Life Cycle Thinking-Based GREENNESS Framework for Advancing Green Chemistry: Case Study with Typical Ionic Liquids for Cellulose Dissolution and Regeneration

Due to its abundance and renewability, cellulose has emerged as a promising candidate to tackle the challenges posed by fossil fuel depletion and global warming impacts in the transition toward green chemistry. In the value-added utilization of cellulose, ionic liquids (ILs) have been increasingly used as green solvents for efficient cellulose dissolution due to their low volatility. However, greenness is a multicriteria concept that has been extensively hyped without a comprehensive assessment in chemical processes or final products. Herein, we propose a comprehensive assessment framework, GREENNESS, to quantify the greenness of three typical ILs employed in cellulose dissolution and regeneration, i.e., 1-allyl-3-methylimidazolium chloride (AmimCl), 1-butyl-3-methylimidazolium chloride (BmimCl), and 1-ethyl-3-methylimidazolium acetate (EmimOAc). To prevent burden shifting across life cycle stages or impact categories, this framework adopts a full life cycle perspective, encompassing IL production through to emission, with a focus on (eco)toxicity. Toxicity tests were conducted on three trophic levels to characterize the freshwater ecotoxicity associated with IL fate, transport, and exposure via the USEtox model. Human noncarcinogenic toxicity was also evaluated. The results indicated that AmimCl is superior to BmimCl and EmimOAc across all environmental categories, which differed from the outcomes observed via the CHEM21 solvent selection guide. Overall, the comprehensive framework GREENNESS can also guide the selection of other solvents to promote environmentally friendly chemistry and chemical engineering, thereby decreasing their impacts on the environment.