Table 3.

Petroleum hydrocarbons existing in petroleum sludge

PHCs and heterocyclics	Average percentage	Constituents
Aliphatic hydrocarbons	75%	Alkanes, and cycloalkanes
Aromatic hydrocarbons		Naphthalene, phenols, polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene, anthracene, chrysene, benzofluorene, and pyrene, as well as benzofluorene and its derivatives (toluene, xylenes), benzene, and its derivatives
Compounds that are nitrogen-sulfur-oxygen (NSO) containing	Less than 3% of the total composition is nitrogen (N). The amount of sulphur (S) is between 0.3 and 10%. Typically, the oxygen (O) level is less than 4.8%.	Naphthenic acids, mercaptans, thiophenes, and pyridines are examples of polar substances.
Asphaltenes		Mixtures of polyaromatic and alicyclic molecules with alkyl replacements, together with colloidal and pentane-insoluble compounds