title: 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.
authors.affiliation: Department of Chemistry, University of Helsinki, A. I. Virtasen Aukio 1, 00014, PO Box 55, Helsinki (Finland).
authors.forename: Ashley J
authors.initials: AJ
authors.lastname: Holding
authors.forename: Mikko
authors.initials: M
authors.lastname: Heikkilä
authors.forename: Ilkka
authors.initials: I
authors.lastname: Kilpeläinen
authors.forename: Alistair W T
authors.initials: AW
authors.lastname: King
mesh_terms: D056804:Biofuels; D018533:Biomass; D001704:Biopolymers / Q000737:chemistry*; D002482:Cellulose / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry*; D015394:Molecular Structure; D009943:Organophosphorus Compounds / Q000737:chemistry; D044367:Phase Transition; D012995:Solubility; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D056804:Biofuels; D001704:Biopolymers; D004573:Electrolytes; D052578:Ionic Liquids; D009943:Organophosphorus Compounds; D013501:Surface-Active Agents; D002482:Cellulose; C109691:microcrystalline cellulose
keywords: ab initio calculations; biomass; hydrophobic effect; ionic liquids; solvent effects