The flame retardants enhance charring reactions at the expense of the degradation 

 reactions which produce combustible volatile products. 



PYROLYSIS PRODUCTS 



A great variety of compounds have been identified among the destructive distillation 

 products of wood and cellulose. Much less is known about the thermal decomposition 

 products of the hemicellulose and lignin. The interest in the pyrolysis of wood 

 originated from the commercial value of naval stores and the destructive distillation 

 products, most of which have been replaced by other chemicals from alternate sources. 

 In 1909 Klason and coworkers identified the products derived from the destructive 

 distillation of cotton cellulose (Klason, Heidenstam, and Norlin 1909); these products 

 are shown in the following tabulation. 



Products 



Percent 





by weight 



Water 



34.52 



Acetic acid 



1 .39 



Acetone 



.07 



Tar 



4.18 



Other organic compounds 



5.14 



Carbon dioxide 



10.35 



Carbon monoxide 



4.15 



Methane 



.27 



Ethylene 



.17 



Coke 



38.82 



Through subsequent research the following products were added to the list: methane 

 formaldehyde; formic acid; acetone; butanone; glyoxal; glycoaldehyde ; a-valerolactone; 

 malthol; 2-furaldehyde (furfural); 5-(hydroxy methyl) -2-furaldehyde; methyl furan; 2,5- 

 dimethyl furan; and tri- and tetramethyl furan (Shafizadeh 1968) . Schwenker and Beck 

 investigated the products derived from cellulose that were pyrolyzed directly into a 

 gas-liquid chromatograph (Schwenker and Beck 1963) . They reported the following major 

 products: fixed gases; formaldehyde; acetaldehyde ; water; propionaldehyde; acetone; 

 acrolein; acetic acid; glyoxal; methanol; n-butyraldehyde ; butanone; furfural; formic 

 acid; lactic acid; and 5- (hydroxy-methyl) -2-furaldehyde . 



Broido and Martin (1961) exposed cellulose sheets to intense irradiation levels 

 of 4.4 to 11.6 cal . cm."" 2 sec. -1 for 0.4 to 0.8 seconds. Using mass spectroscopy, they 

 found the major products to be CO, C0 2 , and lesser amounts of H 2 , CH^, C 2 H 6 , and C 3 Hg 

 in the gases. The liquid phase contained mainly H 2 and small amounts of acetaldehyde, 

 propionaldehyde, butyr aldehyde, acrolein, crotonaldehyde , furan, acetone, butanedione, 

 and methanol. The tar was found to be mostly levoglucosan . 



Recently Lipska and Wodley (1968) have published the results obtained from a study 

 of isothermal pyrolysis of cellulose in a fluidized bed. The volatile products were 

 resolved with a gas liquid chromatograph (GLC) directly coupled to a mass spectrometer. 

 Figure 1 shows a typical chromatogram from their work. Wodley (1969) has compiled a 

 long list of products that so far have been identified from the pyrolysis of cellulose. 



These data indicate that the qualitative and quantitative composition of the 

 pyrolysis products could vary substantially according to the experimental pyrolysis 

 conditions. The most significant variables are the temperature, ambient atmosphere, 

 and the presence of various contaminants or impurities. 



3 



