Coking Kinetics of Asphaltenes as a Function of Chemical Structure

The dependence of coking kinetics on the chemical structure of asphaltenes was examined by reacting five different asphaltenes in 1-methylnaphthalene and tetralin at 430 °C and ca. 9.8 MPa. The selected heptane-insoluble asphaltenes were Athabasca asphaltenes from Canada, Arabian Light and Arabian Heavy from Saudi Arabia, Maya from Mexico, and Gudao from China. The 13 C NMR aromaticity of the asphaltenes ranged from 0.40 to 0.61, and the sulfur contents ranged from 4.44 wt % to 7.47 wt %. The cracking kinetics of the asphaltenes were consistent with a modified kinetic model for coke formation, incorporating phase separation and hydrogen transfer to the asphaltenes. The rate of cracking of asphaltenes in 1-methylnaphthalene correlated with the content of aliphatic sulfur, and the yield coefficient for coke correlated with the aromaticity. These correlations allowed prediction of coking kinetics for Iranian Light and Khafji asphaltenes on the basis of average structural properties of asphaltenes. Hydrogen transfer to the different asphaltenes did not correlate with any single average structural property.