Alkane distribution

As another variation, the production of alkanes can be accomplished by modifying the support with a mineral acid (such as HCl) that is co-fed with the aqueous sorbitol reactant. In general, the selectivities to heavier alkanes increase as more acid sites are added to a non-acidic Pt/alumina catalyst by making physical mixtures of Pt/alumina and silica-alumina. The alkane selectivities are similar for an acidic Pt/silica-alumina catalyst and a physical mixture of Pt/alumina and silica-alumina components, both having the same ratio of Pt to acid sites, indicating that the acid and metal sites need not be mixed at the atomic level. The alkane distribution also shifts to heavier alkanes for the non-addic Pt/alumina catalyst when the pH of the aqueous sorbitol feed is lowered by addition of HCl. The advantages of using a solid acid are... 

A study of the Isua organic matter is still in progress (McKirdy Hahn, 1982)s>. Volatile organics have been found to occur chiefly in quartzites and in silicate-rich BIF. Alkane distributions show great variability, even over distances of a... 

The Class 4 oils are distinguished by their unusual n-alkane distribution, which is unlike that for any of the other classes these oils contain no n-alkanes heavier than about C15, are not condensates and have API gravities that range from 22.9° to 24.7° (Table III). 

In terms of C9-Cn and corresponding range of aromatic compounds, there is a similarity to Class 1 oils (Figures 4 and 5), an observation which would be consistent with a common source. However, there is a difference in the normal alkane distribution when Class 4 oils are compared to Class 1 or Class 2 oils. Class 4 oils have a lower benzene and toluene content and appear more biodegraded relative to Class 1 oils (see Tables I and III). The Class 4 oils are all in a Miocene reservoir, the L-5, which is in permeable contact with the Eocene B sands below. Other oils in the area do not show the same normal alkane distribution, but these differences are insufficient to invoke a separate source rock. The TJ-210 oil (Class 5) is also reservoired in an L-5 sand and is unusual in that it is depleted in normal alkanes between C9 and C13 (Figure 2). It is possible that the Class 5 and the Class 4 oils are related by some process of natural distillation as reported (6) for Trinidad oils. In this process the light ends (C15+)... 

The sequence of their removal is the same as that observed in many other areas and attributed to bacterial degradation. A few oils show unusual normal alkane distributions that are not well explained by currently understood degradation or migration processes. 

Grimalt, J., Albaiges, J., Al-Saad, H.T., and Douabul, A.A.Z. (1985) n-Alkane distributions in surface sediments from the Arabian Gulf. Naturwissenschaften 72, 35-37. 

Parrish, C.C., Eadie, B.J., Gardner, W.S., and Cavaletto, J.F. (1992) Lipid class and alkane distribution in settling particles of the upper Laurentian Great Lakes. Org. Geochem. 18, 33 -0. 

Figure 2. Comparison on n-alkane distribution from Beulah lignite, A, and n-alkane distribution from CPU bottoms recycle product, (Beulah lignite feed coal).

Figure 3 shows four examples of fuel fingerprinting the normal alkane distribution helps to indicate the fuel type. Because of the high resolution in this example, it is possible to obtain useful information from the chromatogram and to be able to compare this output tracing to those... 

Figure 2. GC/MS n-alkane distribution of extracts from (a) reactor recycle cup and (b) reactor outlet line.

Figure 6. Comparison of the normal alkane distribution in shale oil generated by pyrolysis and in bitumen from geological samples with an equivalent stage of thermal...

Briefly, n-alkane distributions with carbon number maxima in the 17-21 range (Cj y-C j ) originate largely from aquatic algal sources, while maxima characterized by higher carbon numbers are... 

Bound aliphatic hydrocarbons comprised 7 of the saponifiable lipid (<1 to 15 ug/g). Unbound/bound ratios of <1 to 67 of this hydrocarbon fraction, with the exception of 603B-29-1, agree with values reported in other studies (, 37). Bound alkane distributions were dominated by C or C-, (Figure 3). Even-carbon predominance of alkanes is an anomaly, but distributions similar to those in the present study have been observed in other North Atlantic deep-sea sediments ( 29). The source of these compounds, however, is unknown. 

Grimalt J., Albaiges J. (1987) Sources and occurrence of C12-C22 re-alkane distributions with even carbon-number preference in sedimentary environments. Geochim. Cosmochim.Acta 51, 1379—84. 

Jovancicevic B, Tasic L, Wehner H, Markovic D, Polic P (1998) n-Alkane Distribution as a tool in the identification of organic type pollution in river sediments. Fresenius Environ Bull 7, 320-326. 

Odd-even ratios are frequently observed to vary from one portion of a given n-alkane distribution to another. For example, see the chromatogram of Core 12-77 from South Shore transect (Figure 6). The CPI ratio for n not greater than 20 is 7.76 and contains a large bias produced by prominent Ci7 and Ci9 biogenic peaks. This is typical of most of the samples listed in Table I. In contrast, the CPI for n not less than 20 is within 20% of 1 in most cases. 

FIGURE 27.5 Quantitative distribution of n-alkanes of the six petroleum products mentioned in Figure 27.4, illustrating distinguishing features of n-alkane distribution patterns between these products. 

Figure 27.10 and Figure 27.11 show w-alkane distribution and target PAH distribution of the ASMB oil at weathered percentages of 0% and 45%, respectively, to illustrate the elfects of physical weathering on the oU chemical compositions. 

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