Low-acid hydrothermal (LAH) fractionation conditions were optimized for the effective degradation of hemicellulose from pine wood (Pinus densiflora). The hemicellulosic sugar yield was maximized at 82.5% when the pine wood was fractionated at 190 °C, with 0.5 wt.% of sulfuric acid, and for 10 min. Consecutively, acidified heat treatment with zinc chloride and solvent extraction with ethyl acetate were carried out for the recovery of bio-based platform chemicals, such as furfural and acetic acid, from liquid hydrolysate through liquid–liquid extraction (LLE). Overall, 61.5% of xylose was decomposed into furfural, and the yield of acetic acid was 62.3% and furfural 66.1%. After LAH fractionation, 64.8% of the solid remained and was pelletized. The pellets showed excellent fuel characteristics, i.e., significant ash rejection (74.5%) and high calorific values (4770 kcal/kg), and the precursors of NO_x and SO_x also decreased by up to 60.0% and 71.4%, respectively.

The parameters of the alkaline fractionation process were investigated and optimized using a statistical analysis method to simultaneously remove hemicellulose and ash from rice husk (RH) concomitantly. After the alkaline fractionation process, the residual solid contained high cellulose, and the recovery yield of hemicellulose was enhanced in the fractionated liquid hydrolyzate. The hemicellulosic sugar recovery yield (71.6%), de-ashing yield (>99%), and lignin removal (>80%) were obtained at the reaction conditions of 150 °C of temperature, 40 min of reaction time, and 6% (w/v) of NaOH concentration. Subsequently, nano-structured silica was synthesized using black liquor obtained as a by-product of this fractionation process. For the production of nano-structured silica, it was observed that the pH of a black liquor and the heat treatment temperature significantly influenced the textural properties of silica product. In addition, the two-stage bleaching of solid residue followed by colloid milling for the production of high value-added CNF with was attempted. As a result, in addition to 119 g of fermentable sugar, 143 g of high-purity (>98%) silica with a surface area of 328 m²g⁻¹ and 273.1 g of high-functional CNF with cellulose content of 80.1% were simultaneously obtained from 1000 g of RH.

The alkaline fractionation of rice husk (RH) with NaOH was optimized for the purpose of obtaining a high-yield recovery of glucan and increasing the removal rate for lignin and ash, resulting in a hemicellulose-rich hydrolysate. The determined optimal conditions were a temperature of 150 °C, reaction time of 45 min, and NaOH concentration of 6% (w/v). The glucan content in the fractionated RH (Fr. RH) was 80.1%, which was significantly increased compared to the raw RH (35.6%). High glucan content in the fractionated solid residue is the most essential factor for minimizing enzyme dosages in enzymatic saccharification. The final enzymatic digestibilities (at 96 h) of raw and NaOH-Fr. RH with cellulase loadings of 30 FPU/g cellulose were 10.5% and 81.3%, respectively. Approximately 71.6% of the xmg content (mainly xylose) was concomitantly degraded into the fractionated hydrolysate (Fr. Hydrolysate). When this hydrolysate was acidified with sulfuric acid and subjected to heat treatment, a furfural production yield of about 64.9% was obtained. The results show that two-stage fed-batch fermentation with glucan-rich Fr. RH has the potential to achieve high-ethanol titers of 28.7 g/L.

This study determined the optimal production of furfural (FuR) from liquid hydrolysate xylan liquor obtained through a two-stage pretreatment process using NaOH for de-ashing and EtOH for the delignification of raw rice husk (RH). The de-ashing pretreatment was conducted at 150 °C, with 6.0% (w/v) NaOH and a reaction time of 40 min. The optimal conditions for delignification pretreatment, performed using an organosolv fractionation method with EtOH, were a reaction temperature of 150 °C, 60% (v/v) EtOH, 0.25% (w/v) H₂SO₄, and a reaction time of 90 min. Through a two-stage pretreatment process, a liquid hydrolysate in the form of xylan liquor was obtained, which was subjected to an acid catalytic conversion process to produce FuR. The process conditions were varied, with reaction temperatures of 130–170 °C, H₂SO₄ catalyst concentrations of 1.0–3.0 wt.%, and reaction times of 0–90 min. The Response Surface Methodology tool was used to identify the optimal FuR yield from xylan liquor. Ultimately, the optimal process conditions for the acid catalytic conversion were found to be a substrate-to-catalyst ratio of 2:8, a reaction temperature of 168.9 °C, a catalyst concentration of 1.9 wt.%, and a reaction time of 41.24 min, achieving an FuR yield of 67.31%.