Effect of temperature on gas composition and char structural features of pyrolyzed agricultural residues

The gases and chars produced during fast pyrolysis of maize stalk, rice straw, cotton straw and rice husk at temperatures ranging from 600 to 1000 °C were studied by Fourier transform infrared spectroscopy, non-dispersive infrared technique, thermal conductivity detection method, ultimate analysis, X-ray diffraction, helium density measurement and N2 adsorption method. The gas yield increased by more than 80% from 600 to 1000 °C, while the char and liquid yield decreased. The content of CO2, CO and CH4 accounted for more than 86%. The CO and CH4 content increased with temperature, while the CO2 content decreased. The hydroxyl, aliphatic CH, carbonyl, olefinic CC and ether groups were lost above 800 °C. Carbon skeleton shrinkage increased by more than 23% when the temperature increased from 600 to 1000 °C. Maximum porosity appeared at 900 °C. This study revealed the relationships between gas composition/char properties and pyrolysis temperature under high heating rate conditions.