Liquid-liquid extraction and mechanism analysis of extracting fuel additive isopropanol from mixture with choline-based deep eutectic solvents as efficient extractants

Deep eutectic solvents (DESs) have wide application prospects in azeotropic separation since of their advantages of good thermal stability, non harmfulness and low raw material price. As a green solvent, DESs has attracted more and more attention in recent years. As a high-quality fuel additive, isopropanol (IPA) has high chemical added value because of its high energy density, low volatile and small corrosive. Therefore, extracting high alcohols such as IPA from azeotropes can effectively improve the combustion efficiency of fossil fuels and reduce tail gas emissions. In this work, ethylene glycol and other hydrogen bond receptors were selected to synthesize three choline-based DESs to extract IPA from n-heptane. The selectivity of DESs to IPA was obtained by liquid–liquid equilibrium (LLE) experiment and the separate efficiency of diverse DESs was compared. To profoundly investigate the intrinsic principle of extracting IPA from DESs, molecular dynamics (MD) simulation method was utilized to acquire the interaction energy between DESs and IPA/n-heptane, as well as the radial distribution function between DESs and IPA and other kinetic analysis data. The data showed that the experiment is in great assertion with the simulation, DESs synthesized from choline chloride and ethylene glycol has the leading extraction impact of IPA among three kinds of DESs, and Cl- played an imperative part in LLE. In addition, the effect of azeotrope ratio on separation efficiency was explored by simulating LLE with different azeotrope composition.