The name crude oil is used for naturally occurring and unprocessed petroleum. Crude oils are mixtures of many componentes, hydrocarbons (mostly alkanes, cycloalkanes, and aromatics) and other organic compounds containing nitrogen, oxygen, sulfur, and traces of metals [1].

Traditionally, these compounds are classified in several complex groups. The most popular is the method of separation into four groups: saturates, aromatics, resins, and asphaltenes (SARA) [2].

In refineries, one of the main criteria for control process is the content of asphaltene. Table 1 shows the composition differences normally found in conventional oils, heavy oils, and residues.