Asphaltenes fractions

In industry, the elimination of asphaltenes from oil involves using propane or butane. The utilization of a lighter paraffin results in the heavier paraffins precipitating along with the asphaltenes thereby diminishing their aromatic character. The oil removed from its asphaltene fraction is known as deasphalted oil or DAO. The precipitated portion is called asphalt. 

However, for the past 30 years fractional separation has been the basis for most asphalt composition analysis (Fig. 10). The separation methods that have been used divide asphalt into operationally defined fractions. Four types of asphalt separation procedures are now in use ( /) chemical precipitation in which / -pentane separation of asphaltenes is foUowed by chemical precipitation of other fractions with sulfuric acid of increasing concentration (ASTM D2006) (2) solvent fractionation separation of an "asphaltene" fraction by the use of 1-butanol foUowed by dissolution of the 1-butanol solubles in... 

Colloidal State. The principal outcome of many of the composition studies has been the delineation of the asphalt system as a colloidal system at ambient or normal service conditions. This particular concept was proposed in 1924 and described the system as an oil medium in which the asphaltene fraction was dispersed. The transition from a coUoid to a Newtonian Hquid is dependent on temperature, hardness, shear rate, chemical nature, etc. At normal service temperatures asphalt is viscoelastic, and viscous at higher temperatures. The disperse phase is a micelle composed of the molecular species that make up the asphaltenes and the higher molecular weight aromatic components of the petrolenes or the maltenes (ie, the nonasphaltene components). Complete peptization of the micelle seems probable if the system contains sufficient aromatic constituents, in relation to the concentration of asphaltenes, to allow the asphaltenes to remain in the dispersed phase. 

Temperature-Controlled Residuiun Oil Supercritical Extraction (ROSE) The Kerr-McCee ROSE process has been used worldwide for over two decades to remove asphaltenes from oil. The extraction step uses a hquid solvent that is recovered at supercritical conditions to save energy as shown in Fig. 20-21. The residuum is contacted with butane or pentane to precipitate the heavy asphaltene fraction. The extract is then passed through a series of heaters, where it goes from the liquid state to a lower-density SCF state. Because the entire process is carried out at conditions near the critical point, a relatively small temperature change is required to produce a fairly large density change. After the light oils have been removed, the solvent is cooled back to the liquid state and recycled. 

In modern terms, asphaltene is conceptually defined as the normal-pentane-insoluble and benzene-soluble fraction whether it is derived from coal or from petroleum. The generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale (8,9). With this extension there has been much effort to define asphaltenes in terms of chemical structure and elemental analysis as well as by the carbonaceous source. It was demonstrated that the elemental compositions of asphaltene fractions precipitated by different solvents from various sources of petroleum vary considerably (see Table I). Figure 1 presents hypothetical structures for asphaltenes derived from oils produced in different regions of the world. Other investigators (10,11) based on a number of analytical methods, such as NMR, GPC, etc., have suggested the hypothetical structure shown in Figure 2. 

The crude oil produced from the Main Zone of the Torrance Field has an API gravity of 18° and contains 5.3 weight percent asphaltenes. The solubility of the asphaltene molecules in Main Zone oil was measured by the Oliensis Test(35). In this test, the solubility parameter Qf ie oil was lowered by adding to the oil successively larger volumes of hexadecane, a poor solvent for asphaltene molecules. The minimum volume (in milliliters) of hexadecane, which when added to 5 g of crude oil, will cause the chromatographic separation of the asphaltene fraction is termed the Oliensis Number. The Oliensis Number for the Main Zone crude oil is 3, indicating that the asphaltene molecules are not well-solubilized in the oil. Small changes in the solubility parameter of the Main Zone oil can cause the asphaltenes to precipitate. 

Products Company and Davison (W.R. Grace) Catalysts) and Hydrocarbon Technologies, Inc. ART provides non-zeolitic catalysts for ebullating residue hydrocracking and fixed bed pretreating HDT [140], A nanoscale iron based, slurry catalyst is recommended for coal liquefaction, while a molecule-sized and chemically in situ generated catalyst is employed for the high conversion of asphaltenic fractions or heavy oils [141],... 

Michael, G. Al-Siri, M. Khan, Z. H., and Ah, F. A., Differences in Average Chemical Structures of Asphaltene Fractions Separated From Feed and Product Oils of a Mild Thermal Processing Reaction. Energy Fuels, 2005. 19 pp. 1598-1605. 

Heavy oils and bitumens are characterized by the presence of large molecules, the asphaltenes, which among their complex molecules also present metal-containing moieties. Typical metals present in petroleum comprise various species (e.g., Ni, V, Fe, Al, Na, Ca, and Mg), which are particularly accumulated in the asphaltene fraction of crude oil [382-384],... 

The open literature does not show any report on microbial conversion of metal prophyrins although degradation of asphaltenic fractions has been eluted. The technical... 

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

Rojas-Avelizapa, N. G. Cervantes-Gonzalez, E. Cruz-Camarillo, R., and Rojas-Avelizapa, L. I., Degradation of aromatic and asphaltenic fractions by Serratia liquefasciens and Bacillus sp. Bulletin of Environmental Contamination and Toxicology, 2002. 69(6) pp. 835-842. 

With the recent progress in Fourier transform infrared (FTIR) spectroscopy, quantitative estimates of the various functional groups can also be made. This is particularly important for application to the higher-molecular-weight solid constituents of petroleum (i.e., the asphaltene fraction). 

Deasphaltening removal of a solid powdery asphaltene fraction from petroleum by the addition of low-boiling liqnid hydrocarbons snch as n-pentane or n-heptane nnder ambient conditions. 

Deasphalting the removal of the asphaltene fraction from petrolenm by the addition of a low-boiling hydrocarbon liqnid snch as n-pentane or n-heptane more correctly, the removal asphalt (tacky, semisolid) from petroleum (as occurs in a refinery asphalt plant) by the addition of liqnid propane or liquid butane under pressnre. 

Figure 7. Comparison of fluorescence spectra of two components in chloroform-solubles fraction with oil and asphaltene fractions of hydrogenated coal (PSOC-1266 solvent-free hydrogenation 400 C 60 min 5% wt sulfided Mo 7 MPa H2 cold).

The soil contained hydrocarbon-degrading Pseudomonas, Rbodococci, Acinetobacter, Mycobacterium, and Arthrobacter. Only the isolated Mycobacterium was able to degrade the asphaltene fraction. 

Heavy hydrocarbons were obtained by solvent extraction (4) of sediments, deasphalting with pentane, and separation by liquid chromatography (5) into saturate, aromatic, NSO-eluted, and asphaltene fractions. Saturate fractions were analyzed by gas-liquid chromatography (6) on these chromatograms (Figures 4 and 6) n-paraffins stand up as peaks above the naphthenic background. 

Residuum desulfurization kinetics are generally not first order. Figure 5 illustrates this with a first-order plot for desulfurization of Arabian light residuum. On this type of plot a first-order reaction would yield a straight line with a slope corresponding to the reaction rate constant. The over-all desulfurization reaction is not therefore first order and can in fact be represented by second-order kinetics. However, the figure shows that it may also be considered as the sum of two competing first-order reactions. The rates of desulfurization of the oil and asphaltene fractions are reasonably well represented as first-order reactions whose... 

Figure 7 Plot of mean S13C (%o/PDB) VS. SD (%o/ SMOW) for the asphaltene fraction of bitumens from different deposits and the archaeological...

The two monoaromatic and di- + triaromatic fractions are practically indistinguishable from each other except for a slightly higher molecular weight of the fractions from the Pitt Seam coal liquids. The spectra of the polyaromatic fractions were too weak and unresolved, and no meaningful calculations could be made from them. Similar problems were encountered when it was attempted to analyze the asphaltenes by NMR. Methods have to be developed to analyze polyaromatic and asphaltene fractions. 

Additional insight can be obtained with the successive use of various light paraffin and polar solvents as a separation strategy. Dean and Whitehead (1963) obtained C7 asphaltenes, a C5-insoluble-C7-soluble fraction (part of the resin), an acetone-immiscible fraction from the C5-soluble fraction and an acetone-miscible fraction for both Boscan and Gach Saran (Iranian Heavy) crude oils. They found that the vanadium was more concentrated in the C7 asphaltene and C5-insoluble-C7-soluable fractions, especially in the C7 asphaltene fraction. However, the metal-lopetroporphyrins were mostly concentrated in the C5-insoluble-C7-soluble and the acetone-miscible fractions. According to their data, only 5% of the metals in the asphaltenes are identified as metallopetroporphy-rins. This is consistent with the expectation that metal porphyrins are less polar than the metal nonporphyrins. 

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