Ivan Antonov, Leonid Sheps 70 th International Symposium on Molecular Spectroscopy CHARACTERIZATION OF REACTION PATHWAYS IN LOW TEMPERATURE OXIDATION OF TETRAHYDROFURAN WITH MULTIPLEXED PHOTOIONIZATION MASS SPECTROMETRY TECHNIQUE

Outline Background on THF: why we study it Generic oxidation mechanism of hydrocarbon fuel Previous studies of THF oxidation Experimental setup and conditions Mass spectra, PIEs, time traces and product assignment Branching fractions of THF oxidation products Discussion of THF oxidation mechanism at low temperature

THF oxidation: why we study Biofuels contain 4- and 5-membered cyclic ethers* Cyclic ethers formed in oxidation of alkanes and alkenes Explosive peroxides are formed in THF over time via chemistry similar to low-temperature oxidation Effects of structure on reactivity – branched vs. linear vs. cyclic, O atom addition etc. ThF → THF *Y. Roman-Leshkov, C. J. Barrett, Z. Y. Liu, and J. A. Dumesic, Nature 447(7147) (2007) 982

Previous studies Experimental studies First studies of THF pyrolysis – 1940s A. LIFSHITZ et al, J. Phys. Chem., 1986 – pyrolysis of THF M. J. MOLERA et al, Int. J. Chem. Kin – Gas-phase oxidation of THF at low temperatures, peroxide formation P. DAGAUT et al, Combust. Sci. and Tech., 1998 – combined shock-tube, JSR and kinetic modeling study T. KASPER et al, Z. Phys. Chem., 2011 – PI/EI-MBMS of laminar THF flame K. MOSHAMMER et al, Combustion and Flame, 2013 – EI-MBMS of laminar 2-M-THF flame Theory J. SIMMIE, J. Phys. Chem. A, 2012 – CBS-QB3, G3, CBS-APNO on THF, 2-M-THF, 2,5-DM-THF with emphasis on radical ring opening mechanism M. VERDICCHIO et al, Proc. Combust. Inst., 2014, CBS-QB3 on pyrolysis of THF

Generic low temperature oxidation mechanism of hydrocarbon fuels R + O 2 ROO QOOH + O 2 OOQOOH alkenecyclic ether - HO 2 - OH - 2OH OQO Ring-opening products O O

What new information can we add? m/z time Experiments: “Sandia Kinetics Machine” Synchrotron-based tunable VUV photoionization mass spectrometry (PIMS) D. Osborn, with C. Taatjes, M. Ahmed, K. Wilson, S. Leone Chemical Dynamics Beamline, LBL’s Advanced Light Source E t- and E-resolved mass spectrum time E 8∙10 12 Cl, 1∙10 17 O 2, 4∙10 14 fuel – LP 7∙10 13 Cl, 3∙10 18 O 2, 7∙10 14 fuel – HP

Integrated mass spectra 70 p-2 p(72) 600 K, 10 torr 600 K, 2 bar a.m.u.

C4H6OC4H6O Identification of products at M = 70: PIE 600 K, 10 torr O O

Identification of products at M = 70: time trace 600 K, 10 torr O O +

Integrated mass spectra p-2p-14 p(72) 600 K, 10 torr 600 K, 2 bar a.m.u.

C3H6OC3H6O Identification of products at M=58: PIE 600 K, 10 torr OH O O ++

Identification of products at M=58: time trace O O K, 10 torr OH O O ++

Integrated mass spectra p+14p-2 p(72) 600 K, 10 torr 600 K, 2 bar a.m.u. 58

Identification of products at M = 86: PIE 600 K, 10 torr O O C4H6O2C4H6O2 O O O O ?

Identification of products at M = 86: time trace O O + C4H6O2C4H6O2 600 K, 10 torr R-dependent

Integrated mass spectra p+30 p+14p-2p-14 p(72) K, 10 torr 600 K, 2 bar a.m.u.

Identification of products at M = 102 and 69: time trace M=102 M= K, 2 bar ms

C4H6O3C4H6O3 Identification of products at M = 102 and 69: PIE O OOH O + + HO 2 + e hνhν 600 K, 2 bar eV M=102 M=69

Product branching at 10 torr O O OH O O 17%1%10%22%36% 550 K 20%1%12%20%36% 600 K 23%0%9%24%55% 650 K M=70M=58

O O OH O O M=70M=58 3%2%3%15%23% 550 K 7%2%5%12%32% 600 K ????? 650 K Product branching at 2 bar

Discussion O O O O O O O OO C 4 H 6 O 2 (M=86) R-R ? +O 2 cyclic OOQOOH O OOH -HO 2 M=102 OH O O M=58 -CO, OH open-chain QOOH +O 2 cyclic QOOH +O 2 ROO -HO 2 O O M=70

Summary THF oxidation at low temperature is studied with MPIMS Primary reaction products and channels are identified Second O 2 addition makes unusual DHF hydroperoxide: pathway observed for the first time Mechanism of M=58 formation is complicated; calculations/isotope substitution experiments are in progress Chain propagation and chain branching pathways should affect ignition behavior

Thank You This work is supported by the Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Basic Energy Sciences, and the U.S. Department of Energy, in part under the Argonne-Sandia Consortium on High-Pressure Combustion Chemistry, (ANL FWP # 59044; SNL FWP # ) Collaborators at Sandia National Lab, Lawrence Berkeley Lab Lenny Sheps, Judit Zádor, Eve Papajak, John D. Savee, David L. Osborn, Craig A. Taatjes Funding: Acknowledgements