Asphalt asphaltene content

Asphaltic—contain relatively a large amount of polynuclear aromatics, a high asphaltene content, and relatively less paraffins than paraffinic crudes. 

Residues containing high levels of heavy metals are not suitable for catalytic cracking units. These feedstocks may be subjected to a demetallization process to reduce their metal contents. For example, the metal content of vacuum residues could be substantially reduced by using a selective organic solvent such as pentane or hexane, which separates the residue into an oil (with a low metal and asphaltene content) and asphalt (with high metal content). Demetallized oils could be processed by direct hydrocatalysis. 

Solvent extraction may also be used to reduce asphaltenes and metals from heavy fractions and residues before using them in catalytic cracking. The organic solvent separates the resids into demetallized oil with lower metal and asphaltene content than the feed, and asphalt with high metal content. Figure 3-2 shows the IFP deasphalting process and Table 3-2 shows the analysis of feed before and after solvent treatment. Solvent extraction is used extensively in the petroleum refining industry. Each process uses its selective solvent, but, the basic principle is the same as above. 

The road asphalt used in this study was obtained from the road as a fresh sample. The road asphalt is composed of asphaltenes (GPC peak at lOOA and petroleum residual oils (15) (GPC peak at n-C QHgo). The GPC of road asphalt is shown in Figure 9. Since petroleum asphaltenes cannot be separated by a lOOA pore size gel column, the asphaltene appears without any separation at the total size exclusion limit of the column. But the nonasphaltene components are separated showing a peak at n-C QHg2. The performance of the road asphalt depends on the asphaltene content as well as on the molecular size distribution of the nonasphaltenic fraction. 

In any of the methods for the determination of the asphaltene content, the crude oil or product (such as asphalt) is mixed with a large excess (usually >30 volumes hydrocarbon per volume of sample) of low-boiling hydrocarbon such as n-pentane or n-heptane. For an extremely viscous sample, a solvent such as toluene may be used before the addition of the low-boiling hydrocarbon but an additional amount of the hydrocarbon (usually >30 volumes hydrocarbon per volume of solvent) must be added to compensate for the presence of the solvent. After a specified time, the insoluble material (the asphaltene fraction) is separated (by filtration) and dried. The yield is reported as percentage (% w/w) of the original sample. 

From the above demonstration, it can be noted that micelle structures are predominant in asphalt with a higher asphaltene content. Three different types of asphalt such as sol (micelle, supermicelle, giant supermicelle), sol-gel (supermicelle, giant supermicelle), gel (liquid crystal) asphalt, can be defined. Most of the paving asphalts belong to the sol-gel type of asphalt, and roofing asphalt belong to the gel (air blown) type of asphalt. 

Muller et al. used SCS derivatives to study the effects of hydrodesulfurization (HDS) on polycyclic aromatic sulfur heterocycles (PASHs) in bitumen residua. Their experiments concentrated on PASHs, which is a predominant class of SCS in vacuum residue bottoms. Asphaltenes were removed by precipitation, followed by the separation of aromatic fractions from saturated fractions by the saturates, aromatics, resins, and asphalts (SARA) method. Several methods can be deployed as the SARA method depending on the type of petroleum sample, one of the more common for more viscous oils is a combination of two methods ASTM D2007 and ASTM D893. Pentane-insoluble (PI) method ASTM D893 is used first to identify the asphaltene content then ASTM D2007 is used to calculate the saturates, aromatics, and resins. 

This test method is useful in quantifying the asphaltene content of petroleum asphalts, gas oils, heavy fuel oils, and crude petroleum. Asphaltene content is defm as those components not soluble in n-heptane. 

Equations 12.9 and 12.10) was found to be linear with correlation coefficients (r) between 0.88 and 0.99. Trasobares et al. (1998) developed a linear relationship between asphaltenes content (insolubles in nCi) and CCR given by Equation 12.11 with r 0.93. Ng (1997) found a linear dependence between density and asphalt content with a correlation coefficient of 0.9129 (Equation 12.12). 

Bitumen Insoluble in Paraffin Maphtha (AASHPO T46). This test designated by the American Association of State Highway and Transportation Officials (AASHTO) is used to indicate the content of naphtha-insoluble asphaltenes in an asphalt. Other solvents such as / -heptane (ASTM D3279), / -hexane, and / -pentane have been substituted for the naphtha solvent. 

Mack (58, 59) points out that asphaltenes from different sources in the same petro-lenes give mixtures of approximately the same rheological type, but sols of the same asphaltenes in different petrolenes differ in flow behavior. Those in aromatic petrolenes show viscous behavior and presumably approach true solution. Those in paraffinic media show complex flow and are considered to be true colloidal systems. Pfeiffer and associates (91) consider that degree of peptization of asphaltene micelles determines the flow behavior. Thus, a low concentration of asphaltenes well peptized by aromatic petrolenes leads to purely viscous flow. High concentrations of asphaltenes and petrolenes of low aromatic content result in gel-type asphalts. All shades of flow behavior between these extremes are observed. 

The effect of make-up of roofing asphalts on weathering properties, in terms of the fractions asphaltenes, resins, and oils, has been studied by Thurston (120). Increase of either asphaltenes or oils reduced resistance to weathering, while apparently an optimum content of resins aided permanence under exposure. Weathering properties were dependent not only on the quantities but also on the sources of these fractions, but the effect of source was not sufficiently clarified. 

Table II shows the results obtained by extracting several Uinta Basin, Utah outcrops with successive organic solvents. All outcrop samples are fairly low in sulfur, most are quite high in nitrogen, and all have low ratios of vanadium to nickel. Only the Raven Ridge sample, which was collected in a creek bed, has a very large fraction of organic material that is not soluble in heptane Benzene-methanol (1 1) and pyridine did not extract much material from any of these samples, so analytical data from these materials are not included in the table. The asphaltenes extracted from P. R. Spring and Southeast Asphalt Ridge tar sands are quite rich in nickel (5/jtmol/g), and nickel porphyrins are found in the heptane-soluble fractions of these tar sands as well as is the heptane-soluble fraction of Whiterocks tar sands. Crudes derived from nonmarine sources are usually much higher in nickel content than in vanadium content, and the Uinta Basin tar sands deposits are all of lacrustine origin and are of tertiary age.

Characterization of Crude Oils and Containants. The first step in selection of emulsion breakers is to obtain as complete an understanding as possible about the crude oil or emulsion. Density (or API gravity) and BS W ranges should be determined. The crude oil should be classified as asphaltic or paraffinic, and the asphaltene and paraffin content should be determined. If treatment will occur at a temperature below the paraffin melting point, the cloud point of the crude oil should be determined. This information will aid in selecting the treating temperature. 

In the more localized context of the Athabasca deposit, inconsistencies arise presumably because of the lack of mobility of the bitumen at formation temperature (approximately 4°C, 39°F). For example, the proportion of bitumen in the tar sand increases with depth within the formation. Furthermore, the proportion of the nonvolatile asphaltenes or the nonvolatile asphaltic fraction (asphaltenes plus resins) in the bitumen also increases with depth within the formation that leads to reduced yields of distillate from the bitumen obtained from deeper parts of the formation. In keeping with the concept of higher proportions of asphaltic fraction (asphaltenes plus resins), variations (horizontal and vertical) in bitumen properties have been noted previously, as have variations in sulfur content, nitrogen content, and metals content. Obviously, the richer tar sand deposits occur toward the base of the formation, but the bitumen is generally of poorer quality. 

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