Asphaltenes Elemental Analysis

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. 

Asphaltenes seem to be relatively constant in composition in residual asphalts, despite the source, as deterrnined by elemental analysis (6). Deterrnination of asphaltenes is relatively standard, and the fractions are termed / -pentane, / -hexane, / -heptane, or naphtha-insoluble, depending upon the precipitant used (5,6,49). After the asphaltenes are removed, resinous fractions are removed from the maltenes-petrolenes usually by adsorption on activated gels or clays. Recovery of the resin fraction by desorbtion is usually nearly quantitative. 

TABLE IV - ELEMENTAL ANALYSIS OF ASPHALTENES IN THE RECOVERED SAMPLES - OIL E -... 

In modern terms, asphaltene is conceptually defined as the normal-pentane-insoluble and benzene-soluble fraction whether it is derived from coal or from petroleum. The generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale (8,9). With this extension there has been much effort to define asphaltenes in terms of chemical structure and elemental analysis as well as by the carbonaceous source. It was demonstrated that the elemental compositions of asphaltene fractions precipitated by different solvents from various sources of petroleum vary considerably (see Table I). Figure 1 presents hypothetical structures for asphaltenes derived from oils produced in different regions of the world. Other investigators (10,11) based on a number of analytical methods, such as NMR, GPC, etc., have suggested the hypothetical structure shown in Figure 2. 

XPS spectra were collected for the same petroleum residua and asphaltene samples used in the XANES studies described above. For all samples the total amount of sulfur relative to carbon as measured by XPS was comparable to that determined by bulk elemental analysis. The spectra were deconvoluted by curve fitting, and the approximate quantifications thus derived are shown in Table 111. 

To test these hypotheses, a tar sand bitumen containing 20 wt % pentane asphaltenes was characterized and processed by hydropyrolysis before and after removal of asphaltenes. Product yields and structure were determined and the influence of asphaltenes on results was determined by inferrence. Feedstocks and products were characterized according to elemental analysis, physical properties, simulated distillation, and carbon-type analysis. Inferences made in this study are discussed in the context of the reported literature. 

Elemental analysis and asphaltene content from results obtained on components. NA—not available. 

Table X. Average Structural Parameters Calculated for Asphaltenes from NMR, GPC, and Elemental Analysis...

Elemental Composition. Elemental analysis data for the three asphaltene samples are presented in Table I. 

The results of the elemental analysis show that asphaltenes derived from retorted shale oils have smaller values of H/C ratio and smaller oxygen and sulfur contents, but greater nitrogen content than that derived from shale bitumen. 

The effect of additives on the asphaltene from the Catalytic Incorporated (Cat. Inc.) coal liquid product was studied. Asphaltene is defined as the pentane insoluble but benzene soluble part of the coal liquid. The fractionation procedure has been described in detail elsewhere(l) and is shown schematically in Figure 1. Some work was also done with A240 petroleum pitch. Elemental analysis for the Wyoming sub-bituminous coal. Cat. Inc. coal liquid product, and Cat. Inc. asphaltene and A240 petroleum pitch are shown in Table I. Measured amounts of the additive compounds to be studied were added to the Cat. Inc. asphaltene and petroleum pitch. The samples were pyrolyzed and the pyrolysis residues examined by cross polarized light microscopy. Elemental analyses of the residues were done. 

Table I. Elemental Analysis (Z) and Aromaticity of Coal. Catalytic Incorporated (Cat. Inc.) Coal Liquid, and Cat. Inc. Asphaltene and A240 Petroleum Pitch...

Table VI. Elemental Analysis of the Sample Residues at Different Pyrolysis Temperatures Sample Cat Inc Coal Liquid Asphaltene + 6% Organic Sulfur + 800 ppm Nickel...

Bitumens are colloid systems, as are crude oils, and consist of the two colloidal components, petroleum resins and asphaltenes, dispersed in a dispersion medium. To investigate the composition of the system, a colloid precipitation according to Neumann [4-10] is carried out. The chemical nature of the bitumen and its components were determined by element analysis, where the atomic ratio H/C includes an indicator of the aromacity. Further characterization is performed by measuring the average relative particle mass (mean of the molecular weight M) by vapor pressure osmometry. 

Table 4-52 Element analysis (wt %) and average relative particle mass M of the asphaltenes...

The vacuum residue from Kirkuk was characterized by elemental analysis, average molecular weight (vapor pressure osmometry), viscosity, density, asphaltenes content, and the usual index numbers of thermogravimetry (table 4-123) ... 

The physical and an tical data, i. e. melting point, MP, boiling point, BP, average relative particle weight, M, element analysis, and atomic ratio H/C are presented in Table 4-195. The simulated distillation curves (by TGA) are shown in Fig. 4-159. The asphaltenes do not contain any volatile components but do undergo a cracking reaction above 400 °C. The distillation (sublimation) curve of n-hexylpyrene is nearly 100°C-150 C below the corressponding curves of the other substances. 

The behavior of a vacuum residue from a Venezuelan crude was simulated by a distillation bitumen B80 (according to DIN 1995). Further, a vacuum residue of a Middle East crude (VR Kuwait) and its colloid components, i.e. dispersion medium, petroleum resins, and asphaltenes were investigated. Those substances were characterized by element analysis and average relative particle weight (molecular weight) (Table 4-200) and by analysis of their colloid composition according to Neumann [4-10] (Table 4-201). 

For general characterization of nitrogen compounds in a coal liquid sample, carbon, hydrogen, and other elements can be determined by conventional elemental analysis for the separated distillate, resins, asphaltenes, preasphaltenes, aromatics, n-paraffins, and nonparaffins. MS is useful for the analysis of saturated fractions [22] and carbon number distributions [23], especially for aromatics. Low-voltage MS (LV-MS) (10 eV) will only ionize aromatics instead of paraffins, since aromatics have lower ionization potentials. 

The Maya crude oil and asphaltene fractions have been studied [75,77,91]. A typical elemental analysis of the Maya crude is listed in Table 33.1, and the fraction weights are shown in Table 33.2. Figure 33.4A shows the mass spectra of the maltene fraction at different levels of LP spectra 1 and 2 barely exceed the ionization threshold, and spectra 4 and 5 show excessive LP with... 

FIGURE 1.51 Pi versus Flmo for kerogens, coals, and asphaltenes (see samples in Table 1.9) with addition of oxidized samples. (From D. Joseph. L oxydation des matieres carbonSes. Thfese d Etat Orleans 1982. D. Joseph and A. Oberlin. Oxidation of carbonaceous matter, (a) Parti Elemental analysis andIR spectrometry. Carbon 21,559-564 (1983) (b) Part II X-ray diffraction and TEM. Carbon 21, 565-571 (1983). With permission.)... 

Table 04 shows the elemental analysis of five Brazilian oils performed in COPOLAB -Laboratory of Development and Optimization of Process Organic, showing considerable amounts of asphaltenes present. 

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. 

Elemental analysis. The carbon, hydrogen, sulfur, and nitrogen contents of the asphaltene samples were determined with a Perkin-Elmer 240 analyzer. Oxygen was calculated by difference. The analyses were performed with 1 mg of sample ground and sieved to <0.2 mm. The results were quoted as the mean of values from four determinations. In all cases, the experimental error was <0.5% of the absolute value. 

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