Comparative Study on the H-Abstraction Reactions of Isopropyl Acetate and Propyl Acetate by HO2 and OH Radicals.

Isopropyl acetate (IPA) and propyl acetate (PA) are recognized as promising biofuels suitable for applications as fuel additives and biodiesel models. The H-abstraction reactions with radicals stand out as the fundamental initiating reactions in the combustion kinetic models for IPA and PA. In the present work, the kinetic calculations of IPA and PA plus HO2 and OH radicals were investigated at M06-2X/cc-pVTZ//G4, M08-HX/maug-cc-pVTZ, and CCSD(T)/jul-cc-pVTZ levels. The thermodynamic calculations were obtained based on the G4 and CBS-APNO methods. Rate coefficients were calculated using both transition state theory and canonical variational transition state theory with tunneling correction at the temperature range of 250-2000 K. The total rate constants for the IPA + OH system were fitted as follows: k = 0.4674 × T3.927 exp(2128/T) (cm3 mol-1 s-1), and for the PA + OH system, the total rate constants were determined using the following equation: k = 0.0161 × T4.373 exp(2220/T) (cm3 mol-1 s-1). The rate coefficients of IPA + OH reactions determined based on the M08-HX/maug-cc-pVTZ level effectively replicate the experimental data, while H-abstraction rate coefficients of PA + OH by the CCSD(T)/jul-cc-pVTZ method accurately reproduce the experimental data. Refining the H-abstraction rate coefficients in the kinetic mechanism of PA, as proposed by Dayma et al. [Proc. Combust. Inst. 37 (2019) 429-436], has been achieved through incorporating the present calculated data, leading to the development of a revised mechanism. The validation of the updated mechanism against jet-stirred reactor data is presented, showcasing its effective performance in predicting JSR data.

Thermochemical and Kinetic Investigation of Pentanol Oxidation Initiated by Hydrogen, Methyl, Hydroxyl, and Hydroperoxyl Radicals.

n-Pentanol is acknowledged as a prospective alternative and a supplement to traditional fossil fuels. H-abstraction reaction assumes a pivotal role in initiating the chain reaction during n-pentanol combustion. To investigate the oxidation characteristics of n-pentanol, the composite quantum chemical methods CBS-QB3 and G4 are employed to obtain thermochemical and kinetic parameters in the H-abstraction reaction of n-pentanol. The calculated isobaric heat capacity provides accurate predictions of the experimental results. Branching ratios underscore that H-abstraction at the Cα site serves as the primary channel between n-pentanol and H/CH3/È®H2. For the reaction between n-pentanol and È®H, the Cß site emerges as the most favorable channel due to the significant variational effect. The overall rate coefficient for H-abstraction from n-pentanol by È®H radicals is expressed as k = 3565.11 × T2.93 exp (1465.44/T) (cm3 mol-1 s-1), and the data obtained at the CBS-QB3 level demonstrate good agreement with experimental observations. Furthermore, the original model is modified based on current results, and the improved model demonstrates superior predictive capabilities for jet-stirred reactor (JSR) data and ignition delay times. Reaction path and sensitivity analyses are employed to identify fuel consumption pathways and critical reactions in the combustion of n-pentanol.

Hydrogen evolution reaction of Ben + H2O (n = 5-9) based on density functional theory.

The structural evolution of Ben clusters with n = 5-9, the adsorption energy created by the Ben@H2O (n = 5-9) complex, and the mechanism of the hydrogen evolution reaction of Ben + H2O (n = 5-9) were all studied using DFT calculations based on the PBE0-D3/Def2TZVP level. Excluding the Be7 cluster, the global minimum structures of beryllium clusters with n = 5-9 showed a higher point group pair formation. Be7 clusters' high point group symmetry is unstable. Be9@H2O released the greatest energy during the complex's creation (-1.45 eV). Exothermic hydrogen evolution occurs in Ben + H2O (n = 5-9), and all transition states, intermediate stages, and products have energies lower than the equilibrium constant (EC). More energy is released when an O-H bond in the Ben@H2O (n = 5-9) complex is broken, and the energy release results in a change in the cluster structure, which is more pronounced in the Be7 + H2O reaction. Interestingly, there are eight transition states in the Be6 + H2O hydrogen evolution reaction, with the second O-H bond break requiring more energy than the first. There are only three transition states in the Be8 + H2O hydrogen evolution reaction, and the reaction energy is the greatest (-4.13 eV).