Transition of Cellulose Crystalline Structure and Surface Morphology of Biomass as a Function of Ionic Liquid Pretreatment and Its Relation to Enzymatic Hydrolysis

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• 作者：Gang Cheng ; Patanjali Varanasi ; Chenlin Li ; Hanbin Liu ; Yuri B. Melnichenko ; Blake A. Simmons ; Michael S. Kent ; Seema Singh
• 刊名：Biomacromolecules
• 出版年：2011
• 出版时间：April 11, 2011
• 年：2011
• 卷：12
• 期：4
• 页码：933-941
• 全文大小：1054K
• 年卷期：v.12,no.4(April 11, 2011)
• ISSN：1526-4602

文摘

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 ([C2mim][OAc]) at 120 and 160 掳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 掳C. For eucalyptus, first evidence of cellulose II required more intense pretreatment (3 h at 160 掳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 掳C). Interestingly, the rate of enzymatic hydrolysis of Avicel was slightly lower for pretreatment at 160 掳C compared with pretreatment at 120 掳C. For the biomass samples, the hydrolysis rate was much greater for pretreatment at 160 掳C compared with pretreatment at 120 掳C. The result for Avicel can be explained by more complete conversion to cellulose II upon precipitation after pretreatment at 160 掳C. By comparison, the result for the biomass samples suggests that another factor, likely lignin鈭抍arbohydrate complexes, also impacts the rate of cellulose hydrolysis in addition to cellulose crystallinity.