Recovery of ionic liquids from dilute aqueous solutions by electrodialysis

Ionic liquid/s (IL/ILs) are ideal solvents for many separation processes, such as cellulose dissolution, extraction of heavy metal ions and coal liquefaction residues, etc. During the above processes, ILs would inevitably remain in effluents. Due to their high costs and potential detrimental impacts on environment, it is extremely important to recycle ILs from dilute aqueous solutions. Electrodialysis (ED) was used for primary separation and recycling ILs. In order to evaluate the performance of ED process, the effects of initial concentration, applied voltage and initial volume of the dilute solutions on the overall current efficiency (η), recovery ratio (R) and concentration ratio (ω) were investigated. Among these experimental results, the highest recovery ratio could reach 85.2% and the highest overall current efficiency could reach 80.9%. The ED energy consumption is also discussed and the highest specific energy consumption (Re) could reach about 1350 g/kW h. The effects of IL cation and anion sizes on concentrating process are also evaluated. The experimental results indicate that ED is an effective method to concentrate IL aqueous solutions.

► Electrodialysis was used to concentrate ionic liquid aqueous solutions.
► Increasing initial concentration will decrease R, η, ω and Re.
► Increasing voltage will increase R, η, ω and Re in a certain range.
► ω increases almost linearly as initial volume of dilute solution increases.
► Cation and anion sizes of ILs may have some influences on ion transport.