Effects of Selected Ionic Liquids on the Vapor-Liquid-Equilibria of Water-2-Propanol System

Abstract

Separation processes involving vapor and liquid phases represent a typical unit operation in most chemical industries, including distillation and absorption. A large fraction of the capital and operating costs is usually devoted to such operations. Owing to the unlikelihood of the complete separation of azeotropic mixtures by distillation, separation processes involving such mixtures remain one of the most pressing challenges in the chemical industry. Using inorganic salts is a common technique in handling azeotropic systems. However, issues such as corrosion and fouling render this technique ineffective. Recently, ionic liquids were introduced as azeotrope-breakers. In this work, the effect of two ionic liquids, i.e., 1-Butyl-1-methylpyrrolidinium chloride [BMPy][Cl], and 1-Butyl-1-methylpyrrolidinium trifluoromethanesulfonate [BMPy][OTf] on the vapor liquid equilibrium (VLE) of the (azeotropic) water + 2-propanol system is investigated. For this purpose, the corresponding binary VLE for water or 2-propanol with each of the two ionic liquids were experimentally measured and reported at 100, 75, and 50 kPa. Based on the observed boiling point elevation, it has been found that [BMPy][Cl] has a higher interaction with both solvents than [BMPy][OTf]. Furthermore, it has been found that [BMPy][Cl] has a higher interaction with water than with 2-propanol, while [BMPy][OTf] interacts with both solvents in a similar manner. The boiling point elevation was found to be independent of the pressure. Most importantly, [BMPy][Cl], at a mole fraction of 0.31in the liquid phase, was capable of completely eliminating the azeotrope of water + 2-propanol system. In contrast, [BMPy][OTf] shifted the azeotrope towards the alcohol-rich region, yet it was not able to completely remove the azeotrope of this system at the studied concentrations. Data were modelled with the non-random, two-liquid (NRTL) model, which could describe the experimental data, with a root mean square deviation (RMSD) less than 0.015 for the solvents’ activity coefficients in the binary systems. For the ternary systems, the RMSD for temperature was found to be less than 2 ºC. Thus, it is concluded that chloride based ionic liquids resemble good entrainers for the extractive distillation of the studied azeotrope.