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Diffusivities in Binary Mixtures of Ammonia Dissolved in n‑Hexane, 1‑Hexanol, or Cyclohexane Determined by Dynamic Light Scattering and Molecular Dynamics Simulations
Ist Teil von
Journal of chemical and engineering data, 2023-10, Vol.68 (10), p.2585-2598
Ort / Verlag
American Chemical Society
Erscheinungsjahr
2023
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Binary mixtures of ammonia (NH3) dissolved in cyclohexane, n-hexane, or 1-hexanol are investigated by dynamic light scattering, polarization-difference Raman spectroscopy (PDRS), and equilibrium molecular dynamics (EMD) simulations. Investigations are performed in macroscopic thermodynamic equilibrium at or close to saturation conditions up to pressures p of 3 MPa and at temperatures T between 303 and 423 K. Besides studying the influence of a polar gas dissolved in a liquid on the Fick or mutual diffusion coefficient D 11, the applicability of EMD simulations to systems consisting of polar/polar or nonpolar/polar solvent/solute combinations is also evaluated. At small compositions of NH3, D 11 in mixtures with cyclohexane or 1-hexanol shows the expected Arrhenius-like increase with increasing T. For mixtures of n-hexane and NH3, a departure from the expected increase with T is observed at low T, which is related to a strong clustering of the NH3 molecules, leading to a slowing down of D 11. This behavior can be related to the weak interactions between polar NH3 and nonpolar n-hexane. In comparison, much stronger interactions are observable between polar NH3 and polar 1-hexanol. The composition-dependent trend of D 11 in mixtures of n-hexane or 1-hexanol with NH3 is also investigated. Here, D 11 increases with increasing amount of dissolved NH3 in mixtures of 1-hexanol + NH3 for all investigated T. For n-hexane + NH3, at the lowest T, D 11 is first constant and increases afterwards with increasing amount of dissolved NH3. At larger T, D 11 is first constant and slightly decreases afterwards. Due to a lack of solubility data, the composition of the investigated mixtures could not be determined by PDRS. Yet, the composition-dependent intensity ratios between contributions related to NH3 and the respective solvent obtained from PDRS are reported. This allows the determination of composition, once reliable solubility data are available.