Pyrolysis Pathways of the Furanic Ether 2-Methoxyfuran

Journal Article · Tue Sep 15 00:00:00 EDT 2015 · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

DOI:https://doi.org/10.1021/acs.jpca.5b06779· OSTI ID:1501371

Urness, Kimberly N. ^[1]; Guan, Qi ^[1]; Troy, Tyler P. ^[2]; Ahmed, Musahid ^[2]; Daily, John W. ^[1]; Ellison, G. Barney ^[3]; Simmie, John M. ^[4]

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1. Univ. of Colorado, Boulder, CO (United States). Dept. of Mechanical Engineering
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
3. Univ. of Colorado, Boulder, CO (United States). Dept. of of Chemistry and Biochemistry
4. National Univ. of Ireland, Galway (Ireland). Combustion Chemistry Centre, School of Chemistry

Substituted furans, including furanic ethers, derived from nonedible biomass have been proposed as second-generation biofuels. In order to use these molecules as fuels, it is important to understand how they break apart thermally. In this work, a series of experiments were conducted to study the unimolecular and low-pressure bimolecular decomposition mechanisms of the smallest furanic ether, 2-methoxyfuran. Electronic structure (CBS-QB3) calculations indicate this substituted furan has an unusually weak O - CH₃ bond, approximately 190 kJ mol^-1 (45 kcal mol^-1); thus, the primary decomposition pathway is through bond scission resulting in CH₃ and 2-furanyloxy (O - C₄H₃O) radicals. Final products from the ring opening of the furanyloxy radical include 2 CO, HC$$\equiv$$CH, and H. The decomposition of methoxyfuran is studied over a range of concentrations (0.0025-0.1%) in helium or argon in a heated silicon carbide (SiC) microtubular flow reactor (0.66-1 mm i.d., 2.5-3.5 cm long) with reactor wall temperatures from 300 to 1300 K. Inlet pressures to the reactor are 150-1500 Torr, and the gas mixture emerges as a skimmed molecular beam at a pressure of approximately 10 μTorr. Products formed at early pyrolysis times (100 μs) are detected by 118.2 nm (10.487 eV) photoionization mass spectrometry (PIMS), tunable synchrotron VUV PIMS, and matrix infrared absorption spectroscopy. Secondary products resulting from H or CH₃ addition to the parent and reaction with 2-furanyloxy were also observed and include CH₂=CH-CHO, CH₃-CH=CH-CHO, CH₃=CO-CH=CH₂, and furanones; under the conditions in the reactor, we estimate these reactions contribute to at most 1-3% of total methoxyfuran decomposition. This work also includes observation and characterization of an allylic lactone radical, 2-furanyloxy (O-C₄H₃O), with the assignment of several intense vibrational bands in an Ar matrix, an estimate of the ionization threshold, and photoionization efficiency. A pressure-dependent kinetic mechanism is also developed to model the decomposition behavior of methoxyfuran and provide pathways for the minor bimolecular reaction channels that are observed experimentally.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
• Grant/Contract Number: AC02-05CH11231; FG02-93ER14364
• OSTI ID: 1501371
• Journal Information: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. 119, Issue 39; ISSN 1089-5639
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY