Aromatic carbon content

The TOTAL correlations calculate aromatic carbon content, hydrogen content, molecular weight, and refractive index using routine laboratory tests. The TOTAL correlations are listed below and are also in Appendix 3. Example 2-2 illustrates the use of TOTAL correlations. 

There is a clear trend, however, in the content of aromatic carbon in a coal and its convertibility at short times. This is shown in Figure 13. It can be seen that high convertibility occurs for coals which are intermediate in aromatic carbon content. This observation is consistent with the common belief that thermal fragmentation occurs at aliphatic positions a or to aromatic rings. 

Pines, A., Aromatic Carbon Contents of Coals, SRCs, and Residues Were Determined by CP-l C-NMR", Under a Subcontract to EPRI, RP-410-1. 

Solid state 13C NMR spectroscopy has emerged as a very useful tool for characterizing SOM (Kinchesh et al. 1995 Preston 1996). Several workers have reported that Koc of HOCs was linearly or exponentially related to the aromatic carbon contents of HAs or whole soils as determined by 13C NMR analysis (Ahmad et al. 2001 Chen et al. 1996 Chin et al. 1997 Gauthier et al. 1987 Perminova et al. 1999). The Koc value of humic materials can vary by as much as an order of magnitude, depending upon their origins (Fig. 1). 

Chiou et al. (1998) attributed the enhanced partitioning of PAHs with respect to other HOCs to relatively high compatibility between the cohesive energy densities of PAHs and the aromatic components in SOM. However, the difference in Koc values between soils and sediments is related to the difference in polar group, rather than aromatic carbon, contents (Kile et al. 1999). The authors concluded that the content of polar groups (O-aryl and carboxyl C) has a large negative influence on Koc values, and hence on HOC sorption in soil and sediment. 

Aromatic carbon content for the soil materials was calculated from the CP/MAS 13C NMR spectra using the ratio of peak area of 106-165 ppm to the total area of 0-230 ppm. 

Fig. 8. Relationship between polarity index ((O + N)/C) and aromaticity of organic sorbents from the literature. The aromatic carbon was calculated as the product of aromatic carbon content (108-165 ppm) from NMR distribution and percentage of carbon contents from elemental analysis.

Thermoplastics for aircraft interiors have been evaluated by this technique (10b) in accordance with the FAA specification (peak rate of heat release of 65 kilowatts per meter squared (Kw/m 2) or less). In these tests (10b) Polyether sulfone demonstrated marginal compliance. For Polyether imide (PHI) and PEI/Polydimethyl siloxane copolymers peak heat-release rates were well below the specified value. The overall trend suggested a possible correlation of peak heat release values with aromatic carbon content in the polymers evaluated. 

Figure 12.6 shows the percentage of aromatic carbon content estimated from H-NMR spectra versus observed Ca (n-d-M method). Although the coefficient of determination, R, for the Ca model prediction is 0.97, the relative error for Ca prediction can be substantial approaching 23% for low Ca values. Interestingly, the Ca correlates the most with protons in di-aromatics and tetra-aromatics, HIO region,... 

Methods of Structural Analysis. The most significant differences between structural models 1 and 2 are the prominent aromatic carbon content in model 1 and the aliphatic alicyclic ring content in model 2. Determinations of aromatic carbon content and ring content of fulvic acid might be useful for identifying sources and processes of degradation and fractionation. However, neither of these procedures is simple and straightforward. 

Aromatic carbon content cannot be directly determined from 13C NMR spectrometry because it overlaps with olefinic carbon. Aromatic and olefinic hydrogens can be resolved in H NMR spectrometry, but the chemical shifts of methine hydrogens on esters of secondary alcohols overlap with chemical shifts of olefinic hydrogen in the NMR spectra of fulvic acids. The ring content (0) is a difference determination between the index of hydrogen... 

Fulvic acid from the Suwannee River was used to calibrate peak-height ratios for aromatic carbon content. The application of this method to fulvic acid samples with known aromatic plus olefinic carbon content from various environments is shown in Table II. Aromatic plus olefinic carbon percentages calculated by the peak-height ratio method using lH NMR data closely agree with these percentages computed from 13C NMR data, with the exception of the Big Soda Lake samples. 

The Sagavanirktok River is intermediate in aromatic carbon content. This river drains the bogs on the Arctic tundra (allochthonous inputs) and several lakes (autochthonous inputs). Samples from the Suwannee and Calcasieu rivers are very similar in peak-height ratios with the exception of peak 2 1 ratio, which is much lower for the Calcasieu River sample. The data in Table II indicate that the Calcasieu River fulvic acid has a greater ring content... 

The Temi River samples had the largest aromatic carbon content because of inclusion of the humic acid fraction. Tropical blackwater rivers are known to contain large percentages (as much as 30%) of humic acid DOM because of the low-conductivity waters and lack of solubility controls associated with the sandy podzols in the tropical rain forest (24, 25). 

ASTM D-5292. Standard Test Method for Aromatic Carbon Contents of Hydrocarbon Oils by High Resolution Nuclear Magnetic Resonance Spectroscopy. 

Traina, S. J., J. Novak, and N. E. Smeck. 1990. An ultraviolet absorbance method of estimating the percent aromatic carbon content of humic acids. Journal of Environmental Quality 19 151... 

Calculation based on previous data show that the aromatic carbon content of the SRC can only be increased to the values shown by data by dehydrogenation reactions. These calculations take into account the carbon types present in residue and in the gases. 

Figure 15. Aromatic carbon content of char from benzenedicarboxylic...

The aromatic carbon content of this sample (28% of 42.4 mmol/g or 11.9 mmol/g) is equivalent to 2.0 mmol/g of benzene rings. If the phenolic hydroxyl content of this sample were to exceed 2.0 mmol/g (as indicated by the wet chemical data), the average aromatic ring in the sample would have to... 

Figures 10 and 11 show some examples of model predictions of the feedstock characterization of crude distillation residues. Figure 10 compares model predictions with the experimental distillation curves of three Arabian atmospheric residues. Figure 11 shows the model ability in predicting the aromatic carbon content and the H/C of different feeds in comparison with some NMR data. A more detailed description and discussion of this residue characterization is reported elsewhere (Bozzano et al., 1995, 1998).

Analysis of the degradation products obtained from pyrolysis and oxidative degradation studies suggests that terrestrial humic substances are highly aromatic (c.70% of total C). However, these techniques tend to overemphasize the importance of aromatic and phenolic units. Non-degradative techniques, such as 1H and 13C nuclear magnetic resonance, probably give more realistic aromatic carbon contents of 20—50% for soil humics,... 

In the case of the magnetic resonance characterization, both 13c NMR and proton NMR were employed to obtain the percentages of aromatic carbon and hydrogen. The results are shown in Table IV. Although the measured levels of aromatic hydrogen are within experimental uncertainty of each other, the difference in aromatic carbon is probably significant. Nevertheless, this difference is small and indicates that the aromatic carbon contents are quite similar. In addition, attempts to discern qualitative differences in the 13c NMR were in vain. These results imply that very little, if any, dealkylation or aromatiza-tion has occurred during the crude distillation procedure. 

We believe that the abundant aromatic carbon content in coals with associated vr-electrons available in the coaly matrix is also probably effective in promoting retention and absorption of polar compounds and aromatic hydrocarbons, but also nonpolar material like alkanes are adsorbed in large proportions (cf Sandvik et al. 1991 Isaksen et al. 1998). 

The solid-state NMR spectra of marine humics are characterized by unsubstituted alkyl carbons [50-52], whereas freshwater humics have a much higher aromatic carbon content [51-53], reflecting the input of material derived from vascular plants. Given that XAD resins recover only 5 - 25 % of the DOC in seawater [26,54], the marine humics characterized by NMR spectroscopy are probably not a major component of DOC. In addition, the similarities in concentration and structural characteristics of humics from a variety of marine environments suggest that it is relatively unreactive. This overall lack of reactivity is confirmed by the C ages of marine humics, which are older than the average (total) C age of DOC [26]. 

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