Theses and dissertations (Applied Sciences)
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Item Molecular interactions of binary mixtures of deep eutectic solvents with organic solutes(2024-05) Molefi, Reitumetse Precious; Kabane, Bakusele; Deenadayalu, NirmalaDeep eutectic solvents are the new emerging solvents formed by the combination of hydrogen bond acceptor and hydrogen bond donor. This type of solvent is still under development for possible industrial application including in chemistry, biotechnology, and pharmaceutical processes. The deep eutectic solvents have attracted much attention because they are characterized as greener solvents when compared to the currently used volatile organic solvents. Deep eutectic solvents are to replace the ionic liquids, which are posed as green solvents, however, their toxic nature has turned to be its drawbacks. The deep eutectic solvents attracted great interest due to their unique properties such as biodegradability, thermal stability, less toxicity, easy and cheap to prepare. This work explores the activity coefficients at infinite dilution of deep eutectic solvents. The deep eutectic solvents under investigation were carefully synthesized using hydrogen bond donors (HBD) and hydrogen acceptors (HBA) at a specific ratio. The analysis of these prepared deep eutectic solvents were analysed using spectroscopic techniques (FTIR and NMR) to confirm the formation of deep eutectic solvents and the type of interaction occurring between the HBD and the HBA. Additionally, thermal stability of the prepared deep eutectic solvents was investigated. The DESs were then used to measure the activity coefficients at infinite dilution for volatile organic compounds (alkanes, alkene, alkynes, aromatic hydrocarbons, ketones, acetonitrile, tetrahydrofuran, alcohols and thiophene) using the chromatography technique. The activity coefficients at infinite dilutions were conducted over a range of temperature (313.15 - 353.15) K. The prepared deep eutectic solvents for this include. DES1 {1- butyl-2,3-dimethylimidazolium chloride + ethylene glycol (1:3)} DES2 {1-butyl-2,3-dimethylimidazolium chloride + diethylene glycol (1:2)} DES3 {1-butyl-2,3-dimethylimidazolium tetrafluoroborate + ethylene glycol (1:3)} DES4 {1 -butyl-2,3-dimethylImidazolium tetrafluoroborate + diethylene glycol (1:3)) The study also focuses on understanding the behaviour of these DES through a comprehensive analysis of their thermophysical characteristics and their ability to dissolve solutes at infinite dilution. The investigation revealed intriguing trends in the solvation behaviour of different classes of solutes within the DES. Alkanes exhibited higher activity coefficients, with a clear dependence on the alkyl chain length. Cyclic hydrocarbons showed distinct behaviour due to stronger interactions with the imidazolium ring. Alkynes demonstrated the lowest activity coefficients, attributed to the presence of triple bonds influencing solute-solvent interactions. Aromatic hydrocarbons exhibited unique solvation behaviour influenced by the delocalized pi- π- electrons on the benzene ring. To use the deep eutectic solvents at an industrial level, it is highly imperative to understand the intermolecular interactions and properties of the pure deep eutectic solvents and their mixtures with volatile organic solutes. The prepared deep eutectic solvents for thermophysical properties include. DES5 (1-butyl-1-methylpyrrolidinium bromide + ethylene glycol) DES6 (1-butyl-3-methylimidazolium chloride + ethylene glycol) Thermophysical properties, such as densities, speed of sound, and refractive indices were measured as a function of temperature. The study investigated the binary mixtures containing (DES5 + acetic acid or ethanol) and (DES 6 + acetic acid or ethanol). These were investigated at temperatures ranging between (293.15 and 313.15) K and at atmospheric pressure (0.1MPa) over a range of mole fraction (𝑥1= 0 to 1) as a function of DES. The measured property values were used to compute the excess properties such as excess molar volumes, isentropic compressibilities, deviation in refractive indices, deviation in isentropic compressibilities and intermolecular free length. The data obtained provides insights into the molecular interactions within the DESs, shedding light on their structural arrangements and overall stability. This study contributes to the fundamental understanding of deep eutectic solvents, offering a detailed exploration of their thermophysical properties and their solvation behaviour at infinite dilution. The findings have implications for the design and optimization of DESs for various applications, including their use as green solvents in chemical processes and separations.Item Thermodynamic properties at infinite dilution of deep eutectic solvents with organic solutes at different temperatures(2023) Manyoni, Lindokuhle; Redhi, Gan G.Many industrial processes in the chemical industry require surge amounts of energy to separate organic mixtures. While numerous separating substances used for this purpose are volatile and have closely related boiling points to the mixtures, they are environmentally harmful. As a result, new separation substances in the space of these solvents should be researched. The latest group of solvents known as deep eutectic solvents (DESs), classified as Type (III), were studied in the space of conventional organic solvents, which are currently used in industrial processes for extraction or separation purposes. In the forecast, deep eutectic solvents have gained significant interest as part of the low melting temperature solvents with many other attractive and unique properties. This includes their physical, thermophysical, and thermodynamic properties. These properties were investigated in this study in order to better understand the intermolecular interactions of 1-ethyl-1-methylpyrrolidinium bromide + glycerol [(EMPYR) Br + Gly] or 1-ethyl1-methylpyrrolidinium bromide + ethylene glycol [(EMPYR) Br + EG], with methanol or ethanol. Hence, the first section of the study investigated the physical properties, including density and sound velocity, of deep eutectic solvents and their binary mixtures, as a function of temperature. The obtained physical properties were used to compute the thermophysical properties, i.e., excess molar volume (Vm E ), intermolecular free length (Lf), variation in isentropic compressibility (∆Ks), and isentropic compressibility (Ks ), to advance the study of the intermolecular interactions of the selected deep eutectic solvents and their binary mixtures. Furthermore, the second section of this study investigated the infinite dilution activity coefficients of five different deep eutectic solvents, including (1) 1-ethyl-1-methylpyrrolidinium bromide + glycerol [(EMPYR) Br + Gly], (2) 1-ethyl-1-methylpyrrolidinium bromide + ethylene glycol [(EMPYR) Br + EG], (3) 1-ethyl-1-methylpyrrolidinium bromide + 1-pentanediol [(EMPYR) Br + 1.5-PDO], (4) 1-ethyl-1-methylpyrrolidinium bromide + 1-hexanediol [(EMPYR) Br + 1.6- HDO], and (5) trihexyltetradecylphosphonium decanoate + ethylene glycol [(THTDP) Dc + EG], with various solutes at different temperatures. The obtained infinite dilution activity coefficients (γ13 ∞ ) were utilized to compute the other thermodynamic properties, viz., enthalpy (∆H1 E,∞), entropy (∆S1 E,∞), and Gibbs free energy (∆G1 E,∞) as well as the selectivity (Sij ∞) and capacity (kj ∞), of the selected organic solutes. The separation was possible with the investigated solvents. As is known, the accurate and precise analysis of the thermodynamic properties of liquid substances such as deep eutectic solvents is of significant interest to the chemical industry as it would help ascertain the implementation of these solvents on a large scale for industrial separation processes.