Simple distillation: Boiling point gap > 25 degC, no azeotrope. Single vaporization-condensation. Examples: water purification, ether (35 degC) from toluene (110 degC).

Fractional distillation: Bp gap < 25 degC. Fractionating column provides multiple theoretical plates (vaporization-condensation cycles). Lower-boiling component enriched in vapor at top. Examples: acetone $\frac{56 degC}{methanol}$ (65 degC), crude oil refining, ethanol/water (but note: 95.6% ethanol/water is an azeotrope — cannot be separated further by distillation alone).

Steam distillation: For compounds that are (1) immiscible with water, (2) have appreciable vapor pressure below 100 degC (steam-volatile), (3) would decompose at their normal boiling point. Principle: total pressure = Pwater + Pcompound = atmospheric, so compound distills well below its normal bp. Examples: aniline (bp 184 degC, steam distills at 98 degC), nitrobenzene, essential oils, clove oil.

Vacuum distillation: Reduces bp by lowering external pressure. For heat-sensitive compounds. Glycerol (bp 290 degC at 1 atm → 180 degC under vacuum).

Azeotropic distillation: Special technique to break constant-boiling mixtures by adding a third component (entrainer). Benzene added to ethanol-water azeotrope → ternary azeotrope removes water → anhydrous ethanol.