Thermogravimetric characteristics and kinetics of herb residues catalyzed by potassium carbonate

摘要

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, nonisothermal 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 (E alpha) 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 masterplots 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.