Editing Fractionating column (section)

==Laboratory fractionating columns==
[[Image:Fractional distillation lab apparatus.svg|thumb|300px|Figure 1: Fractional distillation apparatus using a [[Liebig condenser]].]]
[[File:Vigreux column lab.jpg|thumb|left|200px|Vigreux column in a laboratory setup]]
A laboratory fractionating column is a piece of glassware used to separate vaporized mixtures of liquid compounds with close volatility. Most commonly used is either a [[Vigreux column]] or a straight column packed with glass beads or metal pieces such as [[Raschig ring]]s. Fractionating columns help to separate the mixture by allowing the mixed vapors to cool, [[Condensation|condense]], and vaporize again in accordance with [[Raoult's law]]. With each [[condensation]]-vaporization cycle, the vapors are enriched in a certain component. A larger surface area allows more cycles, improving separation. This is the rationale for a Vigreux column or a packed fractionating column. [[Spinning band distillation]] achieves the same outcome by using a rotating band within the column to force the rising vapors and descending condensate into close contact, achieving equilibrium more quickly.

In a typical fractional distillation, a liquid mixture is heated in the distilling flask, and the resulting vapor rises up the fractionating column (see Figure 1). The vapor condenses on glass spurs (known as [[Theoretical plate|theoretical trays or theoretical plates]]) inside the column, and returns to the distilling flask, [[reflux]]ing the rising distillate vapor. The hottest tray is at the bottom of the column and the coolest tray is at the top. At [[steady-state]] conditions, the vapor and liquid on each tray reach an [[vapor–liquid equilibrium|equilibrium]]. Only the most volatile of the vapors stays in gas form all the way to the top, where it may then proceed through a [[Condenser (heat transfer)|condenser]], which cools the vapor until it condenses into a liquid distillate. The separation may be enhanced by the addition of more trays (to a practical limitation of heat, flow, etc.).

[[Image:Colonne distillazione.jpg|right|thumb|300px|Figure 2: Typical industrial fractionating columns]]