Thermal cracking of the large molecular alcohols in shale oil by experimental study and kinetic modeling

Abstract

There is an important influence of alcohols in shale oil on its thermochemical properties. In this work, the fractions and species of the alcohols in shale oil from retorting oil shale were studied experimentally. The alcohols exist mainly in the form of linear carbon chains with different lengths, as well as different sites of hydroxyls. Then, 7-tetradecanol and pentadecanol were selected for further exploring the pyrolysis mechanisms through theoretical calculation and kinetic modeling, due to their abundance and representativeness in alcohols of shale oil. Density functional theory (DFT) method was utilized to reveal the difficulty of the thermal cracking of these two alcohols. The results indicated that the dissociation energies of C-C bonds are lower than those of C-H bonds, the reaction of eliminating water has a low activation energy. The Mulliken charges imply that there is a large electrostatic attraction between the O atom and its attached C atom in 7-tetradecanol, but an electrostatic repulsion between them in pentadecanol, which is thought to have an effect on the elimination of water. Finally, the detailed pyrolysis kinetic mechanisms of these two alcohols were written in a systematic manner by the GRI-Mech3.0 mechanism. A large number of the kinetic parameters were computed by the group-additivity method, which are consistent with the thermochemical data calculated by DFT. In summary, this research provides a theoretical basis for development of the kinetic mechanisms of large molecular alcohols and the accurate surrogate shale oil model.