FTIR study of pyrolysis products evolving from typical agricultural residues

Pyrolysis of agricultural residues (maize stalk, rice straw and cotton straw) was studied using a thermogravimetric (TG) analyzer and a laboratory scale fixed bed coupled with Fourier transform infrared (FTIR) analyzer. Pyrolysis characteristics of three materials were discussed. The characteristic parameters were determined for the main devolatilization step. Maize stalk showed the highest thermal reactivity, followed by cotton straw and rice straw. Their pyrolysis processes underwent three consecutive stages, corresponding to the evaporation of water, the formation of primary volatiles and the subsequent release of small molecular gases. In order to further study the pyrolysis mechanisms of agricultural wastes, the release of the main volatile and gaseous products were on-line detected by FTIR spectroscopy. The results showed that the major pyrolysis gases for the three materials were similar, including CO2, CO, methane, ethane, ethylene and some organics such as methanol, formaldehyde, formic acid and acetone. HCN was the major nitrogen containing product. At higher temperatures several small molecular gases, such as CO2, CO and methane, could still be monitored.