Fractionation of bitumen

The heavy-end portions (usually called heavy fractions) of bitumen (e.g. asphaltenes, preasphaltenes) can exist both in a random oriented particle aggregate form or in an ordered micelle form, peptized with resin molecules (16.17). In their natural state, asphaltenes exists in an oil-external (Winsor s terminology) or reversed micelle. The polar groups are oriented toward the center, which can be water, silica (or clay), or metals (V, Ni, Fe, etc.). The driving force of the polar groups... 

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

Gel Permeation Chromatography. More and more work with residua and asphaltenes is using GPC as a useful separation method for size separations of the heaviest fractions of bitumens and petroleum residua. In a manner similar to that used in polymer chemistry, attempts have been made to calibrate a GPC MW scale so that it may be brought into accord with MW measurements by other methods (e.g., VPO). In other words, we are trying to relate the peak value (Va) and statistical distribution of the MW across the... 

The resins fraction of bitumen should not be confused with plant resins. When bitumen is mixed with a light hydrocarbon (e.g. pentane) it separates into a soluble fraction, maltenes, and an insoluble fraction, asphaltenes. The maltenes can then be separated chro-matographically into hydrocarbons and resins on the basis of the greater polarity of the resins. 

Fig. 4.12 Composition of disseminated organic matter in sedimentary rocks (afterTissot Welte 1984).The aliphatic and aromatic fractions of bitumen comprise mainly hydrocarbons (c.C5—C40 see Box 4.2).

The fractionation of bitumen (see Box 4.2) can be achieved by liquid chromatography, using a simple column containing suitably activated alumina (the stationary phase) and various solvents as mobile phase, moving under gravity. By increasing the polarity of the solvent it is possible to elute sequentially from the column the saturates (with hexane), aromatics (with toluene) and resins (with methanol). 

Table 8.6 Molecular weight for different fractions of Bitumen 200 Elf.

This picture provides a connection to the structure of oil sands. The arrangement of phases in oil sands is largely determined by the volume fractions of bitumen, water, and quartz sand. The quartz sand forms the bulk of the material, with either the bitumen (in rich oil sands) or the water (in lean oil sands) forming the continuous phase. This structure results in a simple relationship between oil content (grade) and particle size distribution (18, 20, 22, 23). The oil content of oil sands decreases as the median diameter of the particles decreases and as the fraction of particles in the clay-size range increases. 

If the ratio of the volume fraction of bitumen-rich component to that of air in the aggregates is denoted by G, then this value will be constant throughout the froth formation process. The only variable along the path from a dilute dispersion of aggregates to a froth is the relative volume fraction middlings. If G is greater than 2.67, the resultant froth is regarded as stable and has the component volume fractions ... 

G ratio of volume fraction of bitumen-rich component,... 

Fine solids are frequently mentioned as being responsible for W/0 emulsions, especially in systems involving various crude oils. The solids fraction of bitumen consists of fine submicrometer clay particles that have been rendered asphaltene-like due to the adsorption of highly aromatic, polar material on the particle siufaces (45). To determine if this solid fraction played a role in the film stability, a solids-free bitumen was prepared where all solid material larger than lOOnm was removed from the sample. Films of toluene- and heptane-diluted solids-free bitumen showed little or no change in both the drainage patterns and the film thickness, indicating that the fine solids had little or no effect on the behavioiu or stability of water/diluted bitu-men/water films. This is consistent with the observation described in Sec. II, where removal of fine solids from diluted bitumen had no effect on subsequently formed water in diluted bitumen emulsion. 

The distillation of crudes chosen for their yield in heavy fractions is the most common means. Bitumen is extracted from the residue from a vacuum distillation column (a few dozen mm of mercury), the latter being fed by atmospheric distillation residue. Unlike the practice of a decade ago, it is now possible to obtain all categories of bitumen, including the hard grades. 

Solvent deasphalting. This is an extraction of the heaviest fractions of a vacuum residue or heavy distillate. The extract is used to produce the bitumen. The separation is based on the precipitation of asphaltenes and the dissolution of the oil in an alkane solvent. The solvents employed are butane or propane or a butane-propane mixture. By selecting the proper feedstock and by controlling the deasphalting parameters, notably temperature and pressure, it is possible to obtain different grades of bitumen by this process. 

Physical methods of fractionation of tar sand bitumen usually indicate high proportions of nonvolatile asphaltenes and resins, even in amounts up to 50% wt/wt (or higher) of the bitumen. In addition, the presence of ash-forming metallic constituents, including such organometaUic compounds as those of vanadium and nickel, is also a distinguishing feature of bitumen. 

Part 2. Distillation Experiments. Distillation experiments were performed to determine the fraction of the original mass of bitumen in a calorimetric sample that is available for oxidation at each temperature in the range 155-320°C, to determine the quality of this "fuel" as expressed by the molar ratio of hydrogen to carbon,... 

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 liquid hydrocarbon stream to be treated may be a crude oil, heavy crude oil, bitumen, or a refined fraction of the crude oil. The hydrogen gas stream is added to the mixture of the hydrocarbon stream with the organic solvent. The reactor, which is fed upflow, is a packed bed of biocatalyst dispersed on a support and is operated at about 74°C. Alternatively, the reactor can also be a batch reactor under stirring conditions. 

The presence of paraffin wax is usually reflected in the paraffinic nature of the constituent fractions, and a high asphaltic content corresponds with the naphthenic properties of the fractions. As a result, the misconception has arisen that paraffin-base crude oils consist mainly of paraffins and asphalt-base crude oils mainly of cyclic (or naphthenic) hydrocarbons. In addition to paraffin- and asphalt-base oils, a mixed base had to be introduced for those oils that leave a mixture of bitumen and paraffin wax as a residue by nondestructive distillation. 

Fig. 13. Salient features of the GC-MS data for the saturated fraction of a hydrothermal bitumen sam pie from the Mid-Atlantic Ridge (a) TIC - background trace, (b) ra/z 85 fragmentogram (key ion for 3-ethyl-3-methylalkanes and -alkanes), (c) mjz 99, key ion for 3,3-diethylalkanes with -alkanes, and (d) m/z 127, key ion for 5,5-diethylalkanes with w-alkanes. (Numbers refer to total carbon number, dots ovet peaks are -alkanes.)... 

The paddle mill was used to study the effect of surfactant type on a solvent-aqueous-surfactant extraction scheme for the recovery of bitumen from Athabasca tar sand. n the experiments of Figures 4,5 and 6, bitumen recovered from the surface phases was measured as a function of the mole fraction of ethylene oxide in the surfactant and as a function of the extraction step in which the surfactant was added. The results are reported as the % of the total bitumen present in the surface fraction. The amount of surfactant used was that required to give a final aqueous concentration of 0.02% (w/v), but in different sets of experiments the surfactant was added at various stages in the process. 

Bitumen. Naturally occurring, solid or semisolid, hydrocarbons including asphalt, mineral pitch, petroleum and naphtha. The ASTM designates them as the fraction of hydrocarbons which are sol in CS2. They are rich in C and H and burn with a sooty flame... 

Figure 1. Surface tension of water soluble fraction of ozonized bitumen...

Figure 1. Separation and further division of first three fractions of the bitumen...

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