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Soluting-In, Soluting-Out, and Washing-Out Effects of Various Additives on Aqueous 1‑Butanol Solutions

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journal contribution
posted on 21.10.2021, 20:09 authored by Nosaibah Ebrahimi, Ameneh Alidoosti, Rahmat Sadeghi
This work addresses the liquid–liquid demixing (clouding) behavior of 1-butanol aqueous solutions in the presence of various additives, including amino acids, imidazolium-based ionic liquids (ILs), polymers, and 1-/2-propanol, in a wide temperature range (283.1–353.1 K) and at atmospheric pressure (845 hPa). The visual cloud point data revealed that the studied amino acids reduce the water solubility of 1-butanol and expand the immiscibility region (soluting-out effect). At the same amino acid’s molality, the soluting-out aptitude follows the trend serine > glycine > alanine > proline > glutamine. However, the ILs and polymers [poly­(ethylene glycol) (PEG)] act as cosolvents for 1-butanol in aqueous media and broaden the miscibility region (soluting-in effect). An increase in the cation alkyl chain length of ILs and a decrease in PEG molar mass strengthen the soluting-in effect. The clouding phase behavior of aqueous 1-butanol + 1-/2-propanol ternary systems at lower temperatures reveals the expansion of the immiscibility region due to the washing-out effect but at higher temperatures exhibits the soluting-in effect. An increase in the concentration of 1-/2-propanol decreases the extent of the washing-out effect. In all cases, the soluting-in/out effects increase with the increase in the concentration of additives. Soluting effects occurring in the studied systems have been quantified by correlating the experimental cloud point data with Setschenow’s equation, and the clouding process in the systems studied has been carefully discussed from the thermodynamic point of view. From the gathered results, at higher temperatures, the relative contribution of enthalpy to clouding Gibbs free energy in the presence of soluting-in agent additives is mostly higher than that in the presence of soluting-out agents. However, at lower temperatures, the entropy increase is the driving force of clouding in most of the investigated systems.

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