The Collaborative International Dictionary of English v.0.48:

fractionation \frac`tion*a"tion\ n.
   the act or process of separating a mixture into portions of
   different composition, as in distillation or fractional
   crystallization.

   Syn: fractional process.
        [WordNet 1.5 +PJC]

   2. (Petroleum industry) Separation of crude oil into
      components of differing composition by fractional
      distillation.
      [PJC]

WordNet (r) 3.0 (2006):

fractionation
    n 1: a process that uses heat to separate a substance into its
         components [syn: fractionation, fractional process]
    2: separation into portions