Shao-Ni Sun

The role of pretreatment in improving the enzymatic hydrolysis of lignocellulosic materials.

Lignocellulosic materials are among the most promising alternative energy resources that can be utilized to produce cellulosic ethanol. However, the physical and chemical structure of lignocellulosic materials forms strong native recalcitrance and results in relatively low yield of ethanol from raw lignocellulosic materials. An appropriate pretreatment method is required to overcome this recalcitrance. For decades various pretreatment processes have been developed to improve the digestibility of lignocellulosic biomass. Each pretreatment process has a different specificity on altering the physical and chemical structure of lignocellulosic materials. In this paper, the chemical structure of lignocellulosic biomass and factors likely affect the digestibility of lignocellulosic materials are discussed, and then an overview about the most important pretreatment processes available are provided. In particular, the combined pretreatment strategies are reviewed for improving the enzymatic hydrolysis of lignocellulose and realizing the comprehensive utilization of lignocellulosic materials.

Comparative study of alkali-soluble hemicelluloses isolated from bamboo (Bambusa rigida)

The physicochemical properties and structural characteristics of seven alkali-soluble hemicellulosic preparations were determined. These were extracted from bamboo (Bambusa rigida) with 1M NaOH, KOH, LiOH, NH(3)·H(2)O, (CH(3)CH(2))(3)N, Ca(OH)(2), Ba(OH)(2), respectively, at 50°C for 3h, were comparatively studied. Sugar analysis showed that these hemicelluloses contained d-xylose as the major constituent, along with d-glucose and l-arabinose in noticeable amounts. Uronic acids, principally 4-O-methyl-d-glucuronic acid, occurred in a small amount. Furthermore, based on the sugar analysis and FTIR and NMR spectroscopy, it can be concluded that the hemicelluloses consist of a backbone of β-(1→4)-linked d-xylopyranosyl units having branches of arabinose and 4-O-methyl-d-glucuronic acid. Nitrobenzene oxidation revealed that the hemicelluloses obtained are mostly free of bound lignins. Moreover, it is noteworthy that hemicelluloses isolated with the different alkaline solutions presented different chemical compositions and slightly dissimilar structural features, indicating that alkalinity played an important role in cleaving the chemical linkages between the hemicelluloses and the lignins.

Ultrasound-enhanced extraction of lignin from bamboo (Neosinocalamus affinis): Characterization of the ethanol-soluble fractions

Bamboo was submitted to ultrasound-assisted extraction in aqueous ethanol to evaluate the effect of ultrasonic irradiation on the dissolution of lignin. In this case, the dewaxed bamboo culms were subjected to ball milling for 48 h, and then were suspended in 95% ethanol followed by ultrasonic irradiations for varied times at 20 °C to obtain ethanol-soluble fractions. The structural and thermal properties of the ethanol-soluble fractions were comparatively investigated by chemical analysis including alkaline nitrobenzene oxidation, bound carbohydrate determination, FT-IR spectra, HSQC spectra, TG, and DTA. The results showed that the yields of the ethanol-soluble fractions were between 4.29% and 4.76% for the fractions prepared with ultrasonic irradiation time ranging from 5 to 55 min, as compared to 4.02% for the fraction prepared without ultrasonic irradiation. It was found that the lignin content of the fraction increased with the increase of the ultrasonic irradiation time. There was a slight increase of the molecular weight of the lignin with the increase of the ultrasonic irradiation time. Alkaline nitrobenzene oxidation coupled with HSQC analysis indicated that the lignin in the fractions was mainly composed of GSH type units as well as minor amounts of ferulic acids. In addition, the fraction prepared with ultrasonic irradiation exhibited a slightly higher thermal stability as compared to the fraction prepared without ultrasonic irradiation.

Microwave-assisted organic acid extraction of lignin from bamboo: Structure and antioxidant activity investigation

Microwave-assisted extraction in organic acid aqueous solution (formic acid/acetic acid/water, 3/5/2, v/v/v) was applied to isolate lignin from bamboo. Additionally, the structural features of the extracted lignins were thoroughly investigated in terms of C₉ formula, molecular weight distribution, FT-IR, (1)H NMR and HSQC spectroscopy. It was found that with an increase in the severity of microwave-assisted extraction, there was an increase of phenolic hydroxyl content in the lignin. In addition, an increase of the severity resulted in a decrease of the bound carbohydrate content as well as molecular weight of the lignin. Antioxidant activity investigation indicated that the radical scavenging index of the extracted lignins (0.35-1.15) was higher than that of BHT (0.29) but lower than that of BHA (3.85). The results suggested that microwave-assisted organic acid extraction provides a promising way to prepare lignin from bamboo with good antioxidant activity for potential application in the food industry.

Fractionation of bamboo culms by autohydrolysis, organosolv delignification and extended delignification: Understanding the fundamental chemistry of the lignin during the integrated process

Bamboo (Phyllostachys pubescens) was successfully fractionated using a three-step integrated process: (1) autohydrolysis pretreatment facilitating xylooligosaccharide (XOS) production (2) organosolv delignification with organic acids to obtain high-purity lignin, and (3) extended delignification with alkaline hydrogen peroxide (AHP) to produce purified pulp. The integrated process was comprehensively evaluated by component analysis, SEM, XRD, and CP-MAS NMR techniques. Emphatically, the fundamental chemistry of the lignin fragments obtained from the integrated process was thoroughly investigated by gel permeation chromatography and solution-state NMR techniques (quantitative (13)C, 2D-HSQC, and (31)P-NMR spectroscopies). It is believed that the integrated process facilitate the production of XOS, high-purity lignin, and purified pulp. Moreover, the enhanced understanding of structural features and chemical reactivity of lignin polymers will maximize their utilizations in a future biorefinery industry.

Comparative study of the pyrolysis of lignocellulose and its major components: Characterization and overall distribution of their biochars and volatiles

In order to investigate the pyrolysis differences among lignocellulose and its major components, the biochars and volatiles of lignocellulose (bamboo), lignin, hemicellulose and holocellulose (from bamboo), and cellulose (from cotton linter) were studied using elemental analysis, FTIR, XRD, SEM, Py-GC/MS and TGA-FTIR. Result showed that the biochar yield of lignin (48.8%) was much higher than those of hemicellulose (21.1%), cellulose (8.3%), holocellulose (20.4%) and bamboo (15.1%), while no obvious elemental difference among these biochars was found. Results from Py-GC/MS indicated that carbonyl compounds, ethers and alcohols were the major volatiles of polysaccharide component pyrolysis, while aromatic compounds were the major volatiles of lignin pyrolysis. The pyrolysis of polysaccharide component mainly occurred at 200-400°C, while the pyrolysis of lignin happened at 300-700°C.

Assessment of integrated process based on hydrothermal and alkaline treatments for enzymatic saccharification of sweet sorghum stems.

In this study, sweet sorghum stem was subjected to hydrothermal pretreatment (HTP) and alkaline post-treatment to enhance its saccharification ratio by reducing its recalcitrance. The results showed that the HTP (110-210°C, 0.5-2.0h) significantly degraded hemicelluloses, and the pretreatment at the temperature higher than 190°C led to the partial degradation of the cellulose. As compared to the sole HTP, the integrated process removed most of lignin and hemicelluloses, which incurred a higher cellulose saccharification ratio. Under an optimum condition evaluated (HTP at 170°C for 0.5h and subsequent 2% NaOH treatment), 77.5% saccharification ratio was achieved, which was 1.8, 2.0 and 5.5 times as compared to the only HTP pretreated substrates, alkaline treated substrates alone and the raw material without pretreatment, respectively. Clearly, the integrated process can be considered as a promising approach to achieve an efficient conversion of lignocellulose to fermentable glucose.

Mild acetosolv process to fractionate bamboo for the biorefinery: structural and antioxidant properties of the dissolved lignin.

Fractionation of lignocellulosic material into its constitutive components is of vital importance for the production of biofuels as well as other value-added chemicals. The conventional acetosolv processes are mainly focused on the production of pulp from woody lignocelluloses. In this study, a mild acetosolv process was developed to fractionate bamboo under atmospheric pressure to obtain cellulosic pulp, water-soluble fraction, and acetic acid lignin. The structural features of the lignins obtained under various conditions were characterized with elemental analysis, sugar analysis, alkaline nitrobenzene oxidation, gel permeation chromatography (GPC), (1)H nuclear magnetic resonance ((1)H NMR), and heteronuclear single-quantum coherence (HSQC) spectroscopy. As compared to milled wood lignin (MWL) of bamboo, acetic acid lignins had low impurities (carbohydrates 2.48-4.56%) mainly due to the cleavage of linkages between lignin and carbohydrates. In addition, acetic acid lignins showed a low proportion of syringyl (S) units. Due to the cleavage of linkages between lignin units, acetic acid lignins had weight-average molecular weights ranging from 4870 to 5210 g/mol, less than half that of MWL (13000 g/mol). In addition, acetic acid lignins showed stronger antioxidant activity mainly due to the significant increase of free phenolic hydroxyls. The lignins obtained with such low impurities, high free phenolic hydroxyls, and medium molecular weights are promising feedstocks to replace petroleum chemicals.

Homogeneous Esterification of Poplar Wood in an Ionic Liquid under Mild Conditions: Characterization and Properties

Wood meal was completely dissolved under constant conditions (130 °C, 6 h) in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), and the various factors and potential mechanism of the homogeneous esterification of wood in this reaction medium were mainly studied. The physicochemical properties of the esterified wood were also investigated. It has been shown that highly substituted wood esters could be obtained by reacting wood dissolved in [C(4)mim]Cl with octanoyl chloride in the presence of triethylamine as a neutralizer. The weight percent gain was arranged from 121.5% to 297.4%. All reactions were performed under mild conditions, low excess of reagent, and a short reaction time compared to the heterogeneous chemical modification. Meanwhile, characterization of the derivatives confirmed that the homogeneous esterification was successfully processed. It was also found that thermal stability and morphological properties of the esterified wood were significantly different from those in previous reports. Octanoylation of wood meal in the [C(4)mim]Cl homogeneous system reduced the initial temperature of their thermal degradation and decreased the thermal stability compared to those in unmodified wood meal. Furthermore, the fibrillar appearance of wood meal changed into a relatively more homogeneous macrostructure of the esterfied wood. All these results suggested that homogeneous esterification of poplar wood in [C(4)mim]Cl would enhance the compatibility and improve the processability of wood with synthetic polymers.

Hydrothermal conversion of xylose, glucose, and cellulose under the catalysis of transition metal sulfates.

Hydrothermal conversion (HTC) is an important thermochemical process to upgrade low-cost biomass into valuable chemicals or fuels. As compared with non-catalytic HTC, catalytic HTC shows high energy efficiency on biomass upgradation. In this work, the catalytic performances of various transition metal sulfates (Mn(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), and Zn(2+)) in the HTCs of xylose, glucose, and cellulose under different conditions were explored. Among these catalysts, Zn(2+) and Ni(2+) showed obvious effects on the conversions of xylose, glucose, and cellulose into lactic acid, while Cu(2+) and Fe(3+), which could significantly accelerate the hydrolysis of cellulose into glucose at 200°C, displayed high efficiency on converting glucose and cellulose into levulinic acid and formic acid at high temperature. Additionally, significant positive correlative relationships among xylose, glucose, and cellulose degradations were observed. This study is helpful for screening appropriate catalysts for biomass upgradation through catalytic HTC of monosaccharide.