deasphalting

Deasphalting is a refinery process that removes asphaltic components from heavy hydrocarbon fractions, yielding deasphalted oil (DAO) and a byproduct asphalt. The primary goal is to upgrade residues from vacuum distillation or heavy crude to lighter, more valuable feeds for downstream units, while reducing metals, sulfur, and Conradson carbon content.

Solvent deasphalting (SDA) is the most common method. The feed, usually vacuum residue, is contacted with a hydrocarbon solvent such as propane, butane, or pentane. The solvent dissolves maltenes while asphaltenes precipitate as asphalt. The mixture is settled and separated; the DAO is sent to upgrading and the asphalt is recovered. The solvent is flashed and recycled. DAO has lower metals, sulfur and Conradson carbon than the feed. Yields typically range from about 60 to 80 percent of the feed as DAO, depending on solvent, temperature, and feed quality.

Thermal deasphalting (TDA) uses heat to separate asphalt from heavy residues, often with little or no external solvent. This approach relies on high temperatures and residence time to produce a deasphalted oil with different properties. TDA generally has different solvent requirements and capital needs compared with SDA, and may be used when solvent availability or economics are unfavorable.

DAO is used as feed for hydrocracking, hydrotreating, or catalytic cracking to produce distillates and fuels, while asphalt is used for paving and other industrial applications. Recovered solvents may be recycled to improve overall economics.