Studies On Radical Reaction Mechanism And Properties Of Some Main Components In Diesel Oil

Theoretical studies with density functional theory (DFT) method were performed on the structures and properties of a series of alkanes in diesel oil, as well as on the mechanism of hydrogen transfer reactions in the combustion process.In the first section, computations were performed on a series of main component alkanes in diesel oil, using B3LYP, MPWB95, B3P86 and B1B95 functionals with 6-311++G** and 6-31+G** basis sets. The bond dissociation energies (BDE) of the n-alkanes that contain even carbon atoms number is larger than the adjacent n-alkanes that contain odd number of carbon atoms. The energy gaps (△Egap) between the frontier orbitals reduce slightly with the carbon number increasing. For alkanes with the same number of carbon atoms, the energy gaps between the frontier orbits△Egap decrease slightly when the alkanes become more branched. Last, from the heat of formation of lower alkanes, a linear regression equation for the relationship between△fH value and carbon number was established as:△fHmolecular=-21.08×n-31.32. This equation was proved to be valid for higher n-alkanes.In the second section, calculations were performed for a series of the typical cetane number improver using B3LYP functionals with 6-311++G** basis set. The BDE values of alkyl nitrates, peroxides, aldehydes, ketones and aromatic nitro compounds were obtained. And the calculated results show that the BDE of nitrobenzene and nitronaphthalene is larger than those of alkyl nitrates, peroxides, aldehydes and ketones. This indicates that nitrobenzene and nitronaphthalene is not as good as the latters in improving the cetane number (CN). In general, the less branched alkanes have better effect of improving CN value. And the more the number of-NO2 in nitrates, the better the effect of improvement for cetane number improver.In the third section, density functional theory (DFT) calculations were performed to study the mechanism for the intramolecular hydrogen transfer (IHT) reaction of 1-methylbutly peroxide radical. The B3LYP method was used in conjunction with 6-31+G**, 6-311++G** and aug-cc-pVDZ basis sets. The geometries of reactant, products and transition states are initially optimized. Frequency calculations were performed at the same level to verify that the transition states (with one and only one imaginary frequency) are saddle point on its potential energy surface. Intrinsic reaction coordinate (IRC) calculations were performed at the B3LYP/6-31+G**, B3LYP/6-311++G**and B3LYP/aug-cc-pVDZ levels to confirm that the transition state connects the designated intermediates. The activation energies for the IHT reactions ofβ-,γ-andα-H migrations are 90.0,100.8, and 140-152 kJ/mol at the B3LYP/6-311++G** level, respectively. The methyl substituent on (3-position slightly lowers the activation energy, which is in good agreement with the experimental fact. The|3-H transferring is the most favorable process in view of both thermodynamics and kinetics.In the fourth section, density functional theory calculations were performed for the intermolecular hydrogen transfer reaction between 1-methylbutly peroxide radical and H2O. The geometries of reactant, transition states and products are initially optimized at the B3LYP/6-311++G**. Frequency calculations were performed at the same level to verify that the transition states (with one and only one imaginary frequency) are saddle point on its potential energy surface. Intrinsic reaction coordinate (IRC) calculations were performed at the B3LYP/6-311++G** level to confirm that the transition state connects the designated intermediates or products. The activation energies for the intermolecular hydrogen transfer reactions ofα-CH2-,β-CH2-,α-CH3 and y-CH3 migrations, with water as a catalyst, are 112.50,107.88,119.80 and 121.82 kJ/mol, respectively. The activation energy ofβ-CH2-is the smallest, which is in good agreement with the experimental fact. Theβ-H transferring is also the most favorable process when water takes part in the reaction as a catalyst. In addition, the IHT ofα-CH2 andα-CH3 become easier in the existence of water.