Abstract
BackgroundIonic liquid (IL) pretreatment has shown great potential as a novel pretreatment technology with high sugar yields. To improve process economics of pretreatment, higher biomass loading is desirable. The goal of this work is to establish, the impact of high biomass loading of switchgrass on IL pretreatment in terms of viscosity, cellulose crystallinity, chemical composition, saccharification kinetics, and sugar yield.ResultsThe pretreated switchgrass/IL slurries show frequency dependent shear thinning behavior. The switchgrass/IL slurries show a crossover from viscous behavior at 3 wt% to elastic behavior at 10 wt%. The relative glucan content of the recovered solid samples is observed to decrease with increasing levels of lignin and hemicelluloses with increased biomass loading. The IL pretreatment led to a transformation of cellulose crystalline structure from I to II for 3, 10, 20 and 30 wt% samples, while a mostly amorphous structure was found for 40 and 50 wt% samples.ConclusionsIL pretreatment effectively reduced the biomass recalcitrance at loadings as high as 50 wt%. Increased shear viscosity and a transition from ‘fluid’ like to ‘solid’ like behavior was observed with increased biomass loading. At high biomass loadings shear stress produced shear thinning behavior and a reduction in viscosity by two orders of magnitude, thereby reducing the complex viscosity to values similar to lower loadings. The rheological properties and sugar yields indicate that 10 to 50 wt% may be a reasonable and desirable target for IL pretreatment under certain operating conditions.
Highlights
Ionic liquid (IL) pretreatment has shown great potential as a novel pretreatment technology with high sugar yields
We have investigated the impact of high biomass loading on IL pretreatment of switchgrass using [C2mim][OAc]
Though high biomass loading increases the viscosity, there is an increasing enhancement of shear thinning leading to a slurry with a lower complex viscosity at high loadings
Summary
Ionic liquid (IL) pretreatment has shown great potential as a novel pretreatment technology with high sugar yields. The goal of this work is to establish, the impact of high biomass loading of switchgrass on IL pretreatment in terms of viscosity, cellulose crystallinity, chemical composition, saccharification kinetics, and sugar yield. Previous experiments have shown that both chemical composition and physical properties of the pretreated biomass play significant roles in determining saccharification efficiency. IL pretreatment with certain ILs, primarily those with imidazolium cations, has been shown to decrease biomass recalcitrance and increase saccharification efficiency for a wide range of biomass feedstocks [17,31,32]. The focus of the current study is to establish, for the first time, the impact of high biomass loading of switchgrass on IL pretreatment in terms of viscosity, cellulose crystallinity, chemical composition, saccharification kinetics, and sugar yields
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