Browsing by Author "Williams-Wynn, Mark Duncan."

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Applications of fluorocarbons for supercritical extraction in the petroleum industry.
(2016) Williams-Wynn, Mark Duncan.; Ramjugernath, Deresh.; Naidoo, P.
The majority of supercritical processes utilise carbon dioxide (CO2) as the principal solvent, because CO2 has many attributes that make it an ideal supercritical fluid (SCF) solvent. This study investigates the possibility of replacing CO2 with trifluoromethane or hexafluoroethane, because of the poor performance of CO2 in cases where more polar and heavier molecular weight solutes must be extracted. Several applications in the petroleum industry, such as oil sludge treatment and the treatment of contaminated soils, are discussed. Due to the large number hydrocarbons present in such applications, a selection of solutes that could be used to simulate a simplified stream were chosen for these investigations. These selected solutes were n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, 1-hexene, 3-methylpentane, methylcyclohexane, toluene and water. High-pressure vapour-liquid equilibria and vapour-liquidliquid equilibria for binary systems containing either trifluoromethane or hexafluoroethane, with these solutes were measured using a static-analytic apparatus at temperatures of between (272.9 and 313.2) K. For several systems, the phase equilibria data were verified using bubble-point pressures measured with a static-synthetic, variable-volume cell. Parameters for thermodynamic models were obtained by regression of the experimental data for the binary systems. The models provide a good representation of the majority of the systems investigated, and were therefore also used to estimate portions of the critical locus curves. These critical locus curves were compared to the critical loci that were extrapolated from the sub-critical coexistence data as well as critical loci that were measured with a critical point determination apparatus. There is satisfactory agreement between the calculated, the extrapolated and the measured critical loci. The thermodynamic models were used to simulate the separation of several hydrocarbon-water emulsions using either CO2, trifluoromethane, hexafluoroethane or mixtures thereof. The simulations confirmed that trifluoromethane, hexafluoroethane as well as mixtures thereof, provide improved performances (recoveries and yields) when used as alternative solvents in the SCF extraction of these systems. An economic analysis of a SCF extraction process was performed to investigate the performance of the solvents, and if such SCF extraction processes, using a mixture of trifluoromethane and hexafluoroethane, would provide an economically competitive treatment process for hydrocarbon-water emulsions.
An investigation into the potential of NFM, DEG and TEG as replacement solvents for NMP in separation processes.
(2012) Williams-Wynn, Mark Duncan.; Ramjugernath, Deresh.; Naidoo, Paramespri.
Optimisation attempts within the petrochemical industry have led to interest in alternate solvents. The most widely used commercial solvents for the separation of hydrocarbons, by extractive distillation, are N-methylpyrrolidone and sulfolane. There has also been reference made to other solvents, such as N-formylmorpholine and the ethylene glycols [mono-, di-, tri- and tetra], being used. The alternate solvents proposed for this study were N-formylmorpholine, triethylene glycol and diethylene glycol. Infinite dilution activity coefficients, γ∞, provided a means of comparing the ease of separation of the different solutes using different solvents in extractive distillation. There is a substantial database of γ∞ measurements for systems involving N-methylpyrrolidone and hydrocarbons. A fairly large data set of γ∞ values of hydrocarbons in N-formylmorpholine has also been measured. Very little work has been conducted on the γ∞ values of hydrocarbons in either diethylene glycol or triethylene glycol. Gas liquid chromatography is one of the more common methods used to measure γ∞. To enable the measurement of γ∞ at higher temperatures, a pre-saturator was installed prior to the column. This ensured that the carrier gas entering the column was saturated with solvent and prevented the elution of solvent from the column. The γ∞ values of 25 solutes; including n-alkanes, alk-1-enes, alk-1-ynes, alcohols and aromatics; were measured at temperatures of 333.15, 348.15 and 363.15 K. The γ∞ measurements in N-formylmorpholine were used to verify this experimental set up and technique. Once the experimental set up had been proven, γ∞ in N-methylpyrrolidone, triethylene glycol and diethylene glycol were measured. Selectivities and capacities, at infinite dilution, of several solute combinations in the four solvents were then compared. In a few of these separation cases, the alternative solvents appeared to have better separation performance than N-methylpyrrolidone. The γ∞ values of three of the solutes in N-formylmorpholine and N-methylpyrrolidone were also measured using the novel cell design and measurement procedure suggested by Richon. It was found that this new technique required further development for the case of volatile solvents, since the results obtained using this technique did not compare favourably with the literature data.
Liquid-liquid extraction of neodymium.
(2022) Bayeni, Thulani Tholithemba.; Naidoo, Paramespri.; Moodley, Kuveneshan.; Williams-Wynn, Mark Duncan.
Neodymium is classified as a rare earth element (REE). These elements possess a unique set of optical, electrochemical and magnetic properties that allow for their use in electronics manufacturing, medicine, catalysis and clean technologies. The global neodymium supply from primary source mining is isolated to a few countries, therefore developing technologies to recover neodymium and other rare earth elements from electronic waste is an emerging research area with economic incentive. The readiness of these technologies for industrial implementation is dependent on data for the extraction of neodymium from aqueous acidic solution into an organic phase for recovery. The available literature on these processes is limited. To address the gaps in the available literature, in this study, the distribution coefficient of neodymium in liquid-liquid equilibrium systems was measured across a range of nitric acid concentrations (0.1 – 2.9 M). The distribution coefficient is a measure of the affinity of a solute for the organic solvent to the aqueous phase. The extractant solutions used were composed of various concentrations of phosphorous acid diluted with n-dodecane. The tested extractant solutions are 0.1, 0.5 and 1 M of di(-2-ethylhexyl)phosphoric acid in n-dodecane. To investigate possible enhancements to the performance of the extractant, trace amounts of the ionic liquids (ILs) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (at concentrations of 0.019 and 0.19 M) and tributylmethylphosphonium methyl sulfate (at concentrations of 0.01, 0.1 and 0.25 M) were added to the organic extractant (0.5 M HDEHP in n-dodecane). The distribution coefficient data obtained for an extractant concentration of 0.5 M HDEHP was also used to determine its performance in a liquid-liquid extraction column by way of elementary mass balance calculations. The experiments performed in this study were undertaken using a bank of 6 stirred equilibrium cells immersed in a water bath maintained at a temperature of 298.15 K. Each vessel was filled with 5 ml of the aqueous and the organic solutions and mixed vigorously for 12 hours before being allowed to gravimetrically settle for 8 hours. Samples of the aqueous phase were withdrawn from the vessels, diluted using de-ionised water and analysed by way of inductively coupled plasma optical emission spectroscopy (ICP- OES). The equilibrium acid concentration of these samples was measured using acid-base titrations with 0.1 M sodium hydroxide solution. In this work the distribution coefficient data of 10 unique systems are presented, 2 test systems to validate the experimental method and 8 unique configurations of nitric acid concentration and extractant composition. The analysis of the distribution coefficient of neodymium showed that neodymium has an inversely proportional relationship to the aqueous [H+] concentration, established by the nitric acid concentration. For the HDEHP in n-dodecane extractant, the maximum distribution coefficient calculated was 274.26 at a nitric acid concentration of 0.2701 M with the 1.0 M HDEHP in n-dodecane. In the ionic liquid doped systems the maximum calculated distribution coefficients were 158.70 at a nitric acid [H+] concentration of 0.1161 M 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide doped extractant and 23.454 at an aqueous acid concentration of 0.0974 M when neodymium was extracted with the 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide doped extractant. The degree of extraction achievable by the addition of ILs is either decreased or increased, based on the concentration and species of ionic liquid. It was found that when ILs are used to enhance phosphorus acid extractant solutions, phase separation within the extractant occurs readily, decreasing the precision of measurements by more than 10%. The calculations for a liquid-liquid extraction column were performed based on a solution of neodymium and iron in nitric acid media extracted using 0.5 M HDEHP in n-dodecane. The results showed that neodymium with a solvent free purity of 96.75% by mass could be obtained using a column in which the extractant to volumetric feed flow ratio is 3.2. It is recommended that further distribution coefficient studies be undertaken to provide insight into the distribution behaviour of multiple ion-containing systems when extracted with IL containing synergistic extractant solutions.