Microwave assisted pyrolysis of Indian and Indonesian coals and product characterization

Abstract

In this study, microwave assisted pyrolysis of Indian and Indonesian coals are investigated to evaluate the liquid fuel potential of these two coal varieties. Microwave pyrolysis experiments were conducted in a bench scale unit, and the effects of various parameters such as microwave power, coal particle size and coal:susceptor ratio on product yields and oil composition were thoroughly evaluated. The oil composition was semi-quantitatively analyzed using gas chromatography–mass spectrometry. Oil yield was not significantly affected by microwave power and initial particle size of coal. The oil yields were 23±2wt.% and 35±3wt.% for Indian and Indonesian coals, respectively, on dry ash free basis. The use of graphite as susceptor enhanced the heating rate although the oil and gas yields were not significantly affected. Indian coal oil contained a mixture of monoaromatics, naphthalenes, polyaromatics and phenolic compounds, while Indonesian coal oil was rich in only phenolic compounds. The addition of graphite promoted the formation of long chain alkanes and alkenes in C12–C20 range for both the coal varieties. Hydrogen gas constituted a major fraction of the non-condensable gases. Higher heating values of coal oils were estimated to be 33–39MJkg−1, while that of coal chars were in the range of 19–22MJkg−1.