PrintSeparation in Fractional Distillation
The quality of separation in fractional distillation can be calculated using the designated cut points (at 5%vol and 95%vol) for the two adjacent fractions, termed as light and heavy. As shown below, the difference in temperature (ΔT) between 5% vol temperature of the heavy fraction and 95%vol temperature of the light fraction is used to define the quality of separation. A positive value of ΔT(termed ASTM gap) indicates good separation, while a negative value of ΔT (termed ASTM overlap) points to a bad separation.
ASTM distillation temperatures and separation in a distillation process
Fractionation
What defines a good separation?
The relationship between the ASTM distillation temperatures at 95% vol and 5% vol of two adjacent fractions, light and heavy, respectively.
ASTM 5% volT (heavy fraction) - 95% volT (light fraction) = ∆T
(e.g., LGO) (e.g., kerosene)
if ∆T >0, called ASTM gap (good separation)
if ∆T<0, called ASTM overlap (bad separation)