Benzene–toluene fractionation and phase equilibrium calculator
H. K. D. H. Bhadeshia and H. Yan, Queen Mary University of London
Equilibrium stage stepping, temperature–composition coexistence, and column distillation modelling.
How pure benzene is separated from the mixture:
Benzene has the lower boiling point than toluene (80.1 °C vs 110.6 °C, respectively). It preferentially vaporises and travels upwards toward the cold top condenser. Meanwhile, toluene is repeatedly condensed out of the rising vapour by descending colder liquid, causing toluene to "scrub" downwards into the hot part of the column as a liquid. Note that "reflux" is the condensed overhead liquid recycled back into the top of a distillation column to cool the upper trays and scrub less volatile components out of the rising vapour.
Top exit (overhead distillate):
Vapour at the top tray reaches ~80 °C and is >96% pure benzene. It is condensed into liquid distillate.
Bottom exit (liquid bottoms):
Toluene is not extracted as vapour; it is drained as a hot liquid (~110 °C) containing <5% benzene from the reboiler.
Operating parameters
Feed mole fraction benzene0.40
Target distillate purity (xD)0.96
Target bottom purity (xB)0.05
Reflux ratio (R = L/D)2.50
Feed thermal condition (q)
Theoretical stages required8 trays + reboiler
Feed tray locationTray 5 (from top)
Minimum reflux ratio (R_min)1.38
Temperature–composition diagram
Column counterflow and tray gradient
Liquid and vapour composition per theoretical tray