Ming-Fei Li

Recent advances in alcohol and organic acid fractionation of lignocellulosic biomass

Organosolv fractionation is a promising process to separate lignocellulosic biomass for the preparation of multiply products including biofuels, chemicals, and materials. This review presents the state of art of different processes applying alcohols and organic acids to treat lignocellulosic biomass for the production of ethanol, lignin, xylose, etc. The major organosolv technologies using ethanol, formic acid, and acetic acid, are intensively introduced and discussed in depth. In addition, the structural modifications of the major components of lignocelluloses, the technical processes, and the applications of the products were also summarized. The object of the review is to provide recent information in the field of organosolv process for the integrated biorefinery. The perspectives of the challenge and opportunity related to this topic are also presented.

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.

Enhanced enzymatic hydrolysis of bamboo (Dendrocalamus giganteus Munro) culm by hydrothermal pretreatment.

Bamboo was non-isothermally pretreated with hot water at 140-200°C for different times (10-120 min). The effects of pretreatment conditions on the degradation of carbohydrates, cellulose crystallinity, partial removal/relocation of lignin, morphologic change of the feedstock, and glucose yield during the enzymatic hydrolysis were investigated. The effective removal of amorphous cellulose and hemicelluloses led to the increase of crystalline index of the residues. In comparison with the raw material, the surface of the pretreated samples was irregular and numerous lignin droplets appeared on the cellulose bundle surface under the intense pretreatment conditions. The glucose conversion increased with the raise of pretreatment temperature and the prolongation of time, and the maximum conversion of 75.7% was achieved for the sample pretreated at 200°C for 120 min, whereas the untreated sample was only 15.7%. The result illustrated that hydrothermal pretreatment affected the composition of bamboo, and remarkably enhanced the enzymatic hydrolysis efficiency.

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.

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.

Hydrothermal degradation of lignin: Products analysis for phenol formaldehyde adhesive synthesis

Corncob lignin was treated with pressurized hot water in a cylindrical autoclave in current investigation. With the aim of investigating the effect of reaction temperature and retention time on the distribution of degradation products, the products were divided into five fractions including gas, volatile organic compounds, water-soluble oil, heavy oil, and solid residue. It was found that hydrothermal degradation of corncob lignin in pressurized hot water produced a large amount of phenolic compounds with lower molecular weight than the raw lignin. Some phenolic and benzene derivatives monomers such as vanillin, 2-methoxy-phenol, 2-ethyl-phenol, p-xylene, and 1, 3-dimethyl-benzene were also identified in the degradation products. The products were further analyzed by GC-MS, GPC, 2D-HSQC, and (31)P-NMR to investigate their suitability for partial incorporation into phenol formaldehyde adhesive as a substitution of phenol. The results indicated that the reaction temperature had more effect on the products distribution than the retention time. The optimal condition for heavy oil production appeared at 290 °C with retention time 0 min. The compounds of heavy oil had more active sites than the raw lignin, suggesting that the heavy oil obtained from hydrothermal degradation of lignin is a promising material for phenol formaldehyde adhesive synthesis.

InCl3-catalyzed conversion of carbohydrates into 5-hydroxymethylfurfural in biphasic system

InCl3, a water-compatible Lewis acid, was used for the conversion of microcrystalline cellulose to produce 5-hydroxymethylfurfural (HMF) in a H2O/THF biphasic system. Addition of NaCl increased the HMF yield significantly but suppressed the levulinic acid (LA) formation. The HMF yield of 39.7% was obtained in 2h at 200°C in the NaCl-H2O/THF catalytic system catalyzed by InCl3. The catalytic system also showed effectiveness to convert other carbohydrates to HMF, including glucose, fructose, sucrose, starch, which demonstrated great potential towards different feedstocks.

Structural Differences between the Lignin-Carbohydrate Complexes (LCCs) from 2- and 24-Month-Old Bamboo (Neosinocalamus affinis)

The lignin-carbohydrate complex (LCC) was isolated from milled wood lignin of 2- and 24-month-old crude bamboo (Neosinocalamus affinis) culms using acetic acid (AcOH) and then characterized. The results have shown that the LCC preparation from 2-month-old bamboo (L2) exhibited a slightly lower molecular weight than the LCC preparation from the 24-month-old bamboo (L24). Further studies using Fourier transform infrared spectroscopy (FT-IR) and heteronuclear single quantum coherence (2D-HSQC) NMR spectra analyses indicate that the LCC preparations included glucuronoarabinoxylan and G-S-H lignin-type with G>S>>H. The content of the S lignin units of LCC in the mature bamboo was always higher than in the young bamboo. Combined with sugar composition analysis, the contents of phenyl glycoside and ether linkages in the L24 preparation were higher than in the L2 preparation; however, there was a reverse relationship of ester LCC bonds in L2 and L24. Lignin–xylan was the main type of LCC linkage in bamboo LCCs. Lignin–lignin linkages in the LCC preparations included β-β, β-5 and β-1 carbon-to-carbon, as well as β-O-4 ether linkages, but β-1 linkages were not present in L2.

Effect of ionic liquid pretreatment on the structure of hemicelluloses from corncob.

Pretreatment is the key to unlock the recalcitrance of lignocellulosic biomass for the productions of biofuels. Ionic liquid pretreatment has drawn increased attention because of its numerous advantages over conventional methods. In this study, corncob was submitted to pretreatments with 1-ethyl-3-methylimadazolium acetate (EMIMAc) and/or H(2)O/dimethyl sulfoxide (DMSO) followed by alkaline extraction to isolate hemicelluloses. The hemicellulosic fractions obtained were comprehensively characterized with a series of chemical and spectroscopic technologies, including gel permeation chromatography (GPC), thermogravimetric analysis (TGA), high-performance anion-exchange chromatography (HPAEC), Fourier transform infrared (FTIR) spectroscopy, and one- and two-dimensional nuclear magnetic resonance (NMR). The results showed that the fractions prepared with ionic liquid pretreatments exhibited relatively higher average molecular weights (196,230-349,480 g/mol) than the fraction prepared without pretreatment (M(w), 96,260 g/mol). Furthermore, the pretreated fractions demonstrated higher thermal stability compared to the fractions without pretreatment. Structural characterization indicated that all of the fractions had similar structures, which are composed of a (1 → 4)-linked β-D-xylopyranosyl backbone substituted with arabinofuranosyls attached to O-2 and O-3 and with 4-O-methyl-α-D-glucuronic acid also linked to O-2.

Fractionation of rapeseed straw by hydrothermal/dilute acid pretreatment combined with alkali post-treatment for improving its enzymatic hydrolysis

The aim of the research was to evaluate the effect of combined treatments on fermentable sugar production from rapeseed straw. An optimum condition was found to be the combination of hydrothermal pretreatment at 180°C for 45min and post-treatment by 2% NaOH at 100°C for 2h, which was based on the quantity of monosaccharides released during enzymatic hydrolysis. As compared with the raw material without treatment, the combination of hydrothermal pretreatment and alkali post-treatment resulted in a significant increase of the saccharification rate by 5.9times. This process potentially turned rapeseed straw into value added products in accordance with the biorefinery concept.