An Assessment on the Interaction of a Hydrophilic Ionic Liquid with Different Sorbents K. Vijayaraghavan, † Thi Phuong Thuy Pham, ‡ Chul-Woong Cho, ‡ Sung Wook Won, † Sun Beom Choi, † Mao Juan, ‡ Sok Kim, † Young-Ran Kim, ‡ Bong-Woo Chung, †,‡ and Yeoung-Sang Yun* ,†,‡ DiVision of EnVironmental and Chemical Engineering, Research Institute of Industrial Technology, Chonbuk National UniVersity, Chonbuk 561-756, South Korea, and Department of Bioprocess Engineering, Chonbuk National UniVersity, Chonbuk 561-756, South Korea Ionic liquids have received an upsurge in interest as green solvents, primarily as replacements for conventional media in chemical processes. This growing interest may soon lead to their presence in the environment. To evaluate the environmental fate of ionic liquids, their sorption onto different media is an essential parameter. This study presents an experimental verification of the sorption of 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) onto different sorption media. The examined sorption media included two activated carbons (SPS-200 and SPC-100), an ion-exchange resin (IER), a fermentation waste (Corynebacterium glutamicum), and a dried activated sludge. Through HPLC and MS/MS analysis, [BMIM][Cl] was found to be stable only in the pH range 3 to 11. The experimental results reveal that removal of [BMIM][Cl] was only possible using IER and the two forms of activated carbon. The equilibrium solution pH was found to have no significant effect on the sorption ability of IER, whereas, both forms of activated carbon exhibited high sorption under strong alkaline conditions. No significant sorption of [BMIM] was observed with both C. glutamicum and the activated sludge. According to the Langmuir model, the IER can sorb as much as 179.4 mg [BMIM]/g, whereas those of SPS-200 and SPC-100 were 20.6 and 19.6 mg [BMIM]/g, respectively. The sorption kinetics was found to be rapid, with only 15 and 60 min required to attain equilibrium for IER and the two forms of activated carbon, respectively. Only IER exhibited significant sorption ability toward chloride ions which are an anionic part of the IL. 1. Introduction Room temperature ionic liquids have received much attention because of their advantageous chemical and physical properties, such as negligible vapor pressure, high polarity, and good thermal stability. 1,2 These significant properties enable them to act as replacements for the conventional organic solvents employed in various operations. However, recent research reports contradicted the “green solvents” aspect of ionic liquid (IL). 3,4 It has recently been demonstrated that many commonly used ILs have a certain level of toxicity. 4,5 In comparison to some commonly used industrial solvents such as phenol, benzene, and toluene, the substituted ILs are found to be more toxic. 6,7 The toxicity of ILs seems to correlate with the alkyl chain length, with longer chain length giving greater toxicity. 4 Owing to their high stability, ILs also possess low biodegrada- bility. 2,8 Hence, their accumulation in the environment becomes feasible when applied to operational use. A few reports concerning the sorption of ILs to different biological and mineral surfaces have recently been published. 9-11 Sorption has an important effect on the transport, reactivity, and bioavailability of organic compounds within the environ- ment. Gorman-Lewis and Fein 9 suggested the geological retardation of dialkylimidazolium class ILs, due to their adsorp- tion reactions involving mineral and bacterial surfaces, will be minimal when they are dissolved in groundwater systems. Stepnowski et al. 10 recently confirmed that the sorption of three cations, 1-butyl-3-methylimidazolium, 1-hexyl-3- methylimi- dazolium, and 1-butyl-4-methylpyridinium, onto four different soil types was influenced by both the cation exchange capacity and organic matter content. More data on the sorption behavior of the ILs toward different media will be required to better understand their fate and mobility within the environment and to look for appropriate ways to treat ILs-bearing wastewaters. In this study, four sorption media were examined for their retention of 1-butyl-3-methylimidazolium chloride, including two commercial forms of activated carbon, ion-exchange resin, activated sludge, and fermentation waste. The selection of these sorption media was based on their existence in most wastewater schemes. This will enable an understanding of the fate of the ILs on completion of the wastewater treatment process, as well as the interaction of the ILs with these well-known sorbents. The stability as well as sorption of [BMIM][Cl] under different pH conditions was also examined. 2. Experimental Section 2.1. Sorbents and Reagents. The two forms of activated carbon, SPS-200 (sawdust-based) and SPC-100 (coal-based), were obtained in dried powder form from Samchully Activated Carbon Co., Ltd. (Yeongi-gun, Korea). The ion-exchange resin (Amberlite IRN-150) was purchased from Merck KGaA (Dar- rnstadt, Germany). Activated sludge was collected from a municipal wastewater treatment plant (Jeonju, Korea) and extensively washed with deionized water. It was then dried, ground in a mortar, and sieved to obtain particles within the range of 0.25-0.5 mm. The fermentation waste (C. glutamicum biomass) was obtained in dried powder form from a nucleic * To whom correspondence should be addressed. Tel: +82-63- 2702308. Fax: +82-63-2702306. E-mail: ysyun@chonbuk.ac.kr. † Research Institute of Industrial Technology, Chonbuk National University. ‡ Department of Bioprocess Engineering, Chonbuk National University. Ind. Eng. Chem. Res. 2009, 48, 7283–7288 7283 10.1021/ie801825q CCC: $40.75  2009 American Chemical Society Published on Web 07/13/2009