The Fate of Organic Oxygen During Coal Pyrolysis

Oxygen in coal is in more than one form. Oxygen-containing functional groups are thought to play a key role in the structure of coal and have a significant effect on the process of coal pyrolysis. This paper describes the fate of oxygen in coal pyrolysis. Three Chinese coals were heated in high-purity Ar at 10°C/min with a fixed-bed reactor, and the oxygen distribution has been examined in detail. Model compounds containing oxygen were pyrolyzed in a quartz boat using a Pyroprobe 2000 (CDS) coil probe directly coupled to a BIORAD FTIR model FTS-165 spectroscopy. Thermal decomposition results show more than 70% oxygen evolution in the gas-phase oxygen; the major form of gas-phase oxygen was CO and CO2. CO2 was produced at a low temperature, CO at a high temperature. The carboxyl group of coal is related to the evolution of CO2. Large oxygen converted into the gas phase between 400 and 500°C. The conversion to tar-O was always < 10%; phenol and its derivatives in tar are the only stable pyrolysis products. The amounts of phenol tended to decrease with an increase in heating rate. At higher temperatures, lower product yields of phenolic compounds in tar are obtained.