Study On The Process Of Coke Formation During Slurry-Bed Hydrocracking Of Residue

With Merey atmospheric residue and Karamay atmospheric residue as feedstocks,The process of coke formation during slurry-bed hydrocracking of these feedstocks was investigated in the autoclave at various reaction time.The microstructure of coke were observed by microscope and SEM.The change of asphaltene's composition and structure were investigated by ~1H-NMR,FT-IR,SEM and XRD,the relevance between coke formation and asphaltene properties was discussed also.The results showed that the content,molecular weight and condensation of asphaltene increased before coke induction period in the process of coke formation during slurry-bed hydrocracking of residue.At the same time the slice spacing of asphaltene became short.The yield of suspended coke and total coke rose slowly,and the yield of depositional coke was almost invariant during this stage.The content of asphaltene reached maximum and a few of asphaltene polymers with high degree of condensation and closely aromatic layers started to convert into coke fast when reacting coke induction period.The remaining asphaltene's content,molecular weight,condensation degree and the slice spacing declined after coke induction period.The total yield of coke increased obviously.Suspended coke gathered to be sphere and transformed into depositional coke,leading to the increase of depositional coke's content,and the decrease of suspended coke's size and content.The coke induction period was shorter and total yield of coke was higher with increasement of asphaltene's content,heteroatom's content and condensation at the same reaction severity for the reason that asphaltene is the major source of coke formation during slurry-bed hydrocracking of residue.As the asphaltene's molecular weight was lower,the coke's particle size was smaller.Coke's surface was more rough with that substituent group's branching degree was higher.Compared with asphaltene generated by residue,content of asphaltene which generated by maltene of residue was lower.Therefore maltene of residue had lower coke propensity.But there is a resemblance between two kind of asphaltenes'carbon type distribution,hydrogen type distribution and degree of branching.The microstructure of coke was similar.