CELLULOSE PYROLYSIS KINETICS - REVISITED

In the same thermogravimetric analyzer (TGA) under identical condition s, samples of pure, ash-free cellulose (i.e., Avicel PH-105, Whatman C F-11, Millipore ash-free filter pulp, and Whatman #42) obtained from d ifferent manufacturers undergo pyrolysis at temperatures which differ by as much as 30 degrees C. Thus, the pyrolysis chemistry of a sample of pure cellulose is not governed by a universal rate law, as is the c ase with a pure hydrocarbon gas (for example). Nevertheless, the pyrol ytic weight loss of all the samples studied in this work is well repre sented by a high activation energy (228 kJ/mol), first-order rate law at both low and high heating rates. These results do not corroborate t he recent findings of Milosavljevic and Suuberg (Ind. Eng. Chem. Res. 1995, 34, 1081-1091). For a particular cellulose sample (for example, Avicel PH-105), variations in the preexponential constant determined a t different heating rates reflect uncontrolled, systematic errors in t he dynamic sample temperature measurement (thermal lag).