CHAPTER FOUR: EXPERIMENTAL APPARATUS
AND
PROCEDURE
Chapter overview
For each of the two techniques used in this work, the
materials used, the experimental set up and the experimental procedure are
described. Solvents and solutes preparation and purification before
measurements by Gas Liquid Chromatography and the Inert Gas Stripping Technique
are explained. This chapter also presents the main features of the dilutor cell
designed for this study with emphasis on the procedure used to determine its
optimal height. Uncertainties on the experimental parameters and variables are
provided as they allowed determining the errors attached to the experimental
data reported in this work.
4.1. Limiting activity
coefficient measurements by gas liquid chromatography
4.1.1. Chemicals
The reliability and accuracy of an experimental procedure has
to be checked by comparison with data available in the literature. In this
study, systems involving n-hexadecane as the solvent has been used to test the
exactness of the procedure. The following ionic liquids have been used as
solvents:
· Trihexyltetradecylphosphonium tetrafluoroborate,
[3C6C14P] [BF4]
· Trihexyltetradecylphosphonium
bis(trifluoromethylsulfonyl) imide, [3C6C14P] [BTI]
· Trihexyltetradecylphosphonium hexafluorophosphate,
[3C6C14P] [PF6]
· Trioctylmethylammonium bis(trifluoromethylsulfonyl)
imide, [3C8C1N] [BTI]
· 1-ethyl-3-methylimidazolium trifluoromethanesulfonate,
[EMIM] [TfO]
· 1-n-Butyl-3-methylimidazolium hexafluoroantimonate,
[BMIM] [SbF6]
· 1-Octyl-3-methylimidazolium hexafluorophosphate.
[OMIM][PF6]
The above fluorinated ionic liquids, whose structures are
given in appendix B, have been selected because IDAC data for phosphonium-based
FILs were found to be rare. In addition, these ionic liquids were selected
because of their availability. Before use, they were heated at T =
353.15 K for seven hours under vacuum, using a vacuum pump, to remove all
possible traces of impurities, including moisture. For all solvents, stated
purities, densities and refractive indices are provided in tables C-1 through
C-3 in appendix C. Densities of purified samples were measured by the vibrating
tube method using a DMA 5000 Anton Paar densitometer. Refractive index
measurements were carried out using an RX-7000á automatic digital
refractometer. Both properties were measured in the Thermodynamics Research
Unit laboratory. Solutes, including n-alkanes, alk-1-enes, alk-1-ynes,
alkanols, cycloalkanes, alkylbenzenes and
ketones were used without any purification since impurities
were separated by the GC during the measurement process. Diatomaceous earth,
celite (Chromosorb W HP 80/100 mesh) was used as inert solid support onto which
the solvent was coated. It was purified by vacuum heating under the same
conditions as the ionic liquid. Dichloromethane was used as solvent to aid
uniform coating of the ionic liquid onto the inert solid support and removed
afterwards by evaporation. Dry helium was used as carrier gas.
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