EXTRACTION OF ORGANIC CONTAMINANTS USING ROOM TEMPERATURE WATER-IMMISCIBLE IONIC LIQUIDS
Room Temperature Ionic Liquids (RTILs) comprise a new generation of solvents, and their exceptional properties (i.e., non-volatility, non-flammability) promote them as alternative solvents in applications dominated by the well-known volatile organic compounds (VOCs). Although extensive literature exists for ionic liquid behavior as solvents and catalysts for numerous organic and inorganic reactions, their use for environmental applications is an unexplored area. Water immiscible RTILs were selected for investigation of ILs in environmental applications. Specifically, ILs were used as solvents for extracting organic contaminants from aqueous solutions. The higher affinity of the contaminants for ILs, instead of water, contributed to their removal from water and the minimization of the volume of the contaminated stream. Two ILs, 1-ethyl-3-methylimidazolium fluoroethylsulfonyl)imide, [emim]Beti, and 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF 6 , were investigated as solvents for the extraction of chlorophenols from aqueous solutions. Partitioning of phenol, monochlorophenols, dichlorophenols, trichlorophenols, tetrachlorophenols, and pentachlorophenol was measured in both aqueous and ionic liquid phase using High Pressure Liquid Chromatography (HPLC) analysis. Extraction efficiency was found to be higher when [bmim]PF 6 was used and when the pH of the aqueous solution was at least one unit below the value of the dissociation constants (pK a ). In addition, partitioning, for both ILs, was increased as the number of chlorine atoms in the chlorophenol increased, displaying the same behavior as 1-octanol-water partition coefficient. Correlation between the distribution ratio of [emim]Beti-water or [bmim]PF 6 -water and the 1-octanol-water partition coefficient was calculated at 0.950 or 0.938, respectively. The effect of ionic strength on partitioning was also investigated, and showed no impact on the distribution ratio. Finally, the distribution ratio was not influenced by the composition of the initial aqueous solution, since the distribution ratios were the same for the multi-compound and the single-compound solution.Infrared (IR) and Raman spectroscopy methods were used in selected samples for the investigation of the mechanism of interaction of chlorophenols and the ionic liquid phase. The results from IR and Raman analysis indicated a hydrogen bond between the chlorine atoms and the second hydrogen of the imidazolium ring, which may explain their high distribution ratios.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:chlorophenols extraction hplc ir spectroscopy raman
Date of Publication:01/01/2003