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Subject: search.filters.subject.0307 Theoretical and Computational Chemistry

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    Infinite dilution activity coefficients and thermodynamic properties of selected organic solutes and water dissolved in 1, 6-hexanediol
    (Elsevier BV, 2020-12) Nkosi, Nkululeko; Tumba, Kaniki; Ngema, Peterson; Ramsuroop, Suresh
    The experimental activity coefficients (γ13∞) and gas-to-liquid partition coefficients (KL) at infinite dilution for 34 organic solutes and water were determined in 1.6-hexanediol (HDO) by the gas–liquid chromatography technique (GLC) in the temperature range from (323.15 to 353.15) K. Fundamental thermodynamic functions such as excess partial molar enthalpy (ΔHiE,(∞)), excess partial molar Gibbs energy, (ΔGiE,∞) and entropy, (TrefΔSiE,∞) at infinite dilution were calculated from experimental values of γ13∞. Reported data were discussed in terms of solvent-solute interactions, heat effects and mixing spontaneity. Selectivity (Sij∞) and capacity (kj∞) related to different separation problems were calculated from γ13∞ data and compared to the literature values for selected ionic liquids (ILs), deep eutectic solvents (DESs) and industrial solvents. New data reported in this study suggest that HDO may be proposed as an alternative solvent for the separation of alkanes-pyridine and alkanes-thiophene systems. Furthermore, it was found that adding a hydrogen bond acceptor to HDO enhances its performance as a separation solvent.
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    Phase stability conditions for clathrate hydrate formation in (fluorinated refrigerant plus water plus single and mixed electrolytes plus cyclopentane) systems : experimental measurements and thermodynamic modelling
    (Elsevier BV, 2019-09) Ngema, Peterson Thokozani; Naidoo, Paramespri; Mohammadi, Amir H.; Ramjugernath, Deresh
    Phase equilibrium conditions (dissociation data) for clathrate hydrates (gas hydrates) were studied for systems involving fluorinated refrigerants + water + single and mixed electrolytes (NaCl, CaCl2, MgCl2 and Na2SO4) at varying salt concentrations in the absence and presence of cyclopentane (CP). The ternary systems for (R410a or R507) + water + CP were performed in the temperature and pressures ranges of (279.8–294.4) K and (0.158–1.385) MPa, respectively. Measurements for {R410a + water + (NaCl or CaCl2) + CP} were undertaken at salt concentrations of (0.10, 0.15 and 0.20) mass fractions in the temperature and pressure ranges of (278.4–293.7) K and (0.214–1.179) MPa, respectively. The temperature and pressure conditions for the (R410a + water + Na2SO4) system were investigated at salt concentration of 0.10 mass fraction in range of (283.3–291.6) K and (0.483–1.373) MPa respectively. Measurements for {(R410a or R507) + water + mixed electrolytes NaCl, CaCl2, MgCl2} were undertaken at various salt concentrations of (0.002–0.15) mass fractions in the temperature and pressure ranges of (274.5–292.9) K and (0.149–1.119) MPa in the absence and presence of CP, for which there are no published data related to mixed salt and a promoter. The phase equilibrium measurements were performed using a non-visual isochoric equilibrium cell and the pressure-search technique. This study was focused on obtaining equilibrium data that can be utilized to design and optimize for water desalination process and the development of a Hydrate Electrolyte–Cubic Plus Association (HE–CPA) Equation of State based model. The results indicate hydrate dissociation pressure reduction/hydrate dissociation temperature increase up to ambient conditions in the presence of promoter (CP). The experimental results were then modelled. The modelling results are in good agreement with the measured hydrate dissociation data.