| Heavy oils are extremely easy to flocculate and deposit during transportation and processing due to its high viscosity and high content of asphaltenes,causing solid particles to deposit on the conveying and processing equipment,pipeline blockage and serious coking in heating furnace tubes.It has caused heavy economic losses in petroleum industry.Asphaltenes is the key component leading to deposition on account of its high molecular weight,high condensation degree and poor stability.So the better understanding of asphaltene resolving law in distinguishing solvent and the influences of solvent on the asphaltene component and structure would contribute to improving the heavy oil stability and solving the deposition problems.In this paper,two different separation methods(one-step method and two-step method)were used to separate the vacuum residue to get the asphaltenes,heavy resins and maltenes.The yields of residue components separated by two different methods were compared.Then,the effects on the structures and compositions of asphaltene and heavy resin by one-step and two-step methods were investigated by elemental analysis,~1H-NMR,XRD and FT-IR spectroscopy.The B-L method was used to calculate the average structural parameters for building the molecular structure model.The asphaltenes separated by one-step and two-step method were separated again by PNP method to A1,A2 and TC subfraction to study the component inside the asphaltenes.And A1,A2,TC were characterized to discover the differences among them.Finally,the solubility of asphaltene and solvent environment was calculated by molecular dynamics simulation using Materials Studio software.By comparing the solubility parameters of the two separation methods,the differences on the content and structure of the asphaltene were investigated.The results showed that the yield of asphaltenes obtained by two-step method was high,with the yield of heavy resins being low and the yield of maltenes remaining unchanged.The structural analysis of two-method shows,compared to the one-step method,the asphaltene aromatic carbon content,the number of aromatic carbon,the naphthenic carbon ratio,the structural unit of MW and the ring condensation degree decrease,with the alkyl carbon ratio increasing.For the heavy resins obtained by the two-step,its aromatic carbon content decreased,the alkyl carbon ratio,while the naphthenic carbon ratio and the structural unit of MW increased.XRD results showed that the aromatic layer stack height of asphaltenes obtained by one-step method was 23.80?,which was less than 25.59?of the two-step method.The diameter and the height of the aromatic layer decreased.The orderliness of the aromatic layer was stronger,and the arrangement of aromatic sheets was more regular.For VNVR,the stacking order of aromatic sheets in heavy resins by the two-step is reduced or even absent,and the association tendency between molecules is weaker.For LHVR,there were aromatic sheets structure with ordered stacking in the heavy resins by both methods,and its structure was more similar to the asphaltenes.The asphaltenes can be divided into subfractions by PNP method,which are A1,A2,and TC.Among them,A1 has the lowest H/C atomic ratio,the highest aromatic carbon ratio,and the highest condensation degree.For TC,it has the highest H/C atomic ratio and the lowest aromatic carbon ratio.The degree of condensation is the lowest,and the properties of the sub-components of the asphaltenes separated by the two-step method are superior to the one-step method.Finally,the molecular simulation was used to explain that the solvent environment of asphaltenes separated by the one-step method is superior to the two-step method in terms of the asphaltene solubility,and the heavy resins trapping in asphaltenes are almost completely dissolved,resulting in low asphaltene yield. |
