Calculated carbon aromaticity index

Some of the more critical properties related to marine fuels include ash content, carbon residue, calculated carbon aromaticity index (CCAI), density, sulfur, total sediment, and viscosity. A description of these properties and the primary reason for their implementation are provided below ... 

It is impractical to determine the cetane number of residual fuels in the ASTM D-613 cetane engine. Because of this, the Calculated Carbon Aromaticity Index and the Calculated Ignition Index were respectively developed by Shell and BR These values can be determined from the following equations where d = Density in kg/m3 59°F (15°C) and v = Viscosity in cSt 122°F (50°C). 

The n-d-M correlation is an ASTM (D-3238) method that uses refractive index (n), density (d), average molecular weight (MW), and sulfur (S) to estimate the percentage of total carbon distribution in the aromatic ring structure (% C ), naphthenic ring structure (Cj,), and paraffin chains (% Cp). Both refractive index and density are either measured or estimated at 20°C (68°F). Appendix 4 shows formulas used to calculate carbon distribution. Note that the n-d-M method calculates, for example, the percent of carbon in the aromatic ring... 

One method (ASTM D-2501) describes the calculation of the viscosity-gravity coefficient (VGC)—a parameter derived from kinematic viscosity and density that has been found to relate to the saturate/aromatic composition. Correlations between the viscosity-gravity coefficient (or molecular weight and density) and refractive index to calculate carbon type composition in percentage of aromatic, naphthenic, and paraffinic carbon atoms are used to estimate of the number of aromatic and naphthenic rings present (ASTM D-2140, ASTM D-3238). 

Figure 2.22 Graphical measurement of Kovats retention index (/= lOOn ) on a column in the isothermal mode. The number of equivalent carbons n, is found from the logarithm of the adjusted retention time t of X. The chromatogram corresponds to the injection of a mixture of 4 n-alkanes and two aromatic hydrocarbons. The values in italics match the retention times given in seconds. By injecting periodically this mixture the modifications to the Kovats indexes of these hydrocarbons permits the following of the column s performance. The calculations for retention indexes imply that the measurements were effected under isothermal conditions. With temperature programming they yield good results to the condition to adopt an adjusted formula, though this entails a reduction in precision.

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. 

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.

Important characteristics determining the quality of a feedstock are the C/H ratio as determined by elemental analysis and the BMC Index [4.7] (Bureau of Mines Correlation Index), which is calculated from the density and the mid-boiling point resp. the viscosity. Both values give some information on the aromaticity and therefore the expected yield. Further characteristics are viscosity, pourpoint, alkaline content (due to its influence on the carbon black structure), and sulfur content, which should be low because of environmental and corrosion considerations. 

Figure 9.6. Plot of McKnight et al. (2001) fluorescence index (FI) vs. % aromaticity for a variety of isolated fulvic acid samples. The % aromaticity was calculated using C-NMR as the ratio of the area of the aromatic carbon region to the total area of the spectrum. There is a strong correlation between FI and % aromaticity (linear regression equation is y = -O.Qllx + 2.1 (B - = 0.85), and the power function regression is y = 3.94 x where x=% aromaticity and y = FI). Note that while Deer Creek (DC) flows into Snake River (SR), the aromaticity drops due to the aromatic fulvic acids sorbing to iron oxide in the streambed, but there is httle change in the FI, indicating a robustness of the index.

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