A novel hybrid process design for efficient recovery of hydrophilic ionic liquids from dilute aqueous solutions

Ionic liquids (ILs) have received much attention in both academia and industries due to their superior performance in many applications. Efficient recovery/recycling of ILs from their dilute aqueous solutions is essential for the acceptance and implementation of many IL-based technologies by industry. In this work, a practical and cost-effective hybrid process design method that combines aqueous two-phase extraction, membrane separation, and distillation operating at their highest efficiencies is proposed for the recovery of hydrophilic ILs from dilute aqueous solutions. The application of this hybrid process design method is illustrated through case studies of recovering two hydrophilic ILs, n-butylpyridinium trifluoromethanesulfonate ([C₄Py][TfO]) (CAS number: 390423-43-5) and 1-butyl-3-methylimidazolium chloride ([C₄mIm][Cl]) (CAS number: 79917-90-1), from their dilute aqueous solutions. For the recovery of 10 wt.% [C₄Py][TfO] from aqueous solution, the hybrid process using (NH₄)₂SO₄ as the salting-out agent could reduce the total annual cost (TAC) and energy consumption by 57% and 91%, respectively, compared with the pure distillation processes. In the case of recovering 10 wt.% [C₄mIm][Cl] from aqueous solution, the reduction in TAC and energy savings of the hybrid process with salting-out agent (NH₄)₂SO₃ could reach 49% and 87%, respectively, compared with the pure distillation process. Furthermore, uncertainty analysis through Monte Carlo simulations show that the proposed hybrid process design is more robust to uncertainties in energy prices and other material (e.g., equipment and solvent) costs.