Faculty of Applied Sciences
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Item Phase equilibria measurements of ternary mixtures (sulfolane + a carboxylic acid + pentane) at 303.15 K(Elsevier, 2015) Xhakaza, Nokukhanya Mavis; Bahadur, Indra; Redhi, Gan G.; Ebenso, Eno E.The Liquid–liquid equilibrium (LLE) data for the mixtures of {sulfolane (1) + a carboxylic acid (2) + pentane (3)} at 303.15 K are reported, where a carboxylic acid refers to acetic acid, propanoic acid, butanoic acid, 2-methylpropanoic acid, pentanoic acid and 3-methylbutanoic acid. The shape of the binodal curves show that the solubility of pentane in (sulfolane + a carboxylic acid) is very much dependent on the carbon number and the type of carboxylic acid. The area of the two phase heterogeneous region for the carboxylic mixtures decreases in the order of acetic acid > propanoic acid > 2-methylpropanoic acid ∼ butanoic acid > pentanoic acid ∼ 3-methylbutanoic acid. Three parameter equations have been fitted to the binodal curve data. The NRTL and UNIQUAC models were used to correlate the experimental data. The NRTL model fitted the experimental data better than the UNIQUAC model with the average mean square deviation of 0.072 mole fraction as compared to 0.359 mole fraction for UNIQUAC model.Item Liquid–liquid equilibria measurements of ternary systems (acetonitrile + a carboxylic acid + dodecane) at 303.15 K(Elsevier, 2015) Redhi, Gan G.; Bahadur, Indra; Xhakaza, Nokukhanya MavisLiquid–liquid equilibrium (LLE) data are reported for the ternary mixtures of (acetonitrile + a carboxylic acid + dodecane) at 303.15 K under atmospheric pressure, where a carboxylic acid refers to acetic acid, propanoic acid, butanoic acid, 2-methylpropanoic acid, pentanoic acid and 3-methylbutanoic acid. The area of the two-phase heterogeneous region for the carboxylic acid mixtures decreases in the order: acetic acid > propanoic acid > butanoic acid > 2-methylbutanoic acid > pentanoic acid > 3-methylbutanoic acid. The relative mutual solubility of each of the carboxylic acids is higher in acetonitrile layer than in dodecane layer. Three 3-parameter equations have been fitted to the binodal curve data. The NRTL and UNIQUAC models were used to correlate the experimental data. The NRTL model fitted the experimental data far better than the UNIQUAC model with the average mean square deviation of 0.0030 mole fraction as compared to 0.2870 mole fraction for UNIQUAC. Selectivity values for solvent separation efficiency were calculated from the tie-line data and show that separation of carboxylic acids from dodecane is feasible by extraction with acetonitrile.Item Liquid-liquid equilibria related to the separation of organic acids(2012) Xhakaza, Nokukhanya Mavis; Redhi, Gyanasivan GovindsamyThe thesis involves a study of the thermodynamics of ternary liquid mixtures involving carboxylic acids with sulfolane, hydrocarbons and acetonitrile. Carboxylic acids are an important group of polar compounds with many industrial and commercial uses and applications. In South Africa, these carboxylic acids together with many other oxygenates and hydrocarbons are manufactured by SASOL using the Fischer–Tropsch process. The separation of these acids from hydrocarbons is a commercially viable option, and is an important reason for this study. This work focuses on the use of sulfolane in effecting separation by solvent extraction and not by the more common and energy intensive method of distillation. Sulfolane was chosen because of its high polarity and good solvent extraction properties. The first part of this study involves the determination of excess molar volumes (VmE) of binary mixtures of sulfolane (1) + carboxylic acids (2) at different temperatures of 303.15 K and 308.15 K, where carboxylic acids refer to acetic acid, propanoic acid, butanoic acid, 2-methylpropanoic acid, pentanoic acid and 3-methylbutanoic acid respectively. The densities of the binary systems of sulfolane (1) + carboxylic acids (2) were measured at T = 303.15 K and 308.15 K. The excess molar volumes were calculated from the experimental densities at each temperature. The VmE were negative for the entire mole fractions for all the binary systems. It was found that the VmE in the systems studied increase with an increase in temperature, and also VmE decreases with an increase in the carbon chain length of the carboxylic acid. The VmE data results were correlated using Redlich-Kister equation. The second part was the study of the binodal or solubility curves and tie line data for the ternary systems of [sulfolane (1) + carboxylic acids (2) + hydrocarbons (3)] and [acetonitrile (1) + carboxylic acids (2) + hydrocarbon (3)]. Hydrocarbons refer to pentane, hexane, dodecane and hexadecane. The binodal curve experimental data was determined by the cloud point technique. Liquid-liquid equilibrium (LLE) phase diagrams were constructed using the mole fractions and refractive indices (nD). Tie line data were obtained for the sulfolane-rich and hydrocarbon-rich phases as well as the acetonitrile-rich and hydrocarbon-rich phases respectively. The tie lines in both cases were skewed towards the hydrocarbon-rich phases indicating that relative mutual solubility of carboxylic acids is higher in the hydrocarbon-rich phase than in the solvent-rich phase. Selectivity values were calculated from the tie-lines to determine the extraction capabilities of solvents sulfolane and acetonitrile. Selectivity values in all cases were greater than one, meaning that both sulfolane and acetonitrile can be used to separate carboxylic acids from hydrocarbons. Binodal curve data were correlated by the Hlavatý, beta and log equations; average standard deviation error for Hlavatý was 0.012, for beta, 0.023 and for log, 0.021. The NRTL and UNIQUAC models were used to correlate the experimental tie-lines. The calculated values based on the NRTL equation were found to be better than those based on UNIQUAC equation; the average root-mean square deviation, (rmsd), between the phase composition obtained from experiment and that from calculation was 0.061 for the NRTL model, as compared to 0.358 for UNIQUAC model for the ternary systems involving sulfolane. For ternary systems of acetonitrile, the NRTL equation was better than the UNIQUAC with the rsmd of 0.003 and 0.287for UNIQUAC equation.