High-purity Lignin Research Articles

Optimization of Organosolv Based Fractionation Process for Separation of High Purity Lignin from Bagasse

Lignocellulosic biomass is a renewable source for sustainable production of fuels, chemicals, and other materials with the advantages on its carbon-neutral nature. Fractionation of lignocellulosic materials is a pre-requisite in the biorefinery process in order to convert the cellulose, hemicellulose, and lignin to valuable products with maximized economics prospective. In this work, a modified clean fractionation (CF) process using ternary mixture system of ethyl acetate/methanol/water was studied with the use of acid promoters. H2SO4 was found to be the efficient promoter due to low cost compare to other acid promoters. The optimal fractionation conditions operated in the solvent mixture containing 0.025 M H2SO4 at 160°C for 50 min led to 63.72% recovery of the cellulose in the solid pulp while 90% and 59.94% of hemicellulose-derived products and lignin were recovered in the aqueous-alcohol and organic fractions, respectively. The enzymatic digestibility of the cellulose-enriched pulp was increased, resulting increasing glucose yield from 38.32% of the native biomass to 70.04% using the hydrolysis reaction with Cellic Ctech2® at 15 FPU/g. The work demonstrated the applicability of the modified CF process for fractionation of lignocellulose components for integrated biorefinery process.

New Biorefinery Strategy for High Purity Lignin Production

Due to their aromatic nature, lignins are of particular interest for chemical conversions of lignocellulosic resources. Organosolv pulping processes generally provide higher purity lignins, with lower sugar and ash contents than is the case with conventional pulping technologies (kraft, sulfite or soda). The strategy for new organosolv biorefinery presented here was to sequentially remove the extractives before pulping. The products obtained from organosolv pulping of aspen wood with a Lewis acid catalyst were compared to those from processes performed with the same wood and solvent system, but without or with mineral acid as catalyst. The new strategy with Lewis acid catalyst developed in this study proved to allow more efficient recovery of high purity lignin, which was determined to have a high Klason, low sugars, volatiles and ash contents, while preserving a good portion of β-O-4 moieties (31P and HSQC NMR), typical for native lignin. The thermal properties of this lignin were determined to be favorable to its transformation by electrospinning. It was successfully spun without need for any additives or modifications before electrospinning experiments.

Synergetic effect of dilute acid and alkali treatments on fractional application of rice straw.

BackgroundThe biorefinery based on an effective and economical process is to fractionate the three primary constituents (cellulose, hemicelluloses, and lignin) from lignocellulosic biomass, in which the constituents can be respectively converted into high-value-added products. In this study, a successive treatment with dilute acid (0.25–1.0 % aqueous H2SO4, 100–150 °C, 0.5–3.0 h) and alkali (1.5 % aqueous NaOH, 80 °C, 3 h) was performed to produce xylooligosaccharides (XOS), high-purity lignin, and cellulose-rich substrates to produce glucose for ethanol production from rice straw (RS).ResultsDuring the dilute acid pretreatment, the maximum production of XOS (12.8 g XOS/100 g RS) with a relatively low level of byproducts was achieved at a relatively low temperature (130 °C) and a low H2SO4 concentration (0.5 %) for a reaction time of 2.0 h. During the alkali post-treatment, 14.2 g lignin with a higher purity of 99.2 % and 30.3 g glucose with a higher conversion rate by enzymatic hydrolysis were obtained from the successively treated substrates with 100 g RS as starting material. As the pretreatment temperature, H2SO4 concentration, or time increased, more β-O-4 linkages in lignins were cleaved, which resulted in an increase of phenolic OH groups in lignin macromolecules. The signal intensities of G2 and G6 in HSQC spectra gradually reduced and vanished, indicating that a condensation reaction probably occurred at C-2 and C-6 of guaiacyl with the side chains of other lignin.ConclusionsThe present study demonstrated that the successive treatments with dilute acid and alkali had a synergetic effect on the fractionation of the three main constituents in RS. It is believed that the results obtained will enhance the availability of the combined techniques in the lignocellulosic biorefinery for the application of the main components, cellulose, hemicelluloses, and lignin as biochemical and biofuels.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0632-9) contains supplementary material, which is available to authorized users.

Enhancement of high-solids enzymatic hydrolysis of corncob residues by bisulfite pretreatment for biorefinery

Co-production of glucose, furfural and other green materials based on a lignocellulosic biorefinery is a promising way to realize the commercial application of corncob residues. An effective process was developed for glucose production using low temperature bisulfite pretreatment and high-solids enzymatic hydrolysis. Corncob residues from furfural production (FRs) were pretreated with 0.1g NaHSO3/g dry substrate at 100°C for 3h. Lignin was sulfonated and sulfonic groups were produced during pretreatment, which resulted in decreasing the zeta potential of the samples. Compared with raw material, bisulfite pretreatment of FRs increased the glucose yield from 18.6 to 99.45% after 72h hydrolysis at a solids loading of 12.5%. The hydrolysis residues showed a relatively high thermal stability and concentrated high derivatives. Direct pretreatment followed by enzymatic hydrolysis is an environmentally-friendly and economically-feasible method for the production of glucose and high-purity lignin, which could be further converted into high-value products.

Comprehension of an organosolv process for lignin extraction on Festuca arundinacea and monitoring of the cellulose degradation

It is commonly accepted that the current society needs to partially substitute fossil resources by renewable ones. Among many solutions, one approach consists in the development of biorefinery involving lignocellulosic biomass to produce bio-based materials and fuels. This study focuses on the comprehension of an organosolv treatment designed to break the complex lignocellulosic structure for high purity lignin extraction from tall fescue (Festuca arundinacea Schreb.). This grass benefits from an increasing interest in Western Europe and has been suggested as feedstock for biorefinery. However, its use as material for high purity lignin production has not been determined yet. Ethanol/water, 92/8% [v/v] with H2SO4 0.32M was investigated at pilot scale under conventional heating (5°Cmin−1 during 30min and stabilized at 148°C for 5min). Precipitated lignin were analyzed as well as the composition of side-stream products (recovered cellulosic pulp and the aqueous hydrolysate). Lignin has been recovered at a purity level of 90% with a yield of 60%. The main contaminants were nitrogen containing compounds and degraded hemicelluloses. 2D-HSQC NMR (Two Dimension-Heteronuclear Single Quantum Correlation Nuclear Magnetic Resonance) revealed a co-extraction of ferulates and coumarates function as well as arabinoxylan. Cellulose was recovered at 53% purity with 60% yield. The conditions appear to be too harsh for tall fescue and led to significant amount of cellulose degradation. A process using a lower alcohol concentration will be developed to provide better yields of both cellulose and lignin.

Two-stage dilute-acid and organic-solvent lignocellulosic pretreatment for enhanced bioprocessing

A two stage pretreatment approach for biomass is developed in the current work in which dilute acid (DA) pretreatment is followed by a solvent based pretreatment (N-methyl morpholine N oxide – NMMO). When the combined pretreatment (DAWNT) is applied to sugarcane bagasse and corn stover, the rates of hydrolysis and overall yields (>90%) are seen to dramatically improve and under certain conditions 48h can be taken off the time of hydrolysis with the additional NMMO step to reach similar conversions. DAWNT shows a 2-fold increase in characteristic rates and also fractionates different components of biomass – DA treatment removes the hemicellulose while the remaining cellulose is broken down by enzymatic hydrolysis after NMMO treatment to simple sugars. The remaining residual solid is high purity lignin. Future work will focus on developing a full scale economic analysis of DAWNT for use in biomass fractionation.

Synthesis and Characterization of Biodegradable Lignin Nanoparticles with Tunable Surface Properties.

Lignin nanoparticles can serve as biodegradable carriers of biocidal actives with minimal environmental footprint. Here we describe the colloidal synthesis and interfacial design of nanoparticles with tunable surface properties using two different lignin precursors, Kraft (Indulin AT) lignin and Organosolv (high-purity lignin). The green synthesis process is based on flash precipitation of dissolved lignin polymer, which enabled the formation of nanoparticles in the size range of 45-250 nm. The size evolution of the two types of lignin particles is fitted on the basis of modified diffusive growth kinetics and mass balance dependencies. The surface properties of the nanoparticles are fine-tuned by coating them with a cationic polyelectrolyte, poly(diallyldimethylammonium chloride). We analyze how the colloidal stability and dispersion properties of these two types of nanoparticles vary as a function of pH and salinities. The data show that the properties of the nanoparticles are governed by the type of lignin used and the presence of polyelectrolyte surface coating. The coating allows the control of the nanoparticles' surface charge and the extension of their stability into strongly basic regimes, facilitating their potential application at extreme pH conditions.

Purification of Biorefinery Lignin with Alcohols

After hydrothermal pretreatment and enzymatic hydrolysis of wheat straw, a slurry rich in lignin but with a high content of inorganic substances, especially silica, and residual carbohydrates is produced. This slurry was used to develop an ethanol organosolv separation method to produce silica-free lignin fractions. The addition of para toluene sulphonic acid (PTSA) and the use of two alternative long-chain alcohols, oleyl alcohol or nonylphenol, were tested. In every reaction, two lignin fractions were produced and their molecular size and elemental composition were characterized. The yield of each fraction and the change in MWD were studied as a function of temperature and solid to liquid ratio. At 100, 150, and 200°C and with the use of PTSA, high-purity lignin fractions were obtained. After lignin fractionation with nonylphenol, a liquid silica-free product with high lignin content was obtained in yields between 17 and 72%.

High purity lignin from new organosolv biorefinery

High purity lignin from new organosolv biorefinery

Effect of mixing hydrodynamics on the particle and filtration properties of precipitated lignin

The effects of mixing hydrodynamics on the particle and filtration properties of precipitated lignin from black liquor has been investigated. The hydrodynamics were varied in terms of turbulent shear rate and impeller flow pattern in the stirred tank. The precipitated lignin flocs were characterized in terms of particle size, size distribution, and particle shape. Our findings showed that the effect of hydrodynamics on the size and shape of primary lignin particles were negligible. However, the aggregation of primary particles into lignin flocs were affected by the hydrodynamics of the stirred tank. The size distribution and shape of the final lignin flocs could be controlled mainly through the manipulation of turbulent shear rate. Lignin flocs with higher compactness and size showed better filtration and washing properties. Optimal hydrodynamic conditions led to production of lignin with good filtration and washing properties at 1.83E+09m/kg specific filtration resistance, 243kg/hm2 lignin filtration rate, generating high purity lignin at 0.09% ash content. The reproducibility of the findings was validated using three other black liquor samples.

Structural changes in lignin during integrated process of steam explosion followed by alkaline hydrogen peroxide of Eucommia ulmoides Oliver and its effect on enzymatic hydrolysis

Eucommia ulmoides Oliver (EU) wood was successively treated by a combined system based on steam explosion pretreatment (SEP) and alkaline hydrogen peroxide post-treatment (AHPP). In this case, SEP was to disrupt the lignocellulosic structure, and the subsequent AHPP process was to isolate the high-purity lignin and cellulose-rich substrates. Results showed that the lignin fractions obtained during the AHPP exhibited smaller molecular weights, narrow polydispersity, less phenolic OH groups and lower syringyl/guaiacyl ratios (S/G) than those of the milled wood lignin (SEMWL) obtained from the only steam exploded EU. NMR characterization of lignin revealed that the AHPP process has a slight effect on the composition and molecular characteristic of lignin, and the lignin isolated had lower amounts of substructures (aryl-β-ether, resinol, and phenylcoumaran linkages) as compared to those in SEMWL. Moreover, the subsequent SEP followed by AHPP process enhanced the enzymatic hydrolysis of cellulose-rich substrates to a maximum value of 91.69%. It was found that the synergistic treatment removed most of lignin, degraded hemicelluloses, and incurred a higher crystalline index and surface area of the cellulose-rich substrates as compared to the only steam explosion pretreatment. The combination of the SEP and AHPP processes is an environmentally benign and advantageous scheme for the production of high-purity lignin and cellulose-rich substrates, which will be further transformed into the value-added biomaterials and bioethanol.

Structural transformations of triploid of Populus tomentosa Carr. lignin during auto-catalyzed ethanol organosolv pretreatment

Auto-catalyzed ethanol organosolv pretreatment (AEOP) has attracted considerable attention because it can effectively remove the recalcitrance of biomass and therefore benefit the downstream process, e.g., enzymatic hydrolysis. Triploid of Populus tomentosa Carr. chips were subjected to AEOP process. Three lignin preparations, including lignin dissolved in the pretreatment liquor (DL), lignin reprecipitated onto the pretreated residue (PL) and residual lignin in the ethanol-water washing residue (RL) were sequentially isolated. To delineate the structural transformations of lignin during this process, these three fractions were systematically characterized by gel permeation chromatography (GPC), quantitative 13C NMR, 31P NMR, heteronuclear single quantum coherence spectroscopy (2D-HSQC-NMR) and thermogravimetry analysis (TGA), and the results were compared with those of enzymatic hydrolysis lignin (EHL) from raw material. The results demonstrated that certain amounts of aryl-β ether (β-O-4') linkages were cleaved and stilbene units were formed during AEOP process, whereas the resinol (β-β') and phenylcoumaran (β-5') units were intact under the same reaction condition. In addition, DL, PL and RL fractions contained less aliphatic hydroxyl group and more phenolic hydroxyl group than EHL. Moreover, thermal stability of lignin samples was associated with their inherent structures. In short, understanding of fundamental lignin chemistry during AEOP process was beneficial to optimize, control delignification process, and obtain high-purity lignin and digestible substrates for bio-ethanol industry.

Effect of structural changes of lignin during the autohydrolysis and organosolv pretreatment on Eucommia ulmoides Oliver for an effective enzymatic hydrolysis

Eucommia ulmoides Oliver (EU) wood was successively treated by autohydrolysis and organosolv pretreatment integrated process. Autohydrolysis pretreatment facilitated xylooligosaccharides production, subsequent organosolv pretreatment to obtain high-purity lignin and digestible cellulose-rich residue. Results showed that the lignin fractions obtained exhibited smaller molecular weights, narrow polydispersity, more phenolic OH groups and higher syringyl/guaiacyl ratios (S/G) than the milled wood lignin. NMR characterization of the lignin revealed that the β-O-4 linkages significantly cleaved and the structure of stilbene formed, but its resinol (β–β) was resistant to be degraded by organosolv delignification. Moreover, the glucose yield of the integrated residue achieved a maximum value of 89.3% after enzyme hydrolysis, separately about 1.0, 1.3, 3.8 times as compared to that of the ethanol organosolv residue, the hydrothermally treated residue and the EU wood, respectively, which indicated that the integrated process was a promising approach to value-added utilization of the EU wood.

Enhanced enzymatic digestibility of bamboo by a combined system of multiple steam explosion and alkaline treatments

A combined system based on multiple steam explosion pretreatments (direct pretreatment and presoaked in 1% KOH aqueous solution followed by pretreatment under different conditions) and mild alkaline post-treatment has been developed to obtain digestible substrates from bamboo stems for bioethanol production. After the pretreatments, the enzymatic digestibility of cellulose increased to 17.1–32.2%, as compared to that of the untreated bamboo stems (5.8%). Direct pretreatment followed by alkaline treatment increased the enzymatic digestibility of cellulose to a maximum value of 73.8%. Alkaline treatment removed most of lignin and hemicelluloses, and incurred a higher crystalline index of the cellulose-rich residue obtained after a synergistic treatment as compared to the only steam-exploded substrates. The combination of direct pretreatment and alkaline treatment is an environmentally friendly and economical feasible method for the production of glucose and high-purity lignin, which will be further converted into high value-added products based on biorefinery.

Robust enzymatic hydrolysis of Formiline-pretreated oil palm empty fruit bunches (EFB) for efficient conversion of polysaccharide to sugars and ethanol

Oil palm empty fruit bunch (EFB) was pretreated by Formiline process to overcome biomass recalcitrance and obtain hemicellulosic syrup and lignin. Higher formic acid concentration led to more lignin removal but also higher degree of cellulose formylation. Cellulose digestibility could be well recovered after deformylation with a small amount of lime. After digested by enzyme loading of 15 FPU+10 CBU/g solid for 48 h, the polysaccharide conversion could be over 90%. Simultaneous saccharification and fermentation (SSF) results demonstrated that ethanol concentration reached 83.6 g/L with approximate 85% of theoretic yield when performed at an initial dry solid consistency of 20%. A mass balance showed that via Formiline pretreatment 0.166 kg of ethanol could be produced from 1 kg of dry EFB with co-production of 0.14 kg of high-purity lignin and 5.26 kg hemicellulosic syrup containing 2.8% xylose. Formiline pretreatment thus can be employed as an entry for biorefining of EFB.

Isolation of high quality lignin as a by-product from ammonia percolation pretreatment of poplar wood.

A two-step process combining percolation-mode ammonia pretreatment of poplar sawdust with mild organosolv purification of the extracted lignin produced high quality, high purity lignin in up to 31% yield and 50% recovery. The uncondensed fraction of the isolated lignin was up to 34%, close to that the native lignin (40%). Less lignin was recovered after pretreatment in batch mode, apparently due to condensation during the longer residence time of the solubilised lignin at elevated temperature. The lignin recovery was directly correlated with its molecular weight and its nitrogen content. Low nitrogen incorporation, observed at high ammonia concentration, may be explained by limited homolytic cleavage of β-O-4 bonds. Ammonia concentrations from 15% to 25% (w/w) gave similar results in terms of lignin structure, yield and recovery.

Lignin as Co-product of Second Generation Bioethanol Production from Ligno-cellulosic Biomass

To improve the economic viability of the biofuel production from biomass, it is of increasing importance to add value to the lignin produced as a bio-residue. Moreover, to meet the goal to replace 30% of fossil fuel by biofuels by 2030, a huge amount of lignin will soon be produced. The first major step involved to add value to the unconverted lignin is its separation from other biomass constituents to give high purity lignin. In this current work, extraction of lignin from a bio-residue (containing ca. 40% lignin) from second generation bioethanol production is presented. The biomass chosen is Arundo donax L. (or giant reed), which is non-food plant, can tolerate a wide variety of ecological conditions with all types of soils, and has increasingly importance as raw material for industrial purposes as a source of fibers alternative to wood, which availability is decreasing. Slightly different extraction procedures are investigated. Methods used are simple, mild, safe, and avoid destruction of fiber content in the bio- residue, with the final aim to valorize all fractions of the bio-residue, which is an essential step to make biofuel production to be cost effective. Lignins extracted are characterized by morphological analysis, using Scanning Electron Microscopy, SEM, and in terms of thermal behavior -using thermo gravimetric analysis TGA- which is critical for determining suitability of the lignin for polymer composite preparation with improved thermomechanical performance. The method judged as the best of the three leads rapidly to extraction of lignin free from fibers and ash, with thermal behavior suitable for composite preparation.

Fractionation of bamboo culms by autohydrolysis, organosolv delignification and extended delignification: Understanding the fundamental chemistry of the lignin during the integrated process

Bamboo (Phyllostachys pubescens) was successfully fractionated using a three-step integrated process: (1) autohydrolysis pretreatment facilitating xylooligosaccharide (XOS) production (2) organosolv delignification with organic acids to obtain high-purity lignin, and (3) extended delignification with alkaline hydrogen peroxide (AHP) to produce purified pulp. The integrated process was comprehensively evaluated by component analysis, SEM, XRD, and CP-MAS NMR techniques. Emphatically, the fundamental chemistry of the lignin fragments obtained from the integrated process was thoroughly investigated by gel permeation chromatography and solution-state NMR techniques (quantitative (13)C, 2D-HSQC, and (31)P-NMR spectroscopies). It is believed that the integrated process facilitate the production of XOS, high-purity lignin, and purified pulp. Moreover, the enhanced understanding of structural features and chemical reactivity of lignin polymers will maximize their utilizations in a future biorefinery industry.

Pre-treatment of lignocellulosic biomass using ionic liquids: Wheat straw fractionation

This work is devoted to study pre-treatment methodologies of wheat straw with 1-ethyl-3-methylimidazolium acetate ([emim][CH3COO]) and subsequent fractionation to cellulose, hemicellulose and lignin. The method developed and described here allows the separation into high purity carbohydrate and lignin fractions and permits an efficient IL recovery. A versatility of the established method was confirmed by the IL reuse. The fractionation of completely dissolved biomass led to cellulose-rich and hemicellulose-rich fractions. A high purity lignin was also achieved. To verify the potential further applicability of the obtained carbohydrate-rich fractions, and to evaluate the pre-treatment efficiency, the cellulose fraction resulting from the treatment with [emim][CH3COO] was subjected to enzymatic hydrolysis. Results showed a very high digestibility of the cellulose samples and confirmed a high glucose yield for the optimized pre-treatment methodology.

Kinetic Modeling and Mechanisms of Acid-Catalyzed Delignification of Sugarcane Bagasse by Aqueous Acetic Acid

Organosolv pretreatment of lignocellulose pertains to a biomass fractionation process to obtain cellulosic pulp, high-purity lignin, and hemicellulosic syrup. In the present work, sugarcane bagasse was delignified by aqueous acetic acid (AcH) under atmospheric pressure with addition of sulfuric acid (SA) as a catalyst. Based on the multilayered structure of plant cell wall and the inhibitive effect of dissolved lignin on delignification rate, a novel pseudo-homogeneous kinetic model was proposed by introducing the concept of “potential degree of delignification (dD)” into the model. It was found that delignification rate was a first-order reaction with respect to SA concentration, while AcH concentration showed a high reaction order to delignification rate. The activation energy for delignification was determined to be 64.41 kJ/mol. The relationships of kinetic constants and dD with reaction temperature, AcH, and SA concentrations were determined according to experimental data. Mechanism analysis indicated that cleavage of α-aryl ethers bonds were mainly responsible for the formation of lignin fragments. AcH concentration affected the solubility parameter (δ value) of AcH solution and the ability to form hydrogen bonds with lignin fragments. Therefore, the driving force for solubilizing lignin fragments increased with AcH concentration, and thus AcH concentration had a very significant influence on delignification rate.