Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 2, pp. 219−231.
Pleiades Publishing, Ltd., 2010.
Original Russian Text
G.L. Kuranov, N.A. Smirnova, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 2, pp. 222−233.
OF SYSTEMS AND PROCESSES
Calculation of Phase Behavior and Chemical Transformations
a Modiﬁ ed Hole Quasichemical Model
G. L. Kuranov and N. A. Smirnova
St. Petersburg State University, St. Petersburg, Russia
Received November 2, 2009
Abstract—A technique for calculation of phase equilibria over a wide range of temperatures and pressures for
ﬂ uid systems, where chemical interactions lead to the formation of ionic species, was developed. A hole quasi-
chemical model was modiﬁ ed to account for chemical reactions and electrostatic interactions in the liquid phase.
The densities and dielectric permittivity as function of a solution composition was taken into account in describing
the electrostatic contribution to the Gibbs energy (Pitzer approximation) and Born contribution, that is required for
thermodynamic consistency of simulation results. A method of assessing the appropriate relationships for mixtures
of ammonia–water and ternary solutions was suggested. Calculations of the phase behavior of the H
in the entire range of concentrations in the temperature interval 373–588 K at pressures up to 200 bar, and also of
system containing NH
to 30 mol% and CO
up to 14 mol% in the temperature range 373–473 K
at pressures to 88 bar gave satisfactory agreement with experimental data. Concentrations of the molecular and
ionic individuals in the liquid phase, depending on the overall composition of the mixture were evaluated.
For a long time in the literature an increased attention
was attracted by calculation of phase equilibria in the
. In the majority of reports the
equilibrium properties of a liquid solution were simu-
lated with the aid of models for excess Gibbs energy, and
a vapor phase properties were described separately by
the equations of state. The problem of simulation of the
phase behavior in the system H
arose in connection with the problem of puriﬁ cation of
gas emissions, in particular in coal gasiﬁ cation. Since in
these processes the concentration of substances dissolved
in water remained low the Edwards model developed
earlier for aqueous solutions of weak electrolytes 
was applied to the description of the system under study
in . Chemical reactions occurring in this system with
formation of ionic individuals were considered, and the
non-ideal liquid phase was described by Pitzer model.
Later this approach was developed in [3–8] in the light
of new experimental data and the application of different
options for evaluation of the model parameters. A good
description of phase equilibria in the region of the small
concentrations of dissolved gases was achieved, but
deviations of the calculated parameters from the experi-
mental values became much higher upon an increase in
the content of the dissolved gases
At the same time, description of the properties of
over a wide range of concentrations
and temperatures is of considerable interest, that is as-
sociated primarily with the practical problem of ﬁ nding
the optimal conditions for urea synthesis requiring the
system simulation in the range of NH
from 2 to 6, H
one from 0 to 2, temperatures of
440–493 K and pressures of 150–400 bar. In this case
Pitzer model describing aqueous electrolyte solutions and
neglecting the dependence of the properties of the solvent
on its composition is inapplicable. This dependence is
considered in the semi-empirical models of water-organic
solutions of salts .
One of the ﬁ rst models for calculation the equilib-
rium liquid–vapor in these systems was proposed by B.
Sander et al. . It is a UNIQUAC model (UNiversal
QUAsiChemical) supplemented by an electrostatic con-
tribution in the form of the second approximation of the
Debye–Hückel theory extended to the mixed solvent.