The undesirable acetylation of cellulose by the acetate ion of 1-ethyl-3-methylimidazolium acetate

Abstract

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) is considered to be an inert solvent of cellulose and lignocellulosic biomass. Acetylation (1.7% mol, or DS 0.017) of cellulose after dissolution in technical grade [C2mim]OAc (150°C for 20 min), is demonstrated by compositional analysis, FTIR analysis and 13 C NMR spectroscopy (in [C2mim]OAc with 13 C enriched acetate). This acetylation, in the absence of added acylating agents, has not been reported before and may limit [C2mim]OAc utility in industrial scale biomass processing, even at this low extent. For example, cellulose acetylation may contribute to IL loss in processes where the IL is recovered and reused and inhibit enzyme saccharification of cellulose in lignocellulosic biofuel production processes based on saccharification and fermentation.

Ionic liquid-mediated technology to produce cellulose nanocrystals directly from wood

“…Surprisingly, a sharp vibrational peak at 1741 cm −1 characteristic of C O bonds appears again in WR-2 (90% cellulose), suggesting acetylation. Cellulose (and lignin) acetylation as a side reaction using [EMIM][OAc] has been previously reported (Ç etinkol et al, 2010;Hauru et al, 2013;Karatzos, Edye, & Wellard, 2012;King, Xie, Fiskari, & Kilpelaeinen, 2014;Köhler et al, 2007). This structural change will be revisited in the next section.…”

“…Likewise, treating pure cellulose with [EMIM][OAc] results in acetylation (Ç etinkol et al, 2010;Karatzos et al, 2012;Köhler et al, 2007). Cellulose acetylation by [EMIM][OAc] is temperature dependent: at low temperature (80 • C) it is only revealed when a catalyst is used (Köhler et al, 2007); at higher temperature (e.g., 185 • C) it occurs also in the absence of a catalyst (Karatzos et al, 2012;Li et al, 2011). In whole wood, transacetylation from xylan to lignin has also been proposed (King et al, 2014).…”

Swelling, viscoelastic, and anatomical studies on ionic liquid-swollen Norway spruce as a screening tool toward ionosolv pulping

“…[EMIM]OAc is known to deacetylate hemicelluloses and acetylate lignin ( Kilpel ä inen et al 2007 ;Ç etinkol et al 2010 ;Li et al 2011 ;Karatzos et al 2012 ), and such reactions certainly contribute to swelling in [EMIM] OAc followed by dissolution, disintegration, and derivatization of wood. Such effects are not as evident in the case of [BMIM]Ace.…”

Loblolly pine pretreatment by ionic liquid-glycerol mixtures

“…Precipitates formed upon ethanol addition to recovered solv e n t m i x t u r e s o f 2 [OAc] has been reported to acetylate cellulose and may acetylate other biomass components as well, resulting in part of the IL precipitating with biomass fractions [47]. Typically, with IL pretreatment of biomass, addition of an anti-solvent such as ethanol creates a solvation shell around the IL's ions, so that they do not precipitate out with the biomass components.…”