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The Fenske equation in continuous fractional distillation
Fractional distillation

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compound by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate....
 is an equation
Equation

An equation is a mathematics Proposition, in table of mathematical symbols, that two things are exactly the same . Equations are written with an equal sign, as in...
 used for calculating the minimum number of theoretical plates
Theoretical plate

A theoretical plate in many separation processes is a hypothetical zone or stage in which two phases, such as the liquid and vapor phases of a substance, establish an Vapor-liquid equilibrium with each other....
 required for the separation of a binary feed stream by a fractionation column
Fractionating column

A fractionating column or fractionation column is an essential item used in the distillation of liquid mixtures so as to separate the mixture into its component parts, or fractions, based on the differences in their Volatility ....
 that is being operated at total reflux
Reflux

Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations....
 (i.e., which means that no overhead product distillate is being withdrawn from the column).

The equation was derived by Merrell Fenske in 1932 , a professor who served as the head of the chemical engineering
Chemical engineering

Chemical engineering is the branch of engineering that deals with the application of physical science , with mathematics, to the process of converting raw materials or chemicals into more useful or valuable forms....
 department at the Pennsylvania State University
Pennsylvania State University

The Pennsylvania State University is a Commonwealth System of Higher Education, Land-grant university, space grant college public research university located in State College, PA, Pennsylvania, United States....
 from 1959 to 1969.

This is one of the many different but equivalent versions of the Fenske equation:

For ease of expression, the more volatile and the less volatile components are commonly referred to as the light key (LK) and the heavy key (HK), respectively.

If the relative volatility
Relative volatility

Relative volatility is a measure comparing the vapor pressures of the components in a liquid mixture of chemicals. This quantity is widely used in designing large industrial distillation processes. In effect, it indicates the ease or difficulty of using distillation to separate the more Volatility components fro...
 of the light key to the heavy key is constant from the column top to the column bottom, then is simply .






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The Fenske equation in continuous fractional distillation
Fractional distillation

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compound by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate....
 is an equation
Equation

An equation is a mathematics Proposition, in table of mathematical symbols, that two things are exactly the same . Equations are written with an equal sign, as in...
 used for calculating the minimum number of theoretical plates
Theoretical plate

A theoretical plate in many separation processes is a hypothetical zone or stage in which two phases, such as the liquid and vapor phases of a substance, establish an Vapor-liquid equilibrium with each other....
 required for the separation of a binary feed stream by a fractionation column
Fractionating column

A fractionating column or fractionation column is an essential item used in the distillation of liquid mixtures so as to separate the mixture into its component parts, or fractions, based on the differences in their Volatility ....
 that is being operated at total reflux
Reflux

Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations....
 (i.e., which means that no overhead product distillate is being withdrawn from the column).

The equation was derived by Merrell Fenske in 1932 , a professor who served as the head of the chemical engineering
Chemical engineering

Chemical engineering is the branch of engineering that deals with the application of physical science , with mathematics, to the process of converting raw materials or chemicals into more useful or valuable forms....
 department at the Pennsylvania State University
Pennsylvania State University

The Pennsylvania State University is a Commonwealth System of Higher Education, Land-grant university, space grant college public research university located in State College, PA, Pennsylvania, United States....
 from 1959 to 1969.

This is one of the many different but equivalent versions of the Fenske equation:

For ease of expression, the more volatile and the less volatile components are commonly referred to as the light key (LK) and the heavy key (HK), respectively.

If the relative volatility
Relative volatility

Relative volatility is a measure comparing the vapor pressures of the components in a liquid mixture of chemicals. This quantity is widely used in designing large industrial distillation processes. In effect, it indicates the ease or difficulty of using distillation to separate the more Volatility components fro...
 of the light key to the heavy key is constant from the column top to the column bottom, then is simply . If the relative volatility is not constant from top to bottom of the column, then the following approximation may be used:

The above Fenske equation can be modified for use in the total reflux distillation of multi-component feeds.

Another form of the Fenske equation


A derivation of another form of the Fenske equation for use in gas chromatography is available on the U.S. Naval Academy's web site. Using Raoult's law
Raoult's law

Established by Fran?ois-Marie Raoult, Raoult's law states:Once the components in the solution have reached chemical equilibrium, the total vapor pressure p of the solution is:...
 and Dalton's Law
Dalton's law

In chemistry and physics, Dalton's law states that the total pressure exerted by a gas mixture is equal to the sum of the partial pressures of each individual component in a gas mixture....
 for a series of condensation and evaporation cycles (i.e., equilibrium stages), the following form of the Fenske equation is obtained:

See also


  • Continuous distillation
    Continuous distillation

    Continuous distillation, a form of distillation, is an ongoing separation in which a mixture is continuously fed into the process and separated fractions are removed continuously as output streams as time passes during the operation....
  • Distillation
    Distillation

    Distillation is a method of separation process mixtures based on differences in their Volatility in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
  • Fractional distillation
    Fractional distillation

    Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compound by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate....
  • Fractionating column
    Fractionating column

    A fractionating column or fractionation column is an essential item used in the distillation of liquid mixtures so as to separate the mixture into its component parts, or fractions, based on the differences in their Volatility ....
  • McCabe-Thiele method
    McCabe-Thiele method

    The graphical approach presented by McCabe and Thiele in 1925, the McCabe-Thiele method is considered the simplest and perhaps most instructive method for analysis of binary distillation....


External links


  • (R.M. Price, Christian Brothers University
    Christian Brothers University

    Christian Brothers University is the oldest collegiate degree-granting institution in the Memphis, Tennessee. The university is run by the Institute of the Brothers of the Christian Schools, a Roman Catholic religious order founded by Jean-Baptiste de la Salle, the patron saint of teachers....
    , Tennessee)
  • , Y. A. Liu, T.E. Quantrille, and S. Chengt, Ind. Eng. Chem. Res., Volume 29, 1990
  • (M.B. Jennings, San Jose State University
    San José State University

    San Jos? State University is the founding campus of what became the California State University system. The sprawling 154-acre campus in the center of Silicon Valley has an enrollment of about 30,000 students and provides more graduates working in the high tech region than any other college or university....
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