Heteroatoms, saturated cores

The hydrocarbons present in oil can be classified into four main classes saturated (alkanes and cycloparaffins), aromatics (hydrocarbons, mono, di and polyaromatic), resins (fractions consist of polar molecules containing heteroatoms such as N, O or S) and asphaltenes (they are molecules similar to the resins, but with a higher molecular weight and polyaromatic core). This classification is known as SARA (Wang et al, 2002 Speight, 2001 Tissot and Welt, 1978). 

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