Uncovering the True Cost of Ionic Liquids using Monetization

Due to their attractive properties, ionic liquids have found their way into many applications where they show high potential to replace existing chemicals. However, rising concerns over their ecological impacts, e.g., toxicity and biodegradability, and high cost have limited their use. Techno-economic and life cycle assessment studies were carried out to compare ionic liquids with existing solvents, yet the outcome of these analyses is often hard to interpret, as multiple metrics need to be considered simultaneously between which trade-offs exist. Here, for the first time the concept of monetization is coupled with process simulation and life cycle assessment to estimate the true cost of four lignocellulosic biomass pretreament solvents: triethylammonium hydrogen sulfate [TEA][HSO4], 1-methylimidazolium hydrogen sulfate [HMIM][HSO4], acetone from fossil sources and glycerol from renewable sources. The results show that monetized cost can be higher than or as high as the production cost. The real cost of production accounting for externalities can be more than 100% of direct costs estimated using conventional economic assessment methods. Our results show that [TEA][HSO4] has the lowest cost, while glycerol has the highest cost. We expect this to be a starting point for future studies targeting the design of more sustainable ionic liquids.