The phase behavior of Isopropanol/Water/NaCl mixtures at atmospheric pressure and temperatures from 294.15 K up to the boiling point

Abstract

Branched-chain higher alcohols (BCHAs) have potential applications in the preparation of biofuels as they have properties similar to those of gasoline. Isopropanol is the simplest member of the BCHA family and is produced by either a catalytic process or fermentation of biomass. Regardless of the process, the isopropanol is produced as a component of a mixture with water content as high as 80%; therefore, purification is needed to produce fuel-grade isopropanol. Azeotropic and heteroazeotropic distillation are currently used to purify the isopropanol but they are carbon-intensive and costly. The addition of NaCl to an isopropanol/water mixture has two effects: could trigger a liquid–liquid phase split; and increases the relative volatility of the alcohol. These effects could potentially be used as the departure for the design of low-carbon and less expensive purification operations.The phase behavior of isopropanol/water/NaCl mixtures was experimentally mapped at temperatures up to the boiling point at atmospheric pressure. The liquid–solid, liquid–liquid, liquid–liquid–solid, liquid–vapor, liquid–liquid–vapor, liquid–liquid–solid–vapor and liquid–solid–vapor regions were experimentally detected and located in the phase diagram. The equilibrium compositions within the liquid–liquid, liquid–vapor and liquid–liquid–solid–vapor regions were measured. Three well-known methods were employed to assess the reliability of the measured liquid–liquid phase compositions. The temperatures and the composition of the vapor phase in the liquid–liquid–vapor region were also experimentally measured. The collected experimental data was used to construct the phase diagram of isopropanol/water/NaCl mixtures at 5, 10 and 20 wt% NaCl content, at atmospheric pressure, and temperatures from 294.15 K to the boiling point.