Asphaltenes are a group of complex high molecular weight hydrocarbons that are found in crude oil. They are composed primarily of condensed aromatic rings and aliphatic chains and are considered to be the heaviest and most viscous components of crude oil. The word “asphaltene” was given by Boussingault in 1837 when he noticed that the distillation residue of some bitumens had asphalt-like properties. Asphaltenes in the form of asphalt or bitumen products from oil refineries are used as paving materials on roads, shingles for roofs, and waterproof coatings on building foundations.
Asphaltenes play a critical role in the behaviour of crude oil, and their properties can have a significant impact on the production, transportation, and refining of crude oil. For example, asphaltenes can clog pipes and inhibit the flow of crude oil, which can cause problems in the production and transportation of crude oil. They can also cause problems in refining by making it difficult to separate the different components of crude oil.
Asphaltenes have high concentrations of heteroelements like sulfur, nitrogen, nickel and vanadium. Although their content varies from source to source of crude oil. These elements pose a serious problem to the catalytic units and clog the catalyst beds. Asphaltenes are also known to be one of the largest causes of fouling in the heat exchangers of the crude oil distillation preheat train. Therefore, the removal of asphaltenes is much necessitated in petroleum refineries.
In petroleum refineries, the asphaltenes are removed using a propane deasphalting process or vacuum residue is converted to Asphalt or Bitumen by Air Blowing Asphalt Unit. The treated oil separated in the Deasphlating unit becomes the feed of the Catalytic conversion unit or lube oil unit feed. The Asphalt pitch is utilized as an asphalt for road paving applications.
In addition to their impact on the behaviour of crude oil, asphaltenes are also of interest to researchers and industry professionals due to their potential as a source of valuable chemicals and fuels. Studies have shown that asphaltenes can be converted into a wide range of useful chemicals and fuels, including gasoline, diesel, and jet fuel.
Asphaltenes can be analyzed using various analytical techniques such as Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FT-IR), and size exclusion chromatography (SEC). These techniques allow researchers to understand the chemical structure and properties of asphaltenes and to study their behaviour in various conditions
Properties of Asphaltenes
Some of the key properties of asphaltenes include:
Asphaltenes are typically insoluble in n-alkanes and are only slightly soluble in aromatics. They are, however, highly soluble in polar solvents such as toluene and tetrahydrofuran.
Asphaltenes have a high viscosity and are considered to be the heaviest and most viscous components of crude oil.
3. Molecular weight
Asphaltenes have a high molecular weight and a complex chemical structure.
Asphaltenes are relatively stable under normal conditions of temperature and pressure but can become destabilized when exposed to certain conditions such as high temperatures, high pressures, or the presence of certain chemical compounds.
5. Melting point
Asphaltenes have a high melting point and are solid at room temperature.
6. Surface activity
Asphaltenes can adsorb onto surfaces and form a film. They can also act as a dispersant, keeping other components of crude oil in suspension.
7. Inhibiting Nature
Asphaltenes can clog pipes and inhibit the flow of crude oil, which can cause problems in the production, transportation and refining of crude oil.
8. Hydrogen to carbon ratio
The hydrogen to Carbon ratio is high, which makes them less reactive compared to other components of crude oil.
Overall, asphaltenes are a complex and important component of crude oil that have a significant impact on the behaviour of crude oil and have the potential as a source of valuable chemicals and fuels. Understanding the properties of asphaltenes can help in the proper handling and processing of crude oil in refineries and other facilities
- Crude Oil Refining Edited by Jean-Pierre Wauquier