Bitumen elemental analysis

The elemental analysis of oil sand bitumen (extra heavy oil) has also been widely reported (Speight, 1990), but the data suffer from the disadvantage that identification of the source is too general (i.e., Athabasca bitumen which covers several deposits) and is often not site specific. In addition, the analysis is quoted for separated bitumen, which may have been obtained by any one of several procedures and may therefore not be representative of the total bitumen on the sand. However, recent efforts have focused on a program to produce sound, reproducible data from samples for which the origin is carefully identified (Wallace et al., 1988). It is to be hoped that this program continues as it will provide a valuable database for tar sand and bitumen characterization. 

However, in order to define conventional petroleum, heavy oil, and bitumen, the use of a single physical parameter such as viscosity is not sufficient. Other properties such as API gravity, elemental analysis, composition, and, most of all, the properties of the bulk deposit must also be included in any definition of these materials. Only then will it be possible to classify petroleum and its derivatives (Speight, 1999). 

Characterization of Feedstock and Catalysts. The elemental analysis and physical properties of various feedstocks used in this study are given in Table I. The data show that the virgin bitumen contains... 

Table I. Elemental Analysis and Properties of Catalytic Cracking Feedstocks (Asphalt Ridge Bitumen)...

The classic definition of asphaltenes is based on the solution properties of petroleum residuum in various solvents. This generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale. 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. This effort is summarized by Speight and Moschope-dis (i) in their chapter in this volume along with a good summary of the current thinking. Thus, there are petroleum asphaltenes, coal tar asphaltenes, shale oil asphaltenes, tar sands bitumen asphaltenes, and so on. In this chapter I will attempt to show how these materials are special cases of an overall concept based directly on the physical chemistry of solutions and that the idea that they have a specific chemical composition and molecular weight is incorrect even for different crude oil sources. 

Intensive research on elemental analysis has been carried out in this laboratory to overcome difficulties in determining nitrogen and sulfur in heavy fractions of petroleum or bitumens. With existing combustion techniques it was nearly impossible to obtain good overall balances for these elements when individual fractions coming from liquid chromatography were analyzed. Recoveries of 85%-95% of the quantity originally present in the... 

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. 

Feedstock Characteristics. The Sunnyside tar sand sample contains 9.3 wt % bitumen. The extracted bitumen was subjected to deasphaltening and results of three runs were 20.6, 19.9, and 21.4 wt % (20.6% average) of the total bitumen. The elemental analysis and physical properties of the bitumen,... 

Table I. Elemental Analysis of Bitumen and Product Oils...

Analytical methods are described in (2). Standard methods were employed for total organic carbon (TOC) and Fischer Assay (FA) analyses. Kerogen was isolated by solvent extraction to remove bitumen and acid dissolution to remove mineral matter. Elemental analysis was performed only on kerogen with low ash content (<25% by weight). 

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. 

Figure 5a and Table la contain data for a set of samples taken from a 1500 m thick section of the Monterey shales. The kerogens were isolated (HCl, HCl/HF removal of carbonates and silicates and dilute nitric acid to remove the pyrite) for some of the core samples, but the total rock was used for the Rock Eval T ax determination to estimate maturation levels. The was measured for the extracted bitumen of each sample. The increase in T ax with depth is correlated with maturation indicating that burial of the samples increased their maturation. Two trends are indicated by the values one starts at +15.6 and increases to +17.7%o, and the second from +19.0 to +21.3%o. The data indicate that the bitumen produced at higher level of maturation is enriched with the heavier isotope. The elemental analysis of the bitumen shows that the shallowest (1400 m) sample has —11% S, whereas the deepest at 2490 m... 

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 4-49 Element analysis (wt %) and average relative particle mass of the bitumen.

These results had not been expected, considering the different origins of the samples, their different colloid compositions, and their different average molecular weights. Element analysis proved that the H/C ratios of the distillation bitumens, and of the blown bitumens and their colloid components, show very small variations (Tables 4-53 and 4-54). 

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). 

The major exception to these narrow limits is the oxygen content of bitumen, which can vary from as little as 0.2% to as high as 4.5%. This is not surprising, since when oxygen is estimated by difference the analysis is subject to the accumulation of all of the errors in the other elemental data. Also, bitumen is susceptible to aerial oxygen and the oxygen content is very dependent upon the sample history. In addition, the ultimate composition of the Alberta bitumen does not appear to be influenced by the proportion of bitumen in the oil sand or by the particle size of the oil sand minerals. 

Analysis Elemental C, S, H, O, N (typically 79-88% C 7-13% H up to 8% S 2-8% O up to 3% N). Trace metals Fe, Ni, V, Ca, Ti, Mg, Na, Co, Cu, Sn, Zn. Molecular mass typically M, = 500-2500. Acid number typically 0.1-2.8mg KOH per g. Distillation range ASTM D3279. Composition bitumen insoluble in paraffin naphtha (AASFITO T46 or ASTM D3279) bitumen soluble in carbon disulfide (ASTM D4). Purity solubility, ash, water content (ASTM D95). Softening point ASTM D36. Flash point ASTM D92. 

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