Structural characterization of residual hemicelluloses from hydrothermal pretreated Eucalyptus fiber

Structural analysis and biological activity of cell wall polysaccharides and enzyme-extracted polysaccharides from pomelo (Citrus maxima (Burm.) Merr.)

Pomelo peel is a valuable source of pectin, but research on its cell wall polysaccharides is limited. This study compared the cell wall polysaccharides of pomelo peel, enzyme-extracted polysaccharides of pomelo peel, and enzyme-extracted polysaccharides of whole pomelo fruit. Cell wall polysaccharides, including water-soluble pectin (WSP), chelator-soluble pectin (CSP), sodium carbonate-soluble pectin (NSP), 1 mol/L KOH soluble hemicellulose (KSH-1), and 4 mol/L KOH soluble hemicellulose (KSH-2), were obtained by sequence-extraction method. Total polysaccharides from whole pomelo fruit (TP) and peel-polysaccharides from pomelo pericarps (PP) were obtained using enzyme-extraction method. The structural, thermal, rheological, antioxidant properties, and wound healing effect in vitro were described for each polysaccharide. WSP had a uniform molecular weight distribution and high uronic acid (UA) content, suitable for commercial pectin. NSP had the highest Rhamnose (Rha)/UA ratio and a rich side chain with highest viscosity and water retention. PP displayed the highest DPPH radical scavenging activity and reducing capacity at 0.1 to 2.0 mg/mL concentration range, with an IC50 of 1.05 mg/mL for DPPH free radicals. NSP also demonstrated the highest hydroxyl radical scavenging activity and promoted Human dermal keratinocyte proliferation and migration at 10 μg/mL, suggesting potential applications in daily chemical and pharmaceutical industries.

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.

Rapid and massive fractionation of hemicelluloses for purifying cellulose at room temperature by tetramethylammonium hydroxide

The fractionation of hemicelluloses is a promising method to improve the comprehensive utilization of lignocellulosic biomass. However, the effective fractionation of hemicelluloses is always limited by the structural complexity and easy degradability. In this study, tetramethylammonium hydroxide (TMAH) was developed to fractionate hemicelluloses from poplar holocellulose with high molecular weights and high yields at room temperature. Approximately 90% of hemicelluloses could be dissolved at room temperature in 1 h, and the yield was up to 81.9%. Compared with the fractionation using NaOH solution, the hemicelluloses isolated by TMAH solvent showed a more complete structure and higher purity. Meanwhile, the retention rate of cellulose after treatment with TMAH was up to 90.2%, and the crystal structure of cellulose in the residues was practically unchanged. Moreover, the TMAH solvent could be recycled to fractionate hemicelluloses. The work provides an elegant and significantly efficient method towards hemicelluloses fractionation and cellulose purification.

Optimizing tri-acid mixture hydrolysis: An improved strategy for efficient xylooligosaccharides production from corncob

Propionic acid (PA) hydrolysis of corncob for xylooligosaccharides (XOS) production has the advantages of simple operation, high XOS yield and less by-products, but the high price of PA limits its application. Therefore, partially replacing PA with less expensive organic acids, such as formic acid (FA) and acetic acid (AC), may lower the cost of hydrolysis in XOS production. This work investigated the feasibility of XOS production from corncob using a tri-acid mixture of FA, AC and PA. A high XOS yield of 69.1 % was achieved under the optimal FA:PA:AC volume ratio of 1:5:4 at 150 °C for 50 min. Overall, in the XOS production from corncob, it was able to replace 60 % of PA with FA and AC, and decreased the hydrolysis temperature from 170 °C to 150 °C, all of which were important to lower the cost of XOS production using organic acid hydrolysis.

Enabling the complete valorization of hybrid Pennisetum: Directly using alkaline black liquor for preparing UV-shielding biodegradable films

The conversion of lignocellulosic biomass into various high-value chemicals has been a rapid expanding research topic in industry and agriculture. Among them, alkaline removal and utilization of lignin are important for the accelerated degradation of biomass. Modern biorefinery has been focusing the vision on the advancement of economical, green, and environmentally friendly processes. Therefore, it is indispensable to develop cost-effective and simple biomass conversion technologies to obtain high-value products. In this study, the black liquor (BL) obtained from the alkaline pretreatment of biomass was added to polyvinyl alcohol (PVA) solution and used to prepare degradable ultraviolet (UV) shielding films, achieving direct and efficient utilization of the aqueous phase from alkaline pretreatment. This method avoids the extraction step of lignin fraction from black liquor, which can be directly utilized as the raw materials of films preparation. In addition, the direct use of alkaline BL results in films with similar UV-shielding properties, higher physical strength, and similar thermal stability compared with films made by commercial alkaline lignin. Therefore, this strategy is proposed for alkaline-pretreated biorefineries as a simple way to convert waste BL into valuable products and partially recover unconsumed sodium hydroxide to achieve as much integration of biomass and near zero-waste biorefineries as possible.

Chemical and Structural Elucidation of Lignin and Cellulose Isolated Using DES from Bagasse Based on Alkaline and Hydrothermal Pretreatment

The separation of cellulose, hemicellulose, and lignin components using deep eutectic solvent, which is a green solvent, to obtain corresponding chemicals can realize the effective separation and high-value utilization of these components at low cost. In this study, we used waste biomass sugarcane bagasse as the raw material, choline chloride as the hydrogen bond acceptor, and lactic acid as the hydrogen bond donor to synthesize a deep eutectic solvent of choline chloride/lactic acid (L-DES) and treated sugarcane bagasse pretreated by alkali or hydrothermal methods to separate cellulose, hemicellulose, and lignin. In addition, we comparatively studied the effect of different pretreatment methods on lignin removal by DES and found that the lignin removal rate by L-DES after alkaline pretreatment was significantly higher than that after hydrothermal pretreatment, and the mechanism of action causing this difference is discussed.

Efficient production of xylooligosaccharides rich in xylobiose and xylotriose from poplar by hydrothermal pretreatment coupled with post-enzymatic hydrolysis

A promising approach for production of value-added xylooligosaccharides (XOS) from poplar was developed by combining hydrothermal pretreatment and endo-xylanase post-hydrolysis. Results showed that the 35.4% XOS (DP 2-6) and 17.6% low DP xylans (DP > 6) were obtained at the identified optimal condition (170 °C, 50 min) for hydrothermal pretreatment. Structural features of low DP xylans generated during the hydrothermal pretreatment were examined, revealing that low DP xylans are mainly comprised of 4-O-methylglucuronic xylan and are involved in lignin carbohydrate complexes. Moreover, higher pretreatment intensity promoted the cleavage of side-chain substituents including arabinose and glucuronic acid groups. The subsequent endo-xylanase hydrolysis of the pretreatment liquor hydrolyzed low DP xylans, contributing to a significant improvement in xylobiose and xylotriose proportions. This combined strategy resulted in a XOS with conversion yield of 44.6% containing 78.7% xylobiose and xylotriose starting from the initial xylan in raw poplar.

Ultrastructural change in lignocellulosic biomass during hydrothermal pretreatment

In recent years, visualization and characterization of lignocellulose at different scales elucidate the modifications of its ultrastructural and chemical features during hydrothermal pretreatment which include degradation and dissolving of hemicelluloses, swelling and partial hydrolysis of cellulose, melting and redepositing a part of lignin in the surface. As a result, cell walls are swollen, deformed and de-laminated from the adjacent layer, lead to a range of revealed droplets that appear on and within cell walls. Moreover, the certain extent morphological changes significantly promote the downstream processing steps, especially for enzymatic hydrolysis and anaerobic fermentation to bioethanol by increasing the contact area with enzymes. However, the formation of pseudo-lignin hinders the accessibility of cellulase to cellulose, which decreases the efficiency of enzymatic hydrolysis. This review is intended to bridge the gap between the microstructure studies and value-added applications of lignocellulose while inspiring more research prospects to enhance the hydrothermal pretreatment process.

Technologies for Eucalyptus wood processing in the scope of biorefineries: A comprehensive review

Eucalyptus is the most widely planted type of hardwoods, and represents an important biomass source for the production of fuels, chemicals, and materials. Its industrial benefit can be achieved by processes following the biorefinery concept, which is based on the selective separation ("fractionation") of the major components (hemicelluloses, cellulose and lignin), and on the generation of added-value from the resulting fractions. This article provides a in-depth assessment on the composition of Eucalyptus wood and a critical evaluation of selected technologies allowing its overall exploitation. These latter include treatments with organosolvents and with emerging fractionation agents (ionic liquids and deep eutectic solvents). The comparative evaluation of the diverse processing technologies is carried out in terms of degree of fractionation, yields and selectivities. The weak and strong points, challenges, and opportunities of the diverse fractionation methods are identified, focusing on the integral utilization of the feedstocks.

Engineering aspects of hydrothermal pretreatment: From batch to continuous operation, scale-up and pilot reactor under biorefinery concept

Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and engineering aspects from batch to continuous operation. The treatise includes a case study of hydrothermal biomass pretreatment at pilot plant scale and integrated process design.

Rhodotorula toruloides Single Cell Oil Production Using Eucalyptus urograndis Hemicellulose Hydrolysate as a Carbon Source

Microbial oil is a potential substitute for vegetable oils in the biodiesel industry. Efforts to obtain cheap carbon sources for the cultivation of lipid-producing microorganisms comprise an active research area. This work aimed to extract the hemicellulose fraction from Eucalyptus uograndis and to use its hydrolysate as a carbon source for Rhodotorula toruloides (an oleaginous yeast) cultivation for microbial oil production. Hemicellulose hydrothermal extractions were performed at different temperatures, times, and ratios of solid to liquid (S/L). Temperature and time showed a stronger effect on the solubilization of hemicellulose. Hemicellulose extraction at 155 °C, 195 min, and an S/L ratio of 1/2 resulted in a hydrolysate with a xylose content of 37.0 g/l. R. toruloides cultivation in this hydrolysate showed that initial pH had a strong influence on cell growth. At an initial pH of 6.2, cells grew to 6.0 g/l of biomass with a lipid content of 50%. Therefore, we believe that E. urograndis hemicellulose hydrolysate could be a potential substrate for R. toruloides for lipid production based on the biorefinery concept.

Effect of low severity hydrothermal pretreatment on anaerobic digestion performance of corn stover

The anaerobic digestion (AD) performance of corn stover was investigated under low hydrothermal pretreatment (HP) severity. Pretreated corn stover, with and without ammonia was examined at the three temperatures (50, 70, and 90 °C) coupled with different pretreatment time (24-72 h). The results showed that the pH value decreased with increasing pretreatment time for the same temperature. The highest volatile fatty acids (VFAs) concentration (4616.23 mg/L) was achieved at a HP severity of 4.56. The highest removal rate of cellulose, hemicellulose, and lignin were 19.62%, 25.53%, and 32.91% for HP with ammonia (HPA) severities of 3.34, 3.34, and HP severity of 4.35, respectively. The maximum methane yield of corn stover was 148.19 mL/g∙VS under 50 °C held for 24 h (HPA severity of 2.59), which was 31.35% higher than that of the untreated corn stover. The research results suggest that properly pretreatment severity can play an important role in promoting methane production.

Effect of hydrothermal pretreatment severity on the pretreatment characteristics and anaerobic digestion performance of corn stover

The pretreatment characteristics and anaerobic digestion (AD) performance of corn stover were investigated at different hydrothermal pretreatment (HP) severity levels. The pretreatment of corn stover with and without ammonia was performed at different temperatures (100, 150, and 200 °C) and with a holding time of 5-30 mins. Results showed that after HP, the highest volatile fatty acid (VFAs) concentration was 10533.94 mg/L at a HP severity of 7.27, which was 1.72-3.35 times greater than those of others HP severity levels. Similarly, the highest removal rates of hemicellulose and lignin were 95.41% and 13.85% for HP severity levels of 6.81 and 1.98, respectively. The maximum biogas and methane increasing yield at 100 °C holding 30 min without ammonia were 16.26% and 22.74% greater than that of the untreated, respectively. These results suggest that an appropriate HP intensity can promote biogas production.

A novel strategy for efficient anaerobic co-digestion based on the pretreatment of corn stover with fresh vinegar residue

A novel method was advanced for efficient anaerobic co-digestion by using fresh vinegar residue (FVR) as acidifier for pretreating corn stover (CS). FVR acted as one substrate as well as an acidifier by the acids contained in FVR. It was found that the organic acids in FVR could efficiently enhance the hydrolysis of lignocellulose in CS. The biomethane production from co-digestion of FVR and CS pretreated reached 140.48 L/kg VS, which was 35.7% higher than that of unpretreated mixture substrates. The highest biomethane production was obtained when pretreatment was conducted at 150 °C. The increase of biomethane production was contributed to the improved hydrolysis of CS due to the acidic pretreatment. Pretreatment and co-digestion could improve the asynchronism and generate synergistic effect. The study provides one novel method for efficient biomethane conversion from FVR and CS.

Changes of Chemical Composition and Hemicelluloses Structure in Differently Aged Bamboo ( Neosinocalamus affinis) Culms

To study the differences in chemical composition analysis and spatial distribution of young Neosinocalamus affinis bamboo, we used the methods of standard of National Renewable Energy Laboratory and confocal Raman microscopy, respectively. It was found that the acid-soluble lignin and acid-insoluble lignin content showed an inverse relationship with the increasing bamboo age. Raman analysis revealed that Raman signal intensity of lignin in both the secondary cell wall and the compound middle lamella regions showed a similar increase trend with growth of bamboo. In addition, eight hemicellulosic fractions were obtained by successively treating holocellulose of the 2-, 4-, 8-, and 12-month-old Neosinocalamus affinis bamboo culms with DMSO and alkaline solution. The ratio of arabinose to xylose of hemicelluloses was increased with the growth of bamboo. FT-IR and NMR analyses revealed that DMSO-soluble hemicelluloses of young bamboo culms are mainly composed of highly substituted xylans and β-d-glucans.

High added-value products from the hydrothermal carbonisation of olive stones

Olive stones (OS) were submitted to hydrothermal carbonisation (HTC) in order to evaluate the possibility of producing high added-value products, mainly furfural (FU) and 5-hydroxymethylfurfural (5-HMF) on one hand and hydrochars and carbons on the other hand. Temperature (160-240 °C), residence time (1-8 h), initial pH (1-5.5) and liquid/solid ratio (4-48 w/w) were systematically varied in order to study the main products and to optimise FU production. FU production yield up to 19.9 %, based on the hemicellulose content, was obtained. Other minor, but valuable, compounds such as 5-methylfurfural (5-MF) and some phenolic compounds were also produced. The hydrochar was carbonised at 900 °C, and the resultant carbon material was highly ultramicroporous with a peak of pore size distribution centred on 0.5 nm and a surface area as high as 1065 m² g^-1, typical of most carbon molecular sieves.

Influence of lignin level on release of hemicellulose-derived sugars in liquid hot water

Lignin layers surrounding hemicelluloses and cellulose in the plant cell walls protect them from deconstruction. This recalcitrance to sugar release is a major limitation for cost-effective industrial conversion of lignocellulosic biomass to biofuels. Many literatures had reported the contribution of lignin removal to cellulose accessibility to enzyme, but less to the hemicellulose hydrolysis. Herein, beech xylan with lignin addition, partly delignified sugarcane bagasse (SB), energy sorghum hybrids (ESH) were treated in liquid hot water (LHW) to investigate the effect of lignin on hemicellulose decomposition. The addition of lignin can enhance the low degree of polymerization of xylooligomers production resulted from the acid catalyzed cleavage of lignin-derived acidic products. However, a negative correlation was observed initially between the lignin level and the total xylose yield from ESH. Furthermore, samples with lignin addition or high lignin content had a great resistant to harsh reaction environment, about 93.5% total xylose lost but only 52.3% released due to the lack of lignin protection for the sample with 100% lignin removal.

Hydrothermal fractionation of woody biomass: Lignin effect on sugars recovery

Subcritical water was employed to fractionate woody biomass into carbohydrates and lignin. Nine urban trees species (hardwood and softwood) from Spain were studied. The experiments were carried out in a semi-continuous reactor at 250 °C for 64 min. The hemicellulose and cellulose recovery yields were between 30%wt. and 80%wt. while the lignin content in the solid product ranged between 32%wt. and 92%wt. It was observed that an increment of solubilized lignin disfavored the hydrolysis of hemicelluloses. It was determined that the maximum extraction of hemicellulose was achieved at 20 min of solid reaction time while the extraction of celluloses not exhibited a maximum value. The hydrolysis of hemicellulose and cellulose would be governed by the hydrolysis kinetic and the polymers accessibility. In addition, the extraction of hemicellulose was negatively affected by the lignin content in the raw material while cellulose hydrolysis was not affected by this parameter.