A mass spectrometric study of gasoline anti-knocking additives - Part I: Electron impact ionization and fragmentation processes of MTBE

Methyl tert-butyl ether (MTBE) is the most widely used additive for gasoline as it is able to increase the oxygen content and to improve the efficiency in the internal combustion engine, controlling the autoignition. Most of the experimental studies performed on MTBE give information only on neutral particle reaction schemes, preventing a complete understanding of the oxidation and pyrolisis reaction chemistry of MTBE in extreme conditions like for example those experienced in the reactions involved in a knocking engine during the spark ignition. In the Part I of this work electron impact ionisation of MTBE has been studied in the range 25-150 eV by means of a time of flight mass spectrometry (TOF-MS). Total ionisation cross-section for MTBE and for all the ions formed from its fragmentation are evaluated relatively to Argon cross-section. What is learned by studying processes which can be understandable within a mass spectrometer can be applied to larger more applied systems, where the extreme conditions prevent an experimental study of the ion chemistry. In the present study the MTBE cross-sections trends and the isotopic study of deuterated MTBE (MTBE-d(3)) mass spectrum allowed to suggest reaction pathways for MTBE fragmentation. This work will be extended to other two ether molecules, ETBE and TAME, that have been proposed in place of MTBE and the results will be described in the Part II of this paper. (C) 2006 Elsevier B.V. All rights reserved.