DAO
Initialism of de-asphalted oil, a crude oil refinery process stream.
DAO: crude oil stripped of its heaviest, stickiest molecules
De-asphalted oil is the liquid hydrocarbon stream left after removing asphaltenes from crude oil or vacuum residue. Asphaltenes are the densest, most aromatic components of crude, typically black or dark brown solids that precipitate out when crude is exposed to light alkanes like propane or butane. DAO is what remains: a feedstock that is cleaner, lighter, and more processable than the original material.
The separation happens in a solvent deasphalting unit, where vacuum residue (the bottoms from atmospheric and vacuum distillation) contacts a light alkane solvent at elevated temperature and pressure. The asphaltenes flocculate and settle; the DAO stays dissolved in the solvent phase and is recovered by distillation. The yield of DAO from vacuum residue is typically 40 to 70 percent by weight, with the remainder becoming asphalt or coke feedstock.
Uses and downstream processing
DAO typically has an API gravity of 20 to 35 degrees and serves as a valuable intermediate refinery stream. It can be hydrotreated to remove sulfur and nitrogen, then sent to fluid catalytic crackers or hydrocracking units to make gasoline, diesel, or lighter products. Because it is already free of asphaltenes, it causes fewer coking and fouling problems in catalytic reactors than untreated residue would. Some refineries produce DAO specifically as a lube oil base stock feedstock, since the absence of asphaltenes improves the final oil's stability and color.
The solvent choice affects the product: propane deasphalting yields lighter DAO but requires harsher operating conditions; butane is gentler and more widely used in modern units. Some refineries recycle the solvent, making the unit energy-intensive but economical at scale. The asphaltene-rich reject stream is sometimes coked for fuel, sold as bitumen, or further processed into specialty products.
DAO's value depends on crude origin and refinery configuration. In refineries with limited conversion capacity, DAO can become a bottleneck; in advanced complexes, it is a route to maximize liquid product recovery from the heaviest crude fractions. The term is used interchangeably with deasphalted oil, though DAO has become standard in industry shorthand.