Thermodynamic Measurements by Gas-Liquid Chromatography

Abstract

The aim of the first part of this work was to provide solubility data
for the large scale continuous and semi-continuous gas liquid chromatographs
(G.L.C.) in operation in this department by using analytical G.L.C.
equipment.

A commercial dual-channel chromatograph was modified to enable the
partition coefficients of various solutes in polymer stationary phases to
be measured at finite concentrations of the solute. The technique chosen
was "Elution on a Plateau" in which the chromatographic column is first
equilibriated by a carrier gas (nitrogen) containing the solute vapour.
The partition coefficient of the solute is then calculated by measuring
the elution volume of a small sample of the solute injected. The systems
studied were:-
1.
a) α-Pinene/Polypropylene Sebacate at 99.8, 120.0, 140.0, 150.0°C.
b) β -Pinene/ Polypropylene Sebacate at 100.3, 110.1, 120.0, 150.0°C.

2.
a) Dichloro Methane/Silicone Oil MS 200 at 24.8, 29.1, 34.7, 39.8°C.
b) 112, Trichloro trifluoro Ethane (Arklone-P)/Silicone Oil MS 200
at 24.8, 29.1, 34.7°C.
c) 111, Trichloro Ethane (Genklene-P)/Silicone Oil MS 200 at 34.7,
45.1, 60.5, 74.0°C.

A limited amount of ternary data was also obtained whereby the infinite
dilution partition coefficient of a third component was measured in the
presence of the finite concentrations of the other two components, one of
which was the stationary phase. In each case the partition coefficients
were found to increase linearly with the gas phase concentration of the
solute within the gas phase concentration ranges studied (0-3x107" g/em*
for Systems 1 and 0-5x10"* g/cm? for Systems 2).

Activity coefficients were calculated from the partition
coefficients by using the known molecular weights of the solutes and the
stationary phases and the vapour pressures of the solutes. For the binary
systems the activity coefficients were correlated by means of the single
and two-parameter Flory-Huggins Equation, the parameters being evaluated
in this work. In each case the fit was very good, suggesting that this
equation is adequate in describing the behaviour of these polymer
solutions where polar interactions are moderate or small. The data of
Systems 2 was also correlated by the binary Heil Equation with a similar
accuracy to that of the Flory-Huggins Equation.

The ternary form of the Flory-Huggins equation was fitted to the
ternary data and by using the previously calculated binary parameters the
solute-solute interaction parameters were estimated.

The second part of this work was concerned with studying the
separating efficiency of a rotating gas liquid chromatographic unit. This
consisted of 44 20cm long, 2.5 cm ID tubes arranged in a circular bundle
that rotated in the opposite direction to the flow of the carrier gas.
The liquid feed, commercial turpentine with α and β pinenes as the major
components, was continuously fed somewhere in the middle and the gas flow
rate and the speed of rotation were adjusted so that the least absorbed
component (α-pinene) moved with the gas phase, while the other component
( β-pinene) was carried along with the packing. This second component was
then stripped off in a different section of the bundle.

The inlet and off-take operations relied on the seal between
stationary graphlon rings and the rotating surface of the bundle. A
complete seal was found to be impossible to achieve with a minimum of 5%
carrier gas leakage, while up to 50% of the feed was lost. Therefore,
only a few runs could be conducted which showed that a steady state operation was impossible under these circumstances. Although this meant
a partial defeat of the objective of the first part of the work, some
valuable information was gained about the operation of this type of semicontinuous countercurrent equipment.

Date of Award	1973
Original language	English