Revealing the influence of metallic chlorides pretreatment on chemical structures of lignin and enzymatic hydrolysis of waste wheat straw

Improved enzymatic saccharification of bulrush via an efficient combination pretreatment

Glycerol (Gly) was selected as hydrogen-bond-donor for preparing ChCl-based DES (ChCl:Gly), and the mixture of ChCl:Gly (20 wt%) and NaOH (4 wt%) was utilized for combination pretreatment of bulrush at 100 °C for 60 min (severity factor LogRo = 1.78). The effects of DES pretreatment on the chemical composition, microstructure, crystal structure, and cellulase hydrolysis were explored. NaOH-ChCl:Gly could remove lignin (80.1%) and xylan (66.8%), and the enzymatic digestibility of cellulose reached 87.9%. The accessibility of bulrush was apparently increased to 645.2 mg/g after NaOH-ChCl:Gly pretreatment. The hydrophobicity and lignin surface area were reduced to 1.56 L/g and 417 m2/g, respectively. The crystallinity of cellulose was increased from 20.8% to 55.6%, and great changes in surface morphology were observed, which explained the improvement of enzymatic hydrolysis efficiency. Overall, DES combined with alkali treatment could effectively promote the removal of lignin and xylan in bulrush, thus the relative saccharification activity was greatly affected.

In-depth investigation of formic acid pretreatment for various biomasses: Chemical properties, structural features, and enzymatic hydrolysis

Formic acid pretreatment is a promising approach for fractionating biomass, and it has the advantages of efficient recycling and removal of hemicellulose and lignin. Biomass is one of the most plentiful resources on earth, yet its chemical structure differs significantly between woody and herbaceous biomass. The influence of formic acid pretreatment on the fractionation of woody and herbaceous biomasses, as well as changes in physical-chemical properties, was investigated in this study. The results indicated that formic acid is universal in the biorefinery of different biomass, however, herbaceous biomass had greater xylan and lignin removal than woody biomass (especially softwood). Formic acid pretreatment not only considerably improved the enzymatic efficiency of herbaceous biomass, but also had a good effect on the enzymatic efficiency of poplar. This study also found that the correlation between residual xylan content and enzymatic efficiency after pretreatment was much higher than that of lignin content.

Efficient depolymerization of lignin through microwave-assisted Ru/C catalyst cooperated with metal chloride in methanol/formic acid media

Lignin, an abundant aromatic biopolymer, has the potential to produce various biofuels and chemicals through biorefinery activities and is expected to benefit the future circular economy. Microwave-assisted efficient degradation of lignin in methanol/formic acid over Ru/C catalyst cooperated with metal chloride was investigated, concerning the effect of type and dosage of metal chloride, dosage of Ru/C, reaction temperature, and reaction time on depolymerized product yield and distribution. Results showed that 91.1 wt% yield of bio-oil including 13.4 wt% monomers was obtained under the optimum condition. Yields of guaiacol-type compounds and 2,3-dihydrobenzofuran were promoted in the presence of ZnCl₂. Formic acid played two roles: (1) acid-catalyzed cleavage of linkages; (2) acted as an in situ hydrogen donor for hydrodeoxygenation in the presence of Ru/C. A possible mechanism for lignin degradation was proposed. This work will provide a beneficial approach for efficient depolymerization of lignin and controllable product distribution.

Efficient utilization of waste wheat straw through humic acid and ferric chloride co-assisted hydrothermal pretreatment for fermentation to produce bioethanol

The adsorbed ash and lignin contained in waste wheat straw (WWS) have been the essential factors restricting its high-value utilization in biorefinery. Hence, humic acid (HA) and FeCl3 as the additives of hydrothermal pretreatment were applied to simultaneously enhance the removal of lignin and eliminate the acid buffering of ash in WWS, respectively. The results showed that the xylan and lignin removal of WWS pretreated with 10 g/L HA and 20 mM FeCl3 could be efficiently increased from 61.4% to 72.9% and from 14.7% to 38.7%, respectively. The enzymatic hydrolysis efficiency and ethanol yield of WWS were increased this way from 44.4% to 82.7% and from 20.55% to 36.86%, respectively. According to the characterization of WWS, the synergistic interaction between HA and FeCl3 was beneficial to the cellulose accessibility and surface lignin area of WWS changed in positive directions, leading to the improvement of hydrolysis efficiency.

The Effect of Ball Milling Time on the Isolation of Lignin in the Cell Wall of Different Biomass

Ball milling technology is the classical technology to isolate representative lignin in the cell wall of biomass for further investigation. In this work, different ball milling times were carried out on hardwood (poplar sawdust), softwood (larch sawdust), and gramineous material (bamboo residues) to understand the optimum condition to isolate the representative milled wood lignin (MWL) in these different biomass species. Results showed that prolonging ball milling time from 3 to 7 h obviously increased the isolation yields of MWL in bamboo residues (from 39.2% to 53.9%) and poplar sawdust (from 15.5% to 35.6%), while only a slight increase was found for the MWL yield of larch sawdust (from 23.4% to 25.8%). Importantly, the lignin substructure of ß-O-4 in the MWL samples from different biomasses can be a little degraded with the increasing ball milling time, resulting in the prepared MWL with lower molecular weight and higher content of hydroxyl groups. Based on the isolation yield and structure features, milling time with 3 and 7 h were sufficient to isolate the representative lignin (with yield over 30%) in the cell wall of bamboo residues and poplar sawdust, respectively, while more than 7 h should be carried out to isolate the representative lignin in larch sawdust.

The Interplay of Autoclaving with Oxalate as Pretreatment Technique in the View of Bioethanol Production Based on Corn Stover

Bio-based treatment technologies are gaining great interest worldwide, and significant efforts are being afforded to develop technology for the use of lignocellulosic biomass. The potential of corn stover (CS) as a feedstock for bioethanol production was investigated by creating an optimal pretreatment condition to maximize glucose production. The current study undertook the impact of novel physico-chemical pretreatment methods of CS, i.e., autoclave-assisted oxalate (CSOA) and ultrasound-assisted oxalate (CSOU), on the chemical composition of CS and subsequent saccharification and fermentation for bioethanol production. The delignification was monitored by physicochemical characterizations such as SEM, XRD, FTIR, CHNs, and TGA. The results evidenced that delignification and enzymatic saccharification of the CS pretreated by CSOA was higher than CSOU. The optimum enzymatic saccharification operating conditions were 1:30 g solid substrate/mL sodium acetate buffer at 50 °C, shaking speed 100 rpm, and 0.4 g enzyme dosage. This condition was applied to produce glucose from CS, followed by bioethanol production by S. cerevisiae using an anaerobic fermentation process after 72 h. S. cerevisiae showed high conversion efficiency by producing a 360 mg/dL bioethanol yield, which is considered 94.11% of the theoretical ethanol yield. Furthermore, this research provides a potential path for waste material beneficiation, such as through utilizing CS.