Product distribution and carbon structure evolution characteristics of semicoke from isothermal pyrolysis of Naomaohu coal

Abstract

Isothermal pyrolysis of Naomaohu coal was carried out at a temperature ranging from 500 to 750 0C using a fixed-bed reactor. The product distributions of gas and tar were measured using gas chromatography and gas chromatography-mass spectrometry, respectively. In addition, the effect of temperature on carbon structure evolution characteristics of semicokes were also investigated. The results showed that the gas yield increased dramatically from 61.50 to 168.43 mL g−1 when the temperature increased from 500 to 750 0C. CO2 and C2-C3 gases were mainly produced during the primary pyrolysis of lower energy chemical bonds at a lower temperature. The tar content ranges from 18.6 to 20.5 wt%, with the highest at 550 0C. At higher temperature, the branched hydrocarbon and phenols can react with each other to produce more polycyclic aromatic hydrocarbon. The infrared absorption peak area associated with the functional groups of O-H, C-H, CO and C-O initially increased with temperature from 500 to 550 0C before sharply decreasing as the temperature increased from 550 to 750 0C. At a higher pyrolysis temperature, the carbon content of the semicoke and the degree of graphite crystalline structure increased. Semicoke produced at higher pyrolysis temperatures exhibited better crystalline behavior and more pores and cracks.