Carbon number shales

Desulfurisation of polar fractions of relative immature oils and sediment from hypersaline palaeoenvironments yields n-alkanes with strong even-over-odd carbon number predominances (20,42 e.g., Figure 11). This phenomenon is, however, not restricted to samples from hypersaline palaeoenvironments (e.g., Jurf ed Darawish Oil Shale, Monterey Shale). 

Figure 8. Carbon number distribution patterns (C15-C4q) of the midchain 2,5-dialkylthiophenes of the Jurf ed Darawish oil shale samples indicated.

Isoprenoids (terpanes), with a longer chain than pristane, have been detected in fossil fuels (see below the discussion on the analysis of petroleum). C25—C30 isoprane hydrocarbons were analysed in a number of methanogenic bacteria The C40 isoalkane, which was isolated from the saturated fraction of the bitumen of the Green River Shale (USA), is claimed to be the product of total saturation of carotenoids. The analysis of these polyhydrogenated carotenes (PHC) requires special GC high-temperature inert columns (see GC of high carbon number wax hydrocarbons). 

Previous studies on heavy hydrocarbon content of young sediments showed that they contained all the n-paraffin series, but that those containing paraffins with odd numbers of carbon atoms were several times as abundant as those containing even numbers of carbon atoms. Bray and Evans (7) defined a ratio of odd to even paraffins as a carbon preference index (CPI). In Recent sediments (mostly from nearshore environments) the CPI varied from 2.5 to 5.5. Crude oils and extracts from ancient shales exhibited little odd-carbon preference. The CPI for ancient shales varied from 0.9 to 2.3 and that for crude oils from 0.6 to 2.2... 

IRATI FORMATION, by far the largest, which extends from the state of Sao Paulo to the frontier with Uruguai. The very conservative numbers shown in Table II are meant to represent the measured reserves processable by the Petrosix process developed by Petrobras to retort oil shales. These restrictions are mainly related to min ing variables, carbon content, brittleness etc. Indeed, they repre sent only a small fraction (the border) of the Parana Basin. 

The data in Tables I-III have been used to calculate elemental balances. The results are shown in Table V with all of the numbers put on a molar basis and normalized to 100 organic carbons in the starting shale. This treatment makes it easy to follow the movement of the elements and simplifies the discussion of molecular transformations occurring during retorting. The recovery of carbon (organic plus inorganic) is 95-96% for each experiment. 

Figure 2. Distribution of carbon functionalities in Colorado shale and products from retorting in an inert atmosphere. Numbers in parentheses are the percentages ofstarting organic carbon in each fraction.

Fig. 6-9 Ternary diagram showing proportions of dissolved Si(OH)4, carbonate alkalinity (HCOj + CO3"), and (Q + S04 ) in the Orinoco River and Amazon River basins. Charged species are in equivalents Si(OH)4 is in mole units. The curves in the larger figure are numbered in total cation concentration (mEq/L). Unlike previous figures, symbols represent the total cation concentration interval that includes the sample s concentration. The predominant symbol within each interval corresponds to samples whose concentrations plot within that interval. In the smaller figure, the patterned areas correspond to the predominant source of samples whose concentrations plot within the areas (A) streams that drain cratonic areas (B) streams that originate in mountain belts, but that drain large areas of cratons (C) streams that drain mountain belts with extensive black shales (D) streams that drain mountain belts with extensive carbonate rocks and evaporite deposits. Adapted from Stallard (1988) with the permission of Kluwer Academic Publishers.

Solid-state C NMR spectra of oil shales, obtained by CP/MAS with high-power decoupling are broad because of the multitude of resonances from the different carbon types found in these complex materials. A number of af roaches have been taken to improve the resolution of solid-state NMR of fi il fuels. Such tedmiques include variable temperature studies, variable frequency studies, mathematical enhancements and deconvolution techniques, and relaxation rate methods. The most popular method of enhancing solid-state NMR spectra is a relaxation rate method called dipolar dephasing (DD), which is sometimes referred to as interrupted decoupling. The exploitation of relaxation methods in CP NMR of fossil fuels has been reviewed elsewhere. ... 

As noted in Section 2.4 there are a number of ways to improve resolution in the NMR spectra of fossil fuels and to obtain additional structural parameters. Of these, the technique of dipolar dephasing has received the most attention. Dipolar dephasing provides information about the amounts of protonated and nonprotonated aromatic and aliphatic carbons in the sample, from which other structural parameters can be derived. Dipolar dephasing measurements have been made on raw oil shales and kerogens ... 

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