Thermodynamics of liquid mixtures containing carboxylic acids.
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Date
2003
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Abstract
The thesis involves a study of the thermodynamics of ternary liquid mixtures involving
carboxylic acids with nitriles, hydrocarbons including cycloalkanes, and water. Carboxylic
acids are an important class of compounds with a great number of industrial uses and
applications. In many parts ofthe world the separation of carboxylic acids (in particular acetic
and propanoic acid) is an important and desirable task. In South Africa, these carboxylic acids
together with many other oxygenates and hydrocarbons are produced by SASOL using the
Fischer - Tropsch process. The separation of these acids from hydrocarbons and from water
is a commercially lucrative consideration, and is the raison d' etre for this study. The work
focussed on the use of nitriles in effecting separation by solvent extraction and not by the
more common method of distillation. The nitrile compounds were chosen because of their
high polarity. The carboxylic acids used in this study always refer to: acetic acid, propanoic
acid, butanoic acid, 2-methylpropanoic acid, pentanoic acid and 3-methylbutanoic acid.
The first part of the experimental programme is devoted to the determination of excess molar
volumes of mixtures of (a carboxylic acid + nitrile compound), where the nitrile refers to
acetonitrile, butanenitrile or benzonitrile, respectively. Densimetry was used to determine the
excess molar volumes. The work was done in order to get some idea of the interactions
involved between a carboxylic acid and a nitrile.
The second part of the experimental study is concerned with the determination of excess
molar enthalpies of mixtures of( a carboxylic acid + nitrile compound), where the nitrile refers
to acetonitrile, butanenitrile or benzonitrile, respectively. The excess molar enthalpies were
determined using flow microcalorimetry Again, this work was done in order to gain some
insight into the interactions involved between a carboxylic acid and a nitrile.
The third part of the experimental work consists ofternary liquid-liquid equilibria of mixtures
of (acetonitrile + a carboxylic acid + heptane or cyclohexane), (benzonitrile + a carboxylic
acid + water); and (butanenitrile + a carboxylic acid + water), at 298.15 K. The purpose was
to investigate the use of nitriles as solvent extractors in separating carboxylic acids from
hydrocarbons and also carboxylic acids from water. Ternary liquid-liquid equilibrium data are essential for the design and selection of solvents used in the liquid-liquid extraction process.
The final section deals with the fitting of models of liquid mixtures to the experimental data
collected in this work. The NRTL (Non-random, two liquid), UNIQUAC (Universal quasichemical),
and FBT (Flory-Benson-Treszczanowicz) models were used. The modelling work
served three purposes:
• to summarise the experimental data
• to test theories of liquid mixtures
• prediction of related thermodynamic properties
Description
Thesis (Ph.D.)-University of Natal,Durban, 2003.
Keywords
Carboxylic acids., Thermodynamics., Liquids--Thermal properties., Theses--Chemistry.