Characterization of asphaltene

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

Recently, petroleum residua have been studied extensively (I, 2) because of the increasing importance of heavier fuels. Both the asphaltene (pentane-insoluble) and maltene (pentane-soluble) components of residua are of interest, and since their properties overlap, a complete study of petroleum residua must consider both asphaltenes and maltenes. One area that has received considerable attention has been the size characterization of asphaltenes and maltenes (3, 4, 5). Size distribution data are useful both in understanding the fundamental chemistry of asphaltenes and maltenes and in observing the effects of various processes on residua sizes. 

The structure and chemistry of tar sand bitumen asphaltenes were studied indirectly by inference from processing and characterization of virgin bitumen and deasphaltened bitumen (maltenes). Results differ significantly from those derived from characterization of asphaltenes as isolated... 

Table I. Roles of Major Analytical Techniques in Characterization of Asphaltene Fractions...

The laboratory DOPOLAB is currently studying the influence of asphaltenes and resins in the stability of Brazilian oil emulsions. For this, certain physico-chemical characteristics of oil are determined such as viscosity, density, °API, water content, chloride content, total acidity index extraction of asphaltenes following the standard ASTM6560/00 and characterization of asphaltenes and resins through techniques of elemental analysis, IR and iH and 13C NMR. 

Caldas, J. N. (1997), Estudo Experimental e Modelagem Termodinamica da Floculagao dos Asfaltenos, PhD Thesis, COPPE/UFRJ, Rio de Janeiro Calemma, V. Iwanski, R Nali, M. Scotti, R. Montanari, L. (1995). Structural Characterization of Asphaltenes of Different Origins. Energy Fuels, 9, 225-230 Carnahan, N. F., (1989). Paraffin Deposition in Petroleum Production - Journal of Petroleum Technology, v 41,1024 1025... 

Trejo, F., Ancheyta J., (2007). Characterization of Asphaltene Fractions from Hydrotreated Maya Crude Oil. Ind. Eng. Chem. Res., 46, 7571-7579 F. Trejo F. Ancheyta J. Morgan T. J. , Herod A. A., Kandiyoti R., (2007). Characterization of Asphaltenes from Hydrotreated Products by SEC, LDMS, MALDI, NMR, and XRD. Energy Fuels 2007,21,2121-2128... 

Characterization of asphaltene samples from the live different crudes reported here has shown no correlation between asphaltene structure and molecular weight distribution, all samples showing similar molecular weight ranges. 

Ancheyta, J., Centeno, G., Trejo, R, Marroqum, G., Garcia, J.A. 2002. Extraction and characterization of asphaltenes from different crude oils and solvents. Energy Fuels 16 1121-1127. 

Demirba , A. 2002. Physical and chemical characterizations of asphaltenes from different sources. Petrol. Sci. Technol. 20(5-6) 485-495. 

Leyva, C., Ancheyta, J., Berrneco, C., MUlan, M. 2012. Chemical characterization of asphaltenes from various crude oils. Fuel Proc. Tech, (submitted). 

Trejo, F., Ancheyta, J., Morgan, T.J., Herod, A.A., Kandiyoti, R. 2007. Characterization of asphaltenes from hydrotreated products by SEC, LDMS, MALDI, NMR, and XRD. 

By this means, yields of coke, gas, naphtha, and gasoil can be calculated from asphaltene content of the feed, VPO (vapor pressure osmometry) molecular weight of asphaltenes in toluene, and heteroatom content of asphaltenes. The problem with these correlations is that they require characterization of asphaltenes. 

Wandas, R. 2007. Structural characterization of asphaltenes from raw and desulfurized vacuum residue and correlation between asphaltene content and the tendency of sediment formation in H-oil heavy products. Petrol. Sci. Technol. 25 153-168. 

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. 

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. 

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. 

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. 

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). 

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...

Oils and asphaltenes, which constitute a partial characterization of coal liquids according to solvent extraction, are generally considered to be key intermediates in coal liquefaction. In this regard, the present results do reveal that the asphaltenes contain higher molecular weight homologs in many specific-Z series and different compound types than do the oils. However, our study unequivocally demonstrates that compound types are observed in both the oils and asphaltenes that are equivalent in molecular formula and, hence, presumably in molecular structure. Furthermore, the overlap in the compositions of the two fractions is quantitatively appreciable. Thus, isolation of oils and asphaltenes must involve, in addition to solubility, other physical/... 

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