Vacuum Distillation Unit (VDU)

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In petroleum refining, the Vacuum Distillation Unit (VDU) is a secondary processing unit that further refines heavier oils left over after the crude oil feedstock is initially run through the atmospheric distillation unit, also known as the crude distillation unit (CDU). 

In the vacuum distillation unit, residual oils from the CDU are distilled under a vacuum at significantly lower pressures than the CDU. At these lower pressures, the boiling point of the residual oils is low enough that lighter products can vaporize without cracking and impeding the distillation process. 

Heavy distillates produced during the vacuum distillation process include light gas oil and heavy gas oil, which are then sent to the downstream separation and conversion units to be further refined into lube oil base stocks, or as feedstock for hydrocracking to produce light and middle distillates, such as jet fuel, kerosene, and diesel. Any residual oil leftover in the vacuum distillation column is transferred to the coker unit for further refining.


  1. U.S. Energy Information Administration, 2012, “Vacuum distillation is a key part of the petroleum refining process,”

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