Sevil Çetinkaya

Oxidative pyrolysis of Turkish lignites in air up to 500°C

Abstract In this study, DSC, TGA and DTGA systems were used to investigate the oxidative pyrolysis of six lignite samples in air. The original lignite samples were extracted with toluene/ethyl alcohol (1:1) and pyridine. Coal samples were oxidatively pyrolysed in air up to 500°C. An initial endothermic peak between 30°C and 150°C, which was due to the loss of water, and three exothermic oxidation peaks were observed at about 300°C, 400°C and 500°C. Extraction of coals decreased the temperature at which the first oxidation peaks occurred by about 6–15°C compared with that of the non-extracted coals. The third oxidation peaks observed in the thermograms were between 440°C and 492°C, which might be considered as high-temperature oxidation peaks. Since the minerals present in all of the lignites do not decompose at temperatures below 500°C, these peaks were present only because of the oxidation of the organic matter of the coals. The swelling behaviors of the non-extracted coals and of the residues obtained at room-temperature extraction were also studied. FTIR spectroscopy was used to study the chemical properties of the samples and to investigate the effect of oxidation on the coal. The intensities of the bands at 2923–2852 cm −1 (aliphatic), 1700–1740 cm −1 (carbonyl groups), 1120–1160 cm −1 (etheric bands), 1600 cm −1 (aromatic stretching) changed as a result of oxidation reactions and as the oxidation temperature increased to 500°C.