Thermal Decomposition of Potential Ester Biofuels. Part I: Methyl Acetate and Methyl Butanoate.
J Phys Chem A
; 121(24): 4658-4677, 2017 Jun 22.
Article
en En
| MEDLINE
| ID: mdl-28517940
ABSTRACT
Two methyl esters were examined as models for the pyrolysis of biofuels. Dilute samples (0.06-0.13%) of methyl acetate (CH3COOCH3) and methyl butanoate (CH3CH2CH2COOCH3) were entrained in (He, Ar) carrier gas and decomposed in a set of flash-pyrolysis microreactors. The pyrolysis products resulting from the methyl esters were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures in the pulsed microreactor were about 20 Torr and residence times through the reactors were roughly 25-150 µs. Reactor temperatures of 300-1600 K were explored. Decomposition of CH3COOCH3 commences at 1000 K, and the initial products are (CH2âCâO and CH3OH). As the microreactor is heated to 1300 K, a mixture of CH2âCâO and CH3OH, CH3, CH2âO, H, CO, and CO2 appears. The thermal cracking of CH3CH2CH2COOCH3 begins at 800 K with the formation of CH3CH2CHâCâO and CH3OH. By 1300 K, the pyrolysis of methyl butanoate yields a complex mixture of CH3CH2CHâCâO, CH3OH, CH3, CH2âO, CO, CO2, CH3CHâCH2, CH2CHCH2, CH2âCâCH2, HCCCH2, CH2âCâCâO, CH2âCH2, HC≡CH, and CH2âCâO. On the basis of the results from the thermal cracking of methyl acetate and methyl butanoate, we predict several important decomposition channels for the pyrolysis of fatty acid methyl esters, R-CH2-COOCH3. The lowest-energy fragmentation will be a 4-center elimination of methanol to form the ketene RCHâCâO. At higher temperatures, concerted fragmentation to radicals will ensue to produce a mixture of species (RCH2 + CO2 + CH3) and (RCH2 + CO + CH2âO + H). Thermal cracking of the ß C-C bond of the methyl ester will generate the radicals (R and H) as well as CH2âCâO + CH2âO. The thermochemistry of methyl acetate and its fragmentation products were obtained via the Active Thermochemical Tables (ATcT) approach, resulting in ΔfH298(CH3COOCH3) = -98.7 ± 0.2 kcal mol-1, ΔfH298(CH3CO2) = -45.7 ± 0.3 kcal mol-1, and ΔfH298(COOCH3) = -38.3 ± 0.4 kcal mol-1.
Texto completo:
1
Colección:
01-internacional
Banco de datos:
MEDLINE
Tipo de estudio:
Prognostic_studies
Idioma:
En
Revista:
J Phys Chem A
Asunto de la revista:
QUIMICA
Año:
2017
Tipo del documento:
Article