ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 2, pp. 218!222. + Pleiades Publishing, Ltd., 2008.
Original Russian Text + D.G. Cherkasov, M.P. Smotrov, K.K. Il’in, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 2, pp. 229 !233.
OF SYSTEMS AND PROCESSES
Equilibrium in the Liquid3Liquid System and Critical
Phenomena in the Ternary System Constituted
by Water, Pyridine, and Butyric Acid
in the Temperature Range 5355oC
D. G. Cherkasov, M. P. Smotrov, and K. K. Il’in
Chernyshevsky State University, Saratov, Russia
Received May 2, 2007
Abstract-Visual-polythermic method was used to study the mutual solubility of the components and critical
phenomena in the system constituted by water, pyridine, and butyric acid in the temperature range 5.0355.0oC.
The temperature dependence of the composition of the critical solubility point was determined.
Extractive methods of extraction, separation, and
concentration of substances are widely used in the tech-
nological practice. These methods have a number of
disadvantages, the main of which is use of easily
volatile and combustible solvents, hydrocarbons. This
problem can be solved by using unconventional ter-
nary extractive systems  containing no hydrocar-
bons. System of this kind are frequently characterized
by a closed binodal curve, whose appearance was at-
tributed by Mertslin  and, later, by his followers
 to chemical interaction of the components of
a binary boundary system. In this system, a new com-
pound with limited solubility in water is formed.
The wide diversity of stratifying systems and the sim-
plicity and high selectivity of methods for recovery
of various substances indicate that these methods
The most complete pattern of phase equilibria,
necessary for optimization of extractive processes,
can be obtained by constructing solubility diagrams
and determining the coordinates of the critical point
of the stratification region. The position of the critical
point on a stratification isotherm characterizes the in-
teraction of components in a system, and, therefore
the problem of its coordinates and factors affecting
its composition are rather important in a study of
the mutual solubility of liquids. As temperature is
raised or lowered, the closed stratification region
may disappear via, respectively, the upper or lower
three-component critical solubility point (UTCSP or
LTCSP) . Unfortunately, the compositions of
the critical points in the solubility isotherms are un-
known for the overwhelming majority of systems
with a closed stratification region and the coordinates
of UTCSP and LTSCP have been occasionally de-
termined inaccurately and not for all systems.
In , the system constituted by water, pyridine,
and butyric acid was studied by the method of isother-
mal titration and closed binodal curves were plotted
in the concentration triangle at 12, 25, 38, and 50oC.
The area of the stratification field decreased as tem-
perature was elevated. The mutual solubility minima
in the binodals demonstrated that an unstable com-
pound was formed in the system with pyridine and
butyric acid, with the component ratio of 1 : 2, re-
spectively. The dissociation of this compound became
stronger upon heating. The authors suggested that
the given system has a UTCSP at 53oC and provided
an approximate critical composition (wt %): C
26, and H
O 55. However, the composi-
tions of the critical points in the solubility isotherms
were not determined and the UTCSP coordinates
were found approximately.
In the present study, the effect of temperature on
the mutual solubility of the components and the com-
position of the critical solution for the system
constituted by water, pyridine, and butyric acid in
the temperature range 5.0355.0oC was analyzed in
order to reveal fundamental aspects of the topological
transformation of the solubility diagrams of ternary
systems with a closed stratification region.