Screening of ionic liquids as entrainers for the separation of 1-propanol + water and 2-propanol + water mixtures using COSMO-RS model

ABSTRACT

The COSMO-RS model was used to screen potential ionic liquids for the separation of aqueous azeotropic mixtures 1-propanol + water and 2-propanol + water. A combination of 22 cations (involving imidazolium, pyridinium, pyrrolidinium, quinolinium, and ammonium) and 36 anions were investigated. The anions chloride [Cl] and dihydrogen phosphate [H₂O₄P] were found to strongly influence the vapor liquid equilibrium behavior, whereas the ammonium-based cations diethanol ammonium [(Et)₂AMM]⁺ and tetra methyl ammonium [M₄AMM]⁺ were the most promising cations. In addition, the study of mixing enthalpy and excess Gibbs free energy confirmed that the molecular interaction of ionic liquids with water was found to be much larger than that with alcohols 1-propanol and 2-propanol, indicating the presence of a strong hydrogen bonding between the ionic liquids and water. Further, the addition of ionic liquids to the alcohol–water mixture reduces the activity coefficient of water and increases the relative volatility of the mixture, facilitating easier separation. Ionic liquids [(Et)₂AMM][Cl], [(Et)₂AMM][H₂O₄P], [M₄AMM][Cl], and [M₄AMM][H₂O₄P] are expected to be effective entrainers for the separation of the industrially important 1-propanol + water and 2-propanol + water systems.

KEYWORDS:

• COSMO-RS model
• excess Gibbs free energy
• excess mixing enthalpy
• polarity
• relative volatility
• vapor–liquid equilibrium