Effect Of Asphaltene Dispersants On Coke Formation And Its Mechanism During Residue Thermal Reaction

In order to improve the coking and fouling condition in the reactor during residue upgrading, the effects of asphaltene dispersants on coke formation and reactor wall fouling during residue thermal reaction were investigated in an autoclave; these resiudes included Karamay residue oil (KLAR) , Lungu atmospheric residue oil (LGAR) and Liaohe atmospheric residue oil (LHAR) . The mechanisms of dispersants'effects were elucidated through X-ray photoelectron spectroscopy (XPS) analysis, UV-Vis spectroscopy analysis, FT-IR analysis and the measurement of electric conductivity and viscosity.The results of UV-vis analysis showed that asphaltene dispersants were effective on asphaltene stability until their concentration exceeds a certain concentration. AD1 was the most effective on LHAR and LGAR asphaltene stability among the dispersants studied; and the effect of AD8 was the best to KLAR asphaltene. The aggregation number of asphaltene in toluene decreased by addition of AD1, AD3 and AD5. The effect of solvation was enhanced too. The more acidic of dispersant molecule's functional groups, the more effective to dispersing asphaltene the dispersants were. Through the XPS and FT-IR analysis, the mechanism was deduced as follow: The dispersants absorbed on the surface of asphaltene via their polar head groups, through acid-base interaction or hydrogen bonding, and formed the steric layer by the tail group, which could inhibit the aggregation of asphaltene.The results of conductivity measurements showed that the colloidal stability of LHAR was enhanced with the addition of AD2 and AD1, and so did LGWO with the addition of AD7 and AD1.The average size of coke particles of LHAR with AD1, AD2 and AD3 addictives, was smaller than LHAR without dispersants. The dispersants could increase the suspending ability of coke particle in oil, and therefore, restrict adherence of coke to the reactor inside wall. The mechanism could be concluded as follow: the dispersant depressed the coke formation at the initial period of residue thermal reaction, producing more but smaller coking centers. Subsequently, the coke size was decreased because the coking center was more compared with the same coke yield. Interestingly, the suspending ability of the coke particles was improved. Therefore, the coke content deposited on the reactor bottom was reduced.