Environmentally friendly and effective removal of Br− and Cl− impurities in hydrophilic ionic liquids by electrolysis and reaction

Environmentally friendly and effective removal of Br− and Cl− impurities in hydrophilic dialkylimdazolium or butylpyridinium ionic liquids was investigated and developed at room temperature to 80 °C and atomspheric pressure. Constant elelctrolysis was applied to oxidize Br− and Cl− to their corresponding Br2 and Cl2, then the BF4- and NO3- ions from HBF4 and HNO3 solution in the cathode zone move to anode zone through an anion exchange membrane and combine with dialkylimdazolium or butylpyridinium cation to form ionic liquids. The Br2 and Cl2 in electrolyzed ionic liquids are treated with ethylene to afford the corresponding 1,2-dibromo (or dichloro) ethane which could easily be removed by volatilisation under vacuum (ca. 10 mm Hg). Removal of Br− and Cl−impurities (0.94–4.47 wt%) from hydrophilic dialkyl imdazolium or butylpyridinium ionic liquids through electrolysis and ethylene treatment could be achieved at 0.06%–0.29% without any additional solvents and ionic liquid loss.