ASTM D3238 Calculation of Carbon Distribution and Structural Group Analysis of Petroleum Oils by the n-DM Method
Carbon distribution and ring content data are used in characterization of oils in the refining-manufacturing process and can also correlate to critical performance properties. Refractive Index, Density and Molecular Weight (n-DM) are used to calculate the following values:
|% CA||Percentage of Aromatic Carbon|
|% CN||Percentage of Naphthenic Carbon|
|% Cp||Percentage of paraffinic Carbon|
|RA||Average Number of aromatic rings per Molecule|
|RN||Average Number of naphthene rings per Molecule|
|RT||Average Number of rings per Molecule|
The mass % Sulfur must be determined in order to calculate values for RT and RN.
The n-DM and Sulfur content are determined by the following:
|Refractive Index (n)||ASTM D1218|
|Density at 20°C (d)||ASTM D1481|
|Average Molecular Weight (M)||ASTM D2502|
|Sulfur Content (mass %)||ASTM D2622|
Applicability of the method is limited to the following:
In terms of carbon distribution – up to 75% carbon atoms in ring form; % aromatic less than or equal to 1.5 times the % naphthenic rings.
In terms of ring content – up to four rings per molecule with not more than half of them aromatic.