Thermogravimetric characteristics and kinetics of herb residues catalyzed by potassium carbonate

Abstract

Thermal conversion technology of Chinese herb residues (CHR) becomes one of the most promising technologies in the large-scale clean utilization of herb residues due to its short process and high efficiency. In this study, non-isothermal thermogravimetric analysis of CHR samples without and with K2CO3 (5%K- 9%K) was implemented at 300-1125 K and the heating rates of 10-40 K/min. A model-free Starink method was applied to evaluate the thermal decomposition behavior and apparent activation energy (Eα) values. The estimated average activation energy decreases from 206.3 kJ/mol of raw CHR to 143.8-160.6 kJ/mol of CHR with K2CO3. K2CO3 catalysts significantly promote the catalytic pyrolysis reaction of the hemicellulose and cellulose of CHR samples at the main devolatilization stage from 425 K to 700 K with over 82.02% mass loss. The pyrolysis temperature of the raw CHR is higher than traditional lignocellulosic biomass without decoction. By using the generalized master-plots method, it was found that the CHR pyrolysis could be described by a modified Dn-Jader model, but values of n and A tend to change measurably with heating rates for the CHR samples with catalysts due to the remarkably catalytic effect of K2CO3.