Role of Solvent Parameters in the Regeneration of Cellulose from Ionic Liquid Solutions

Abstract

The ionic liquids 1-ethyl-3-methylimidazolium acetate [emim]OAc, N,N,N,N-tetramethylguanidium propionate [TMGH]EtCO(2), and N,N,N,N-tetramethylguanidium acetate [TMGH]OAc, and the traditional cellulose solvent N-methylmorpholine N-oxide NMMO were characterized for their Kamlet-Taft (KT) values at several water contents and temperatures. For the ionic liquids and NMMO, thresholds of regeneration of cellulose solutions by water were determined using nephelometry and rheometry. Regeneration from wet IL was found to be asymmetric compared to dissolution into wet IL. KT parameters were found to remain almost constant at temperatures, between 20-100 °C, even at different water contents. Among the KT parameters, the β value was found to change most drastically, with an almost linear decrease upon addition of water. The ability of the mixtures to dissolve cellulose was best explained by the difference β-α (net basicity), rather than β alone. Regeneration of cellulose starts at thresholds values of approximately β < 0.8 (β-α < 0.35) and displayed four phases.

Efficient biomass pretreatment using ionic liquids derived from lignin and hemicellulose

“…A slight shielding of the methylene carbons in the α position were also observed when converting the amine δ = 45.9 ppm (2C) and δ = 54.8 ppm (1C) to the IL δ = 45.3 ppm (2C) and δ = 54.6 ppm (1C PO 4 ] were also selected based on their subtle differences in polarity and substituent effects. The polarity of an IL has been correlated with its ability to solubilize both lignin (42,43) and cellulose (44)(45)(46) PO 4 ] were used to dissect the role of these substituents on the relative acidity of the cation and relate these effects to biomass pretreatment.…”

“…Kamlet-Taft solvent parameters have been used to measure the ability of a solvent to donate a hydrogen bond (α), and accept a hydrogen bond (β) (51). It has been shown that basicity (β) correlates well with an IL's ability to dissolve lignocellulose (52), and that net basicity correlates with an IL's ability to dissolve cellulose (46,53). A recent experimental study on a range of cations in combination with the same anion demonstrated that cation acidity is also important for cellulose dissolution (54) PO 4 ], one would expect the differential substitution of the electron-donating groups to affect the N atom's affinity for the H 3 PO 4 proton.…”

Effect of methylimidazole on cellulose/ionic liquid solutions and regenerated material therefrom

“…The possibility to pair anions with cations yields an almost endless library of ILs, and they are used in numerous fields, such as separation technology, electrochemistry, catalysis, and as solvents [3,4]. In the last decade, ILs as solvents for biomass in general and cellulose in particular have been widely investigated [5][6][7] since 2002 when Swatloski published the pioneering work on dissolution of cellulose in 1-butyl-3-methylimidazolium chloride (BMIMCl) [8]. This relatively new solvent class has shown great versatility in the field of cellulose technology, including dissolution for regeneration purposes [9,10], homogeneous derivatization [11,12], and biomass processing including wood component separation [13][14][15].…”

Probing cellulose amphiphilicity

“…Recent molecular dynamics simulations, carried out on cellulose oligomers and 1-ethyl-3-methylimidazolium acetate (C2mimOAc), indeed suggest that the cations are in close contact with the cellulose through hydrophobic interactions (Liu et al 2010). Closely related, Hauru et al found that cellulose regeneration from IL solutions goes via the hydrophobic association of the less polar regions of cellulose (Hauru et al 2012). An interesting work of Mostofian et al suggests a synergistic approach for cellulose dissolution in IL (Mostofian et al 2014).…”