Lignin is a type of biomass that is generally found in nature and has a wide range of applications as a functional material. A novel sorbent, aminated lignin (AL), was synthesized in a one-step method to improve its adsorption capabilities. The AL was characterized through Brunauer–Emmett–Teller surface area analysis, thermogravimetric analysis, scanning electron microscopy, and zeta potential analysis. AL was small in size and had a clear obvious porous structure with a surface area of 47.1 m²·g⁻¹, nearly ten times larger than that of kraft lignin, which was 4.75 m²·g⁻¹. AL was utilized for the adsorption of cationic dyes (crystal violet, CV) and anionic dyes (Congo red, CR) from aqueous solutions. The maximum CV and CR adsorption of AL at 25 °C were 97.09 and 129.87 mg·g⁻¹, respectively. Five factors affecting adsorption including adsorption time, pH of dyes, initial dye concentration, AL dosage, and adsorption temperature were investigated. The fitting results of the two dyes revealed that the adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm equation. This study demonstrates that AL can be used as a low-cost adsorbent for both cationic and anionic dyes from wastewater.

The crystalline structure is a biomass recalcitrance factor that hinders chemical or biological access to degrade the plant cell-wall structure. However, controversy persists over whether a ratio of the crystalline region, the crystallinity index, is a critical biomass recalcitrance factor. In this study, an alkaline treatment modified from mercerization was adopted to alleviate the crystalline structure in the xylem of eucalyptus, along with hemicellulose and lignin removal via autohydrolysis and acid–chlorite treatment, respectively. Then, the glucose yield of the treated solid residues was used as a parameter of biomass recalcitrance. The alkaline treatment successfully reduced the crystallinity index, and the maximal reduction ratio was 84.9% when using an 8% sodium hydroxide solution. However, the reduction ratio of the crystallinity index was dependent on the remaining lignin content in the treated solid residues. Additionally, the lignin removal ratio showed critical influence to improve the glucose yield that was even observed in the treated solid residue having a low reduction ratio of the crystallinity index. Consequently, the cellulose crystalline structure is minimally involved with biomass recalcitrance, especially cellulase activity, at least in eucalyptus.

This study optimizes furfural production from pentose released in the liquid hydrolysate of hardwood using an aqueous biphasic system. Dilute acid pretreatment with 4% sulfuric acid was conducted to extract pentose from liquid Quercus mongolica hydrolysate. To produce furfural from xylose, a xylose standard solution with the same acid concentration of the liquid hydrolysate and extracting solvent (tetrahydrofuran) were applied to the aqueous biphasic system. A response surface methodology was adopted to optimize furfural production in the aqueous biphasic system. A maximum furfural yield of 72.39% was achieved at optimal conditions as per the RSM; a reaction temperature of 170 °C, reaction time of 120 min, and a xylose concentration of 10 g/L. Tetrahydrofuran, toluene, and dimethyl sulfoxide were evaluated to understand the effects of the solvent on furfural production. Tetrahydrofuran generated the highest furfural yield, while DMSO gave the lowest yield. A furfural yield of 68.20% from pentose was achieved in the liquid hydrolysate of Quercus mongolica under optimal conditions using tetrahydrofuran as the extracting solvent. The aqueous and tetrahydrofuran fractions were separated from the aqueous biphasic solvent by salting out using sodium chloride, and 94.63% of the furfural produced was drawn out through two extractions using tetrahydrofuran.