Research On Degradation And Removal Of Ionic Liquids From Their Aqueous Solution

In recent years, room temperature ionic liquids (ILs) have received great attention as primary alternatives to the organic solvents traditionally used in chemical processes. ILs having negligible vapor pressures and stable thermal properties are often regarded as "green solvents", but this does not mean that they are not harmful to the environment. Till now some studies have been reported on their environmental impact in terms of ecotoxicity, in contrast the studies on how to degrade and remove them from aqueous solutions are scarce. In this paper we reported the degradation ability of some ILs by four kinds of advanced oxidation methods and adsorptive removal with six kinds of adsorbents at various operation conditions.The main contents of this research include two parts as follows:(1)Using three ILs as prototypes, i.e. 1-butyl-3-methylimidazolium chloride and hexafuorophoshate ([Bmim]Cl and [Bmim]PF6),and 1-methyl-3-methylimidazolium dimethylphosphate ([Mmim]DMP),we studied their degradability by four different approaches, namely advanced oxidation and Hoffman decomposition reaction methods, and compared their performance and characteristics. The results show that (a)Fenton reagent can only change the structure of the alkyl substitute of imidazolium cation of [Bmim]Cl, but not totally destroy the cation or [Bmim]Cl; (b)The cation of ILs [Bmim]Cl and [Bmim]PF6 can not be converted to volatile tertiaryamines by Hoffman reaction at 180℃within 24 h in the presence of NaOH; (c)The removal ability of Fe/active carbon/cements composite for ILs originates predominantly from the adsorption performance of active carbon, while the voltaic oxidation of Fe/C micro cells is negligible; (d)Wet catalytic oxidation at high temperature can completely destroy the structure of [Bmim]Cl leading to the production of HCl and serious sevier corrosion to the steel reacor, however, this method shows a bad degradation ability for [C1MIm][Me2PO4].(2)The adsorption performance of six adsorbents, namely montmorillonite, activated clay, artificial zeolite, active carbon and hydrotalcite on six ILs are studied, viz. [Bmim]Cl, [Bmim]BF4, [Bmim]PF6, [Bmim]DBP, [Hmim]Cl and [Omim]Cl. The results show that (a) temperature has a profound influence on the adsorption performance of active carbon, but little influence on the remaining adsorbents; (b) For IL [Bmim]Cl, the adsorption ability of the adsorbents follows the order of montmorillonite> activeated clay> active carbon> artificial zeolite> hydrotalcite; and hydrotalcite has no adsorption to the IL studied; (c) Montmorillonite has nearly the same adsorption ability for four ILs with the same cation, i.e. [Bmim]Cl, [Bmim]BF4, [Bmim]PF6, and [Bmim]DBP, indicating that the adsorption is of cation exchange type; (d) The equilibrium adsorption of montmorillonite for three ILs with the same anion followeds the order of [Bmim]Cl>[Hmim]Cl>[Omim]Cl, that is, the equilibrium adsorption decreases gradually with the increase of the sidechain length of the ILs due to the limitation of the pore size of the adsorbents and the increasing size of ILs from [Bmim]Cl to [Omim]Cl.