Bull. Spec. CORESTA Congress, Lisbon, 2000, p. 206, STPOST3
A kinetic study of cellulose pyrolysis - II. Mechanistic considerations
Philip Morris USA, Richmond, VA, USA
As shown in the previous paper, A kinetic study of cellulose I., the mechanism for the production of the pyrolysis products observed, formaldehyde, hydroxyacetaldehyde, CO, CO2 and tar, involves competing reactions. The pattern of the values observed for the rate constants suggests that the primary pathways of cellulose decomposition provide the rate limiting steps for the formation of all of the species studied. The initial phase of cellulose pyrolysis which is thought to involve a reduction in the degree of polymerization of cellulose was not observed. The starting species in the mechanism is, thus, cellulose with a reduced degree of polymerization. The high temperature pathway appears to involve fragmentation leading to formaldehyde, hydroxyacetaldehyde and CO. The low temperature pathway involving depolymerization yields CO2 and the condensable tars including levoglucosan. The results are compared with several published mechanisms. It is shown that the present rate constants are consistent with a diffusion mechanism for the evolution of tar, accurately predict the hydroxyacetaldehyde-levoglucosan split as a function of temperature and are in agreement with weight loss data. A new mechanism for cellulose pyrolysis is presented.