Kinetics and phase behavior in asphaltene cracking

The formation of coke from reacting asphaltenes is significantly affected by both reactions with the liquid components and the solvent properties of the liquid medium. Both the kinetics and phase behavior in the cracking of asphaltenes were studied in this thesis. The kinetics of solvent interactions with asphaltenes were studied by reacting Athabasca asphaltenes in a closed batch reactor at 430°C. Reactions of asphaltene in maltene at different concentrations and reactions in a series of aromatic solvents (1-methyl naphthalene, naphthalene and tetralin) were used to investigate the role of solvent properties and hydrogen donation reactions. The most important characteristics of the liquid phase were hydrogen donating ability and the ability to initiate cracking reactions. The latter mechanism was confirmed by adding n-dodecyl sulfide as an initiator compound. A modified kinetic model for coke formation, incorporating phase separation and hydrogen transfer to the asphaltenes, was consistent with the experimental results over a range of asphaltene concentrations and solvent conditions.;Coking kinetics as a function of asphaltenes structure were also examined by reacting several different asphaltenes from around the world in 1-methyl naphthalene and tetralin. The selected asphaltenes were Athabasca asphaltenes from Canada, Arabian Light and Arabian Heavy from Saudi Arabia, Maya from Mexico and Gudao from China. The data from the cracking reactions could be fitted to the modified phase separation model. The two fitting parameters for the thermolysis in 1-methyl naphthalene were found to correlate with two structural properties of the asphaltenes. Consequently, the model can be used for the prediction of coke formation in 1-methyl naphthalene from the structural properties of asphaltenes.;Phase behavior during coke formation was investigated by examining the coke produced from selected reactions under scanning electron microscopy (SEM). Asphaltenic material from Athabasca bitumen, with and without fine solids, was reacted in liquid phase mixed with either 1-methyl naphthalene or maltene fractions from Athabasca. Both fine solids and solvents were found to help the dispersion of coke spheres. Phase inversion was observed in some sections of coke produced from pure asphaltene. The thermodynamic feasibility of phase inversion was confirmed by calculating the entropy difference for a set of representative conditions.