Asphalt fractionation

Peat Waxes. Peat waxes are much like montan waxes in that they contain three main components a wax fraction, a resin fraction, and an asphalt fraction. The amount of asphalt in the total yield is influenced strongly by the solvent used in the extraction. Montan waxes contain ca 50 wt % more of the wax fraction than peat waxes, and correspondingly lower percentages of the resin and asphalt fractions. The wax fraction in peat wax is chemically similar to that of the wax fraction in montan wax. 

The foremnner of the modern methods of asphalt fractionation was first described in 1916 (50) and the procedure was later modified by use of fuller s earth (attapulgite [1337-76-4]) to remove the resinous components (51). Further modifications and preferences led to the development of a variety of fractionation methods (52—58). Thus, because of the nature and varieties of fractions possible and the large number of precipitants or adsorbents, a great number of methods can be devised to determine the composition of asphalts (5,6,44,45). Fractions have also been separated by thermal diffusion (59), by dialysis (60), by electrolytic methods (61), and by repeated solvent fractionations (62,63). 

LEDA [Low energy de-asphalting] A process for removing the asphalt fraction from petroleum residues by liquid-liquid extraction in a special rotating disc contactor. The extractant is a C3-C6 aliphatic hydrocarbon or a mixture of such hydrocarbons. Developed in 1955 by Foster Wheeler USA Corporation and still widely used 42 units were operating in 1996. 

The close interplay of analytical methods gives much additional information especially in those areas where the analyzed substances are very complex. Thus, while ultracentrifuge analyses for petroleum (32, 33, 34) gave much information, the broad approach used by others (35, 36, 37) involved x-ray scattering, infrared, NMR, oxidation rates, GPC, MS, pyrolysis, and vapor pressure osmometry (VPO) applied to macrostructures of asphaltic fractions. Molecular complexes substantially larger than the foregoing macrostructures are difficult to characterize by methods short of ozonolysis (38) and general pyrolysis (39). 

Residua and heavy oils, like any other petroleum, can be fractionated by a variety of techniques (Speight, 1999) to provide broad general fractions termed asphaltenes, resins, aromatics, and saturates (Figure 6-6). By convention, the asphaltene and resin fractions are often referred to as the asphaltic fraction because of their insolubility in liquid propane and subsequent separation from a liquid propane solution of residua as asphalt. 

Briefly, the asphaltene fraction of crude oil is that fraction which is precipitated by the addition of a large excess of a low-boiling liquid hydrocarbon (usually n-heptane) (Chapter 3). On the other hand, resins are those materials which remain soluble in the pentane but will be adsorbed by a surface-active material such as fuller s earth, while the oils fraction is soluble in pentane but is not adsorbed from the pentane solution by any surface-active material. The asphaltic fraction of any petroleum, heavy oil, or residuum is usually a combination of the asphaltene and resin fraction and, in many instances, may constitute a large portion of a heavy oil or, especially, of a residuum. 

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. 

Mastral et al.23,24 have also investigated the effect of the main components present in tyres (carbon black, styrene-butadiene copolymer and polybutadiene) on the liquefaction of coal. Coprocessing of coal and carbon black confirmed the catalytic role of the latter, as it promotes hydrocracking reactions leading mainly to the formation of gaseous products. The addition of SBR to coal improves the yield of gases, oil and asphalt fractions, even at relatively low temperatures (350-375 °C). It is proposed that SBR favours the stabilization of the radicals involved in the process through alkylation reactions... 

Metals are generally associated with contaminant (a), the heterocycles, and contaminant (c), the asphaltic fraction. 

Nitrogen superhyperfine splitting in asphaltic fractions was observed. ... 

Ge and Ga varied as a function of depth and age of reservoir rock and that the metals were concentrated in the asphaltic fraction of the oils. Similar conclusions were reached by Katchenkov and Flegentova, Botneva, Mileshina, et and Nurev and Dzhab-... 

Very little is known of the nature of metals other than Ni and V in crude oils. In several studies cited previously f f it was demonstrated that the metals occurred in oil soluble form and some authors have noted the association of metals with the asphaltic fraction of petroleum... 

The largest percentage of metals in crude oil apparently collects in the asphalt fraction. This material is used primarily in road construction and for roofing. The available data on the metal contents of asphalt are shown in Table 7.6. The minimum and maximum amounts of metals per inch of asphalt per mile of two-lane highways are also shown in Table 7.6. 

Because SEC responds directly to apparent molecular size, it appears to be a simple method for obtaining the molecular weight distribution of asphalt. However, it turns out not to be a straightforward determination for a number of reasons. The first, already discussed, is that some asphaltic fractions associate in solution. These same fractions also may tend to be adsorbed in the column. A final factor is the chemical complexity of asphalt. It is well known that the order of elution of polar and nonpolar compounds can be considerably altered... 

The only universal detector sensitive enough to detect asphalt (because of its relatively low molecular weight) is the Viscotek differential viscometer (108,109). It utilizes a Wheatstone bridge flow resistance scheme that measures intrinsic viscosity differences between the column eluant and the carrier solvent. Other viscosity detectors measure absolute intrinsic viscosity of the eluant and are not as precise. In Figure 19, several supercritically refined asphalt fractions having a variety of molecular weights (MJ are seen to have similar RI and IV... 

May include aged asphalt material, air-blown residue, asphalt fractions, or crude oils. 

Dickie, J.P. Yen, T.F. (1967). Macrostrucutres of Asphaltic Fractions by Various Instrumental Methods. Anal Chem, Vol.39, pp. 1847-1852... 

The properties and behavior of asphalts are critically dependent on the nature of the constituents, which consist of hydrocarbon and heterocyclic or nitrogen-, sulfur-, and oxygen-containing compounds. Separation of the various asphalt fractions (Table 4) is usually based on their different boiling points, molecular weights, and solubilities in solvents of different polarities. 

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