•Milled solid residue was isolated from residue.•Acid insoluble residue increased after 220 °C.•Milled solid residue was mainly re-polymerization fraction.Cornstalk liquefaction in sub- and super-critical ethanol was carried out in an autoclave at various temperatures. The characteristics of solid residue were investigated by XRD and sugar analysis. Milled solid residue fraction was isolated from the solid residue, and its chemical characteristics were comparatively investigated with milled wood lignin of cornstalk by gel permeation chromatography, FT-IR, and 2D HSQC NMR. The results showed that the structure of xylan in cornstalk was not broken down completely under the reaction temperatures and those liquefaction conditions were unable to break effectively apart the inter/intra chain hydrogen bonding in cellulose fibrils. Characterization of milled solid residue showed that the de-polymerization of lignin was more dominant than the re-polymerization as reaction temperature increased from 180 to 300 °C. The β-O-4, ferulate, tricin substructures almost disappeared from the spectrum of milled solid residue, which indicated the re-polymerization or decomposition of those bonds in lignin during cornstalk liquefaction process. The result showed that characterization of solid residue fractions provided some new information of the mechanisms about cornstalk liquefaction in ethanol.

•Atmospheric pressure pretreatment was developed for a second-generation biofuel.•The pretreatment media were formic acid and alkaline H2O2 aqueous solution.•Pretreatment caused effective removal of recalcitrant components.•A high conversion rate of cellulose into glucose (99.36%) was achieved.•The lignin obtained exhibited great potential to produce liquid fuel.For the production of the second generation bioethanol, enzymatic saccharification to prepare a high yield of fermentable sugars is an essential step for the conversion of energy from lignocellulose. In this case, a mild two-step pretreatment using anhydrous formic acid and alkaline hydrogen peroxide aqueous solution was developed to fractionate lignocellulose to highly digestible cellulose for enzymatic saccharification as well as value-added lignin. Bamboo was pretreated with anhydrous formic acid at 40–100 °C for 4 h and then extracted with alkaline hydrogen peroxide aqueous solution (containing 1% NaOH and 1% H2O2) at 80 °C for 2 h. The lignin dissolved in anhydrous formic acid was isolated and further treated with the alkaline solution obtained from the pretreatment and then recovered. The produced cellulose residue had a rather high conversion rate of cellulose into glucose (99.36%) under an enzymatic hydrolysis for 72 h. In addition, the lignin obtained preserved good functionalities, which exhibited great potential to produce liquid fuels, thus implementing the philosophy of biorefinery. The results indicated that the two-step formic acid-alkaline hydrogen peroxide pretreatment effectively broke the recalcitrant nature of lignocellulose, producing a good feedstock for the conversion into energy.Download high-res image (66KB)Download full-size image

Bamboo was hydrothermally torrefied in hydrochloric acid solution assisted by microwave heating at 180 °C for 5–30 min. For bamboo torrefied in water, the yield of the torrefied bamboo decreased slightly from 96.15% to 85.83% and the hemicellulose content decreased from 31.78% to 25.71% with increased torrefaction severity from 3.27 to 3.89. Whereas for bamboo torrefaction in acid solutions, the yield of the torrefied bamboo was below 51% and hemicellulose was completely removed as evidenced by the fact that the solid residue contained no hemicellulose. The carbon content of bamboo was 48.82% and it increased slightly after torrefaction in water. It raised largely up to 67.03% under torrefaction with 0.4 M HCl solution at 180 °C for 30 min. The atomic H/C and O/C ratios of bamboo were 1.479 and 0.694, and as bamboo was wet torrefied, they were in the range of 0.891–1.454 and 0.313–0.676, respectively. The higher heating value (HHV) of the torrefied bamboo increased by 45.20% after torrefaction at 0.2 M HCl for 30 min, which (24.86 MJ kg–1) was higher than that of Converse School-Sub C coal (21.67 MJ kg–1) and comparable with that of German Braunkohole lignite (25.10 MJ kg–1). In addition, the structural modifications of bamboo during the torrefaction process were investigated by chemical component and elemental analyses, CP/MAS 13C NMR, FTIR, XRD complemented with TG/DTA.Keywords: Bamboo; Higher heating value; Hydrochloric acid; Structural modification; Wet torrefaction;

Bamboo was hydrothermally carbonized in a batch reactor using an oxalic acid solution at 190 °C for the production of hydrochar and aqueous products. The influences of oxalic acid concentration and retention time were examined, and the products obtained were characterized in terms of energy yield, chemical components and structural properties. It was found that the energy densification values at a high acid concentration of 0.8 mol L−1 were comparable to those of most torrefied lignocelluloses. No hemicelluloses were detected in the hydrochar obtained under the conditions of highest severity (0.8 mol L−1 acid concentration and 20 min), indicating that the lignocellulose hemicelluloses were completely removed. In addition, cellulose also showed some degradation; the highest degradation rate of cellulose was 56.69% at the highest carbonization severity. The lignin content showed an increasing trend in the hydrochar with increasing carbonization severity. The thermal stability of the hydrochar increased with the carbonization severity. The aqueous solution obtained had a high antioxidant capacity with a inhibition rate of 63.5% for 2,2-diphenyl-1-picrylhydrazyl, higher than that of a commercial antioxidant, butylated hydroxytoluene (46.4%). The present study indicated that the hydrothermal carbonization of bamboo produced a solid hydrochar with high potential for fuel applications and degraded chemicals with high potential as antioxidants.

Lignin was modified through incorporation of lipophilic and hydrophilic groups for the preparation of a surfactant. In this case, alkaline lignin reacted with dodecyl glycidyl ether in the presence of dimethyl benzyl amine to incorporate lipophilic long alkyl chains, and then sulfonated with chlorosulfonic acid for the introduction of hydrophilic sulfonic acid groups. Results showed that the reaction between dodecyl glycidyl ether and carboxy group in lignin was the predominant reaction at 95–110 °C. It was found that the surface tension of the synthesized lignin surfactant solution was lower than that of commercial surfactant sodium dodecylbenzenesulphonate when the concentration was below 0.4%, indicating that the surfactant prepared from alkaline lignin had a good surface activity. A lowest critical micelle concentration of 0.50 g L−1 and the corresponding surface tension at 29.17 mN m−1 were achieved when the surfactant was derived from the lignin grafted with dodecyl glycidyl ether at 110 °C. The anionic lignin surfactants prepared in this study are a promising feedstock as detergents or to enhance oil recovery.

A novel integrated process with ambient formic acid combining alkaline hydrogen peroxide was developed to achieve efficient delignification of furfural residue. Furfural residue was treated with 88% formic acid at room temperature for 0.5 h followed by post-treatment with 1% alkaline hydrogen peroxide at 80 °C for 1.5 h. Results showed that 87.9% of the original lignin was removed and the solid residue obtained contained 84.6% cellulose. The glucose yield of the solid residue increased to 83.7% after 96 h enzymatic hydrolysis under a low enzymatic loading of 7 FPU/g cellulose. The analysis of the physicochemical property of the solid residue and lignin fractions indicated that there was an unapparent effect on formylation of cellulose during the ambient formic acid treatment, and the lignin rich in phenolic and carboxylic OH was easily removed. The insoluble-formsovl lignin in solid residue was effectively removed by alkaline hydrogen peroxide treatment.

•Bamboo was valorized by γ-valerolactone/acid/water.•Digestible cellulose, degraded sugars and lignin were obtained.•Enzymatic hydrolysis was enhanced by 6.7-fold after treatment.•The lignin obtained had high purity, low molecular weight and polydispersity.A novel pretreatment process was developed to achieve valorization of bamboo components into digestible cellulose, degraded sugars and lignin. In this case, bamboo was pretreated with 60% γ-valerolactone (GVL)/40% water containing 0.05 mol/L H2SO4, yielding solid fraction rich in cellulose. The resulting liquor was further treated with the addition of NaCl and ultrasound, resulting in water phase rich in degraded sugars and GVL phase containing lignin, which was easy to recover. Results showed that the enzymatic hydrolysis was enhanced by 6.7-fold after treatment as compared to the control. The degraded sugars released in water phase contained monosaccharides (70.72–160.47 g/kg) together with oligo- and polysaccharides (46.4–181.85 g/kg). The lignin obtained had high purity, low molecular weight (1820–2970 g mol−1) and low polydispersity (1.93–1.98). The present study creates a novel pretreatment process for the conversion of Gramineae biomass into useful feedstocks with potential applications in the fields of fuels, chemicals and polymers.Download high-res image (139KB)Download full-size image

•Poplar was torrefied under carbon dioxide at 240–320 °C for 30–120 min.•Temperature showed a greater influence on mass and energy yields than time.•Torrefaction led to substantial changes of the structural properties of poplar.•Combustion reactivity increased to 4.98%/(min °C) after torrefaction.Populus tomentosa was torrefied under carbon dioxide in a tubular reactor to investigate the effects of temperature (240–320 °C) and reaction time (30–120 min) on the solid char. The influences of the reaction conditions on mass yield, energy yield and higher heating value (HHV) were investigated by using response surface methodology. The structural and thermal properties of the torrefied poplar were comprehensively characterized with multiple techniques. Results indicated that torrefaction temperature showed a greater influence on mass yield, energy yield and HHV than time. Torrefaction led to substantial changes of the structural properties of poplar, as evidenced by the variation of microstructure, elements, and CrI value. The torrefied sample showed good thermal stability as determined by the thermal analysis. In addition, the combustion reactivity increased from 4.13%/(min °C) in the raw material to 4.98%/(min °C) for the sample subjected to torrefaction at 280 °C for 75 min. The data provides meaningful insight on the upgradation of poplar through torrefaction.