| Ionic liquids are regarded as green solvents in comparison with the conventional organic solvents and have been widely used in the fields of biological, environmental and chemical industry. Following the deeper investigation, the defects of ionic liquids in the fields of synthesis, purification, recycling and application were discovered. Present studies indicated that most of ionic liquids were toxic, and some of them are even fatal. Meanwhile, ionic liquids in water could become a kind of emerging persistent pollutant because of their poor biodegradability. Therefore, the removal of ionic liquids from aqueous streams is very important.Treatment techniques such as chemical degradation, biodegradation and adsorption have been used for the removal of ionic liquids from aqueous streams. Among them, the adsorption method was demonstrated to be an effective technique due to it being cost-effective, easy handling in operation. The key is the choice of adsorbent for adsorption method. Activated carbon is the most commonly used adsorbent and it has been demonstrated to be effective for ionic liquid removal. However, its adsorption capacity needs to be improved in order to be used in practice much better.We used activated carbon modified by HNO3, H2O2 and ammonium persulfate to adsorb two imidazolium-based ionic liquids with different hydrophilic/hydropholic, including 1-butyl-3-methyl-imidazolium chloride ([BMIM]Cl) and 1-octyl-3-methylimidazolium chloride ([OMIM]C1), to study the effect of the surface chemistry of the activated carbon on removal of ionic liquids. Moreover, the adsorption dynamics, and the effect of pH and ionic strength on the adsorption process were investigated.The results showed that the adsorption process was obviously affected by the surface chemistry of the activated carbon as well as the hydrophilic/ hydrophobic nature of ionic liquids. The adsorption capacity of hydrophilic ionic liquid [BMIM]Cl on modified activated carbon increased by 50% due to the increased oxygenated surface groups of AC, promoting the hydrogen bonding interactions between IL and AC, however, the adsorption quantity of hydropholic ionic liquid [OMIM]Cl on modified activated carbon wasn’t increased. Compared with three kinds of oxidized activated carbon, the adsorption effect of ionic liquid on activated carbon oxidized by ammonium persulfate was better due to the increased number of carboxyl and acid groups, even though the adsorbent had a low surface area and pore volume. The content of oxygenated groups and surface chemical property of activated carbon are also the key influence factors besides the pore structure parameters during the adsorption process. The results showed that the adsorption isotherms of ionic liquid on oxidized activated carbon could be well described with the Freundlich model and the adsorption kinetics could be well described using the pseudo-second-order kinetics, the pH and ionic strength had a great influence on the adsorption process.After activated carbon was oxidized by acid, the adsorption capacity can be improved, but only to hydrophilic nature of ionic liquids and the method is complicated to operate. Therefore, further studies are hoped to search new and more efficient adsorbent for the removal of ionic liquids. We selected (3 zeolite as an exploration of adsorbent in this paper, compared to the existing other adsorbent to remove the ionic liquid, the material has a low price, easy preparation, with good hydrothermal stability and moderate acidity and hydrophobic. In the research, used two β zeolites with varied Si/Al ratios (mole ratio of SiO2 to Al2O3) of 31.66 and 190.73 to adsorb three imidazolium-based ionic liquids, including 1,3-Dimethyllmidazolium Chloride ([DMIM]Cl), 1-butyl-3-methyl-imidazolium chloride ([BMIM]Cl) and 1-octyl-3-methylimidazolium chloride ([OMIM]C1), and discussed the adsorption dynamic and adsorption mechanism of diffusion process of ionic liquid onto β zeolites to study the effect of Si/Al ratios on the adsorption process.The results showed that the adsorption isotherms of ionic liquid on β zeolites were well described with the Freundlich model, and the adsorption capacity of [DMIM]Cl, [BMIM]Cl and [OMIM]C1 on β1 zeolite were 0.62,0.67 and 0.73 mmol·g-1, respectively, while the adsorption capacities on β2 zeolite were 0.23,0.38 and 0.55 mmol·g-1, respectively. The β1 zeolite was proved to have higher adsorption capacity than β2 zeolite, and the difference in the adsorption capacities of β1 and β2 zeolites decreases with the number of the carbon atoms of the substituted alkyl chains. The adsorption of ionic liquid over β zeolites could be well described using the pseudo-second-order kinetics, and β1 zeolite has a higher adsorption capacity and shorter adsorption equilibrium time than β2 zeolite. The adsorption rate constants of [DMIM]Cl and [OMIM]C1 onto (3, zeolite were 0.025 g·mg-1·min-1 and 0.011 g·mg-1·min-1, respectively, and were 0.017 g·mg-1·min-1 and 0.0033 g·mg-1’min-1 onto β2 zeolite, respectively. The adsorption capacities of [BMIM]Cl and [OMIM]Cl on β zeolite are much higher than those reported on activated carbon, highlighting the potential of zeolite as promising adsorbents for the removal of ionic liquids in water. |
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