Lignin monomer in steam explosion assist chemical treated cotton stalk affects sugar release
Introduction
Cotton is one of the most important crops in the world, accompanied with which an abundance of cotton stalk resources is produced, on the basis of a large planting area of cotton every year. However, some cotton stalks were piled up in the field casually, other parts were burnt by farmers, which resulted in the waste of natural resources and environment polluted (Kaur et al., 2012). In fact, cotton stalk is a valuable biomass resources rich in lignocellulose, which can be utilized for bioconversion and energy reproduction, and is considered to be a main resource for biofuels (Sun et al., 2014).
As like other biomass materials, cotton stalk is mainly composed of cellulose, hemicellulose and lignin. Lignin is linked to cellulose and hemicellulose, which plays a protective role on the cell wall of plants. Lignin has a three-dimensional network structure which composed of three phenylpropane units linked together by ether and carbon–carbon bonds. According to the molecular structure and source, lignin can be divided into three major phenylpropane units: p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S). Given the structural diversity and chemical heterogeneity of lignin, evaluation of lignin effect on biomass digestibility could be difficult (Fu et al., 2011, Xie and Peng, 2011). Furthermore, due to the high content of lignin, it is extremely difficult for cotton stalk to achieve direct saccharification or biotransformation. Therefore, pretreatment should be firstly carried out to destroy the structure of lignocellulose, increase the porosity of biomass, raising the contact specific surface area and the accessibility of enzymes to cellulose, thereby improving the conversion efficiency of cellulose and hemicellulose. Advanced technologies should be implemented as far as possible to realize the following goals: (1) reduce crystallization and increase the surface area of cellulose used for enzymatic digestion; (2) avoid carbohydrate degradation to inhibit the subsequent hydrolysis and fermentation process; (3) avoid using chemical reagents that would require high quality of reactor materials and produce serious environmental pollution; and (4) require minimum heat and energy so as to reduce production costs (Singh et al., 2017).
The pretreatment methods of biomass stalk can be divided roughly into physical pretreatment, chemical pretreatment, physical-chemical process and biological pretreatment at present, which have been explored by multiple previous studies described as follows. For example, Silverstein et al. (2007) reported the conversion efficiency of cotton stalk to ethanol in sulfuric acid, sodium hydroxide, hydrogen peroxide and ozone solutions. Binod et al. (2012) removed lignin effectively by high temperature assisted alkali pretreatment, which greatly improved the total process economy of ethanol production from cotton waste. Du et al. (2013) explored high-pressure assist alkali pretreatment of cotton stalks, and found that high pressure and high NaOH concentration were conducive to lignin dissolution, which resulted in the cellulose content and conversion yield increased. Haykir et al. (2013) carried out a study related to the pretreatment of cotton stalk by different kinds of ionic liquids. Gaur et al. (2016) optimized dilute acid hydrolysis of cotton stalk in laboratory scale by using central composite design (CCD) of response surface methodology (RSM). Singh et al. (2017) investigated microwave-assisted FeCl3 pretreatment of cotton stalk.
Steam explosion (SE) is a perfect pretreatment method which has the advantages, such as dissolve hemicellulose, increase substrate spaces, enlarge the contact area of cellulose and/or hemicellulose to enzymes, and environmental friendliness etc. (Kim, 2018). Although steam explosion can effectively remove hemicellulose, lignin in pretreated biomass substrates may block the pathways of polysaccharides and make the access of enzymes to cellulose ineffective (Kellock et al., 2017). Fortunately, the negative effects of lignin can be modified by introducing chemical additives, which in turn highlights the necessity of combination of steam explosion with chemical treatment.
The study was performed aiming at screening out a method of extracting lignin and/or hemicellulose effectively, and seeking out the optimal combination of pretreatment and enzymatic hydrolysis, so as to provide a basis for commercialization of cotton stalk conversion and utilization. In this study, reducing sugar yields released from cotton stalk, which were pretreated by steam explosion combined with different concentrations of strong monobasic acid (HCl), weak monobasic acid (CH3COOH), strong monobasic alkali (NaOH) and weak monobasic alkali (NH3·H2O), were comparable investigated in detail. Furthermore, H-monomer, G-monomer and S-monomer levels were detected so as to evaluate how did monolignins affect fermentable sugar released from cotton stalk.
Section snippets
Materials
Cotton stalk samples were obtained from experimental farmland in Xinjiang, China, and the collected stalk was air-dried at room temperature to a moisture content of less than 10% and stored in a dry container until further use. Cellulase (originated from Penicillium sp.), and xylanase (originated from Aspergillus niger) were bought from Heshibi Biological Technology Ltd. (Yinchuan, Ningxia Province, China). The standard samples used for HPLC quantification were from Sigma and of chromatographic
Steam explosion effectively removes hemicellulose
The raw materials of cotton stalk were pretreated by steam explosion at different pressures (1 MPa, 2.4 MPa). As shown in Table 1, cellulose and hemicellulose accounted for 42.30% and 24.56% of dry weight in untreated raw materials of cotton stalk, respectively, with total carbohydrate content accounting for over 60%, which made cotton stalk be a cheap biomass material with great potential for renewable energy. However, after steam explosion, the hemicellulose content decreased from 24.56% to
Conclusions
A new strategy was developed in this study, SE-2.4 MPa-5%NH3·H2O followed by enzymatic hydrolysis could release 73.22% of reducing sugar from cotton stalk samples. Evaluation of monolignins (H, G, S) in cotton stalk substrates indicates that there was a positive correlation between substrates rich in G and S-monomer and sugar release, while H monomer seemed to exhibit a certain inhibitory effect. Therefore, modification of lignin monomer in plant cell walls might benefit degradation and
Acknowledgements
We gratefully acknowledge financial support provided by National Natural Science Foundation of China (Grant No. 21464011) and the Scientific Research Program of Shihezi University (RCZX201208).
References (28)
- et al.
High temperature pretreatment and hydrolysis of cotton stalk for producing sugars for bioethanol production
Fuel
(2012) - et al.
High pressure assist-alkali pretreatment of cotton stalk and physiochemical characterization of biomass
Bioresour. Technol.
(2013) - et al.
Bench scale dilute acid pretreatment optimization for producing fermentable sugars from cotton stalk and physicochemical characterization
Ind. Crops Prod.
(2016) - et al.
Intensification of steam explosion and structural intricacies impacting sugar recovery
Bioresour. Technol.
(2017) - et al.
Steam explosion distinctively enhances biomass enzymatic saccharification of cotton stalks by largely reducing cellulose polymerization degree in G. barbadense and G. hirsutum
Bioresour. Technol.
(2015) - et al.
Ethanol production from alkali- and ozone-treated cotton stalks using thermotolerant Pichia kudriavzevii HOP-1
Ind. Crops Prod.
(2012) - et al.
Lignin-derived inhibition of monocomponent cellulases and a xylanase in the hydrolysis of lignocellulosics
Bioresour. Technol.
(2017) - et al.
Improved enzymatic saccharification of steam exploded cotton stalk using alkaline extraction and fermentation of cellulosic sugars into ethanol
Bioresour. Technol.
(2016) - et al.
A review on alkaline pretreatment technology for bioconversion of lignocellulosic biomass
Bioresour. Technol.
(2015) - et al.
Lignin depolymerization/repolymerization and its critical role for deligniWcation of aspen wood by steam explosions
Bioresour. Technol.
(2007)
Aqueous ammonia pretreatment of sugar beet pulp for enhanced enzymatic hydrolysis
Bioprocess. Biosyst. Eng.
Mild alkali-pretreatment effectively extracts guaiacyl-rich lignin for high lignocellulose digestibility coupled with largely diminishing yeast fermentation inhibitors in Miscanthus
Bioresour. Technol.
Lignin monomer composition affects Arabidopsis cell-wall degradability after liquid hot water pretreatment
Biotechnol. Biofuels
A comparison of chemical pretreatment methods for improving saccharification of cotton stalks
Bioresour. Technol.
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