The influences of compositional and structural evolutions of asphaltenes on coking behavior during slurry-bed hydrocracking

Asphaltenes is the most complex components in the slurry-bed hydrocracking reaction system, and affects the coke formations significantly. In order to studied the influences of compositional and structural evolutions of asphaltenes on coking behavior, Slurry-bed hydrocracking of Xinjiang residue in the presence of oil soluble Mo/Ni catalyst was carried out in an autoclave at 435 ? under initial hydrogen pressure of 7 MPa for various reaction times. The dynamic changes of asphaltenes were investigated by element analysis, vapor pressure osmometry (VPO), H-1 NMR, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-Ray diffraction (XRD) and the dynamic changes of coke were investigated by microscope, SEM and XRD. The results showed that the yield, molecular weight (MW), condensation degree and the number of aromatic layers of asphaltenes increased, while the slice spacing (d(m)) decreased rapidly before reaction time of 20 min. The yield, MW, H-AU/C-A and d(m) of asphaltenes all reached an extreme value of 5.86%, 2502, 0.19 and 0.3465 nm when the reaction time was 20 min, and then the yield and MW decreased to 4.01%, 1689 while the H-AU/C-A and d(m) increased to 0.29, 0.3500 nm when the reaction time was 60 min, respectively. The asphaltenes were easily formed and condensed significantly into large aromatic compounds which seem to be the precursor of coke in the hydrocracking. A little amount of small sized coke particles appeared at the beginning of the reaction. But the yield and size of coke particles increased rapidly after reaction time of 20 min. Besides, the correlation between the evolutions of asphaltenes and coking behavior was proposed for slurry-bed hydrocracking of residue in the presence of oil soluble catalyst.