Evolution of chemical functional groups during torrefaction of rice straw

Abstract

The evolution of CHON functional groups during torrefaction of rice straw at 200–300 °C were investigated. The results showed that 300 °C was more suitable for rice straw torrefaction due to the ideal fuel ratio, energy densification, energy-mass co-benefit index and the significantly improved HHV of the torrefied products. The functional groups such as O–H, N–H, C–H, C = O in the solids decreased with rising temperature accompanied by the releases of H2O, CH4, CO2, CO and NH3, et al. At 300 °C, 40.04% of fuel-N was released in the form of NH3, HCN, HNCO et al. due to the decomposition of N-A which was the overall N-functionality in the raw rice straw. It is worth noting that the absorbance of NH3 and HCN has the same order of magnitude as CO. Therefore, the releases of N-containing gases should be highly concerned for the application of torrefaction technology from the environmental perspective.