Pyrolysis of polysaccharide

A recent study extensively investigated the pyrolysis of polysaccharide binders, with and without a silylating agent [56]. Some of the main results relative to the pyrolysis silylation of sugars and polysaccharide binders can be summarised as follows [56 59] ... 

G.R. Ponder and G.N. Richards, A review of some recent studies on mechanisms of pyrolysis of polysaccharides Biomass Bioenerg., 7,1 24 (1994). 

Mok and Antal [70,71] proposed a reaction tree, see Figure 51, consisting of both concurrent and consecutive pathways to describe the pyrolysis of polysaccharides taking place in the particle phase (Figure 42). The relative importance of each pathway is influenced by the intraparticle solid phase temperature, the presence of additives, pressures, etc [61]. 

The pyrolysis chemistry of lignin, proposed by Antal [67], is quite similar to the pyrolysis of polysaccharides, see Figure 53. There exist a low temperature pathway (1), a moderate temperature pathway (2), and a high temperature patway (3), which are analogous to the pyrolysis of polysaccharides. 

A variety of small molecules are formed during pyrolysis of polysaccharides, and hydroxyacetone, 2-furaldehyde, 2-hydroxycyclopent-2-en-1-one, 5-hydroxymethyl-2-furaldehyde and 1,5-anhydro-4-deoxy-glycero-hex-1-en-3-ulose are more common pyrolysis products. However, only the anhydrosugars, also formed in significant proportion during pyrolysis, are diagnostic for a specific monosaccharide unit because the stereoisomerism is not lost during pyrolysis. 

Pyrolysis of polysaccharides from algae was performed using both Py-MS and Py-GC/MS techniques (e.g. [2, 3, 64]). Py-MS studies [2] showed it was possible to obtain structural information on the primary and secondary structure of the polysaccharide from specific ions in its spectrum. Particularly El spectra at 14 eV ionization energy were used for compound differentiation. Four examples of such spectra are shown below in Figure 7.8.1. 

The general pyrolysis mechanisms of polysaccharides have been determined from model studies on cellulose and involve the splitting of the polysaccharide structure by three basic chemical reaction mechanisms dehydration, retroaldolization, and decarboxylation. Using these basic pyrolysis mechanisms, it is possible to explain the pyrolysis of polysaccharides and evolved pyrolysis products. The hexose degradation pathway for cellulose results in formation of furan- and pyran-type fragments and smaller acyclic aldehyde and ketone fragments. ... 

Pyrolysis of polysaccharides has been a subject for investigation on flame retardants, sources of fuel, and preparation of chemical feedstocks. When powdery cellulose or starch are treated at high temperature under reduced pressure, a complex mixture of tar and gaseous substances... 

Although the pyrolysis of some classes of polysaccharide materials has been studied quite extensively in the food, petrol and tobacco industry, very little has been published specifically on polysaccharide binders (arabic gum, tragacanth gum, fruit tree gum, honey and starch). The pyrolysis of glucane based polymers, especially cellulose, has been studied in detail [6,55], highlighting how anhydrosugars and furan derivatives are the main pyrolysis products, together with one-, two- and three-carbon aldehydes and acids. 

Hell eur, R.J. Thibault, P. Optimization of Pyrolysis-Desorption CI-MS and Tandem Mass Spectrometry of Polysaccharides. Can. J. Chem. 1994, 72, 345-351. 

However, in general, the global mechanism of polysaccharide pyrolysis involves three competing reactions [61] ... 

Fig. 5.2(A) presents the pyrolysis mass spectrum for the soil extract. In previous work (ref. 358,359,365) it was shown that complex organic materials like polysaccharides, proteins, lignins, and soil humic fractions have characteristic peaks yielding a typical pattern, which give preliminary information about the composition of the pyrolysis fragments. Thus, characteristic peaks for polysaccharides were observed at 60, 68, 82, 84, 96, 98, 110, 112, and 126 m/z, which were also present in the soil extract. They were shown to be related to acetic acid, furan, methylfuran, hydroxyfuran, furfural, furfuryl alcohol, methylfurfural, methoxy-methylfuran, and a typical pyrolysis fragment of polysaccharides with hexose and/or deoxyhexose units, respectively.

Schulten, H.-R., and Gortz, W. (1978). Curie-point pyrolysis and field ionization mass spectrometry of polysaccharides. Anal. Chem. 50,428-433. 

The list of pyrolysis products of cottonwood shown in Table VII (llj reflects the summation of the pyrolysis products of its three major components. The higher yields of acetone, propenal, methanol, acetic acid, CO, water and char from cottonwood, as compared to those obtained from cellulose and xylan, are likely attributed to lignin pyrolysis. Other results are similar to those obtained from the pyrolysis of cell-wall polysaccharides. This further verifies that there is no significant interaction among the three major components during the thermal degradation of wood. 

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. 

Lomax, J. A., Commandeur, J. M., andBoon, J. J. (1991). Pyrolysis mass spectrometry of polysaccharides. Biol. Mass Spectrom. 19, 65-79. 

Radlein D, Piskorz J, Scott DS, Fast Pyrolysis of Natural Polysaccharides as a Potential Industrial Process , J. Anal. Appl. Pyrol., 19,41-63, 1991. 

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