Amphiphilic and Phase‐Separable Ionic Liquids for Biomass Processing

Abstract

One main limiting factor for the technoeconomics of future bioprocesses that use ionic liquids (ILs) is the recovery of the expensive and potentially toxic IL. We have demonstrated a new series of phase-separable ionic liquids, based on the hydrophobic tetraalkylphosphonium cation ([PRRRR](+)), that can dissolve lignin in the neat state but also hemicellulose and high-purity cellulose in the form of their electrolyte solutions with dipolar aprotic solvents. For example, the IL trioctylmethylphosphonium acetate ([P8881][OAc]) was demonstrated to dissolve up to 19 wt % of microcrystalline cellulose (MCC) at 60 °C with the addition of 40 wt % of DMSO. It was found that the MCC saturation point is dependent on the molar ratio of DMSO and IL in solution. At the optimum saturation, a ∼1:1 molar ratio of [P8881][OAc] to anhydroglucose units is observed, which demonstrates highly efficient solvation. This is attributed to the positive contribution that these more amphiphilic cation-anion pairs provide, in the context of the Lindman hypothesis. This effective dissolution is further illustrated by solution-state HSQC NMR spectroscopy on MCC. Finally, it is also demonstrated that these electrolytes are phase separable by the addition of aqueous solutions. The addition of 10 % NaOAc solution allows a near quantitative recovery of high-purity [P8881][OAc]. However, increased volumes of aqueous solution reduced the recovery. The regenerated material was found to partially convert into the cellulose II crystalline polymorph.

Effects of phosphonium-based ionic liquids on phospholipid membranes studied by small-angle X-ray scattering

“…Tributyl(tetradecyl)phosphonium acetate ([P14444][OAc]; M=458.7 g·mol -1 ) was synthesized by anion metathesis as described in previous articles (Holding et al, 2014;Mikkola et al, 2015). 140…”

“…Trioctylmethylphosphonium acetate ([P8881][OAc]; M=445.9 g·mol -1 ) was synthesized as described previously in (Holding et al, 2014;Labafzadeh et al, 2015 ), was synthesized as described in our previous article (Ruokonen et al, 2016).…”

Homogenous esterification of cellulose pulp in [DBNH][OAc]

“…The chemical properties of ILs vary according to the composition. For instance, the ability to dissolve cellulose is often dependent on the basicity of the IL (Fukaya et al 2006(Fukaya et al , 2008King et al 2012;Parviainen et al 2013), but there are exceptions, e.g., tetraalkylphosphonium salts Holding et al 2014), which are basic but require a dipolar aprotic co-solvent to dissolve cellulose. In previous literature, the use of imidazolium based ILs, with alkyl substituents (ethyl, methyl, and allyl) and chloride, bromide or acetate anions, typifies most publications on cellulose dissolving ILs (Heinze et al 2008;Swatloski et al 2002).…”

Efficiency of hydrophobic phosphonium ionic liquids and DMSO as recyclable cellulose dissolution and regeneration media

“…[30][31][32][33][34] Typical combinations include imidazolium 30,31,[34][35][36][37][38] or onium cation [39][40][41][42] ionic liquids paired with basic anions, mixed with DMSO (dimethylsulfoxide), DMI (1,3-dimethyl-2-imidazolidinone), DMA (N,N-dimethylacetamide), DMF (N,N-dimethylformamide), TMU (1,1,3,3-tetramethylurea), 34 as well as g-butyrolactone and g-valerolactone. 43 Recently, researchers have demonstrated the possibility of spinning regenerated cellulose bres from ionic liquid solutions, such as in the 'IONCELL-F' process, 24 based on Lyocelltype process, whereby strong bres (having a higher tenacity than both the N-methylmorpholine-N-oxide (NMMO) based Lyocell and the sulphite based viscose bres) can be produced by dry-jet wet (air-gap) spinning from an ionic liquid dope into a water bath.…”