Analysis of pyrolysis characteristics and kinetics of sweet sorghum bagasse and cotton stalk

Abstract

The pyrolysis kinetic behavior of sweet sorghum bagasse (SSB) and cotton stalk (CS) samples was investigated in this work. Thermogravimetric analysis of two samples at five heating rates (15, 25, 35, 45 and 55 °C min−1) in nitrogen atmosphere was performed. Results show that the pyrolysis trends of SSB and CS in their respective five heating rates are similar. The thermal decomposition process of the SSB and CS can be divided into four stages. With the heating rate increasing, the main pyrolysis stage appeared thermal hysteresis phenomenon, the whole TG and DTG curves shifted to the higher temperature area, and the maximum pyrolysis rate increased too. For the kinetic analysis, fifteen degrees of conversion (α) were selected between 10 and 80% using the two isoconversional methods of Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). The average activation energies for SSB and CS were found to be between 154.61 and 142.93 kJ mol−1 by KAS method and 155.61 and 145.39 kJ mol−1 using FWO method, respectively. Also, the variation of activation energy with the degree of conversion shows the apparent activation energies changed with the conversion degree, rising in an irregular jagged trend. The apparent activation energy value of SSB is also seen to be higher than that of CS at the same degree of conversion (α) except when it is 80% which gives lower value. The works therefore provide useful information for understanding energy requirement in pyrolysis process of biomass and in pyrolysis system design.