Study On The Activity Variation Of Oil-soluble Mo Catalyst During Slurry-phase Hydrocracking For Residue

The slurry-phase hydrocracking technology is a promising route to process heavy oils for its material universality and considerable conversion.However,it’s necessary to research the change of catalytic efficiency and coke restraining ability considering the fast deactivation process and nonnegligible catalyst cost.With Merey atmospheric residue as feedstocks,coke on the unit catalyst and relative coke restraining ratio were chosen as the indexes to represent catalytic efficiency and coke restraining activity of oil-soluble Mo catalyst respectively in the autoclave at various catalyst dosage and reaction time.Solvent titration method and SRAR method were used to study the changes of the colloidal properties of the system.Simultaneously,SEM,TEM,FT-IR,XPS and other characterization methods were used to analyze the toluene-insoluble after reaction.The composition of suspended coke and depositional coke was correlated with the active phase MoS₂ of the catalyst in order to explain the reasons for the change in catalytic efficiency and coke restraining ability preliminarily.The results showed that compared with the hydrogen thermal cracking reaction,the existence of dispersed catalyst significantly improved the colloidal stability of the reaction system,restricted the conversion of suspended coke into depositional coke and at the same time,promoted the cracking of the aliphatic chain chains,thereby resulting in the reduce of structure gap between suspended coke and depositional coke.With the gradual increase of catalysts,the catalytic efficiency rose first and tended to be flat and reached the top when catalyst dosage was 300μg·g^-1.Meanwhile,the colloidal stability of the system increased first and then decreased,and excessive catalysts would contribute to more coke formation.On one hand,the decrease of colloidal stability which resulted from excessive catalysts added could promote coke formation.On the other hand,the high hydrogenation activity of Mo（Ⅳ）on the surface of MoS₂ was reduced in contrast to Mo（Ⅵ）even though more active phase of MoS2 was formed with more catalysts added.Accordingly,the oil-soluble Mo catalyst could achieve the maximal efficiency when its dosage was 300μg·g^-1 and the least coke was produced.With the increase of reaction time,coke restraining ability of the catalyst first increased and then decreased.The catalyst reached a maximum coke restraining ability until 60min for the initial heating period was shorter and the cracking degree was lower before 60min.After 90min,the amount of suspended coke and depositional coke increased significantly,and coke restraining ability declined rapidly.The amount of MoS₂ on the surface of suspended coke was continuously decreasing and irregular structures on the MoS₂ and Mo（Ⅳ）was relatively decreased,which indicated that the high hydrogenation activity of Mo（Ⅳ）was more easily covered by coke and coke restraining ability of the catalyst was decreased gradually.Therefore,the reaction time should be controlled within 90min under the experimental conditions considering the coke restraining ability combining with the acceptable coke yield the in experimental installation.