The structure and properties of lignin isolated from various lignocellulosic biomass by different treatment processes.

The structure and properties of lignin can vary depending on the type of lignocellulosic biomass it comes from and the separation techniques used, and also affects its suitability for different applications. In this work, the structure and properties of lignin isolated from moso bamboo, wheat straw, and poplar wood by different treatment processes were compared. Results show that deep eutectic solvent (DES) extracted lignin exhibits well-preserved structures (including ß-O-4, ß-ß, and ß-5 linkages), a low molecular weight (Mn = 2300-3200 g/mol), and relatively homogeneous lignin fragments (1.93 < PDI < 2.33) compared to dealkaline lignin (DL) and milled wood lignin (MWL). Besides, lignin samples extracted by DES have a regular nanostructure, higher carbon residue content (>40 %), and excellent antioxidant properties (the free radical scavenging index >20). Among the three types of biomass, the structural destruction of lignin in straw is the most obvious, which is due to the degradation of ß-O-4 and ß-ß linkages during DES treatment. These findings can contribute to a better understanding of the structural changes that occur in various treatment processes from different lignocellulosic biomass, and help maximize the targeted development of their applications based on the characteristics of lignin.

Multistage treatment of bamboo powder waste biomass: Highly efficient and selective isolation of lignin components.

Bamboo pulp and papermaking produce a lot of bamboo powder waste, and its resource utilization is of great significance for biomass refining and environmental protection. Here, we propose an integrated approach involving mechanical activation, hydrothermal extraction, and deep eutectic solvents (DESs) multiple delignification for the efficient separation of bamboo powder. Among seven carboxylic acids based DESs, choline chloride (ChCl)-lactic acid (La) DES (1:1) is the most effective, with over 78.0% lignin removal and 88.9% cellulose retained after mechanical-hydrothermal (180 °C, 5 h)-DES (110 °C, 12 h) treatment. Notably, 84.7% of delignification is achieved after three times of ChCl-La DES treatment at 70, 90, and 110 °C respectively. The delignification rate is negatively correlated with the amount of carboxyl group in the DESs. The lower the pKa value, the higher the delignification rate. Additionally, the selectivity for lignin is improved with decreasing solvent polarity. DES treatment effectively degrades the guaiacyl unit lignin fractions and disrupts several ß-aryl-ether bonds (e.g., ß-O-4, ß-ß, and ß-5). Furthermore, DESs exhibit good recyclability, with less than 10% reduction in delignification after three cycles. Theory calculations confirm that ChCl-carboxylic acid DESs could compete with lignin to break hydrogen bonds in lignocellulosic biomass by providing their chloride, hydroxyl, and carboxyl groups. Overall, this study demonstrates the practical significance of multistage treatment for the effective fractionation of biomass into its three components.

Enhanced hydrolysis of mechanically pretreated cellulose in water/CO2 system.

The aim of this work was to study promotion of ball milling and CO2 assistance on cellulose hydrolysis kinetics in water medium. Kinetic behaviors were analyzed based on first-order and shrinking core models. The results showed that cellulose hydrolysis is enhanced by ball milling and CO2 assistance. Ball milling reduced crystallinity and particle size of cellulose, resulting in high cellulose conversion, while hydrolysis promoted by CO2 assistance was weaker. Double-layer hydrolysis was observed for ball-milled cellulose, and rate constant in active layer is higher. Based on double-layer shrinking core model (DL-SCM), activation energy of cellulose conversion decreased from 73.6 to 39.8 kJ/mol when ball milling and CO2 assistance were applied. Hydrolysis active layer was about 0.9 µm, representing activated thickness of ball-milled cellulose. Hydrolysis promotion by crystallinity and particle size reduction was distinguished via DL-SCM, and crystal evolution possesses greater improvement than particle size decrease on hydrolysis of ball-milled cellulose.