11 Ionic Liquids Recycling for Reuse

ly or in an absolute sense. Despite the excitement of ILs, chemists are much too cautious about the propaganda of ILs’ greenness. In the first major US meeting on ionic liquids, held in 2001 at the American Chemical Society meeting in San Diego, Robin Rogers (the Director of Center for Green Manufacturing at the University of Alabama in Tuscaloosa) said: “Before we can say that ionic liquids are green, we have to look at their entire life cycle. People are calling ionic liquids green because they are not volatile, but we have to look at how they are made all the way through to recycling and disposal” [Sen, 2006]. Rogers added: “Researchers also need to find better ways to recycle ionic liquids. ” Many processes for cleaning up ionic liquids involve washing with water or VOCs. “This needs more work. We don’t want to create a secondary waste. ” Although ILs are invariably described as highly stable green solvents, thorough investigations to quantify their environmental impact have lagged behind the pace of other research in the area [Scammells et al., 2005]. These issues are extremely important as well as the approaches for the recovery of the ILs (after their use) for further reuse (i.e., recycling). A very important challenge is to use the unique solvent properties of the ILs to develop efficient method for product separation and IL recycling [Galán Sánchez, 2008; Marsh et al., 2004; Gordon, 2001; Welton, 2004; Meindersma et al., 2005; Heintz, 2005; Olivier-Bourbigou & Magna, 2002; Wasserscheid & Keim, 2000; Wasserscheid & Welton, 2003; Wishart & Castner, 2007; Seddon et al., 2002; Holbrey & Seddon, 1999; Holbrey, 2004; Olivier, 1999]. Despite their extremely low vapor pressure that prevents IL emission to the atmosphere, they are, at least, partially miscible with water and will inevitably end up in the aqueous environment (as what happens in the application of ILs for the electro-deposition of metals). During industrial application, ILs will get mixed with other products that necessitate efficient separation and recycling of ILs for economical and ecological needs [Haerens et al., 2010]. Many researchers have pointed out the major concern in the use of ILs is their relative high cost, which makes their recycling an important issue for further study [Laali & Gettwert, 2001; Gonzalez et al., 2006; Verma et al., 2008]. Currently, ionic liquids are quite expensive in comparison with conventional molecular solvents, and large amounts of ILs are needed in the various applications, thus efficient recycling of ILs is important for their economic use, especially in large-scale applications [Wagner & Hilgers, 2008]. However, the cost of ILs is expected to decrease, due to their higher production levels, which is expected to render ILs economically competitive with organic solvents [Khodadoust et al., 2006]. To overcome the cost problem, some low cost and simple synthesis of the ILs are essential for their recycling and reuse. Attri et al. (2010), for example, recovered ILs from binary mixtures of ILs/N,N-dimethyl formamide (DMF) by the removal of the DMF component under vacuum. No appreciable change in the physical properties of the recovered ILs was observed and the recovered ILs were reused at least four times without loss of their purity. Ionic liquids are now available from a number of commercial manufacturers and from many suppliers. However, IL preparation, work-up to separate/extract products and their recycling usually involve other solvents (e.g., VOCs) to extract unwanted residues, which are toxic persistent (to some extent). However, this diminishes the “green” aspect of their usage due to the cross-contamination arising from the use of organic solvents. Some ILs are certainly toxic and have been shown to have a detrimental effect on aquatic life that will tend to persist in local environment, on land/sea, etc. Thus there are worries about ILs end of life disposal, and materials incompatibility [Rayner, N.D. ; Weatherley, N.D. ]. One should