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10 páginas.-- 5 figuras.-- 3 tablas.-- 39 referencias.-- Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jaap.2018.05.012, Straw and pig slurry Solid-State Anaerobic Digestion (SS-AD) was carried out in a pilot-scale apparatus using percolate recirculation technology. The digestion experiments were performed using 1, 2 and 4 recirculations per day; an additional experiment without percolate recirculation was used as control. The initial mixture and the digestates were analysed by means of chemical analyses and Pyrolysis–Gas Chromatography/Mass Spectrometry (Py–GC/MS), a direct analytical technique that allows investigating the changes in the organic matter (OM) composition of digestates and the effect of percolate recirculation frequency. Chemical analyses suggested a positive effect of percolate recirculation on OM degradation. The highest values of OM loss were found with 2 (26%) and 4 (31%) recirculation cycles per day, that also corresponded with the lowest values of the hydrophilic water extractable organic matter fraction (5.5 and 6.3% respectively). Py-GC/MS showed that the anaerobic digestion proceeded with progressive polysaccharide degradation (from c. 19% in the initial mixture to 10–8% with 2–4 recirculation cycles) and selective enrichment of lignin derived compounds (from c. 58% in the initial mixture to 67–69% with 2–4 recirculation cycles). In addition, a shift in the fatty acids distribution was observed with a decrease in the long/short chain ratio of fatty acid methyl esters. These results indicate that under our experimental conditions, percolate recirculation had a positive effect on the OM degradation. Also OM stabilization is observed with relative increases in recalcitrant lignin at the expense of the more liable polysaccharide fraction. This paper represents the first attempt to apply Py-GC/MS to evaluate the OM quality in digestates obtained by SS-AD of pig slurry and straw optimized by percolate recirculation., The Spanish Ministry of Economy, Industry and Competitiveness (MINEICO) the Agencia estatal de Investigacíon and FEDER programme are thanked for funding the projects CGL2016-76498-R and CGL2016-78937-R (AEI/FEDER, UE). J.M. De la Rosa thanks MINEICO for funding his “Ramon y Cajal” contract (RYC2014-16338). Alba Carmona Navarro and Desire Monis Carrere are recognized for their technical assistance with analytical pyrolysis

Important parameters that influence biochar properties include charring temperature and biomass type. We characterized the molecular properties of biochars from five agricultural residues with pyrolysis gas chromatography mass/spectrometry (pyrolysis-GC/MS) in comparison with atomic H/C and N/C ratios. Feedstocks included chicken manure, eucalyptus sawdust, coffee husk, sugarcane bagasse and pine bark. Biochars produced at three different temperatures (Tchar) were analyzed, including 350, 450 and 750 °C, as well as the uncharred materials. The optimum temperature during analysis with pyrolysis-GC/MS (Tpy) was examined. Tpy 600 °C gave the best results for all Tchar by showing a larger diversity of pyrolysis products compared to Tpy 700 °C and 800 °C; Tpy 600 °C was therefore used for qualitative and quantitative comparison of the samples. Charring temperature was the dominant factor that determined the chemical composition of the biochar pyrolysates. Uncharred feedstocks had the largest contribution from carbohydrates, lignin phenols and long chain n-alkanes, all of which rapidly decreased with charring; biochars produced at Tchar 350 and 450 °C showed the largest contribution from phenols, mid-chain n-alkanes, benzofurans, indenes, biphenyls and PAHs, from which the benzofurans, indenes, biphenyls and PAHs were particular abundant in samples produced at Tchar 450 °C; pyrolysates of biochars produced at Tchar 750 °C were characterized by branched aliphatics, short chain n-alkanes/n-alkenes and low molecular weight (LMW) benzenes. Factor analysis showed that the variation of products differed largely within some chemical groups. For the N-containing compounds, caffeine, C16 alkylnitrile and diketopiperazines were associated with uncharred materials, benzonitriles and quinolines were associated with Tchar 350–450 °C. Another part of the variation of N-containing compounds was associated with chicken manure, and to a lesser extend also coffee husk, independently of Tchar. For all five agricultural residues, the highest chemical diversity was found for biochar produced at Tchar 350 °C. As the charring temperature increased, the diversity of pyrolysis products diminished.

Rice straw and chestnut wood were heated between 200 and 1000 °C (T CHAR) to produce Black C 'thermosequences'. The molecular properties of the charred residues were assessed by pyrolysis-GC/MS to investigate the relation between charring intensity and pyrolysis fingerprint. Samples obtained at T CHAR > 500 °C (wood) or >700 °C (straw) gave low quality pyrograms and poor reproducibility because of high thermal stability, but pyrolysis-GC/MS allowed to track the thermal degradation of the main biocomponents (polysaccharides, lignin, methylene chain-based aliphatics, triterpenoids, chlorophyll and proteins) in the lower temperature range, mostly occurring between T CHAR 250 and 500 °C. With increasing T CHAR, the charred residues of these biocomponents lose characteristic functional groups, aromatise and finally condense into non-pyrolysable biomass. The proportions of the pyrolysis products of unspecific origin (benzene, toluene, PAHs, etc.), increase with charring intensity, while the ratios that reflect the abundance of alkyl cross-linkages between aromatic moieties (e.g. benzene/toluene, naphthalene/alkylnaphthalene) decrease. These results provide the guidelines to using pyrolysis-GC/MS for the molecular characterisation of different components in Black C and biochar, which is an important parameter for predicting Black C/biochar behaviour in soil. Results are consistent with earlier studies of these samples using the BPCA (benzenepolycarboxylic acid) method and the ring current-induced 13C benzene chemical shift NMR (Nuclear Magnetic Resonance) approach. Pyrolysis-GC/MS provides more information on molecular structures in the low temperature range (T CHAR ≤ 500 °C) while the BPCA and NMR ring current methods provide more reliable estimations of charring intensity, especially at higher temperatures (T CHAR ≥ 500 °C). © 2012 Elsevier Ltd., This study was partly funded by the Spanish Ministry of Science and Education under the framework of the CONSOLIDER-INGENIO 2010 program TCP (CSD2007-00058).

7 páginas, 3 figuras, 3 tablas., The chemical structure of the milled-wood lignin isolated from Paulownia fortunei wood was investigated. The lignins were characterized by analytical pyrolysis and two-dimensional NMR that indicated a predominance of guaiacyl (G) over syringyl (S) units, and only showed small amounts of p-hydroxyphenyl (H) units, with a H:G:S molar ratio of 1:59:40. The heteronuclear single quantum correlation (HSQC) NMR spectrum gave additional information about the relative abundances of the different inter-unit linkages present in the lignin structure. Paulownia lignin showed a predominance of β-O-4' aryl ether linkages (62% of total side-chains), followed by β-β' resinol-type (12%) and β-5' phenylcoumaran-type structures (11%) and with lower amounts of other condensed structures such as spirodienone (3%) and dibenzodioxocin (2%) structures. The high lignin content (ca. 23% Klason lignin), together with the low S/G ratio and the abundance of condensed (carbon-carbon linked) structures (together with the low abundance of the most labile ether-linked structures) could contribute to the low reactivity of paulownia lignin during alkaline pulping., This study has been funded by the Spanish project AGL2005- 01748 and the BIORENEW EU-Project (NMP2-CT-2006-026456). J.R. thanks the CSIC for an I3P fellowship and G.M. thanks the Spanish MEC for a FPI fellowship.

Most knowledge about the degradation of lignocellulose in natural environments is based on woody tissue and aerobic systems; however, in peatlands the contribution of graminoids to organic matter (OM) is often significant and anaerobic conditions prevail. In order to reconstruct past environmental conditions from peatlands and predict possible feedback mechanism between peatlands and climate change, a better understanding of the decomposition of graminoid tissue and the effects of anaerobic conditions on decomposition are needed. Samples (51) from the upper 1 m of the graminoid-dominated Penido Vello peatland (Xistral Mountains, Galicia, NW Spain) were analysed with pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) and 13C cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (13C CPMAS NMR). Carbon and nitrogen contents were also determined. Depth profiles of molecular groups identified using 13C CPMAS NMR were consistent with those of depth-related distributions of quantified pyrolysis products (aliphatics, polysaccharides and aromatics). Molecular proxies were selected from peat pyrolysates to reflect the state of decay of 1) lignocellulose (the summed lignin and polysaccharide pyrolysis products, Lg and Ps, respectively), 2) lignified cellulose (levoglucosan/Ps) and hemicellulose (4-hydroxy-5,6-dihydro-(2H)-pyran-2-one/Ps), 3) macromolecular lignin including syringyl (S), guaiacyl (G) and p-hydroxyphenyl (H) ratios (S/G; H/(S + G), and side chain oxidation and shortening (vanillic acid/G, syringic acid/S, 4-acetylguaiacol/G, 4-acetylsyringol/S, C3-guaicols/G and C3-syringols/S) and 4) non-lignin phenolic acids (4-vinylphenol/H, 4-vinylguaiacol/G). Factor analysis was applied to these proxies and 120 quantified pyrolysis products to examine the influence of possible underlying factors that could explain the observed variation. Botanical changes and several degradation stages including surface decay (both aerobic and anaerobic), aerobic sub-surface decay and depth related decay (long-term anaerobic) were identified with factor analysis and all affected the variance of lignin-based decomposition proxies. The net effect of these environmental factors on the lignin proxies was examined using their depth records. This revealed that some lignin decomposition proxies were not in agreement with the literature: 1) G and S moieties with a C3 alkyl side chain showed no correlation with bog hydrology at the time of peat formation; 2) G and S moieties with acetyl side chains were related to both relatively dry (secondary aerobic decay) and wet (first stage of decay) conditions; 3) vanillic acid and syringic acid were related partly to ericoids (indicating dry conditions) and partly to free phenolic acids (less depleted under wet conditions); and 4) preferential decay of G over S moieties was found during the first stage of decay (both aerobic and anaerobic) and long-term anaerobic decay. These contradictions can be explained by the dominance of non-woody lignin sources (graminoids) and the prominence of anaerobic decay in peatlands. Our findings indicate that the effect of anaerobic decay and source vegetation should be considered when using lignin proxies to deduce aerobic decay in peat records.

Gorse species (Ulex sp.) are ubiquitous in the shrublands of NW Spain and have the potential to become key players in an integral biofuel/biochar program in NW Spain. Here we present molecular characterization (using pyrolysis-GC/MS) of a biochar >thermosequence> obtained by laboratory heating of Ulex europaeus wood in a muffle furnace between 200 and 600°C (T CHAR). Low temperature chars (T CHAR ≤ 350°C) produced significant amounts of pyrolysis products of which the precursor biopolymer could be recognized, while high-temperature chars (T CHAR ≥ 400°C) produced mainly phenols and monocyclic and polycyclic aromatic hydrocarbons, which are not specific for any biopolymer. Carbohydrate could hardly be recognized at T CHAR ≥ 350°C. The thermal rearrangement of polyphenols, mainly lignin, was reflected in more detail (1) C 3-side chain shortening and probably depolymerization (T CHAR 200-350°C), (2) demethoxylation of syringyl and probably also some guaiacyl lignin (T CHAR 300-400°C), (3) elimination of virtually all remaining methoxyl groups (T CHAR 350-400°C), through dehydroxylation and demethoxylation, (4) almost complete dehydroxylation of lignin and other biopolymers (T CHAR 400-500°C), (5) progressive condensation into polyaromatic structures (T CHAR 300-500°C) and (6) partial elimination of alkyl bridges between (poly)aromatic moieties (T CHAR 450-500°C). These results were supported by Fourier transform infrared spectroscopy (FTIR) of the same samples. We conclude that pyrolysis-GC/MS can be used as a rapid molecular screening method of gorse-derived biochar. Molecular properties elucidation is an essential part of predicting the stability and agronomical behavior of gorse-derived biochar after future implementation in soils. © 2012 Elsevier B.V. All rights reserved., This study was partly funded by the Spanish Ministry of Science and Education under the framework of the CONSOLIDER-INGENIO 2010 program TCP (CSD2007-00058).

Sequential extraction method was applied to lignins from hardwood and softwood isolated by kraft and VTT organosolv processes. Solvent extraction was found to fractionate lignin according to the molecular weight: small molecular weight lignin is dissolved in the organic solvents and the lignin with higher molecular weight is enriched into the residue. Isolated acetone fractions of lignin are more homogeneous with narrow molecular weight distributions. Based on the31P NMR results, both total hydroxyl content and the content of phenolic hydroxyl units are higher in the acetone fraction than in the residue. Pyrolysis-GC/MS of all lignins showed thatp-hydroxy phenols are enriched to the residues. Preferential dissolution of syringyl type lignin in acetone was observed for hardwood kraft lignin, whereas the opposite behavior was seen for the hardwood organosolv lignin. Glass transition temperatures of all acetone soluble fractions were notably low compared to starting and residue lignins, which gives possibilities for future applications as a material with specific properties.

Lignin changes during plant growth were investigated in a selected Eucalyptus globulus clone. The lignin composition and structure were studied “in situ” by a new procedure enabling the acquisition of 2D-NMR spectra on wood gels formed in the NMR tube, as well as by analytical pyrolysis (Py-GC/MS). In addition, milled-wood lignins were isolated and analyzed by 2D-NMR, Py-GC/MS, and thioacidolysis. The data indicated that p-hydroxyphenyl (H) and guaiacyl (G) units are deposited at the earlier stages, whereas the woods are enriched in syringyl (S) lignin during late lignification. Wood 2D-NMR showed that β-O-4′ and resinol linkages were predominant in the eucalypt lignin, whereas other substructures were present in much lower amounts. Interestingly, open β-1′ structures could be detected in the isolated lignins. Phenylcoumarans and cinnamyl end-groups were depleted with age, while spirodienone abundance increased, and the main substructures (β-O-4′ and resinols) were scarcely modified. Thioacidolysis revealed a higher predominance of S units in the ether-linked lignin than in the total lignin and, in agreement with NMR, also indicated that resinols are the most important non-ether linkages. Dimer analysis showed that most of the resinol-type structures comprised two S units (syringaresinol), the crossed G-S resinol appearing as a minor substructure and pinoresinol being totally absent. Changes in hemicelluloses were also shown by the 2D-NMR spectra of the wood gels, without polysaccharide isolation. These include decreases of methyl galacturonosyl, arabinosyl and galactosyl (anomeric) signals, assigned to pectin and related neutral polysaccharides, and increases of xylosyl (which are ~50% acetylated) and 4-O-methylglucuronosyl signals.

The structural characteristics of the lignin from jute (Corchorus capsularis) fibers, which are used for high-quality paper pulp production, were studied. The lignin content (13.3% Klason lignin) was high compared to other nonwoody bast fibers used for pulp production. The lignin structure was characterized by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), 2D-NMR, and thioacidolysis. Upon Py-GC/MS, jute fibers released predominantly products from syringylpropanoid units with the S/G ratio being 2.1 and a H/G/S composition of 2:33:65. 2D-NMR of the milled wood lignin (MWL) isolated from jute fibers showed a predominance of β-O-4 aryl ether linkages (72% of total side chains), followed by β-β resinol-type linkages (16% of total side chains) and lower amounts of β-5 phenylcoumaran (4%) and β-1 spirodienone-type (4%) linkages and cinnamyl end groups (4%). The high predominance of the S-lignin units, together with the high proportion of β-O-4 aryl ether linkages, which are easily cleaved during alkaline cooking, are advantageous for pulping. On the other hand, a small percentage (ca. 4%) of the lignin side chain was found to be acetylated at the γ-carbon, predominantly over syringyl units. The analysis of desulphurated thioacidolysis dimers provided additional information on the relative abundances of the various carbon-carbon and diaryl ether bonds and the type of units (syringyl or guaiacyl) involved in each of the above linkage types. Interestingly, the major part of the β-β dimers included two syringyl units, indicating that most of the β-β substructures identified in the HSQC spectra were of the syringaresinol type (pinoresinol being absent), as already observed in the lignin of other angiosperms., This study has been funded by the Spanish project AGL2005-01748 and the EU BIORENEW Project (NMP2-CT-2006-026456). J.R. thanks the Spanish CSIC for a I3P fellowship; G.M. thanks the Spanish Ministry of Education for a FPI fellowship.