(610e) Low-Cost Ionic Liquids for the Delignification of Lignocellulosic Biomass

We have developed a highly effective method for delignification of lignocellulosic biomass using low cost (ca. $1/kg) ionic liquids. These ionic liquids differ from their more widely studied counterparts, whose approach is based on complete dissolution of biomass, by focussing on de-lignification only, with the carbohydrate portions left undisturbed [1]. We have termed this the Ionosolv process, after the similar organosolv pretreatment.

The Ionosolv approach uses ionic liquids with neutral or acidic anions that do not dissolve holocellulose but instead separate dissolved lignin from the cellulose solid. A study from our lab reported recovery of over 60% compared to the lignin content of untreated Miscanthus after pretreatment with [C₄C₁im][HSO₄] water mixtures [2]. Use of the more acidic ionic liquid [HC₄im][HSO₄] resulted in a precipitate yield of nearly 100%. This presentation will discuss pretreatment conditions, saccharification yields, pulp quality, lignin characterisation, ionic liquid interactions with the biopolymers, and manufacturing costs.

Almost quantitative removal of lignin appears to have been achieved, assayed by solid-state NMR. This is likely to be due to the neutral acidic nature of the ionic liquids employed by the Ionosolv process, which act as catalytic delignifiers.  It is important to this process that the cellulose fraction be as free of ionic liquid as possible to avoid unwanted enzyme deactivation, placing a great deal of importance on efficient cellulose washing. We have tried various wash solvents (water, ethanol, methanol, isopropanol, acetone) and conditions and found that Soxhlet extraction with ethanol is sufficient to quantitatively remove the IL from the cellulose pulp. Although the recovered ionic liquid does not need to be fully dried, as ca. 20% water will be required for the deconstruction step, this is likely to be highly energy intensive, requiring careful consideration of the physical interactions with biomass [3] and the various energies required throughout the process [4].

[1] A. Brandt, J. Grasvik, J. Hallett, T. Welton, Green. Chem. 15, 550-583 (2013).

[2] A. Brandt, M.J. Ray, T.Q. To, D.J. Leak, R.J. Murphy, T. Welton, Green Chem. 13, 2489 (2011).

[3] A. Brandt, A., J.P. Hallett, D.J. Leak, R.J. Murphy, T. Welton, Green Chem. 12, 672 (2010).

[4] A. Brandt, J.K. Erickson, J.P. Hallett, R.J. Murphy, A. Potthast, M.J. Ray, T. Rosenau, M. Schrems, T. Welton, Green Chem. 14, 1079 (2012).