The impact of the thermal lag on the interpretation of cellulose pyrolysis

Abstract

The influence of the accuracy of the sample temperature determination on the pyrolysis of cellulose has been investigated by thermogravimetric analysis and numerical modelling. Experiments were carried out using cellulose employing seven different heating rates (HR). The developed numerical model enabled a determination of the thermal lag, taking into consideration the dependence of the properties of sample, crucible and surrounding gases on their true temperature. It was found that the limited heat transfer has a much greater impact on the true sample temperature than previously considered. At low HR the uncertainty of the sample temperature determination did not exceed 4.8 K, while for high HR it reached even 56.2–130 K. The temperature measurement inaccuracy affected the kinetic parameters by even 40–50% however it should not be attributed to the difference in maximum reactivity temperature observed for different HR. Opposed to other models presented in the literature, the developed one indicated that the decrease of cellulose activation energy observed for high conversion rates could not be in any way attributed to thermal phenomena. Moreover, observations made at HR 0.5 K min−1 indicated that the mechanism of cellulose pyrolysis should also consider the third pathway of reaction, resulting in enhanced formation of char.