Pyrolysis Of Lignin Research Articles

Catalytic Reforming Characteristics of Volatiles From Lignin Pyrolysis Based on a Ce-Promoted Ni/Magnesium Slag Catalyst

Catalytic Reforming Characteristics of Volatiles From Lignin Pyrolysis Based on a Ce-Promoted Ni/Magnesium Slag Catalyst

Isolating key reaction energetics and thermodynamic properties during hardwood model lignin pyrolysis.

Computational studies on the pyrolysis of lignin using electronic structure methods have been largely limited to dimeric or trimeric models. In the current work we have modeled a lignin oligomer consisting of 10 syringyl units linked through 9 β-O-4' bonds. A lignin model of this size is potentially more representative of the polymer in angiosperms; therefore, we used this representative model to examine the behavior of hardwood lignin during the initial steps of pyrolysis. Using this oligomer, the present work aims to determine if and how the reaction enthalpies of bond cleavage vary with positions within the chain. To accomplish this, we utilized a composite method using molecular mechanics based conformational sampling and quantum mechanically based density functional theory (DFT) calculations. Our key results show marked differences in bond dissociation enthalpies (BDE) with the position. In addition, we calculated standard thermodynamic properties, including enthalpy of formation, heat capacity, entropy, and Gibbs free energy for a wide range of temperatures from 25 K to 1000 K. The prediction of these thermodynamic properties and the reaction enthalpies will benefit further computational studies and cross-validation with pyrolysis experiments. Overall, the results demonstrate the utility of a better understanding of lignin pyrolysis for its effective valorization.

Conversion of lignin pyrolysis oil to cyclohexyl methyl ethers as a promising biomass-derived solvent

A mixture of cyclohexyl methyl ethers was prepared from Kraft lignin pyrolysis oil for use as a biomass-derived aliphatic solvent.

Catalytic Pyrolysis Mechanism of β-O-4 Type of Lignin Dimer: The Role of H Proton

In the preparation of monocyclic benzenes by catalytic pyrolysis of lignin, how to break the bonds of pyrolysis macromolecules into small molecules is the key point for the transformation. In this ...

FeN@N-doped graphitic biochars derived from hydrothermal-microwave pyrolysis of cellulose biomass for fuel cell catalysts

Iron-nitrogen moieties encapsulated in the N-doped graphitic and hierarchical biochars are derived from the hydrothermal pyrolysis and microwave NH3 activation of cellulose and lignin. The physicochemical properties of these biochars are identified by using various analytical instruments and their application as electrocatalysts in oxygen reduction reaction (ORR) is also evaluated in alkaline solution. As compared to the lignin-derived biochars (named as L-y), the cellulose-derived biochars (named as C-x) have superior activities toward ORR due to the formation of highly graphitic carbon shells (as proofed by using X-ray diffraction and high-resolution transmission electron microscope) in the biochars. Moreover, the C-1% (i.e., 1% of iron in the cellulose-derived biochars) exhibits the best electrocatalytic performance (onset potential = −0.05 V vs. Ag/AgCl) and follows a near four-electron ORR route, which could be ascribed to the more active iron-nitrogen sites (as evidenced by X-ray photoelectron and X-ray absorption spectroscopy) covered with hierarchical carbon shells (as identified by N2 adsorption-desorption isotherms). The cellulose-derived biochars with distinctive iron-nitrogen retained in the shell of N-doped graphitic and hierarchical carbons by employing a time-saving and energy-efficient microwave activation procedure may render a potential application in the ORR.

Evidence of a Phenolic Pool as a Key Intermediate for Zeolite-Catalyzed Lignin Pyrolysis.

The phenolic pool is considered to be an important intermediate during the catalytic conversion of biomass. However, no direct evidence has been reported on its full picture on a molecular level due to the huge challenges in probing the reactive and lowly volatile phenolic oligomers with state-of-the-art technologies. Herein, we report the online detection and structural identification of a phenolic pool by utilizing in-situ atmospheric-pressure photoionization mass spectrometry, demonstrating that the phenolic pool is formed through repolymerization of monomers with an equidistant group pattern and acts as a key mechanistic step for both valuable aromatic products and undesired coke. The exploration of the real reactive species is also of great importance for the rational design and synthesis of advanced catalysts with high activity.

Evidence of a Phenolic Pool as a Key Intermediate for Zeolite‐Catalyzed Lignin Pyrolysis

AbstractThe phenolic pool is considered to be an important intermediate during the catalytic conversion of biomass. However, no direct evidence has been reported on its full picture on a molecular level due to the huge challenges in probing the reactive and lowly volatile phenolic oligomers with state‐of‐the‐art technologies. Herein, we report the online detection and structural identification of a phenolic pool by utilizing in‐situ atmospheric‐pressure photoionization mass spectrometry, demonstrating that the phenolic pool is formed through repolymerization of monomers with an equidistant group pattern and acts as a key mechanistic step for both valuable aromatic products and undesired coke. The exploration of the real reactive species is also of great importance for the rational design and synthesis of advanced catalysts with high activity.

A new insight of lignin pyrolysis mechanism based on functional group evolutions of solid char

To elucidate the mechanism of biomass lignin pyrolysis, the functional group evolution in lignin chars derived at 200–600 °C was investigated using two-dimensional perturbation correlation infrared spectroscopy, associated with the properties of the volatile products. Results from 2D-PCIS pointed that the change in the alcohol groups C–OH occurs earlier than that in the carbonyl groups CO before 250 °C, corresponding to the reaction of keto–enol tautomerization: C–OH → CO, and the cleavage of bonds and remodeling reactions of the side chains of the benzene rings are synchronous. Besides, the formation of simple substituted benzene structures was earlier than complex substituted benzene structures. Decarbonylation, dehydrogenation and dealkylation were intensified during polycondensation of benzene rings. These findings are significant for achieving an in-depth understanding of lignin pyrolysis.

A novel interaction mechanism in lignin pyrolysis: Phenolics-assisted hydrogen transfer for the decomposition of the β-O-4 linkage

Abstract Pyrolysis of lignin involves complex unimolecular decomposition and bimolecular interaction mechanisms. Unimolecular decomposition of lignin model compounds has been widely investigated, while bimolecular interactions are far from well elucidated. Currently, only two radical reaction-based interactions, i.e., hydrogen abstraction and hydrogen-bond-induced homolysis mechanisms, have been proposed to explain the interactions in the lignin pyrolysis process, which ignores the concerted reaction-based interactions involving the pyrolytic products of lignin. Particularly, a large number of phenolics are produced in the pyrolysis of lignin, which can further affect the concerted pyrolysis reactions of lignin. In the present work, a novel interaction mechanism, phenolics-assisted hydrogen transfer (phenolics-AHT) process for the concerted reactions, is confirmed and carefully investigated. Phenylethyl phenyl ether (PPE), a typical β-O-4 lignin dimer, is used as the model compound to reveal the phenolics-AHT mechanism in the lignin pyrolysis system. Density functional theory (DFT) calculation, electrostatic potential (ESP) analysis, and fast pyrolysis experiment results are combined to reveal that the phenolic products participate in the hydrogen transfer process of the concerted Maccoll elimination reaction by means of their phenolic hydroxyl structures and significantly reduce the energy barrier, thus promoting the cleavage of the β-O-4 linkage. On the contrary, phenolics-AHT has no obvious effect on the concerted retro-ene fragmentation. At medium pyrolysis temperatures, the hydrogen transfer processes induced by phenolic products play a more significant role in the dissociation of the β-O-4 linkage than the hydrogen abstraction induced by radicals, due to the limited amount of free radicals. In addition, DFT calculation results further suggest that decarbonylation, decarboxylation, dehydration, tautomerism, and other concerted reactions can also be promoted by phenolics-AHT.

Ternary Phase Diagram of Water/Bio-Oil/Organic Solvent for Bio-Oil Fractionation

Separating bio-oil by fractionation with different chemical compositions is a critical step to refine these oils and obtain high-value products. Cold water precipitation of pyrolytic lignin from bi...

Correlation between bacterial decay and chemical changes in waterlogged archaeological wood analysed by light microscopy and Py-GC/MS

AbstractErosion bacteria are the main degraders of archaeological wood excavated from waterlogged environments. Light microscopy and analytical pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) were exploited to study waterlogged archaeological wood (Pinus sylvestrisL.) at different stages of bacterial decay. The research explored the biochemical changes related to erosion bacteria degradation of the secondary cell wall in the wood cells and the chemical changes related to abiotic processes induced by the long-term waterlogged burial environment. Erosion bacteria were demonstrated by chemical analysis to cause significant holocellulose depletion. Detailed analysis of the holocellulose and lignin pyrolysis products revealed only minor chemical changes in the residual structure even after heavy erosion bacteria decay. Chemical changes in the lignin polymer is associated to enzymatic unlocking of the lignocellulose to gain access to the holocellulose fraction of the cell wall. Chemical changes in the holocellulose fraction are suggested to stem from depolymerisation and from alterations in the polymer matrix of the residual wood cell wall structure. Interestingly, a difference was observed between the sound reference wood and the waterlogged archaeological wood without erosion bacteria decay, indicating that long-term exposure in waterlogged environments results in partial decay of the holocellulose even in absence of bacterial activity.

Effect of using regenerated combined FAU and MOR zeolites as catalysts during the pyrolysis of kraft lignin

The SiO2/Al2O3 mole ratio, pore size, and acid sites are the key parameters of zeolite’s activity in lignin pyrolysis. In this study, the comparison of individual Y and M zeolites, the combined ‘Y + M’ sample after regeneration, and their effect on lignin pyrolysis were studied in five cycles (regeneration and reuse). The results were explained using Brunauer, Emmet, and Teller (BET), micropore surface area (MSA), and total acid sites (TAS) analyses. In comparison with the individual Y or M zeolite sample, the consistent higher catalytic activities of the combined ‘Y + M’ sample in repeated cycles were observed. Pyrolysis heavy oils were characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The NMR analyses revealed that with increased zeolite regeneration cycles, p-hydroxy phenyl and methoxyl groups increased. Decreases in guaiacyl phenolic hydroxyl were less for the combined ‘Y + M’ sample than the individual Y and M zeolites. Lower weight average (Mw) of heavy oil for the combined ‘Y + M’ sample indicated the enhanced cleavage of lignin structures in pyrolysis. These results support the higher catalytic activity of regenerated zeolites for the combined ‘Y + M’ sample compared with individual Y and M zeolites due to the improved MSA and TAS.

Catalytic mechanisms of potassium salts on pyrolysis of β-O-4 type lignin model polymer based on DFT study

In this study, the possible catalytic mechanisms of potassium salts on lignin pyrolysis was investigated with two β-O-4 type lignin model dimers with different oxygen functional groups on Cα using density functional theory (DFT) calculations. It was found that potassium salts (such as KOH and K2CO3) can react with phenol hydroxyl in lignin to form organic-K and further catalyze pyrolysis progress. Through this catalytic mechanism, potassium salts promoted the removal of Cα on specific intermediates and the demethylation of methoxy groups during β-O-4 type lignin pyrolysis, promoted the decomposition of intermediates, and facilitated the formation of phenol and CO2.

Phenol-derived products from fast pyrolysis of organosolv lignin

Lignin is the largest aromatic bio-polymer feedstock with a huge potential of being refined for aromatic chemical platform and building block. Organosolv process for lignin extraction has a low impact on the environment due to its low chemical requirement, the absence of sulfur, and as it is more practical for chemical recovery. Therefore, refinement of extracted lignin to valuable molecular compounds such as purified lignin and its derivative is the key success for biorefinery industry. In this study, sugarcane bagasse from a local sugar manufacturer in Thailand, noted as BG-lignin, was selected as feedstock for lignin extraction using ethanol and water. The chemical composition of this lignin was slightly different than that of commercially available organosolv lignin, noted as Comm-OS-lignin, in that BG-lignin has more combustible constituents (volatile organic compounds and fixed carbon) of 96.14% and low ash content of 0.09%. The chemical structure of BG-lignin contains a higher number of aliphatic hydrocarbon and aliphatic hydroxy side chains than Comm-OS-lignin, as confirmed by the FT-IR and 1H-NMR analyses. The study on fast pyrolysis of lignin, using Py-GCMS technique, found 2, 3-dihydrobenzofuran as a major constituent at any tested pyrolysis temperature. H-unit, G-unit, and S-unit are distributed in resemble fraction with a H∕G∕S ratio of 1∕1∕0.7 and 0.8∕1∕1 for Comm-OS-lignin and BG-lignin, respectively, at pyrolysis temperature of 400–600 °C, except for H-unit which was enhanced at 700 °C to 28.82% of Comm-OS-lignin and 29.66% of BG-lignin. At a temperature of 400–600 °C, phenolic selectivity of pyrolyzed products, mainly methoxy phenol (Ph-OCH3) and alkylated phenol (R-Ph-OCH3), was done. A higher pyrolysis temperature of 700 °C led to the elimination of aromatic side group and is more favorable in alkyl phenol (R-Ph) and phenol selectivity. However, reduction of the phenolic compound was observed with a higher temperature due to thermal fragmentation of the C–C linkage in the aromatic structure. Products selectivity related to lignin feedstock and pyrolysis temperature could be applied as a conceptual guideline for conducting further study of chemical upgrading process to obtain high-value biochemical products.

Pyrolysis of herb waste: Effects of extraction pretreatment on characteristics of bio-oil and biochar

The extracted herbal residue, an agricultural waste, was pyrolyzed to produce value-added products by exploring the impact of extraction pretreatment on the pyrolysis performance of herbal feedstock. The Artemisia capillaris thumb, a kind of Chinese herbal medicine, was extracted with ethanol to get the herbal waste. The herbal residue and herbal feedstock were pyrolyzed at different pyrolysis temperature. The results showed the extraction of the herb with ethanol affected both the yields and composition/properties of bio-oil/biochar. Extraction of the herb also affected the pyrolysis of cellulose, hemicellulose or lignin in distinct ways. Compared with the extracted herbs, the yield of ketones, acids and furans in bio-oils produced by herb pyrolysis at 300 °C was higher than 11, 14 and 41%, respectively, which belonged to the derivates from the cellulose component or hemicellulose component. However, when the herb was pyrolyzed at 500 °C, it was compared with when the extract herb was pyrolyzed at 500 °C that the yield of the phenolics with monocyclic ring or fused ring structures in the bio-oil was lower than 3%. According to the DRIFTS analysis, the evolution of the carbonyl-containing organics during the pyrolysis was also affected by the extraction of the herb. As for the char, more carbonyl group was retained in the char from the extracted herb. Nevertheless, the results from thermal analysis showed that thermal stability of the char from extracted herb was remarkably lower than that from herb feedstock.

Renewable aromatic hydrocarbons production from catalytic pyrolysis of lignin with Al-SBA-15 and HZSM-5: Synergistic effect and coke behaviour

With a focus on converting waste to energy, this study integrated the macromolecular reaction ability of Al-SBA-15 and the shape selectivity of HZSM-5 for the production of renewable aromatic hydrocarbons. Results demonstrated that the catalytic pyrolysis of lignin with both Al-SBA-15 and HZSM-5 was able to improve the mono-aromatic hydrocarbons (MAHs) production while inhibiting the formation of undesirable poly-aromatic hydrocarbons (PAHs), thus controlling the MAHs and PAHs content in the bio-oil. At optimal operation conditions (pyrolysis temperature: 550 °C, Al-SBA-15/HZSM-5 ratio: 1:3), the MAHs content was 42.57% higher than that catalyzed by HZSM-5 only (28.30%). The PAHs content was only 27.13%. Typical MAHs (benzene, toluene and xylene, denoted as BTX) and PAHs selectivities were determined as 55.91% and 38.92%, respectively. Thermogravimetry-differential thermogravimetric (TG-DTG) analysis indicated that the used HZSM-5 was principally composed of graphite-like coke and a negligible content of fibrous-like coke. The coke content was observed as 5.65% compared to 10.52% in the HZSM-5 only. Furthermore, the efficient synergistic effect of Al-SBA-15 and HZSM-5 resulted in the deep conversion and directional reforming of the lignin pyrolysis vapors. This study can promote the high-grade utilization of lignin through the application of feasible fixed-bed catalytic pyrolysis technology.

Understanding the enhanced production of poly-aromatic hydrocarbons during the pyrolysis of lignocellulosic biomass components under pressurized entrained-flow conditions

The entrained-flow pressurized pyrolysis of lignin, cellulose, and xylan was investigated to determine the composition of pyrolysis products and the reaction mechanisms. The influence of biomass components (lignin, cellulose, and xylan) and pyrolysis conditions was investigated. The results showed that under atmospheric pressure, the decomposition of lignin formed saturated aliphatic hydrocarbons (SAHCs), phenolics, and PAHs, while cellulose and xylan mainly generated phenolics, sugars, carbonyls, alcohols, and PAHs. Increasing the pyrolysis pressure and temperature was found to drastically promote the generation of PAHs, accompanied by a decrease in phenolics, SAHCs, sugars, carbonyls, and SRAHCs. The ring growth via Diels-Alder cycloaddition reaction pathways in combination with hydrogen abstraction/C2H2 addition (HACA) was postulated to be the mechanism of the formation of PAHs. The 4-ring PAHs (pyrene, fluoranthene) and 3-ring PAHs (phenanthrene, fluorene) were found to dominate the lignin bio-oil, while the bio-oil from cellulose and xylan mainly contained 2-ring PAHs (naphthalene). Elevated pressures and temperatures were also found to significantly increase the selectivity of H2 in the bio-gas.

Demethylation of a methoxy group to inhibit repolymerization during alkaline lignin pyrolysis

The methoxy group in lignin was demethylated using iodocyclohexane; then, lignins with different methoxy group contents and six model compounds were pyrolyzed at 600 °C to investigate the role of methoxy groups during lignin pyrolysis. The results indicated that iodocyclohexane modification not only promotes methoxy demethylation but also causes side chain ether bond breakage. Demethylation of the methoxy group could inhibit the repolymerization reaction and reduce the activation energy during later lignin pyrolysis, and could also promote the homolysis of Ar-Cα. The pyrolysis experiments of the model compounds showed that the methoxy group is not an essential factor for the formation of pyrolytic char; however, it could promote the repolymerization reaction by intramolecular interaction with phenolic hydroxyl.

Investigation of biomass components on the slow pyrolysis products yield using Aspen Plus for techno-economic analysis

Prior information on the pyrolysis product behaviour of biomass components-cellulose, hemicellulose and lignin is critical in the selection of feedstock as components have a significant influence on the pyrolysis products yield. In this study, the effect of biomass components on the yield of slow pyrolysis products (char, bio-oil and syngas) is investigated using a validated ASPEN Plus® model. The model is simulated at a temperature of 450 °C, a heating rate of 10 °C/min and a solid residence time of 30 min. The results indicated that at the given conditions, lignin contributed 2.4 and 2.5 times more char yield than cellulose and hemicellulose. The hemicellulose contributed 1.33 times more syngas yield than lignin while the cellulose and hemicellulose contributed 8.67 times more bio-oil yield than lignin. Moreover, the cost involved in the production of char using lignin (110 $/ton) is significantly economical than using cellulose (285 $/ton) and hemicellulose (296 $/ton). The net CO2 emission of lignin pyrolysis is 4.14 times lower than cellulose pyrolysis and 3.94 times lower than hemicellulose pyrolysis. It can be concluded that lignin pyrolysis is more advantageous than cellulose and hemicellulose pyrolysis. In the selection of feedstock for the slow pyrolysis, the feedstock with more lignin content is preferred.Graphical abstract

EPR detection of key radicals during coking process of lignin monomer pyrolysis

Lignin pyrolysis is a promising method for the sustainable production of phenolic compounds from biomass. However, detailed knowledge about the radicals involved in this process and their influence during the coking is missing. Herein, we report on the pyrolysis of guaiacol, a lignin monomer at 600 °C under inert and hydrogen gas conditions. During the pyrolysis process, the formed radicals were detected by two improved electron paramagnetic resonance spectroscopy methods. Successfully observed o-phenyl semiquinone radical anion, cyclopentadienyl radical, methyl radical, hydroxyl radical, methoxy radical, phenyl radical, phenoxy radical, etc. during the pyrolysis of guaiacol, as well as the changes of related radicals in different pyrolysis stages. It was found that o-semiquinone radical anions and cyclopentadienyl radicals were the key free radicals in the generation of coke and tar during the pyrolysis process. And through hydrogenation pyrolysis experiments, it was verified that the relative content of o-semiquinone radical and the solid coke were reduced with a hydrogen supply source. Our results showed that by controlling the key free radicals in the coking process, the formation of coke can be suppressed and the conversion efficiency can be improved.