S/C atomic ratio

Figure 4. S/C atomic ratios from kerogens of living plants, modem sediments, and buried sediments of the three main types of organic matter encountered in the Abu Dhabi recent sedimentary system, (A) the microbial mats, (B) the Avicennia mangrove, (C) the lagoonal seaweeds.

The S/C atomic ratios of kerogens of modem and buried microbial mats covers a large range of values. The lowest S/C values were found for the modem microbial mat with thick carbonate-sand layers collected near the lagoon. Landward, as the carbonate layers get thinner and more muddy, the S/C values increase progressively, until they reach the maximum value which is found in the modem samples, in the massive mat with lumps filled with H2S. This could be explained, if we consider the aptitude of this thick mineral layers to allow water circulation, and so a better oxygenation of the system. On the contrary the massive mat with the much thinner mineral layers seems to form a much closer system as suggested by the occurrence of lumps filled with H2S. 

TABLE 1. Variation of S/C Atomic Ratio of Humic Substances in Core KL9 from the Oman Sea"... 

In addition, the use of different hydrocarbon liquids for the separation yields asphaltene fractions that are substantially different from each other (I, 25). For example, the H/C ratios of the heptane precipitate are lower than those of the pentane precipitate, indicating a higher aromaticity in the heptane precipitate. The N/C, O/C, and S/C atomic ratios are usually higher in the heptane precipitate, indicating higher proportions of the heteroelements in this material (26). 

The XPS Cls and S2p core-level lineshapes for the thiophene oligomers, thiophene polymers and alkyl-substituted thiophene polymers are well documented in the literature [117,123—126]. Table 3.4 summarizes the Cl s, S2p BE values, their linewidths (full width at half maximum, FWHM) and the S/C atomic ratios for several thiophene oligomers and polymers [117]. In general, the a and p carbons in thiophene polymers with a BE separation of only 0.34 eV cannot be resolved from the main Cls component. Two other minor Cls components located at above 2.6 eV and 5.2 eV above the main peak have been assigned to the shake-up structures. The S2p core-level spectrum is curve-fitted with two components with BEs at about 163.8 and 165.5 eV, corresponding to the respective spin-orbit split doublets (S2p3/2 and S2pi/2). An n transition shake-up structure is also discernible at... 

Table 3.4. Cls and S2p energy values (eV), spectral linewidths (FWHW) and S/C atomic ratios for several thiophene oligomers and polymers. (Reprinted with permission from ref 117, Am. Inst. Phys.)...

The examination of the sulfur isotope variation in the different species and oxidative states reveals very interesting behavior (Fig. 2). This figure should be examined in relation to Fig. 3 that presents the values versus S/C atomic ratio. Following the interstitial water sulfate isotope profile with depth into the core shows that the supply of sea water is open for the lake (top) and through the sand barrier seepage (bottom). This keeps the values close to open sea... 

Pyrite in the bituminous rocks appears as both framboids and single crystals (<50 /rm) that are undetected by X-ray diffraction analysis because they are coated with OM (Spiro, 1980 Spiro et al, 1983a,b). Very small amounts of humic matter occur in these samples, but more than 95% of the OM in the bimminous rocks is high sulfur kerogen (8-10% w/w). The richest samples in both TOC and organically bonded sulfur occur in the Nabi Musa (Israel) area (S/C atomic ratio 0.05-0.065). Various maturity parameters indicate that all of the kerogens are immature with an H/C ratio of 1.3-1.6. 

S/C atomic ratio increased in general as the oil became heavier, in line with the higher proportion of this heteroatom in the asphaltenes. N/C atomic ratio showed values more or less constant. 

Two spectra of sulfided catalysts in Fig. 4.16 show that sulfur can also be detected, albeit with lower sensitivity, because of the Z2 dependence of the cross section in (4-6). Figure 4.17 gives the S/Mo atomic ratio as a function of sulfidation temperature. It indicates that sulfur uptake by M0O3 is already significant at room temperature and increases to the expected S/Mo ratio of 2 above 100 °C. Combination of these results with SIMS and XPS data have led to a detailed mechanism for the sulfidation of silica-supported molybdenum catalysts [21] (see also Chapter 9). 

At sulfidation temperatures above 125 °C, the Mo 3d XPS spectra shift to those characteristic of Mo4+, whereas at temperatures of 250 °C and higher the Mo and S XPS spectra become equal to those of MoS2. The S22 groups gradually disappear to leave S2 as the only state of sulfur the S/Mo atomic ratio as determined with RBS reaches values between 2 and 2.5, as expected for MoS2 (see Fig. 9.16). 

In general, the refractive index decreases with the increment of the fluorine content in a polymer because of the small polarizability of fluorine. Column 6 in Table 1 shows refractive indexes of S-type fluorides. As the reaction temperature increases, the refractive index tends to decrease. This tendency is in good agreement with that of F/C atomic ratio. On the basis of the Maxwell s theory of electro-magnetism, the dielectric constant, e is equal to the square of refractive index, n under a fixed frequency. The dielectric constants of the S-type fluoride calculated based on the relation are also shown in Table 1, Column 7. The dielectric constant slightly decreased with increasing the fluorination temperature. 

At higher temperatures, the influence of phosphorus on the sulfidation of the promotors is completely different. Mangnus et al. 70) reported that the temperature required to obtain complete sulfidation of cobalt in Co—P/Al increases with increasing phosphorus content. The S/Co atomic ratio after sulfidation at 1000°C decreases from 1.3 to 0.39 as a result of phosphorus addition because of the formation of nonsulfided compounds such as cobalt phosphides, according to the following reactions ... 

The extent of pyrite decomposition was followed by obtaining S/Fe atomic ratios at various points across selected pyrite inclusions, the latter in the size range 10-20 pm. Figure 1 is a plot of this ratio versus "distance from interface within pyrite for each of the coals at different temperatures. The results indicate that, for pyrite of this size, decomposition to pyrrhotite occurs in the temperature range 450-500°C, for all the coals studied. The reaction essentially was complete at 500°C. 

In 1973 Labes et ah 8,9) synthesized crystalline bundles of impure (SN)a. flbers. Although the S N atomic ratio was 1 1, the material contained 5.48% impurity (4.93% 0, 0.42% H, and 0.13% C). However, metallic-like conductivity was observed in directions parallel to the (SN), flbers, and this increased sharply with decrease in temperature. Six different samples had conductivities at room temperature of 10, 89, 230, 640, 1470, and 1730 ohm" cm" Since the electrical conductivity of an anisotropic substance can be affected enormously by even traces of impurities, we decided that it was most important to attempt to synthesize analytically pure crystals of (SN). and to examine the physical and chemical properties of the material. Only in this way would it be possible to determine whether the metallic-like properties reported for (SN). (8, 9) were characteristic of the pure material. 

Table 4 shows the relative atomic concentrations of the dominant elements on the surface of both polysulfone membranes, although other elements (impurities) such as calcium in D-PS or sodium and chlorine in P-PS were also observed in relative concentrations lower than 0.5 %. According to the theoretical molecular structure of poly-(ether sulfone) (Vitrex) the 0/C and S/0 atomic ratios are 0.25 and 0.33, respectively while for polysulfone (Udel) the 0/C ratio is 0.15 and the S/0 ratio is 0.25. As can be observed from the 0/C ratio indicated in Table 4, both polysulfone membranes show an excess of oxygen with respect to sulfur atoms, and an excess of carbon with respect to oxygen atoms, which points out the presence of atypical chemical compounds containing also carbon and oxygen atoms. 

N, S, and minerals in varying portions. The approximate range of the H/C atomic ratio and 0/C atomic ratio for various rank coals which seems to affect the reactivity is shown in Fig. 3. 

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