Investigation of mechanism and kinetics of non-isothermal low temperature pyrolysis of perhydrous bituminous coal by in-situ FTIR

Abstract

Perhydrous coal has advantages as a fuel source and raw material for hydrocarbon production over other coal with similar rank. Good understanding of thermal characterization of perhydrous coal can provide important information for control of the pollutants release and enhancement of the conversion rate of coal during its utilization. A perhydrous bituminous coal from Dingji Coal Mine, China was selected for the investigation of the non-isothermal pyrolysis process below 500°C in N2 flow by in-situ transmission FIIR. Evolutions of the main functional groups in coal, including aliphatic groups, aromatic CC and CH, carbonyl, CO and hydroxyl could be divided into several stages. The thermal characterization of each stage was discussed. The aliphatic groups and aromatic CC content decreased slightly with the volatilization of small molecules below 400°C, while the amount of aromatic CH increased with the loss of substituent groups. The conversion of CO to CO contributes to the slight increase in the CO amount below 370°C, and the decrease of hydroxyl was attributed to loss of water and the condensation and elimination of hydroxyl groups. The amount of all functional groups except for the aromatic CH declined rapidly with the cracking of CC bonds after 400°C. The kinetic characterization of pyrolysis stages for three functional groups, including aliphatic groups, CO and hydroxyl, was studied with modified integral method. Activation energy of pyrolysis stages of the three functional groups increased with rising temperature. Kinetics for the different stages of functional groups were fitted with different kinetic models. The initial loss of aliphatic groups and CO was controlled by diffusion. Then, the reaction of the three functional groups fitted on the first-order or third-order reaction models. The results obtained by in-situ FTIR revealed more detail information about thermal characterization and kinetic characterization and can be expected to lead to good understanding of pyrolysis of a perhydrous coal.