User:WilfriedC/Playground/Lydersen method

The Lydersen method is a group contribution method for the estimation of critical properties temperature (Tc), pressure (Pc) and volume (Vc). 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 establishs a relation between the normal boiling point and the critical temperature.

Critical temperature
$$T_c=\frac{T_b}{0.567+\sum G_i-\left(\sum G_i\right)^2}$$

Guldberg has found that the normal boiling point Tb is approximately at 2/3 (in absolute temperature) of the critical temperature. The Lydersen uses this basic idea but calculates better values than this value of 2/3 which has proved to be only a very rough estimate.

Critical pressure
$$P_c=\frac{M}{\left(0.34+\sum G_i\right)^2}$$

Critical volume
$$V_c\,=\,40+\sum G_i$$

M is the molar mass and Gi are the group contributions (different for all three properties) for functional groups of a molecule.

Example calculation


Acetone 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 the values 215.90 cm3, 230.5 cm3 and 209.0 cm3 are published.