PEG-functionalized ionic liquids for cellulose dissolution and saccharification†
Cellulose-dissolving ionic liquids (ILs) have become powerful neoteric solvents in the pretreatment of cellulosic biomass for ethanol fuel production. There are, however, a number of challenges to using current ionic solvents at large scales (imidazolium-based salts, in particular), including their relatively high costs and viscosities and their sluggish biodegradability. Aiming to overcome these hurdles, we have prepared a new series of poly(ethylene glycol) (PEG)-functionalized ILs comprising inexpensive alkylammonium or piperidinium cations paired with acetate anions. Some of these new ILs are capable of dissolving 8–12 wt% cellulose, while displaying low viscosities and acceptable thermal stabilities at the required process temperature. Our XRD and SEM data further confirm that regenerative pretreatment of cellulose by these PEGylated ILs can effectively transform the cellulose I structure to cellulose II, reducing the crystallinity of cellulose and increasing the structural homogeneity. Most excitingly, cellulose regenerated from these ILs can be rapidly hydrolyzed to glucose, in ∼90% glucose yield after 2 h, using a commercial cellulase supplemented with β-glucosidase.