Study Of The Fractionated Thermal Dissolution Of Asphaltene In Tahe Residual Oil And Its Residue Hydrocracking Properties

The samples of C₅-As,C₆-As and C₇-As asphaltene were separated from the Tahe atmospheric residue（THAR）by n-pentane,n-hexane and n-heptane solvent respectively.The structure was characterized by GPC,element analysis and XPS.Using the way of fractionated and sequential thermal dissolution,the structure characteristics of C₆ asphaltene were analyzed by analyzing the components of the products of the thermal dissolution,and the products distribution characteristics of the hydrothermal cracking of the thermal dissolution residue were examined.The results of the study are as follows:（1）With the increasing of the length of carbon chain,the yield of asphaltene sample decreases,the particle size decreases,the specific surface area increases,the average relative molecular mass increases,and the ratio of hydrogen to carbon decreases.The aliphatic chain in asphaltene molecular structure decreases,and the polycyclic aromatic hydrocarbons in the molecular structure unit are increased.（2）The main form of carbon is C-H and C-C,the main form of oxygen is carbon-oxygen single bond,the main form of nitrogen is pyridine and pyrrole,the main form of sulfur is aliphatic sulfur and thiophenic sulfur in the surface of asphaltenes.（3）The cracking activity of C₅-As,C₆-As and C₇-As decreased with the increase of the length of carbon chain,the corresponding thermal stability and the amount of carbon residue increased,and the activation energy of pyrolysis was also increased.The yield of secondary saturation,aromatic,resin and gas in the product of three samples was gradually decreasing,and the yield of secondary asphaltene and coke increased gradually.（4）For sequential the thermal dissolution of C₆ asphaltene,with the increase of thermal dissolution temperature,the yield decreased first and then increased and then decreased slightly,and the cumulative yield is 4.01 wt.%.The products of sequential thermal dissolution is mainly composed of alkanes and a small amount of aromatics,olefins and oxygenated compounds.The thermogravimetry carbon residue of C₆asphaltene thermal dissolution residue is increasing gradually from 52.48 wt.%of100℃to 60.41 wt.%of 300℃,which increases by 7.93 percentage points.（5）The yield of R_PE300 in the solvent of acetone,cyclohexane and methyl isobutyl ketone at 300℃is 2.26%,3.04%and 2.46%respectively,and the total yield is 7.76%.The thermal dissolution substances in the acetone solvent are the majority of the hot soluble residues in the acetone solvent,followed by alkanes,few aromatic hydrocarbons and olefins;and more than half of oxygen-containing the thermal dissolution substances in the solvent of cyclohexane,but the types of alkanes are much more,and the relative content is more than acetone solvent thermal dissolution.Dissolved substances;in methyl isobutyl ketone solvents,the thermal dissolution substances accounted for 81.42%of the oxygenated substances,of which the relative content of ester compounds was the highest 39.78%.The weight loss of R_A300,R_C300and R_M300decreased at final temperature of 1000,which were 38.18 wt.%,37.67 wt.%and 36.65 wt.%,respectively.（6）The yield of Sa*,Re*and Ar*in R_PE300,R_A300,R_C300and R_M300 hydrothermal cracking decreased,of which the yield of Re*and Ar*decreased slowly,the yield of Sa*decreased greatly;the yield of Gas,As*and Coke increased,especially the coke rate Coke,which increased greatly.The thermal weight loss of R_PE300-coke,R_A300-coke,R_C300-coke and R_M300-coke is 12.08 wt.%,11.61 wt.%,11.42 wt.%and 11.38 wt.%,respectively.The peak temperature corresponding to the maximum weight loss of coke varies little.The first maximum thermogravimetric peak appears in the range of230～245℃,and the second maximum thermogravimetric peaks appear in the range of510～525℃.（7）The nine stage thermal dissolution products were mainly alkanes,the yield was 5.50%,followed by oxygen containing substances,and the yield was 4.97%.the yield of aromatics and olefins were less,and their values are 0.75%and 0.55%respectively.（8）Compared to C₆-As samples,the content of secondary saturation,gas and coke in products of R_M300hydrocracking increased by 9.96,8.56 and 7.00percentage points,respectively,and the content of secondary aromatic,secondary resin and secondary asphaltenes in products of R_M300hydrocracking decreased by 15.03,4.62and 6.60 percentage points respectively.