Simultaneous achievement of efficient hemicellulose separation and inhibition of lignin repolymerization using pyruvic acid treatment

Efficient Separation of Poplar Lignin Using a New Carboxylic Acid-Based Deep Eutectic Solvents - Choline Chloride/Malonic Acid

Separation of lignin by pretreatment is an important step in biomass refining. This study investigated how a novel dicarboxylic acid-based deep eutectic solvent (DES) - choline chloride (ChCl)/malonic acid (MA) - affected the process of separating lignin from poplar. At 140 °C for 3.0 h, with a ChCl: MA molar ratio of 1: 3.5, the ideal pretreatment conditions were met, and 91.8 % lignin was obtained. Even after five DES reuses, the consistent and effective separation efficiency of 77.9 % remains unchanged. The hydrolysate contained 92.4 % of the recovered lignin, with a purity of 94.6 %. Moreover, the regenerated lignin obtained through the new DES pretreatment exhibited a high phenolic hydroxyl content of 1.9 mmol g-1 and a low polydispersity index of 1.4. The results showed efficient and selective separation of lignin using the new binary carboxylic acid-based DES pretreatment was achieved. This research offers a novel approach to effectively separate wood fiber biomass and extract valuable lignin.

Lignin-derived deep eutectic solvent for biomass fractionation based on α,γ-diol lignin stabilization strategy

Overcoming the biomass recalcitrance is crucial for thermal converting raw biomass into high-value chemicals. Consequently, the growing emphasis on sustainable and efficient pretreatment methods has become a key goal of research in the biorefinery field. This study proposes a novel lignin-derived deep eutectic solvent (LDES) pretreatment method to promote biomass pyrolysis based on α,γ-diol lignin stabilization strategy. It effectively deconstructed the complex biomass structure while significantly inhibiting lignin recondensation and undesirable deposition. This process achieved exceptional delignification (97.05 %) and hemicellulose removal (83.09 %), while maintaining 84.12 % of the cellulose, thus facilitating a high levoglucosan yield of 38.93 wt% in subsequent pyrolysis. Additionally, the isolated lignin had a low molecular weight (1873 g/mol) and well-preserved β-O-4 linkages (28.37/100Ar), rendering it ideal for the preparation of platform chemicals and lignin-based materials. This study highlights the potential of tunable and functional LDES as a promising pretreatment solvent, facilitating efficient fractionation and valorization of biomass, and achieving the concept of "closed-loop" biorefinery.

Rapid and efficient separation of eucalyptus hemicellulose by synergistic catalysis of acid and ketone in α-ketoglutaric acid pretreatment

The efficient catalytic hydrolysis and mitigation of unstable structural transitions in lignin are essential for the commercialization of organic acid pretreatment. A novel binary carboxylic acid pretreatment utilizing α-ketoglutaric acid (AKA) was developed, which exploits a distinctive ion-pair biomimetic catalytic mechanism along with the activation of the ketone group. Under optimal AKA pretreatment conditions (5 % acid concentration, 150 °C, 45 min), the hemicellulose separation yield reached 85.21 %. The rapid and efficient separation of eucalyptus hemicellulose results from the low pKa value and the ion-pair biomimetic catalytic mechanism of AKA. The lignin structure exhibited greater integrity (β-O-4: 47.45 %) and a higher phenolic hydroxyl content (1.82 mmol·g-1) compared to conventional binary carboxylic acid pretreatments (maleic and oxalic acids). These findings indicated that the recondensation of lignin, which occurs after the cleavage of aryl-ether bonds during acidic catalysis, was inhibited by the activation of ketone groups during AKA pretreatment. This study introduces an innovative methodology for developing efficient binary carboxylic acid pretreatment procedures focused on selective hemicellulose separation, emphasizing effective catalytic hydrolysis and the maintenance of lignin reactivity.

Fast and sustainable extraction of light-colored lignin using oxalic acid dihydrate: Toward structural elucidation and UV/oxidation resistance

Lignin, an abundant and complex biopolymer, offers significant potential for high-value applications in diverse industries due to its antioxidant and UV-absorbing properties. However, its utilization in cosmetic formulations, particularly sunscreens, is impeded by its dark coloration. Herein, this study introduced an innovative approach for extracting light-colored lignin with well-preserved structure from wheat straw using oxalic acid dihydrate (OAD) under mild conditions. The OAD method significantly improved lignin color, accelerated the extraction process (within 5 min), and emphasized environmental sustainability, representing a marked improvement over traditional technique. Lignin isolated by the OAD method achieved yields up to 91.24 %, with an attractive light color and elevated purity. Comprehensive structural analyses revealed a substantial enrichment in phenolic hydroxyl groups and an advantageous S/G ratio, indicating superior antioxidant and UV-blocking efficacy. The antioxidant capacity, evaluated through DPPH radical scavenging assays, was exceptional, with an IC50 value below 0.1 mg/mL. Moreover, the addition of 5 % OAD-extracted lignin to pure cream indicated that SPF (SPFinvitro = 7.52) was higher than P25 (SPFinvitro = 5.92). This study underscores a highly efficient and environmentally benign method for producing premium, light-colored lignin, advancing its application in natural, sustainable cosmetic formulations.

Optimizing lignin demethylation using a novel proton- based ionic liquid: 1, 2-propanediamine/glycolic acid catalyst

Demethylation modification of lignin is an effective strategy to overcome the barrier to its high-value conversion. The purpose of this study focuses on the new proton-based ionic liquid (PIL) 1, 2-propanediamine/glycolic acid (PD/GA) as a catalyst and solvent to achieve the targeted oxidation of lignin. The PD/GA solvents have higher selectivity and efficiency. Optimal phenolic hydroxyl (PH)-increment was achieved, demonstrating enhanced demethylating effect on lignin by modulating the acid-base molar ratio, reaction temperature, and reaction time. Compared to ethanolamine/acetic acid (CE/AC) treatment, the PD/GA treatment at molar ratio 1.25, temperature 60 °C, and 3 h increased the PH-content from 37.74 to 59.91 %. Additionally, the lignin treated with PD/GA exhibited excellent recyclability, featuring a larger Brunauer-Emmett-Teller surface area (1.45 m2.g-1), total pore volume (9.51*10-3 cm3.g-1), and mesoporous size (26.15 nm). The treated lignin yielded maximum ultraviolet resistance and antioxidant activity. These results present new avenues for the development of green and efficient lignin demethylation methods.

Efficient production of xylooligosaccharides from Camellia oleifera shells pretreated by pyruvic acid at lower temperature

XOS production from lignocellulose using organic carboxylic acids and alkyd acids has been widely reported. However, it still faces harsh challenges such as high energy consumption, high cost, and low purity. Pyruvic acid (PYA), a carbonyl acid with carbonyl and carboxyl groups, was used to produce XOS due to its stronger catalytic activity. In this work, XOS was efficiently prepared from COS in an autoclave under the condition of 0.21 M PYA-121 °C-35 min. The total yield of XOS reached 68.72 % without producing any toxic by-products, including furfural (FF) and 5-hydroxymethylfurfural (5-HMF). The yield of xylobiose (X2), xylotriose (X3), xylotetraose (X4), and xylopentaose (X5) were 20.58 %, 12.47 %, 15.74 %, and 10.05 %, respectively. Meanwhile, 89.05 % of lignin was retained in the solid residue, which provides a crucial functional group for synthesizing layered carbon materials (SRG-a). It achieves excellent electromagnetic shielding (EMS) performance through graphitization, reaching -30 dB at a thickness of 2.0 mm. The use of a PYA catalyst in the production of XOS has proven to be an efficient method due to lower temperature, lower acid consumption, and straightforward operation.

Synthesis of Aminomethylpyridine-Decorated Polyamidoamine Dendrimer/Apple Residue for the Efficient Capture of Cd(II)

Water contamination irritated by Cd(II) brings about severe damage to the ecosystem and to human health. The decontamination of Cd(II) by the adsorption method is a promising technology. Here, we construct aminomethylpyridine-functionalized polyamidoamine (PAMAM) dendrimer/apple residue biosorbents (AP-G1.0-AMP and AP-G2.0-AMP) for adsorbing Cd(II) from aqueous solution. The adsorption behaviors of the biosorbents for Cd(II) were comprehensively evaluated. The maximum adsorption capacities of AP-G1.0-AMP and AP-G2.0-AMP for Cd(II) are 1.40 and 1.44 mmol·g-1 at pH 6. The adsorption process for Cd(II) is swift and can reach equilibrium after 120 min. The film diffusion process dominates the adsorption kinetics, and a pseudo-second-order model is appropriate to depict this process. The uptake of Cd(II) can be promoted by increasing concentration and temperature. The adsorption isotherm follows the Langmuir model with a chemisorption mechanism. The biosorbents also display satisfied adsorption for Cd(II) in real aqueous media. The adsorption mechanism indicates that C-N, N═C, C-O, CONH, N-H, and O-H groups participate in the adsorption for Cd(II). The biosorbents display a good regeneration property and can be reused with practical value. The as-prepared biosorbents show great potential for removing Cd(II) from water solutions with remarkable significance.

Selective separation of hemicellulose from poplar by hydrothermal pretreatment with ferric chloride and pH buffer

As an environmentally friendly lignocellulosic biomass separation technology, hydrothermal pretreatment (HP) has a strong application prospect. However, the low separation efficiency is a main factor limiting its application. In this study, the poplar components were separated using HP with ferric chloride and pH buffer (HFB). The optimal conditions were ferric chloride concentration of 0.10 M, reaction temperature of 150 °C, reaction time of 15 min and pH 1.9. The separation of hemicellulose was increased 34.03 % to 77.02 %. The pH buffering resulted in the highest cellulose and lignin retention yields compared to ferric chloride pretreatment (FC). The high efficiency separation of hemicellulose via HFB pretreatment inhibited the degradation of xylose. The hydrolysate was effectively reused for five times. The fiber crystallinity index reached 60.05 %, and the highest C/O ratio was obtained. The results provide theoretical support for improving the efficiency of HP and promoting its application.