Deoxygenation of Chinese long-flame coal in low-temperature pyrolysis

Long-flame coal is a typical low-ranked coal that is not fully utilized and has a huge global reserve. High-content oxygen is a significant negative factor for low-rank coal utilization. The TG–FTIR–GC/MS method was applied to investigate the migration behavior of oxygen and the variation in the properties of Chinese long-flame coal during low-temperature pyrolysis. It was found that the oxygen migration ratios in long-flame coal toward gas and tar were 47.7 and 5.2%, respectively, at 550 °C, that the initial oxygen migration temperatures of hydroxyl, carboxyl, carbonyl and ether bonds were 500, 200, 300 and 350 °C, respectively, that the decomposition rates were 8.2, 90, 99.2 and 86% at 550 °C, respectively, that the oxygen in gas existed mainly in the form of CO2 and CO, and that the oxygen in tar existed mainly in the form of phenolic compounds. The further removal of oxygen was due to the decomposition of hydroxyl and a small amount of stable ether bonds. Furthermore, deoxygenation suggested that the decrease in oxygen had a positive effect on coal liquefaction and resulted in a decrease in its hydrophilicity.