In thermodynamic theory, the Klincewicz method is a predictive method based both on group contributions and on a
correlation
In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistics ...
with some basic molecular properties. The method estimates the
critical temperature
Critical or Critically may refer to:
*Critical, or critical but stable, medical states
**Critical, or intensive care medicine
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*Critical Software, a company specializing in ...
, the critical pressure, and the critical volume of pure components.
Model description
As a
group contribution method the Klincewicz method correlates some structural information of a chemical
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
with the critical data. The used structural information are small
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...
s which are assumed to have no interactions. This assumption makes it possible to calculate the thermodynamic properties directly from the sums of the group contributions. The correlation method does not even use these functional groups, only the molecular weight and the number of atoms are used as molecular
descriptors.
The prediction of the critical temperature relies on the knowledge of the normal boiling point because the method only predicts the relation of the normal boiling point and the critical temperature and not directly the critical temperature. The critical volume and pressure however are directly predicted.
Model Quality
The quality of the Klincewicz method is not superior to older methods, especially the method of Ambrose gives somewhat better results as stated by the original authors and by Reid et al.
[Reid R.C., Prausnitz J.M., Poling B.E., "The Properties of Gases & Liquids", Monograph, McGraw-Hill, 4 Ed., 1-742, 1987] The advantage of the Klincewicz method is that it is less complex.
The quality and complexity of the Klincewicz method is comparable to the Lydersen method from 1955 which has been used widely in chemical engineering.
The aspect where the Klincewicz method is unique and useful
are the alternative equations where only very basic molecular data like the molecular weight and the atom count are used.
Deviation diagrams
The diagrams show estimated critical data of
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
s together with experimental data. An estimation would be perfect if all data points would lie directly on the diagonal line. Only the simple correlation of the Klincewicz method with the molecular weight and the atom count have been used in this example.
Image:TCKlincewicz.png , Critical temperatures
Image:PCKlincewicz.png , Critical pressures
Image:VCKlincewicz.png , Critical volumes
Equations
Klincewicz published two sets of equations.
[Klincewicz, K. M., "Prediction of Critical Temperatures, Pressures, and Volumes of Organic Compounds from Molecular Structure," S.M.Thesis, Massachusetts Institute of Technology, Cambridge, Massachusetts, 1982] The first uses contributions of 35 different groups. These group contribution based equations are giving somewhat better results than the very simple equations based only on correlations with the
molecular weight
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
and the atom count.
Group-contribution-based equations
Equations based on correlation with molecular weight and atom count only
with
Group contributions
The group XCX is used to take the pairwise interaction of halogens connected to a single carbon into account. Its contribution has to be added once for two halogens but three times for three halogens (interactions between the halogens 1 and 2, 1 and 3, and 2 and 3).
Example calculations
Example calculation for acetone with group contributions
*used normal boiling point Tb= 329.250 K
Example calculation for acetone with molecular weight and atom count only
Used molecular weight: 58.080
g/
mol
Used atom count: 10
For comparison, experimental values for Tc, Pc and Vc are 508.1 K, 47.0 bar and 209 cm
3/mol, respectively.
References
{{DEFAULTSORT:Klincewicz Method
Thermodynamic models