Thermal Degradation Of Lignin Research Articles

Degradation of the lignin in roasted sesame seed hull improves the oxidation stability of sesame oil

Sesame seed hulls are rich in lignin. Sesame oil extracted from roasted sesame seeds has a high oxidation stability. To investigate the influence of roasting on lignin and the oxidation stability of sesame oil, the degradation products (L190, L220, and L250) and solid residues were obtained from sesame seed hull lignin heated at three temperatures (190 °C, 220 °C, and 250 °C). The results showed that roasting caused partial degradation of lignin. The degree of lignin degradation became more severe with increasing roasting temperature. This degradation leads to the production of low-molecular-weight phenolic compounds, such as vanillin and 1-(4-hydroxy-3-methoxyphenyl)butan-1-one. As the roasting temperature increased, the kinds and amounts of phenolic compounds produced increased. These compounds were high in antioxidants, the increasing of roasting temperature correlated significantly with the decrease in peroxide value (rPOV = −0.977, p < 0.05) and p-anisidine value (rp-AnV = −0.988, p < 0.05) of sesame oils with added products of lignin degradation. The products of lignin degradation inhibited sesame oil oxidation, with L250 showing the strongest ability to improve the oxidative stability of sesame oil, similar to sesamol. This study demonstrated that the thermal degradation of lignin during roasting of sesame seed hulls enhanced the oxidative stability of sesame oil.

Particulate organic emissions from incense-burning smoke: Chemical compositions and emission characteristics

Incense burning is a common practice in Asian cultures, releasing hazardous particulate organics. Inhaling incense smoke can result in adverse health effects, yet the molecular compositions of incense-burning organics have not been well investigated due to the lack of measurement of intermediate-volatility and semi-volatile organic compounds (I/SVOCs). To elucidate the detailed emission profile of incense-burning particles, we conducted a non-target measurement of organics emitted from incense combustion. Quartz filters were utilized to trap particles, and organics were analyzed by a comprehensive two-dimensional gas chromatography-mass spectrometer (GC × GC–MS) coupled with a thermal desorption system (TDS). To deal with the complex data obtained by GC × GC–MS, homologs are identified mainly by the combination of selected ion chromatograms (SICs) and retention indexes. SICs of 58, 60, 74, 91, and 97 were utilized to identify 2-ketones, acids, fatty acid methyl esters, fatty acid phenylmethyl esters, and alcohols, respectively. Phenolic compounds contribute the most to emission factors (EFs) among all chemical classes, taking up 24.5 % ± 6.5 % of the total EF (96.1 ± 43.1 μg g−1). These compounds are largely derived from the thermal degradation of lignin. Biomarkers like sugars (mainly levoglucosan), hopanes, and sterols are extensively detected in incense combustion fumes. Incense materials play a more important role in shaping emission profiles than incense forms. Our study provides a detailed emission profile of particulate organics emitted from incense burning across the full-volatility range, which can be used in the health risk assessments. The data processing procedure in this work could also benefit those with less experience in non-target analysis, especially GC × GC–MS data processing.

Efficient non-catalytic depolymerization of lignin in hydrogen donor solvent for monomeric phenols and its pathways

Thermal degradation of lignin in hydrogen donor solvent (HDS) has been reported to be an efficient method to generate aromatics and phenols. High pressure H2 and catalyst are not required which simplifies this degradation method. This work aims to advance the knowledge of reaction pathway with depolymerization of enzymatic hydrolysis lignin (EHL) in 9,10-dihydroanthracene (DHA) as an example. For this purpose, the liquid products were characterized in detail by GC, GPC, 31P NMR and 2D-HSQC NMR. Results indicate that the yield of monomeric phenols is up to 20.2 wt% at 375–400 °C. This yield is comparable to literature results with high-pressure H2 and catalysts at 220–320 °C. The depolymerization starts with the cleavage of ether linkages and decarboxylation of acrylate linkages, which are followed by the removal of aliphatic-OH, hydrogenation of Cal = Cal, decarbonylation of Cal = O, dealkylation of alkyl substituents and demethylation of aromatic-methoxy groups. The amount of phenolic-OH is about 2.78 mmol/g in the liquid product obtained at 400 °C: 36% from the cleavage of β-O-4 and α-O-4 linkages and about 16% from the demethylation of aromatic-methoxy group. The number-average molecular weight is roughly inversely proportional to the amount of bond cleavage.

Identification of Optimal Binders for Torrefied Biomass Pellets

The pretreatment of biomass through torrefaction is an effective means of improving the fuel quality of woody biomass and its suitability for use in existing facilities burning thermal coal. Densification of torrefied biomass produces a fuel of similar energy density, moisture content, and fixed carbon content to low-grade coals. Additionally, if the torrefaction conditions are optimized, the produced torrefied pellet will be resistant to weathering and biological degradation, allowing for outdoor storage and transport in a manner similar to coal. In untreated biomass, lignin is the primary binding agent for biomass pellets and is activated by the heat and pressures of the pellet extrusion process. The thermal degradation of lignin during torrefaction reduces its binding ability, resulting in pellets of low durability not suitable for transportation. The use of a binding agent can increase the durability of torrefied pellets/briquettes through a number of different binding mechanisms depending on the binder used. This study gives a review of granular binding mechanisms, as they apply to torrefied biomass and assesses a variety of organic and inorganic binding agents, ranking them on their applicability to torrefied pellets based on a number of criteria, including durability, hydrophobicity, and cost. The best binders were found to be solid lignin by-product derived from pulp and paper processing, biomass tar derived from biomass pyrolysis, tall oil pitch, and lime.

Degradation of Alkaline Lignin in the Lactic Acid-Choline Chloride System under Mild Conditions

Lignin is a natural polymer, second only to cellulose in natural reserves. Degradation is one of the ways to achieve the high-value transformation of lignin. Deep eutectic solvent (DES) thermal degradation of lignin can be used as an excellent green degradation method. This paper introduces the degradation mechanism and effect of the lactic acid-choline chloride DES system in dissolving and degrading alkaline lignin, and the final solvent recovery. It can also be found from the scanning electron microscope (SEM) images that the surface of the degraded solid product is transformed from smooth to disordered. Fourier transform infrared (FTIR) spectroscopy and 1 H-NMR spectroscopy were used to characterize the changes in lignin functional groups during DES treatment. The results showed that the content of phenolic hydroxyl groups increased after degradation, indicating that the β-O-4 ether bond was broken. The molecular weight of the degraded lignin was observed by gel permeation chromatography (GPC), and the lignin residue with low molecular weight and narrow polydispersity index was obtained. The lowest average molecular weight (Mw) reached 2512 g/mol. The ratio of oxygen to carbon atoms in lignin increased substantially during degradation as measured by X-ray photoelectron spectroscopy (XPS), probably because DES treatment was accompanied by many oxidation reactions, which led to significant structural changes in lignin and a large number of ether bond breakage reactions during the reaction. The main final degradation products are aromatic monomers, vanillin, butyrovanillone, etc.

Termite Resistance, Chemical and Mechanical Characterization of Paulownia tomentosa Wood before and after Heat Treatment

The introduction of new species in forest management must be undertaken with a degree of care, to help prevent the spread of invasive species. However, new species with higher profitability are needed to increase forest products value and the resilience of rural populations. Paulownia tomentosa has an extremely fast growth. The objective and novelty of this work was to study the potential use of young Paulownia trees grown in Portugal by using heat treatment to improve its properties, thereby allowing higher value applications of the wood. The average chemical composition of untreated and heat-treated wood was determined. The extractive content was determined by successive Soxhlet extraction with dichloromethane (DCM), ethanol and water as solvents. The composition of lipophilic extracts was performed by injection in GC-MS with mass detection. Insoluble and soluble lignin, holocellulose and α-cellulose were also determined. Physical (density and water absorption and dimensional stability) and mechanical properties (bending strength and bending stiffness) and termite resistance was also determined. Results showed that extractive content increased in all solvents, lignin and α-cellulose also increased and hemicelluloses decreased. Compounds derived from the thermal degradation of lignin were found in heat-treated wood extractions. Dimensional stability improved but there was a decrease in mechanical properties. Resistance against termites was better for untreated wood than for heat-treated wood, possibly due to the thermal degradation of some toxic extractives.

The Complexity of Lignin Thermal Degradation in the Isothermal Context

Thermal degradation of lignin in nitrogen atmosphere is evaluated by linear heating and isothermal tests. While linear heating suggests that thermal decomposition in the 200–400 °C range mainly consists of a single step, a careful analysis of isothermal tests points to different lignin fractions having different stabilities. This is an important point for practical predictions, since kinetics obtained as if the degradations at different temperatures were the same would lack practical utility. Instead, stairway type tests are proposed to evaluate the degradation rates and sample quantities involved at the temperatures of interest.

Torrefaction of oil palm empty fruit bunch pellets: product yield, distribution and fuel characterisation for enhanced energy recovery

In this study, the non-oxidative torrefaction of oil palm empty fruit bunch (OPEFB) pellets was investigated from 250 to 300 °C for 30 min in a horizontal fixed bed tubular reactor. The effects of the selected conditions on the yields, distributions and fuel characteristics of the torrefaction products were examined. The mass or solid yield (MY) decreased from 68.1 to 36.2%, whereas the liquid yield (LY) and gas yield (GY) increased from 19.4–40.1% and 12.5–23.7%, respectively, due to drying, devolatilization and depolymerisation during torrefaction. Physicochemical and calorific analyses showed that the torrefied OPEFB pellets have high carbon but low oxygen contents, which accounts for the high heating values (HHV = 22.83–25.81 MJ/kg). The torrefied OPEFB pellets also exhibit lower moisture (2–4%) and volatile matter (34.38–65.31 wt.%) but high ash (4–20 wt.%) and fixed carbon (28.69–41.62 wt.%) compared to the raw pellets. The OPEFB pellet fuel properties, namely pH that ranged from 6.65 to 7.74, hydrophobicity from 100 to 23.04% and grindability from 53.66 to 108, were markedly enhanced after torrefaction at 300 °C. The LY consisted of organics (67.64–62.62%) and water (32.36–37.38%) fractions characterised by high acidity (pH = 2.89–3.22) and dark hues formed by holocellulose and lignin thermal degradation at higher torrefaction temperatures. Based on the findings, the torrefied OPEFB pellets is a highly grindable, hydrophobic, thermally stable and promising solid biofuel for firing, co-firing or substituting coal in power plants provided the existing challenges that affect global biomass supply chains are addressed in detail.

Cellulose nanofiber thin-films as transparent and durable flexible substrates for electronic devices

This work reports for the first time an exceptionally high thermal stability of cellulosic nanofibers films at 190 °C after a 5 h exposure, a threshold required for their design and manufacturing in flexible electronic devices. A long-term durability validation of a flexible cellulose nanofiber over a period of 10 years exposure under ambient condition validated their life-span over a long period of operating condition. Arresting quinoid oxidative reactions pathways and thermal degradation of lignin or lignin-less cellulose are demonstrated to be two fundamental routes to enhance thermal processing of cellulose nanofiber substrates and to achieve long service life of energy devices made from them. One of the main highlights of this work is the first time validation of a long operating service life for a light-emitting device made from a cellulose nanofibers substrate, while continuously illuminating the fabricated prototype under ambient condition for an equivalent of 10 years. The unique durability of this flexible substrate will have potential applications in flexible lighting, energy and sensing devices.

Thermal characterization and pyrolysis of digestate for phenol production

Digestate, the residue following of anaerobic digestion, had attracted great attention recently as potential feedstock of pyrolysis. The results of component analysis verified that digestate was suitable for phenol production due to its considerable lignin content. The thermal degradation of lignin in digestate mainly occurred around 350–450 °C in thermogravimetric analysis. The amorphous cellulose in digestate decomposed to short-chain acids, water and syngas rather than furfural at low temperature around 280 °C. Pyrolysis of digestate for phenol production was conducted under different reaction temperature and pressure. High reaction temperature contributed to phenol formation by facilitating the cleavage reactions of β-O-4 and C–C linkages among three phenylpropane units in lignin. Pyrolysis pressure promoted secondary monomolecular dissociation reactions of methoxyphenol to yield phenol and alkyl-phenol. The maximum phenolics (70.4%) and phenol (42.6%) contents were achieved at 450 °C with 5 MPa pressure in this work.

Fractionation and physicochemical characterization of lignin from waste jute bags: Effect of process parameters on yield and thermal degradation

In this work lignin was extracted from waste jute bags using soda cooking method and effect of varying alkali concentration and pH on yield, purity, structure and thermal degradation of lignin were studied. The Lignin yield, chemical composition and purity were assessed using TAPPI method and UV–vis spectroscopy. Yield and purity of lignin ranged from 27 to 58% and 50–94%, respectively for all the samples and was maximum for 8% alkali concentration and at pH 2 giving higher thermal stability. Chemical structure, thermal stability and elementary analysis of lignin were studied using FTIR, HNMR, thermo gravimetric analysis (TGA) and Elemental analyzer. FTIR and HNMR results showed that core structure of lignin starts breaking beyond 10% alkali concentration. S/G ratio shows the dominance of Syringyl unit over guaiacyl unit.

Thermophysical properties of model compounds of the lignin structural unit

Sixteen lignin related aromatic compounds formed by the thermal degradation of lignin and being potentially valuable products of the processing of renewable raw materials were studied using differential scanning calorimetry. The temperatures, enthalpies, and entropies of melting were determined. The temperature dependences of isobaric heat capacities for the studied compounds were obtained. The relationship between the structures of the lignin related compounds and their thermochemical properties is considered.

Catalytic Deoxygenation of Guaiacol Using Methane

Guaiacol, produced by thermal degradation of lignin, represents a model compound for upgrading of fast pyrolysis bio-oils by deoxygenation. In our prior work, with Pt/C catalyst, such a process using H2 was studied. To overcome the high cost of H2, methane is used in this work to deoxygenate guaiacol. On Pt/C catalyst, in terms of guaiacol conversion and product distribution, methane is found to exhibit as good deoxygenation performance as H2. The lifetime of this catalyst, however, is short (<3 h). The lifetime of Pt–Bi/C catalyst is extended (no significant deactivation in 5 h), by addition of bismuth as a promoter. This work provides a new approach for bio-oil upgrading using methane as a reductant instead of hydrogen.

Natural weathering performance of three fast-growing Eucalypt woods

We investigated the effect of outdoor exposure on the wood surface from three fast-growing Brazilian eucalypts through color, wetting and thermal analyzes. Gympie messmate (Eucalyptus cloeziana), rose gum (Eucalyptus grandis) and blue gum (Eucalyptus saligna) woods were exposed outdoors in a subtropical region for 360 days. We performed three collections every 120 days. We investigated color changes of untreated and weathered woods through a spectrophotometer (CIEL*a*b* system) and changes in macro compounds of wood through thermogravimetric analysis. In addition, the apparent contact angle and work of adhesion were evaluated using a goniometer. Outdoor exposure for 120 days provided significant increment in grayish of wood surface. Thermogravimetric curves of wood changed after the weathering, especially in the regions related to hemicelluloses and lignin thermal degradation. Outdoor exposure for 360 days converted hydrophilic wood surface into a very hydrophilic one, wherein occurrence of microcracks contributed to fully spreading of water droplets.

Conversion of Guaiacol on Noble Metal Catalysts: Reaction Performance and Deactivation Studies

Guaiacol, a phenol derived compound produced by the thermal degradation of lignin, was selected as a model compound to study the catalytic hydrodeoxygenation (HDO) process for upgrading pyrolysis bio-oils. Guaiacol is among the major components of bio-oils; however, it is thermally unstable which leads to catalyst deactivation. In the present study, four noble metal catalysts (Pt, Pd, Rh, and Ru) supported on activated carbon were tested in a fixed-bed reactor at atmospheric pressure and their performance for the guaiacol HDO process was measured. Our results showed that, among the tested catalysts, Pt has higher deoxygenation activity and shows little deactivation for 5 h. Additionally, the operating temperature for the Pt catalyst was optimized and found to be 300 °C. Finally, results from catalyst characterization demonstrated that polyaromatic deposits, especially the condensed ring compounds, are the most likely cause for catalyst deactivation.

Effect of water vapor in air on thermal degradation of paper at high temperature

Abstract Thermal degradation of lignocellulosic materials has been studied widely because of its importance in several applications. While a variety of thermal treatment setups has been proposed, this paper introduces a thermal treatment method where high temperature is combined with presence of water vapor in an atmospheric oven chamber. The performance of the device was evaluated at temperature and volume fraction of water vapor ranges of 175–300 °C and 1–98%, respectively. The impact of the treatment was assessed by observing the changes in paper sheets, specifically brightness, light absorption coefficient, burst strength, ultraviolet resonance Raman spectra and the degree of polymerization of cellulose. The results demonstrated that the adapted thermal treatment device functions within the tested ranges of temperature and volume fraction of water vapor. In this study water vapor was found to accelerate hydrolytic thermal degradation of fully bleached paper sheets in terms of thermal yellowing and strength deterioration. In contrast, the empirical findings with lignin-containing paper provided new information on how the residual lignin increases its resistance towards water vapor introduced thermal degradation. This was demonstrated by the results of ultraviolet resonance Raman spectra and light absorption coefficient, which suggested that the thermal degradation of lignin is substantially enhanced in the presence of oxygen.

Molecular Products and Radicals from Pyrolysis of Lignin

Thermal degradation of lignin under two reaction regimes (pyrolysis in N(2) and oxidative pyrolysis in 4% O(2) in N(2)) has been investigated in a tubular, isothermal, flow-reactor over the temperature range 200-900 °C at a residence time of 0.2 s. Two experimental protocols were adopted: (1) Partial pyrolysis in which the same lignin sample was continuously pyrolyzed at each temperature and (2) conventional pyrolysis, in which new lignin samples were pyrolyzed at each pyrolysis temperature. The results identified common relationships between the two modes of experiments, as well as some differences. The majority of products from partial pyrolysis peaked between 300 and 500 °C, whereas for conventional pyrolysis reaction products peaked between 400 and 500 °C. The principal products were syringol (2,6-dimethoxy phenol), guaiacol (2-methoxy phenol), phenol, and catechol. Of the classes of compounds analyzed, the phenolic compounds were the most abundant, contributing over 40% of the total compounds detected. Benzene, styrene, and p-xylene were formed in significant amounts throughout the entire temperature range. Interestingly, six ringed polycyclic aromatic hydrocarbons were formed during partial pyrolysis. Oxidative pyrolysis did not result in large differences from pyrolysis; the main products still were syringol, guaiacol, phenol, the only significant difference being the product distribution peaked between 200 and 400 °C. For the first time, low temperature matrix isolation electron paramagnetic resonance was successfully interfaced with the pyrolysis reactor to elucidate the structures of the labile reaction intermediates. The EPR results suggested the presence of methoxyl, phenoxy, and substituted phenoxy radicals as precursors for formation of major products; syringol, guaiacol, phenols, and substituted phenols.

Particulate organic compounds emitted from experimental wildland fires in a Mediterranean ecosystem

Fine (PM 2.5) and coarse (PM 2.5–10) smoke particles from controlled biomass burnings of a shrub-dominated forest in Lousã Mountain, Portugal, enabled the quantification by chromatographic techniques of several molecular tracers for the combustion of Mediterranean forest ecosystems, which could be conducive to source apportionment studies. The major organic components in the smoke samples were pyrolysates of vegetation cuticles, mainly comprising steradienes and sterol derivatives, carbohydrates from the breakdown of cellulose, aliphatic lipids from vegetation waxes and methoxyphenols from the lignin thermal degradation. Most of these compounds are chiefly found in fine particles. Polycyclic aromatic hydrocarbons (PAH) were also present as minor constituents. Anhydrosugar and PAH molecular diagnostic ratios were applied as source assignment tools. Some biomarkers are reported for the first time in biomass burning smoke.

Mechanisms of Thermochemical Biomass Conversion Processes. Part 1: Reactions of Pyrolysis

The present work is a study on the pyrolysis mechanisms of biomass structural constituents. Biomass resources include wood and wood wastes, agricultural crops and their waste byproducts, municipal solid waste, animal wastes, waste from food processing, and aquatic plants and algae. The major organic components of biomass can be classified as cellulose, hemicelluloses, and lignin. The pyrolysis is thermal degradation of biomass by heat in the absence of oxygen, which results in the production of charcoal (solid), bio-oil (liquid), and fuel gas products. Thermal degradation of cellulose proceeds through two types of reaction: a gradual degradation, decomposition, and charring on heating at lower temperatures; and a rapid volatilization accompanied by the formation of levoglucosan on pyrolysis at higher temperatures. The hemicelluloses reacted more readily than cellulose during heating. Of the hemicelluloses, xylan is the least thermally stable, because pentosans are most susceptible to hydrolysis and dehydration reactions. Dehydration reactions around 473 K are primarily responsible for thermal degradation of lignin. Between 423 K and 573 K, cleavage of α- and β-aryl-alkyl-ether linkages occurs. Around 573 K, aliphatic side chains start splitting off from the aromatic ring.

Volatile composition and sensory characteristics of Chardonnay wines treated with American and Hungarian oak chips

Toasted or non-toasted chips of oak woods of different geographical provenances were macerated in Chardonnay wines (4 g/l) during a period of 25 days. Oak lactones were detected in significant quantities in wines treated with American oak. Only trace amounts of oak lactones were detected in the wines treated with Hungarian oak. Toasting of the oaks increased the quantities of the compounds derived from the thermal degradation of lignin: vanillin, eugenol, guaiacol and its derivatives and the pyrolysis of cellulose and hemicellulose: furfural and 5-methyl furfural, and decreased the concentrations of the two isomers of oak lactones. The concentrations of the majority of the volatile compounds did not present statistically significant differences between 15 and 25 days. However, the wines preferred by the tasters and with maximum intensity of the sensory attributes acquired were those treated with oak chips for 25 days. Chemical and sensorial analyses of wines revealed that the effect of the toasting of oak chips on wine characteristics was greater than the type of oak used. All wines studied were positively evaluated by the panellists.