for a stoichiometric n-butane/oxygen/argon mixture (composition = 4/26/70 in mol%). The ratio of inert gas was set slightly below the ratio in air to obtain the largest amounts of products without the occurrence of strong thermal phenomena.

Simulations have been made using a mechanism for the low-temperature oxidation of n

Conclusion

Using a new system coupling a jet-stirred reactor to molecular beam mass spectrometry combined with tunable synchrotron vacuum ultraviolet photoionization, the hydroperoxides responsible for the auto-ignition of n-butane have been identified:

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Methylhydroperoxide,
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Ethylhydroperoxide,
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Butylhydroperoxides,
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Butylhydroperoxides including a carbonyl group (ketohydroperoxides).

Supporting the identification of ketohydroperoxides, the formation of deriving species, C₄ molecules including either two carbonyl

Acknowledgements

This work was supported by European Commission (“Clean ICE” ERC Advanced Research Grant), Région Lorraine, Chinese Academy of Sciences, Natural Science Foundation of China (50925623), and Ministry of Science and Technology of China (Grant Nos. 2007DFA61310 and 2007CB815204). The authors gratefully acknowledge Dr. Paul Winter, Prof. Timothy Zwier, and Mr. Jaime Stearns in Purdue University for supplying the computer program used to evaluate the Franck–Condon factors. We thank Prof. J.F. Pauwels

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Citation Excerpt :
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New experimental evidences about the formation and consumption of ketohydroperoxides

Abstract

Introduction

Section snippets

Experimental facility

Experimental and simulation results

Conclusion

Acknowledgements

Combust. Flame

Combust. Flame

Combust. Flame

Chem. Phys. Lett.

Combust. Flame

Combust. Flame

Acc. Chem. Res.

Science

Hydrocarbons

Combust. Flame