Enzymatic Mild Acidolysis Lignin Research Articles

The glass transition temperature of isolated native, residual, and technical lignin

Abstract The glass transition temperatures (T g) of native, residual, and technical lignins are important to lignocellulose pulping, pulp processing and side stream utilization; however, how the structural changes from native to residual and technical lignin influences T g has proven difficult to elucidate. Since the T g of macromolecules is greatly influenced by the molecular weight, low-molecular-weight fractions, such as milled wood lignin (MWL), are poor representatives of lignin in the cell wall. To circumvent this problem, lignins of both high yield and purity were isolated from Norway spruce and softwood kraft pulp using the enzymatic mild acidolysis lignin (EMAL) protocol. Technical softwood kraft lignin was also fractionated into groups of different molecular weights, to acquire lignin that spanned over a wide molecular-weight range. A powder sample holder for dynamic mechanical analysis (DMA), was used to determine the T g of lignins, for which calorimetric methods were not sensitive enough. The T gs of EMAL were found to be closer to their in situ counterparts than MWL.

Selecting Suitable Near-Native Lignins for Research.

There are several methods to isolate near-native lignins, including milled-wood lignin, enzymatic lignin, cellulolytic enzyme lignin, and enzymatic mild-acidolysis lignin. Which one is the most representative of the native lignin? Herein, near-native lignins were isolated from different plant groups and structurally analyzed to determine how well these lignins represented their native lignin counterparts. Analytical methods were applied to understand the molecular weight, monomer composition, and distribution of interunit linkages in the structure of the lignins. The results indicated that either enzymatic lignin or cellulolytic enzyme lignin may be used to represent native lignin in softwoods and hardwoods. None of the lignins, however, appeared to represent native lignins in grasses (monocot plants) because of substantial syringyl/guaiacyl differences. Complicating the understanding of grass lignin structure, large amounts of hydroxycinnamates acylate their polysaccharides and, when released, are often conflated with actual lignin monomers.

Insights into bamboo delignification with acidic deep eutectic solvents pretreatment for enhanced lignin fractionation and valorization

Deep eutectic solvent (DES) as novel and green solvents can efficiently promote the fractionation of high-purity lignin from lignocellulosic biomass pretreatment. Revealing the fundamental chemistry of lignin during DES pretreatment will improve methodology to optimize the pretreatment in an integrated biorefinery. Herein, an acidic biomass-derived DES (choline chloride/oxalic acid) pretreatment was developed to deconstruct the recalcitrance of bamboo for enhanced lignin fractionation and valorization. The structure transformation of the regenerated lignin samples obtained at different pretreatment temperatures has been investigated in comparison with enzymatic mild acidolysis lignin (EMAL) by state-of-the-art NMR (2D HSQC, quantitative 13C, 31P), GPC, and TGA analysis. The results revealed that acidic DES assisted bamboo delignification and promoted the cleavage of β-O-4′ linkages at elevated reaction temperature, leading to an increase in the sustained rise of phenolic OH groups and lower molecular weights. Those lignin samples exhibited higher thermal stability and excellent antioxidant activity, suggesting great potential applications in lignin-based chemicals and material. Lignin condensation with unsaturated reactive intermediates which is accompanied by the depolymerization process during this acidic DES system. The results also highlight the utilization of acidic DES as a low-cost, high performance with a long delignification durability and thermal stability. Overall, the insights gained here could shed new light on the design and fabrication of efficient and durable DES-based pretreatment for the production of bio-fuel, bio-based materials and bio-chemicals.

Lignin waste as co-substrate on decolorization of azo dyes by Ganoderma lucidum

Improvement of dye removal efficiency is beneficial to development of bioremediation for textile effluent. In this study, the effect of lignin model compounds (LMCs) and enzymatic/mild acidolysis lignin (EMAL) from rice straw as co-substrate on dye decolorization by Ganoderma lucidum EN2 were evaluated. Two azo dyes, Remazol Brilliant Violet 5R (RBV5) and Sunset Yellow (SY) were tested. Eight of the thirty tested LMCs could significantly improve both RBV5 and SY decolorization, including 3,4,5-trimethoxycinnamic acid, 4-hydroxycinnamic acid, 3,5-dimethoxy-4 -hydroxybenzaldehyde, 3-hydroxybenzoic acid, 3‑hydroxy-4-methoxycinnamic acid, guaiacol, acetosyringone, and 2,6-dimethoxyphenol. The decolorization of RBV5 (from 87.04% to 97.90%) and SY (from 62.41% to 97.40%) by G. lucidum EN2 could be efficiently enhanced in the presence of EMAL. The addition of EMAL could increase the decolorization of higher concentration of azo dyes which is more difficult to be decolorized alone. Noteworthy, laccase activity increased with the increasing amount of EMAL. EMAL showed a positive effect on fungal growth but a negligible effect on pH. These results indicated that EMAL may act as inducer to stimulate the laccase production, and the increase of laccase activity accelerated dye decolorization.

How well do isolated lignins mimic the inhibitory behaviour of cell wall lignins during enzymatic hydrolysis of hydrothermally treated softwood?

Lignin in pretreated lignocellulosic substrates frequently inhibits enzymatic hydrolysis by non-productively binding hydrolytic enzymes. Isolated lignins are commonly used to study these lignin-enzyme interactions. To determine how well isolated lignins mimic the inhibitory behaviour of in situ lignins, we compared inhibition by in situ lignins within hydrothermally pretreated Pinus radiata wood to inhibition by the corresponding isolated lignins added to bleached kraft pulp. This was done as a function of pretreatment severity, enzyme cocktail and dose, and response to added polyethylene glycol. Two different types of isolated lignins, PTL (protease treated lignin-rich residue) and EMAL (enzymatic mild acidolysis lignin), were compared. The inhibitory effect of isolated lignins increased with both pretreatment severity and the amount of lignin added, and was associated with greater condensation and more phenolic groups in the lignins. Overall, isolated lignins provide a good predictor of the inhibitory behaviour of in situ lignins, provided other factors including the origin of the isolated lignin, and amount and accessible surface area of lignin are taken into account.

Structural elucidation of lignins from corncob acid hydrolysis residue by enzymatic mild acidolysis and deep eutectic solvent pretreatment

Achieving mild and efficient extraction of high purity lignin from corncob acid hydrolysis residue is essential for efficient lignin application. In this study, enzymatic/mild acidolysis lignin (EMAL) and deep eutectic solvent (DES)-lignin were extracted from corncob acid hydrolysis residue. The structural features of the two lignin fractions were investigated by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and 31P-nuclear magnetic resonance (31P-NMR). The highest DES-lignin yield of 58.8 wt% was achieved at 120 °C with a choline chloride-to-lactic acid (ChCl-to-Lac) molar ratio of 1:10 and a reaction time of 12 h. The FTIR analysis indicated a higher amount of guaiacyl units in EMAL than DES-lignin. Furthermore, condensation and fragmentation occurred simultaneously under DES pretreatment, but the fragmentation reaction was dominant. The structural characteristics investigated will allow for more effective lignin usage.

Unraveling the Structural Transformation of Wood Lignin During Deep Eutectic Solvent Treatment

Deep eutectic solvents (DESs) can efficiently promote the efficiency of cellulose enzymatic hydrolysis through the removal of lignin component in lignocellulosic biomass pretreatment. Unraveling the fundamental structural variant of lignin during DES treatment would facilitate to understand the DES-based biomass pretreatment in a clear perspective. Herein, an enzymatic mild acidolysis lignin (EMAL) and a series of β-O-4 lignin model compounds were employed to be treated with ChCl/LA (1:2) DES, from which the structural variant of all lignin fractions can be realized in a detailed version. The β-O-4 linkages, existed in either realistic lignin or model compounds, could be cleaved by ChCl/LA, thus leading to the decrease of molecular weight and the rise of hydroxyl groups. The influence of reaction temperature and time was also examined in view of some key structural parameters. Experimental evidences from model compounds confirmed that the repolymerization occurs with the depolymerization of lignin, which may account for the low production of monomeric products during DES treatment.

Characterization and comparison of lignin derived from corncob residues to better understand its potential applications

Lignocellulosic biomass is regarded as an ideal renewable resource for replacing traditional fossil fuels. Corncob residues (CRs) generated after hemicelluloses pre-extraction of corncobs were potential feedstocks to produce lignin-based products. Three lignin fractions, i.e., dioxane lignin (DL), milled-wood lignin (MWL), and enzymatic mild acidolysis lignin (EMAL), were isolated from CRs and characterized by HPLC, GPC, FT-IR, NMR, and TGA to reveal characteristics of CRs lignin to better understand its potential applications. The results showed that the yield of DL, MWL and EMAL were 12.8%, 14.7% and 15.6%, respectively. The molecular weight of DL, MWL and EMAL were 2001, 5391, and 2629 g/mol, respectively. The EMAL and MWL had similar structural features including guaiacyl and syringyl units, β-O-4′ aryl ether, p-coumaric acids, ferulates, and phenylcoumarans, while the structure of DL was relatively simple. It is expected that this work will provide some useful information for the utilization of CRs in view of biorefinery.

Extraction and characterization of lignin from corncob residue after acid-catalyzed steam explosion pretreatment

Corncob residue after acid catalyzed steam explosion (CRSE) is rich in cellulose and lignin. However, the structure of the lignin present in the CRSE has not been studied in detail and this hinders its application. An enzymatic mild acidolysis lignin (EMAL) extraction is adopted to process the CRSE where the extraction conditions are modified to improve lignin recovery and purity. Extraction severity factor is calculated and correlations between it and lignin recovery, lignin purity and total phenolic groups are evaluated. The best extraction condition produces lignin with a purity of 99.0% and a yield of 57.3%. A comparative study between lignin samples extracted under the best condition from the CRSE and untreated corncob (CC) is conducted. The structures of extracted lignin samples are investigated by using 31P NMR, 2D-HSQC NMR, FTIR and GPC. Although SE pretreatment caused degradation of lignin, the abundance per 100 aromatic units of β-O-4′ linkages is 46.0, which is higher than most technical lignins. The molecular weight of CRSE EMAL is found to be higher than that of CC EMAL due to condensation reactions. Antioxidant property of CC EMAL and CRSE EMAL is measured and compared. The data shows that CRSE EMAL possesses better antioxidant activity (IC50 = 128 μg/mL) than CC EMAL (IC50 = 238 μg/mL), which makes CRSE EMAL an ideal additive for polymer composites.

Understanding structural changes in the lignin of Eucalyptus urophylla during pretreatment with an ionic liquid-water mixture

Lignin is the second most abundant natural biopolymer found on earth. For sustainable use of lignin, the development of effective techniques for its depolymerization is necessary. In this study, the depolymerizations of enzymatic mild acidolysis lignin (EMAL) and Alcell lignin (AL), isolated from the eucalyptus urophylla using an ionic liquid (IL)-water mixture, were analyzed and compared. The results showed that the addition of a certain amount of water to IL could enhance the efficiency of lignin hydrolysis. The maximum solubilities of EMAL (41.5 wt.%) and AL (37.1 wt.%) were obtained in the [C2C1im][OAc]85%-water and [C2C1im][OAc]15%-water solutions, respectively. The structures of regenerated lignin fractions are changed according to the proportion of water added to the IL, and were thoroughly characterized by GPC, FT-IR, 2D-HSQC NMR, and TGA. The results indicated that the molecular weight of regenerated lignin decreased, especially in the AL fractions, which were dissolved due to a high proportions of water (35–85 wt.%) in the mixture. The increased syringyl (S) to guaiacyl (G) ratio (S/G) of EMAL indicated the preferential breakdown of G-unit lignin. For AL, the S-unit lignin was easy to be removed by the mixture, indicating different mechanism for the lignin depolymerization. The study provides a better understanding of IL-water mixture as a solvent for dissolving lignin, thus encouraging further use of lignin.

Selective Fragmentation of Biorefinery Corncob Lignin into p-Hydroxycinnamic Esters with a Supported Zinc Molybdate Catalyst.

Lignin is the largest renewable resource of bioaromatics, and the catalytic fragmentation of lignin into phenolic monomers is increasingly recognized as an important starting point for lignin valorization. Herein, we report that ZnMoO4 supported on MCM-41 can catalyze the fragmentation of biorefinery technical lignin, enzymatic mild acidolysis lignin, and native lignin derived from corncob to yield lignin oily products that contain 15-37.8 wt % phenolic monomers, in which the high selectivities towards methyl coumarate (1) and methyl ferulate (2) were obtained (up to 78 %). The effects of some key parameters such as the influence of the solvent, reaction temperature, time, H2 pressure, and catalyst dosage were examined in view of activity and selectivity. The loss of Zn from the catalyst is discussed as the primary cause of deactivation, and the catalytic activity and selectivity can be well preserved in at least six runs by thermal calcination. The high selectivity to 1 and 2 leads to their easy separation and purification from lignin oily product to provide sustainable monomers for the preparation of functional polyether esters and polyesters.

Analytical Pyrolysis Characteristics of Enzymatic/Mild Acidolysis Lignin (EMAL)

Fast pyrolysis is a promising method that is being investigated for application in the degradation of lignin into phenolic chemicals. In this study, enzymatic/mild acidolysis lignin (EMAL) isolated from eucalyptus (E-EMAL) and wheat straw (W-EMAL) were characterized by pyrolysis-gas chromatography/mass spectrometry. The results showed that the compositions and yields of the products were determined by the lignin type and pyrolysis temperature. The identified products from the E-EMAL and W-EMAL pyrolysis mainly included G-phenols such as 2-methoxy-4-vinylphenol and guaiacol, S-phenols such as syringol and 2,6-dimmethoxy-4-(2-propenyl)-phenol, and H-phenols such as phenol, 2-methylphenol, and 4-vinylphenol. The overall yield of these phenolics varied with the investigated conditions. The G- and S-phenols were the primary products during the E-EMAL pyrolysis, while more H-phenols were produced during the W-EMAL pyrolysis. A compromise mild pyrolysis temperature of 450 °C to 650 °C resulted in a high phenolics yield, while a temperature greater than 650 °C led to the production of more aromatic hydrocarbons.

Effect of Copper Oxide on Fast Pyrolysis of Enzymatic/mild Acidolysis Lignin

Abstract The effect of copper oxide on fast pyrolysis of enzymatic/mild acidolysis lignin (EMAL) isolate from moso bamboo were investigated under nitrogen and atmospheric pressure. The products distributions were closely linked with the addition of CuO. The experiment was set on a tubular reactor furnace at the addition of CuO by 1%, 3%, 5%, 10%, 15% based on the weight of EMAL. With the addition of about 5% CuO based on the weight of EMAL, the bio-oil yield reached to its highest level, and the amount of polycyclic aromatic hydrocarbon decreased obviously. Simultaneously, it increased the relative content of phenols. In gas products, CO and C 2 H 4 decreased obviously while H 2 , CH 4 , C 2 H 6 almost stayed the same.

Chemical Elucidation of Structurally Diverse Willow Lignins

A new fast-growing wood raw material, willow (Salix matsudana cv. Zhuliu), was subjected to pulping to identify the structure of its lignin. Thus, the black liquor lignin (AL) and enzymatic mild acidolysis lignin (EMAL) were prepared, and their molecular structure and molecular weight of the isolated lignin polymers were comprehensively investigated by Fourier transform infrared spectroscopy (FT-IR), two-dimensional nuclear magnetic resonance (2D-NMR HSQC), 13C nuclear magnetic resonance (13C-NMR), and gel permeation chromatography (GPC). The NMR results showed that syringyl (S) unit was the predominant structural monomeric unit in willow lignin, as opposed to guaiacyl (G) and p-hydroxyphenyl (H) units. The S/G ratio for the EMAL was found to be 2.02, whereas that for the AL was 0.94. The lignin in the black liquor (AL) fraction was modified during pulping, as shown by its reduced molecular weight. The two isolated lignin polymers, EMAL and AL showed low weight-average molecular weight: 4127 g/mol and 3522.5 g/mol, and in addition they exhibited low polydispersity index (Mw/Mn < 2.0).

Temperature Impact on the Hydrothermal Depolymerization of Cunninghamia lanceolata Enzymatic/Mild Acidolysis Lignin in Subcritical Water

In the present work, enzymatic/mild acidolysis lignin (EMAL) was isolated from the raw material Cunninghamia lanceolata, and hydrothermal depolymerization was carried out in subcritical water (from 250 to 350 °C) using a cylindrical autoclave. The results revealed that the lowest yield of solid residue and highest liquid product yield were achieved at 325 °C. The liquid products were primarily composed of phenolic monomers and oligomers. As the reaction temperature increased, repolymerization of the liquid products and dehydrogenation and deoxidation of the solid residues occurred. The high heating value (HHV) of the residues was larger than that of the EMAL, and it reached a maximal level at 275 °C. Hydrothermal depolymerization and condensation reactions took place simultaneously even under mild conditions (250 °C). Carbonization of the EMAL was remarkable when the reaction temperature reached 325 °C.

Impact of steam explosion on the wheat straw lignin structure studied by solution-state nuclear magnetic resonance and density functional methods.

Chemical changes of lignin induced by the steam explosion (SE) process were elucidated. Wheat straw was studied as the raw material, and lignins were isolated by the enzymatic mild acidolysis lignin (EMAL) procedure before and after the SE treatment for analyses mainly by two-dimensional (2D) [heteronuclear single-quantum coherence (HSQC) and heteronuclear multiple-bond correlation (HMBC)] and (31)P nuclear magnetic resonance (NMR). The β-O-4 structures were found to be homolytically cleaved, followed by recoupling to β-5 linkages. The homolytic cleavage/recoupling reactions were also studied by computational methods, which verified their thermodynamic feasibility. The presence of the tricin bound to wheat straw lignin was confirmed, and it was shown to participate in lignin reactions during the SE treatment. The preferred homolytic β-O-4 cleavage reaction was calculated to follow bond dissociation energies: G-O-G (guaiacyl) (69.7 kcal/mol) > G-O-S (syringyl) (68.4 kcal/mol) > G-O-T (tricin) (67.0 kcal/mol).

Structural Analysis of Lignin and its Thermal Performance under Supercritical Water Conditions

This study investigated the application of supercritical water as green and environmentally friendly treatment medium for hydrolysis and decomposition lignin in order to obtain the relation the products of phenolic compounds and the lignin structural. The processes were studied using three different biomass feed-stocks: poplar alkali lignin (AL), corncob enzymatic/mild acidolysis lignin (EMAL), and cornstalk or benzene–ethanol-extracted lignin (BEL), and lignin were identified by elemental analysis, FTIR, 31P-NMR. Experiments were performed in a batch stainless steel reactor at supercritical water 375°C at residence time of 10min. Main phenolic compounds from decomposition of lignin were identified by external standard method. Results indicated that the functional groups of AL, EMAL and BEL had a marked influence on the produces. More phenol OH groups and more benzene and phenolic contents could be gained under supercritical water conditions. The total produces reached to 74mg/g of dry EMAL and which was a high quality raw material as the source of phenol and 4-ethylphenol. The AL compositions of guaiacol, 4-methylguaiacol, 3-methoxycatechol, 2,6-dimethoxyphenol, 1,2,3-trimethoxybenzene had more than EMAL and BEL.

Characterization and Hydrothermal Conversion of Lignin Produced from Corncob Acid Hydrolysis Residue

Lignin is one of the main components of corncob acid hydrolysis residue (CAHR). It can be used as a feedstock for biomaterial and biochemical production via biorefining. In this study, CAHR lignin was extracted, and enzymatic/mild acidolysis lignin (EMAL) was produced to ensure efficient lignin recovery. Next, hydrothermal conversion of the EMAL was carried out. The influences of process conditions including the temperature, time, and mass ratio of deionized water to EMAL on the hydrothermal conversion were thoroughly investigated to quantify analysis of the aromatics. EMAL produced from CAHR had a structure of the G-S-H type, in which the p-hydroxyphenyl unit was the primary structural unit, followed by the guaiacyl structural unit. The syringyl structural unit was less common. The yields (wt. %) of phenol, guaiacol, and 4-ethyl-phenol reached maxima of 1.26%, 0.75%, and 1.16%, respectively, at a reaction temperature of 310 °C and time of 30 min with a mass ratio of 80:1.

Characterization and analysis of the molecular weight of lignin for biorefining studies

AbstractThe molecular weight of lignin is a fundamental property that influences the recalcitrance of biomass and the valorization of lignin. The determination of the molecular weight of lignin in native biomass is dependent on the bioresources used and the isolation and purification procedures employed. The three most commonly employed isolation methods are milled wood lignin (MWL), cellulolytic enzyme lignin (CEL), and enzymatic mild acidolysis lignin (EMAL). Common characterization techniques for determining the molecular weight of lignin will be addressed, with an emphasis on gel permeation chromatography (GPC). This review also examines the mechanisms behind several biological, physical, and chemical pre‐treatments and their impact on the molecular weight of lignin. The number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index (D) all vary in magnitude depending on the biomass source, pre‐treatment conditions, and isolation method. Additionally, there is a growing body of literature that supports changes in the molecular weight of lignin in response to genetic modifications in the lignin biosynthetic pathways. This review summarizes different procedures for obtaining the molecular weight of lignin that have been used in recent years and highlight future opportunities for applications of lignin. © 2014 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Chemical Changes of Raw Materials and Manufactured Binderless Boards during Hot Pressing: Lignin Isolation and Characterization

Thermomechanical pulp (TMP) is used for fiber production in binderless boards industries. Milled wood lignin (MWL) and enzymatic mild acidolysis lignin (EMAL) isolated from raw material and from binderless boards (BB) were comparatively analyzed to investigate the effects of chemical changes on the bonding performance in BB. The results showed that acid-insoluble lignin of the BB were increased during the sodium silicate solution pretreatment after hot-pressing. The lignin fractions obtained were characterized by gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, and 1H-13C correlation heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectroscopy. Results showed that 31.1% of EMAL (based on Klason lignin) with low molecular weight (Mw=1630 g/mol) was isolated from the BB. The increased total phenolic OH groups (3.97 mmol/g) of EMAL from sodium silicate solution pretreated BB indicated that there was degradation of lignin and cleavage of lignin-carbohydrate linkages during hot-pressing. In addition, the content of β-O-4' aryl ether linkages of EMAL from the BB increased to 69.2%, which was higher than that of the untreated sample (60.1%). It was found that S units (syringyl-like lignin structures) were preferentially condensed by hot pressing over G (guaiacyl-like lignin structures) units, and the S/G ratio increased after the hot-pressing process.