Pyrolysis can be simply defined as the thermal degradation of a molecule into 

 various products. The pyrolysis of cellulosic material is defined as the thermal de- 

 gradation into volatile and nonvolatile products prior to combustion. This means it 

 is usually isolated from combustion by performing experiments in an inert atmosphere 

 or in vacuum. In general the pyrolysis products of wood and wood components are vola- 

 tiles, tar, and char. The volatile products consist mainly of CO2 H 2 0, various acids, 

 and carbonyl compounds. The tar includes extractives and higher molecular weight 

 degradation products. When cellulose is pyrolyzed, the major component of the tar is 

 1 ,6-anhydro-3-D-glucopyranose, commonly known as levoglucosan . 



The tar from the xylan component of the hemicelluloses consists mostly of D-xylose 

 dimers and trimers . 1 Char is the carbonaceous residue, the composition of which depends 

 on the extent of pyrolysis. 



The pyrolysis of cellulose can be represented graphically as follows 



CO, 



Cellulose 



dehydration 

 oxidation 



levoglucosan — ^-polymer 



^ U 



depolymerization 

 degradation 



■PYROLYSIS- 



2 



CO 



H 2 



Char 



O, 



Glowing 



Flammable 2 Flaming 



volatiles — 



tar 



COMBUSTION- 



At temperatures below 250° C. pyrolysis of cellulose occurs very slowly and the 

 main products are C0 2 , CO, H 2 0, and char. In the presence of 2 the char could undergo 

 localized surface oxidation or glowing. At temperatures above 320° C. pyrolysis occurs 

 at a much faster rate and leads to the formation of levoglucosan and other volatile 

 degradation products. In an oxygen atmosphere the combustible volatiles burn with 

 flaming combustion. Levoglucosan follows the same sort of route 2 or forms a polymer 

 which can likewise pyrolyze by the two routes . 3 Preliminary work with 4-0-methylglu- 

 cronoxylan (xylan) has shown this hemicellulose to have the same general action with 

 the exception that no levoglucosan is formed. 4 Levoglucosan has been considered as an 

 intermediate pyrolysis product of cellulose and it has been shown that it could undergo 

 the same type of charring and degradation reactions (Shafizadeh 1968, Ostojic, 2 and 

 Shafizadeh and others 3 ) . 



1 G. D. McGinnis. Pyrolysis of xylan and model compounds. 1970. (Unpublished 

 Ph.D. Thesis on file at the Univ. of Mont., Missoula.) 



2 N. Ostojic. Pyrolysis of levoglucosan. 1970. (Unpublished master's thesis on 

 file at the Univ. of Mont., Missoula.) - 



3 F. Shafizadeh, C. W. Philpot, and N . Ostojic. Thermal analysis of 1 , 6- 8-D-gluco- 

 pyranose. USDA Forest Serv., Intermountain Forest and Range Exp. Station, Ogden, Utah 

 84401. (Manuscript in preparation.) 



^McGinnis, op. cit. 



2 



