Protic, Aprotic, and Choline-Derived Ionic Liquids: Toward Enhancing the Accessibility of Hardwood and Softwood

Abstract

A side-by-side comparison of softwood (pine) vs hardwood (eucalyptus) pretreatment using 3 protic, 3 aprotic, and 3 choline-derived ionic liquids (ILs) is proposed. While the protic ionic liquid 2-hydroxyethylammonium formate leads to alkali lignin dissolution at 30 °C after 1 h, the lack of interactions with the whole-cell wall limits the biomass disruption. On the contrary, the protic ionic liquid 1-methylimidazolium chloride produces a catalytic effect that extracts almost all of the hemicelluloses, and partially the lignin. Remarkable digestibilities are obtained with choline acetate ([Ch][OAc]) in eucalyptus (69%), while in pine, protic, and choline-derived ILs tested do not appear to be real "greener" alternatives to conventional ILs such as 1-ethyl-3methylimidazolium acetate (the highest digestibility, 84%). Solid morphology revealed a smoother surface in pine pretreated with [Mim][Cl], and confocal fluorescence microscopy was used to distinguish surface holocellulose and lignin, highlighting differences in the accessibility of hardwood vs softwood due to the presence of surface lignin. Two-dimensional nuclear magnetic resonance spectroscopy of saccharified samples pretreated with [Ch][OAc] showed the presence of groups derived from acetate. Finally, thermogravimetric analysis and spectroscopy techniques reveal the difficulties in recovering the ionic liquid and conclude a work that describes the strengths and weaknesses of the ILs and biomasses studied.

Thermophysical Properties of Protic Ionic Liquids Monoethanolamine, Diethanolamine, and Triethanolamine Lactate in Water

“…Despite some studies done on the use of ammonium-based ILs including hydrogen bond-promoted lignin solubilization, absorption behavior of acid gases, as highly biodegradable solvents, etc., − few reports have been made on the thermophysical properties of PILs, especially with anion lactate in the dilute region.…”

Deconstruction of Woody Biomass via Protic and Aprotic Ionic Liquid Pretreatment for Ethanol Production

“…14 To overcome cost and biocompatibility issues, certain choline-based aprotic ILs were investigated and have been demonstrated for compatibility with both enzymes and microbes, allowing the transition towards a one-pot reaction system where all the steps of the process are carried out in a single vessel without any separations. 17 [Ch][Lys] has been effectively used and achieves high cellulose to glucose conversion yields in grasses and more recently in hardwoods and softwoods. 18 To date, we have demonstrated that [Ch][Lys] is effective at promoting high glucose yields in switchgrass (96.5%) and corn stover (>80%).…”

Evaluating the potential of a novel hardwood biomass using a superbase ionic liquid

“…24 Despite many reports on agricultural wastes and grasses, there are few reports on hardwood waste pretreatment using ionic liquids. 25,26 These wood wastes can be an economic source of biorenery products. The abundance of Acacia hardwood and its fast growing nature make wastes of this hardwood a viable candidate for biomass processing in countries like Pakistan.…”