Page 223 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN004E-182 June 8, 2001 18:16

Distillation

M. R. Resetarits
Koch-Glitsch, Inc.

M. J. Lockett
Praxair, Inc.

I. Distillation Equipment
II. Distillation Theory
III. Distillation Column Design
IV. Applications of Distillation
Including EnergyConsiderations

GLOSSARY Reflux ratio Ratio of the flow rate of the liquid that is
returned to the top of the column (the reflux) to the
Azeotrope Mixture that does not change in composition flow rate of the overhead product.
on distillation and usually has a boiling point higher or Relative volatility Ratio of the K values of two com-
lower than any of its pure constituents. ponents; a measure of the ease with which the two
Column (tower) Vertical cylindrical vessel in which dis- components can be separated by distillation.
tillation is carried out. Theoretical stage Contact process between vapor and
Distillate Product of distillation formed by condensing liquid such that the exiting vapor and liquid streams
vapor. are in equilibrium.
Efficiency (overall column efficiency) Ratio of the num- Trays (plates) Perforated metal sheets, spaced at regular
ber of theoretical stages required to effect a distillation intervals within a column, on which intimate contact
separation to the number of actual trays. of vapor and liquid occurs.
Height of a theoretical plate (HETP) Height of packing Vapor pressure Pressure at which a liquid and its vapor
in a distillation column that gives a separation equiva- are in equilibrium at a given temperature.
lent to one theoretical stage.
K value Ratio of the concentration of a given component
in the vapor phase to its concentration in the liquid DISTILLATION is a physical process for the separation
phase when the phases are in equilibrium. of liquid mixtures that is based on differences in the boil-
Packing Specially shaped metal, plastic, or ceramic ma- ing points of the constituent components. The art of dis-
terial over which the liquid trickles to give a large sur- tillation is believed to have originated in China around
face area for contact with the vapor. 800 BC. Early applications of the process were concerned

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