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The Lydersen method is a group contribution method for the estimation of critical properties temperature ( ''T''c), pressure ( ''P''c) and volume (''V''c). The method is named after Aksel Lydersen who published it in 1955. The Lydersen method is the prototype for and ancestor of many new models like Joback, Klincewicz,
Ambrose,
Gani-Constantinou and others.
The Lydersen method is based in case of the critical temperature on the Guldberg rule which establishes a relation between the normal
boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envi ...
and the critical temperature
Critical or Critically may refer to:
*Critical, or critical but stable, medical states
**Critical, or intensive care medicine
*Critical juncture, a discontinuous change studied in the social sciences.
*Critical Software, a company specializing in ...
.
Equations
Critical temperature
: Guldberg has found that a rough estimate of thenormal boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envi ...
''T''b, when expressed in kelvins (i.e., as an absolute temperature
Thermodynamic temperature, also known as absolute temperature, is a physical quantity which measures temperature starting from absolute zero, the point at which particles have minimal thermal motion.
Thermodynamic temperature is typically expres ...
), is approximately two-thirds of the critical temperature ''T''c. Lydersen uses this basic idea but calculates more accurate values.
Critical pressure
:Critical volume
: M is themolar mass
In chemistry, the molar mass () (sometimes called molecular weight or formula weight, but see related quantities for usage) of a chemical substance ( element or compound) is defined as the ratio between the mass () and the amount of substance ...
and Gi are the group contributions (different for all three properties) for functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
s of a molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
.
Group contributions
Example calculation
Acetone
Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...
is fragmented in two different groups, one carbonyl group and two methyl groups. For the critical volume the following calculation results:
Vc = 40 + 60.0 + 2 * 55.0 = 210 cm3
In the literature (such as in the Dortmund Data Bank
The Dortmund Data Bank (short DDB) is a factual data bank for thermodynamic and thermophysical data. Its main usage is the data supply for process simulation where experimental data are the basis for the design, analysis, synthesis, and optimiz ...
) the values 215.90 cm3, 230.5 cm3 and 209.0 cm3 {{cite journal , last1=Kobe , first1=Kenneth A. , last2=Crawford , first2=Horace R. , last3=Stephenson , first3=Robert W. , title=Industrial Design Data—Critical Properties and Vapor Presesures of Some Ketones , journal=Industrial & Engineering Chemistry , publisher=American Chemical Society (ACS) , volume=47 , issue=9 , year=1955 , issn=0019-7866 , doi=10.1021/ie50549a025 , pages=1767–1772 are published.
References