Separation and Purification Technology, Vol.215, 134-142, 2019
Destruction of environmentally hazardous halogenated hydrocarbons in stable ionic liquids with superoxide ion radical
Ionic liquids (ILs) have been investigated as a media for destruction of halogenated hydrocarbons (HHCs) because of their affinity to solubilize pollutants, hydrophobicity, ability to generate and maintain free radicals, and long term stability with superoxide ion radical (O-2(center dot)-). Three HHCs (CCl4, CHCl3, and CHBr3) were successfully destructed by O-2(center dot-) in 13 hydrophobic ILs, including two piperidinium (PIP-ILs), four pyrrolidinium (PYRR-ILs), and seven ammonium-cation based ILs (AM-ILs). The effects of contact time and potassium superoxide (KO2) dose on the destruction efficiency were evaluated using analysis of variance. 1-propyl-1-methylpiperidinium, 1-octyl-1-Methylpyrrolidinium, and octyltriethylammonium paired with bis (trifluoromethylsulfonyl) imide were found to be the best performers amongst PIP-ILs, PYRR-ILs, and AM-ILs. CHCl3, CCl4 and CHBr3 consumed about 8, 11, and 14 KO2/HHC mole ratio to achieve 95% of optimum destruction efficiency. High viscosity was identified as the main drawback of [N8881][Tf2N] and [N4441][Tf2N]. Destruction was moderately fast and steady state efficiency was achieved within 30 min. The strong correlations between empirical polarity E-T(N) of HHCs, work as co-solvents, and destruction efficiencies were obtained with R-2 values higher than 0.99. The study presents a useful insight to use ILs as alternative solvents for treatment of hazardous wastes.