Kinetic triplet of Colombian sawmill wastes using thermogravimetric analysis

Abstract

The potential of sawmill wastes as a raw material in pyrolysis process is presented in this study. Non-isothermal thermogravimetric analysis (TGA and DTG) and isoconversional methods were employed to determine triplet kinetic (activation energy, reaction model and pre-exponential factor). Through TGA and DTG, the conversion degree is described as a function of temperature for five heating rates (10, 20, 30, 40 and ${50}^o$ C/min) and four model-free methods (Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Friedman, and Vyazovkin) with temperatures ranging from 25 to 1000 ^° C were employed. Isoconversional lines were built for every method at different isoconversional degrees $\alpha \in \left[\mathrm{0,1}\right]$ . The activation energy E was found as a function of α in the interval ${\chi }_{II}=[0.2,0.7]$ where each isoconversional methods were in agreement and the estimated error was sufficiently small. Findings show the same activation energy profile independently of the isoconversional method. In particular the total variation of E in ${\chi }_{II}$ was as follows: 209.909-228.238 kJ/mol (FWO); 211.235-229.277 kJ/mol (KAS); 223.050-188.512 kJ/mol (Friedman), and 211.449 kJ/mol-229.512 kJ/mol (Vyazovkin). The reaction model of the process in ${\chi }_{II}$ matched with a two-dimensional diffusion ( $D_2$ ) by using a master-plot analysis. The calculated and reported parameters are fundamental information for the pyrolysis reactor design using Sawmill wastes as feedstock.

Keywords: Chemical engineering; Energy engineering; Isoconversional methods; Kinetic triplet; Materials chemistry; Physical chemistry; Pyrolysis; Sawmill wastes.