State-of-the-art and limitations in the life cycle assessment of ionic liquids

Even though the development and use of ionic liquids (ILs) has rapidly grown in recent years, in the literature, information addressing the environmental performance of these substances in a life cycle context is comparatively scarce. This review critiques the state-of-the-art environmental life cycle assessment (LCA) studies on ILs in the literature, identifies the existing shortcomings, which could be delaying complete employment of the LCA framework to the field of ILs, and also identifies strategies for overcoming these shortcomings. This review indicates that there are several limitations associated with the implementation of the LCA in all steps and discusses them. Since data about manufacturing at industrial scale are generally inaccessible, a set of methods and assumptions have been used in previous studies to determine the life cycle inventories (LCIs), such as simplified LCA, “tree life-cycle approach”, use of energy monitor devices, thermodynamic methods, chemical simulation process and other secondary data. However, the analysis of the data quality has not always been performed. Also, currently, there is a shortage of the characterization factors of ILs for human toxicity and ecotoxicity impact categories, which prevent its inclusion within the life cycle impact assessment (LCIA) step. Therefore, sufficient and complete life cycle inventory data for ionic liquids and precursor chemicals are essential for inventory analysis; and the LCIA needs to be clearly defined about the level of detail on the IL emissions. Current LCA studies on ILs have not covered all these aspects. To improve the present situation, it is proposed herein that for future LCA of processes involving ILs each of the LCA steps must be completed as far as scientific advances allow