Structural comparison and enhanced enzymatic hydrolysis of the cellulosic preparation from Populus tomentosa Carr., by different cellulose-soluble solvent systems

doi:10.1016/j.biortech.2010.12.088

Bioresource Technology

Volume 102, Issue 6, March 2011, Pages 4524-4529

https://doi.org/10.1016/j.biortech.2010.12.088 Get rights and content

Abstract

This study aims to establish an efficient pretreatment process using cellulose-dissolution solvents to enhance the enzymatic saccharification. LiOH/urea, LiCl/DMAc, concentrated phosphoric acid, ionic liquid (1-butyl-3-methylimidazolium chloride; [BMIM]Cl) and N-methyl-morpholine-N-oxide (NMMO) were selected as the cellulose dissolution agents. Except the cellulosic sample regenerated from LiCl/DMAc system, all the other treated samples exhibited lower cellulose crystallinity and degree of polymerization (DP), and consequently, exhibited a significant enhancement on enzymatic hydrolysis kinetic. Ionic liquid pretreatment offered unique advantages in the hydrolysis rate in the first 10 h, probably due to the extensively structural transformation of cellulose from the crystalline to the amorphous region. Meanwhile, the regenerated cellulose from concentrated phosphoric acid almost completely consisted of cellulose II, and achieved the highest saccharification yield.

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).

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Structural comparison and enhanced enzymatic hydrolysis of the cellulosic preparation from Populus tomentosa Carr., by different cellulose-soluble solvent systems

Abstract

Introduction

Section snippets

Materials and chemicals

Crystal structure analysis

Conclusions

Acknowledgements

Carbohydr. Res.

Enzyme Microb. Technol.

Bioresour. Technol.

Polym. Degrad. Stabil.

Bioresour. Technol.

J. Biotechnol.

Infrared and Raman spectroscopy of cellulose

Phase transformations in microcrystalline cellulose due to partial dissolution

Cellulose

Observations by high-resolution carbon-13 nuclear magnetic resonance of cellulose I related to morphology and crystal structure

Macromolecules

Cellulose molecular weights determined by viscometry

J. Appl. Polym. Sci.

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