Enhanced enzymatic hydrolysis and structural features of corn stover by FeCl3 pretreatment
Introduction
Biorefining of lignocellulosic biomass generally involves several sequential steps—lignocellulose pretreatment, enzymatic hydrolysis, and fermentation. Currently, the biggest technological and economic challenge in biomass biorefining is the cost-effective release of fermentable sugars from biomass materials (Himmel et al., 2007, Moxley et al., 2008, Wyman, 2007).
The lignocellulosic biomass has a complex structure in which cellulose, hemicellulose, and lignin are the major components. During the process of converting lignocellulose to fermentable sugars, the chemical and structural features of the biomass affect liquid penetration and/or enzyme accessibility and activity (Himmel et al., 2007). Also as a result of the strong interchain hydrogen-bonding network, crystalline cellulose is resistant to enzymatic hydrolysis, whereas hemicellulose and amorphous cellulose are readily digested. Once the hemicellulose barrier associated with cell-wall microfibrils has been compromised by chemical pretreatment, cellulase can be used to hydrolyze the crystalline cellulose cores of these structures.
Biomass materials that were not pretreated were directly used for enzymatic hydrolysis; however, only approximately 20% of the theoretical glucose yield was achieved due to the recalcitrance of the material to enzymatic hydrolysis (Kim et al., 2006, Koullas et al., 1992). The pretreatment step is usually carried out to reduce biomass recalcitrance, which generally involves depolymerization and solubilization of hemicellulose into monosaccharides and oligosaccharides that can be further hydrolyzed or fermented. Therefore, pretreatment is necessary in the case of lignocellulosic biomass in order to increase the conversion yield of lignocellulose into fermentable sugars.
The pretreatment employed also determines the accessibility of the enzymes to cellulose and the degree of crystallinity and has a significant effect on the ratio of key enzyme components required in the subsequent hydrolysis step to effectively release the sugars present (Yang and Wyman, 2008b). Enzyme accessibility has been proposed as a limiting factor in the enzymatic conversion of cellulose present in the biomass to glucose (Ishizawa et al., 2007). Removal of hemicellulose from the microfibrils is thought to expose the crystalline cellulose core, which can then be hydrolyzed by cellulase. In addition, pretreatment typically breaks down the macroscopic rigidity of the biomass and reduces the physical barriers to mass transport.
The findings of our previous study indicated that FeCl3 pretreatment could easily and effectively solubilize hemicellulose into monomeric and oligomeric sugars in liquor. Hence, it was possible to obtain the liquid fraction with large amounts of xylose, which could then be used as a raw material for xylitol production. The solid fraction after pretreatment was used as the substrate for enzymatic hydrolysis of cellulose to generate the maximal amount of glucose (Lu et al., 2007).
Therefore, we wanted to verify the effectiveness and feasibility of FeCl3 pretreatment as a pretreatment method for lignocellulosic biomass in order to enhance the enzymatic hydrolysis of cellulose to glucose. To accomplish this, corn stover was pretreated with FeCl3, and the effects of the pretreatment procedure were evaluated on the basis of the yields obtained in the subsequent enzymatic hydrolysis step using cellulase and β-glucosidase. Various structural characteristics of the pretreated corn stover were also assessed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses.
Section snippets
Materials
The air-dried corn stover used in this study was Jiyuan No. 1 collected from Tongzhou District, Beijing. The material was manually cut into pieces, milled, and screened to obtain the −20 to +80 mesh fraction. It was necessary to remove nonstructural material from corn stover to prevent interference with the structural analyses performed later. In the preparation of feedstocks, a two-step extraction process was followed to remove water-soluble and ethanol-soluble material by the NREL LAP Soxhlet
FeCl3 pretreatment
The lignocellulose pretreatment conditions affect the substrate characteristics and result in different enzymatic hydrolysis performances, in terms of sugar yields and hydrolysis rates, at different enzyme loadings (Wyman et al., 2005a, Wyman et al., 2005b). Fig. 1A shows the monomeric and oligomeric xylose yield in the liquid fraction and the amount of xylan remaining in the residue after enzymatic hydrolysis of FeCl3-pretreated corn stover. Three typical pretreatment temperatures, i.e., 140
Conclusions
This study demonstrates FeCl3 pretreatment is a more competitive approach to xylose release from corn stover and enhances the recovery of hemicellulose and the enzymatic hydrolysis of cellulose. Enzymatic hydrolysis yield of FeCl3-pretreated corn stover at 160 °C for 20 min was up to 98.0%. FeCl3 pretreatment disrupted recalcitrant structures, removed amorphous components, and increased the external surface area, thereby improving the enzymatic digestibility of pretreated corn stover.
Acknowledgements
This study is financially supported by the National Science Foundation of China (No. 20876166). The authors thank Dr. Shuhao Wang for help in reviewing this paper and Mr. Zhenning Han for providing the equipment for this study.
References (35)
- et al.
Improved enzymatic hydrolysis yield of rice straw using electron beam irradiation pretreatment
Bioresour. Technol.
(2009) - et al.
Characterization of dilute acid pretreatment of silvergrass for ethanol production
Bioresour. Technol.
(2008) - et al.
Lime pretreatment and enzymatic hydrolysis of corn stover
Bioresour. Technol.
(2005) - et al.
Effect of structural features on enzyme digestibility of corn stover
Bioresour. Technol.
(2006) - et al.
Pretreatment and fractionation of corn stover by ammonia recycle percolation process
Bioresour. Technol.
(2005) - et al.
Partial flow of compressed-hot water through corn stover to enhance hemicellulose sugar recovery and enzymatic digestibility of cellulose
Bioresour. Technol.
(2005) - et al.
Combined sugar yields for dilute sulfuric acid pretreatment of corn stover followed by enzymatic hydrolysis of the remaining solids
Bioresour. Technol.
(2005) - et al.
Optimization of pH controlled liquid hot water pretreatment of corn stover
Bioresour. Technol.
(2005) - et al.
Enzymatic hydrolysis of lime-pretreated corn stover and investigation of the HCH-1 model: inhibition pattern, degree of inhibition, validity of simplified HCH-1 model
Bioresour. Technol.
(2007) - et al.
Enhanced enzymatic hydrolysis of wheat straw by aqueous glycerol pretreatment
Bioresour. Technol.
(2008)
Characteristics of degraded lignins obtained from steam exploded wheat straw
Polym. Degrad. Stab.
What is (and is not) vital to advancing cellulosic ethanol
Trends Biotechnol.
Comparative sugar recovery data from laboratory scale application of leading pretreatment technologies to corn stover
Bioresour. Technol.
Coordinated development of leading biomass pretreatment technologies
Bioresour. Technol.
Characterization of the degree of polymerization of xylooligomers produced by flowthrough hydrolysis of pure xylan and corn stover with water
Bioresour. Technol.
Fundamental factors affecting biomass enzymatic reactivity
Appl. Biochem. Biotechnol.
Effect of particle size based separation of milled corn stover on AFEX pretreatment and enzymatic digestibility
Biotechnol. Bioeng.
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