Ionic Liquids in the Biorefinery: How Green and Sustainable Are They?
Potential uses of ionic liquids (ILs) and the related deep eutectic solvents (DESs) in second-generation biorefineries are reviewed, with a focus on the question of whether or not their use is green and sustainable. Early work with first-generation ILs, mainly derived from dialkylimidazolium cations and weakly coordinating anions, demonstrated proof of concept but was not really green and sustainable. In contrast, second-generation ILs, protic ILs and the related deep eutectic solvents, derived from renewable resources, do appear to meet the criteria of biocompatibility, biodegradability and economically viable price levels. Even so, efficient recovery and recyclability still needs to be demonstrated under practical operating conditions.