Vacuum Distillation is an important part of Petroleum processing in the United States. According to the EIA, approximately 80% of the refiners operating in the US have a Vacuum distillation unit (VDU).¹ This is a secondary processing unit added to petroleum refineries, consisting of vacuum distillation columns.² This process helps to produce petroleum from that of heavier oils that are left over from traditional atmospheric distillation.¹ In the refining process, the atmospheric distillation unit (ADU) separates the lighter hydrocarbons from heavier oils based on boiling process. The ADU can reach boiling point of crude oil up to 750 F, above which oil would usually thermally crack, or break apart, which hinders the distillation process.² The bottoms left over from the ADU then can be run through a vacuum distillation column to further refine and improve yield.¹ The products from vacuum distillation are slightly heavier than middle distillates, but can be further refined to make products such as gasoline and naptha.¹

To determine the temperature at which vacuum distillation can be used tp further process the petroleum, the Watson Characterization factor can be utilized. The plot of the Watson characterization is information showing the range of temperatures which can be used to avoid cracking, which would slow the refinery process. The Watson Characterization factor defines the upper bound temperature limit for vacuum distillation as a means to avoid cooking of the feed stock. Below the indicated bound, cooking risk would be minimal and above it, cooking could be a potential risk.

1. Vacuum distillation is a key part of the petroleum refining process http://www.eia.gov/todayinenergy/detail.cfm?id=9130