The determination of activity coefficients at infinite dilution using gas liquid chromatography.
Loading...
Date
1991
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The aim of this investigation was to develop and test a theory that allowed for the
calculation of the activity coefficients at infinite dilutions (l' ~ 3) from G.L.C.
measurements using moderately volatile solvents. The solvents chosen for study were
straight chained (Cs to C7) and cyclic (Cs, C6 and benzene) liquid hydrocarbons using
cis- and trans-decahydronaphthalene (decalin) as the stationary liquid phase (solvent).
The systems were studied at two different temperatures, 283.15 K and 298.15 K. The
solutes were n-pentane~ n-hexane, n-heptane, cyclopentane, cyclohexane and benzene.
This method for the determination of activity coefficients has the advantage of being
able to work at infinite dilution, whereas in other techniques, extrapolation to infinite
dilution of finite-concentration data is necessary. In addition solutes are separated from
impurities when chromatographed so that only very small quantities of moderately
pure material need beĀ· used. However the technique is also limited since the solute
studied (injected reagent) needs to be volatile, while the solvent (liquid stationary
phase) should be involatile. The solvents chosen in this experiment (cis- and transdecalin)
are moderately volatile which introduces many limitations since the theory
developed for the determination of activity coefficients at infinite dilution is restricted
to involatile solvents. However a novel method for working with moderately volatile
solvents is developed by relating the loss of solvent to its partial pressure and
modifying the existing theory. In the past the use of precolumns and/or saturators,
coarse packing, small pressure gradients, and internal standards were used when
working with volatile solvents. However employing this new method excludes the use
of precolumns, saturators, or internal standards, and allows any type of packing and
pressure gradient to be used.
The calculated activity coefficients are compared with literature values, where the
wor~ers employed G.L.C. techniques, and with predicted values. The activity
coefficients calculated at both temperatures are used in the calculation of excess
partial molar enthalpies. These results are compared with values obtained from finite
concentration data by other workers.
Description
Thesis (M.Sc.)-University of Natal, Durban, 1992.
Keywords
Gas chromatography., Activity coefficients., Theses--Chemistry.