Write a post explaining the need for vacuum distillation and discuss the utility of Watson Characterization for selecting the vacuum distillation temperature.

Vacuum distillation is essential in petroleum refining. Through this method the distillates can be separated into light vacuum oils, heavy vacuum oils, and vacuum residue. The lighter components of the crude can then be removed out of the top of the distillation column so that the heavier non-volatile compounds remain on the bottom. A vacuum is needed for this method in order have properly met temperatures and pressures within the distillation column. It also is needed in order to avoid thermal cracking.

The heaviest and most contaminated portion of the crude oil is known as the vacuum distillation residue, found on the very bottom. This residue is actually able to be upgraded into a usable fuel source through various processes such as deasphalting, visbreaking, and coking. Deasphalting requires hydrotreating whereas both visbreaking and coking require thermal cracking with coking being more severe.

In catastrophic instances a distillation unit is shut down. This puts a refinery in a very bad position. Very major coking cases can actually block the path of flow in a distillation column and force it to be shut down. Because of this reason it is very important to select the proper temperature in a vacuum distillation column. Doing so will control the risk of coking within the column. The Watson Factor, known as Kw, is used to estimate the upper temperature limit for vacuum distillation to avoid coking and ensure that the process within the distillation column occurs smoothly without any clogging. This is essential to keep a refinery up and running and not have to stop for maintenance.