Residual Lignin Research Articles

Catalytic hydrogenolysis lignin to obtain phenols: A review of selective cleavage of ether bonds

Lignin depolymerized phenolic compounds and biofuel precursors are ideal value-added products for lignin residues generated in biorefineries and modern paper pulp facilities. Hydrogenolysis of lignin is an efficient depolymerization method for the production of carbon-neutral sustainable fuels and platform chemicals. Lignin is underutilized due to its complex structure, mainly because of its complex interunit linkage crosslinks such as α-O-4, β-O-4, 4-O-5, and β-5. This paper centers on the hydrolysis reaction of three major ether bonds (α-O-4, β-O-4, 4-O-5) in lignin and lignin model compounds based on different catalysts for hydrogenative degradation and catalytic systems. The methods and strategies to inhibit the condensation reactions are summarized. In particular, density functional theory calculation of the reaction pathways are combined with isotopically labeled reaction pathways to deeply analyze the hydrogenation degradation mechanism of biomass and further improve the yield of monophenols during the hydrogenation degradation of lignin. Finally, a brief summary of the challenges and prospects of lignin hydrogenation degradation is proposed.

The effect of oxygen bleaching on reactivity of syringyl and guaiacyl units of Eucalyptus tereticornis pulps lignin

Dioxin lignin of Eucalyptus tereticornis kraft pulps and its oxygen-treated pulps with kappa number 21.32, 12.84; 13.03, 12.18 were isolated and subjected to alkaline nitrobenzene oxidation studies to determine the structural changes during oxygen bleaching. HPLC quantitatively identified eight compounds during nitrobenzene oxidation of dioxin lignin in alkaline media. Lignin obtained from E. tereticornis has syringyl and guaiacyl units. Residual lignin composition in pulps was studied and found that during oxygen delignification, the syringyl unit was degraded more in comparison to guaiacyl and p-hydroxy phenyl unit, i.e., the molar ratio of syringyl unit is lower than guaiacyl and p-hydroxy phenyl unit. The results are adequately described in the research.

Effect of pretreatment severity on the inhibitory behaviors of larch lignins in enzymatic hydrolysis

To explore the underlying reasons for the decreased enzymatic hydrolysis yields of the acid pretreated softwood under the higher pretreatment severity, the residual bulk lignins, as one type lignin fraction with stronger inhibition, were isolated from larch (softwood) pretreated with different pretreatment severity in this study. The lignin structure changes during the pretreatment were comprehensively investigated by nuclear magnetic resonance (NMR) analysis. The larch lignins addition decreased the enzymatic hydrolysis of Avicel from 68.43% to 25.9–39.3%. The pretreatment intensified the inhibition of isolated lignins on enzymatic hydrolysis of Avicel. Furthermore, quartz crystal microbalance (QCM) analysis was applied to investigate the interaction between enzyme and lignins, distinguishing the reversible and irreversible enzyme adsorption. It demonstrated that the obviously higher irreversible adsorption of enzyme was observed on lignins from pretreated substrates with the higher severity. Additionally, the correlation between structure and inhibition of residual lignins in the enzymatic hydrolysis was then investigated with Pearson’s correlation heatmap. The findings can be used to develop theoretical guidelines for alleviating the residual lignin inhibition in the enzymatic hydrolysis of acidic pretreated softwood.

H2O2 Solution Steaming Combined Method to Cellulose Skeleton for Transparent Wood Infiltrated with Cellulose Acetate

Hydrogen peroxide (H2O2) steaming, a green and highly efficient delignification method, has been demonstrated to provide a wood skeleton with a very low content of residual lignin in the manufacturing of transparent wood. It usually requires a long reaction time and a large amount of H2O2 because the piece of wood is treated using steaming equipment. Herein, a H2O2 solution steaming method was developed for the highly efficient removal of lignin from wood. Specifically, several wood samples were simultaneously immersed in a hot H2O2 solution to obtain delignified wood with a relatively high content of residual lignin, which provided a high strength and preserved the cellulose skeleton. Subsequently, the delignified wood with a relatively high content of residual lignin was further treated with H2O2 steam to obtain a very low lignin delignified wood. Compared with the previous H2O2 steaming method, the reaction time and used H2O2 volume of the H2O2 solution steaming method was reduced by 37.3% and 52.7%, respectively. All-biomass transparent wood could be obtained by infiltrating the delignified wood with cellulose acetate, which showed both a high transmittance of 83.0% and a low thermal conductivity of 0.30 Wm-1K-1.

Anaerobic digestion of recycled paper crumb and effects of digestate on concrete performance

Paper crumb (PC) is a type of paper sludge residue from the wastepaper recycling industry. It is a by-product from the various fiber purification stages that is particularly composed of short cellulose fibers, lignin, organic compounds and inorganic filler residues. Despite representing a reject material for the paper recycling sector, this feedstock can be turned into a bioresource to enable cross-sector industrial symbiosis in the form of a more sustainable concrete, hence an opportunity for novel Net Zero supply chains. This study sought to valorise the PC by the sequential anaerobic digestion to produce methane (CH4) from the organic compounds, followed by utilization of the digestate as a water replacement in concrete. The 21-day digestion of PC yielded 163 ml CH4 per gram volatile solids and the resulting digestate improved concrete compressive strength up to 50% water replacement grade, meeting the requirements for structural grade (C32/40) applications with substitution grades up to 50% and 25%, with and without the addition of plasticiser respectively. In a minor capacity, the digestate reduced workability of the concrete mix, however we demonstrate this issue can be resolved by the addition of plasticiser or increased water to cement ratios. The admixture addition is important to facilitate pumpability on site and ensure satisfactory compaction. This study highlights the potential of anaerobic digestate as a concrete supplement (additive), which would improve the sustainability of both the construction and the paper sector.

Development of an Integrated Biorefinery System for Bioconversion of Lignocellulosic Biomass to Polyhydroxyalkanoates and Biohydrogen

A sustainable lignocellulosic biomass-based biorefinery requires complete utilization and valorization of the biomass components. In the present study, a phase-separated pretreatment (chemo mechanical─delignification followed by bacterial pretreatment) was performed to fractionate lignin and cellulose-rich residue from rice straw biomass (RSB) to utilize lignin for polyhydroxyalkanoates (PHA) and cellulose-rich residue for biohydrogen production. A higher lignin removal of 81.4% was obtained through combined H2O2–homogenizer pretreatment. The lignin was utilized as a substrate by Bacillus cereus for PHA production. The cellulose-rich delignified RSB was hydrolyzed with cellulase-secreting bacteria. A higher chemical oxygen demand solubilization of 38.2% was achieved in delignified and bacterially (Delig-Bac) pretreated RSB than bacterially pretreated (Bac) alone (22.9%) and control (3.43%). A higher cellulose solubilization of 35.8% was obtained in Delig-Bac pretreated RSB than Bac alone (21.5%). A higher PHA concentration, content, and yield of 480 mg/L, 56%, and 561 mg/g were obtained from 2.970 g/L of lignin. Higher biohydrogen production of 66 mL/gVS was achieved in Delig-Bac pretreated RSB. The economic analysis revealed that Delig-Bac was found to be economically feasible with a net profit of 4.18 USD/m3 when compared to Bac (−457.4 USD/m3).

Agricultural residue lignin from novel low-temperature pretreatment as potential raw material for LPF resins

Agricultural residue lignin from novel low-temperature pretreatment as potential raw material for LPF resins

Dry biorefinery conversion of cadmium-contaminated rice grain and straw to ethanol with complete collection and recycling of cadmium

Cadmium contaminated rice should be carefully treated by considering two aspects: full recovery of cadmium without risks of emission to environment, and energy balance between input and consumption. Separate treatment of rice grain and rice straw not only generates cadmium contained wastewater but also produces solid residue with livestock feed potentials. This study investigated a dry biorefining treatment to convert whole rice biomass (both grain and straw) into bioethanol at a reasonable energy balance and without solids residue potentials. The cadmium contained wastewater was significantly reduced and further completely evaporated into cadmium-free steam for recycled use in the treatment. The cadmium contained lignin solids were completely burned to evaporate the wastewater. The final cadmium content in combustion ash was enriched by 5–7 folds compared to raw rice biomass. The simulation showed that the heat generation from lignin residue combustion compensated for the energy requirement of wastewater evaporation. This study provides a fully converged treatment method of cadmium contaminated rice biomass on both cadmium and energy consumption with value added bioethanol production.

Simple adsorptive removal of crystal violet, a triarylmethane dye, from synthetic wastewater using Fe (III)-treated pine needle biochar.

Untreated and Fe (III)-treated pine needle biochar (PNB) were evaluated at different pH for the removal of toxic crystal violet (CV) dye from synthetic wastewaters. Adsorption kinetics followed the pseudo-first-order kinetics involving intra-particle diffusion process. The adsorption rate constant increased with Fe treatment of PNB especially at pH 7.0. Adsorption data of CV conformed well to Freundlich adsorption isotherms and both adsorption capacity (ln K) and order of adsorption (1/n) of CV were nearly doubled with Fe (III) treatment of PNB at pH 7.0. Desorption of adsorbed CV from both untreated and Fe (III)-treated PNB could be accounted satisfactorily by third-degree polynomial equations. An increase in ionic strength and temperature enhanced dye adsorption onto untreated and Fe (III)-treated PNB. Adsorption of CV was an endothermic and spontaneous reaction with an increase in entropy of the system. FTIR spectra revealed that C = O of carboxylic acid aryls and C = O and C-O-C in lignin residues of PNB reacted with Fe (III) besides the formation of some iron oxyhydroxide minerals. The changes in FTIR confirmed the possible bonding of positively charged moiety of CV with the untreated and Fe-treated PNB. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed the porous surfaces of PNB with clear accumulation of Fe (III) after treatment and deposition of CV dye on surfaces and pores of PNB. Iron (III)-treated PNB at pH 7.0 can serve as an ecofriendly and cost-effective adsorbent for the efficient removal of CV dye from wastewaters.

Lignin-Based Admixtures: A Scientometric Analysis and Qualitative Discussion Applied to Cement-Based Composites.

The development of lignin-based admixtures (LBAs) for cement-based composites is an alternative to valorizing residual lignins generated in biorefineries and pulp and paper mills. Consequently, LBAs have become an emerging research domain in the past decade. This study examined the bibliographic data on LBAs through a scientometric analysis and in-depth qualitative discussion. For this purpose, 161 articles were selected for the scientometric approach. After analyzing the articles' abstracts, 37 papers on developing new LBAs were selected and critically reviewed. Significant publication sources, frequent keywords, influential scholars, and contributing countries in LBAs research were identified during the science mapping. The LBAs developed so far were classified as plasticizers, superplasticizers, set retarders, grinding aids, and air-entraining admixtures. The qualitative discussion revealed that most studies have focused on developing LBAs using Kraft lignins from pulp and paper mills. Thus, residual lignins from biorefineries need more attention since their valorization is a relevant strategy for emerging economies with high biomass availability. Most studies focused on production processes, chemical characterizations, and primary fresh-state analyses of LBA-containing cement-based composites. However, to better assess the feasibility of using different LBAs and encompass the multidisciplinarity of this subject, it is mandatory that future studies also evaluate hardened-sate properties. This holistic review offers a helpful reference point to early-stage researchers, industry professionals, and funding authorities on the research progress in LBAs. It also contributes to understanding the role of lignin in sustainable construction.

Treatment of Pulp Black Liquor with an Ionic Liquid: Optimisation by Using Response Surface Methodology.

: In this study, selective extraction towards ionic liquid trihexyltetradecylphosphonium chloride ([P66614]Cl) of lignin residues, polysaccharides and organic acids present in black liquor (BL), the main principal wastewater of pulping industry was studied. With the objective of finding optimized conditions allowing to extract lignin resideus while polysaccharides and organic acids remain in aqueous solution, a design of experiments approach based on a response surface methodology was used. Three continuous factors, namely initial pH varying from 9 to 13.5, dilution of BL varying from 5 to 20 and volumetric ratio of black liquor vs. ionic liquid RV., varying from 1 to 19, were investigated. Concentration of ligni residues, polysaccharides and organic acids were measured using Folin-Ciocalteu method, the anthrone method and HPLC, respectively. Results showed that a multi-response optimization led to the extraction of 84.8 % of lignin residues, 66.0 % of polysaccharides, and no extraction of OA under optimised conditions.

Design and techno–economic analysis of levulinic acid production process from biomass by using co-product formic acid as a catalyst with minimal waste generation

Levulinic acid (LA) is an essential biomass-derived platform chemical that can be converted into value–added chemicals such as polymers, fertilisers, and pharmaceuticals. However, the high energy demand and cost required in the separation process are significant issues in the LA production process. Recently, formic acid (FA), the co–product in biomass–LA reaction, has been focused on as a catalyst for both biomass pretreatment and LA production. This study designed and numerically simulated a novel process for producing LA from wheat straw (feed rate: 100 kg/h) using an FA aqueous catalyst system (60, 70, and 80 wt%). The reaction data were referred to previous kinetics studies in order to evaluate the feasible reaction time from an economic perspective. The minimised waste generation process was designed by recovering the FA catalyst and using solid residues (lignin and humins) as heat sources. Another byproduct, furfural, was utilised as an extractant for purifying the LA and recovering unreacted products. The minimum selling price (MSP) of the LA and furfural was calculated with an internal rate of return of 6.1% for 20 years. The MSPs were calculated to be 9.59–12.8 USD/kg–products, which was higher than the market price and previous studies. However, the net required energy in this process was − 5.37 to − 32.1 MJ/kg–LA, indicating that the combustion of the solid residue can supply all of the energy required for the process. Our novel concept based on the byproduct utilisation for heat source and extractant can be an effective strategy for an implication of the biorefinery process that can circulate energy with minimum waste generation.

Effect of Lignin-Rich Microfiber on Handsheet Strength

This study explores the effects of using lignin-rich microfibers as a reinforcing material to enhance paper strength. The microfibers prepared by alkaline kneading of organosolv pulp for 1 to 3 hours were characterized in terms of fiber dimensions, residual lignin content, freeness, and water retention value. Longer alkaline kneading times were more effective for improved fiber micronization. In addition, freeness decreased and water retention value increased as a result of the kneading treatment. The microfibers were added at increasing amounts (1%, 3%, and 5% based on oven-dry weight) to commercial bleached kraft pulp to evaluate the effect of microfiber content on handsheet strength. The results showed that microfibers at a level of 5% increased the tensile index of the handsheet by up to 8%, indicating that lignin-rich microfibers have a high potential for use as paper strength additives.

Enhanced bio-ethanol production from bamboo residues by alkali-aided Fenton reaction pretreatment and enzymatic saccharification

Alkali extraction was used to assist the Fenton pretreatment for overcoming the recalcitrance of bamboo and producing more sugar-based chemicals and bioethanol. The alkali-aided Fenton pretreatment showed the delignification of 55.33% and xylan removal of 80.76%. The surface lignin coverage, hydrophobicity, specific surface area, and cellulose crystallinity index were obviously changed by the combined pretreatment, which made cellulose accessibility increased by about 2-folds than Fenton pretreatment alone. The cleavage of β-O-4 linkage, the decrease of condensed structure and syringyl unit were observed in the residual lignin from the NaOH-Fenton pretreated D. brandisii, all of which reduced the nonproductive adsorption between enzymes and lignin. When NaOH-Fenton pretreated four bamboo residues were performed enzymatic hydrolysis, glucose yields of 66–74% and ethanol concentration of 11–16 g/L were obtained. The sequential NaOH-Fenton pretreatment should be considered as an environmentally-friendly bamboo biorefinery technology in the future.

Production of Diethyl Maleate via Oxidative Depolymerization of Organosolv Lignin from Wheat Stalk over the Cooperative Acidic Ionic Liquid Pair

Lignin, the second largest component of biomass, is considered as an important alternative source of fossil reserves for the production of fuels and chemicals. Here, we developed a novel method to oxidatively degrade organosolv lignin into value-added four-carbon esters, particularly diethyl maleate (DEM), with the cooperative catalyst consisting of 1-(3-sulfobutyl) triethylammonium hydrogen sulfate ([BSTEA]HSO4) and 1-butyl-3-methylimidazolium ferric chloride ([BMIM]Fe2Cl7). Under optimized conditions (1.00 MPa initial O2 pressure, 160 °C, 5 h), the lignin aromatic ring was effectively cleaved by oxidation to form DEM with a yield of 15.85% and a selectivity of 44.25% in the presence of the synergistic catalyst of [BMIM]Fe2Cl7-[BSMIM]HSO4 (1/3, mol/mol). The structure and composition analysis of lignin residues and liquid products confirmed that the aromatic units in lignin were effectively and selectively oxidized. Furthermore, the catalytic oxidation of lignin model compounds was explored for obtaining a possible reaction pathway of oxidative cleavage of lignin aromatic units to DEM. This study provides a promising alternative method for the production of traditional petroleum-based chemicals.

Structural alteration of cocoa bean shell fibers through biological treatment using Penicillium roqueforti

Lignocellulosic residues, such as cocoa bean shell (FI), are generated in large quantities during agro-industrial activities. Proper management of residual biomass through solid state fermentation (SSF) can be effective in obtaining value-added products. The hypothesis of the present work is that the bioprocess promoted by P. roqueforti can lead to structural changes in the fibers of the fermented cocoa bean shell (FF) that confer characteristics of industrial interest. To unveil such changes, the techniques of FTIR, SEM, XRD, TGA/TG were used. After SSF, an increase of 36.6% in the crystallinity index was observed, reflecting the reduction of amorphous components such as lignin in the FI residue. Furthermore, an increase in porosity was observed through the reduction of the 2θ angle, which gives the FF a potential candidate for applications of porous products. The FTIR results confirm the reduction in hemicellulose content after SSF. The thermal and thermogravimetric tests showed an increase in the hydrophilicity and thermal stability of FF (15% decomposition) in relation to the by-product FI (40% decomposition). These data provided important information regarding changes in the crystallinity of the residue, existing functional groups and changes in degradation temperatures.

Bioactive Absorbent Chitosan Aerogels Reinforced with Bay Tree Pruning Waste Nanocellulose with Antioxidant Properties for Burger Meat Preservation.

As a transition strategy towards sustainability, food packaging plays a crucial role in the current era. This, carried out in a biorefinery context of agricultural residues, involves not only obtaining desirable products but a comprehensive utilization of biomass that contributes to the circular bioeconomy. The present work proposes the preparation of bioactive absorbent food pads through a multi-product biorefinery approach from bay tree pruning waste (BTPW). In a first step, chitosan aerogels reinforced with lignocellulose and cellulose micro/nanofibers from BTPW were prepared, studying the effect of residual lignin on the material's properties. The presence of micro/nanofibers improved the mechanical performance (up to 60%) in addition to increasing the water uptake (42%) when lignin was present. The second step was to make them bioactive by incorporating bay leaf extract. The residual lignin in the micro/nanofibers was decisive, since when present, the release profiles of the extract were faster, reaching an antioxidant power of more than 85% after only 30 min. Finally, these bioactive aerogels were used as absorbent pads for fresh meat. With the use of the bioactive aerogels (with ≥2% extract), the meat remained fresh for 10 days as a result of delayed oxidation of the food during storage (20% metmyoglobin proportion).

Nitric acid-potassium hydroxide fractionation of rice straw: an integrated biorefinery initiative

Abstract Pulping of rice straw was studied using mild nitric acid in mild conditions. Spent nitric acid was chosen as soil nutrient rather than followed by the liquor recovery. The rice straw was treated with 11.03% nitric acid at 90 °C for 3 h, yielded 53.09% pulp. Nitric acid treated rice straw pulp had high residual lignin and minerals. However, further treatment with 7% potassium hydroxide reduced the residual lignin and produced pulp with kappa number 20.36. The papermaking properties of the nitric acid followed by KOH treated pulp showed better quality than the nitric acid pulp. The spent nitric acid liquor was reused repeatedly, pulp yield decreased and residual lignin content increased in each step of spent nitric acid reusing. The spent nitric acid liquor and potassium hydroxide liquor-mixed together to get a neutral effluent liquor which was rich with potassium, nitrogen and biomass. The nutritional capacity of the effluent liquor was assessed by incubation with control soil. The labile form of organic carbon, nitrogen, potassium phosphorous and iron increased in the incubated soil.

Horse manure as resource for biogas and nanolignocellulosic fibres

Nanofibrillated cellulose (NFC) has key applications in composites, water filters and as emulsifiers. The affinity of NFC to water is a challenge, as it negatively influences its integrity. Lignin, a major component of plant biomass, is a natural hydrophobiser. Anaerobic digestion (AD) of biomass to produce biomethane allows to up-concentrate lignin in the fermentation residue containing lignocellulosic fibres. Horse manure was used as substrate for biogas production from which nanolignocellulose fibres (LCNF) were extracted. A biogas yield of 207 LN kgVS−1 with a methane concentration of 65 % was achieved. From the fermentation residue LCNFs, in yields of up to 41 %, with lignin contents between 23 and 29 wt% depending on fermentation time were obtained. Nanopapers produced from LCNFs possessed tensile strengths and moduli of 45 to 91 MPa and 7 to 8 GPa, respectively. The increased lignin content was responsible for decreased water absorption capacity of nanopapers.

Isolation of Pure Lignin and Highly Digestible Cellulose from Defatted and Steam-Exploded Cynara cardunculus.

In this work, a three-step approach to isolate the main components of lignocellulosic cardoon, lignin and cellulose, was investigated. The raw defatted biomass, Cynara cardunculus, after steam explosion was subjected to a mild organosolv treatment to extract soluble lignin (L1). Then, enzymatic hydrolysis was performed to achieve decomposition of the saccharidic portion into monosaccharides and isolate residual lignin (L2). The fractionation conditions were optimized to obtain a lignin as less degraded as possible and to maximize the yield of enzymatic hydrolysis. Furthermore, the effect of the use of aqueous ammonia as an extraction catalyst on both fractions was studied. Each fraction was characterized by advanced techniques, such as elemental analysis and 31P nuclear magnetic resonance (NMR), 13C-1H two-dimensional (2D)-NMR, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), and UV-vis spectroscopies for lignin and X-ray diffraction (XRD), Klason compositional analysis, elemental analysis, and ATR-FTIR spectroscopy for cellulose-rich fractions. The impact of the cellulose-rich fraction composition and crystallinity was also correlated to the efficiency of the hydrolysis step, performed using the enzymatic complex Cellic CTec3.