Asphaltene fractions, structural parameters

Fractionation of an asphaltene by stepwise precipitation with hydrocarbon solvents (heptane to decane) allows separation of the asphaltene by molecular weight. The structural parameters determined using the x-ray method (Table II) show a relationship to the molecular weight (16). For the particular asphaltene in question (Athabasca), the layer diameters (La) increase with molecular weight to a limiting value similar relationships also appear to exist for the interlamellar distance (c/2), micelle height (Lc), and even the number of lamellae (Nc) in the micelle. 

Table II. Structural Parameters of Asphaltene Fractions Derived by the X-ray Method...

Hydrocarbon Structures. Early postulates of asphaltene structure centered around a variety of polymer structures based on aromatic systems (36, 37). More recent information has related to the structural parameters and carbon skeleton of petroleum fractions, and asphaltenes structures have been derived from spectroscopic studies of asphaltenes isolated from various petroleum and bitumen (38-46). 

These NMR methods developed for dilute solutions of the intractable fractions of petroleum asphaltenes [75,91,92] have supported the high average mass measurements of asphaltenes by LD-MS through evaluation of average structural parameters from the NMR spectra. Briefly, for the sample mass data to match the measured... 

In recent decades, NMR has been used as a tool for the characterization of mixtures, especially the NMR, providing relevant information about the structure of complex systems such as asphaltenes. Simultaneous use of and NMR allows the determination of a series of structural parameters such as fraction of aromatic carbon, the average number of carbons in an alkyl attached to aromatic systems and the percentage replacement of this system (Skoog et al, 2002). 

Asphaltene particles are dispersed in saturates and aromatic hydrocarbons (gas-oil) with resins as peptizing agents in asphalt or heavy oil. The interaction between resin and asphaltene micelles is not well understood. In the present study, asphaltene has been dispersed into aromatic hydrocarbons (such as toluene), and the precipitations due to additions of paraffinic hydrocarbons (such as pentane) in the presence of a number of amphiphiles have been studied. These amphiphiles certainly affect the asphaltene precipitation, either by retardation or by enhancement, depending on the structural types and quantities of the amphiphiles. We have found that the nature of resin is that it behaves as an amphiphile, since the polar fractions of resin do contain amphiphiles. The solubility parameter spectra of these asphaltenes are discussed. 

In this work, the goal was to identify the differences in the average molecular parameters of asphaltenes obtained during the simulation of atmospheric distillation in the laboratory on five different temperatures. Significant changes were observed in the structures of each of the fractions obtained from two Brazilian oils called A and B, especially in the higher cut temperatures. 

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