J.C. del Río

Pyrolysis derivatization of humic substances 1. Pyrolysis of fulvic acids in the presence of tetramethylammonium hydroxide

Abstract Humic Acids (HAs) extracted from soils of very different origin have been analyzed by pyrolysis in the presence of tetramethylammonium hydroxide. The thermal degradation products consisted mainly of aliphatic series such as fatty acids methyl esters and α,ω-methoxy fatty acid methyl esters. Triterpenoid compounds with ursane, oleanane and hopane skeletons were also detected in several samples. Aromatic units derived from lignin moieties were also detected although in minor amounts and corresponded mainly to guaiacyl and syringyl units. This procedure seems to release the more labile, aliphatic moieties attached to the aromatic nuclei of the HA structure.

Structural characterization of bio- and geo-macromolecules by off-line thermochemolysis with tetramethylammonium hydroxide

A new analytical procedure, tetramethylammonium hydroxide thermochemolysis, was used to structurally characterize a variety of bio-and geo-polymers. The technique cleaves esters and some ethers in macromolecular organic matter, yielding low-molecular-mass monomers such as methyl esters of carboxylic acids and methyl ethers of alcohols that are amenable to gas chromatographic analysis. This procedure can be conducted in sealed glass ampoules, which means that it can be easily implemented in any laboratory having gas chromatographic capabilities, in contrast to other chemolytic or pyrolytic procedures. A set of biogeomacromolecules, ranging from gymnosperm and angiosperm woods, natural polyesters such as cutin, dissolved organic matter in natural and oceanic waters, and humic substances were characterized with this procedure. The information obtained provides molecular-level details which can be used to infer structural composition.

Thermally assisted hydrolysis and alkylation of lignins in the presence of tetra-alkylammonium hydroxides

Three different milled lignins isolated from bamboo, pine and beech, corresponding to the three different structural groups, have been subjected to pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH). Pyrolysis of the lignins in the presence of TMAH releases the methyl esters and methyl ethers of the different lignin monomers. Several moieties bearing carboxylic acid groups, not previously detected using pyrolytic techniques, could be released from the three lignins, suggesting that the presence of these moieties in the lignin structure have been underestimated.

Chemical composition of lipophilic extractives from Eucalyptus globulus Labill. wood

Summary The composition of lipophilic extractives in the chloroform soluble fraction of the acetone extract from Eucalyptus globulus wood has been examined. The lipid extract was fractionated by solid-phase extraction on aminopropyl-phase cartridges into four different fractions of increasing polarity. The total lipid extract and the resulting fractions were analyzed by gas chromatography and gas chromatography-mass spectrometry, using high temperature capillary columns. The main compounds identified included sterols, sterol esters, fatty acids, steroid ketones, hydrocarbons and triglycerides. Minor compounds such as fatty alcohols, mono- and diglycerides, waxes and tocopherols were also identified among the lipids from E. globulus wood.

Thermally assisted hydrolysis and alkylation as a novel pyrolytic approach for the structural characterization of natural biopolymers and geomacromolecules

Abstract The high-temperature reaction of macromolecules with tetra-alkylammonium hydroxides has significantly improved the use of the conventional pyrolytic procedures which are widely used for the structural characterization of natural biopolymers and geomacromolecules. This new pyrolytic approach has overcome some of the analytical limitations of conventional pyrolysis allowing the detection of polar compounds as their alkyl derivatives. We report recent developments of the high-temperature hydrolysis and alkylation procedure, carried out in the presence of tetra-alkylammonium hydroxides, for the structural characterization of natural biopolymers and geomacromolecules such as lignins, humic substances, coals, asphaltenes and kerogens.

Biodegradability of extractives in sapwood and heartwood from Scots pine by sapstain and white rot fungi

Summary The fungal degradation of lipophilic extractives in sapwood and heartwood from Scots pine (Pinus sylvestris) was studied. In sapwood, the white rot fungi, Bjerkandera sp. and Funalia trogii, removed higher amounts of extractives than the sapstain strains, Ophiostoma ainoae and Ceratocystis allantospora. Triglycerides, long chain fatty acids, steryl esters and waxes in pine sapwood were almost completely degraded by all the fungi. Sterols and resin acids were also extensively degraded by the white rot strains; however, these components were not or only poorly removed by the sapstain fungi. The removal of total extractives by all the fungal strains was higher in sapwood as compared to heartwood. The highly concentrated extractive fraction in pine heartwood mainly consists of resin acids. As observed in sapwood, sapstain were also poorly effective in the degradation of the resin acids present in heartwood. The fungal degradation of heartwood extractives was not only limited by the degradative ability of the various test microorganisms, but also by the inhibitory effect exerted by the extractive fraction. The white rot fungus F. trogii was particularly inhibited on heartwood. Bjerkandera sp. showed a higher tolerance to toxic extractives and was the most efficient fungus in degrading extractive constituents in both Scots pine heartwood and sapwood. Therefore, Bjerkandera sp. strain BOS55 should be considered as a potential agent for pitch control in pulp and paper manufacture.

Identification of residual lignin markers in eucalypt kraft pulps by Py–GC/MS

Abstract Pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) has been used to characterize the residual lignin in eucalypt ( Eucalypt globulus ) kraft pulp during the pulping and bleaching processes. The composition and structure of eucalypt wood lignin and kraft lignin have also been studied by Py–GC/MS and 13 C-nuclear magnetic resonance (NMR). Pulp samples were collected at different stages of the pulping process (after cooking, oxygen delignification, and bleaching with chlorine dioxide or hydrogen peroxide). By comparison with lignin pyrolysis products obtained from Py–GC/MS of eucalypt wood and kraft lignin, characteristic features of lignin in the different pulps have been established. The main lignin-derived markers detected in pulps were guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-vinylguaiacol, syringol, 4-methylsyringol, 4-ethylsyringol, 4-vinylsyringol and trans -4-propenylsyringol, all of them in very low amounts. Analytical pyrolysis was also used to characterize the changes in the residual lignin after kraft pulping of eucalypt wood pretreated with two lignin-degrading fungi ( Bjerkandera adusta and Poria subvermispora ) in wood ‘biopulping’ experiments. In general, Py–GC/MS has shown to be valuable in the characterization of residual lignin markers in kraft pulps due to the sensitivity of the technique when individual-ion chromatographic profiles for selected lignin markers are used.

Py–GC/MS study of Eucalyptus globulus wood treated with different fungi

The degradation patterns of Eucalyptus globulus wood by several wood-rotting fungi from the groups of ascomycetes, basidiomycetes and deuteromycetes were studied by analytical pyrolysis coupled to gas chromatography/mass spectrometry. The pyrograms of sound and degraded eucalypt wood showed several major peaks from lignin breakdown, identified as guaiacol, 4-methylguaiacol, 4-vinylguaiacol, eugenol, syringol, trans-isoeugenol, 4-methylsyringol, 4-ethylsyringol, 4-vinylsyringol, 4-allylsyringol, syringaldehyde, trans-4-propenylsyringol, acetosyringone, syringylacetone and propiosyringone. Products arising from carbohydrate pyrolysis could also be recognized. Similar pyrolysis compounds were found during analysis of sound and decayed wood, but differences were observed in their relative abundances. Relative peak areas were calculated for guaiacyl (G) and syringyl-type (S) lignin breakdown products, as well as for compounds arising from carbohydrates. Several basidiomycetes were found to be the most efficient lignin degraders on eucalypt wood as revealed by lignin/carbohydrate ratio from pyrolysis products. Among them, Poria subvermispora caused the most intense removal of lignin moiety from eucalypt wood. A decrease of lignin S/G ratio was observed during wood delignification, the lowest ratio being found also in the wood treated with P. subvermispora. This is due to the preferential biodegradation of ether-linked S-lignin yielding a residue enriched in G-lignin that is more recalcitrant towards fungal attack because of its higher condensation degree. On the other hand, deuteromycetes preferentially degraded the carbohydrate moiety while the ascomycetes included in this study did not show any particular preference in the degradation of eucalypt wood constituents.

Characterization of humic acids from low-rank coals by 13C-NMR and pyrolysis-methylation. Formation of benzenecarboxylic acid moieties during the coalification process

Abstraet--Humic acid (HA) fractions isolated from a peat and lignite deposit were studied by CP/MAS ~3C-NMR and pyrolysis-methylation. Loss of carbohydrates, removal of methoxyls and formation of catechols during the coalification process was evident. Pyrolysis-methylation released a great variety of components, the lignin-derived monomers being the most prominent. A very striking feature was the release of benzenecarboxylic moieties after pyrolysis-methylation which have not been observed previously by pyrolytic techniques. These moieties were released in higher amounts from the lignite HA, suggesting that the content in carboxylic groups increase with coalification, at least up to the lignite stage. Oxidation of the C-3 side chain of the lignin structure would produce these benzenecarboxylic acids and benzylic ketones.

Ease of delignification assessment of wood from different Eucalyptus species by pyrolysis (TMAH)-GC/MS and CP/MAS 13C-NMR spectrometry

Abstract Flash-pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) of woods from different species of Eucalyptus yields series of guaiacyl-type (G) and syringyl-type (S) units in slightly but characteristically different relative proportions. Such differences have been used to suggest a fine and appropriate index of the ease of delignification of the different Eucalyptus species when pulped by the Kraft process. The pyrolytic data were in agreement with those obtained from CP/MAS 13C-NMR spectra of the woods. On the other hand, the various eucalypt woods showed additional differences in their pyrolytic patterns regarding the relative amounts and structure of the high molecular weight aromatic compounds arising from the pyrolysis of polyphenolic wood constituents, which might be used as a basis for chemotaxonomic differentiation of the origin of the woods