Analytical Pyrolysis of Lignins

In the first type of technique, which attempts to solubilize the cellulosic material, there are several procedures generating lignin  

Among the second type of procedures, which solubilize the lignin followed by reprecipitation, are the following  

Idealized structures for lignin were proposed [3], for example, as a polymer of coniferyl alcohol (4-hydroxy-3-methoxycinnamyl alcohol). However, lignin is not a repetitive polymer. Also, it is necessary to specify which lignin is considered when a specific structure is proposed. 

Combining the results regarding the type and number of functionalities in different lignins as determined by different analyses, several model structures were proposed such as Freudenberg structure which is shown below [2]  

Some other repeating units of lower importance were also indicated in lignin and they are shown below  

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A catalog of degradation products from the analytical pyrolysis of lignin has been published recently (Faix et al. 1990a,b). The compilation comprises retention time data and the complete mass spectra of 82 compounds. 

Kleen, M. and Gellerstedt, G., Influence of inorganic species on the formation of polysaccharide and lignin degradation products in the analytical pyrolysis of pulps. J Analytical Appl Pyrolysis 1995, 35 (1), 15-41. 

Muller M (1980) Beitrag zum Einsatz der Curie Punkt-Pyrolyse Massenspektrometrie in der Analytik von Naturstoffen Dissertation ETH 6743, Zurich Obst JR (1983) Analytical pyrolysis of hardwood and softwood lignins and its use in lignin type determination of hardwood vessel elements J Wood Sci Technol 3 377-397 Pouwels AD, Boon JJ (1987) Analysis of lignin and chlorohgntn residues in a beech xylan fraction by pyrolysis gas chromatography mass spectrometry J Wood Sci Technol 7 197— 213... 

Judging from the success of the analytical model in Section 7.4.3.1 to reproduce substituent effects on a//3-selectivities, we will soon be able to model the pyrolysis of lignin model compounds including a complete set of relevant reactions. In a future vision, the combination of hundreds of computational studies of model compounds in the kinetic simulation of biomass conversion will enable us to bridge the gap between molecular understanding and industrially applicable processing techniques. 

In an attempt to delineate the degree of preservation of lignin in pre-Tertiary coal, we examined numerous coalified wood samples ranging in age from Carboniferous to Cretaceous. The samples were initially screened by solid-state l C nuclear magnetic resonance to detect the possible presence of methoxyl carbon. Once such carbons were detected, the samples were subjected to analytical pyrolysis to determine the relative yields of methoxyphenols which would provide an indication of the state of preservation of the lignin-derived structu units. We report here on the identification of lignin-derived methoxyphenols in the coalified wood samples selected for analytical pyrolysis. 

The analysis of lignitic woods by analytical pyrolysis has shown that lignin structural units can be preserved as biomaikers in samples as old as Carboniferous age, or approximately 300 million years. At least half or more of the pyrolysis products in lignitic wood of Cretaceous age are methoxyphenols characteristic of lignin. The pn uct distributions in these Cretaceous samples indicate that the lignin is mainly altered in the 3-carbon side chains. Phenols, cresols, catechols, and other methylated phenols account for most of the remaining pyrolysis products. It is likely diat these products are also derived frx>m li in, especially lignin that has been altered by coalification reactions. 

Recently, many useful applications of analytical pyrolysis for the analysis of diverse lignin samples have been reported. The method has proven to be extremely useful for a quick comparison of lignins of different origins. Based on the peak areas of H-, G-, and S-derived pyrolysis products in the pyrogram, lignins can be easily classified as G- or G/S-type. The results of such a comparison are shown in Fig. 4.7.11. Pyrograms of MWLs from spruce, teak, beech and whitewood show clearly the increase in S-derived pyrolysis products. 

Saiz-Jimenez et al. (1987) applied analytical pyrolysis-gas chromatography to recent and buried alder, oak, and spruce woods. In comparison with the native woods, the yields of pyrolysis products from the guaiacyl and syringyl lignins were significantly higher in the alder and oak woods, while for spruce, this increase was less significant. 

A thermo-analytical study of untreated and CCA treated wood samples (more or less cylindrically shaped with diameter less than 2 mm) was performed in order to examine the influence of the presence of CCA on the pyrolytic behaviour of wood samples (TG study), as well as the release of metals (Cu, Cr and As) during the pyrolysis process in the kinetically controlled regime. Since arsenic is the most problematic compound during pyrolysis of CCA treated wood and almost all arsenic is present in the treated wood as CrAs04 (precipitated on cellulose or complexed with lignin) [9], a... 

Kuroda, K.I. (2000) Pyrolysis-trimethylsilylation analysis of lignin preferential formation of cinnamyl alcohol derivatives. Journal of Analytical and Applied Pyrolysis, 56,79-87. 

A typical Py-GC-MS trace from a wood sample (Figure 9) contains 50-100 individual peaks corresponding to at least that many products. The individual pyrolysis products include fiirans plus a variety of carbonyl compounds that are typical of polysaccharides, particularly cellulose and hemi-cellulose (42). In addition, many different lignin-derived phenols are obtained that, like the CuO reaction products, retain the methoxylation pattern of the parent structural units and carry diagenetic information on their side chains (43). Characteristic pyrolysis products of wood extractives such as resin acids also can be detected (44) thus, this analytical method is... 

Hosoya, T., Kawamoto, H., Saka, S., 2007. Cellulose—hemicellulose and cellulose—lignin interactions in wood pyrolysis at gasification temperature. Journal of Analytical and Applied... 

Nowakowski, D.J., et al, 2010. Lignin fast pyrolysis results from an international collaboration. Journal of Analytical and Applied Pyrolysis 88 (1), 53—72. 

Tumbalam Gooty, A., Li, D., Berruti, F., Briens, C., 2014. Kraft-lignin pyrolysis and Ifactional condensation of its bio-oil vapors. Journal of Analytical and Applied Pyrolysis 106,33—40. http //dx.doi.0rg/lO.lOl6/j.jaap.2Oi3.i2.OO6. 

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