The ability to assess the environmental performance of early-stage technologies at production scale is critical for sustainable process development. This paper presents a systematic methodology for uncertainty quantification in life-cycle assessment (LCA) of such technologies using global sensitivity analysis (GSA) coupled with a detailed process simulator and LCA database. This methodology accounts for uncertainty in both the background and foreground life-cycle inventories, and is enabled by lumping multiple background flows, either downstream or upstream of the foreground processes, in order to reduce the number of factors in the sensitivity analysis. A case study comparing the life-cycle impacts of two dialkylimidazolium ionic liquids is conducted to illustrate the methodology. Failure to account for the foreground process uncertainty alongside the background uncertainty is shown to underestimate the predicted variance of the end-point environmental impacts by a factor of two. Variance-based GSA furthermore reveals that only few foreground and background uncertain parameters contribute significantly to the total variance in the end-point environmental impacts. As well as emphasizing the need to account for foreground uncertainties in LCA of early-stage technologies, these results illustrate how GSA can empower more reliable decision-making in LCA.

Advantages of ionic liquids (ILs) over volatile organic solvents in chemical processes include no or negligible evaporative losses and high tunability. However, the conventional production of aprotic ILs via metathesis can be unattractive (both economically and environmentally) because of its high complexity, while the performance of other synthesis routes remains unclear. Existing life-cycle assessments furthermore fail to combine the production and use phases of these solvents, leading to erroneous conclusion about their sustainability credentials. This paper compares a one-pot, halide-free production route to 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] against metathesis and two conventional fuel desulfurization solvents, namely, acetonitrile and dimethylformamide (DMF). Halide-free synthesis is predicted to reduce the cost and environmental impacts associated with the production of [BMIM][BF4] by 2-5-fold compared to metathesis. Upon including the use phase of the solvents in fuel desulfurization and accounting for the uncertainty in background data, halide-free [BMIM][BF4] consistently presents the lowest cost and environmental impacts, while DMF is the worst in class. As well as exemplifying the importance of synthesis routes of ILs on their sustainability, these results highlight the need to include the use phase of solvents for more comprehensive life-cycle assessments.

Halometallate ionic liquids provide new opportunities for industrial catalytic processes because of their unique blend of physical and chemical properties. Tunability underpins the success of ionic liquids because small structural changes can have drastic effects on either property. Catalysis can be optimised by adjusting structures to target properties such as Lewis basicity and acidity, but the structural changes have simultaneous impacts on physical properties. In this work, we provide a thorough, methodical, and reliable list of thermal parameters to help define temperature limits to prevent catalyst poisoning and limit the need to replace costly and environmentally demanding solvents. Mechanistic insights show that decomposition is particularly detrimental for halometallate ionic liquids, and life cycle analysis highlights that lower levels of organic cations are better for economic and environmental sustainability.

A balance between cost, impact, and physicochemical properties is crucial for halometallate ILs, especially considering their susceptibility to catalytic poisoning.

................................................................................................... 2 Acknowledgments ....................................................................................... 3 Glossary ................................................................................................... 4 List of Figures ............................................................................................. 9 List of Graphs ............................................................................................. 9 List of Tables ............................................................................................. 10 Introduction ............................................................................................... 11 Part I. Background ...................................................................................... 13 1. Ionic Liquid ......................................................................................... 13 1.1. General ........................................................................................ 13 1.2. Physicochemical Properties .............................................................. 14 1.3. Stability ......................................................................................... 15 1.4. Protic Ionic Liquids .......................................................................... 15 1.5. Toxicity ......................................................................................... 18 2. Biomass Conversion ............................................................................. 18 2.1. Lignocellulose ................................................................................ 19 2.1.1. Cellulose ................................................................................. 20 2.1.2. Hemicellulose .......................................................................... 21 2.1.3. Lignin .................................................................................... 21 2.2. Deconstruction of Lignocellulose ....................................................... 22 2.3. Bleaching ...................................................................................... 25 2.4. Conclusion .................................................................................... 26 2.5. Life-cycle Assessment ..................................................................... 27

This paper presents a methodology for combining foreground and background uncertainty in the life-cycle assessment (LCA) of processes and products at a low technology-readiness level. We compare the LCA of two ionic liquids, 1-butyl-3-methyl-imidazoliumtetrafluoroborate [bmim][BF4] and 1-butyl-3-methyl-imidazolium hexafluorophosphate [bmim][PF6]. The nominal scenario predicts that [bmim][BF4] generates lower end-point environmental impacts than [bmim][PF6]. However, the uncertainty ranges around these nominal predictions overlap significantly, with [bmim][BF4] causing higher impacts than those of [bmim][PF6] in up to 30% of the uncertainty scenarios. On top of this, accounting for uncertainty in the foreground data more than doubles the estimated impact ranges in several damage categories. This case study, therefore, demonstrates the need for combining foreground and background data uncertainty for more reliable life-cycle assessments.

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.

Ionic liquids have found their way into many applications where they show a high potential to replace traditional chemicals. But concerns over their ecological impacts (toxicity and biodegradability) and high cost have limited their use so far. The outcome of existing techno-economic and life-cycle assessments comparing ionic liquids with existing solvents has proven hard to interpret due to the many metrics used and trade-offs between them. For the first time, this paper couples the concept of monetization with detailed process simulation and life-cycle assessment to estimate the true cost of ionic liquids. A comparative case study on four solvents used in lignocellulosic biomass pretreatment is conducted: triethylammonium hydrogen sulfate [TEA][HSO4], 1-methylimidazolium hydrogen sulfate [HMIM][HSO4], acetone from fossil sources, and glycerol from renewable sources. The results show that the total monetized cost of production accounting for externalities can be more than double the direct costs estimated using conventional economic assessment methods. [TEA][HSO4] is found to have the lowest total cost, while glycerol presents the highest total cost. We expect this methodology to provide a starting point for future research and development in sustainable ionic liquids.