Computational Kinetic Study for the Unimolecular Decomposition Pathways of Cyclohexanone

There has been evidence lately that several endophytic fungi can convert lignocellulosic biomass into ketones among other oxygenated compounds. Such compounds could prove useful as biofuels for internal combustion engines. Therefore, their combustion properties are of high interest. Cyclohexanone was identified as an interesting second-generation biofuel (Boot, M.; et al. Cyclic Oxygenates: A New Class of Second-Generation Biofuels for Diesel Engines? Energy Fuels 2009, 23, 1808−1817; Klein-Douwel, R. J. H.; et al. Soot and Chemiluminescence in Diesel Combustion of Bio-Derived, Oxygenated and Reference Fuels. Proc. Combust. Inst. 2009, 32, 2817–2825). However, until recently (Serinyel, Z.; et al. Kinetics of Oxidation of Cyclohexanone in a Jet- Stirred Reactor: Experimental and Modeling. Proc. Combust. Inst. 2014; DOI: 10.1016/j.proci.2014.06.150), no previous studies on the kinetics of oxidation of that fuel could be found in the literature. In this work, we present the first theoretical kinetic study of the unimolecular decomposition pathways of cyclohexanone, a cyclic ketone that could demonstrate important fuel potential. Using the quantum composite G3B3 method, we identified six different decomposition pathways for cyclohexanone and computed the corresponding rate constants. The rate constants were calculated using the G3B3 method coupled with Rice–Ramsperger–Kassel–Marcus theory in the temperature range of 800–2000 K. Our calculations show that the kinetically more favorable channel for thermal decomposition is pathway 2 that produces 1,3-butadien-2-ol, which in turn can isomerize easily to methyl vinyl ketone through a small barrier. The results presented here can be used in a future kinetic combustion mechanism

A Chemical Kinetic Investigation on Butyl Formate Oxidation: Ab Initio Calculations and Experiments in a Jet-Stirred Reactor

Biofuels are expected to play a significant role in the quest for greener energy generation. In this perspective, esters produced from biomass are promising candidates. This work presents the first computational kinetic study on n-butyl formate (BF) oxidation under combustion conditions coupled to an experimental study in a jet-stirred reactor. Absolute rate constants for hydrogen abstraction reactions by the OH radical were calculated using the G3//MP2/aug-cc-pVDZ model chemistry, in conjunction with statistical rate theory (TST). Subsequently, the fate of the butyl formate radicals was also investigated by calculating absolute rate constants for combustion relevant decomposition channels such as β-scission and hydrogen transfer reactions. The derived rate expressions were used in the presently developed detailed kinetic mechanism, which was validated over experimental data obtained in a jet-stirred reactor at 10 atm and for three different mixtures (φ = 0.45, 0.9, and 1.8). Rate of production analyses were finally used to understand the oxidation kinetics of butyl formate over the temperature range of 500–1300 K and highlighted the importance of the unimolecular decomposition reactions of the fuel, producing formic acid and 1-butene

Mineral Oxides Change the Atmospheric Reactivity of Soot: NO₂ Uptake under Dark and UV Irradiation Conditions

The heterogeneous reactions between trace gases and aerosol surfaces have been widely studied over the past decades, revealing the crucial role of these reactions in atmospheric chemistry. However, existing knowledge on the reactivity of mixed aerosols is limited, even though they have been observed in field measurements. In the current study, the heterogeneous interaction of NO₂ with solid surfaces of Al₂O₃ covered with kerosene soot was investigated under dark conditions and in the presence of UV light. Experiments were performed at 293 K using a low-pressure flow-tube reactor coupled with a quadrupole mass spectrometer. The steady-state uptake coefficient, γ_ss, and the distribution of the gas-phase products were determined as functions of the Al₂O₃ mass; soot mass; NO₂ concentration, varied in the range of (0.2–10) × 10¹² molecules cm^–3; photon flux; and relative humidity, ranging from 0.0032% to 32%. On Al₂O₃/soot surfaces, the reaction rate was substantially increased, and the formation of HONO was favored compared with that on individual pure soot and pure Al₂O₃ surfaces. Uptake of NO₂ was enhanced in the presence of H₂O under both dark and UV irradiation conditions, and the following empirical expressions were obtained: γ_ss,BET,dark = (7.3 ± 0.9) × 10^–7 + (3.2 ± 0.5) × 10^–8 × RH and γ_ss,BET,UV = (1.4 ± 0.2) × 10^–6 + (4.0 ± 0.9) × 10^–8 × RH. Specific experiments, with solid sample preheating and doping with polycyclic aromatic hydrocarbons (PAHs), showed that UV-absorbing organic compounds significantly affect the chemical reactivity of the mixed mineral/soot surfaces. A mechanistic scheme is proposed, in which Al₂O₃ can either collect electrons, initiating a sequence of redox reactions, or prevent the charge-recombination process, extending the lifetime of the excited state and enhancing the reactivity of the organics. Finally, the atmospheric implications of the observed results are briefly discussed

A Chemical Kinetic Investigation on Butyl Formate Oxidation: <i>Ab Initio</i> Calculations and Experiments in a Jet-Stirred Reactor

Biofuels are expected to play a significant role in the quest for greener energy generation. In this perspective, esters produced from biomass are promising candidates. This work presents the first computational kinetic study on <i>n</i>-butyl formate (BF) oxidation under combustion conditions coupled to an experimental study in a jet-stirred reactor. Absolute rate constants for hydrogen abstraction reactions by the OH radical were calculated using the G3//MP2/aug-cc-pVDZ model chemistry, in conjunction with statistical rate theory (TST). Subsequently, the fate of the butyl formate radicals was also investigated by calculating absolute rate constants for combustion relevant decomposition channels such as β-scission and hydrogen transfer reactions. The derived rate expressions were used in the presently developed detailed kinetic mechanism, which was validated over experimental data obtained in a jet-stirred reactor at 10 atm and for three different mixtures (φ = 0.45, 0.9, and 1.8). Rate of production analyses were finally used to understand the oxidation kinetics of butyl formate over the temperature range of 500–1300 K and highlighted the importance of the unimolecular decomposition reactions of the fuel, producing formic acid and 1-butene

A Chemical Kinetic Investigation on Butyl Formate Oxidation: <i>Ab Initio</i> Calculations and Experiments in a Jet-Stirred Reactor

Biofuels are expected to play a significant role in the quest for greener energy generation. In this perspective, esters produced from biomass are promising candidates. This work presents the first computational kinetic study on <i>n</i>-butyl formate (BF) oxidation under combustion conditions coupled to an experimental study in a jet-stirred reactor. Absolute rate constants for hydrogen abstraction reactions by the OH radical were calculated using the G3//MP2/aug-cc-pVDZ model chemistry, in conjunction with statistical rate theory (TST). Subsequently, the fate of the butyl formate radicals was also investigated by calculating absolute rate constants for combustion relevant decomposition channels such as β-scission and hydrogen transfer reactions. The derived rate expressions were used in the presently developed detailed kinetic mechanism, which was validated over experimental data obtained in a jet-stirred reactor at 10 atm and for three different mixtures (φ = 0.45, 0.9, and 1.8). Rate of production analyses were finally used to understand the oxidation kinetics of butyl formate over the temperature range of 500–1300 K and highlighted the importance of the unimolecular decomposition reactions of the fuel, producing formic acid and 1-butene

A Chemical Kinetic Investigation on Butyl Formate Oxidation: <i>Ab Initio</i> Calculations and Experiments in a Jet-Stirred Reactor

Biofuels are expected to play a significant role in the quest for greener energy generation. In this perspective, esters produced from biomass are promising candidates. This work presents the first computational kinetic study on <i>n</i>-butyl formate (BF) oxidation under combustion conditions coupled to an experimental study in a jet-stirred reactor. Absolute rate constants for hydrogen abstraction reactions by the OH radical were calculated using the G3//MP2/aug-cc-pVDZ model chemistry, in conjunction with statistical rate theory (TST). Subsequently, the fate of the butyl formate radicals was also investigated by calculating absolute rate constants for combustion relevant decomposition channels such as β-scission and hydrogen transfer reactions. The derived rate expressions were used in the presently developed detailed kinetic mechanism, which was validated over experimental data obtained in a jet-stirred reactor at 10 atm and for three different mixtures (φ = 0.45, 0.9, and 1.8). Rate of production analyses were finally used to understand the oxidation kinetics of butyl formate over the temperature range of 500–1300 K and highlighted the importance of the unimolecular decomposition reactions of the fuel, producing formic acid and 1-butene