Effect of preheating treatment on oxygen migration during lignite pyrolysis

The effect of preheating treatment (140-230 ℃) on the oxygen migration rule of Hulunbuir lignite which is pyrolyzed at 650 ℃ has been discussed by using the proximate and ultimate analyses, the Fourier transform-infrared spectroscopy, and the gas chromatography-mass spectrometry analysis. Results show that the amount of oxygen migrated to the pyrolysis water and semi-coke is decreased by 7.55% and 1.43%, respectively due to the effect of preheating at 200 ℃. Furthermore, the amount of oxygen transferred to tar and gas is increased by 6.66% and 1.61% respectively, and phenolic oxygen in tar is getting doubled. The decrease of hydrogen bonding and the increase of phenolic compounds are noted as the result of preheating process of lignite, as evidenced by in-situ infrared diffuse reflectance spectroscopy, this could be due to the dissociation of OH…π, OH…N bonds. Hydroxyl self-association hydrogen bonds have also broken down and transformed during the preheating process with the formation of free OH·, which result in the increase of phenol and cresol contents.