Fraction of alkanes including normal alkanes, ramified alkanes (isoalcanes) and cycle alkanes (naptene).
Aromatic compounds, polycyclic aromatic hydrocarbons. In this group, there are the volatile mono-aromatics compouns like benzene, toluene, xylene, etc. Also, there are the naptene-aromatics and aromatic sulfur compounds like the thiophene and benzothiophene. These compounds are very important due to its toxicity and tendency to bio-accumulate.
The polar fractions are resines (piridines, quinolines, carbazol, sulphoxides and amides) and asphaltenes (phenols, fatty acids, acetones, esters and porphyrines).
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