Preliminary Investigation On Behaviors Of Asphaltenes Conversion During Thermal Cracking Of Heavy Oils In The Presence Of Hydrogen And Dispersed Catalysts

The quality of petroleum resource is becoming increasingly poor and heavy. Meanwhile, the demand for clean motor fuels is increasing. In this background, slurry hydrocracking technologies have became an important research field of major oil companies for their superiority in treating different quality oil feedstocks and high conversion. As the most difficult fractions contained in heavy oils to convert, asphaltenes, especially the partial converted asphaltenes is a big challenges during upgrading heavy oils. Therefore, the behaviors of asphaltenes conversion have been investigated during thermal cracking of heavy oils in the presence of hydrogen and dispersed catalyst.The conversion of reacted asphaltenes contained in the tail oil stock which is come from the first reactor of slurry hydrocracking of TaHe vacuum residue has been investigated. The results showed that the cracking conversion, removal of asphaltenes, carbon residue and heteroatoms increase with the rising of reaction temperature. A proper amount of dispersed catalysts controls coke formation very well. However, a trend of increasing formation of solids is observed at high catalyst concentrations, indicating asphaltenes not be converted effectively to light product. Asphaltenes from the TaHe vacuum residue feedstock and unconverted asphaltenes have been characterized using FT-ICR MS coupled with APPI+. The results suggest that the relative amount of sulfur families is drastically lowered for it has been removed effectively from the asphaltenes. On the contrary, the relative amount of aromatic structures and nitrogen families are increased. The most condensed aromatic structures remain in the unconverted asphaltenes indicating the polycyclic aromatic structures are the most difficult part of conversion in the asphaltenes. For a deeper understanding of the hydroconversion of polycyclic aromatic hydrocarbons, the reaction of FCC slurry has been investigated under the condition of hydroconversion in the presence of hydrogen and dispersed catalysts. The work clearly shows that the presence of dispersed molybdenite have certain effect to the hydroconversion of polycyclic aromatic hydrocarbons; however, no increasing of conversion is observed at high catalyst concentrations. The rate of hydrogenation increases with the rising of reaction temperature at a certain temperature range. The conversion rate of polycyclic aromatic hydrocarbons is increased while prolonging reaction time at a low temperature, but it is limited by the thermodynamic equilibrium. At a high temperature, there would be more thermal cracking reactions leading to complex system. Under the same reaction conditions, polycyclic aromatic hydrocarbons with different condensation forms exhibit different hydroconversion behaviors, the hydrogenation of Peri-condensed aromatic structures is more difficult than that of cata-condensed aromatic structures.