Article

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

ABSTRACT

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.

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    • "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). "
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    • "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). "
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    • "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. "
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