(418c) Precipitation of Cellulosic Biomass from Ionic Liquid/Cosolvent Mixtures By a Non-Reactive and Energy Efficient Gas Antisolvent Method

Select ionic liquids (ILs) demonstrate inherently large cellulose dissolution capacities making them highly touted solvents for biomass processing.   Through an ionic liquid based dissolution and precipitation process cellulose crystallinity is largely reduced consequently enhancing subsequent chemical and biochemical reaction processes.  Conventional antisolvents for biomass precipitation from ILs include polar protic liquids (i.e. H₂O, EtOH, etc.) which are highly effective at disrupting IL-cellulose interactions.  Recently we have found that these liquid antisolvents are so effective that as little as 1 mass% residual water on an IL can reduce its cellulose capacity by as much as 55%.  Therefore, ILs must be highly purified from liquid antisolvents prior to recycle.  Preliminary analyses indicate that quantitative separation of an IL from a liquid antisolvent is highly energy intensive and could potentially impede large scale viability.   Therefore, as an alternative to conventional liquid antisolvent processes we have developed a novel gas antisolvent method which precipitates cellulosic biomass from IL/cosolvent mixtures by compressed carbon dioxide at low to moderate pressures (i.e. 23 to 66 bar).  The gas antisolvent separation process is especially unique as it is non-reactive and completely reversible.  By simple depressurization of CO₂ to just a few bar pressure below the separation point,ionic liquid solvation power for cellulose is completely regenerated.  This presentation will highlight the solid-liquid phase equilibrium effects of both conventional and novel separation processes.  Additionally, the advantages of polar aprotic cosolvents will be highlighted as they apply to cellulose dissolution in IL/solvent mixtures and the gas antisolvent process.  Spectroscopic techniques will identify key trends within the separation data.  Finally an energy analysis will be presented to demonstrate the advantages of this novel CO_{2 ­}based precipitation process relative to liquid antisolvent separations.