1070-4272/05/7808-1245 + 2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 8, 2005, pp. 1245!1248. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 8, 2005,
Original Russian Text Copyright + 2005 by Sladkov, Pobedonostseva.
OF SYSTEMS AND PROCESSES
Calculation of the Critical Parameters of Inorganic
Compounds by the Additive Method
I. B. Sladkov and E. V. Pobedonostseva
St. Petersburg State Polytechnic University, St. Petersburg, Russia
Received April 7, 2005
Abstract-A set of 100 substances was studied to obtain data that would allow application of the additive
method to calculation of critical parameters of inorganic compounds. An additive scheme that makes it pos-
sible to improve the accuracy of calculation of the critical pressure of inorganic compounds was suggested.
At present, methods of the thermodynamic similar-
ity theory are widely used to prognosticate physico-
chemical properties of substances [1, 2]. In this case,
the critical parameters of substances serve as input
data for a calculation. Published data on critical pa-
rameters are rather scarce. Experimental determination
of critical parameters involves severe difficulties.
Of particular practical importance in this context is
determining the critical parameters by calculation.
A possible way to calculate the critical parameters
is to sum up the corresponding increments for the el-
ements constituting the molecule of a compound. This
method is attractive in that it is based on the mini-
mum amount of information about the substance un-
der study, which frequently does not include any data
except the stoichiometric formula.
The additive method for calculation of critical pa-
rameters is widely used for prognosticating the critical
parameters of organic substances [1, 3]. The potenti-
alities of this technique, as applied to determination of
the critical parameters of molecular inorganic com-
pounds, are unknown. This is because the increments
are available in the literature for less than 10 elements.
These are nonmetals (C, H, O, S, N, F, Cl, Br, I),
which constitute molecules of organic substances.
However, data on the increments for metals contained
in molecules of inorganic and organometallic sub-
stances are lacking completely.
The goals of this study were as follows: (a) to ob-
tain missing information about the increments of
metals from experimental data on critical parameters
and (b) to determine, using the data obtained, the ac-
curacy of calculation of the critical parameters by
the additive method for inorganic and organometallic
The most widely used in the literature is the addi-
tive scheme suggested by Leadersen . In this tech-
nique, atomic constituents (increments) of the reduced
temperature at the boiling point are summed up for
determining the critical temperature:
q = T
are, respectively, the temperatures
at the normal-boiling and critical points.
The calculational formula for determining G for
a binary compound of the AB
type has the form
q = 0.576 + SD
(A) + nD
(A) and ,
(B) are the increments of the re-
duced boiling point G for elements A and B, respec-
tively; and n is the number of B atoms in compound
The critical volume is found in the Leadersen
method by the formula
The critical pressure (MPa) is given by
where M is the molecular weight of the compound.
In Eqs. (4) and (5), the sum of increments ,
is calculated in accordance with Eq. (3).