Recycled ionic liquid vs. deep eutectic solvent in cellulose nanocrystals production: Characterization, techno-economic analysis, and life cycle assessment

Three scenarios involving aqueous mixtures of neoteric solvents have been evaluated as solvents and catalysts for the cellulose hydrolysis reaction to obtain CNC in high yields (>70%). The scenarios considered were: scenario 1 (S1) involves a recyclable ionic liquid dilution of [Hmim][(HSO4)(H2SO4)]/H2O (64 wt% IL); scenario 2 (S2) another recyclable dilution of [Hmim][(HSO4)(H2SO4)]//H2O (80 wt% IL) and scenario 3 (S3) a non-recyclable ternary deep eutectic solvent (60 wt% DES: choline chloride: oxalic acid/30 wt% PA/10 wt% water). Experimental analysis, techno-economic, and life cycle analysis (LCA) indicate that S1 emerges as a suitable scenario among the three analyzed. S1 demonstrated the highest competitiveness, with a lower raw material cost per gram of CNC produced (US$0.81/g) and lower environmental contributions concerning climate change and fossil fuel depletion, accounting mainly for its recyclability. Therefore, the recyclable dilution of 64 wt% IL used in S1 appears to be the most viable option for sustainable and environmentally conscious CNC production. Besides, the physicochemical properties of the CNC were revealed: aspect ratio range 7–8, high dispersion stability related to zeta potential > −40 mV, good crystallinity range 50–80%, and thermal stability with Tonset> 300 °C. These results guided towards a scenario with crucial advantages: a diluted IL that retains its acidity after reuse cycles by a facile recovery process, maintaining high CNC production performance and providing low environmental impacts. [Display omitted] •CNC production was environmentally assessed using three scenarios on a pilot scale.•A techno-economic and environmental study used deep eutectic versus ionic solvents.•High performance and profitability were obtained with recycled ionic liquid.•The MSP of nanocrystal cellulose produced by recycled ionic liquid 64 wt% was $0.81/g.•The recycled ionic solvent dilution (64%) involved lower environmental contributions.