Ozonation of ionic liquid 1-butyl-3-methylimidazolium chloride under basic condition

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Although ionic liquids (ILs) have unique properties so that utilization in industry has been increased, the methodology of its disposal or decomposition have not been well studied. Since ILs are polar and nonvolatile substances, decomposition in liquid phase is the promising treatment for them. This research aimed at evaluating the decomposition efficiency of 1-butyl-3-methylimidazolium chloride (bmimCl), one of the major ILs, by ozone in basic condition at pH 8. We observed that 20 mg L−1 of ozone decomposed 0.1 mmol L−1 of bmimCl in 40 minutes. The stoichiometric amount of ozone to decompose 1 mol of bmimCl decreased from 0.72 mol in the beginning of the reaction to 0.1 mol when 94% of bmimCl decomposition was attained. Although bmimCl concentration decreased, we did not observe a decrease of total organic carbon (TOC), which suggested that a mineralization of bmimCl did not occur. A rapid increase of absorbance at 214 nm of wavelength followed by a gradual decrease indicated a formation of initial bmimCl oxidation byproducts that are transformed into other byproducts.

To study the insight of the reaction, we applied the methodology of quantum chemistry using Gaussian©. Density distribution on the bmim molecule in water in the absence and presence of chloride atom provides the reactive sites where electrophilic hydroxyl radical and ozone attempt to attack. The analysis revealed that C-H bond in which the carbon bonds with two nitrogen with C=N bond are most vulnerable sites that tends to be attached by O3 or hydroxyl radical.

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Published by the American Chemical Society.

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ACS National Meeting 2014