Study On The Relationship Of Asphaltene And The Coke Formation Characteristics During Slurry-Bed Hydrocracking Of Residue

With Merey and Liaohe atmospheric residue as feedstocks,the C₇-maltene and the C₇-asphaltene were isolated and blended.Then a series of mixed residue containing different asphaltene content or different types of asphaltenes were obtained by mixing different proportions of C₇-asphaltene into the C₇-maltene of MRAR.The effect of asphaltene content and structure on the coke yield was investigated in the autoclave.The coke formation process and the morphology of coke were investigated by the SEM and polarizing microscope.And then the relationships between the coke formation and the associated state of raw asphaltene or reacted asphaltene were investigated by SAXS.The results showed that the coke formation process and the coke morphology of the blended residue with different asphaltene content or different types of asphaltene was similar,but the coke size was different.Asphaltene condensed into the lamellar structural coke and the coke was irregular and curly in the early stage of coke formation.Then the olive-like structural coke was staked by multi-layer lamellar structural coke which packaged small particles.Eventually,the regular sphere structural coke formed and grew up by dissolving small size coke.And the formation of suspended coke’s network structure was necessary for coke deposite.The process of coke deposition was codetermined by the content,size and degree of crosslinking of the suspended coke.The process of asphaltene associated into coke during slurry bed hydrocracking of residue was investigated.The asphaltene aggregate size was less than 10 nm before the residue heated up to 350°C.There was almost no free radical reaction when the reaction temperature was between 350 to 410°C.However,the asphaltene aggregate size increased to33nm due to solvent and thermal effects.The size of the aggregate decreased due to side chain breaking seriously around 420℃.The condensation reaction intensified with the developing of the reaction.The size of the aggregate increased to the extreme and then the asphaltene converted into coke in large amount around the coke induction period.The raw asphaltene aggregate size and the reacted asphaltene aggregate size generated during hydrocracking were all the key factors affecting coke formation.When the asphaltene content in the residue was more,the raw asphaltene aggregate size was larger and the reacted asphaltene aggregate size also was lager due to colloid instability of reaction system during hydrocracking.The large-sized raw asphaltene and the large-sized reacted asphaltene promoting together the formation of coke.Therefore,the coke induction period was shorter and the suspended coke content was more,coke size was lager and the degree of crosslinking was also more serious for which the suspended coke was easier to deposit.The characteristics of association and coke formation was closely related to the asphaltene chemical composition.When the condensation degree and substituent group’s branching degree of raw asphaltene were higher,the average molecular structure of asphaltene was larger.And when the amount of pyridinic type,COO-,C-OH functional groups on raw asphaltene’s surface was higher,the polarity of asphaltene was greater.Therefore,the reacted asphaltene aggregate size was larger and the coke induction period was shortened.And the high degree of asphaltene condensation was not conducive to the stability of the colloidal system.Therefore,the suspended coke was easier to deposit.