Experimental Mapping of the Liquid–Liquid Envelope of Mixtures Alcohol/Water/Salt at Ambient Conditions (297 K and 1 bar). Alcohols: Ethanol and Isopropanol; Salts: Na2CO3 and K2CO3

Abstract

Adding NaCO₃ or K₂CO₃ to a binary mixture ethanol/water or isopropanol/water triggers a liquid–liquid phase split at ambient conditions. One of the phases is rich in alcohol, and the other is rich in water. This phenomenon could be potentially used in the development of low-carbon separation technologies for alcohols produced from biomass fermentation. In this study, the phase behavior of the following mixtures was investigated at ambient conditions: ethanol/water/sodium carbonate (Na₂CO₃), ethanol/water/potassium carbonate (K₂CO₃), isopropanol/water/Na₂CO₃, and isopropanol/water/K₂CO₃. To do so, the entire liquid–liquid (LL) envelope was experimentally mapped by detecting the liquid ↔ liquid/liquid (L ↔ LL) and liquid/liquid ↔ solid/liquid/liquid (LL ↔ SLL) boundaries. LL tie lines were also measured. The measured LL boundaries and tie lines were used for locating the plait point using a well-known methodology. The quality of the data was assessed by using graphical methods that allowed the detection of outliers. The internal consistency of the measured tie lines was verified by comparing the measured data with pure predictions from the electrolyte version of the UNIQUAC model. The internal consistency of the measured L ↔ LL boundary was assessed by comparison with predictions from an empirical model developed by fitting the measured LL tie lines.