KINETICS OF THE THERMAL-DECOMPOSITION OF CELLULOSE IN SEALED VESSELS AT ELEVATED PRESSURES - EFFECTS OF THE PRESENCE OF WATER ON THE REACTION-MECHANISM

The thermal decomposition of Avicel cellulose was studied by non-isothermal differential scanning calorimetry in hermetically sealed sample holders. The experimental results, which were published earlier, showed a marked catalytic effect of the water on the cellulose decomposition. Here we propose a reaction scheme containing two rate determining reactions to describe the result. The corresponding model resulted in a good fit between the experimental and the calculated data. The results indicate that the reaction starts with cellulose hydrolysis which may be followed immediately by decomposition reactions to intermediate products. The intermediates undergo further water-catalyzed decomposition reactions giving char, water and gases. The results may help in the understanding of biomass pyrolysis under experimental or industrial conditions where the thickness of the layer, the size of particles or the enclosure of the reactor keeps part of the water vapor formed during the reaction in the pores or between the particles of the decomposing material.