Original Lignin Research Articles

An efficient process for lignin extraction and enzymatic hydrolysis of corn stalk by pyrrolidonium ionic liquids

In recent years, lignocellulosic biomass has drawn increasingly attention as a platform for its transformation into biofuels. However, the complex structures of lignocelluloses limit their conversion into fermentable sugars or other valuable products. In this work, a series of pyrrolidonium-based ionic liquids with a simple synthetic procedure were investigated for the pretreatment of corn stalk at 90°C for 30min. Both ionic liquids alone and ionic liquids with deionized water were studied. Fourier transform infrared spectroscopy (FTIR) analysis, scanning electron microscopy (SEM) analysis and nuclear magnetic resonance spectroscopy (NMR) analysis were employed to determine the chemical characteristics of regenerated lignin or cellulosic feedstock. A significant yield of lignin was achieved, as high as 19.07%, which accounted for 85.94% of the original lignin of corn stalk. A high yield of reducing sugar (91.81%) was obtained from regenerated cellulosic feedstock after enzymatic hydrolysis. High yields of glucose (79.63%) and cellobiose (13.66%) were observed as determined by high performance liquid chromatography (HPLC).

Microwave-assisted functionalized lignin with dithiocarbamate for enhancing adsorption of Pb(II)

This study firstly reported a microwave-assisted functionalized lignin with dithiocarbamate (LD) for enhancing adsorption of Pb(II) in water. It was found that LD particles were about 1µm in diameter with plenty of dithiocarbamate functional groups. LD showed a fast adsorption to Pb(II) with an equilibration time of 45min. The saturated adsorption capacity to Pb(II) was 106mg/g, which was 7.5 times of the original lignin and also higher than other lignin-based adsorbents. The prepared material can not only effectively adsorb Pb(II) in water, but also be easily prepared. These findings demonstrate that LD has great potential applications in adsorption and separation.

Structure of Brewer's Spent Grain Lignin and Its Interactions with Gut Microbiota in Vitro.

Lignin is part of dietary fiber, but its conversion in the gastrointestinal tract is not well understood. The aim of this work was to obtain structural information on brewer's spent grain (BSG) lignin and to understand the behavior of the polymeric part of lignin exposed to fecal microbiota. The original BSG and different lignin fractions were characterized by pyrolysis-GC/MS with and without methylation. Methylation pyrolysis proved that the ratio between guaiacyl and syringyl units was similar in all lignin samples, but the ratio between p-coumaric and ferulic acids varied by the isolation method. Combined pyrolysis results indicated higher acylation of γ-OH groups in syringyl than in guaiacyl lignin units. The polymeric lignin structure in the alkali-soluble fraction after enzymatic hydrolysis was slightly altered in the in vitro colon fermentation, whereas lignin in the insoluble residue after enzymatic treatments remained intact.

Lignin Modification for Biopolymer/Conjugated Polymer Hybrids as Renewable Energy Storage Materials.

Lignin derivatives, which arise as waste products from the pulp and paper industry and are mainly used for heating, can be used as charge storage materials. The charge storage function is a result of the quinone groups formed in the lignin derivative. Herein, we modified lignins to enhance the density of such quinone groups by covalently linking monolignols and quinones through phenolation. The extra guaiacyl, syringyl, and hydroquinone groups introduced by phenolation of kraft lignin derivatives were monitored by (31) P nuclear magnetic resonance and size exclusion chromatography. Electropolymerization in ethylene glycol/tetraethylammonium tosylate electrolyte was used to synthesize the kraft lignin/polypyrrole hybrid films. These modifications changed the phenolic content of the kraft lignin with attachment of hydroquinone units yielding the highest specific capacity (around 70 mA h g(-1) ). The modification of softwood and hardwood lignin derivatives yielded 50 % and 23 % higher charge capacity than the original lignin, respectively.

Structural and Morphological Changes in Kraft Lignin during Hydrothermal Carbonization

In this paper we have investigated the changes in kraft lignin structure and morphology upon hydrothermal carbonization (HTC) at 240 °C with and without the presence of carbonization catalysts. The main conclusion of this study is that the structure of kraft lignin was altered only slightly during the hydrothermal carbonization. The main changes in the kraft lignin’s structure were demethylation and dealkylation as well as cleavage of β-O-4 bonds. The final product had a more thermally stable and complex cross-linked structure. More pronounced changes occurred in the material structure and morphology upon the addition of catalysts. The energy density of the resulting materials was not significantly different from the energy density of the original kraft lignin.

Fractionation of corn stover into cellulose, hemicellulose and lignin using a series of ionic liquids

Lignocellulosic biomass is increasingly being promoted as an environmentally and economically sustainable fuel. However, the complex structure of lignocellulose makes it difficult to be fractionated, which limits its conversion into valuable products. In this work, a series of functional acidic ionic liquids (ILs) with a simple synthetic procedure were prepared. Fractionation of corn stover into cellulose, hemicellulose and lignin was successfully performed in ultrasound-assisted ILs at a low reaction temperature of 70°C for 3h followed by alkaline extraction. IL-isolated lignin, alkaline lignin, hemicellulose and cellulose were obtained in good yields and their chemical properties were analyzed by FTIR. Significantly, a good yield of IL-isolated lignin was obtained, which accounted for 60.48% of the original lignin. The IL-isolated lignin was S-G-H type indicating by 13C NMR and 13C–1H correlation 2D NMR (HSQC) analysis. Enzymatic hydrolysis of cellulose was performed successfully. A high yield of 97.77% reducing sugar was achieved. Glucose and cellobiose were measured by HPLC analysis, which accounted for 92.55% of cellulose conversion. Both of the hydrogen bond capability and the acidity of ILs contributed to achieve the effective fractionation. These ILs have a great potential for the preparation of biofuel.

Comparative study on topochemistry of delignification from Japanese cedar and Japanese beech by hydrothermal treatment

The difference in decomposition behavior of lignin from Japanese cedar (Cryptomeria japonica) as softwood and Japanese beech (Fagus crenata) as hardwood treated by hot-compressed water was investigated. The obtained residual lignin was then evaluated by the alkaline nitrobenzene oxidation analysis, the relative proportion of ether type linkages had decreased for both species as the hot-compressed water treatment was prolonged. Furthermore, the microscopic observation of the residual lignin indicated that lignin in tracheid cell walls was removed to a greater extent than that in middle lamella in Japanese cedar. Similarly in Japanese beech, lignin in fiber cell walls was removed more extensively, with middle lamella lignin remaining after two-step treatment. Such observation was supported by a result obtained from the methoxyl content analysis per C9 unit of the residual lignin. Based on these lines of evidence, lignin in middle lamella must be rich in condensed type, and these differences between softwood and hardwood can be attributed to the intrinsic characteristics of the original lignin and its topochemistry in woods.

Lignin preparation from oil palm empty fruit bunches by sequential acid/alkaline treatment – A biorefinery approach

Lignin is an important raw material for the sustainable biorefineries and also the forerunner of high-value added products, such as biocomposite for chemical, pharmaceutical and cement industries. Oil palm empty fruit bunches (OPEFB) were used for lignin preparation by successive treatment with 1% (w/w) H2SO4 at 121°C for 60min and 2.5% NaOH at 121°C for 80min resulting in the high lignin yield of 28.89%, corresponding to 68.82% of the original lignin. The lignin obtained was characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The results indicated a lignin with molecular masses ramping from 4500kDa to 12,580kDa. FTIR and NMR of these lignins showed more syringyl and p-hydroxyphenyl than guaiacyl units. Moderate acid/alkaline treatment provided lignin with high industrial potential and acid hydrolyzates rich in fermentable sugars and highly porous cellulosic fibers.

Surface-Functionalized Porous Lignin for Fast and Efficient Lead Removal from Aqueous Solution.

The development of ecofriendly sorbents for fast and efficient removal of heavy metals from aqueous media still remains a significant challenge. Here, we report that this task can be addressed by creating a porous naturally occurring polymer, as illustrated by functionalizing lignin with large numbers of mesopores and functional groups. We show that surface-functionalized porous lignin (SFPL), obtained by a two-step process, has a large surface area of 22.3 m2/g, 12 times that of lignin, and a high density of dithiocarbamate groups (2.8 mmol/g). SFPL was found to exhibit an excellent adsorption performance toward lead ions dissolved in water. For example, 99% of the lead ions from 50 mL of a solution containing 20 mg/L lead ions was removed in just 30 min by 0.01 g of SFPL. The saturated adsorption capacity of SFPL for lead ions was found to be 188 mg/g, which is 13 times that of the original lignin and 7 times that of activated carbon. The adsorption process is endothermic and involves intraparticle diffusion and chemical adsorption between lead ions and the functional groups of SFPL. The cost effectiveness and environmental friendliness of SFPL make it a promising material for removing lead and other heavy metals from wastewater.

Kraft Lignin Depolymerization in an Ionic Liquid without a Catalyst

In this paper, the depolymerization of lignin was successfully achieved by the thermal treatment of kraft lignin in butyl-1,8-diazabicyclo[5.4.0]undec-7-enium chloride ([DBUC4+][Cl-]) without a catalyst. The thermal treatment experiments were performed in an oven at 150, 200, and 250 °C for 1 h. The changes in kraft lignin structure over the course of depolymerization were characterized by gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and 1H / 31P NMR analyses. GPC chromatograms indicated that the retention time of the original kraft lignin had shifted toward higher values after the thermal treatment, which indicated lignin depolymerization. The average molecular weight of the lignin obtained after 1 h reaction time decreased by 23, 70, and 58 wt% for the treatment at 150, 200, and 250 °C, respectively. FTIR spectra indicated the cleavage of β-O-4 bonds of kraft lignin. The 1H NMR spectra showed demethylation of all treated kraft lignins. Moreover, the 31P NMR analysis demonstrated that the demethylation phenomenon of the treated kraft lignin contributed to the formation of catechol groups.

Thermal Analysis and Calorimetric Study of the Combustion of Hydrolytic Wood Lignin and Products of Its Pyrolysis

Thermal decomposition of hydrolyzed lignin is studied in the 300-700eC range in an inert gas atmosphere. The yields of solid, liquid, and gaseous decomposition products are determined. It is demonstrated by combustion calorimetry that the carbonaceous residue of lignin pyrolysis has the highest calorific value. The calorific value of the carbonaceous residue of pyrolysis resin is higher than that of the original lignin. It is shown by thermogravimetry and differential scanning calorimetry with mass spectrometric detection of gases that lignin and its thermal decomposition products could undergo thermolysis with formation of various volatile compounds. Thermal decomposition starts at roughly the same temperature and is 320eC. The loss of sample mass increases in the following sequence: carbonaceous residue < lignin < liquid fraction.

Sugarcane hybrids with original low lignin contents and high field productivity are useful to reach high glucose yields from bagasse

Five sugarcane hybrids plus a reference material were evaluated according to the glucose yields obtained after alkaline-sulfite pretreatment and enzymatic hydrolysis. Sugarcane hybrids with varied original chemical compositions were used to assess how contrasting samples might influence the integrated pretreatment and hydrolysis process. The hydrolysis efficiency of six samples treated at three different chemical loads, suggested that lignin and hemicellulose removals during the pretreatment were not the single factor necessary to reach high cellulose conversion levels in the enzymatic hydrolysis step. Pretreated samples with the highest total acid contents (mainly sulfonic acids) were also the most digestible materials. The glucose yields were heavily dependent not only on the digestibility of the pretreated materials but also on the field productivity of the plants. One of the hybrids, presenting high glucan yields after pretreatment and high digestibility, produced low glucose yields because it presented very low biomass productivity. In contrast, one of the hybrids that presented low glucan yield after pretreatment, but was highly digestible and presented high biomass productivity, provided the highest glucose yields in the data set, producing 4192 and 5629 kg of glucose per hectare after enzymatic hydrolysis for 24 h and 72 h, respectively.

Preparation and characterization of graft copolymer from dealkaline lignin and styrene

ABSTRACTGraft copolymerization of styrene onto dealkaline lignin by ferrous chloride and hydrogen peroxide coinitiator has been achieved successfully. The influence of temperature and reaction time as well as the amount of the styrene monomer, initiator, and catalyst on the grafting copolymerization was investigated. The optimum reaction conditions were determined as follows: c (styrene) = 20.00 mmol, c (H2O2) = 5.00 mmol, c (FeCl2) = 0.10 mmol, T = 30°C and t = 48 h. The optimum yield (Y), total conversion (TC), grafting efficiency (GE), and degree grafted (DG) values were 96.6, 96.3, 59.5, and 53.7%, respectively. The copolymer of lignin grafted PS was separated and characterized by elemental analysis, differential scanning calorimetry, Fourier transform infrared, thermogravimetry analysis, field emission‐scanning electron microscopy, gel permeation chromatography, and nuclear magnetic resonance. It was demonstrated that the solubility what the copolymer exhibited turned out to be the very reverse of the original lignin. The surface properties and structure of lignin were completely changed after grafting copolymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41900.

Microwave-assisted oxidative digestion of lignin with hydrogen peroxide for TOC and color removal.

Dilute lignin solution was successfully digested into colorless and clarified liquor under microwave-assisted oxidative digestion with hydrogen peroxide. High dosage of hydrogen peroxide is needed to effectively digest lignin, but excessive hydrogen peroxide may lead to recondensation of formed fragments in digested lignin. Microwave irradiation greatly facilitates the oxidative digestion of lignin. Compared with conventional heating technique, microwave-assisted digestion achieves the same or higher digestion rate within a shorter time and/or at lower temperature. After digestion, total organic carbon content of lignin solution decreases by 93.9%, and a small amount of aliphatic alkane, alcohol, acid and ester are formed via the cleavage of aromatic rings as well as the deprivation of side chains in original lignin. This work provides an alternative way to efficiently treat spent pulping liquor.

Thermal Melting of Lignin Derivatives Prepared from Dried Black Liquor Powder of Softwood Soda-AQ Cooking and Polyethylene Glycol

Softwood lignin prepared by soda-anthraquinone (AQ) cooking does not have thermal melting characteristics. To improve the properties of softwood soda-AQ lignin, we have invented a new method of lignin modification using dried black liquor powder by a spray dryer system and polyethylene glycol (PEG). In this process, black liquor powder was directly treated with PEG under alkaline conditions to produce PEG-modified lignin (alkaline PEG treatment). Dried black liquor powder prepared by a spray dryer was dissolved into PEG and heated at either 120 or 160 °C at atmospheric pressure. The modified lignin (alkaline PEG-treated lignin) was precipitated with acid and recovered by filtration. The alkaline PEG-treated lignin showed adequate thermal melting characteristics. The treatment temperature and the molecular weights of PEG considerably affected the thermal properties of the alkaline PEG-treated lignin. There was an addition reaction of the PEG to the lignin hydroxyl group at the alpha- (-) carbon. However, in the acid precipitation step, if the mixture was allowed to set unfiltered for a long time, the PEG bonded with the lignin was hydrolyzed, which yielded the original soda-AQ lignin and PEG polymer.

High Shear Homogenization of Lignin to Nanolignin and Thermal Stability of Nanolignin‐Polyvinyl Alcohol Blends

A new method to prepare nanolignin using a simple high shear homogenizer is presented. The kraft lignin particles with a broad distribution ranging from large micron- to nano-sized particles were completely homogenized to nanolignin particles with sizes less than 100 nm after 4 h of mechanical shearing. The (13) C nuclear magnetic resonance (NMR) and (31) P NMR analysis showed that there were no major changes in the chemical composition between the starting kraft lignin particles and the nanolignin obtained after 4 h of mechanical treatment. The nanolignin particles did not show any change in molecular weight distribution and polydispersity compared to the original lignin particles. The nanolignin particles when used with polyvinyl alcohol (PVA) increased the thermal stability of nanolignin/PVA blends more effectively compared to the original lignin/PVA blends.

Fractionation and characterization of industrial lignins

Three industrial lignins (Indulin AT Kraft softwood, Protobind 1000, and corn stover) were fractionated in methanol to obtain soluble and insoluble fractions. The original lignin and obtained lignin fractions were characterized chemically by a combination of FTIR spectroscopy, pyrolysis-gas chromatography–mass spectrum (py-GC–MS), and derivatization followed by reductive cleavage (DFRC). The methanol soluble lignin fractions contained fewer condensed structures than the original lignin and methanol insoluble fractions. The thermal (e.g. glass transition temperature (Tg) and thermal stability) and rheological properties of the lignins were characterized by a combination of DSC, TMA, TGA and parallel plate rheology. TMA and modulated temperature DSC (MTDSC) proved to be sensitive techniques in determining Tg. The methanol soluble lignin fractions had the lowest Tg values relative to the original lignin and methanol insoluble fractions. The original lignin and methanol insoluble fractions had a higher thermal degradation temperature relative to the methanol soluble lignin. Solvent partitioning offers a practical approach to fractionate lignin into low Mw and Tg fractions which show promise as starting materials for making lignin-copolymers.

Integration of Ambient Formic Acid Process and Alkaline Hydrogen Peroxide Post-Treatment of Furfural Residue To Enhance Enzymatic Hydrolysis

A novel integrated process with ambient formic acid combining alkaline hydrogen peroxide was developed to achieve efficient delignification of furfural residue. Furfural residue was treated with 88% formic acid at room temperature for 0.5 h followed by post-treatment with 1% alkaline hydrogen peroxide at 80 °C for 1.5 h. Results showed that 87.9% of the original lignin was removed and the solid residue obtained contained 84.6% cellulose. The glucose yield of the solid residue increased to 83.7% after 96 h enzymatic hydrolysis under a low enzymatic loading of 7 FPU/g cellulose. The analysis of the physicochemical property of the solid residue and lignin fractions indicated that there was an unapparent effect on formylation of cellulose during the ambient formic acid treatment, and the lignin rich in phenolic and carboxylic OH was easily removed. The insoluble-formsovl lignin in solid residue was effectively removed by alkaline hydrogen peroxide treatment.

Hydrothermal carbonization of various lignocellulosic biomass

As a non-food, renewable energy resource, lignocellulosic biomass can be used for reducing greenhouse gas emissions. Hydrothermal carbonization (HTC) is a process to prepare the lignocellulosic biomass for subsequent thermochemical conversion. Biomass is reacted in hot compressed water at temperatures between 200 and 275 °C and at pressures sufficient to maintain liquid water. HTC was performed on corn stover, rice hulls, Tahoe mix (Jeffrey pine and white fir), switch grass, and Loblolly pine. These biomass sources encompass a variety of types, including a primary agricultural residue, a secondary agricultural residue, a forest product removed to reduce wildfires, a primary energy crop, and a primary forest crop. HTC reaction temperature was found to be the process variable with the greatest effect. For the five biomass studied, hydrochar mass yields were found to decrease with increasing reaction temperature, while higher heating values increased with increasing reaction temperature. Differences in these results among biomass sources were found to correlate with their original hemicellulose, lignin, aqueous soluble, and ash contents. These components appeared to be observable in scanning electron microscope images of hydrochar.

Control of Lignin Solubility and Particle Formation Modulates Its Antioxidant Efficiency in Lipid Medium: An In Situ Attenuated Total Reflectance FT-IR Study

Lignin is an abundant plant polymer usually regarded as waste material. In the present work, antioxidant properties of lignin preparations with differing lipid solubility were studied using biodiesel as a convenient lipid test substrate. In place of formerly used assays, we used attenuated total reflectance (ATR) FT-IR spectroscopy to follow in situ biodiesel autoxidation on a heated ATR crystal as a function of time. The study demonstrates that a complex balance between intrinsic (chemical) efficiency, solubility, and particle formation controls the antioxidant efficiency of differently prepared lignin fractions. It was found that solubility and particle formation of lignin preparations strongly modulate its antioxidant efficiency and that these properties might depend on the presence of lipid components within the original lignin source.