DFT Study of Oxidation Reaction Paths for Ethanol Gasoline

A DFT study of oxidation reaction for ethanol molecule and representative conventional molecule in gasoline was performed. At first, the homolytic dissociation energy of the different C-H bond in ethanol and hydrocarbon molecules was calculated and the C-H active sites most likely to be attacked by oxygen molecule were obtained. Then, the reaction barrier of oxidation initiation reaction for different molecules was compared to conclude that the barrier energy of ethanol molecule was lower than the conventional gasoline molecule. It was found that the lower energy gap between the HOMO orbital of ethanol molecule and the LUMO orbital of oxygen molecule was the driving force to the oxidation initiation reaction. In addition, the possible further reaction paths of ethanol free radical after dehydrogenation have also been investigated, which may generate acetaldehyde or acetic acid. The two reaction paths actually existed at the same time, though compared with the acetic acid steps, the reaction path was shorter for generating acetaldehyde. It was indicated that ethanol gasoline is more prone to oxidation than conventional gasoline, which leads to changes in its molecular composition and physical and chemical properties. We should pay attention to the oxidation stability of ethanol gasoline during its storage and use.