Liquid-Liquid Demixing Behavior of Aqueous 1-Butanol Solutions in the Presence of Various Organic and Inorganic Ammonium Salts: Effect of Temperature, Cation Alkyl Chain Length, and Anion Type of Salts on Salting Coefficients and Thermodynamic Functions

In this work, the effects of various organic and inorganicammoniumsalts on the liquid-liquid demixing (clouding) behavior ofaqueous 1-butanol (BuOH), as a thermo-responsive material, solutionswere investigated in the temperature range of 283.15-353.15K. The inorganic salts used are NH4Cl and NH4Br, and the organic ones are tetramethylammonium bromide (TMAB),tetraethylammonium bromide (TEAB), tetrapropylammonium bromide (TPAB),tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC),tetrabutylammonium hydrogen sulfate (TBAH), dodecyltrimethylammoniumbromide (DTAB), and cetyltrimethylammonium bromide (CTAB). The inorganicammonium halides reduced the water-solubility of BuOH and inducedthe salting-out effect. As the concentration of inorganic ammoniumsalts increased, the strength of the salting-out effect and the areaof the biphasic region increased. However, all the investigated tetraalkylammoniumsalts had the salting-in effect on BuOH and increased its solubilityin water. The extent of the monophasic region and also the intensityof the salting-in effect (co-solvency) enhanced with increasing theconcentration of the tetraalkylammonium salts. The effects of thecharge density of the salt anion as well as the alkyl chain lengthof the salt cation, on the immiscibility region of aqueous BuOH solutions,were studied. From the correlation of the measured cloud point datawith Setschenow's relation, the salting effects occurring inthe investigated systems were also quantified. Finally, the valuesof different thermodynamic functions of phase separation were determined,from which the driving force of clouding at different conditions wasdiscussed.