In-silico investigation of acetic acid extraction from aqueous solution using hydrophobic ionic liquids: a molecular dynamics simulation and COSMO-SAC approach

Acetic acid (AA) is an essential industrial compound widely used in pharmaceuticals, food production, biofuels, and textiles, serving as a key precursor for synthesising drugs, dyes, perfumes, and plastics. However, its separation from aqueous solutions remains challenging due to its low concentration in fermentation broth and strong water affinity. This study employed molecular dynamics (MD) simulations and the COSMO-SAC thermodynamic model to evaluate the extraction capability using two organic solvents, <i>n</i>-butyl acetate and ethyl acetate, along with three imidazolium-based hydrophobic Ionic Liquids (ILs) ([BMIM][Tf₂N], [BMIM][PF₆], and [BMIM][TfO]). The MD-derived liquid–liquid extraction (LLE) tie-lines, with RMSD values below 7.6%, demonstrated the reliability of the simulation. Distribution coefficient and selectivity analysis identified [BMIM][Tf₂N] as the most effective solvent, achieving superior extraction with minimal water co-extraction. Radial distribution function (RDF), spatial distribution function (SDF), and hydrogen bonding analyses further supported the computational findings, highlighting favourable interactions between AA and the solvents, mainly through hydrogen bond formation. Additionally, COSMO-SAC predictions confirmed [BMIM][Tf₂N] as the most effective solvent, as indicated by lower activity coefficients for AA, signifying stronger interactions. In contrast, higher activity coefficient values for water suggest weaker interactions, reinforcing ILs’ effectiveness in extracting AA from aqueous solutions selectively.