Increasing Cellulose Accessibility Is More Important Than Removing Lignin: A Comparison of Cellulose Solvent-Based Lignocellulose Fractionation and Soaking in Aqueous Ammonia

Biological Systems Engineering Department, Virginia Polytechnic Institute and State University, 210-A Seitz Hall, Blacksburg, Virginia 24061, USA.
Biotechnology and Bioengineering (Impact Factor: 4.13). 01/2011; 108(1):22-30. DOI: 10.1002/bit.22919
Source: PubMed


While many pretreatments attempt to improve the enzymatic digestibility of biomass by removing lignin, this study shows that improving the surface area accessible to cellulase is a more important factor for achieving a high sugar yield. Here we compared the pretreatment of switchgrass by two methods, cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) and soaking in aqueous ammonia (SAA). Following pretreatment, enzymatic hydrolysis was conducted at two cellulase loadings, 15 filter paper units (FPU)/g glucan and 3 FPU/g glucan, with and without BSA blocking of lignin absorption sites. The hydrolysis results showed that the lignin remaining after SAA had a significant negative effect on cellulase performance, despite the high level of delignification achieved with this pretreatment. No negative effect due to lignin was detected for COSLIF-treated substrate. SEM micrographs, XRD crystallinity measurements, and cellulose accessibility to cellulase (CAC) determinations confirmed that COSLIF fully disrupted the cell wall structure, resulting in a 16-fold increase in CAC, while SAA caused a 1.4-fold CAC increase. A surface plot relating the lignin removal, CAC, and digestibility of numerous samples (both pure cellulosic substrates and lignocellulosic materials pretreated by several methods) was also developed to better understand the relative impacts of delignification and CAC on glucan digestibility.

Download full-text


Available from: Noppadon Sathitsuksanoh
  • Source
    • "Examining the H-AFEX-treated substrate in tandem with physical and chemical features should switch light on fundamental mechanisms which contributing to the recalcitrance of lignocellulosic biomass. Some researchers using SEM micrographs and XRD crystallinity measurements reported that improving the surface area accessible to cellulase is more important than lignin removal for achieving a high sugar yield (Rollin et al., 2011). Fourier transform infrared spectroscopy (FTIR) was used to investigate the changes of cellulose structures and characteristics of lignin during pretreatment (Gabov et al., 2014; Ma et al., 2015). "
    [Show abstract] [Hide abstract]
    ABSTRACT: To effectively improve enzymatic digestibility of carbohydrate in lignocellulosic biomass, hydrogen peroxide presoaking prior to ammonia fiber expansion (H-AFEX) was applied as pretreatment to corn stalk. Enzymatic hydrolysis using cocktail enzymes including cellulase, β-glucosidase and xylanase at 72. h after pretreatment under optimal conditions, the glucan and xylan conversions of 88.9% and 86.3% were achieved, respectively. It was about 3.31-fold in sugar yield for H-AFEX-treated corn stalk compared with untreated material. The results of composition analysis and enzymatic hydrolysis showed that H-AFEX pretreatment was effective to remove lignin and improve glucan digestibility. The characteristics of biomass surface and cell wall, biomass crystallinity, and chemical structure changes of H-AFEX-treated corn stalk were determined by digital microscope system, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR), respectively. The results demonstrated that H-AFEX pretreatment induced some morphology changes including partial damages in vascular bundle and deconstruction of cell wall, and the modified biomass structure could increase surface area accessibility and create favorable conditions for enzymatic hydrolysis obviously. Due to removal amorphous substances, the crystallinity index of H-AFEX-treated corn stalk increased comparing with that of raw material. FTIR data showed that H-AFEX process induced changes in chemical structure and cross linking such as removal/dissolution of lignin and hemicelluloses, cleavage of bonds linkage, and decrystallization of cellulose. As a result, H-AFEX pretreatment effectively reduced recalcitrance of corn stalk, and promoted subsequent enzymatic hydrolysis.
    Full-text · Article · May 2016 · Industrial Crops and Products
  • Source
    • "It was reported that ILs initially liquefy the cellulose and then the hemicelluloses (Miyafuji et al. 2009). Cellulose solvent (concentrated phosphoric acid) and organic solvent-based lignocellulose fractionation (COSLIF) result in the disruption of highly ordered hydrogen bonds in the crystalline cellulose and the removal of some acid-insoluble lignin (Rollin et al. 2011). COSLIF works well on a wide range of feedstocks (Sathitsuksanoh et al. 2013). "
    [Show abstract] [Hide abstract]
    ABSTRACT: As an immerging lignocellulose pretreatment strategy, cellulose solvent-based pretreatment can break down inter- and intra-molecular hydrogen bonds and disrupt the rigid structure of cellulose. Two cellulose solvent pretreatments were examined and compared in this study: NaOH/urea and concentrated phosphoric acid. Pretreated corn stover substrates were characterized by optical microscopy, confocal laser scanning microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and chemical analyses. It was found that both alkaline- and acid-based cellulose solvent pretreatments can disrupt cell wall structures and cause partial dissolution of the cell wall components. The results indicated that the alkaline-based cellulose solvent was more effective at removing lignin as compared with the phosphoric acid-based cellulose solvent. The initial enzymatic saccharification rate of corn stover pretreated by alkaline-based cellulose solvent was greatly enhanced; complete saccharification of the glucans was achieved within 24 h at an enzyme loading of 15 filter paper units (FPU)/g substrate. The enzymatic digestibility of corn stover pretreated by phosphoric acid was lower than that of the alkaline-based system; this was probably caused by the presence of a high concentration of lignin.
    Full-text · Article · Jan 2016 · Bioresources
  • Source
    • "The mechanism of CIL pretreatment to overcome the recalcitrance of eucalyptus bark was also investigated in this study by controlling the level of the fractionation. Although factors limiting enzymatic hydrolysis of biomass have been extensively studied[18,19], the biomass recalcitrance are still not fully understood due to the complex interactions between the plant cell wall and biomass pretreatment. Understanding the compositional changes during different pretreatment processes is critically important to improve the current bio-refinery technologies. "
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel pretreatment method-concerted ionic liquid (CIL) pretreatment was proposed and the mechanism of CIL pretreatment to overcome the recalcitrance of biomass was investigated in this study. The CIL refers to a combination of a protic ionic liquid (PIL) pyrrolidinium acetate ([Pyrr][AC]) and an aprotic ionic liquid (AIL) 1-butyl-3-methylimidazolium acetate ([BMIM][AC]) in varied proportion. In the CIL system, [Pyrr][AC] selectively dissolves lignin from biomass and [BMIM][AC] dissolves part of cellulose and hemicelluloses. Besides lignin, hemicelluloses are also an important factor of biomass recalcitrance. Optimized [BMIM][AC] fraction in the CIL pretreatment resulted in the efficient removal of lignocellulose complex while [Pyrr][AC] selectively fractionated lignin component. CILs exhibited superior efficiency in overcoming the recalcitrance of eucalyptus bark over that of the individual constituent ionic liquids. Compared to pretreatments by individual ILs of the pair, the CIL pretreatment increased the glucose yield by 30% from the cellulose of eucalyptus bark. High cellulose conversion of 91% (wt%) was achieved from enzymatic conversion of eucalyptus bark by optimizing the lignin and hemicelluloses removal.
    Full-text · Article · Sep 2015 · PROCESS BIOCHEMISTRY
Show more