Asphaltene characterization

Bkhar, F. Pelet, R. 1984 Asphaltene characterization by pyrolysis and chromatography. Journal of Analytical Applied Pyrolysis, 1, 121 135. 

All the problems briefly described above justify the large effort to characterize asphaltenes by techniques seldom found elsewhere in the petroleum industry. One of these is to analyze asphaltenes by steric exclusion... 

Crude oils form a continuum of chemical species from gas to the heaviest components made up of asphaltenes it is evidently out of the question, given the complexity of the mixtures, to analyze them completely. In this chapter we will introduce the techniques of fractionation used in the characterization of petroieum as well as the techniques of elemental analysis applied to the fractions obtained. 

Many attempts have been made to characterize the stabiUty of the colloidal state of asphalt at ordinary temperature on the basis of chemical analysis in generic groups. For example, a colloidal instabiUty index has been defined as the ratio of the sum of the amounts in asphaltenes and flocculants (saturated oils) to the sum of the amounts in peptizers (resins) and solvents (aromatic oils) (66) ... 

Leon, O. Rogel, E. Espidel, J., and Torres, G., Asphaltenes Structural Characterization, Self-Association, and Stability Behavior. Energy Fuels, 2000. 14 pp. 6-10. 

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],... 

Petroleum is typically described in terms of its physical properties (such as density and pour point) and chemical composition (such as percent composition of various petroleum hydrocarbons, asphaltenes, and sulfur). Although very complex in makeup, crude can be broken down into four basic classes of petroleum hydrocarbons. Each class is distinguished on the basis of molecular composition. In addition, properties important for characterizing the behavior of petroleum and petroleum products when spilled into waterways or onto land and/or released into the air include flash point, density (read specific gravity and/or API gravity), viscosity, emulsion formation in waterways, and adhesion to soil. 

Isotopic characterization SI3C and SD values, asphaltene in bitumen samples, 146, 148/ 149/... 

Asphaltenes may contain both porphyrin and nonporphyrin metals, depending upon the origin of the crude oil. Yen et al. (1969) characterized the vanadium complexes in a petroleum asphaltene by mass spectroscopy, optical spectroscopy, and ESR. Porphyrins (Etio and DPEP), acid-resistant porphyrin macrocycles of increased aromaticity (Rhodo), and nonporphyrins with mixed donor complexes were identified. Baker (1966) and Baker et al. (1967) extracted porphyrins from Boscan crude oil asphaltenes and also found Etio and DPEP as the two major porphyrin series. These homologous series range in molecular weight by 7 to 18 methylene groups. Gallegos (1967) observed by mass spectroscopy that asphaltenes and maltenes from a Boscan crude oil had nearly identical porphyrins in terms of mass distribution. 

Porphyrin and nonporphyrin metals associated with asphaltenes have not been easy to identify in terms of molecular structure. This is partly due to the fact that the characteristics (i.e., spectra) of all possible model nonporphyrin compounds have not been studied. Nonporphyrin metals are probably small polar molecules that precipitate as asphaltenes (Filby, 1975) or complex at defect sites in large aromatic sheet structures of the type shown in Fig. 10. Porphyrins with increased aromaticity and systems with low aromaticity due to discontinued ring conjugation are both characterized as nonporphyrin species. These compounds do not have the characteristic visible absorption spectra and hence are not readily identified. It is also possible that some of the porphyrin in the residuum may not be extracted and identified due to intermolecular association with the asphaltene-generating molecules. 

A spectrum of metal compound reactivities in petroleum could arise for several reasons. Nickel and vanadium exist in a diversity of chemical environments. These can be categorized into porphyrinic and non-porphyrinic species vanadyl and nonvanadyl or associated with large asphaltenic groups and small, isolated metal-containing molecules. Each can be characterized by unique intrinsic reactivity. Reaction inhibition which occurs between the asphaltenes and the nonasphaltenes, as well as between Ni and V species, can also contribute to reactivity distributions. The parallel reaction interpretation of the observed reaction order discrepancy is therefore compatible with the multicomponent nature of petroleum. Data obtained at low conversion could appear as first order and only at higher conversions would higher-order effects become obvious. The... 

Thirty crude oils from the BCF were collected (1) along two parallel and generally southwest-northeast trends. The areal extent of the BCF showing locations of wells sampled is shown in Figure 1. These oils were characterized by their API gravity, percent saturates, aromatics, NSO and asphaltene compounds, gas chromatograms for whole oils, CA-C7 fractions, and aromatics. Concurrently, 24 associated waters were also sampled and analyzed for Ca++, Mg++, Na+, HC03, C03 , SOA , pH, and total dissolved solids (TDS) (1). 

The thermal instability of hydrorefined SRC creates another parameter which requires careful consideration. If, for example, topping operations reverse some of the depolymerization occurring in the SRC process, this equates to a hydrogen penalty. Additional work needs to be done to characterize the asphaltenes generated thermally vs. the starting asphaltenes from coal. 

The liquids require a hydrorefining step to stabilize their reactive properties, to reduce the asphaltenes and preasphaltenes, to reduce sulfur, nitrogen, and oxygen, and to make the liquids more distillable. The extent of hydrorefining depends on the end use of liquids—fuel oil or chemical feedstocks. The objective of this work is to evaluate the hydrorefining processibility of ORC flash pyrolysis coal tar as a part of the tar characterization task. Results of the initial phase of catalyst screening tests are reported in this chapter. 

For the characterization of RCC feedstocks, it was determined that a more detailed molecular description of the feedstock was necessary. The more detailed molecular description of RCC feedstocks involves dividing the feedstock into six molecular types 1) saturates 2) monoaromatics 3) diaromatics 4) greater than diaromatics 5) polar aromatics and 6) asphaltenes. This separation of the RCC feedstock is accomplished by using high performance liquid chromatography. 

CCB was fractionated into six asphaltene-free distillate fractions of varying boiling ranges and an asphaltene-rich non-distillable residue. Characterization of the distillate and the non-distillable fractions indicate significant differences in the asphaltene, ash, aromaticity, molecular weight and aromatic ring distributions. 

The substances called asphaltenes are important intermediates in the hydrogenation of coals in the liquid phase. How the word asphaltene originated and how these substances have been characterized are the subjects of the first part of this chapter. 

We believe it is important, at this time, to establish a documented historical review of asphaltenes and the separation/characterization procedures used by early petroleum and coal chemists to profile crude oils and the products of coal hydrogenation. We shall explore the most important differences between petroleum- and coal-derived asphaltenes. 

An early characterization of asphaltenes separated from petroleum by their solubility in carbon tetrachloride was put forth by Nellensteyn in 1930... 

For a discrete molecule with a simple structure, a microstructure is sufficient to characterize the given molecule. For a complex system such as that of asphaltene, the information required for characterization has to include association as well as micelle formation. The microstructure has been chosen arbitrarily to refer to short-range bonding, that is, distances between 0.5 A-2.0 A whereas the macrostructure (bulk structure) pertains to molecular interactions or orders at larger distances (20 A-2000 A). 

Structural information obtained from various methods can usually be represented by a set of structural parameters, S. These parameters are related to the physical and chemical properties of a given substance. A given set of properties, Pjt is unique to a given substance. Therefore, a given set of structural parameters can be used to characterize a given asphaltene ... 

Microstructure. The characterization of coal-derived asphaltene is quite similar to that of petroleum-derived asphaltene. Since it is anticipated that coal-derived asphaltene will have acid/neutral and base characteristics (26, 36), the average structure of both must be considered. In Table III, Structure I is amphoteric (or slightly basic), and Structure II is an acid/neutral representation. A mixture of both may be typical of the average structure of a coal-derived asphaltene. At present, we will illustrate this by an asphaltene obtained from coal liquid of the Synthoil process. (The coal is hvAb, West Kentucky, Homestead Seam the coal liquid is obtained by catalytic hydrogenation at 450° C and 4000 psig having %C, 86.7 %H, 8.38 %N, 0.93 %S, 0.09 %Q, 3.2 and %Ash, 0.7.)... 

Table IV. Parameters for the Characterization of the Macrostructure of Coal-Derived Asphaltenes and Related Derivatives...

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