Vacuum Pot Still: ASTM D5236 for Distillation of Heavy Hydrocarbons

The vacuum pot still distills crude oil residue from 370 ºC up to 565 ºC.  D5236 is the ASTM test number. It is most commonly used to distill the residue from ASTM D2892 true boiling point test. There are four sizes of distillation column shown in the table below with corresponding boiling flask and sample size.

Vacuum Pot Still (D5236)
Column Diameter	25 mm	36 mm	50 mm	70 mm
Sample Size	1-2 L	2-4 L	4-8 L	8-16 L
Boiling Flask Size	2-3 L	3-6 L	6-12 L	12-24 L

D5236 is distillation column that models the vacuum distillation unit in a refinery.  It has two entrainment separators. These separators force rising vapor through a choke point where entrained liquid drops form larger droplets. Eventually the droplets become large enough that the force of gravity is larger than the force of the rising vapor. This causes the drops to fall back to the boiling flask. This process ensures that only distilled vapors are collected.