Sustainability Assessment of Alternative Synthesis Routes to Aprotic Ionic Liquids: The Case of 1-Butyl-3-methylimidazolium Tetrafluoroborate for Fuel Desulfurization

Abstract

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][BF 4 ] 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][BF 4 ] 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][BF 4 ] 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.

History repeats itself again: Will the mistakes of the past for ILs be repeated for DESs? From being considered ionic liquids to becoming their alternative: the unbalanced turn of deep eutectic solvents

“…349 It is also worth highlighting the publication of an analysis focused on cost and impact of ILs considering both production and use. 350 On the basis of per-weight efficiency of the desulfurized-fuel process, the use-cost of [C 4 C 1 im]BF 4 obtained via traditional metathesis reaction became comparable to acetonitrile and lower than DMF, while the halide-free mixture of imidazolium ILs prepared through the statistical reaction of formaldehyde, amines and glyoxal became the cheapest option.…”

Global Sensitivity Analysis in Life-Cycle Assessment of Early-Stage Technology using Detailed Process Simulation: Application to Dialkylimidazolium Ionic Liquid Production

“…The proposed case study compares the environmental impacts associated with the production at scale of two dialkyl-imidazolium ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF 4 ] and 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF 6 ]. Process flowsheeting in Aspen-HYSYS (version 9) is used to scale-up experimental synthesis procedures for [BMIM][BF 4 ] and [BMIM][PF 6 ], 50 which comprise the foreground system. Process flowsheeting is also used to bridge inventory gaps for two of their precursors in ecoinvent as part of the background system, namely, 1-butyl-3-methylimidazolium chloride [BMIM][Cl] and 1-chlorobutane.…”

Halometallate ionic liquids: thermal properties, decomposition pathways, and life cycle considerations

“…For this reason, protic ionic liquids have been identified as more sustainable alternatives because they are produced by acid-base neutralisation, 63 which avoids problematic steps such as alkylation and ion metathesis. 64 Although halometallate ionic liquids still require an alkylation reaction, their synthesis involves direct mixing of two components, as opposed to salt metathesis in solution. Halides are particularly problematic when looking at environmental impacts of ionic liquids.…”

“…Halides are particularly problematic when looking at environmental impacts of ionic liquids. 64 However, with halometallate ionic liquids, halides are an integral part of the end product, and as the ratio of MCl 2 increases so does the halide content. Therefore, LCA analysis of halometallate ionic liquid can provide a valuable insight to production of the most industrially relevant ionic liquids.…”