Separation Of Hemicellulose Research Articles

Small Molecules Effective for Conversion of Lignocellulosic Biomass to Furfural and Its Derivatives

This review summarizes recent applications of small organic and inorganic molecules as catalysts or solvents (chemical hands and scissors) in the production of furfural (FA), 5-(hydroxymethyl)furfural (HMF), and 5-(chloromethyl)furfural (CMF). The possible transformation of lignocellulosic biomass into a one-pot configuration and two-step technique based on the preliminary separation of hemicellulose, lignin and cellulose with the subsequent hydrolysis of separated polysaccharides is compared and discussed. Interestingly, these rather simple and cheap molecules are catalytically active and enable a high rate of conversion of polysaccharides into furfural and its derivatives. Usually, elevated pressure and reaction temperatures above 150 °C are necessary for effective hydrolysis and dehydration of in situ formed monosaccharides; nevertheless, ionic liquids or deep eutectic solvents enable a significant decrease in the reaction temperature and performance of the discussed process at ambient pressure.

Integral fractionation of Arundo donax using biphasic mixtures of solvents derived from biomass: An environmentally friendly approach

Arundo donax, one of the most invasive plants in the world, but also a promising source of lignocellulose materials was employed as a feedstock for a biorefinery process. Water-extracted Arundo donax samples were subjected to one-step biphasic fractionation in catalyzed media containing water and 1-butanol, an environmentally-friendly solvent. The effects of selected operational variables (catalyst concentration, temperature and reaction time) on the measured effects (solid recovery yield and compositions of the solid, aqueous and organic phases resulting from treatments) were assessed using statistical methods. The results allowed a quantitative discussion on aspects regarding the selectivity of component separation (lignin, glucan, and hemicelluloses), the overall recovery of valuable products, and the selection of operational conditions enabling extensive delignification (around to 90 %) and high recovery rates of glucan and hemicellulose-derived sugars (above 80 % and 75 %, respectively). This study provides new insights into biphasic fractionation, highlighting the selective separation of hemicellulose, cellulose and lignin into a single and sustainable process, thereby by enhancing biomass resource while reducing environmental impact.

Simultaneous preparation of lignin-containing cellulose nanocrystals and lignin nanoparticles from wood sawdust by mixed organic acid hydrolysis

In the global search for sustainable and environmentally friendly materials, the efficient utilization of biomass resources has become a hot research topic. Due to the high specific surface area, nanocellulose crystals (CNCs) have attracted considerable attention. However, CNC preparation often requires the separation of lignin and hemicellulose, which wastes resources. In this study, lignin-containing cellulose nanocrystals (LCNCs) and lignin nanoparticles (LNPs) were prepared from p-toluenesulfonic acid (p-TsOH)/formic acid (FA) pretreated poplar wood in one-step. The process was performed in a mixed acid system with a mass ratio of p-TsOH, FA, and deionized water (DI) of 3:5:2, and mechanical stirring at 80 ºC for 3 h. Under these conditions, the lignin removal rate was about 70 %, and the LCNCs yield was more than 40 %. The p-TsOH is regained by vacuum distillation and recrystallization, and the recovery rate can reach 60 %. The prepared LCNCs were then carbonized and used as an electrode for electrochemical testing. The electrode obtained by carbonizing LCNC exhibits an areal capacitance of 156.4 F g−1 (0.5 A g−1). The study provided a new prospect for the efficient utilization of lignocellulosic nanomaterials.

Combined pretreatment of malic acid and kraft pulping for the production of fermentable sugars and highly active lignin

The separation and utilization of cellulose, hemicellulose, and lignin in lignocellulosic biorefineries present significant challenges. This study proposes a pretreatment method for biomass refining by combining acid and kraft pulping. Firstly, the biomass was pretreated by malic acid, resulting in the isolation of xylo-oligosaccharides (XOS) with a yield of 86.26 % with optimized conditions of 180 °C, 1 wt% concentration, 40 min. Secondly, a mixture of 12.98 wt% NaOH and 1.043 wt% Na2S is employed to achieve lignin removal efficiency up to 63.42 %. Physical refinement techniques are then applied to enhance the enzyme digestion efficiency of cellulose, resulting in an increase from 55.03 % to 91.4 % for efficient cellulose conversion. The reacted samples exhibit a lignin composition rich in β-O-4 ether bonds, facilitating their high-value utilization. The results indicated that the combined pretreatment approach demonstrates high efficiency in separating cellulose, hemicellulose, and lignin while obtaining XOS, highly active lignin, and enzyme-digested substrates.

Organic Acid-Based Hemicellulose Fractionation and Cellulosic Ethanol Potential of Five Miscanthus Genotypes

The pretreatment of lignocellulosic biomass such as Miscanthus grown on marginal agricultural land is very challenging and requires severe conditions to fractionate cell wall polymers for further valorization. The current study aimed to determine organic acid-based mild conditions to pretreat contrasting lignocellulosic Miscanthus genotypes for the efficient fractionation of cell wall components, with special focus on hemicellulose extraction. In doing so, five Miscanthus genotypes were subjected to four different acid treatments (sulfuric acid, oxalic acid, malonic acid, and citric acid) in a vertical high-pressure steam sterilizer. The results demonstrated that, among the organic acids, oxalic acid was identified as the most effective pretreatment solvent for hemicellulose separation, whereas citric acid yielded the highest amount of galacturonic acid, varying from 15 to 17 mg mL−1 across genotypes. One best performing genotype was selected for the enzymatic hydrolysis. Overall, M. floridulus genotypes exhibited the optimal quality traits for efficient bioconversion with second best in terms of ethanol production potential.

Selective Removal of Hemicellulose by Diluted Sulfuric Acid Assisted by Aluminum Sulfate.

Hemicellulose can be selectively removed by acid pretreatment. In this study, selective removal of hemicellulose was achieved using dilute sulfuric acid assisted by aluminum sulfate pretreatment. The optimal pretreatment conditions were 160 °C, 1.5 wt% aluminum sulfate, 0.7 wt% dilute sulfuric acid, and 40 min. A component analysis showed that the removal rate of hemicellulose and lignin reached 98.05% and 9.01%, respectively, which indicated that hemicellulose was removed with high selectivity by dilute sulfuric acid assisted by aluminum sulfate pretreatment. Structural characterizations (SEM, FTIR, BET, TGA, and XRD) showed that pretreatment changed the roughness, crystallinity, pore size, and functional groups of corn straw, which was beneficial to improve the efficiency of enzymatic hydrolysis. This study provides a new approach for the high-selectivity separation of hemicellulose, thereby offering novel insights for its subsequent high-value utilization.

Efficient hemicellulose removal from lignocellulose by induced electric field-aided dilute acid pretreatment

This study evaluated the effectiveness of induced electric field (IEF) as a novel electrotechnology to assist dilute acid pretreatment of wheat straw (WS) at atmospheric pressure and low temperature (90 °C). The effects of acid concentration and duration on cellulose recovery, hemicellulose and lignin removal were investigated. Meanwhile, the differences between IEF pretreatment and hydrothermal pretreatment were compared by quantitative and qualitative analysis. The optimal pretreatment condition was acid concentration 1 % with the period of 5 h. Under the parameters, the hemicellulose removal of WS after IEF pretreatment was up to 73.6 %, and the enzymatic efficiency was 55.8 %. In addition, the irregular surface morphology, diminished functional groups associated with hemicellulose, increased specific surface area and pore volume, as well as improved thermal stability of the residual WS support the remarkable effect of IEF pretreatment. The feasibility of IEF pretreatment is might be due to the fact that the magneto-induced electric field promotes ionization of H+ and formation of hydrated hydrogen ions, increasing the acidity of the medium. Secondly, electroporation disrupts the anti-degradation structure of WS and increases the accessibility of cellulose to cellulases. It indicated that IEF is a green and efficient strategy for assisting the separation of hemicellulose from lignocellulose.

Optimization of microwave-expanding pretreatment and microwave-assisted extraction of hemicellulose from bagasse cells with the exploration of the extracting mechanism

Hemicellulose is mainly distributed in the tightly packed S2 layer of the plant cell wall and the middle lamella. This rigid microstructure of wood and interactions among hemicellulose, lignin, and cellulose jointly restrict the separation and transformation of hemicellulose in the wood matrix. To address this issue, a method combined with microwave-expanding pretreatment (MEP) and microwave-assisted extraction (MAE) with a NaOH solution was carried out. We found that the MEP could effectively create new pathways for bagasse cells in mass transferring. More specifically, 195 % of the specific surface area (m2/g) with 193 % of the pores (>50 nm) increased after MEP; the SEM images also confirmed that the microstructure of bagasse was modified. MAE could considerably exfoliate hemicellulose from cellulose fiber and accelerate mass transfer. Additionally, we optimized MEP and MAE by using response surface methodology (RSM). The optimal parameters were 370 K, 3.7 min, 1081 W microwave power, and 9.9 wt% NH4HCO3 consumption for the MEP and 1100 W microwave power, 2.5 wt% NaOH concentration, 34.6 min reaction time for MAE, respectively. Moreover, molecular dynamics (MD) simulation suggests that NaOH could significantly lower the work needed to peel off the xylan chain from cellulose nanofibril.

Integrating ball milling assisted enzymatic hydrolysis of bamboo cellulose for controllable production of xylo-oligosaccharides, monosaccharides and cellulose nanofibrils

Green bioconversion technology has been regarded as a fundamental solution to energy challenges and environmental issues. During bioconversion, a combination of mechanical and enzymatic treatment on lignocellulosic biomass can not only conformity with environmental concepts but also enable efficient conversion. In this study, a ball milling assisted enzymatic treatment was applied for full utilization of bamboo cellulose. In addition to the production of soluble saccharides, the residues that remained after enzymatic hydrolysis were collected for producing high-quality nanocellulose. Ball milling efficiently broke the hydrogen bonding interactions between glucan chains thus promoting the following xylanase and cellulase conversion. The highest Xylo-oligosaccharides (XOS) yield reached 21.6%. Meanwhile, xylanase facilitated cellulase hydrolysis by separation of hemicellulose on cellulose. With a low commercial cellulase loading of 5 FPU/g glucan, a maximum yield of 76.6% glucose and 53.3% xylose was reached. Finally, nanocellulose was extracted from the enzymatic hydrolyzate residue with a minimum width of 3.5 nm and an average size of 294.8 nm. The present study proposed an efficient combination of mechanical treatment assisted enzymatic digestion, which is not only environmentally friendly but also allows for complete bioconversion of bamboo cellulose.

A novel liquid-liquid phase-change solvent with upper critical solution temperature for simultaneous pretreatment and separation of lignin, cellulose and hemicellulose from lignocellulosic biomass

The compact dimensional aggregate structure and the complex chemical components of lignocellulose go against its high value utilization. The mixture of dilute hydrochloric acid and n-butanol, which had a characteristic of homogeneous phase at high temperature and phase separation at low temperature, was proposed for lignocellulosic hydrolysis and hydrolysates separation. The results showed that lignocellulose was hydrolyzed under the synergy effect of hydrochloric acid and n-butanol in homogeneous condition, and hemicellulose and lignin hydrolysates were transferred automatically into dilute hydrochloric acid phase and n-butanol phase during the phase separation of the solvent after pretreatment, respectively. N-butanol accelerated lignin hydrolysis and protected β-O-4 linkage within lignin during the pretreatment. Meanwhile, the cellulose within solid phase product from the pretreatment was of high crystallinity, and its glucose yield in enzymatic saccharification at 48 and 72 h were 73.5% and 97.3%, respectively. This study provides a new method for lignocellulose hydrolysis and hydrolysates separation, and lays a theoretical foundation for lignocellulosic utilization of all component.

H2O2-enhanced alkaline pretreatment and separation of tobacco stems for biocellulose composite films with potential application in food preservation

Utilizing biological resources facilitates alleviating energy shortage and environmental pollution problems, but high-value utilization of these resources requires breaking the biomass structure. This study realized the clean and efficient separation of cellulose, hemicellulose, and lignin from tobacco stems using a sustainable H2O2-enhanced alkaline pretreatment combined with acid and ethanol precipitation. The purity and thermal stability of the separated cellulose increased from 32.49% to 92.41% and 261 °C to 369 °C, respectively. Changes in the cellulose crystal form and the solubilization mechanisms of hemicellulose and lignin were elucidated. In addition, a food-preservation film was prepared from the obtained biocellulose using the solution-casting method. After adding glycerol and sorbitol as plasticizers, the tensile strength and water-contact angle (a hydrophobicity indicator) of the biocellulose composite film increased from 125 MPa to 154 MPa and from 50.48° to 73.16°, respectively. This study provides a platform for lignocellulosic biomass separation, renewable utilization, and a practical route toward functional biomaterial production.

Green bio-based aprotic solvents for efficient fractionation of hemicellulose and targeted value addition of lignin

It is of great significance to inhibit the repolymerization of lignin when removing hemicellulose by acid pretreatment. Adding a lignin fragment scavenger is an effective method to inhibit its repolymerization. Here, the effect of a bio-based polar aprotic solvent, levulinic acid (Lev), and γ-valerolactone (GVL) coupled pretreatment system on the separation yield of poplar biomass components was investigated. The optimum pretreatment conditions were a Lev concentration was 7.0%, reaction temperature was 170 °C, pretreatment time was 60 min, and GVL concentration was 9.0%. The separation yield of hemicellulose was 84.54%, which was a 4.53% increase over that with Lev pretreatment. The retention yield of cellulose was 89.68%. In addition, the separation efficiency was significantly improved when the pretreatment time was reduced by 40 min. The reaggregation of lignin was suppressed under the condition of maximum hemicellulose separation. In the lignin samples the content of β-O-4 was as high as 47.81%. Simultaneously, the content of phenolic and aliphatic hydroxyl increased. The results revealed that Lev/GVL pretreatment had good hemicellulose separation selectivity and excellent lignin fragment removal efficiency. This provides a new strategy for suppressing adverse effects on the lignin structure in the efficient separation of hemicellulose in pretreatment.

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.

Microwave-assisted formic acid/cold caustic extraction for separation of cellulose and hemicellulose from biomass

Effective separation of cellulose and hemicellulose from lignocellulosic biomass is an essential step for creating high-value products. In this study, a modified treatment process was proposed for cellulose purification via microwave-assisted formic acid catalytic hydrolysis followed by cold caustic extraction. The sugar content in the extract was determined using UV spectrophotometer and dual-wavelength visible spectrophotometry. Combined microwave-assisted formic acid (M-FA) with cold caustic extraction (CCE) treatments achieved rapid separation and removal of hemicelluloses from waste hardwood pulp fibers. The hemicelluloses content decreased from 28.6% to 2.3%, and the lignin content changed from 27.8% to 6.1%, which resulted in a maximal cellulose content of 91.5% under the optimal M-FA/CCE treatment conditions. In addition, the crystallinity index of pulp fibers increased from 54.3% to 67.1%, and the initial decomposition temperature decreased from 335.4 to 270.2 °C with the decrease of hemicellulose and lignin content. The modified process provided a sustainable and effective method for hemicellulose separation and lignin removal from cellulosic fibers.

Novel dual-action vanillic acid pretreatment for efficient hemicellulose separation with simultaneous inhibition of lignin condensation

Aromatic acids play a selective role in the separation of hemicellulose. Phenolic acids have demonstrated an inhibitory effect on lignin condensation. In the current study, vanillic acid (VA), which combines the characteristics of aromatic and phenolic acids, is used to separate eucalyptus. The efficient and selective separation of hemicellulose is achieved simultaneously at 170 °C, 8.0% VA concentration, and 80 min. The separation yield of xylose increased from 78.80% to 88.59% compared to acetic acid (AA) pretreatment. The separation yield of lignin decreased from 19.32% to 11.19%. In particular, the β-O-4 content of lignin increased by 5.78% after pretreatment. The results indicate that VA, as a “carbon positive ion scavenger”, it preferentially reacts with the carbon-positive ion intermediate of lignin. Surprisingly, the inhibition of lignin condensation is achieved. This study provides a new starting point for the development of an efficient and sustainable commercial technology by organic acid pretreatment.

Direct Oxidation of Hibiscus cannabinus Stalks to Vanillin Using CeO2 Nanostructure Catalysts.

Biomass lignin can be used to produce vanillin through an oxidation process. Although its purity is high, the processing time and separation efficiency are not ideal. This research aims to produce vanillin directly from Kenaf stalks without separating the lignin first from the lignocellulosic biomass. This method is greener because it does not require the separation of cellulose and hemicellulose from the biomass, thus minimizing the use of acid and alkaline solutions and saving time. A high oxygen storage capacity and release capacity of ceria as an oxidation catalyst contribute to the reversable redox properties between Ce4+ and Ce3+ in ceria lattice. Cerium oxide nanostructures were synthesized using a hydrothermal method treated under alkaline NaOH, followed by drying at 120 °C for 16 h and calcining at different temperatures between 400 and 600 °C for the direct oxidation of Kenaf stalks to vanillin under microwave irradiation. The catalysts were characterized for their physicochemical properties using XRD, N2 adsorption-desorption isotherms and TEM. All synthesized CeO2 nanostructures showed the presence of diffraction peaks assigned to the presence of cubic fluorite. The N2 adsorption-desorption isotherms showed that all catalysts possess a Type IV isotherm, indicating a mesoporous structure. The TEM image shows the uniform shape of the CeO2 nanostructures, while HRTEM images show that the CeO2 nanostructures are single-crystalline in nature. All catalysts were tested for the direct oxidation of Kenaf stalks using H2O2 as the oxidizing agent in temperatures ranging from 160 to 180 °C for 10-30 min with 0.1-0.3 g catalyst loading under 100-500 W of microwave irradiation. The CeO2-Nps-400 catalyst produced the highest vanillin yields of 3.84% and 4.32% for the direct oxidation of Kenaf stalks and extraction of lignin from Kenaf stalks, respectively. Compared to our earlier study, the highest vanillin yields of 2.90% and 3.70% for direct biomass and extracted lignin were achieved using a Ce/MgO catalyst.

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

The efficiency of organic acid treatment in the conversion of lignocellulosic biomass fractions has been widely recognized. In this study, a novel green pyruvic acid (PA) treatment is proposed. The higher separation efficiency of eucalyptus hemicellulose was obtained at 4.0% PA and 150 °C. The hemicellulose separation yield was increased from 71.71 to 88.09% compared to glycolic acid (GA) treatment. In addition, the treatment time was significantly reduced from 180 to 40 min. The proportion of cellulose in the solid increased after PA treatment. However, the accompanying separation of lignin was not effectively controlled. Fortunately, a six-membered ring structure was formed on the diol structure of the lignin β-O-4 side chain. Fewer lignin-condensed structures were observed. High-value lignin rich in phenol hydroxyl groups were obtained. It provides a green path for the simultaneous achievement of efficient hemicellulose separation and inhibition of lignin repolymerization using organic acid treatment.

Rapid and mild fractionation of hemicellulose through recyclable mandelic acid pretreatment

The development of organic acid pretreatments from biological sources is essential to facilitate the progress of green and sustainable chemistry. In this study, the effectiveness of mandelic acid pretreatment (MAP) was analyzed for eucalyptus hemicellulose separation. 83.66% of xylose was separated under optimal conditions (temperature: 150 °C; concentration: 6.0 wt%; time: 80 min). The hemicellulose separation selectivity is higher than acetic acid pretreatment (AAP). The stable and effective separation efficiency (56.55%) is observed even after six reuses of the hydrolysate. Higher thermal stability, larger crystallinity index and optimized surface element distribution in the samples were demonstrated by MAP. Lignin condensation is effectively inhibited through MAP, as determined from the structural of different lignin. In particular, the demethoxylation of lignin by MA was found. These results open up a new way to construct a novel organic acid pretreatment for separating hemicellulose with high efficiency.

Mannitol assisted oxalic acid pretreatment of poplar for the deconstruction and separation of hemicellulose

The effect of mannitol (MA) on the poplar separation using mannitol-assisted oxalic acid (M/OA) pretreatment was revealed. The effects of reaction parameters on the separation efficiency were studied. The optimized conditions were OA 7.0%, MA 7.0%, temperature 150 °C, and time 60 min. The hemicellulose separation was 79.08%. The separation of cellulose and lignin decreased from 12.43% and 21.82–8.58% and 16.11%, respectively, under hemicellulose separation similar to those of conventional OA pretreatment. Smooth fiber surfaces with less lignin deposition were observed. There were more β-O-4 and fewer β-β in lignin. Additionally, larger amounts of aliphatic hydroxyl groups and smaller amounts of phenolic hydroxyl groups were observed, which implies that MA addition prevented lignin from condensing. An effective and environmentally friendly separation of hemicellulose was achieved by M/OA pretreatment. This provides a practical approach for resolving the stubborn problems of lignin cleavage and condensation during organic acid pretreatment.

Microwave-assisted separation hemicellulose from hemp stalk: Extracting performance, extracting mechanism and mass transfer model

Herein, a novel microwave-assisted alkali extraction process was proposed for further high-efficiency extraction of hemicellulose from hemp stalk. The hemicellulose extraction yield of the peeled hemp stalk surpasses 60% under mild conditions (4% alkali content, 80 °C, 30 min). Meanwhile, the hemicellulose presented a high weight-average and number-average molecular weight of 25331, 6067 g/mol. The improved efficiency could be thanks to the looser structure created by microwave expansion pretreatment via breaking the intricate structure and shielding of the hemp stalk cell wall, detailed as the specific surface area, total pore volume, and average pore size of the hemp stalk increased from 1.30 m²/g, 0.003 cm3/g, 10.66 nm to 1.85 m²/g, 0.006 cm3/g and 13.08 nm after the microwave expansion pretreatment. Furthermore, the higher expansion rate (36.74%) and water retention value (265%) of the hemp stalk also demonstrated the effective disrupting effect on the fiber structure. Finally, the empirical mass transfer model of extraction hemicellulose from hemp stalk was established. The predicted value and the experimental data showed a good correlation (R2 = 0.9998) and the model displayed excellent stability (relative deviation within 5%). Therefore, microwave-assisted alkali extraction has great potential application in the hemicellulose separation industry.