Ionic liquid pretreatment of cellulosic biomass: Enzymatic hydrolysis and ionic liquid recycle

Abstract

Ionic liquids (ILs) are promising solvents for the pretreatment of biomass as certain ILs are able to completely solubilize lignocellulose. The cellulose can readily be precipitated with an anti-solvent for further hydrolysis to glucose, but the anti-solvent must be removed for the IL to be recovered and recycled. We describe the use of aqueous kosmotropic salt solutions to form a three-phase system that precipitates the biomass, forming IL-rich and salt-rich phases. The phase behavior of [Emim][Ac] and aqueous phosphate salt systems is presented, together with a process for recycling the [Emim][Ac] and enzymatically hydrolyzing the cellulose. This process reduces the amount of water to be evaporated from recycled IL, permitting efficient recycle of the IL. Material balances on the process, with multiple recycles of the [Emim][Ac], quantify the major components from a Miscanthus feedstock through the pretreatment, separation, and enzymatic hydrolysis steps. A more rapid and higher yielding conversion of cellulose to glucose is obtained by use of the three-phase system as compared to the cellulose obtained from biomass pretreated with IL and precipitated with water. The addition of a kosmotropic salt during the precipitation results in partial delignification of the biomass, which makes the substrate more accessible, enhancing the enzymatic hydrolysis.

Identification and characterization of a multidomain hyperthermophilic cellulase from an archaeal enrichment

“…S10), its activity was measured in the presence of the ionic liquids 1, 3-dimethylimidazolium dimethyl phosphate (DMIM)DMP) and 1-ethyl-3-methylimidazole acetate ((EMIM)OAc), which could potentially be used to pretreat substrates like Miscanthus 17 . The concentrations tested, 25 and 50% (v/v), are well above the expected residual ionic liquid of 10-15% that may be carried over after pretreatment 18 .…”

Effect of Ionic Liquids on Oil Palm Biomass Fiber Dissolution

“…Liu et al (2012) reported that lignin showed better solubility results than cellulose in amino-acid based IL. In another study, Shill et al (2011) indicated that the p-p interactions of the IL cation with lignin assisted in lignin solubilization. However, complete delignification of biomass is difficult due to the location of lignin within the lignin-carbohydrate complex, strong poly-ring bonds of C-O-C, C-C, and hydrophobicity (Kim et al 2003).…”

Pyrrolidinium Ionic Liquids as Effective Solvents for Lignin Extraction and Enzymatic Hydrolysis of Lignocelluloses

“…For chloride-based ILs, the presence of water should coordinate with chloride ions (Shill et al 2011) (Fig. 2).…”