ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 12, pp. 2045!2048. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + O.V. Surov, M.I. Voronova, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 12, pp. 1967!1269.
OF SYSTEMS AND PROCESSES
Determination of Partial Pressures of Components
of the Water!Dimethylsulfoxide System
with a Double Effusion Chamber
O. V. Surov and M. I. Voronova
Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
Received September 17, 2007
Abstract-Knudsen’s method with a double effusion chamber was used to determine the partial pressures
of water and dimethylsulfoxide over their solutions and over the water3dimethylsulfoxide3cellulose system.
Knudsen’s effusion method is widely and success-
fully used to study substances with low saturated va-
por pressure. However, it has, despite advantages,
certain limitations: the upper applicability level of
Knudsen’s method does not exceed a pressure of
10 Pa, and the radius of the effusion orifice, 1 mm.
This is due to the fact that the conditions of molecular
outflow of a vapor from the effusion orifice are only
satisfied in the case when the mean free path of mol-
ecules within the cavity of the effusion chamber sub-
stantially exceeds the diameter of the effusion orifice.
When pressures substantially exceeding 10 Pa are
measured, various corrections are commonly intro-
duced to take into account deviations of the vapor
outflow mode from the molecular conditions . Pro-
vided that an appropriate calibration is carried out,
the effusion method can be successfully used to de-
termine the equilibrium water vapor pressure and cal-
culate the thermodynamic characteristics of the de-
sorption process .
The aim of our study was to develop a technique
for determining the partial vapor pressures of com-
ponents of a binary mixture with the use of a double
effusion chamber. This method markedly extends
the number of systems accessible to study and enables
analysis of real technological processes that com-
monly occur at pressures exceeding the Knudsen limit
The experimental effusion installation and the meth-
od for determining the equilibrium water vapor pres-
sure were described in detail in . We chose as
object of study the system water!dimethylsulfoxide
(DMSO) previously examined with an MI-1201 mass
spectrometer . We used a double effusion chamber
schematically shown in Fig. 1. Under our experi-
mental conditions, changes in the mixture composi-
tion during measurements were negligible. Thus,
the whole body of the data obtained can be related
to the state of the system, which is characterized by
the starting composition.
A solution to be analyzed was placed in chamber I
(evaporation chamber). After the solution was heated
to a temperature T, vapors of its components passed
through a connecting channel into chamber II (effu-
sion chamber), where the effusion occurred. With this
design of the effusion unit, the pressure in the effu-
sion chamber 5
at a given temperature T will be
determined by the vapor pressure in the evaporation
, and by the relative throughputs of
Fig. 1. Schematic of a double effusion chamber. Chamber:
(I) evaporation and (II ) effusion; (1) connecting channel
and (2) effusion orifice.