Shale asphaltene from

Figure 1. Atomic H/C vs. O/C ratios for asphaltenes from a variety of sources (M) petroleum crude (Alberta, Cretaceous, Carboniferous, and Devonian) ( ) Middle East crude (w) North and South American crude (+) shale oil (+) oil sands and (A) liquids from Kentucky coal at 4000 psi hydrogen and West Virginia coal at (O) 4000 psi, and (U) at 2000 psi hydrogen (21)...

A Comparison of Asphaltenes from Naturally Occurring Shale Bitumen and Retorted Shale Oils The Influence of Temperature on Asphaltene Structure... 

Figure 2. H-l NMR spectrum of asphaltene from shale bitumen...

Speight, J. G. Long R.B. Trowbridge, T.O., (1984). Factors influendng the separation of asphaltenes from heavy petroleum feedstock s. Fuel, 63, 616-621 Speight, J. G., (1992) Molecular Models for Petroleum Asphaltenes and Implications for Processing. Kentucky University e U.S. DOE EAST, oil Shale. Symposium Proceedings, 177... 

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. 

Perhaps, where these fuels differ most is in the amount of resins, asphaltenes, and benzene insolubles. The shale oils contain a very large amount of resins from 12 to 69%, or approximately 50% by weight on a total shale oil basis. The tar sand bitumen contains only half as much resins, and the coal liquids contain much less. On the other hand, the asphaltenes are significant in the tar sand bitumen and in the Pitt Seam coal liquids. These latter materials are the only ones to contain a significant amount of benzene insolubles. 

Asphaltene is an essential component of any dark-colored, heavy, viscous and nonvolatile oil, regardless of the oil source. Asphaltene can be obtained from the oil extracted from a naturally occurring organic-rich fossil material by a simple solvent fractionation. Asphaltene also can be obtained from the chemical conversion product of a solid fuel, such as pyrolysis or catalytic hydrogenation of coal or shale. The former is an example of the asphaltene isolated from native petroleum oil. An example of the latter is the asphaltene obtained from a synthetic crude, such as shale oil or coal liquid. 

Many questions concerning the nature of petroleum asphaltenes remain unresolved (1) What is the chemical composition of petroleum asphaltenes (2) What are the molecular weights of asphaltene components (3) Why are asphaltenes precipitated from solution in petroleum by the addition of a hydrocarbon solvent such as n-pentane In this chapter we attempt to answer these questions. In addition, we suggest that asphaltene formation is a general phenomenon that is pertinent to the chemistry of coals, tar sand bitumens, shale oil, and other complex solutions of organic compounds. 

Isolation of Asphaltene. Asphaltenes were isolated by pre-ciptating with a 20-fold volume of n-pentane. The oil/resin fraction was separated from the preciptate by filtration through the thimble followed by Soxhlet extraction with n-pentane. The asphaltene fraction was obtained by Soxhlet extraction of the residue with benzene. In the following text, the three asphaltenes will be abbreviated as Bitu, R425 an< Rsoo rePresenti-nS bitumen asphaltene and asphaltenes derived from shale oils retorted at 425 and 500°C respectively. 

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. 

In these petroporphyrins he identified vanadium as well as iron. He established the well-known chemical association between chlorophyll in marine plants and the process of petroleum formation. It was not until 1948 that the second major metallic components in nickel were established. In the intervening years, a number of investigators have found that petroporphyrins are concentrated in the gas oil, resin and asphaltene fractions. " Baker, et at. determined the yields of petroporphyrins from a number of asphaltenes of native crudes and other bituminous materials. Data of ten sources of crude oil as well as tar sands, oil shale and gilsonite are listed in Table 1.3. 

A 35° API gravity Devonian oil from the WCSB in Alberta, Canada was topped at 35°C for 2.5 h under vacuum and the C9+ fraction was used as the starting material for the pyrolysis experiments The topped oil stable carbon isotope ratio is — 29.47%o relative to PDB. The composition of the topped oil is 64% saturates, 23% aromatics, 6.5% resins and 6.5% asphaltenes. The oil falls into the Cynthia shale oil family of Exploration Staff, Chevron Standard Limited (1979) and Allan and Creaney (1991). Oil pyrolysis was performed isothermally in sealed gold tubes at temperatures ranging from 350°C to 400°C, time ranging from 3 to 33 days and pressure of 650 bars. Details of the experimental procedure were discussed previously (Hill et al, 1994, 1996, 2003). 

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