Zhang Yi, Bakshi Bhavik R, Demessie E Sahle
Department of Chemical & Biomolecular Engineering, The Ohio State University, Columbus, Ohio 43210, USA.
Environ Sci Technol. 2008 Mar 1;42(5):1724-30. doi: 10.1021/es0713983.
Ionic liquids (ILs) have been claimed as "greener" replacements to molecular solvents. However, the environmental impacts of the life cycle phases and comparison with alternative methods have not been studied. Such a life cycle assessment (LCA) is essential before any legitimate claims of "greenness" can be made and is the subject of this paper. The model IL selected is 1-butyl-3-methyl-imidazolium tetrafluoroborate ([Bmim][BF4]) and its use as a solvent for the manufacture of cyclohexane and in a Diels-Alder reaction was assessed. These uses are compared with more conventional synthesis methods. The results indicate that processes that use IL are highly likely to have a larger life cycle environmental impact than more conventional methods. Sensitivity analysis shows that the result is robust to errors and variation in the data. For cyclohexane synthesis, the industrial gas phase process is the greenest, but the three solvents compared for the Diels-Alder reaction showed comparable life cycle impact. Although ILs are not the most attractive alternatives, the result may change if their separation efficiency, stability and recyclability are improved. Because there are many kinds of ILs, with many applications, two examples are not enough to reach any general conclusions about the greenness of all ILs. However, the life cycle data and approach of this study can be used for evaluating the greenness of more kinds of solvents, processes, and emerging technologies.
离子液体（ILs）已被宣称是分子溶剂的“更绿色”替代品。然而，其生命周期各阶段的环境影响以及与替代方法的比较尚未得到研究。在能够做出任何关于“绿色”的合理宣称之前，这样的生命周期评估（LCA）是必不可少的，而这正是本文的主题。所选用的模型离子液体是1-丁基-3-甲基咪唑四氟硼酸盐（[Bmim][BF4]），并评估了其作为环己烷制造溶剂以及在狄尔斯-阿尔德反应中的应用。这些应用与更传统的合成方法进行了比较。结果表明，使用离子液体的工艺在生命周期内对环境的影响很可能比更传统的方法更大。敏感性分析表明，该结果对数据中的误差和变化具有稳健性。对于环己烷合成，工业气相法是最绿色的，但用于狄尔斯-阿尔德反应所比较的三种溶剂显示出相当的生命周期影响。尽管离子液体并非最具吸引力的替代品，但如果其分离效率、稳定性和可回收性得到提高，结果可能会改变。由于离子液体种类繁多且应用广泛，仅两个例子不足以对所有离子液体的绿色程度得出任何一般性结论。然而，本研究的生命周期数据和方法可用于评估更多种类的溶剂、工艺和新兴技术的绿色程度。
