The structural characteristics of softwood (Chinese fir) lignin and hardwood (Maple) lignin prepared by Klason method were identified by elemental analysis and Fourier transform infrared (FTIR) ...spectrometry, and the pyrolytic behaviors of lignin were examined by means of thermogravimetric-Fourier transform infrared spectrometry (TG-FTIR) and Pyrolylisis-gas chromatography/mass spectrometry (Py-GC/MS). It was found that maple (hardwood) lignin contained more methoxyl groups than Chinese fir (softwood) lignin due to the enrichment of syringol units, presenting the chemical formula as C4.64H4.017O2.482 against C4.939H5.255O2.219 for Chinese fir lignin. The amounts of phenolics, methanol and CH4 evolved from pyrolysis of maple lignin were all remarkably larger than that of Chinese fir lignin through TG-FTIR analysis. For both two lignins, aromatic compounds (such as benzene, toluene and xylene) were predominantly released between 650 °C and 800 °C, due to the intensive cleavage of aryl-O-R linkages and dehydroxylation reaction on benzene-ring. The distribution of produced volatiles during lignin fast pyrolysis against furnace temperature was intensively discussed, finding that the cleavage of typical inter-unit linkages under relatively low temperature produced the guaiacol-type and syringol-type compounds, whereas the elevated temperature facilitated the cracking of methoxyl group, giving rise to the notable increase of phenol-type, catechol-type compounds and aromatic hydrocarbons.
•2-methoxyphenol transformed to catechol by removal of the carbonyl group.•l-(2-hydroxy-5-methylphenyl) ethanone transformed to p-cresol by removal of methyl.•The broken alcoholic or phenolic CO bond ...was the major reaction in lignin degrading.•The methyl in methoxyl groups could be easily removed from methoxyl to form CH4.
To investigate the pyrolysis behavior of guaiacol lignin (G-lignin) at 400–750 °C and its major decomposition mechanisms, ginkgo MWL as a typical G-lignin was decomposed in a micro-pyrolyzer, coupling two-dimensional gas chromatography with time-of-flight mass spectrometric detection (Py-GC × GC/TOF-MS) and an in-situ infrared pyrolysis reactor (in-situ FTIR). The pyrolysis products showed that a large amounts of guaiacol phenols were produced at low temperature, which indicated that guaiacol phenols were an important intermediate product, and other lignin-derived aromatic chemicals formed from guaiacol phenols by de-methyl, de-methoxyl reactions, and broken off branch structures. Relatively high contents of 2-methoxyphenol and l-(2-hydroxy-5-methylphenyl) ethanone were obtained at 450 °C, up to 19.46% and 16.35%, respectively. However, when temperature increased, 2-methoxyphenol and l-(2-hydroxy-5-methylphenyl) ethanone should be transformed to catechol and p-cresol by the removal of the carbonyl group from the branch and methyl from the methoxyl group, respectively. The methyl breakage of 4-ethyl-2-methoxyphenol and de-methoxyl of mequinol caused the formation of creosol and phenol, respectively, when temperatures increased. Two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) was introduced to analyze the in-situ FTIR spectra, and it was found that the cleavage of alcoholic or phenolic C-O bond was the major reaction in G-lignin decomposition, and the methyl in methoxyl groups could be easily removed from methoxyl to form CH4. Based on 2D-PCIS, reaction pathways involving the change sequence of several functional groups from G-lignin were proposed. Three reaction paths were provided from a model lignin with β-O-4, α-O-4 and 5-5′ connection to 1-(2-hydroxy-5-methylphenyl) ethanone, 2-methoxyphenol, catechol, trans-isoeugenol, p-cresol, phenol and benzene.
► Fast (Py-GC/MS) and slow pyrolysis (TGA/FTIR) of three lignins. ► Lignin pyrolysis yields ten compounds or so that amount to about 50% of volatiles. ► PCG releases most light volatiles/least amount ...of char than aspen and Kraft lignins. ► Aspen lignin produces more pyrolytic products than PCG and Kraft lignins.
A study is undertaken to assess the effectiveness of lignin extracted from prairie cordgrass as a pyrolysis feedstock. The effects of variability of lignin source on fast and slow pyrolysis products are also investigated. To accomplish these goals, Py-GC/MS and TGA/FTIR are employed in the pyrolysis of three types of lignin: prairie cordgrass (PCG) lignin extracted from prairie cordgrass, aspen lignin extracted from aspen trees (hardwood), and synthetic Kraft lignin. Fast pyrolysis results from Py-GC/MS show that for PCG lignin, only ten of the detected compounds have relative peak area percentiles that exceed 2% and make up over 52% of the total area. For aspen lignin, excluding butanol that is used in the extraction process, only eight compounds are found to have relative peak areas exceeding 2% that make up over 52% of the total area. For Kraft lignin, only eight compounds exceeding 2% are found to make up more than 45% of the total area. Both techniques, Py-GC/MS and TGA/FTIR, indicate that PCG lignin releases more alkyls than aspen and Kraft lignin. TGA/FTIR results indicate that PCG lignin also releases by far the most light volatile products (<200°C) while producing the least amount of char among the three types of lignin studied. These characteristics make PCG lignin a good choice in producing good quality bio-oil and thus decreasing upgrade requirements. Py-GC/MS results conclude that aspen lignin produces significantly more pyrolytic products than PCG lignin. This is indicative of the potential of aspen lignin to result in higher conversion rates of bio-oil than the other two lignins.
Lignin from four different sources, extracted by various methods, were pyrolyzed at 650
°C using analytical pyrolysis methods (Py-GC/MS). Pyrolysis was carried out in the absence and presence of two ...heterogeneous catalysts, an acidic zeolite (HZSM-5) catalyst and a mixed metal oxide catalyst (CoO/MoO
3). Non-catalytic Py-GC/MS was used to identify the lignin as characterized by their H-, G- or S-lignin makeup and also served as the control basis to evaluate the effect of the said catalysts on the production of aromatic hydrocarbons from these lignin sources. Experiments show that the selectivity to particular aromatic hydrocarbons varies with the composition of the lignin for both catalysts. The major pathway for hydrocarbon production over HZSM-5 is likely increased depolymerization efficiency that releases and converts the aliphatic linkers of lignin to olefins followed by aromatization. Simple phenols produced from the deconstruction of the lignin polymer are likely to be a source of zeolite deactivation. The CoO/MoO
3 is likely to produce aromatic hydrocarbons through a direct deoxygenation of methoxyphenol units.
Summary
It is of both theoretical and practical importance to develop a universally applicable approach for the fractionation and sensitive lignin characterization of lignin–carbohydrate complexes ...(LCCs) from all types of lignocellulosic biomass, both natively and after various types of processing. In the present study, a previously reported fractionation approach that is applicable for eucalyptus (hardwood) and flax (non‐wood) was further improved by introducing an additional step of barium hydroxide precipitation to isolate the mannan‐enriched LCC (glucomannan‐lignin, GML), in order to suit softwood species as well. Spruce wood was used as the softwood sample. As indicated by the recovery yield and composition analysis, all of the lignin was recovered in three LCC fractions: a glucan‐enriched fraction (glucan‐lignin, GL), a mannan‐enriched fraction (GML) and a xylan‐enriched fraction (xylan‐lignin, XL). All of the LCCs had high molecular masses and were insoluble or barely soluble in a dioxane/water solution. Carbohydrate and lignin signals were observed in 1H NMR, 13C CP‐MAS NMR and normal‐ or high‐sensitivity 2D HSQC NMR analyses. The carbohydrate and lignin constituents in each LCC fraction are therefore believed to be chemically bonded rather than physically mixed with one another. The three LCC fractions were found to be distinctly different from each other in terms of their lignin structures, as revealed by highly sensitive analyses by thioacidolysis‐GC, thioacidolysis‐SEC and pyrolysis‐GC.
•Use PY-GC/MS to pyrolyze aspen lignin in the presence of zeolite catalysts.•Quantified 24 aromatic hydrocarbons and 37 phenolic compounds.•HZSM-5 most effective in converting phenolic compounds to ...aromatic hydrocarbons.•4wt% oxygen content, HHV of 46MJ/kg of detected aromatic/phenolic products.•Toluene 6.6wt% and p-xylene 6.3wt% most abundant hydrocarbons formed with HZSM-5.
Aspen lignin extracted by an organosolv process was pyrolyzed in the presence of catalysts and analyzed using Py-GC/MS. The pyrolysis products detected are mostly aromatic hydrocarbons and phenolic compounds. The lignin and catalysts were either mixed or arranged in layers. Two different micro-porous zeolite catalysts, HZSM-5 and HY, were compared in the study. The effects of the catalysts on the production of aromatic hydrocarbons and phenolic compounds were assessed quantitatively. The HZSM-5 catalyst was found to produce from 2.5 to 40 times more aromatic hydrocarbons than the HY catalyst, by converting phenolic compounds into aromatic hydrocarbons. For the HZSM-5 catalyst, the effects of placement of catalyst were not as pronounced as were for HY. The data suggest that for any catalyst type and placement there exists an optimum catalyst-to-lignin ratio that maximizes the total production of aromatic hydrocarbons and phenolic compounds. For HZSM-5 in the mixture arrangement, a catalyst-to-lignin ratio of 3:1 was found to maximize both the aromatic hydrocarbons and the aggregate sum of aromatic hydrocarbons and phenolic compounds. At this ratio, 23% yield of aromatic hydrocarbons and 28% yield of the aggregate sum were obtained. Also at these conditions, the products detected are estimated to have a total oxygen content of about 4% and higher heating value of 46MJ/kg, roughly the same as gasoline and diesel. Toluene and p-xylene were the two most abundant hydrocarbons formed in the presence of catalysts. Up to 6.6% and 6.3% of the original lignin were converted into toluene and p-xylene, respectively. We estimate that if all the lignin produced in pulp and paper mills was catalytically pyrolyzed, the amount of toluene produced would be more than 30% of the current annual production of toluene from fossil sources worldwide.
•Analytical TGA–FTIR and Py–GC/MS were conducted on pyrolysis process of alkali lignin.•Drying, fast degradation and slow degradation were the main three stages of alkali lignin pyrolysis.•The ...aromatics and phenols were the dominant components according to the FTIR spectrum.•The activation energy was raised from 124 to 721kJ/mol as the conversion rate increasing.•The guaiacol type (G-), phenol type (P-), syringol type (S-), and catechol type (C-) phenolic compounds were the main products from Py–GC/MS experiment.
Alkali lignin, an aromatic polymer extracted from soda pulping black liquor, is considered to be a potential source of phenolic-rich bio-oil using pyrolysis technology. This paper investigated the pyrolysis behaviors and kinetics of alkali lignin using thermogravimetric analyzer coupled with Fourier transform infrared spectrometry (TGA–FTIR) and pyrolyzer coupled with gas chromatography/mass spectrometer (Py–GC/MS). Results showed that the pyrolysis process of alkali lignin consisted of the three stages: drying stage, fast degradation stage and slow degradation stage. The weight loss rate reached its maximum value of 0.2448 mass%/°C at the temperature of 327°C. The aromatics (at 1512cm−1) and phenols (at 1261cm−1) were the dominant volatile components according the FTIR spectrum. As the conversion rate increased from 0.05 to 0.9, the activation energy estimated from Flynn-Wall-Ozawa (FWO) method, was raised from 124 to 721kJmol−1. The phenolic compounds, namely guaiacol type (G-), the phenol type (P-), the syringol type (S-), and the catechol type (C-) were the main products from Py–GC/MS experiment. The total phenols and the G-type phenols reached their maximum contents of 78% and 63.43% at 500°C, respectively. The content of S-type phenols decreased from 17.63% to 10.2% as the temperature increasing from 400°C to 700°C, while the contents of P-type and C-type phenols increased from 0.81% to 8.16% and 0.12% to 3.11%, respectively.
Lignin stands the most abundantly available source of renewable aromatic compounds which is generated as a useless waste by-product in numerous industrial processes, e.g., in pulp and paper ...manufacturing as well as during second-generation ethanol production. The present work aims to investigate the effect of reaction conditions (particularly the reaction atmosphere type) on the composition of the volatiles that evolved during the pyrolysis of lignin. The pyrolytic studies were carried out using coupled microscale techniques, i.e., Py-GC-MS, and Py-FT-IR. The pyrolysis is usually carried out under an inert atmosphere. Herein, there was additionally studied comprehensively the effect of oxidizing (CO2 and air) and reducing atmosphere (H2). There was found a profound impact of the processing temperature on the composition changes of volatiles. A minor effect was noted for the pyrolysis atmosphere on the qualitative composition of the volatiles, but certain quantitative differences between their concentration were observed. Their composition confirmed the complex molecular structure of lignin. Among the identified compounds, there were found phenol derivatives as primary products of cleavage of lignin structures as well as aliphatic oxygen compounds and aromatic hydrocarbons as the products of the secondary decomposition and deoxygenation thereof.
•Pyrolysis of wheat straw lignin via Py-FTIR and Py-GC-MS within 300–800 °C was done.•The effect of inert, CO2, H2 and air reaction atmospheres in pyrolysis was studied.•A minor effect of pyrolysis atmosphere on the volatiles qualitative composition.•Impact of pyrolysis reaction atmosphere on quantitative composition of volatiles.•Py-FT-IR and Py-GC-MS as complementary techniques for fast pyrolysis investigation.
The structure of the lignin from brewer’s spent grain (BSG) has been studied in detail. Three different lignin preparations, the so-called “milled-wood” lignin (MWL), dioxane lignin (DL), and ...cellulolytic lignin (CEL), were isolated from BSG and then thoroughly characterized by pyrolysis GC/MS, 2D-NMR, and derivatization followed by reductive cleavage (DFRC). The data indicated that BSG lignin presents a predominance of guaiacyl units (syringyl/guaiacyl ratio of 0.4–0.5) with significant amounts of associated p-coumarates and ferulates. The flavone tricin was also present in the lignin from BSG, as also occurred in other grasses. 2D-NMR (HSQC) revealed that the main substructures present are β-O-4′ alkyl-aryl ethers (77–79%) followed by β-5′ phenylcoumarans (11–13%) and lower amounts of β-β′ resinols (5–6%) and 5-5′ dibenzodioxocins (3–5%). The results from 2D-NMR (HMBC) and DFRC indicated that p-coumarates are acylating the γ-carbon of lignin side chains and are mostly involved in condensed structures. DFRC analyses also indicated a minor degree of γ-acylation with acetate groups, which takes place preferentially on S lignin (6% of S units are acetylated) over G lignin (only 1% of G units are acetylated).
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