Cellulose is inherently resistant to breakdown, and the native crystalline structure (cellulose I) of cellulose is considered to be one of the major factors limiting its potential in terms of ...cost-competitive lignocellulosic biofuel production. Here we report the impact of ionic liquid pretreatment on the cellulose crystalline structure in different feedstocks, including microcrystalline cellulose (Avicel), switchgrass ( Panicum virgatum ), pine ( Pinus radiata ), and eucalyptus ( Eucalyptus globulus ), and its influence on cellulose hydrolysis kinetics of the resultant biomass. These feedstocks were pretreated using 1-ethyl-3-methyl imidazolium acetate (C2mimOAc) at 120 and 160 °C for 1, 3, 6, and 12 h. The influence of the pretreatment conditions on the cellulose crystalline structure was analyzed by X-ray diffraction (XRD). On a larger length scale, the impact of ionic liquid pretreatment on the surface roughness of the biomass was determined by small-angle neutron scattering (SANS). Pretreatment resulted in a loss of native cellulose crystalline structure. However, the transformation processes were distinctly different for Avicel and for the biomass samples. For Avicel, a transformation to cellulose II occurred for all processing conditions. For the biomass samples, the data suggest that pretreatment for most conditions resulted in an expanded cellulose I lattice. For switchgrass, first evidence of cellulose II only occurred after 12 h of pretreatment at 120 °C. For eucalyptus, first evidence of cellulose II required more intense pretreatment (3 h at 160 °C). For pine, no clear evidence of cellulose II content was detected for the most intense pretreatment conditions of this study (12 h at 160 °C). Interestingly, the rate of enzymatic hydrolysis of Avicel was slightly lower for pretreatment at 160 °C compared with pretreatment at 120 °C. For the biomass samples, the hydrolysis rate was much greater for pretreatment at 160 °C compared with pretreatment at 120 °C. The result for Avicel can be explained by more complete conversion to cellulose II upon precipitation after pretreatment at 160 °C. By comparison, the result for the biomass samples suggests that another factor, likely lignin−carbohydrate complexes, also impacts the rate of cellulose hydrolysis in addition to cellulose crystallinity.
Ionic liquids (ILs) have been shown to affect cellulose crystalline structure in lignocellulosic biomass during pretreatment. A systematic investigation of the swelling and dissolution processes ...associated with IL pretreatment is needed to better understand cellulose structural transformation. In this work, 3–20 wt % microcrystalline cellulose (Avicel) solutions were treated with 1-ethyl-3-methylimidazolium acetate (C2mimOAc) and a mixture of C2mimOAc with the nonsolvent dimethyl sulfoxide (DMSO) at different temperatures. The dissolution process was slowed by decreasing the temperature and increasing cellulose loading, and was further retarded by addition of DMSO, enabling in-depth examination of the intermediate stages of dissolution. Results show that the cellulose I lattice expands and distorts prior to full dissolution in C2mimOAc and that upon precipitation the former structure leads to a less ordered intermediate structure, whereas fully dissolved cellulose leads to a mixture of cellulose II and amorphous cellulose. Enzymatic hydrolysis was more rapid for the intermediate structure (crystallinity = 0.34) than for cellulose II (crystallinity = 0.54).
► Assessment of the potential of agave bagasse as a biofuel feedstock using ionic liquid (IL) pretreatment. ► The total sugar yield was higher for agave bagasse (AGB) than for switchgrass (SWG). ► ...The initial enzymatic hydrolysis rate was lower for AGB than for SWG. ► Pretreatment resulted in higher delignification for AGB (45.5%) than for SWG (38.4%). ► XRD patterns showed highly crystalline peaks for AGB which decreased with pretreatment.
Lignocellulose represents a sustainable source of carbon for transformation into biofuels. Effective biomass to sugar conversion strategies are needed to lower processing cost without degradation of polysaccharides. Since ionic liquids (ILs) are excellent solvents for pretreatment/dissolution of biomass, IL pretreatment was carried out on agave bagasse (AGB-byproduct of tequila industry) and digestibility and sugar yield was compared with that obtained with switchgrass (SWG). The IL pretreatment was conducted using (C2mimOAc) at 120 and 160°C for 3h and 15% biomass loading. While pretreatment using C2mimOAc was very effective in improving the digestibility of both feedstocks, IL pretreatment at 160°C resulted in higher delignification for AGB (45.5%) than for SWG (38.4%) when compared to 120°C (AGB-16.6%, SWG-8.2%), formation of a highly amorphous cellulose structure and a significant enhancement of enzyme kinetics. These results highlight the potential of AGB as a biofuel feedstock that can produce high sugar yields with IL pretreatment.
Previous studies of agave bagasse (AGB-byproduct of tequila industry) presented unidentified crystalline peaks that are not typical from common biofuel feedstocks (e.g. sugarcane bagasse, switchgrass ...or corn stover) making it an important issue to be addressed for future biorefinery applications. Ionic liquid (IL) pretreatment of AGB was performed using 1-ethyl-3-methylimidazolium acetate (C2mimOAc) at 120, 140 and 160 °C for 3 h and a mass fraction of 3% in order to identify these peaks. Pretreated samples were analyzed by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electronic microscopy (FE-SEM), thermal analysis (TGA-DSC) and wet chemistry methods. Previous unidentified XRD peaks on AGB at 2θ = 15°, 24.5° and 30.5°, were found to correspond to calcium oxalate (CaC2O4) in a monohydrated form. IL pretreatment with C2mimOAc was observed to remove CaC2O4 and decrease cellulose crystallinity. At 140 °C, IL pretreatment significantly enhances enzymatic kinetics and leads to ∼8 times increase in sugar yield (6.66 kg m−3) when compared to the untreated samples (960 g m−3). These results indicate that IL pretreatment can effectively process lignocellulosic biomass with high levels of CaC2O4.
•Chemical behavior of agave bagasse pretreated by ionic liquid (IL) is assessed.•Previously unidentified XRD peaks correspond to calcium oxalate (CaC2O4).•Total sugar yield and initial enzymatic hydrolysis rate were higher at 140 °C.•IL pretreatment can effectively process biomass with high levels of CaC2O4.•Increasing the temperature of IL pretreatment causes the agglomeration of CaC2O4.
Mixed-linkage glucan (MLG) is a cell wall polysaccharide containing a backbone of unbranched (1,3)-and (l, 4)-linked β-glucosyl residues. Based on its occurrence in plants and chemical ...characteristics, MLG has primarily been associated with the regulation of cell wall expansion due to its high and transient accumulation in young, expanding tissues. The Cellulose synthase-like F (CslF) subfamily of glycosyltransferases has previously been implicated in mediating the biosynthesis of this polymer. We confirmed that the rice (Oryza sativa) CslF6 gene mediates the biosynthesis of MLG by overexpressing it in Nicotiana benthamiana. Rice cslf6 knockout mutants show a slight decrease in height and stem diameter but otherwise grew normally during vegetative development. However, cslf6 mutants display a drastic decrease in MLG content (97% reduction in coleoptiles and virtually undetectable in other tissues). Immunodetection with an anti-MLG monoclonal antibody revealed that the coleoptiles and leaves retain trace amounts of MLG only in specific cell types such as sclerenchyma fibers. These results correlate with the absence of endogenous MLG synthase activity in mutant seedlings and 4-week-old sheaths. Mutant cell walls are weaker in mature stems but not seedlings, and more brittle in both stems and seedlings, compared to wild type. Mutants also display lesion mimic phenotypes in leaves, which correlates with enhanced defense-related gene expression and enhanced disease resistance. Taken together, our results underline a weaker role of MLG in cell expansion than previously thought, and highlight a structural role for MLG in nonexpanding, mature stem tissues in rice.
To date, there are few published reports on the fundamental physicochemical changes that occur in the biopolymers comprising lignocellulosic biomass during IL pretreatment. In particular changes to ...the degree of polymerization upon IL pretreatment although assumed have not been reported. In this study, we employ thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to determine the impact of IL pretreatment on two of the primary biopolymers present in biomass – lignin and cellulose. IL pretreatment was carried out on technical biomass components (Avicel, Kraft lignin and low sulfonate alkali lignin) and on potential bioenergy feedstocks (switchgrass, pine and eucalyptus) at 120 and 160 °C for 1, 3, 6 and 12 h. The depolymerization and formation of lower molecular weight cellulose as a result of IL pretreatment were inferred from TGA/DSC results and were further confirmed by size exclusion chromatography (SEC). The results also confirm that there is a decrease in cellulose crystallinity in the biomass as a result of pretreatment. These results provide insight into the mode of depolymerization and breakdown of lignin and cellulose.
•IL pretreatment depolymerizes biomass lignocellulosic.•Extent of depolymerization depends on biomass, pretreatment time and temperature.•Temperature dependent crystallinity changes is observed.•The crystalline material formed at 160 °C undergoes exothermic decomposition.•Resultant lignin in pretreated biomass has a higher calorific value.
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► Tracked syringyl and guaiacyl ratios during IL pretreatment of switchgrass and eucalyptus. ► Kamlet–Taft properties of C2mimOAc at 120°C and 160°C suggest two mechanisms. ► ...Preferential breakdown of S-lignin in both eucalyptus and switchgrass was observed at 160°C. ► Breakdown of G-lignin for eucalyptus was observed at 120°C. ► Insight on IL pretreatment mechanism demonstrates selective removal of S or G lignin is feasible.
Ionic liquids (ILs) have shown great potential for the reduction of lignin in biomass after pretreatment. Although dilute acid and base pretreatments have been shown to result in pretreated biomass with substantially different lignin composition, there is scarce information on the composition of lignin of IL pretreated biomass. In this work, temperature dependent compositional changes in lignin after IL pretreatment were studied to develop a mechanistic understanding of the process. Panicum virgatum and Eucalyptus globulus were pretreated with 1-ethyl-3-methylimidazolium acetate (C2mimOAc). Measurement of syringyl and guaiacyl ratio using pyrolysis–GC/MS and Kamlet–Taft properties of C2mimOAc at 120°C and 160°C strongly suggest two different modes of IL pretreatment. Preferential breakdown of S-lignin in both eucalyptus and switchgrass at high pretreatment temperature (160°C) and breakdown of G-lignin for eucalyptus and no preferential break down of either S- or G-lignin in switchgrass was observed at lower pretreatment temperatures (120°C).
BACKGROUND: Lignin is often overlooked in the valorization of lignocellulosic biomass, but lignin-based materials and chemicals represent potential value-added products for biorefineries that could ...significantly improve the economics of a biorefinery. Fluctuating crude oil prices and changing fuel specifications are some of the driving factors to develop new technologies that could be used to convert polymeric lignin into low molecular weight lignin and or monomeric aromatic feedstocks to assist in the displacement of the current products associated with the conversion of a whole barrel of oil. We present an approach to produce these chemicals based on the selective breakdown of lignin during ionic liquid pretreatment. RESULTS: The lignin breakdown products generated are found to be dependent on the starting biomass, and significant levels were generated on dissolution at 160°C for 6 hrs. Guaiacol was produced on dissolution of biomass and technical lignins. Vanillin was produced on dissolution of kraft lignin and eucalytpus. Syringol and allyl guaiacol were the major products observed on dissolution of switchgrass and pine, respectively, whereas syringol and allyl syringol were obtained by dissolution of eucalyptus. Furthermore, it was observed that different lignin-derived products could be generated by tuning the process conditions. CONCLUSIONS: We have developed an ionic liquid based process that depolymerizes lignin and converts the low molecular weight lignin fractions into a variety of renewable chemicals from biomass. The generated chemicals (phenols, guaiacols, syringols, eugenol, catechols), their oxidized products (vanillin, vanillic acid, syringaldehyde) and their easily derivatized hydrocarbons (benzene, toluene, xylene, styrene, biphenyls and cyclohexane) already have relatively high market value as commodity and specialty chemicals, green building materials, nylons, and resins.
BACKGROUND: Cost-efficient generation of second-generation biofuels requires plant biomass that can easily be degraded into sugars and further fermented into fuels. However, lignocellulosic biomass ...is inherently recalcitrant toward deconstruction technologies due to the abundant lignin and cross-linked hemicelluloses. Furthermore, lignocellulosic biomass has a high content of pentoses, which are more difficult to ferment into fuels than hexoses. Engineered plants with decreased amounts of xylan in their secondary walls have the potential to render plant biomass a more desirable feedstock for biofuel production. RESULTS: Xylan is the major non-cellulosic polysaccharide in secondary cell walls, and the xylan deficient irregular xylem (irx) mutants irx7, irx8 and irx9 exhibit severe dwarf growth phenotypes. The main reason for the growth phenotype appears to be xylem vessel collapse and the resulting impaired transport of water and nutrients. We developed a xylan-engineering approach to reintroduce xylan biosynthesis specifically into the xylem vessels in the Arabidopsis irx7, irx8 and irx9 mutant backgrounds by driving the expression of the respective glycosyltransferases with the vessel-specific promoters of the VND6 and VND7 transcription factor genes. The growth phenotype, stem breaking strength, and irx morphology was recovered to varying degrees. Some of the plants even exhibited increased stem strength compared to the wild type. We obtained Arabidopsis plants with up to 23% reduction in xylose levels and 18% reduction in lignin content compared to wild-type plants, while exhibiting wild-type growth patterns and morphology, as well as normal xylem vessels. These plants showed a 42% increase in saccharification yield after hot water pretreatment. The VND7 promoter yielded a more complete complementation of the irx phenotype than the VND6 promoter. CONCLUSIONS: Spatial and temporal deposition of xylan in the secondary cell wall of Arabidopsis can be manipulated by using the promoter regions of vessel-specific genes to express xylan biosynthetic genes. The expression of xylan specifically in the xylem vessels is sufficient to complement the irx phenotype of xylan deficient mutants, while maintaining low overall amounts of xylan and lignin in the cell wall. This engineering approach has the potential to yield bioenergy crop plants that are more easily deconstructed and fermented into biofuels.
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