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The conversion of lignocellulosic biomass from agricultural wastes, woods or energy crops into liquid biofuels is a critical route to meet the increasing worldwide demand [1]. Highly efficient pretreatment of lignocellulosic biomass for subsequent enzymatic hydrolysis and fermentation is critical because of its impact on cost and downstream processing. Over the past several years, we have studied the selective lignin extraction as a pretreatment method that uses room temperature ionic liquids (RTILs) [2].Such process enables efficient extraction of pristine lignin (that may be used as a valuable product), while the crystal structure of cellulose and the hydrogen bonding network of lignocellulosic biomass subcomponents is disrupted. We have further determined that the ability to disrupt the crystal structure of cellulose can be predicted by measuring the Kamlet-Taft β parameter of RTILs [3]. More recently, we have demonstrated that RTILs have the ability to carry out the pretreatment of lignocellulosic biomass at high solid loadings (up to 35%) acting more as an additive and not a solvent4. In addition, RTILs can be reused up to 10 cycles of pretreatment without being regenerated [4]. Such observations have an impact on the pretreatment feasibility.

 

biofuel

Figure 1. Interaction of ILs with cellulose and lignin. A: The semi- crystalline structure of cellulose is a result of the hydrogen-bonding network among the polysaccharide chains. B: Incubation with ILs disrupts cellulose crystalline structure because of the IL's ability to accept hydrogen bonds (blue spheres indicate the cation and green spheres indicate the anion). C: Following pretreatment amorphous cellulose can be depolymerized by cellulases. D: Interaction between lignin and [Emim] cation by π- πinteractions.

 

sem image of maple wood2

Figure 2. SEM Images of untreated maple wood flour (A and B), maple wood flour pretreated in [Emim][OAc] (C), [Bmim][OAc] (D), and [Bmim][MeSO4] (E), [Emim][OAc] with 10% (w/w) added water (F), [Bmim][OAc] with 10% (w/w) added water (G), and [Bmim][MeSO4] with 10% (w/w) added water (H). All images are the same scale.

 

Reference

  1. M. Mora-Pale, L. Meli, T.V. Dohert, R.J. Linhardt, J.S. Dordick (2011) "Room Temperature Ionic Liquids as Emerging Solvents for the Pretreatment of Lignocellulosic Biomass", Biotechnology and Bioengineering 108, 1229-1245.
  2. S.H. Lee, T.V. Doherty, R.J. Linhardt, J.S. Dordick (2009) "Ionic liquid-mediated selective extraction of lignin from wood leading to enhanced enzymatic cellulose hydrolysis", Biotechnology and Bioengineering 102, 1368-1376.
  3. T.V. Doherty, M. Mora-Pale, S.E. Foley, R.J. Linhardt, and J.S. Dordick (2010) "Ionic liquid solvent properties as predictors of lignocellulose pretreatment efficacy", Green Chemistry 12, 1967-1975.
  4. 4. H. Wu, M. Mora-Pale, J. Miao, T.V. Doherty, R.J. Linhardt, and J.S. Dordick (2011) "Facile Pretreatment of Lignocellulosic Biomass at High Loadings in Room Temperature Ionic Liquids", Biotechnology and Bioengineering 108, 2865-2875.