Main-Product

In a refinery, Unconverted oil (UCO), is the part of the feedstock, usually heavy hydrocarbons, that does not undergo the desired conversion into lighter products like gasoline or diesel during processes like hydrocracking and remains as a heavier hydrocarbon fraction. The term UCO is most commonly associated with hydrocracking units, where vacuum gas oil (VGO) or heavier fractions are processed. However, it can also appear in other conversion processes, though less frequently.

UCO is typically a heavy oil with a high boiling point, rich in paraffinic and naphthenic components. UCO molecular weight is typically between 300 and 500 g/mol, depending on the refinery’s feedstock, like vacuum gas oil, and the hydrocracking process’s severity. For example, UCO optimized for base oil production might have a higher MW due to its paraffinic content. The typical density of UCO in a refinery is around 0.92 to 0.96 g/cm³, with an average of about 0.95 g/cm³ at 15°C, varying by feedstock and process.

UCO can be used as a feedstock for lubricant base oil production, where it undergoes further hydroisomerization to isomerize n-paraffins and saturate aromatics , to make Group II or III base oils, which are important for engine oils. In some refineries, UCO is recycled back into the hydrocracking unit to try and convert more of it, or it might be blended into fuel oil. UCO is also a high-quality feedstock for the Fluid Catalytic Cracking (FCC) process. 

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