Hemicellulose Lignin Research Articles

Integration of Deep Eutectic Solvents and Hydrotalcites for Biomass Conversion and Aldol Condensation: Toward Platform Chemicals and Jet Fuel Synthesis—A Review

AbstractThe abundance and renewability of lignocellulosic biomass have made it a suitable alternative to fossil fuels in the reduction of global warming. The complex nature of the cellulose–hemicellulose–lignin bonds in the biomass makes it difficult to directly obtain platform chemicals. Pretreatment of the biomass has become a solution to remove lignin and obtain cellulose and or hemicellulose to produce platform chemicals. Platform chemicals such as hydroxymethylfurfural, furfural, and levulinic acid are viable feedstocks for aldol condensation to produce C8–C15 fuels. This review reports on deep eutectic solvents and microwave‐assisted pretreatment as green techniques for the delignification and platform chemicals production. Emphasis is placed on the use of hydrotalcites (HTs) as catalysts in platform chemicals production and aldol condensation for C8–C15 alkane fuels. Additionally, the hydrogenation of furfural into cyclopentanone and successive conversion into C10 and C15 alkanes with HTs was reviewed.

Thermogravimetric investigation of anisotropy of dimensional shrinkage of softwood and hardwood during carbonization

Thermogravimetric analysis (TGA) was performed on five softwood and five hardwood thin wood samples in the longitudinal (L) and radial (R) directions. Dimensional changes were monitored using a charge-coupled device camera under a nitrogen flow. A comparison of the TG and derivative TG (DTG) curves revealed that shrinkage in the R direction began when the weight was reduced to 79–92% at 305–330 °C and 87–96% at 275–290 °C for softwoods and hardwoods, respectively. Hemicellulose is mainly degraded in this temperature range. In contrast, shrinkage in the L direction started at temperatures close to the DTG peaks, i.e., 360–380 °C and 345–370 °C, respectively, at which temperatures cellulose is mainly degraded. In general, the R/L shrinkage anisotropy was greater for hardwoods than for softwoods, but the species variation was large and the magnitude was directly related to the difference in the shrinkage onset temperatures between the R and L directions, regardless of the wood species. Therefore, shrinkage anisotropy can be attributed to the relative reactivity of hemicellulose and cellulose in wood cell walls. The shrinkage mechanism during carbonization is discussed in terms of the cell wall ultrastructure, in which cellulose microfibrils are covered by a hemicellulose–lignin matrix, and the orientation of the cells in the L and R directions.

Exploration of the Linkages between Lignin and Carbohydrates in Kraft Pulp from Wheat Straw Using a 13C/2H Isotopic Tracer.

To further our understanding of the change in association between lignin and carbohydrates after kraft pulping, isotope-labeled kraft pulp (KP) was prepared using 13C and D double-isotope-labeled wheat straw, and it was subjected to enzymatic hydrolysis and ionic liquid treatment to explore the linkages between lignin and carbohydrate complexes in wheat straw. Isotope abundance determination showed that 13C and D abundances in the experimental groups were substantially higher than those in the control group, indicating that the injected exogenous coniferin-[α-13C], coniferin-[γ-13C], and d-glucose-[6-D2] were effectively absorbed and metabolized during wheat internode growth. Solid-state CP/MAS 13C-NMR spectroscopy showed that lignin was mainly linked to polysaccharides via acetal, benzyl ether, and benzyl ester bonds. Kraft pulp (KP) from the labeled wheat straw was degraded by cellulase. The obtained residue was fractionated using the ionic liquid DMSO/TBAH to separate the cellulose-lignin complex (KP-CLC) and xylan-lignin complex (KP-XLC). X-ray diffractometer determination showed that the KP-CLC regenerated cellulose type II from type I after the ionic liquid conversion. The 13C-NMR spectrum of Ac-En-KP-CLC showed that the cellulose-lignin complex structure was chemically bonded between the lignin and cellulose through acetal and benzyl ether bonds. The 13C-NMR spectrum of En-KP-XLC showed a lignin-hemicellulose complex structure, wherein lignin and xylan were chemically bonded by benzyl ether and acetal bonds. These results indicate that the cross-linking between lignin and carbohydrates exists in lignocellulosic fibers even after kraft pulping.

Cellulose-Hemicellulose-Lignin Interaction in the Secondary Cell Wall of Coconut Endocarp.

The coconut shell consists of three distinct layers: the skin-like outermost exocarp, the thick fibrous mesocarp, and the hard and tough inner endocarp. In this work, we focused on the endocarp because it features a unique combination of superior properties, including low weight, high strength, high hardness, and high toughness. These properties are usually mutually exclusive in synthesized composites. The microstructures of the secondary cell wall of the endocarp at the nanoscale, in which cellulose microfibrils are surrounded by hemicellulose and lignin, were generated. All-atom molecular dynamics simulations with PCFF force field were conducted to investigate the deformation and failure mechanisms under uniaxial shear and tension. Steered molecular dynamics simulations were carried out to study the interaction between different types of polymer chains. The results demonstrated that cellulose-hemicellulose and cellulose-lignin exhibit the strongest and weakest interactions, respectively. This conclusion was further validated against the DFT calculations. Additionally, through shear simulations of sandwiched polymer models, it was found that cellulose-hemicellulose-cellulose exhibits the highest strength and toughness, while cellulose-lignin-cellulose shows the lowest strength and toughness among all tested cases. This conclusion was further confirmed by uniaxial tension simulations of sandwiched polymer models. It was revealed that hydrogen bonds formed between the polymer chains are responsible for the observed strengthening and toughening behaviors. Additionally, it was interesting to note that failure mode under tension varies with the density of amorphous polymers located between cellulose bundles. The failure mode of multilayer polymer models under tension was also investigated. The findings of this work could potentially provide guidelines for the design of coconut-inspired lightweight cellular materials.

Analysis of Interactions Occurring during the Pyrolysis of Lignocellulosic Biomass

This paper presents a review of the recent advances in research on the interactions between the components of lignocellulosic biomass. The literature reports on the effects of interaction between lignocellulosic biomass components, such as cellulose-lignin, lignin-hemicellulose, and hemicellulose-cellulose, were discussed. The results obtained by other researchers were analyzed from the viewpoint of the interactions between the pyrolysis products formed along with the impact effects of the organic and inorganic components present or added to the biomass with regard to the yield and composition of the pyrolysis products. Disagreements about some statements were noted along with the lack of an unequivocal opinion about the directivity of interactions occurring during biomass pyrolysis. Based on the data in the scientific literature, it was suggested that the course of the pyrolysis process of biomass blends can be appropriately directed by changes in the ratio of basic biomass components or by additions of inorganic or organic substances.

Structural features of lignin–hemicellulose–pectin (LHP) orchestrate a tailored enzyme cocktail for potential applications in bark biorefineries

A decision-making protocol/tool is developed in which bark analytical data can be the input to predict the most appropriate enzymic systems to employ.

Effect of Loblolly Pine (Pinus taeda L.) Hemicellulose Structure on the Properties of Hemicellulose-Polyvinyl Alcohol Composite Film.

Hemicellulose is the second most abundant natural polysaccharide and a promising feedstock for biomaterial synthesis. In the present study, the hemicellulose of loblolly pine was obtained by the alkali extraction-graded ethanol precipitation technique, and the hemicellulose-polyvinyl alcohol (hemicellulose-PVA) composite film was prepared by film casting from water. Results showed that hemicellulose with a low degree of substitution is prone to self-aggregation during film formation, while hemicellulose with high branching has better compatibility with PVA and is easier to form a homogeneous composite film. In addition, the higher molecular weight of hemicellulose facilitates the preparation of hemicellulose-PVA composite film with better mechanical properties. More residual lignin in hemicellulose results in the better UV shielding ability of the composite film. This study provides essential support for the efficient and rational utilization of hemicellulose.

Structural evolution of lignin after selective oxidation of lignin-carbohydrate complex by chlorine dioxide

Lignin–carbohydrate complexes (LCCs) are important from the perspective of the anti-depolymerization barrier of lignocellulosic biomass, as it limits the high-value utilization of lignocellulosic biomass resources. In this study, the unit structure of lignin in the LCC has been investigated in depth. Oxidation of a selective lignin unit by chlorine dioxide revealed that the LCC structures are enriched with xylanase-macroporous resins, and the structure that was not oxidized in LCC was also identified. At a chlorine dioxide concentration of 90.93 mg/L, 1 g of LCC lignin is oxidized by 0.7 g chlorine dioxide. The purified residual hemicellulose lignin was mainly H-type. The β-O-4′ signal was the strongest for the bond between lignin and carbohydrates. Therefore, it is speculated that most of the residual lignin in bamboo-alkali hemicellulose exists in the form of non-phenolic structural units. This study provides a reference for further studies on the specific structures of LCC.

Elucidation of the interaction effects of cellulose, hemicellulose and lignin during degradative solvent extraction of lignocellulosic biomass

The degradative solvent extraction (DSE) method has been recently developed to deoxygenate and upgrade lignocellulosic biomass wastes into high-quality extracts with a variety of value-added applications. Lignocellulosic biomass is mainly composed of cellulose, hemicellulose and lignin, and the interaction of the three components during the DSE process still remains unclear and needs to be elucidated. Therefore, in this study, the synthetic component mixtures (cellulose/hemicellulose (CH), cellulose/lignin (CL) and hemicellulose/lignin (HL)) were firstly prepared with the model compounds (cellulose, hemicellulose and lignin), and the conversion characteristics of the component mixtures and the superposition of individual component during the DSE process under the same operating conditions were compared to reveal the interaction effect between the three components. The extract yields of cellulose, hemicellulose and lignin were 44.16%, 27.4% and 18.25% respectively, indicating that cellulose contributed mostly to the formation of the extract (the target product) compared with hemicellulose and lignin. Significant interactions were observed for cellulose/lignin and hemicellulose/lignin mixtures, while the interaction effect between cellulose and hemicellulose was relatively small. The interaction intensity between cellulose, hemicellulose and lignin was in the order of HL > CL > CH. The interaction between cellulose/lignin and hemicellulose/lignin promoted the thermal degradation of lignin. Specifically, the interaction between the hemicellulose and lignin mixture reduced the yield of residue by 9.26%. The interaction mechanism between the three components was discussed and revealed based on the detailed characterization of the DSE products. The interaction between the three components could facilitate the production of gaseous products (mainly CO2), indicating that the interaction between the three components significantly promoted the decarboxylation reaction. The interaction between two of the three components all inhibited the aromatization reaction and reduced the aromaticity of the extracts. During the DSE process of cellulose/lignin or hemicellulose/lignin mixtures, the small-molecular free radicals generated by the decomposition of cellulose or hemicellulose could occupy the active sites on lignin fragments, leading to the significant inhibition of the condensation reactions between different lignin fragments. These interactions leaded to the decrease of the extract yields and residue yields during the DSE process of cellulose/lignin or hemicellulose/lignin mixtures.

Effects of Thermal Aging on the Adhesion Forces of Biopolymers of Wood Cell Walls.

Wood is the most important, industrially used renewable resource on the planet, but the aging mechanism of biopolymers on cell walls is poorly understood. Adhesion properties are of critical importance for wood and many other lignocellulosic materials. We used atomic force microscopy and defined the jump-off force ratio in the retract force–displacement curve to study the adhesion force phenomenon and the effects of heat treatments. Here, we identified two sigmoidal curves describing the shift of the adhesion force and the jump-off force ratio: the first curve was attributed to the movement of extractives and the second to the degradation of the hemicellulose–lignin matrix. We confirmed the hypothesis formulated in this paper by the cell wall surface topography, the analysis of the treated samples by Fourier transform infrared spectroscopy, and the analysis of volatiles during heating by headspace gas chromatography-mass spectrometry.

Process parameter optimization of pretreated pineapple leaves fiber for enhancement of sugar recovery

Pineapple leaves fibers (PALF) is one of the abundant biofibers that have high cellulose content. The complex structure arrangement of PALF that contains a bundle of packed fiber filled with fiber matrix makes it hard to remove lignin and disrupt hemicellulose–lignin complex structure, thus difficult to produce reducing sugar. Dilute sulfuric acid (H2SO4), sodium hydroxide (NaOH), and hot water pretreatment were employed in this study to determine the digestibility of PALF prior to enzyme hydrolysis as a pretreatment method. PALF pretreated with 0.5 % (w/v) NaOH gave the highest yield of reducing sugar (11.65 mg/mL) compared to dilute H2SO4 (8.11 mg/mL) and hot water pretreatment (6.50 mg/mL). The structural changes of PALF after pretreatments were observed through scanning electron microscopy (SEM) and confirmed the structural modification caused by NaOH pretreatment. The optimization of NaOH pretreatment was further carried out by using Box–Behnken design (BBD) to enhance the yield of reducing sugar from PALF and the parameters considered for the optimization include NaOH concentration (0.5 %–2.5 % (w/v)), temperature (80–100 °C), and pretreatment time (30–90 min). The model developed for the response (reducing sugar yield) indicates that the optimum operating condition is 2.43 % (w/v) of NaOH, 87 °C, and 57.15 min of pretreatment time with 17.26 mg/mL of reducing sugar via enzymatic hydrolysis. This result indicates that the pretreatment condition significantly improved the rate of enzymatic hydrolysis and sugar recovery.

Hybrid films based on holistic celery nanocellulose and lignin/hemicellulose with enhanced mechanical properties and dye removal

The endeavor to isolate celery lignocellulosic components and reconstruct into nanocellulose filled and holistic biocomposite films is to demonstrate the potential of re-engineering vegetables into nanocomposite films. The structure−properties relations of these hybrid films were analyzed systematically. The work explored that celery was isolated into the cellulose-rich solid and lignin/hemicellulose (LH) solution using moderate alkali immersions. The 16.1% LH yield was obtained, and cellulose nanofibrils (CCNF) were derived from the solid, at 43.1% yield of the original celery by oxalic acid hydrolysis. Oxalic acid hydrolysis followed by microfluidization was used to separate CCNF with dimensions of 5–6 nm and 1.3–1.7 μm. The LH solution containing CCNF was cast into film structures that exhibited significantly improved mechanical and flexibility properties. Moreover, results suggested that these hybrid films showed a high MB removal efficiency, which ranged from 192.1 to 429.9 mg/g. Totally, over 67.9% celery hybrids were used and it provided an effective and value-added utilization technology for celery and other vegetables.

Slow pyrolysis of biomass: effects of effective hydrogen-to-carbon atomic ratio of biomass and reaction atmospheres

ABSTRACT In this study, slow pyrolysis of eight biomass feedstocks was examined at 350°C for 60 min. The effects of the biomass effective hydrogen-to-carbon atomic ratio (H/Ceff) and reaction atmosphere (N2, H2, CO2, and CH4) on the product yields and properties of the pyrolysis oil were studied. Basically, biomass with a higher H/Ceff ratio produced a higher pyrolysis oil yield and a lower solid yield, which varied between 4.66 and 45.57 wt.% and 22.10 and 54.17 wt.%, respectively. The pyrolysis oil yield is proportional to the protein+lipid content, while the solid yield is proportional to the cellulose +hemicellulose lignin content of the biomass feedstock. Lignin is the most difficult component of the biomass feedstock to convert. The effect of the reaction atmosphere on the pyrolysis product distribution depends on the biomass H/Ceff. The pyrolysis oil+gas yield decreased in the order H2> N2> CO2> CH4 with biomass H/Ceff ≤ 0.61, CH4> H2> CO2> N2 with biomass H/Ceff between 0.61 and 0.96, and N2> CO2> H2> CH4 with biomass H/Ceff ≥0.97. The gaseous products mainly consisted of CO2, CH4, CO, H2, C2H6, and C3H8, and CO2 always had the highest yield. All the pyrolysis oils had higher C and H content and lower O and S content compared with that of the biomass feedstock, and biomass with a higher H/Ceff ratio produced a pyrolysis oil with a higher H/Ceff ratio. Furthermore, biomass with a higher H/Ceff ratio produced a pyrolysis oil with a higher saturated hydrocarbon content, while biomass with a lower H/Ceff ratio produced a pyrolysis oil with a higher content of ketones and phenolic compounds.

Pretreatment of Lignocellulosic Biomass Using Vortex-Based Devices for Cavitation: Influence on Biomethane Potential

Lignocellulosic biomass (LCB) is an abundant renewable resource that can be used to produce fuels and chemicals. Valorization of LCB is, however, a challenge due to its recalcitrant nature posed by the strongly interlinked cellulose–lignin–hemicellulose structures. A range of physicochemical and biological LCB pretreatment methods has been reported in the literature for enhancing its bioutilization. In this work, we used hydrodynamic cavitation (HC) based on vortex devices as a chemical-free, environmentally friendly LCB pretreatment method to enhance biomethane production. A bench scale pretreatment setup using a vortex-based cavitation device was established for the pretreatment of two common LCBs: grass silage (GS) and sugar cane bagasse (SCB). Dried and powdered feedstocks were used in all the experiments. HC was carried out by operating the cavitation device at a flow rate of ∼1.5 m3/h. The feedstocks before and after pretreatment were characterized for morphological and compositional differences using a range of analytical techniques. Liquid phase products produced upon cavitation were also analyzed using an HPLC-RI. Biomethane potential (BMP) was measured for GS and SCB with and without pretreatment, and a first order model was used to describe the kinetics. Up to 40% enhancement was observed in BMP after cavitation pretreatment using vortex-based devices. A brief discussion on preliminary cost considerations based on the experimentally observed enhancement in BMP is included. The results indicate significant promise of harnessing hydrodynamic cavitation-based pretreatment using vortex-based devices for enhancing biomethane production from LCB.

A novel deep eutectic solvent from lignin-derived acids for improving the enzymatic digestibility of herbal residues from cellulose

A novel lignin-derived deep eutectic solvent (DES) was synthesized from choline chloride (ChCl) and p-coumaric acid (PCA). The results showed that after pretreatment with lignin-derived DES, the dense cellulose–hemicellulose–lignin structure of herb residues of Cortex albiziae (HRCA) was effectively broken down and this facilitated subsequent enzymatic hydrolysis. The optimum pretreatment conditions were ChCl/PCA molar ratio of 1:1, 160 °C-5 h, and a solid–liquid ratio of 1:10. Compared with untreated HRCA, 72-h enzymatic digestibility increased from 48.08 to 84.62%. When a ChCl–PCA–water pretreatment was used, the 72-h digestibility level of the residue reached 99.36%. Moreover, the recycling and reusability of this novel DES were evaluated. The results showed that synthesis and utilization of green, environment-friendly and recyclable lignin-derived DES can offer a new way of utilizing lignin which has considerable potential in the refining of biomass. A novel lignin-derived deep eutectic solvent was synthesized, this DES pretreatment can improve the enzymatic digestibility of HCRA cellulose efficiently.

Enzymatic biocatalysis of bamboo chemical constituents to impart antimold properties

Current antimold agents that capitalize on broad spectrum biocidal toxicity for their efficacy can create potential hazards in the environment, as in many cases these biocides are not chemically bonded to the wood. They can therefore leach into the ecosystem to jeopardize off-target organisms. In this study, “bio-catalysis” of potassium iodide (KI) was used to impart non-diffusible antimold properties to 4-year-old bamboo, and the mechanisms of how this system works against Aspergillus niger and Trichoderma viride fungi were also studied. In addition to the bamboo block material tested, powdered samples of lignin, cellulose and hemicellulose were studied to better understand binding of iodide to the chemical subcomponents of the bamboo cell walls. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were used to investigate the sample chemistries and antimold mechanisms, respectively. The results revealed that a specific ratio of laccase enzyme with a laccase-mediator functioned best in binding KI to bamboo. Lignin samples showed the greatest changes in FTIR, especially relative to the methoxyl groups and aromatic skeleton. Additionally, enzyme activity on lignin moieties showed much more differences than on hemicellulose and cellulose after biocatalyzed KI modification. Moreover, the XPS binding energy readings of 621.1 and 632.7 eV (Aromatic region) for lignin were consistent with I–C binding associated with its phenolic structures. While the 620.7 eV (Aliphatic region) suggested I–C bonding that associated with residual lignin in hemicellulose, no peaks were observed for the iodine 3d XPS spectra of treated cellulose. XPS analyses of the O/C and C1/C2 ratios revealed that the formation of I–C bonds was likely due to the substitution of oxygen-contained groups which were formed from laccase-catalyzed oxidation. Thus, enzyme-catalyzed formation of I–C bonds with bamboo chemical constituents is a highly effectual, as well as an ecological method to protect bamboo against mold colonization in the present research.

Effect of acidic pretreatment on the chemistry and distribution of lignin in aspen wood and wheat straw substrates

In this work, aspen and wheat straw substrates were pretreated using aqueous dilute acid (DA) and chemimechanical (CM) pretreatment, and the impact of these pretreatments on biomass lignin was investigated. Here DA pretreatment refers to the acidic treatment of biomass powders and CM pretreatment refers to the acidic treatments of chips or stalks followed by disc refining. The resulting substrates were observed using advanced microscopy techniques to determine changes in lignin distribution throughout the fiber cell wall due to the acid treatments. Following acid treatment, lignin within the cell wall was divided into spherical or elongated bundles. The surface of DA and CM pretreated substrates were shown to differ, with CM pretreated aspen exhibited a more cellulose-rich surface. X-ray Photoelectron Spectroscopy data indicated reduced surface lignin on CM pretreated aspen and increased surface lignin on CM pretreated wheat straw. Fourier transform infrared spectroscopy (FT-IR) spectra illustrated changes in bands related to hemicellulose lignin, and surface hydroxyl content suggesting possible differences in lignin chemistry. It was hypothesized that differences in lignin distribution based on biomass type and pretreatment method were due to interactions between the chemical treatment and the mechanical size reductions steps. Particle size prior to chemical treatment could impact the movement of lignin onto sample surface, and chemical treatment prior to size reduction could impact the fracture plane during the downsizing process. It is expected that both these effects could impact lignin distribution within the sample and on the sample surface.

Observations of Wood Cell Walls with a Scanning Probe Microscope

Scanning Probe Microscopes (SPMs) observe specimen surfaces with probes by detecting the physical amount of a material between the cantilever and the surface. SPMs have a high resolution and can measure mechanical characteristics such as stiffness, adsorptive properties, and viscoelasticity. These features make it easy to identify the surface structure of complex materials; therefore, the use of SPMs has increased in recent years. Wood cell walls are primarily composed of cellulose, hemicellulose, and lignin. It is believed that hemicellulose and lignin surround the cellulose framework; however, their detailed formation remains unknown. Therefore, we observed wood cell walls via scanning probe microscopy to try to reveal the formation of the cellulose framework. We determined that the size of the cellulose microfibril bundle and hemicellulose lignin module composite was 18.48 nm based on topography and that the size of the cellulose microfibril bundle was 15.33 nm based on phase images. In the viscoelasticity image, we found that the viscoelasticities of each cell wall of the same cell were not the same. This is because the cellulose microfibrils in each cell wall lean in different directions. The angle between the leaning of the cellulose microfibril and the cantilever affects the viscoelasticity measurement.

On the formation of lignin polysaccharide networks in Norway spruce

In this study we were mirroring suggested in vivo phenomena of lignin–hemicellulose complex formation in vitro, by cross-linking Norway spruce (Picea abies) galactoglucomannans, xylans and lignin moieties to high molecular weight complexes by laccase treatment. We were able to observe the oxidation and cross-linking of non-condensed guaiacyl-type phenolic moieties attached to both of the hemicelluloses by 31P NMR and size-exclusion chromatography. We suggest that hemicelluloses–lignin complexes form covalently linked structural units during the early stages of lignification via radical enzymatic cross-linking catalyzed by laccase. This work shows that the hemicellulose molecules in wood are covalently linked to two or more lignin units thereby making them suited for forming network structures.

Production of fermentable sugar from elephant grass (Pennisetum purpureum).

En el presente artículo se muestran, los resultados de la obtención de azúcares fermentables utilizando como materia prima pasto elefante (Pennisetum purpureum). Se evaluó el efecto de la concentración del ácido acético (CH3COOH) y el clorito de sodio (NaClO2) sobre la eliminación del complejo lignina hemicelulosa. Se realizó una comparación del método utilizando pretratamientos básicos con hidróxido de sodio (NaOH) y peróxido de hidrógeno (H2O2). La etapa de sacarificación se cumplió utilizando el método de hidrólisis enzimática y con el uso de celulasa y β-glucosidasa. Los resultados muestran que empleando el pretratamiento con CH3COOH y NaClO2 presenta un porcentaje de sacarificación del 80,87% en comparación con el pretratamiento con NaOH con un porcentaje de 56,82% y del peróxido de hidrógeno con un porcentaje de 44,75%.