Structural comparison and enhanced enzymatic hydrolysis of the cellulosic preparation from Populus tomentosa Carr., by different cellulose-soluble solvent systems
Introduction
In recent years, the rapid growing demand for energy and the emergence of global warming by use of fossil fuels have rekindled a strong interest in pursuing alternative and renewable energy sources (Lee et al., 2009). Lignocellulosic biomass has the potential to act as a low cost and renewable feedstock for bioconversion into fermentable sugars, which then can be further utilized for biofuel production by various microorganisms (Himmel et al., 2007). Compared with starchy biomass, it is considered as a rather recalcitrant material due to its highly lignified and crystalline structure. The individual cellulose chains are joined by a network of inter- and intra-molecular hydrogen bonding and van der Waals forces. Cellulase is most often employed to hydrolyze cellulose to glucose, and its accessibility to the limited adsorption sites on crystalline cellulose structure is generally believed to play an important role in determining the cellulose hydrolysis rate. In the bioconversion route, pretreatment is essential if we want to open up the biomass structure and refine them more efficiently (Galbe and Zacchi, 2007). Generally, a number of various pretreatments have been investigated over the years, including dilute acid, steam explosion, hot water, lime and organic solvent, and have their own drawbacks in large scale application.
Recently, a series of cellulose-soluble solvents had been used as pretreatment method to disrupt the tight packing arrangement of cellulose fibrils in the crystalline domains, such as N-methyl-morpholine-N-oxide (NMMO) (Shafiei et al., 2010), ionic liquids (Lee et al., 2009, Zhang et al., 2005, Zhao et al., 2009), concentrated phosphoric acid (Zhang et al., 2006), LiOH/urea system (Liu and Zhang, 2009), and LiCl/N,N-dimethylacetamide (DMAc) system. As a low-energy demanding and environmentally friendly process, dissolution of cellulose will disrupt the hydrogen bonding networks in cellulose by forming new H-bonds between solvents and cellulose. After regeneration, the original architecture of cellulose fiber is predominantly lost due to the crystal structure transformation. Correspondingly, a rapid decomposition of cellulose could be achieved because of the lower packing density or inflated structure (Igarashi et al., 2007). However, the starting materials adopted mainly in the relative researches were the commercial products (Avicel cellulose, cotton, etc.). As we have known, the distribution of lignin and hemicelluloses in the natural lignocellulosic materials is thought to influence the dissolution and enzymatic hydrolysis of cellulose (Robinson et al., 2003, Selig et al., 2007). Besides, the comparable study of the changes in the structure of cellulose regenerated from different cellulose-soluble solvent systems is limited. The relationship between the complexity of the biomass crystal structure and the following enzymatic hydrolysis remains to be thoroughly investigated.
Triploid of Populus tomentosa Carr., a kind of fast-growing poplar widely planted in China to prevent wind erosion and control desertification, has a considerable economical and ecological importance. It is a lignocellulosic feedstock with high potential in the production of paper, board, and bioethanol in China. The primary focus of this work is to compare the performances of crystal structure, and enzymatic hydrolysis of the regenerated cellulose from different dissolution processes. LiOH/urea aqueous solution, LiCl/DMAc system, concentrated phosphoric acid, N-methyl-morpholine-N-oxide (NMMO) and ionic liquids ([BMIM]Cl) were employed to dissolve the natural cellulosic preparation from P. tomentosa Carr.
Section snippets
Materials and chemicals
The chips of triploid P. tomentosa Carr., 4 years old, were obtained from Shandong Province, China. The main components of raw hybrid poplar (P. tormentosa Carr.) were determined as: cellulose 53.2%, polypentanose 20.5%, lignin 16.7%, and ash 0.7% (the standard deviations less than 3%). After being ground to pass a 20 mesh sieve, the poplar powder was dewaxed with ethanol/toluene (1:2, v/v) for 8 h. Delignification process was performed using sodium chlorite under pH 3.8–4.2 adjusted by acetic
Crystal structure analysis
The degree of crystallinity of cellulose has been considered as an important factor in resisting enzymatic degradation. Therefore, the crystal features of the regenerated cellulosic samples after different dissolution processes were examined by powder X-ray diffraction and also compared to the untreated cellulosic sample. This measurement is a reliable indicator of the transformation of cellulose structure (Matsuo et al., 1990, Nishiyama et al., 2002, Nishiyama et al., 2003). The untreated
Conclusions
Five cellulose-soluble solvent systems were used to dissolve the cellulosic preparation from P. tomentosa Carr. The mechanism of solvation process, the crystal transformation of cellulose, and the enzymatic hydrolysis kinetics were highly connected. The regenerated cellulose from DMAc/LiCl system remained most of the original crystal structure, and consequently, exhibited a slightly enhancement on enzymatic hydrolysis. Meanwhile, the obvious crystal transformation from cellulose I to cellulose
Acknowledgements
This work was supported by the grants from the Natural Science Foundation of China (Nos. 30930073 and 30710103906), China Ministry of Education (No. 111, 2007B55), Ministry of Science and Technology (973-2010CB732204), State Forestry Administration (200804015), and China Scholarship Council (2009651012).
References (35)
- et al.
Effect of solvent exchange on the supramolecular structure, the molecular mobility and the dissolution behavior of cellulose in LiCl/DMAc
Carbohydr. Res.
(2008) - et al.
The fermentability of concentrated softwood-derived hemicellulose fractions with and without supplemental cellulose hydrolysates
Enzyme Microb. Technol.
(2003) - et al.
Pretreatment of spruce and oak by N-methylmorpholine-N-oxide (NMMO) for efficient conversion of their cellulose to ethanol
Bioresour. Technol.
(2010) - et al.
Enzymatic hydrolysis of cellulose I is greatly accelerated via its conversion to the cellulose II hydrate form
Polym. Degrad. Stabil.
(2010) - et al.
Influence of steaming explosion time on the physic-chemical properties of cellulose from Lespedeza stalks (Lespedeza crytobotrya)
Bioresour. Technol.
(2009) - et al.
Regenerating cellulose from ionic liquids for an accelerated enzymatic hydrolysis
J. Biotechnol.
(2009) Infrared and Raman spectroscopy of cellulose
- et al.
Phase transformations in microcrystalline cellulose due to partial dissolution
Cellulose
(2007) - et al.
Observations by high-resolution carbon-13 nuclear magnetic resonance of cellulose I related to morphology and crystal structure
Macromolecules
(1981) - et al.
Cellulose molecular weights determined by viscometry
J. Appl. Polym. Sci.
(1989)
Pretreatment of lignocellulosic materials for efficient bioethanol production
Adv. Biochem. Eng. Biotechnol.
Biomass recalcitrance: engineering plants and enzymes for biofuels production
Science
Activation of crystalline cellulose to cellulose III results in efficient hydrolysis by cellobiohydrolase
FEBS J.
X-ray structure of mercerized cellulose II at 1 Å resolution
Biomacromolecules
Ionic liquid-mediated selective extraction of lignin from wood leasing to enhanced enzymatic cellulose hydrolysis
Biotechnol. Bioeng.
Cellulose crystallinity and ordering of hemicelluloses in pine and birch pulps as revealed by solid-state NMR spectroscopic methods
Cellulose
Understanding the interactions of cellulose with ionic liquids: a molecular dynamics study
J. Phys. Chem. B
Cited by (44)
Synthesis of an adsorbent-bioactive complex with antioxidant properties: Thermal stability
2023, Chemical Engineering Research and DesignLignocellulosic Biomass in Biotechnology
2021, Lignocellulosic Biomass in BiotechnologyPreparation of furfural from Eucalyptus by the MIBK/H<inf>2</inf>O pretreatment with biphasic system and enzymatic hydrolysis of the resulting solid fraction
2018, Energy Conversion and ManagementCitation Excerpt :Based on the CrI and the data of enzymatic hydrolysis of the substrates, it was found that a positive correlation between the CrI and enzymatic hydrolysis. However, the CrI was lowered during some specific conditions, such as phosphoric acid and ionic liquid pretreatments, which resulted in the substrates obtained were more readily hydrolysis by cellulase [43,44]. Moreover, the destruction of morphologic structure by the pretreatments with different systems exhibited large amounts of adsorption sites of enzymes, leading to enhancing the enzymatic hydrolysis efficiency.
The integration of different pretreatments and ionic liquid processing of eucalyptus: Hemicellulosic products and regenerated cellulose fibers
2017, Industrial Crops and ProductsCitation Excerpt :Similarly, the C4 resonance region (80–90 ppm) was consisted of a broader upfield signal at around 83.6 ppm, which was originated from the disordered and less ordered cellulose chains. The signal at 89.1 ppm was ascribed to the highly ordered interiors (Wang et al., 2011). The peaks of C4 at around 85 ppm shifted to higher magnetic fields than that of the holocellulose (89.1 ppm) and the signal intensity decreased significantly, verifying a reduction of crystallinity as a result of the reforming of the cellulose molecules during the dissolution and coagulation processes.
Potential of Brachiaria mutica (Para grass) for bioethanol production from Loktak Lake
2017, Bioresource Technology