Structural Difference Of Oil Sands Asphaltenes And Its Effect On Toluene Residue

Organic solvents are widely used in the mining and processing of oil sands.The interaction of solvents with heavy oil molecules can lead to incomplete separation of solvents after normal operation,resulting in solvent loss.However,the interaction of heavy oil components,especially asphaltene components,in unconventional petrole-um with solvent molecules has rarely been reported.Due to the complexity and varia-bility of the structure of asphaltenes and other components,the mixture system with solvent is difficult to accurately describe by existing thermodynamics,especially at low solvent content,and finally the relationship between solvent residue and heavy oil components is difficult to obtain accurately.In this paper,three typical unconventional petroleum oils such as Canadian oil sands,Indonesia oil sands and Iranian oil sands are used as raw materials,and the most complex component of oil sand bitumen,asphaltene,is studied as the main re-search object to explore the action characteristics of asphaltenes and solvent mole-cules.To study the difference of three unconventional petroleum asphaltene s mole-cules,EA,ICP-OES,FT-IR,GPC and ¹H NMR were used to analyze the three as-phaltenes.The results showed that the number average molecular weights of the three asphaltenes were:Indonesian asphaltenes（1662 Da）<Canadian asphaltenes（2482 Da）<Iranian asphaltenes（2578 Da）.The average structural parameters of the three as-phaltenes were calculated by B-L method.It was found that the aromaticity factor（f A）and condensation degree of aromatic rings(H_AU/C_A)of the Iran asphaltenes were the biggest,while the f A andH_AU/C_Aof the Canadian asphaltenes were the lowest.The unit sheet weight of the Iranian asphaltenes（usw=1105.0）is the smallest,and the unit sheet weight of Canadian asphaltenes（usw=1448.7）is the largest.Taking toluene as extraction solvent,the asphaltenes samples were treated by different methods,and the different asphaltenes samples were analyzed by thermo-gravimetric mass spectrometry（TG-MS）,which confirmed the existence of residual toluene in asphaltenes.The residual toluene would be separated from asphaltenes at temperatures above 148～163°C.It was found that the residual amount of toluene in asphaltenes was affected by origin of asphaltenes.Iran asphaltenes had the strongest force on toluene molecules,resulting in the highest separation temperature of toluene（162.4°C）and the most amount of residual toluene.Combining the molecular struc-ture parameters of the three asphaltenes,the larger the aromaticity factor（f A）and condensation degree of aromatic rings(H_AU/C_A)of asphaltenes and the smaller the unit sheet weight（usw）are,the more the amount of residual toluene is.In addition,it was found that all three asphaltenes would pyrolyze at around 460°C,and toluene would be produced by pyrolysis of three asphaltenes.Combined with the characteris-tic and structure of asphaltenes,a preliminary mechanism for the retention of toluene in asphaltenes was proposed.The three kinds of bitumen extracted by toluene were detected by thermogravi-metric mass spectrometry to investigate whether toluene molecules would remain in bitumen.The results showed that the three kinds of bitumen all could encapsulate toluene.The amount of relative residual toluene in three kinds of bitumen（<225°C）was different:Indonesian bitumen>Iran bitumen>Canadian bitumen.Moreover,for the same bitumen,when the asphaltene content is in the range of 10 wt%to 50 wt%,the amount of toluene remaining in the asphalt increases exponentially for every 10 wt%of the asphaltene content.Through the research in this subject,the basic structural information of three as-phaltenes was obtained,and the residual toluene in oil sand bitumen and asphaltenes was identified.The preliminary mechanism of toluene remaining in asphaltenes was proposed.It is found that the toluene residue in different kinds of oil sand bitumen and asphaltene is different,and the higher the asphaltene content in the same oil sand bitumen,the more the toluene residue is.It provides a theoretical basis for the study of solvent loss in the treatment of heavy oil solids,and provides new ideas and meth-ods for the subsequent study of asphaltene-solevent interaction.