Cellulose pyrolysis: the kinetics of hydroxyacetaldehyde evolution

The kinetics of formaldehyde, hydroxyacetaldehyde, CO and CO2 evolution during the pyrolysis of cellulose, Whatman 41, were studied in a fast evolved gas-FTIR apparatus (EGA). The samples were subjected to exponential temperature increases from ambient to final temperatures ranging from 400 degreesC to 800 degreesC within about 1 min. The yields of formaldehyde, hydroxyacetaldehyde and CO approximately doubled with heating rate over the experimental range of heating rates while that of CO2 decreased slightly. The kinetics for CO2 evolution are consistent with a single first order reaction. The kinetics of formaldehyde and CO formation require a pair of competing first order reactions. The behavior of hydroxyacetaldehyde is more complex. In this case a third reaction step is required following the initial pair of competing reactions. The reactions involved in the evolution of all four gases, with the exception of the third step in the hydroxyacetaldehyde mechanism, exhibit essentially identical activation parameters. This suggests their formation involves common rate limiting steps. These are, most likely, the decomposition pathways of cellulose which are followed by rapid secondary reactions to yield the individual gases. (C) 2001 Elsevier Science B.V. All rights reserved.