Herbaceous Lignin Research Articles

Herbaceous lignin valorization through integrated copper-catalyzed hydrogenolysis and chemical functionalization

Lignin is an important biomass resource to replace petrochemical industry for carbon neutrality. However, it is challenged by unyielding the trade-off between activity and selectivity owing to the chemical complexity and inherent heterogeneity of lignin biomacromolecule. Herein, we report that copper nanomaterial (CuO/C) derived from metal-organic framework (HKUST-1) could effectively catalytic hydrogenolysis of herbaceous plants into monomeric phenols (up to 29.5 wt%) through a lignin-first strategy, affording methyl 3-(4-hydroxyphenyl) propionate (1-H) and methyl 3-(4-hydroxy-3-methoxyphenyl) propionate (2-G) as the main monophenols with high selectivity of 31.9% and 17.3%. Moreover, we proposed two synthetic routes based on the purification and functionalization of those two compounds (1-H and 2-G) to synthesis 3-(4-carboxyphenyl) propionic acid and functional polyesters. Subsequent studies revealed that the temperature of 50% mass loss of the two polyesters reached 430–440 °C, indicating their robust thermal stability; while the DSC curves showed the difference between the two polymers in glass conversion temperature (Tg) and crystallization. In brief, this work opens a new avenue for the production of lignin-derived chemicals and materials.

Application of 2D NMR Spectroscopy in Combination with Chemometric Tools for Classification of Natural Lignins.

Lignin is considered a promising renewable source of valuable chemical compounds and a feedstock for the production of various materials. Its suitability for certain directions of processing is determined by the chemical structure of its macromolecules. Its formation depends on botanical origin, isolation procedure and other factors. Due to the complexity of the chemical composition, revealing the structural differences between lignins of various origins is a challenging task and requires the use of the most informative methods for obtaining and processing data. In the present study, a combination of two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy and multivariate analysis of heteronuclear single quantum coherence (HSQC) spectra is proposed. Principal component analysis and hierarchical cluster analysis techniques demonstrated the possibility to effectively classify lignins at the level of belonging to classes and families of plants, and in some cases individual species, with an error rate for data classification of 2.3%. The reverse transformation of loading plots into the corresponding HSQC loading spectra allowed for structural information to be obtained about the latent components of lignins and their structural fragments (biomarkers) responsible for certain differences. As a result of the analysis of 34 coniferous, deciduous, and herbaceous lignins, 10 groups of key substructures were established. In addition to syringyl, guaiacyl, and p-hydroxyphenyl monomeric units, they include various terminal substructures: dihydroconiferyl alcohol, balanopholin, cinnamic acids, and tricin. It was shown that, in some cases, the substructures formed during the partial destruction of biopolymer macromolecules also have a significant effect on the classification of lignins of various origins.

LigninGraphs: lignin structure determination with multiscale graph modeling

Lignin is an aromatic biopolymer found in ubiquitous sources of woody biomass. Designing and optimizing lignin valorization processes requires a fundamental understanding of lignin structures. Experimental characterization techniques, such as 2D-heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectra, could elucidate the global properties of the polymer molecules. Computer models could extend the resolution of experiments by representing structures at the molecular and atomistic scales. We introduce a graph-based multiscale modeling framework for lignin structure generation and visualization. The framework employs accelerated rejection-free polymerization and hierarchical Metropolis Monte Carlo optimization algorithms. We obtain structure libraries for various lignin feedstocks based on literature and new experimental NMR data for poplar wood, pinewood, and herbaceous lignin. The framework could guide researchers towards feasible lignin structures, efficient space exploration, and future kinetics modeling. Its software implementation in Python, LigninGraphs, is open-source and available on GitHub.Graphical abstract

Producing Methyl p-Coumarate from Herbaceous Lignin via a "Clip-Off" Strategy.

As the most abundant renewable aromatic resource on Earth, lignin is a preferred starting material for producing bulk chemicals via a sustainable route. In this study, we provide a novel and efficient "clip-off" approach for producing methyl p-coumarate, an important and versatile fine chemical by selective cleavage of the ester linkage in herbaceous lignin in the presence of commercial metal chlorides. When bagasse lignin was depolymerized at 155 °C for 4 h, a 12.7% yield of aromatic chemicals was obtained in the presence of CuCl2, 71.7% of which was identified as methyl p-coumarate (the yield was 9.1%). Further investigation of the structural evolution of lignin revealed that the ester linkages in lignin were efficiently broken via intensive transesterification with methanol accompanied by the simultaneous weakening of the inter-/intramolecular hydrogen bonds. Moreover, this observation of selective cleavage of ester linkages could be further confirmed by the conversion of model compounds with characteristic bonds under identical reaction conditions. Therefore, this work provides a new insight into the production of value-added chemicals from renewable resources.

Performance and Economic Analysis of Organosolv Softwood and Herbaceous Lignins to Activated Carbons as Electrode Materials in Supercapacitors

In this work, yellow pine (YP, softwood) and switchgrass (SG, grass) lignins were extracted as a coproduct of an organosolv γ-valerolactone (GVL) biorefinery that also produces biofuels and furfural. The extracted lignins were converted to carbon precursors for synthesizing porous activated carbon electrodes for high energy-density supercapacitors. This research details the impact of lignin composition on the derived porous structures and electrochemical properties of activated carbons. Lignin precursors with various syringyl (S) to guaiacyl (G) contents were characterized using31P nuclear magnetic resonance (NMR) and two-dimensional1H‒13C NMR. A two-step activation process, using steam and carbon dioxide as the activating agents, enabled the formation of porous carbons structures with high surface area. The capacitive behavior of supercapacitors was systematically characterized by cyclic voltammetry, charge-discharge cycling, and electrochemical impedance spectroscopy. The specific capacitance of YP and SG capacitors reached 367 and 221 F g−1, respectively. Both types of capacitors demonstrated remarkably stable capacitance (capacitance retention >90%) along with excellent Coulombic efficiency (>99%) over 10,000 cycles. Compared to SG electrode, the better electrochemical performance achieved with YP electrodes was mainly due to shorter diffusion path, improved ionic mobility, and increased active surface area. The inexpensive lignin-based porous electrodes synthesized in this work can be used for various electrochemical devices for improved performance, decreased cost, and enhanced durability. This work also demonstrates that the selection of feedstock and appropriate processing conditions can tailor the structure of carbon composites for targeted applications. Techno-economic analysis indicates that YP and SG activated carbons can be produced at a minimum selling price of $8,493 and $6,670 per ton, respectively, which is competitive with the commercially available supercapacitor-grade activated carbons.

Hydrogenolysis of lignin to phenolic monomers over Ru based catalysts with different metal-support interactions: Effect of partial hydrogenation of C(sp2)-O/C

Catalytic hydrogenolysis of lignin to phenolic monomers has received a lot of attention, but it is still a challenge because the cleavage of the strong C(sp2)-O/C bonds between structural units is usually under harsh conditions, resulting in the presence of the competing reaction of hydrogenation. Herein, hydrogenolysis of an herbaceous lignin into phenolic monomers was performed over Ru supported on various (non)-functionalized graphitized carbon nanotubes (CNT, CNT-OH, CNT-COOH, and CNT-NH2), which were featured by different hydrogenation performances originally from the diverse metal-support interactions. Among the investigated supports, CNT-NH2 enables the formation of the finest Ru nanoparticles with an average size of 1.86 nm, leading to the highest yield of phenolic monomers from lignin hydrogenolysis. The best hydrogenolysis performance of Ru@CNT-NH2 was mainly from the partial hydrogenation of C(sp2)-O/C bonds to C(sp3)-O/C bonds in lignin, thus reducing their bond dissociation energy (BDE). The intimacy between hydrogenolysis and hydrogenation was further proved by depolymerization of a lignin β-O-4 model compound.

Comparative Analysis of Lignins of Various Plant Forms by 31P NMR Spectroscopy

Lignin is one of the most abundant biopolymers. Information about the functional composition and structure of various lignins may be useful in the study of biosynthesis processes in plants. The subject of the article is the determination of 31P NMR spectroscopy possibilities to identify lignins obtained from various plant forms. To obtain spectra on 31P nuclei, a modification of the studied samples was applied by phosphitylating their OH-groups with a special reagent. We obtained qualitative and quantitative analysis of samples of softwood and hardwood lignins and herbaceous plants. According to the NMR spectra we noted the differences in composition and structure of the studied lignins. We confirmed that the structure of lignins of softwood and hardwood wood mainly contain guaiacilpropane and syringylpropane structural units, respectively. We found that lignins of herbaceous plants contain all types of OH-groups characteristic for lignins, including p-hydroxyphenyl groups. It was observed that samples of herbaceous plants lignins contain fragments of flavonoid structures in most cases. The 31P NMR spectrum of quercetin, as the flavonoids representative, was registered and also modeled using the ACDLabs software package to confirm the presence of flavone structures in the macromolecules of the herbaceous lignins.

Production of Methyl p-Hydroxycinnamate by Selective Tailoring of Herbaceous Lignin Using Metal-Based Deep Eutectic Solvents (DES) as Catalyst

Catalytic conversion of lignin to versatile aromatic compounds is attracting increasing attention. However, it is highly desirable but challenging to produce a specific chemical with high yield thr...

Physiochemical characterization and thermal kinetics of lignin recovered from sustainable agrowaste for bioenergy applications

In this study, lignin, one of the commonly occurring natural polymers, is extracted from banana agro-waste. Lignin is recovered from the spent liquor produced during alkaline pre-treatment of agro-waste and precipitated by acidification. This study focuses on the physio-chemical characterization and thermal degradation behaviour of lignin extracted from agro-waste biomass. The extracted lignin yield accounts for nearly 12% of the biomass composition. Spectral analysis, FTIR and NMR explain purity and carbon skeleton characteristics of herbaceous lignin monomers, majorly G and S units. Morphological analysis by SEM showed hollow spherical structures with large surface area for the extracted lignin. The calorific value of extracted lignin was experimentally found to be 21.4276 MJ/kg, which suggests the possible use of extracted lignin as an alternative to sub-bituminous coal. Thermal studies of lignin showed that lignin degrades in a wide temperature range releasing CO2, CH4, H2O, CO and H2. The volatile content of extracted lignin is found to be 31.42%, which suggests its possibility for gasification process. The overall outcome supported that recovered lignin from agro-waste is a potential resource for bioenergy.

COMPARATIVE ANALYSIS OF LIGNINS OF VARIOUS PLANT FORMS BY 31P-NMR

Lignin is one of the most abundant biopolymers. Information about the functional composition and structure of various lignins may be useful in the study of biosynthesis processes in plants. The subject of the article is the determination of 31P-NMR spectroscopy possibilities to identify lignins obtained from various plant forms. To obtain spectra on 31P nuclei, a modification of the studied samples was applied by phosphitylating their OH-groups with a special reagent. We obtained qualitative and quantitative analysis of samples of softwood and hardwood lignins and herbaceous plants. According to the NMR spectra we noted the differences in composition and structure of the studied lignins. We confirmed that the structure of lignins of softwood and hardwood wood mainly contain guaiacilpropane and syringylpropane structural units, respectively. We found that lignins of herbaceous plants contain all types of OH-groups characteristic for lignins, including p-hydroxyphenyl groups. It was observed that samples of herbaceous plants lignins contain fragments of flavonoid structures in most cases. The 31P-NMR spectrum of quercetin, as the flavonoids representative, was registered and also modeled using the ACDLabs software package to confirm the presence of flavone structures in the macromolecules of the herbaceous lignins.

Influence of impregnated catalyst on the phenols production from pyrolysis of hardwood, softwood, and herbaceous lignins

The production of phenols through catalytic pyrolysis of different types of lignin was investigated. Samples from eucalyptus (hardwood), pine (softwood), and sugarcane bagasse (herbaceous) were impregnated with the catalysts, Al2O3, ZnO, NaOH and KOH, in quantities equivalent to 1% of the lignin mass. Pyrolysis was conducted using thermogravimetric analyser (TGA), and the released phenols were captured in thermal desorption (TD) tubes for quantification by gas chromatography/mass spectrometry (GC/MS). From the TGA profiles, some modifications in the primary mechanisms were observed, especially with the hydroxide catalysts. In comparison to non-catalysed lignin pyrolysis, KOH produced the most statistically significant effect on the total phenols yields from sugarcane bagasse (S-S) lignin, with increases up to +26%, while NaOH increased the yield from Eucalyptus (E-K) lignin by +40%. Syringol was the main S-type phenol product, with the highest yield increase by NaOH from E-K lignin (+90%) and a final yield of 1.86 wt.%. NaOH also produced the highest yield increases of G-type phenols from E-K lignin, especially 4-vinylguaiacol (+39% and yield of 2.80 wt.%). The increased production of primary compounds (S-type and G-type) by these hydroxides was probably correlated with the enhanced depolymerisation in the first decomposition stages, as observed by TGA. Oxide catalysts had limited effects on the production of S-type and G-type compounds but were more selective towards the production of P-type phenols, especially ZnO with S-S lignin (+36%) due to the enhancement of demethoxylation reaction.

Selective catalytic tailoring of the H unit in herbaceous lignin for methyl p-hydroxycinnamate production over metal-based ionic liquids

Selective catalytic tailoring of herbaceous lignin for the production of methyl p-hydroxycinnamate (MPC).

Potential of producing carbon fiber from biorefinery corn stover lignin with high ash content

ABSTRACTThe possibility of producing carbon fiber from an industrial corn stover lignin was investigated in the present study. As‐received, high‐ash containing lignin was subjected to methanol fractionation, acetylation, and thermal treatment prior to melt spinning and the changes in physiochemical and thermal properties were evaluated. Methanol fractionation removed most of the impurities in the raw lignin and also selectively removed the molecules with high melting points. However, neither methanol fractionation nor thermal treatment rendered melt‐spinnable precursors. The precursors were highly viscous and decomposed easily at low temperatures, attributed to the presence of H, G phenolic units, and abundant hydroxycinnamate groups in herbaceous lignin. A two‐step acetylation of methanol fractionated lignin greatly improved the mobility of lignin, while enhancing the thermal stability of the precursor during melt‐spinning. Fourier Transform Infrared and 2D‐NMR analysis showed that the contents of phenolic and aliphatic hydroxyls, as well as the hydroxycinnamates, decreased in the acetylated precursors. The optimum precursor was a partially acetylated lignin with a glass transition temperature of 85 °C. Upon oxidative stabilization and carbonization, the carbon fibers with an average tensile strength of 454 MPa and modulus of 62 GPa were obtained. The Raman spectroscopy showed the ID/IG ratio of the carbon fiber was 2.53. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45736.

Improving Processing and Performance of Pure Lignin Carbon Fibers through Hardwood and Herbaceous Lignin Blends.

Lignin/lignin blends were used to improve fiber spinning, stabilization rates, and properties of lignin-based carbon fibers. Organosolv lignin from Alamo switchgrass (Panicum virgatum) and yellow poplar (Liriodendron tulipifera) were used as blends for making lignin-based carbon fibers. Different ratios of yellow poplar:switchgrass lignin blends were prepared (50:50, 75:25, and 85:15 w/w). Chemical composition and thermal properties of lignin samples were determined. Thermal properties of lignins were analyzed using thermogravimetric analysis and differential scanning calorimetry. Thermal analysis confirmed switchgrass and yellow poplar lignin form miscible blends, as a single glass transition was observed. Lignin fibers were produced via melt-spinning by twin-screw extrusion. Lignin fibers were thermostabilized at different rates and subsequently carbonized. Spinnability of switchgrass lignin markedly improved by blending with yellow poplar lignin. On the other hand, switchgrass lignin significantly improved thermostabilization performance of yellow poplar fibers, preventing fusion of fibers during fast stabilization and improving mechanical properties of fibers. These results suggest a route towards a 100% renewable carbon fiber with significant decrease in production time and improved mechanical performance.

Lignin Valorization through Thermochemical Conversion: Comparison of Hardwood, Softwood and Herbaceous Lignin

In the present study, milled wood lignin (MWL) and organosolv lignin isolated from red oak (hardwood), loblolly pine (softwood) and corn stover (herbaceous biomass) were characterized by TGA, elemental analyzer, GPC, FTIR, 2D-HSQC NMR, and then pyrolyzed in the absence and presence of a zeolite catalyst. For all three biomass species, organosolv lignins contained fewer volatiles in comparison to the corresponding MWLs. Red oak lignin was affected most by the organosolv process, evident by the greatest decrease in volatile content and increase in carbon content of the organosolv lignin. Compared to the corresponding MWLs, organosolv lignins produced more char and less phenolic oil upon pyrolysis. Organosolv lignins also convert to catalytic coke and light hydrocarbons in higher selectivity in comparison to the MWLs during catalytic pyrolysis. When pyrolyzed, corn stover MWL produced 16.26% of phenolic monomers, which is a significantly higher yield compared to 8.61% from red oak MWL and 9.51% from loblolly...

Role of Physicochemical Structure of Organosolv Hardwood and Herbaceous Lignins on Carbon Fiber Performance

Lignin was extracted from Alamo switchgrass (Panicum virgatum) and yellow polar (Liriodendron tulipifera) by organosolv fractionation at different pretreatment temperatures, and its chemical structure was studied by means of elemental analysis and spectroscopy. Thermal properties of lignins were investigated using thermogravimetric analysis and differential scanning calorimetry. Lignin fibers were produced via melt-spinning by a twin-screw extruder with a custom spinneret. Fibers were thermostabilized at different rates and finally carbonized. In both species, lignin obtained from higher severity organosolv fractionation had fewer impurities, higher content of phenolic hydroxyl groups, and more condensed structures as a result of extensive cleavage of aryl ether linkages. Higher organosolv severity improved the ability to spin fibers; in the case of switchgrass, only the high severity sample was spinnable. High severity also decreased thermostabilization time and increased tensile strength and modulus of ...

A Stochastic Method to Generate Libraries of Structural Representations of Lignin

Efforts to derive value-added chemicals from lignin are hindered in part because of its great structural complexity and heterogeneity. Lignin is a polydisperse, random copolymer with varying proportions of monomers and interunit linkage types, forming a hyperbranched topology. Structural models comprising a single macromolecular representation have been proposed for specific biomass sources; these representations, although consistent with experimental observations, are not unique. Alternative models consisting of populations of representations whose average properties match experiment have also been proposed. Expanding on this latter approach, we have developed a stochastic method of generating libraries of diverse and complex structural representations of lignin that is generally applicable to any biomass source. For demonstration purposes, the method is applied to create libraries of wheat straw lignin, a representative herbaceous lignin. The libraries are statistically validated through the χ2 goodness...

High Performance Phenolic Resin Based on Untreated Natural Herbaceous Lignin

In this study, the aim was to prepare a high performance phenolic resin based on natural lignin and to reveal its characteristics. Generally, even though natural lignin is simply added to phenolic resins, and since the reactivity of lignin with the thermal fluidity is low, modification of phenolic resin by such lignin does not proceed sufficiently. Therefore, natural herbaceous lignin which is reactive with phenolic resins was used as the natural lignin, and the preparation and properties of the phenolic resin based on herbaceous lignin were investigated. The properties of the phenolic resin modified with herbaceous lignin were determined and compared to the same phenolic resin with normal woody lignin and without any lignin. It was found that the phenolic resin modified with herbaceous lignin showed good heat resistance, mechanical properties, dimensional stability and electrical insulation properties compared with those of the phenolic resin with the woody lignin and without lignin.

Exploring Allylation and Claisen Rearrangement as a Novel Chemical Modification of Lignin

The conversion of lignin into value-added products is traditionally hampered by its stochastic structure and its complex reactivity. The allylation reaction and the aromatic Claisen rearrangement of the allyl group on lignin as chemical modifications are reported for the first time in this work. This approach is aimed at the development of new lignin-based materials and the improvement of its compatibility and ease of processing. In particular, the Claisen rearrangement of lignin is foreseen as a valuable approach to release phenolic groups in an already chemically modified lignin, giving additional reactive sites for further transformation. These reactions were carried out on a purely guaiacylic lignin (TMP), taken as reference material due to its simplicity, and on a more structurally complex herbaceous lignin (P1000®). The Claisen rearrangement of the allylic chain was successfully achieved by treatment in dimethylformamide at reflux temperature for 15 hours. Finally, a screening of the antioxidant activity of reference, allylated, and Claisen rearranged lignins was carried out. Rearranged lignins exhibited satisfactory antioxidant activities if compared to the reference ones.

Photodegradation of Herbaceous Lignin and Unsaturated Polyester with a Novel TiO2 Photocatalyst System

Photodegradation of a herbaceous lignin and unsaturated polyester was carried out with a novel TiO2/polyethylene oxide (PEO) + methyl linoleate (ML) photocatalyst system. The lignin and unsaturated polyester photodegradation ratios were 51 and 40 %, respectively, showing that the TiO2/PEO + ML had high photocatalyst activity. The ML· produced by the TiO2 photocatalyst was able to attack the lignin and unsaturated polyester because of its hydrophobic molecular structure and worked well as the initiator. In order to study the detailed mechanism of photodegradation with the TiO2/PEO + ML, the chloroform soluble fraction of the photodegraded unsaturated polyester was characterized with 1H-NMR measurement. The result showed that the TiO2/PEO + ML preferentially cleaved carbon–carbon bond.