Organosolv Lignin Research Articles

Chemically Activated Spruce Organosolv Lignin as a Carbocatalyst for Heterogeneous Oxidative Dehydrogenations in the Liquid Phase

Chemically Activated Spruce Organosolv Lignin as a Carbocatalyst for Heterogeneous Oxidative Dehydrogenations in the Liquid Phase

Lignin micro/nanoparticles: synthesis, properties, and application to endow polyvinyl alcohol film with multi-functionality

Lignin, as an abundant natural polymer, has great potential in the synthesis of multifunctional micro/nanoparticles. However, the synthesis methods and parameters during the preparation process impact the controllability of lignin micro/nanoparticles (LMNPs), thereby affecting the performance of composite materials containing LMNPs. In this study, a green, simple, and applicable method for organosolv lignin was proposed for the synthesis of LMNPs using recyclable γ-valerolactone and the parameters (lignin concentration, stirring speed, dropping speed, water/solvent ratio, and lignin structure) were systematically investigated. The tuning of multiple properties of the composites was investigated by mixing LMNPs with polyvinyl alcohol (PVA). Results indicated that synthesis parameters affected the LMNPs formation, leading to aggregation/fusion of LMNPs. The obtained spherical LMNPs were electrostatically stable in pH 4–12, uniform (0.09 PDI), and excellent in thermal stability and antioxidant activity. Based on diffusion-restricted cluster–cluster aggregation, LMNPs around 157–442 nm were fabricated through π-π interactions. The PVA/LMNPs composite films showed excellent properties in terms of mechanical properties, thermal stability, UV shielding capacity, and hydrophobicity. The LMNPs with different structures improved the properties of polyvinyl alcohol films, providing a controllable approach for the development of biodegradable food/medical packaging materials and UV-shielding biomaterials.

Lignin recovery from a mixture of SIX lignocellulosic biomasses within a biorefinery scheme based on a sequential process of autohydrolysis and organosolv

A mixture of six lignocellulosic biomasses could be a solution for sustainable biorefinery supply throughout the year compared with seasonal feedstock. In this study, a sequential process of autohydrolysis and organosolv was used for this mixture. To optimize lignin extraction, an experimental design was used to study the impacts of temperature, ethanol concentration, and time on lignin yield and related characteristics of the organosolv process. A highly pure organosolv lignin (OL) (ca. 90% Klason lignin) was recovered. FTIR analysis showed the main lignin structure was almost unchanged. NMR confirmed this and revealed the presence of guaiacyl-syringyl type with small amounts of p-hydroxyphenyl units (25% G, 70% S, and 5% H), predominantly presenting β-O-4 units (ca. 80%). Tg from 73 to 85 °C was detected. OL showed radical scavenging activity as high as the commercial antioxidant BHT. Moreover, enzymatic susceptibility of delignified biomass was accessed, in which 50% glucose yield was achieved.

Photocatalytic lignin C-C bonds cleavage in lignin models via Fe-doped graphene carbon nitride in micellar aqueous medium

Photocatalytic depolymerization of lignin to prepare value-added chemicals by breaking lignin Cα-Cβ bonds (LCCD) is sustainable because of its green and mild reaction conditions. However, photocatalytic cleavage of LCCD still faces great challenges because of the complexity and stubbornness of lignin structure. Here, Fe-doped graphene carbon nitride (g-C3N4) photocatalysts were successfully prepared. The doping of Fe ions reduces the band gap of g-C3N4 and accelerates the migration ability of photogenerated carriers. 8FeCN can efficiently break LCCD in β-1 lignin model compounds and ethanol organosolv lignin, producing aromatic aldehydes, alcohol and acids as the main products. Hydroxyl radicals are generated through Fe-induced Fenton reactions, which increase the reaction pathway for breaking LCCD. The mechanism studies showed that photocatalytic cleavage of LCCD mainly followed the improved Cβ radical and single electron transfer mechanism. In addition, micellar aqueous media further accelerates the cleavage of LCCD, as water participates in the photocatalytic reaction and provided the O and H atoms needed for the formation of photocatalytic products. This work offers a fresh concept for the high-value utilization of lignin by oxidizing cleavage of LCCD.

Comparing physicochemical characteristics and depolymerization behaviors of lignins derived from different pretreatment processes

Lignin valorization is an important part of increasing the economic viability of sustainable biorefineries. Various methods have been proposed for lignin depolymerization. However, the relationship between lignin structure and its depolymerization behavior hasn't been extensively investigated. This research aims to clarify how the structure and composition of lignins derived from different pretreatment processes affect the downstream catalytic conversion. Herein, optimal organosolv lignin yield above 50% in three different solvent systems were obtained. Meanwhile, three types of hydrolyzed lignin were used as reference lignins. Various lignins were comprehensively characterized by elemental analysis, FT-IR, TGA-DSC and Py-GC/MS techniques. Compared with hydrolyzed lignin, organosolv lignin has higher purity, wider functional group distribution, more uniform structure, as well as a lower G/S ratio. Moreover, lignin depolymerization was carried out with a non-noble metal catalyst Ni/Al2O3 and without the addition of H2. The results showed that transetherification and alkylation reaction were enhanced significantly for organosolv lignin. Total depolymerized aromatics yield from organosolv lignin was 4 to 11 times higher than that of hydrolyzed lignin-rich residues. Notably, Methanol-extracted lignin obtained an optimal yield of 29.7 wt% of monomeric aromatics. Methanol can effectively protect benzylic carbocations formed during organosolv pretreatment, thus minimizing the formation of CC bonds.

Use of Photo isomers to enhance the removal of lignin from woody biomass hydrolysate: UV irradiated photo isomerization of 4,4-diethoxy-azobenzene enhances precipitation of organosolv lignin from extraction solvents

Conversion of lignocellulose to bioproducts and biofuels is often initiated with a hydrolytic pretreatment process that helps to depolymerize the native polymers in biomass and produce a cellulose rich pulp stream. Extracting dissolved components (lignin) from this hydrolysate is an important step to derive value from the biomass components other than cellulose. In this investigation we propose a novel method to enable precipitation of desired solutes using photo-isomers in the extraction solvent. This photo-switchable solvent enables dissolution or precipitation of desired components using alternating UV or visible light to modify the solubility of the compounds of interest. It was found that among different combinations of three solvents and three photo-isomers, the combination of acetone with 4,4′-diethoxy azobenzene solution was most efficient at precipitating dissolved Organosolv lignin in response to UV light exposure. To our knowledge this is the first demonstration of this approach to separating lignin from organic solvents. This method is significant because it minimizes the high energy demands of traditional lignin extraction methods that involve distillation or large amounts of dilution using antisolvents.

Valorisation of crude glycerol in the production of liquefied lignin bio-polyols for polyurethane formulations

Bio-polyols, produced by liquefying lignin with polyhydric alcohols, offer a promising alternative to conventional polyols for polyurethane production. To enhance the sustainability on the production of these bio-polyols, this study proposes the use of crude glycerol and microwave-assisted liquefaction as substitutes for conventional methods and commercial glycerol. This approach reduces the energy requirements of the reaction while also adding value to this by-product. The synthesis of bio-polyols with suitable properties to produce elastic and rigid polyurethane was carried out using previously optimised reaction conditions. Organosolv lignins obtained from Eucalyptus globulus and Pinus radiata were employed, using polyethylene glycol and crude glycerol as solvents and sulphuric acid as a catalyst. Several parameters of the bio-polyols were analysed, including hydroxyl number (IOH), acid number (An), and functionality (f), suggesting that the bio-polyols were suitable for polyurethane synthesis. Bio-polyols formulated to produce rigid polyurethanes exhibited IOH values of 554 and 383 (mg KOH/g), An values of 1.91 and 4.21 (mg KOH/g), and functionalities of 4.16 and 3.14 for Eucalyptus globulus and Pinus radiata lignin. In the case of bio-polyols for elastic polyurethanes, the values were 228 and 173 (mg KOH/g) (IOH), 20.94 and 25.09 (mg KOH/g) (An), and functionalities of 3.51 and 2.08.

Direct extraction of biphasic organosolv lignin for producing aromatic aldehydes via alkaline oxidation

Lignin can be a sustainable source of aromatic compounds, whereas the utilization is limited because of its complex three-dimensional structure. Organosolv method is promising for the valorization of lignin because of its mild conditions as compared with industrial pulping processes. Aromatic aldehydes, widely used in various industries, are obtained by catalytic oxidation of lignin. Organosolv treatment of various types of lignocellulose in water/1-butanol solvent was conducted using a batch type reactor. During the solvent removal from 1-butanol phase containing organosolv lignin, the concentrated lignin was denatured, which was evaluated by measuring particle size distribution and thermal decomposition behavior of the lignin. The recovery procedure of lignin was improved, and the extraction of organosolv lignin from 1-butanol phase to alkaline solution was developed. The improved extraction method definitely showed a higher yield of aromatic compounds regardless of the type of lignocellulose, yielding 14 C-mol% of aromatic aldehydes after alkaline oxidation of willow-derived lignin. After the alkaline oxidation reaction, a simple solvent fractionation was applied for refining the oxidized products. The solvent fractionation of the oxidized products was achieved using ethyl acetate and n-heptane. n-Heptane-soluble fraction selectively contained the lighter fraction with maintaining the content of aromatic compounds.

Photocatalytic depolymerization of lignin via oxidizing cleavage of Cα-Cβ bonds in micellar aqueous media

Photocatalytic depolymerization of lignin to prepare high-value chemicals is a promising way to promote the valuable utilization of lignin. However, the complexity and stubbornness of lignin structure seriously decrease the photocatalytic efficiency and selectivity. Herein, the micellar aqueous media (SDS-8/HCl) consisting of sodium lauryl sulfonate and hydrochloric acid was successfully prepared. Photocatalyst TiO2 and SDS-8/HCl system can effectively depolymerize the typical β-1 lignin models and ethanol organosolv lignin to value-added chemicals by oxidizing cleavage of lignin Cα-Cβ bonds. The addition of hydrochloric acid solution (1 mol/L) improves the selectivity of photocatalytic breaking of lignin Cα-Cβ bonds. Chlorine ions are oxidized to chlorine radicals by photogenerated holes and hydroxyl radicals, dramatically increasing the photocatalytic efficiency. Electron paramagnetic resonance technique and Gas chromatography–mass spectrometry were used to demonstrate the presence of chlorine radicals. Under optimal conditions, the conversion of substrate Dpol is 98.4 %, and the obtained products are mainly benzaldehyde and benzoic acid. Isotope labeling experiments show that water is also involved in photocatalytic reactions and the oxygen needed to form the product benzaldehyde comes from water. Single-electron transfer processes are possible photocatalytic mechanisms that differ from the previous reports. Importantly, water and chlorine ions were found to be involved in photocatalytic reactions for the first time and promote the cleavage of lignin Cα-Cβ bonds. This work provides new ideas for photocatalytic cleavage of lignin Cα-Cβ bonds in heterogeneous photocatalytic systems using micellar aqueous media.

Encapsulation of AgNPs in a Lignin Isocyanate Film: Characterization and Antimicrobial Properties.

Lignin isolated from agricultural residues is a promising alternative for petroleum-based polymers as feedstocks in development of antimicrobial materials. A polymer blend based on silver nanoparticles and lignin-toluene diisocyanate film (AgNPs-Lg-TDIs) was generated from organosolv lignin and silver nanoparticles (AgNPs). Lignin was isolated from Parthenium hysterophorus using acidified methanol and used to synthesize lignin capped silver nanoparticles. Lignin-toluene diisocyanate film (Lg-TDI) was prepared by treating lignin (Lg) with toluene diisocyanate (TDI) followed by solvent casting to form films. Functional groups present and thermal properties of the films were evaluated using Fourier-transform infrared spectrophotometry (FT-IR), thermal gravimetry (TGA), and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM), UV-visible spectrophotometry (UV-Vis), and Powder X-ray diffractometry (XRD) were used to assess the morphology, optical properties, and crystallinity of the films. Embedding AgNPs in the Lg-TDI films increased the thermal stability and the residual ash during thermal analysis, and the presence of powder diffraction peaks at 2θ = 20, 38, 44, 55, and 58⁰ in the films correspond to lignin and silver crystal planes (111). SEM micrographs of the films revealed the presence of AgNPs in the TDI matrix with variable sizes of between 50 to 250 nm. The doped films had a UV radiation cut-off at 400 nm as compared to that of undoped films, but they did not exhibit significant antimicrobial activity against selected microorganisms.

Surfactants facilitated glycerol organosolv pretreatment of lignocellulosic biomass by structural modification for co-production of fermentable sugars and highly reactive lignin

This study reported that surfactants could facilitate the organosolv pretreatment of lignocellulosic biomass (LCB) to produce fermentable sugars and highly active lignin. Under the optimized conditions, the surfactant-assisted glycerol organosolv (saGO) pretreatment achieved 80.7% delignification with a retention of 93.4% cellulose and 83.0% hemicellulose. The saGO pretreated substrate exhibited an excellent enzymatic hydrolyzability, achieving 93% of glucose yield from the enzymatic hydrolysis at 48 h. Structural analysis showed that the saGO lignin contained rich β–O–4 bondings with less repolymerization and lower phenolic hydroxyl groups, thus forming highly reactive lignin fragments. The analysis evidenced that the surfactant graft the lignin by structural modification, which was responsible for the excellent substrate hydrolyzability. The co-production of fermentable sugars and organosolv lignin almost recovered a gross energy (87.2%) from LCB. Overall, the saGO pretreatment holds a lot of promise for launching a novel pathway towards lignocellulosic fractionation and lignin valorization.

Acid-based organosolv lignin extraction from acai berry bagasse

Lignin is the second most prevalent natural material on the planet with applications as dispersants, wound dressings, animal feed, chemicals and fuel. A promising source for lignin extraction is from acai, a palm tree from the Amazonian floodplain. In this study, lignins were extracted, for the first time from acai berry bagasse using an acetic acid-based organosolv approach, and the effects of reaction time and acid concentration on the delignification yield were assessed through a statistical relationship. The lignins were then characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). According to the results, the higher the acid concentration, the shorter the extraction time to obtain the maximum delignification yield. The best condition to isolate pure lignin from the bagasse was 92.5 % (v/v) acetic acid concentration and 10 h of reaction time.

Polylactic acid biocomposites with high loadings of melt-flowable organosolv lignin

Polylactic acid (PLA) was blended with a new type of organosolv lignin, called Bioleum (BL) using a melt extrusion method to obtain biocomposites with BL loadings as high as 40 wt%. Two plasticizers, namely polyethylene glycol (PEG) and triethyl citrate (TEC) were also introduced to the material system. Gel permeation chromatography, rheological analysis, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and tensile testing were performed to characterize the biocomposites. The results revealed that BL exhibits a melt-flowable characteristic. The biocomposites' tensile strength was found to be higher than most of the previously reported cases. Overall, the BL domain size increased as the BL content was increased, causing a drop in the strength and ductility. Even though the addition of both PEG and TEC improved the ductility, PEG proved to significantly outperform TEC. With the introduction of 5 wt% PEG, the elongation at break of PLA_BL20 was increased >9 times, even exceeding that of the neat PLA by several folds. Consequently, PLA_BL20_PEG5 produced a toughness that is twice as the of the neat PLA. The findings suggest a great promise of BL to develop scalable and melt processable composites.

Mild catalytic transfer hydrogenolysis of lignin for efficient monophenol production over lignin-coordinated N-doped ultrafine Ni nanocluster catalyst

Lignin hydrogenolysis into monophenols presents a promising route for lignin-based chemical and fuel production but still suffers from harsh reaction conditions (e.g. high temperature and high external H2 pressure). Herein, we report an ultrafine Ni nanocluster anchored on N-doped carbon nanosheets (Ni/LNC) for efficient catalytic transfer hydrogenolysis of poplar organosolv lignin. The catalyst was fabricated through a simple pyrolysis process of lignin‑nickel complex mixed with melamine, in which the lignin coordination greatly improved the Ni dispersion and the strong NiN interaction inhibited the Ni nanocluster growth, resulting in the ultrafine particle size (1–2 nm). Under mild conditions (160 °C, 1 h), 22.08% of monophenol yield was obtained over the catalyst, which was significantly higher than those over the two reference catalysts (Ni/AC and Ni/LC) as well as other previously reported Ni-based catalysts. The excellent catalytic activity can be attributed to both the substantial increase in catalytic active sites and the enhancement in H transfer from methanol resulted from the electron-rich N-doped nanosheet support. Finally, magnetically recycled Ni/LNC showed excellent recycling stability. Consequently, this work presents a facile and low-cost approach for the synthesis of N-doped carbon nanosheet supported ultrafine Ni nanocluster and further demonstrates its superior applicability in lignin hydrogenolysis.

Selective photocatalytic aerobic oxidative cleavage of lignin C–O bonds over sodium lignosulfonate modified Fe3O4/TiO2

Lignocellulose shows significantly potential in sustainable conversion to high-quality fuel and value-added chemicals with the demands for realizing the rapid cycle of carbon resources and helping to reach carbon neutrality in nature. Selective tailoring of α-O-4, β-O-4, etc. linkages in lignin has always been viewed as “death blow” for its depolymerization. Herein, novel sodium lignosulfonate (SL) modified Fe3O4/TiO2 (SL-Fe3O4/TiO2) spherical particles have been developed and used as catalysts for selectively photocatalytic oxidative cleavage of organosolv lignin. As expected, 80% selective conversion of lignin in C2–C4 esters has been achieved, while C–O bonds in lignin model compounds can be effectively cleaved. Other than normal hydroxyl radical-mediated photocatalytic depolymerization of lignin over TiO2-based materials, in this contribution, mechanism studies indicate that photogenerated holes and superoxide anion radicals are main active species, which trigger the cleavage of α/β-O-4 bond, and the isotope-labeling study confirms the crucial factor of Cβ–H dehydrogenation in cleavage of β-O-4 bonds.

Effect of Pd/C catalytic extraction on the hydrothermal depolymerization properties of ethanol organosolv lignin (EOL) in supercritical ethanol

This study investigated the effect of a Pd/C catalytic extraction process on the hydrothermal depolymerization product properties of ethanol organosolv lignin (EOL) in supercritical ethanol. Phenolic products were separated and analyzed by gel permeation chromatography (GPC) and thermogravimetric (TG) analyses. The gas chromatography–mass spectrometry (GC-MS) analyses of obtained liquid oil products from depolymerized EOL confirmed the presence of value-added phenolics. Scanning electron microscopy (SEM) was used to observe the morphology of the char product. During ethanol organosolv lignin extraction, 90.5% purity of EOL was obtained. A high yield of EOL up to 39.6% from bamboo without catalysts and with higher yield of EOL up to 44.0% from 1% Pd/C catalyst under 200 °C. A high yield of liquid oil products, up to 65.4%, was recovered from EOL depolymerization under conditions of 240 °C, 240 min, 100 vol % ethanol, and 2% EOL, with only 24% solid residue. The main phenolic products were 2-methoxyphenol, 4-ethylphenol, 4-methoxy-2-methylphenol, 4-ethyl-2-methoxyphenol, 2,6-dimethoxy-phenol, and 2-methoxy-4-propylphenol.

Urea–Lignin/Chitosan Nanocomposite as Slow-Release Nanofertilizer

Urea is a universal fertilizer, but its use efficiency hardly exceeds 30–35%, and more than 70% is lost to the environment, causing eutrophication in aquatic systems. This research focuses on encapsulating urea molecules using a lignin-chitosan composite. The nanocomposite was developed as a suitable carrier for entrapping nitrogenous fertilizer. Coconut coir contains plenty of lignin, which was extracted using the organosolv process by using ethanol as a solvent. Organosolv lignin (OSL) yielded spherical lignin nanoparticles (LNPs) via the solvent displacement method. Finally, a nitrogen source was loaded into the chitosan/lignin nanocomposite fertilizer (lignorea), which consists of LNPs, chitosan, and a cross-linker. The nanocomposite was characterized using PSA, SEM, TEM, UV–vis, FTIR, and XRD. The morphology of the OSL and LNPs was examined under SEM (626 ± 40 nm) and TEM (26 ± 9 nm). The noncrystallinity of both lignin and crystallinity after entrapment in nanocomposite was validated by XRD. The specific functional group pertaining to the lignin backbone had aromatic vibrations at 1511 cm–1 (OSL) and 1507 cm–1 (LNPs), and the presence of an amide peak after loading N was observed in FTIR. The lignin samples have their corresponding spectral absorbance at 281 and 288 nm wavelengths obtained in UV–vis. The size and stability of the extracted OSL and LNPs were verified by a particle size analyzer and zeta potential, respectively. The compatibility and interactions of the developed nanofertilizer were confirmed with molecular modeling and simulation. The developed nanofertilizer has total nitrogen of 30–35% which slowly releases up to 15 days in the soil. The study clearly suggests that lignin with chitosan served as a perfect template to hold and release N in a regulated pattern that collectively contributes to improved N use efficiency.

Life Cycle Environmental Impact Considerations in the Design of Novel Biobased Polyurethane Coatings

Substituting fossil-based with biobased chemical building blocks can potentially decrease the environmental impact of polyurethane (PU) coating production. This study applies life cycle assessment methods in the early development of three processes that incorporate biobased elements into PU coating production: a fully biobased coating made with organosolv lignin (OSL) and a biobased cross-linker from vanillic acid (VA) and two hybrid coatings made with a fossil-based cross-linker and either OSL or depolymerized OSL. Coatings with biobased elements had impacts of 1.5, 2.6, and 19.9 kg CO2eq/kgcoating for coatings made with OSL, depolymerized OSL, and the fully biobased coating, respectively. Emissions are mostly associated with the fossil-based cross-linker in hybrid coatings and with solvents and heat needed for the production of the biomass-derived cross-linker. While this study demonstrates that the use of biobased compounds in hybrid coatings can reduce the environmental impacts of PU coatings in comparison to fossil-based versions, additional development of biobased cross-linkers and research into end-of-life scenarios are needed to further reduce the environmental impacts of biobased PU coating production.

Beyond Yield Optimization: The Impact of Organosolv Process Parameters on Lignin Structure

AbstractWhen optimizing the process parameters of the acidic ethanolic organosolv process, the aim is usually to maximize the delignification and/or lignin purity. However, process parameters such as temperature, time, ethanol and catalyst concentration, respectively, can also be used to vary the structural properties of the obtained organosolv lignin, including the molecular weight and the ratio of aliphatic versus phenolic hydroxyl groups, among others. This review particularly focuses on these influencing factors and establishes a trend analysis between the variation of the process parameters and the effect on lignin structure. Especially when larger data sets are available, as for process temperature and time, correlations between the distribution of depolymerization and condensation reactions are found, which allow direct conclusions on the proportion of lignin's structural features, independent of the diversity of the biomass used. The newfound insights gained from this review can be used to tailor organosolv lignins isolated for a specific application.

Mild hydrogenolysis of lignin model compound and organosolv lignin over non-noble bimetallic Ni–Fe/TiN catalyst

Lignin is one of the most promising feedstocks for renewable aromatics production. Conversion of such feedstock into aromatics can be attained through catalytic hydrogenolysis. In this work, NixFey/TiN bimetallic catalysts were evaluated in the hydrogenolysis of both: (i) benzyl phenyl ether (BPE) as a model compound for lignin and (ii) real organosolv lignin feedstock under low temperature (150 °C) and low H2 pressure (12 bar). All bimetallic catalysts exhibited superior performance over single-component materials and were shown to compose of uniformly/highly dispersed and intimately mixed Ni and Fe nanoparticles. Among bimetallic materials, Ni5Fe2/TiN possesses the highest activity in BPE hydrogenolysis, which is comparable to that of a 5% Pd/C commercial catalyst while showing significantly higher aromatic selectivity. Ni5Fe2/TiN catalyst also outperformed Pd/C in hydrogenolysis of organosolv lignin, shown by its higher oil yield, greater content of phenolic monomers, and lower content of dimers. This material exhibited good stability in BPE conversion with no noticeable deactivation over 5 recycling cycles. XANES analysis suggests the electron transfer from Ni to Fe, which explains the superior activity observed with Ni5Fe2/TiN.