title: Low-temperature combustion chemistry of biofuels: pathways in the initial low-temperature (550 K-750 K) oxidation chemistry of isopentanol.
abstract: The branched C(5) alcohol isopentanol (3-methylbutan-1-ol) has shown promise as a potential biofuel both because of new advanced biochemical routes for its production and because of its combustion characteristics, in particular as a fuel for homogeneous-charge compression ignition (HCCI) or related strategies. In the present work, the fundamental autoignition chemistry of isopentanol is investigated by using the technique of pulsed-photolytic Cl-initiated oxidation and by analyzing the reacting mixture by time-resolved tunable synchrotron photoionization mass spectrometry in low-pressure (8 Torr) experiments in the 550-750 K temperature range. The mass-spectrometric experiments reveal a rich chemistry for the initial steps of isopentanol oxidation and give new insight into the low-temperature oxidation mechanism of medium-chain alcohols. Formation of isopentanal (3-methylbutanal) and unsaturated alcohols (including enols) associated with HO(2) production was observed. Cyclic ether channels are not observed, although such channels dominate OH formation in alkane oxidation. Rather, products are observed that correspond to formation of OH viaβ-C-C bond fission pathways of QOOH species derived from β- and γ-hydroxyisopentylperoxy (RO(2)) radicals. In these pathways, internal hydrogen abstraction in the RO(2)⇄ QOOH isomerization reaction takes place from either the -OH group or the C-H bond in α-position to the -OH group. These pathways should be broadly characteristic for longer-chain alcohol oxidation. Isomer-resolved branching ratios are deduced, showing evolution of the main products from 550 to 750 K, which can be qualitatively explained by the dominance of RO(2) chemistry at lower temperature and hydroxyisopentyl decomposition at higher temperature.
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, California 94551-0969, USA. onwelz@sandia.gov
authors.forename: Oliver
authors.initials: O
authors.lastname: Welz
authors.forename: Judit
authors.initials: J
authors.lastname: Zádor
authors.forename: John D
authors.initials: JD
authors.lastname: Savee
authors.forename: Martin Y
authors.initials: MY
authors.lastname: Ng
authors.forename: Giovanni
authors.initials: G
authors.lastname: Meloni
authors.forename: Ravi X
authors.initials: RX
authors.lastname: Fernandes
authors.forename: Leonid
authors.initials: L
authors.lastname: Sheps
authors.forename: Blake A
authors.initials: BA
authors.lastname: Simmons
authors.forename: Taek Soon
authors.initials: TS
authors.lastname: Lee
authors.forename: David L
authors.initials: DL
authors.lastname: Osborn
authors.forename: Craig A
authors.initials: CA
authors.lastname: Taatjes
mesh_terms: D056804:Biofuels; D017665:Hydroxyl Radical / Q000737:chemistry; D007536:Isomerism; D010084:Oxidation-Reduction; D000439:Pentanols / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry; D013696:Temperature
chemical_list: D056804:Biofuels; D000439:Pentanols; D010545:Peroxides; C049375:perhydroxyl radical; D017665:Hydroxyl Radical; C029683:isopentyl alcohol